National Library of Energy BETA

Sample records for uctio ns se

  1. NS&T MANAGEMENT OBSERVATIONS

    SciTech Connect (OSTI)

    Gianotto, David

    2014-06-01

    The INL Management Observation Program (MOP) is designed to improve managers and supervisors understanding of work being performed by employees and the barriers impacting their success. The MOP also increases workers understanding of managements expectations as they relate to safety, security, quality, and work performance. Management observations (observations) are designed to improve the relationship and trust between employees and managers through increased engagement and interactions between managers and researchers in the field. As part of continuous improvement, NS&T management took initiative to focus on the participation and quality of observations in FY 14. This quarterly report is intended to (a) summarize the participation and quality of managements observations, (b) assess observations for commonalities or trends related to facility or process barriers impacting research, and (c) provide feedback and make recommendations for improvements NS&Ts MOP.

  2. NS&T Management Observations

    SciTech Connect (OSTI)

    Gianotto, David

    2014-09-01

    The INL Management Observation Program (MOP) is designed to improve managers and supervisors understanding of work being performed by employees and the barriers impacting their success. The MOP also increases workers understanding of managements expectations as they relate to safety, security, quality, and work performance. Management observations (observations) are designed to improve the relationship and trust between employees and managers through increased engagement and interactions between managers and researchers in the field. As part of continuous improvement, NS&T management took initiative to focus on the participation and quality of observations in FY 14. This quarterly report is intended to (a) summarize the participation and quality of managements observations, (b) assess observations for commonalities or trends related to facility or process barriers impacting research, and (c) provide feedback and make recommendations for improvements NS&Ts MOP.

  3. NetSim Project contributions to ns-3

    Energy Science and Technology Software Center (OSTI)

    2012-05-01

    ns-3 is an external (non-LLNL) open-source framework for modeling computer networks. The LLNL NetSim project uses the ns-3 framework to address specific questions in computer network design, operation, and security. As part of the NetSim work, we develop bug fixes, deature enhancements, and new capabilities for the ns-3 framework. The virtual package referenced here, ns-3-contrib, consists of those developments we have (or will) contribute back to the ns-3 project in source code form, for inclusionmore » in future releases of ns-3.« less

  4. NS Solar Material Co Ltd | Open Energy Information

    Open Energy Info (EERE)

    Jump to: navigation, search Name: NS Solar Material Co Ltd Place: Kitakyushu, Fukuoka, Japan Product: Special Purpose Vehicle to commercialise polysilicon owned by Nippon Steel...

  5. NS&T Managment Observations - 1st Quarter

    SciTech Connect (OSTI)

    David Gianotto

    2014-06-01

    The INL Management Observation Program (MOP) is designed to improve managers and supervisors understanding of work being performed by employees and the barriers impacting their success. The MOP also increases workers understanding of managements expectations as they relate to safety, security, quality, and work performance. Management observations (observations) are designed to improve the relationship and trust between employees and managers through increased engagement and interactions between managers and researchers in the field. As part of continuous improvement, NS&T management took initiative to focus on the participation and quality of observations in FY 14. This quarterly report is intended to (a) summarize the participation and quality of managements observations, (b) assess observations for commonalities or trends related to facility or process barriers impacting research, and (c) provide feedback and make recommendations for improvements NS&Ts MOP.

  6. NS&T Management Observations - 3rd Quarter

    SciTech Connect (OSTI)

    David Gianotto

    2014-07-01

    The INL Management Observation Program (MOP) is designed to improve managers and supervisors understanding of work being performed by employees and the barriers impacting their success. The MOP also increases workers understanding of managements expectations as they relate to safety, security, quality, and work performance. Management observations are designed to improve the relationship and trust between employees and managers through increased engagement and interactions between managers and researchers in the field. As part of continuous improvement, NS&T management took initiative to focus on the participation and quality of observations in FY 14. This quarterly report is intended to (a) summarize the participation and quality of managements observations, (b) assess observations for commonalities or trends related to facility or process barriers impacting research, and (c) provide feedback and make recommendations for improvements NS&Ts MOP.

  7. STATE YJ#wIY STbNs

    Office of Legacy Management (LM)

    Pap lb. 26 12121167 6EmcFi 3, 1987 STATE YJ#wIY STbNs SlTEN4E . TLFrS CMEEE FfCoP~ MY IWICATE TMT THIS SITE DID ESEMUX TIE WE WILL HOT BE INULWJ IN Flmw. SITE IS uiwl LIENSE. SITE w ItMSTIGMED As R NJTRiTIk FWW SITE, Ho RRDI&iZTCV!N FOUWD. ELIHlNMION PWH w DWLETES 111 CYIWb, hu ww REEDM XTIW IS REWIW. tEVRE?ENT OF EXTRKTIOH OF UuwIUn t-KW Lx ANP bt&LYSIS a cm FM TtE bfc / N.E. RbD!ccoGIC.@L EQLTNLb6 k?T!W. LEbD U.S. PUBLIC KALTH mvrE nom LRNDFILL

  8. MHK Projects/Wavemill Energy Cape Breton Island NS CA | Open...

    Open Energy Info (EERE)

    Wavemill Energy Cape Breton Island NS CA < MHK Projects Jump to: navigation, search << Return to the MHK database homepage Loading map... "minzoom":false,"mappingservice":"googlem...

  9. Laser parametric instability experiments of a 3ω, 15 kJ, 6-ns laser

    Office of Scientific and Technical Information (OSTI)

    pulse in gas-filled hohlraums at the Ligne d'Intégration Laser facility (Journal Article) | SciTech Connect Laser parametric instability experiments of a 3ω, 15 kJ, 6-ns laser pulse in gas-filled hohlraums at the Ligne d'Intégration Laser facility Citation Details In-Document Search Title: Laser parametric instability experiments of a 3ω, 15 kJ, 6-ns laser pulse in gas-filled hohlraums at the Ligne d'Intégration Laser facility Experimental investigation of stimulated Raman (SRS) and

  10. Solon SE | Open Energy Information

    Open Energy Info (EERE)

    to: navigation, search Name: Solon SE Place: Berlin, Berlin, Germany Zip: D-12489 Sector: Solar Product: Manufacturer of PV modules and tracking systems, and integrator of solar...

  11. Resources-PHaSe-EFRC

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Resources This webpage is provided for legacy archive purposes only, as of 30 April 2015. However, the facilities and resources created under PHaSE (thanks to the support of the U.S. Department of Energy) remain available for their original purpose of investigating organic-based electronic materials. Resources As a national and regional center of excellence for energy research, PHaSE has access to many resources linked from the Department of Energy and the greater UMass Amherst campus, as well

  12. News-PHaSe-EFRC

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    News and Highlights Saxony This page shows highlights and news items about PHaSE activities, research achievements, and people; archived items can be accessed by year at the menu to the left. If you have questions about any items, or want to know more, please contact either Tom Russell or D. Venkataraman. Final archive date: 26 April

  13. Photoinduced Surface Oxidation and Its Effect on the Exciton Dynamics of CdSe Quantum Dots

    SciTech Connect (OSTI)

    Hines, Douglas A.; Becker, Matthew A.; Kamat, Prashant V.

    2012-11-14

    With increased interest in semiconductor nanoparticles for use in quantum dot solar cells there comes a need to understand the long-term photostability of such materials. Colloidal CdSe quantum dots (QDs) were suspended in toluene and stored in combinations of light/dark and N{sub 2}/O{sub 2} to simulate four possible benchtop storage environments. CdSe QDs stored in a dark, oxygen-free environment were observed to better retain their optical properties over the course of 90 days. The excited state lifetimes, determined through femtosecond transient absorption spectroscopy, of air-equilibrated samples exposed to light exhibit a decrease in average lifetime (0.81 ns) when compared to samples stored in a nitrogen/dark environment (8.3 ns). A photoetching technique commonly used for controlled reduction of QD size was found to induce energetic trap states to CdSe QDs and accelerate the rate of electron-hole recombination. X-ray absorption near edge structure (XANES) analysis confirms surface oxidation, the extent of which is shown to be dependent on the thickness of the ligand shell.

  14. I2SE | Open Energy Information

    Open Energy Info (EERE)

    I2SE Jump to: navigation, search Name: I2SE Place: Leipzig, Germany Zip: 4103 Sector: Efficiency Product: IT company providing solutions for energy efficiency and data...

  15. SE Project Srl | Open Energy Information

    Open Energy Info (EERE)

    search Name: SE Project Srl Place: San Pietro, Italy Zip: 35010 Sector: Solar Product: Italian manufacturer and supplier of solar modules and solar technology. References: SE...

  16. Dipole-dipole broadening of Rb ns-np microwave transitions

    SciTech Connect (OSTI)

    Park, Hyunwook; Tanner, P. J.; Claessens, B. J.; Shuman, E. S.; Gallagher, T. F.

    2011-08-15

    The dipole-dipole broadening of ns-np microwave transitions of cold Rb Rydberg atoms in a magneto-optical trap has been recorded for 28{<=}n{<=}51. Since the electric dipole transition matrix elements scale as n{sup 2}, a broadening rate scaling as n{sup 4} is expected and a broadening rate of 8.2x10{sup -15}n{sup 4} MHz cm{sup 3} is observed. The observed broadening is smaller than expected from a classical picture due to the spin-orbit interaction in the np atoms. The broadened resonances are asymmetric and cusp shaped, and their line shapes can be reproduced by a diatomic model which takes into account the dipole-dipole interaction, including the spin-orbit interaction, the strengths of the allowed microwave transitions, and the distribution of the atomic spacings in the trap.

  17. First Argon Gas Puff Experiments With 500 ns Implosion Time On Sphinx Driver

    SciTech Connect (OSTI)

    Zucchini, F.; Calamy, H.; Lassalle, F.; Loyen, A.; Maury, P.; Grunenwald, J.; Georges, A.; Morell, A.; Bedoch, J.-P.; Ritter, S.; Combes, P.; Smaniotto, O.; Lample, R.; Coleman, P. L.; Krishnan, M.

    2009-01-21

    Experiments have been performed at the SPHINX driver to study potential of an Argon Gas Puff load designed by AASC. We present here the gas Puff hardware and results of the last shot series.The Argon Gas Puff load used is injected thanks to a 20 cm diameter nozzle. The nozzle has two annuli and a central jet. The pressure and gas type in each of the nozzle plena can be independently adjusted to tailor the initial gaz density distribution. This latter is selected as to obtain an increasing radial density from outer shell towards the pinch axis in order to mitigate the RT instabilities and to increase radiating mass on axis. A flashboard unit produces a high intensity UV source to pre-ionize the Argon gas. Typical dimensions of the load are 200 mm in diameter and 40 mm height. Pressures are adjusted to obtain an implosion time around 550 ns with a peak current of 3.5 MA.With the goal of improving k-shell yield a mass scan of the central jet was performed and implosion time, mainly given by outer and middle plena settings, was kept constant. Tests were also done to reduce the implosion time for two configurations of the central jet. Strong zippering of the radiation production was observed mainly due to the divergence of the central jet over the 40 mm of the load height. Due to that feature k-shell radiation is mainly obtained near cathode. Therefore tests were done to mitigate this effect first by adjusting local pressure of middle and central jet and second by shortening the pinch length.At the end of this series, best shot gave 5 kJ of Ar k-shell yield. PCD detectors showed that k-shell x-ray power was 670 GW with a FWHM of less than 10 ns.

  18. The potassium ion channel opener NS1619 inhibits proliferation and induces apoptosis in A2780 ovarian cancer cells

    SciTech Connect (OSTI)

    Han Xiaobing; Xi Ling; Wang Hui; Huang Xiaoyuan; Ma Xiangyi; Han Zhiqiang; Wu Peng; Ma Xiaoli; Lu Yunping; Wang, Gang Zhou Jianfeng; Ma Ding

    2008-10-17

    Diverse types of voltage-gated potassium (K{sup +}) channels have been shown to be involved in regulation of cell proliferation. The maxi-conductance Ca{sup 2+}-activated K{sup +} channels (BK channels) may play an important role in the progression of human cancer. To explore the role of BK channels in regulation of apoptosis in human ovarian cancer cells, the effects of the specific BK channel activator NS1619 on induction of apoptosis in A2780 cells were observed. Following treatment with NS1619, cell proliferation was measured by MTT assay. Apoptosis of A2780 cells pretreated with NS1619 was detected by agarose gel electrophoresis of cellular DNA and flow cytometry. Our data demonstrate that NS1619 inhibits the proliferation of A2780 cells in a dosage and time dependent manner IC{sub 50} = 31.1 {mu}M, for 48 h pretreatment and induces apoptosis. Western blot analyses showed that the anti-proliferation effect of NS1619 was associated with increased expression of p53, p21, and Bax. These results indicate that BK channels play an important role in regulating proliferation of human ovarian cancer cells and may induce apoptosis through induction of p21{sup Cip1} expression in a p53-dependent manner.

  19. A system to measure isomeric state half-lives in the 10 ns to 10 ?s range

    SciTech Connect (OSTI)

    Toufen, D. L.; Allegro, P. R. P.; Medina, N. H.; Oliveira, J. R. B.; Cybulska, E. W.; Seale, W. A.; Ribas, R. V.; Linares, R.; Silveira, M. A. G.

    2014-07-15

    The Isomeric State Measurement System (SISMEI) was developed to search for isomeric nuclear states produced by fusion-evaporation reactions. The SISMEI consists of 10 plastic phoswich telescopes, two lead shields, one NaI(Tl) scintillation detector, two Compton suppressed HPGe ?-ray detectors, and a cone with a recoil product catcher. The new system was tested at the 8 UD Pelletron tandem accelerator of the University of So Paulo with the measurement of two known isomeric states: {sup 54}Fe, 10{sup +} state (E = 6527.1 (11) keV, T{sub 1/2} = 364(7) ns) and the 5/2{sup +} state of {sup 19}F (E = 197.143 (4) keV, T{sub 1/2} = 89.3 (10) ns). The results indicate that the system is capable of identifying delayed transitions, of measuring isomeric state lifetimes, and of identifying the feeding transitions of the isomeric state through the delayed ?-? coincidence method. The measured half-life for the 10{sup +} state was T{sub 1/2} = 365(14) ns and for the 5/2{sup +} state, 100(36) ns.

  20. Photoluminescence studies of type-II CdSe/CdTe superlattices

    SciTech Connect (OSTI)

    Li Jingjing; Johnson, Shane R.; Wang Shumin; Ding Ding; Ning Cunzheng; Zhang Yonghang; Yin Leijun; Skromme, B. J.; Liu Xinyu; Furdyna, Jacek K.

    2012-08-06

    CdSe/CdTe type-II superlattices grown on GaSb substrates by molecular beam epitaxy are studied using time-resolved and steady-state photoluminescence (PL) spectroscopy at 10 K. The relatively long carrier lifetime of 188 ns observed in time-resolved PL measurements shows good material quality. The steady-state PL peak position exhibits a blue shift with increasing excess carrier concentration. Self-consistent solutions of the Schroedinger and Poisson equations show that this effect can be explained by band bending as a result of the spatial separation of electrons and holes, which is critical confirmation of a strong type-II band edge alignment between CdSe and CdTe.

  1. Q Cells SE | Open Energy Information

    Open Energy Info (EERE)

    Name: Q-Cells SE Place: Thalheim, Brandenburg, Germany Zip: 6766 Product: German PV cell manufacturer; also makes strategic venture capital and corporate investments....

  2. Facilities-Resources-PHaSe-EFRC

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Facilities Glove box photo UMass Amherst PHaSE EFRC participants and collaborators have access to the main Photovoltaic & Optical Spectroscopy Facility in Conte B523524 and its...

  3. Li2Se as a Neutron Scintillator

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Du, Mao-Hua; Shi, Hongliang; Singh, David J.

    2015-06-23

    We show that Li2Se:Te is a potential neutron scintillator material based on density functional calculations. Li2Se exhibits a number of properties favorable for efficient neutron detection, such as a high Li concentration for neutron absorption, a small effective atomic mass and a low density for reduced sensitivity to background gamma rays, and a small band gap for a high light yield. Our calculations show that Te doping should lead to the formation of deep acceptor complex VLi-TeSe, which can facilitate efficient light emission, similar to the emission activation in Te doped ZnSe.

  4. Oxidation of ultrathin GaSe

    SciTech Connect (OSTI)

    Thomas Edwin Beechem; McDonald, Anthony E.; Ohta, Taisuke; Howell, Stephen W.; Kalugin, Nikolai G.; Kowalski, Brian M.; Brumbach, Michael T.; Spataru, Catalin D.; Pask, Jesse A.

    2015-10-26

    Oxidation of exfoliated gallium selenide (GaSe) is investigated through Raman, photoluminescence, Auger, and X-ray photoelectron spectroscopies. Photoluminescence and Raman intensity reductions associated with spectral features of GaSe are shown to coincide with the emergence of signatures emanating from the by-products of the oxidation reaction, namely, Ga2Se3 and amorphous Se. Furthermore, photoinduced oxidation is initiated over a portion of a flake highlighting the potential for laser based patterning of two-dimensional heterostructures via selective oxidation.

  5. Oxidation of ultrathin GaSe

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Thomas Edwin Beechem; McDonald, Anthony E.; Ohta, Taisuke; Howell, Stephen W.; Kalugin, Nikolai G.; Kowalski, Brian M.; Brumbach, Michael T.; Spataru, Catalin D.; Pask, Jesse A.

    2015-10-26

    Oxidation of exfoliated gallium selenide (GaSe) is investigated through Raman, photoluminescence, Auger, and X-ray photoelectron spectroscopies. Photoluminescence and Raman intensity reductions associated with spectral features of GaSe are shown to coincide with the emergence of signatures emanating from the by-products of the oxidation reaction, namely, Ga2Se3 and amorphous Se. Furthermore, photoinduced oxidation is initiated over a portion of a flake highlighting the potential for laser based patterning of two-dimensional heterostructures via selective oxidation.

  6. Templates-Resources-PHaSe-EFRC

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    templates 36 inch high by 48 inch wide, landscape poster template with PHaSE acknowledgements (PPT file download) 36 inch high by 48 inch wide, landscape poster template with PHaSE acknowledgements, 12-panel layout (typical pattern used by UMass PSE) (PPT file download) 42 inch high by 48 inch wide, landscape poster template with PHaSE acknowledgements (PPT file download) 36 inch high by 48 inch wide, portrait poster template with PHaSE acknowledgements (PPT file download) 16:9 Slide Templates

  7. Contact Us-About-PHaSe-EFRC

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    contact us The following information is for legacy archival purposes only, as of 30 April 2015! PHaSE EFRC Main Office Conte Research Center A515 (area code=413) Phone 413-577-0041, FAX 413-545-1510 Thomas P. Russell (Conte A515) Polymer Science & Engineering PHaSE EFRC Co-Director 577-1516 Paul M. Lahti (Goessmann 141) Chemistry PHaSE EFRC Co-Director 545-4890 Volodimyr Duzhko (Conte A529) Facility Director Photovoltaic Facility Director 577-0902 External Advisory Board Members Gui Bazan

  8. SE Drive Technik | Open Energy Information

    Open Energy Info (EERE)

    Drive Technik Jump to: navigation, search Name: SE Drive Technik Place: Bochum, Germany Zip: 44791 Product: Germany-based R&D subsidiary of Indian turbine maker Suzlon. References:...

  9. Modeling of ns and ps laser-induced soft X-ray sources using nitrogen gas puff target

    SciTech Connect (OSTI)

    Vrba, P.; Vrbova, M.; Zakharov, S. V.

    2014-07-15

    Gas puff laser plasma is studied as a source of water window radiation with 2.88?nm wavelength, corresponding to quantum transition 1s{sup 2} ? 1s2p of helium-like nitrogen ions. Spatial development of plasma induced by Nd:YAG laser beam is simulated by 2D Radiation-Magneto-Hydro-Dynamic code Z*. The results for nitrogen gas layer (0.72?mm thickness, 1?bar pressure) and two different laser pulses (600 mJ/7?ns and 525 mJ/170 ps), corresponding to the experiments done in Laser Laboratory Gottingen are presented.

  10. 2013 Archives-News-PHaSe-EFRC

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    3 Archives Volodimyr Duzhko photo Volodimyr Duzhko promoted to (extension) Assistant Professor of Polymer Science & Engineering. PHaSE is pleased to announce that Facility Director Dr. Volodimyr Duzhko has been promoted to extension Assistant Professor of Polymer Science & Engineering. Volodimyr is a semiconductor physicist with considerable experience in polymer materials. Since joining PHaSE, he has trained over 70 people to use 10 instruments in the Photovoltaic & Optical

  11. Investigation of Fe:ZnSe laser in pulsed and repetitively pulsed regimes

    SciTech Connect (OSTI)

    Velikanov, S D; Zaretskiy, N A; Zotov, E A; Maneshkin, A A; Chuvatkin, R S; Yutkin, I M; Kozlovsky, V I; Korostelin, Yu V; Krokhin, O N; Podmar'kov, Yu P; Savinova, S A; Skasyrsky, Ya K; Frolov, M P

    2015-01-31

    The characteristics of a Fe:ZnSe laser pumped by a single-pulse free-running Er : YAG laser and a repetitively pulsed HF laser are presented. An output energy of 4.9 J is achieved in the case of liquid-nitrogen cooling of the Fe{sup 2+}:ZnSe active laser element longitudinally pumped by an Er:YAG laser with a pulse duration of 1 ms and an energy up to 15 J. The laser efficiency with respect to the absorbed energy is 47%. The output pulse energy at room temperature is 53 mJ. The decrease in the output energy is explained by a strong temperature dependence of the upper laser level lifetime and by pulsed heating of the active element. The temperature dependence of the upper laser level lifetime is used to determine the pump parameters needed to achieve high pulse energies at room temperature. Stable repetitively-pulsed operation of the Fe{sup 2+}:ZnSe laser at room temperature with an average power of 2.4 W and a maximum pulse energy of 14 mJ is achieved upon pumping by a 1-s train of 100-ns HF laser pulses with a repetition rate of 200 Hz. (lasers)

  12. A transferable force field for CdS-CdSe-PbS-PbSe solid systems

    SciTech Connect (OSTI)

    Fan, Zhaochuan; Vlugt, Thijs J. H.; Koster, Rik S.; Fang, Changming; Huis, Marijn A. van; Wang, Shuaiwei; Yalcin, Anil O.; Tichelaar, Frans D.; Zandbergen, Henny W.

    2014-12-28

    A transferable force field for the PbSe-CdSe solid system using the partially charged rigid ion model has been successfully developed and was used to study the cation exchange in PbSe-CdSe heteronanocrystals [A. O. Yalcin et al., Atomic resolution monitoring of cation exchange in CdSe-PbSe heteronanocrystals during epitaxial solid-solid-vapor growth, Nano Lett. 14, 36613667 (2014)]. In this work, we extend this force field by including another two important binary semiconductors, PbS and CdS, and provide detailed information on the validation of this force field. The parameterization combines Bader charge analysis, empirical fitting, and ab initio energy surface fitting. When compared with experimental data and density functional theory calculations, it is shown that a wide range of physical properties of bulk PbS, PbSe, CdS, CdSe, and their mixed phases can be accurately reproduced using this force field. The choice of functional forms and parameterization strategy is demonstrated to be rational and effective. This transferable force field can be used in various studies on II-VI and IV-VI semiconductor materials consisting of CdS, CdSe, PbS, and PbSe. Here, we demonstrate the applicability of the force field model by molecular dynamics simulations whereby transformations are initiated by cation exchange.

  13. Nanosecond pulsed electric fields (nsPEFs) low cost generator design using power MOSFET and Cockcroft-Walton multiplier circuit as high voltage DC source

    SciTech Connect (OSTI)

    Sulaeman, M. Y.; Widita, R.

    2014-09-30

    Purpose: Non-ionizing radiation therapy for cancer using pulsed electric field with high intensity field has become an interesting field new research topic. A new method using nanosecond pulsed electric fields (nsPEFs) offers a novel means to treat cancer. Not like the conventional electroporation, nsPEFs able to create nanopores in all membranes of the cell, including membrane in cell organelles, like mitochondria and nucleus. NsPEFs will promote cell death in several cell types, including cancer cell by apoptosis mechanism. NsPEFs will use pulse with intensity of electric field higher than conventional electroporation, between 20100 kV/cm and with shorter duration of pulse than conventional electroporation. NsPEFs requires a generator to produce high voltage pulse and to achieve high intensity electric field with proper pulse width. However, manufacturing cost for creating generator that generates a high voltage with short duration for nsPEFs purposes is highly expensive. Hence, the aim of this research is to obtain the low cost generator design that is able to produce a high voltage pulse with nanosecond width and will be used for nsPEFs purposes. Method: Cockcroft-Walton multiplier circuit will boost the input of 220 volt AC into high voltage DC around 1500 volt and it will be combined by a series of power MOSFET as a fast switch to obtain a high voltage with nanosecond pulse width. The motivation using Cockcroft-Walton multiplier is to acquire a low-cost high voltage DC generator; it will use capacitors and diodes arranged like a step. Power MOSFET connected in series is used as voltage divider to share the high voltage in order not to damage them. Results: This design is expected to acquire a low-cost generator that can achieve the high voltage pulse in amount of ?1.5 kV with falltime 3 ns and risetime 15 ns into a 50? load that will be used for nsPEFs purposes. Further detailed on the circuit design will be explained at presentation.

  14. 2011 Archives-News-PHaSe-EFRC

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    1 Archives solar cells video clip Solar Cells from Plastics? Mission Possible at the PHaSE energy research center, UMass Amherst!, a YouTube video about work at PHaSE, debuted on 24 March 2011. This video is part of our center's contributions to the Energy Frontier Research Centers Summit & Forum on 25-27 May 2011, which is further described below. Many thanks to Harihara Venkatraman (DV group, ERG 1) and Dr. Emily Pentzer (Emrick group, ERG 1) for starring in the video clip, along with

  15. Anisotropy in CdSe quantum rods

    SciTech Connect (OSTI)

    Li, Liang-shi

    2003-09-01

    The size-dependent optical and electronic properties of semiconductor nanocrystals have drawn much attention in the past decade, and have been very well understood for spherical ones. The advent of the synthetic methods to make rod-like CdSe nanocrystals with wurtzite structure has offered us a new opportunity to study their properties as functions of their shape. This dissertation includes three main parts: synthesis of CdSe nanorods with tightly controlled widths and lengths, their optical and dielectric properties, and their large-scale assembly, all of which are either directly or indirectly caused by the uniaxial crystallographic structure of wurtzite CdSe. The hexagonal wurtzite structure is believed to be the primary reason for the growth of CdSe nanorods. It represents itself in the kinetic stabilization of the rod-like particles over the spherical ones in the presence of phosphonic acids. By varying the composition of the surfactant mixture used for synthesis we have achieved tight control of the widths and lengths of the nanorods. The synthesis of monodisperse CdSe nanorods enables us to systematically study their size-dependent properties. For example, room temperature single particle fluorescence spectroscopy has shown that nanorods emit linearly polarized photoluminescence. Theoretical calculations have shown that it is due to the crossing between the two highest occupied electronic levels with increasing aspect ratio. We also measured the permanent electric dipole moment of the nanorods with transient electric birefringence technique. Experimental results on nanorods with different sizes show that the dipole moment is linear to the particle volume, indicating that it originates from the non-centrosymmetric hexagonal lattice. The elongation of the nanocrystals also results in the anisotropic inter-particle interaction. One of the consequences is the formation of liquid crystalline phases when the nanorods are dispersed in solvent to a high enough concentration. The preparation of the stable liquid crystalline solution of CdSe nanorods is described, as well as the large-scale alignment of the nanorods by taking advantage of the long-range orientational correlation in the liquid crystals. In addition, we investigated the phase diagram of the nanorod solution, as a step toward understanding the possible role of the long-range attractive interaction between the nanorods in the formation of lyotropic liquid crystals.

  16. UMass-Resources-PHaSe-EFRC

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    UMass Resources UMass logo The following links provide information about important local (UMass Amherst) campus and departmental offices and resources, including major interdepartmental research centers that pursue work closely akin to research that was initiated or expanded under PHaSE. The last four links go to sites with energy or research news of potential interest to scientists interested in organic electronic materails. Major UMass User Facilities Vice-Chancellor for Research UMass

  17. EFRC Resources-Resources-PHaSe-EFRC

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    EFRC Resources EFRC map Last update 30 April 2015. The following links mostly provide information about accessing specialty equipment and the main instrument facilities that were created by PHaSE during 2009-2015. The last three links guide readers to information that is useful to anyone seriously interested in photovoltaics. Photovoltaic & Spectroscopy Facility Specialty Equipment for Electronic Materials Facility User Reservation Site NREL AM1.5 Solar Radiance Standard NREL Solar Cell

  18. Organization-About-PHaSe-EFRC

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    About Mission Statement (PDF) Organization Contact Us organization This webpage is provided for legacy archive purposes only, as of 30 April 2015. The day to day operations of the University of Massachusetts Amherst PHaSE EFRC are administered by co-directors. Russell is the Samuel Conte Distingushed Professor of Polymer Science and Engineering, with years of previous experience at IBM Research, over 620 publications and 21 patents for polymer chemistry and physics. Lahti has over 29 years at

  19. 2010 Archives-News-PHaSe-EFRC

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    0 Archives PHaSE welcomes Dr. Lawrence Friedman as our new Managing Director. Larry comes to us with strong backgrounds in both academic and industrial experience. He is well acquainted with UMass Amherst from his time at Bayer Materials Science, where he was much involved in doctoral level recruiting and in academic/industrial liaison work as Head of University Relations. Before this, he was at Polaroid doing work in flims research as a manager and senior scientist. His academic credentials

  20. 2013 Archives-News-PHaSe-EFRC

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    4 Archives PHaSE EFRC work was featured in an MRS-TV video production, UMASS Amherst -- Optimal Design: Interdisciplinary Teamwork from Synthesis to Production, that was highlighted on electronic signage throughout the Fall 2014 Boston Materials Research Society meeting. Major vignettes were shown from Maroudas group, DV group, Emrick group. Both faculty and undergraduates/graduates/postdocs described EFRC work and work being carried out by closely allied groups interested in energy-related

  1. 2009 Archives-News-PHaSe-EFRC

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    09 Archives U.S. DOE Announces Energy Frontier Research Centers (08/2009) UMass Amherst EFRC Proposal (08/2009) EFRC Funding Distributed to Successful Centers (08/2009) PHaSE co-director Paul Lahti led off a set of presentations organized by the UMass Amherst Research & Liaison office to meet with a delegation of scientists from various technical research centers of the Gipuzkoa province in the Basque region of northern Spain. The delegation was organized through the Tecnalia Corporation,

  2. 2012 Archives-News-PHaSe-EFRC

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    2 Archives Tom Russell photo Joint work by Tom Russell, Alex Briseno, and coworkers describes fabrication and a significant degree of device optimization of a low band polymer pDPP/PCBM solar cell, in an article published in Advanced Materials. Photoconversion efficiency up to 5.6% with a fill factor of 60% were obtained. Morphology control based on solvent mixture tuning was critically important for best electrical output. [read more] PHaSE members D. Venkataraman and Tom Russell have edited a

  3. Haier: Compromise Agreement (2011-SE-1428) | Department of Energy

    Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site

    Compromise Agreement (2011-SE-1428) Haier: Compromise Agreement (2011-SE-1428) April 23, 2013 DOE and Haier America Trading, LLC entered into a Compromise Agreement to resolve a ...

  4. SeQuential Pacific Biodiesel LLC | Open Energy Information

    Open Energy Info (EERE)

    Pacific Biodiesel LLC Jump to: navigation, search Name: SeQuential-Pacific Biodiesel LLC Place: Oregon Sector: Biofuels Product: JV between SeQuential Biofuels, Pacific Biodiesel,...

  5. LgCOOleS, Se*&,,

    Office of Legacy Management (LM)

    ; "Ofice Mem . m *" ' ' *IilCl:t Consists of & " ' / Of LgCOOleS, Se*&,, es * UNITED STATES G-OVERNM NT <;$)~~ 3i;t-j /Lj ' , ~~~' jCjC;O c) TO I LT. :s. Clnr!te, ,;or,~~~,~' , -.,,..:-:-Y"' r~-;i~.L.-Z.:r DATE: uL"C!.,?r 6, 1' ?L9 A meting mj: !1:1d in i:1CG bet,. _ ^ .- ',cel representatives 51 ;.2rshz:i sr.3 the A;.35 to nwotiztc .the prices for producing FY-1: (brow oxise), _1 I%-; (green salt and .?T-12 (he::.-iZluoriic) fcr the sc2or.d 3,uarter of

  6. Synthesis and optical study of green light emitting polymer coated CdSe/ZnSe core/shell nanocrystals

    SciTech Connect (OSTI)

    Tripathi, S.K.; Sharma, Mamta

    2013-05-15

    Highlights: ► Synthesis of Polymer coated core CdSe and CdSe/ZnSe core/shell NCs. ► From TEM image, the spherical nature of CdSe and CdSe/ZnSe is obtained. ► Exhibiting green band photoemission peak at 541 nm and 549 nm for CdSe core and CdSe/ZnSe core/shell NCs. ► The shell thickness has been calculated by using superposition of quantum confinement energy model. - Abstract: CdSe/ZnSe Core/Shell NCs dispersed in PVA are synthesized by chemical method at room temperature. This is characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV/Vis spectra and photoluminescence spectroscopy (PL). TEM image shows the spherical nature of CdSe/ZnSe core/shell NCs. The red shift of absorption and emission peak of CdSe/ZnSe core/shell NCs as compared to CdSe core confirmed the formation of core/shell. The superposition of quantum confinement energy model is used for calculation of thickness of ZnSe shell.

  7. SE-72/AS-72 generator system based on Se extraction/ As reextraction

    DOE Patents [OSTI]

    Fassbender, Michael Ernst; Ballard, Beau D

    2013-09-10

    The preparation of a .sup.72Se/.sup.72As radioisotope generator involves forming an acidic aqueous solution of an irradiated alkali bromide target such as a NaBr target, oxidizing soluble bromide in the solution to elemental bromine, removing the elemental bromine, evaporating the resulting solution to a residue, removing hydrogen chloride from the residue, forming an acidic aqueous solution of the residue, adding a chelator that selectively forms a chelation complex with selenium, and extracting the chelation complex from the acidic aqueous solution into an organic phase. As the .sup.72Se generates .sup.72As in the organic phase, the .sup.72As may be extracted repeatedly from the organic phase with an aqueous acid solution.

  8. MgSe/ZnSe/CdSe coupled quantum wells grown on InP substrate with intersubband absorption covering 1.55??m

    SciTech Connect (OSTI)

    Chen, Guopeng; Shen, Aidong; De Jesus, Joel; Tamargo, Maria C.

    2014-12-08

    The authors report the observation of intersubband (ISB) transitions in the optical communication wavelength region in MgSe/ZnSe/CdSe coupled quantum wells (QWs). The coupled QWs were grown on InP substrates by molecular beam epitaxy. By inserting ZnSe layers to compensate the strain, samples with high structural quality were obtained, as indicated by well resolved satellite peaks in high-resolution x-ray diffraction. The observed ISB transition energies agree well with the calculated values.

  9. SE-MA-NO Electric Coop | Open Energy Information

    Open Energy Info (EERE)

    SE-MA-NO Electric Coop Jump to: navigation, search Name: SE-MA-NO Electric Coop Place: Missouri Phone Number: (417) 924-3291 Website: www.semano.com Facebook: https:...

  10. Goodman Manufacturing: Order (2011-SE-4301) | Department of Energy

    Energy Savers [EERE]

    Goodman Manufacturing: Order (2011-SE-4301) Goodman Manufacturing: Order (2011-SE-4301) March 2, 2012 DOE ordered Goodman Manufacturing Company, L.P., to pay a $14,800 civil penalty after finding Goodman had manufactured and distributed in commerce in the U.S. at least 74 units of commercial package air conditioner basic model CPC180*. PDF icon Goodman Manufacturing: Order (2011-SE-4301) More Documents & Publications Goodman Manufacturing: Proposed Penalty (2011-SE-4301) Goodman

  11. Perlick: Order (2013-SE-14001) | Department of Energy

    Energy Savers [EERE]

    Order (2013-SE-14001) Perlick: Order (2013-SE-14001) May 14, 2015 DOE ordered Perlick Corporation to pay a $168,200 civil penalty after finding Perlick had manufactured and distributed in commerce in the U.S. 841 units of basic model HP24F, a noncompliant freezer. The Order adopted a Compromise Agreement, which reflected settlement terms between DOE and Perlick. PDF icon Perlick: Order (2013-SE-14001) More Documents & Publications Perlick: Proposed Penalty (2013-SE-14001) Perlick: Order

  12. Morris: Order (2013-SE-5403) | Department of Energy

    Energy Savers [EERE]

    Order (2013-SE-5403) Morris: Order (2013-SE-5403) July 21, 2015 DOE ordered Morris Products, Inc. to pay a $170,720 civil penalty after finding Morris had manufactured and distributed in commerce in the U.S. a large quantity of noncompliant metal halide lamp fixtures. The Order adopted a Compromise Agreement, which reflected settlement terms between DOE and Morris. PDF icon Morris: Order (2013-SE-5403) More Documents & Publications Morris: Proposed Penalty (2013-SE-5403) Morris:

  13. Wide emission-tunable CdTeSe/ZnSe/ZnS core-shell quantum dots...

    Office of Scientific and Technical Information (OSTI)

    Title: Wide emission-tunable CdTeSeZnSeZnS core-shell quantum dots and their conjugation with E. coli O-157 Highlights: * QDs with variety morphology were obtained via an ...

  14. Two-dimensional GaSe/MoSe2 misfit bilayer heterojunctions by van der Waals epitaxy

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Li, Xufan; Lin, Ming-Wei; Lin, Junhao; Huang, Bing; Puretzky, Alexander A.; Ma, Cheng; Wang, Kai; Zhou, Wu; Pantelides, Sokrates T.; Chi, Miaofang; et al

    2016-04-01

    Two-dimensional (2D) heterostructures hold the promise for future atomically-thin electronics and optoelectronics due to their diverse functionalities. While heterostructures consisting of different transition metal dichacolgenide monolayers with well-matched lattices and novel physical properties have been successfully fabricated via van der Waals (vdW) or edge epitaxy, constructing heterostructures from monolayers of layered semiconductors with large lattice misfits still remains challenging. Here, we report the growth of monolayer GaSe/MoSe2 heterostructures with large lattice misfit by two-step chemical vapor deposition (CVD). Both vertically stacked and lateral heterostructures are demonstrated. The vertically stacked GaSe/MoSe2 heterostructures exhibit vdW epitaxy with well-aligned lattice orientation between themore » two layers, forming an incommensurate vdW heterostructure. However, the lateral heterostructures exhibit no lateral epitaxial alignment at the interface between GaSe and MoSe2 crystalline domains. Instead of a direct lateral connection at the boundary region where the same lattice orientation is observed between GaSe and MoSe2 monolayer domains in lateral GaSe/MoSe2 heterostructures, GaSe monolayers are found to overgrow MoSe2 during CVD, forming a stripe of vertically stacked vdW heterostructure at the crystal interface. Such vertically-stacked vdW GaSe/MoSe2 heterostructures are shown to form p-n junctions with effective transport and separation of photo-generated charge carriers between layers, resulting in a gate-tunable photovoltaic response. In conclusion, these GaSe/MoSe2 vdW heterostructures should have applications as gate-tunable field-effect transistors, photodetectors, and solar cells.« less

  15. Spectral photoresponse of ZnSe/GaAs(001) heterostructures with CdSe ultra-thin quantum well insertions

    SciTech Connect (OSTI)

    Valverde-Chvez, D. A.; Sutara, F.; Hernndez-Caldern, I.

    2014-05-15

    We present a study of the spectral photoresponse (SPR) of ZnSe/GaAs(001) heterostructures for different ZnSe film thickness with and without CdSe ultra-thin quantum well (UTQW) insertions. We observe a significant increase of the SPR of heterostructures containing 3 monolayer thick CdSe UTQW insertions; these results encourage their use in photodetectors and solar cells.

  16. Twinning effect on photoluminescence spectra of ZnSe nanowires

    SciTech Connect (OSTI)

    Xu, Jing; Wang, Chunrui Wu, Binhe; Xu, Xiaofeng; Chen, Xiaoshuang; Oh, Hongseok; Baek, Hyeonjun; Yi, Gyu-Chul

    2014-11-07

    Bandgap engineering in a single material along the axial length of nanowires may be realized by arranging periodic twinning, whose twin plane is vertical to the axial length of nanowires. In this paper, we report the effect of twin on photoluminescence of ZnSe nanowires, which refers to the bandgap of it. The exciton-related emission peaks of transverse twinning ZnSe nanowires manifest a 10-meV-blue-shift in comparison with those of longitudinal twinning ZnSe nanowires. The blue-shift is attributed to quantum confinement effect, which is influenced severely by the proportion of wurtzite ZnSe layers in ZnSe nanowires.

  17. CuInSe/sub 2/-based photoelectrochemical cells: their use in characterization of thin CuInSe/sub 2/ films, and as photovoltaic cells per se

    SciTech Connect (OSTI)

    Cahen, D.; Chen, Y.W.; Ireland, P.J.; Noufi, R.; Turner, J.A.; Rincon, C.; Bachmann, K.J.

    1984-05-01

    Photoelectrochemistry has been employed to characterize the p-CuInSe/sub 2/ component of the CdS/CuInSe/sub 2/ on-metal and a nonaqueous electrolyte containing a redox couple not specifically adsorbed onto the semiconductor, we can test the films for photovoltaic activity and obtain effective electronic properties of them, before CdS deposition, in a nondestructive manner. Electrochemical decomposition of CuInSe/sub 2/ was investigated in acetonitrile solutions to determine the mechanism of decomposition (n and p) in the dark and under illumination. Electrochemical, solution chemical and surface analyses confirmed at the light-assisted decomposition of CuInSe/sub 2/ resulted in metal ions and elemental chalcogen. On the basis of the results from the electrochemical decomposition, and studies on the solid state chemistry of the (Cu/sub 2/Se)/sub x/(In/sub 2/Se/sub 3/)/sub 1-x/ system and surface analyses, the CuInSe/sub 2//polyiodide interface was stabilized and up to 11.7% conversion efficiencies were obtained.

  18. Thermoelectric transport of Se-rich Ag{sub 2}Se in normal phases and phase transitions

    SciTech Connect (OSTI)

    Mi, Wenlong; Lv, Yanhong; Qiu, Pengfei; Shi, Xun E-mail: cld@mail.sic.ac.cn; Chen, Lidong E-mail: cld@mail.sic.ac.cn; Zhang, Tiansong

    2014-03-31

    Small amount of Se atoms are used to tune the carrier concentrations (n{sub H}) and electrical transport in Ag{sub 2}Se. Significant enhancements in power factor and thermoelectric figure of merit (zT) are observed in the compositions of Ag{sub 2}Se{sub 1.06} and Ag{sub 2}Se{sub 1.08}. The excessive Se atoms do not change the intrinsically electron-conducting character in Ag{sub 2}Se. The detailed analysis reveals the experiment optimum carrier concentration in Ag{sub 2}Se is around 5??10{sup 18}?cm{sup ?3}. We also investigate the temperature of maximum zT and the thermoelectric transport during the first order phase transitions using the recently developed measurement system.

  19. Glass formation and the third harmonic generation of Cu{sub 2}SeGeSe{sub 2}As{sub 2}Se{sub 3} glasses

    SciTech Connect (OSTI)

    Reshak, A. H.; Klymovych, O. S.; Zmiy, O. F.; Myronchuk, G. L.; Zamuruyeva, O. V.; Alahmed, Z. A.; Chysk, J.; Bila, Jiri; Kamarudin, H.

    2014-10-14

    We have performed the investigation of the nonlinear optical properties namely the third harmonic generation (THG) of the glass-formation region in the Cu{sub 2}SeGeSe{sub 2}As{sub 2}Se{sub 3} system. The samples were synthesized by direct single-temperature method from high-purity elementary substances. We have found that the value of disorder parameter ? depends on the composition of the glassy alloys. The measurements show that increasing the Cu{sub 2}Se concentration leads to increased slope of the absorption edge, which may be explained by the decrease of the height of random potential relief for the electrons in the tails of the state density which border the band edges. A very sharp increase in the THG at low temperature was observed. Significant enhancement in THG was obtained with decreasing the energy gap, which agreed well with the nonlinear optical susceptibilities obtained from other glasses.

  20. Philips: Order (2014-SE-48006) | Department of Energy

    Energy Savers [EERE]

    Order (2014-SE-48006) Philips: Order (2014-SE-48006) April 14, 2015 DOE ordered Philips Lighting North America Corp. to pay a $75,000 civil penalty after finding Philips had manufactured and distributed in commerce in the U.S. at least 12,275 units of a variety of illuminated exit sign models. The Order adopted a Compromise Agreement, which reflected settlement terms between DOE and Philips. PDF icon Philips: Order (2014-SE-48006) More Documents & Publications Philips: Proposed Penalty

  1. Everest Refrigeration: Order (2015-SE-42001) | Department of Energy

    Energy Savers [EERE]

    Order (2015-SE-42001) Everest Refrigeration: Order (2015-SE-42001) June 9, 2015 DOE ordered Bu Sung America Corporation (dba Everest Refrigeration) to pay a $12,080 civil penalty after finding Bu Sung had manufactured and distributed in commerce in the U.S. at least 64 units of noncompliant commercial refrigerator basic model ESGR3. The Order adopted a Compromise Agreement, which reflected settlement terms between DOE and Bu Sung. PDF icon Everest Refrigeration: Order (2015-SE-42001) More

  2. U-105:Oracle Java SE Critical Patch Update Advisory

    Broader source: Energy.gov [DOE]

    Multiple vulnerabilities were reported in Oracle Java SE. A remote user can execute arbitrary code on the target system. A remote user can cause denial of service conditions.

  3. Research Forum Schedule-Research-PHaSe-EFRC

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Research Forum Schedule PHaSE Research Fora and Talks This webpage is provided for legacy archive purposes only, as of 30 April 2015.

  4. SeQuential Biofuels LLC | Open Energy Information

    Open Energy Info (EERE)

    Biofuels LLC Jump to: navigation, search Name: SeQuential Biofuels LLC Place: Portland, Oregon Zip: 97231 Sector: Biofuels Product: A biofuels marketing and distribution company...

  5. SE Idaho Load Service Update - June 10, 2015

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    SE-Idaho-Load-Service-Update---June-10,-2015 Sign In About | Careers | Contact | Investors | bpa.gov Search Doing Business Expand Doing Business Customer Involvement Expand...

  6. CdSe self-assembled quantum dots with ZnCdMgSe barriers emitting throughout the visible spectrum

    SciTech Connect (OSTI)

    Perez-Paz, M. Noemi; Zhou Xuecong; Munoz, Martin; Lu Hong; Sohel, Mohammad; Tamargo, Maria C.; Jean-Mary, Fleumingue; Akins, Daniel L.

    2004-12-27

    Self-assembled quantum dots of CdSe with ZnCdMgSe barriers have been grown by molecular beam epitaxy on InP substrates. The optical and microstructural properties were investigated using photoluminescence (PL) and atomic force microscopy (AFM) measurements. Control and reproducibility of the quantum dot (QD) size leading to light emission throughout the entire visible spectrum range has been obtained by varying the CdSe deposition time. Longer CdSe deposition times result in a redshift of the PL peaks as a consequence of an increase of QD size. AFM studies demonstrate the presence of QDs in uncapped structures. A comparison of this QD system with CdSe/ZnSe shows that not only the strain but also the chemical properties of the system play an important role in QD formation.

  7. Wide emission-tunable CdTeSe/ZnSe/ZnS core-shell quantum dots and their

    Office of Scientific and Technical Information (OSTI)

    conjugation with E. coli O-157 (Journal Article) | SciTech Connect Wide emission-tunable CdTeSe/ZnSe/ZnS core-shell quantum dots and their conjugation with E. coli O-157 Citation Details In-Document Search Title: Wide emission-tunable CdTeSe/ZnSe/ZnS core-shell quantum dots and their conjugation with E. coli O-157 Highlights: * QDs with variety morphology were obtained via an injection controlled process. * 3-D PL spectra of core-shell QDs show different excitation wavelength dependence. *

  8. CdSe/ZnSe quantum dot structures grown by molecular beam epitaxy with a CdTe submonolayer stressor

    SciTech Connect (OSTI)

    Sedova, I. V. Lyublinskaya, O. G.; Sorokin, S. V.; Sitnikova, A. A.; Toropov, A. A.; Donatini, F.; Dang, Si Le; Ivanov, S. V.

    2007-11-15

    A procedure for formation of CdSe quantum dots (QDs) in a ZnSe matrix is suggested. The procedure is based on the introduction of a CdTe submonolayer stressor deposited on the matrix surface just before deposition of the material of the QDs. (For CdTe/ZnSe structure, the relative lattice mismatch is {delta}a/a {approx} 14%.) The stressor forms small strained islands at the ZnSe surface, thus producing local fields of high elastic stresses controlling the process of the self-assembling of the QDs. According to the data of transmission electron microscopy, this procedure allows a considerable increase in the surface density of QDs, with a certain decrease in their lateral dimensions (down to 4.5 {+-} 1.5 nm). In the photoluminescence spectra, a noticeable ({approx}150 meV) shift of the peak to longer wavelengths from the position of the reference CdSe/ZnSe QD structure is observed. The shift is due to some transformation of the morphology of the QDs and an increase in the Cd content in the QDs. Comprehensive studies of the nanostructures by recording and analyzing the excitation spectra of photoluminescence, the time-resolved photoluminescence spectra, and the cathodoluminescence spectra show that the emission spectra involve two types of optical transitions, namely, the type-I transitions in the CdSeTe/ZnSe QDs and the type-II transitions caused mainly by the low cadmium content (Zn,Cd)(Se,Te)/ZnSe layer formed between the QDs.

  9. Traulsen: Order (2015-SE-42002) | Department of Energy

    Energy Savers [EERE]

    Order (2015-SE-42002) Traulsen: Order (2015-SE-42002) August 31, 2015 DOE ordered Traulsen - ITW Food Group LLC to pay a $52,600 civil penalty after finding Traulsen had manufactured and distributed in commerce in the U.S. at least 284 units of commercial refrigerator-freezer basic model RDT132DUT-HHS, a noncompliant product. The Order adopted a Compromise Agreement, which reflected settlement terms between DOE and Traulsen. PDF icon Traulsen: Order (2015-SE-42002) More Documents &

  10. Victory: Order (2015-SE-42033) | Department of Energy

    Energy Savers [EERE]

    Order (2015-SE-42033) Victory: Order (2015-SE-42033) October 27, 2015 DOE ordered Victory Refrigeration to pay a $1,600 civil penalty after finding Victory had manufactured and distributed in commerce in the U.S. at least 8 units of commercial refrigerator-freezer basic model RFS-1D-S1-EW-PT-HD, a noncompliant product. The Order adopted a Compromise Agreement, which reflected settlement terms between DOE and Victory. PDF icon Victory: Order (2015-SE-42033) More Documents & Publications

  11. Optical Probing of metamagnetic phases in epitaxial EuSe

    SciTech Connect (OSTI)

    Galgano, G. D.; Henriques, A. B.; Bauer, G.; Springholz, G.

    2011-12-23

    EuSe is a wide gap magnetic semiconductors with a potential for applications in proof-of-concept spintronic devices. When the temperature is lowered, EuSe goes through sharp transitions between a variety of magnetic phases and is thus described as metamagnetic. The purpose of the present investigation is to correlate the magnetic order to the sharp dichroic doublet, discovered recently in high quality thin epitaxial layers of EuSe, grown by molecular beam epitaxy. We report detailed measurements of the doublet positions and intensities as a function of magnetic field in low temperatures, covering several magnetic phases.

  12. Optical Properties of CdSe Nanoparticle Assemblies

    SciTech Connect (OSTI)

    Huser, T; Gerion, D; Zaitseva, N; Krol, D M; Leon, F R

    2003-11-24

    We report on three-dimensional fluorescence imaging of micron-size faceted crystals precipitated from solutions of CdSe nanocrystals. Such crystals have previously been suggested to be superlattices of CdSe quantum dots [1,2]. Possible applications for these materials include their use in optical and optoelectronic devices. The micron-size crystals were grown by slow evaporation from toluene solutions of CdSe nanocrystals in the range of 3-6 nm, produced by traditional wet-chemistry techniques. By using a confocal microscope with laser illumination, three-dimensional raster-scanning and synchronized hyper-spectral detection, we have generated spatial profiles of the fluorescence emission intensity and spectrum. The fluorescence data of the micro-crystals were compared with spectra of individual nanocrystals obtained from the same solution. The results do not support the assertion that these microcrystals consist of CdSe superlattices.

  13. Enhanced thermoelectric power and electronic correlations in RuSe?

    SciTech Connect (OSTI)

    Wang, Kefeng; Wang, Aifeng; Tomic, A.; Wang, Limin; Abeykoon, A. M. Milinda; Dooryhee, E.; Billinge, S. J.L.; Petrovic, C.

    2015-03-03

    We report the electronic structure, electric and thermal transport properties of Ru??xIrxSe? (x ? 0.2). RuSe? is a semiconductor that crystallizes in a cubic pyrite unit cell. The Seebeck coefficient of RuSe? exceeds -200 V/K around 730 K. Ir substitution results in the suppression of the resistivity and the Seebeck coefficient, suggesting the removal of the peaks in density of states near the Fermi level. Ru?.?Ir?.?Se? shows a semiconductor-metal crossover at about 30 K. The magnetic field restores the semiconducting behavior. Our results indicate the importance of the electronic correlations in enhanced thermoelectricity of RuSb?.

  14. Synthesis and properties of new CdSe-AgI-As{sub 2}Se{sub 3} chalcogenide glasses

    SciTech Connect (OSTI)

    Kassem, M.; ULCO, LPCA, EAC CNRS 4493 F-59140 Dunkerque ; Le Coq, D.; Fourmentin, M.; Hindle, F.; Bokova, M.; Cuisset, A.; Masselin, P.; Bychkov, E.; ULCO, LPCA, EAC CNRS 4493 F-59140 Dunkerque

    2011-02-15

    Research highlights: {yields} Determination of the glass-forming region in the pseudo-ternary CdSe-AgI-As{sub 2}Se{sub 3} system. {yields} Characterization of macroscopic properties of the new CdSe-AgI-As{sub 2}Se{sub 3} glasses. {yields} Far infrared transmission of chalcogenide glasses. {yields} Characterization of the total conductivity of CdSe-AgI-As{sub 2}Se{sub 3} glasses. -- Abstract: The glass-forming region in the pseudo-ternary CdSe-AgI-As{sub 2}Se{sub 3} system was determined. Measurements including differential scanning calorimetry (DSC), density, and X-ray diffraction were performed. The effect resulting from the addition of CdSe or AgI has been highlighted by examining three series of different base glasses. The characteristic temperatures of the glass samples, including glass transition (T{sub g}), crystallisation (T{sub x}), and melting (T{sub m}) temperatures are reported and used to calculate their {Delta}T = T{sub x} - T{sub g} and their Hruby, H{sub r} = (T{sub x} - T{sub g})/(T{sub m} - T{sub x}), criteria. Evolution of the total electrical conductivity {sigma} and the room temperature conductivity {sigma}{sub 298} was also studied. The terahertz transparency domain in the 50-600 cm{sup -1} region was pointed for different chalcogenide glasses (ChGs) and the potential of the THz spectroscopy was suggested to obtain structural information on ChGs.

  15. Seaga: Noncompliance Determination (2015-SE-52001) | Department of Energy

    Energy Savers [EERE]

    Seaga: Noncompliance Determination (2015-SE-52001) Seaga: Noncompliance Determination (2015-SE-52001) June 19, 2015 DOE issued a Notice of Noncompliance Determination to Seaga Manufacturing, Inc. finding that the refrigerated bottle and canned beverage vending machine (BVM) basic model with name plate model SP536R does not comport with the energy conservation standards. DOE determined the product was noncompliant based on DOE testing. Seaga must immediately notify each person (or company) to

  16. Philips: Noncompliance Determination (2014-SE-48006) | Department of Energy

    Energy Savers [EERE]

    Noncompliance Determination (2014-SE-48006) Philips: Noncompliance Determination (2014-SE-48006) March 26, 2015 DOE issued a Notice of Noncompliance Determination to Philips Lighting North America Corp. finding that a variety of illuminated exit sign models do not comport with the energy conservation standards, based on information provided to DOE by Philips. DOE determined the products were noncompliant based on testing information provided by the company. Philips must immediately notify each

  17. Macrospin modeling of sub-ns pulse switching of perpendicularly magnetized free layer via spin-orbit torques for cryogenic memory applications

    SciTech Connect (OSTI)

    Park, Junbo; Rowlands, G. E.; Lee, O. J.; Buhrman, R. A.; Ralph, D. C.

    2014-09-08

    We model, using the macrospin approximation, the magnetic reversal of a perpendicularly magnetized nanostructured free layer formed on a normal, heavy-metal nanostrip, subjected to spin-orbit torques (SOTs) generated by short (?0.5?ns) current pulses applied to the nanostrip, to examine the potential for SOT-based fast, efficient cryogenic memory. Due to thermal fluctuations, if solely an anti-damping torque is applied, then, for a device with sufficiently low anisotropy (H{sub anis}{sup 0}???1 kOe) suitable for application in cryogenic memory, a high magnetic damping parameter (??0.1?0.2) is required for reliable switching over a significant variation of pulse current. The additional presence of a substantial field-like torque improves switching reliability even for low damping (??0.03).

  18. The influence of interfaces on properties of thin-film inorganic structural isomers containing SnSeNbSe? Subunits

    SciTech Connect (OSTI)

    Alemayehu, Matti B.; Falmbigl, Matthias; Ta, Kim; Johnson, David C.

    2015-08-28

    Inorganic isomers ([SnSe]1+?)m(NbSe?)n([SnSe]1+?)p(NbSe?)q([SnSe]1+?)r(NbSe?)s where m, n, p, q, r, and s are integers and m + p + r = n + q + s = 4 were prepared using the modulated elemental reactant technique. This series of all six possible isomers provides an opportunity to study the influence of interface density on properties while maintaining the same unit cell size and composition. As expected, all six compounds were observed to have the same atomic compositions and an almost c-axis lattice parameter of ?4.90 (5) nm, with a slight trend in the c-axis lattice parameter correlated with the different number of interfaces in the isomers: two, four and six. The structures of the constituents in the ab-plane were independent of one another, confirming the nonepitaxial relationship between them. The temperature dependent electrical resistivities revealed metallic behavior for all the six compounds. Surprisingly, the electrical resistivity at room temperature decreases with increasing number of interfaces. Hall measurements suggest this results from changes in carrier concentration, which increases with increasing thickness of the thickest SnSe block in the isomer. Carrier mobility scales with the thickness of the thickest NbSe? block due to increased interfacial scattering as the NbSe? blocks become thinner. The observed behavior suggests that the two constituents serve different purposes with respect to electrical transport. SnSe acts as a charge donor and NbSe? acts as the charge transport layer. This separation of function suggests that such heterostructures can be designed to optimize performance through choice of constituent, layer thickness, and layer sequence. A simplistic model, which predicts the properties of the complex isomers from a weighted sum of the properties of building blocks, was developed. A theoretical model is needed to predict the optimal compound for specific properties among the many potential compounds that can be prepared.

  19. Heterojunctions of model CdTe/CdSe mixtures

    SciTech Connect (OSTI)

    van Swol, Frank; Zhou, Xiaowang W.; Challa, Sivakumar R.; Martin, James E.

    2015-03-18

    We report on the strain behavior of compound mixtures of model group IIVI semiconductors. We use the StillingerWeber Hamiltonian that we recently introduced, specifically developed to model binary mixtures of group IIVI compounds such as CdTe and CdSe. We also employ molecular dynamics simulations to examine the behavior of thin sheets of material, bilayers of CdTe and CdSe. The lattice mismatch between the two compounds leads to a strong bending of the entire sheet, with about a 0.5 to 1 deflection between neighboring planes. To further analyze bilayer bending, we introduce a simple one-dimensional model and use energy minimization to find the angle of deflection. The analysis is equivalent to a least-squares straight line fit. We consider the effects of bilayers which are asymmetric with respect to the thickness of the CdTe and CdSe parts. We thus learn that the bending can be subdivided into four kinds depending on the compressive/tensile nature of each outer plane of the sheet. We use this approach to directly compare our findings with experimental results on the bending of CdTe/CdSe rods. To reduce the effects of the lattice mismatch we explore diffuse interfaces, where we mix (i.e. alloy) Te and Se, and estimate the strain response.

  20. Heterojunctions of model CdTe/CdSe mixtures

    SciTech Connect (OSTI)

    van Swol, Frank; Zhou, Xiaowang W.; Challa, Sivakumar R.; Martin, James E.

    2015-03-18

    We report on the strain behavior of compound mixtures of model group II-VI semiconductors. We use the Stillinger-Weber Hamiltonian that we recently introduced, specifically developed to model binary mixtures of group II-VI compounds such as CdTe and CdSe. We also employ molecular dynamics simulations to examine the behavior of thin sheets of material, bilayers of CdTe and CdSe. The lattice mismatch between the two compounds leads to a strong bending of the entire sheet, with about a 0.5 to 1° deflection between neighboring planes. To further analyze bilayer bending, we introduce a simple one-dimensional model and use energy minimization to find the angle of deflection. The analysis is equivalent to a least-squares straight line fit. We consider the effects of bilayers which are asymmetric with respect to the thickness of the CdTe and CdSe parts. We thus learn that the bending can be subdivided into four kinds depending on the compressive/tensile nature of each outer plane of the sheet. We use this approach to directly compare our findings with experimental results on the bending of CdTe/CdSe rods. To reduce the effects of the lattice mismatch we explore diffuse interfaces, where we mix (i.e. alloy) Te and Se, and estimate the strain response.

  1. EMPaSE: an Extensible Multi-Paradigm Simulation Environment

    Energy Science and Technology Software Center (OSTI)

    2010-08-05

    EMPaSE is a hierarchical, extensible, modular modeling environment for developing and running hybrid simulations of sequential-modular, systems dynamics, discrete-event, and agent-based paradigms. It contains two principle components: a multi-paradigm simulation engine and a graphical user interface. EMPaSE models are defined through a hierarchically-defined set of computational modules that define the simulation logic. Inter-module communication occurs through two complimentary systems: pull-based "ports" for general computation patterns and push-based "plugs" for event processing. Entities (i.e. agents) withinmore » the simulation operate within an abstract multi-network environment. The EMPaSE simulation engine is designed around a flexible plug-in architecture, allowing simulations to import computational modules, engine customizations, and interfaces to external applications from independent plug-in libraries. The EMPaSE GUI environment provides an environment for graphically constructing, executing, and debugging EMPaSE models. As with the simulation engine, the GUI is constructed on top of an extensible architecture that supports rapid customization of the user experience through external plug-in libraries.« less

  2. Heterojunctions of model CdTe/CdSe mixtures

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    van Swol, Frank; Zhou, Xiaowang W.; Challa, Sivakumar R.; Martin, James E.

    2015-03-18

    We report on the strain behavior of compound mixtures of model group II-VI semiconductors. We use the Stillinger-Weber Hamiltonian that we recently introduced, specifically developed to model binary mixtures of group II-VI compounds such as CdTe and CdSe. We also employ molecular dynamics simulations to examine the behavior of thin sheets of material, bilayers of CdTe and CdSe. The lattice mismatch between the two compounds leads to a strong bending of the entire sheet, with about a 0.5 to 1° deflection between neighboring planes. To further analyze bilayer bending, we introduce a simple one-dimensional model and use energy minimization tomore » find the angle of deflection. The analysis is equivalent to a least-squares straight line fit. We consider the effects of bilayers which are asymmetric with respect to the thickness of the CdTe and CdSe parts. We thus learn that the bending can be subdivided into four kinds depending on the compressive/tensile nature of each outer plane of the sheet. We use this approach to directly compare our findings with experimental results on the bending of CdTe/CdSe rods. To reduce the effects of the lattice mismatch we explore diffuse interfaces, where we mix (i.e. alloy) Te and Se, and estimate the strain response.« less

  3. GE Appliances: Order (2012-SE-1403) | Department of Energy

    Energy Savers [EERE]

    Appliances: Order (2012-SE-1403) GE Appliances: Order (2012-SE-1403) October 3, 2012 DOE ordered GE Appliances, a Division of General Electric Company to pay a $63,000 civil penalty after finding GE had privately labeled and distributed in commerce in the U.S. the 4-cubic-foot capacity refrigerator basic model SMR04GAZCS, which includes models SMR04GAZACS and SMR04GAZBCS. The Order adopted a Compromise Agreement, which reflected settlement terms between DOE and GE. PDF icon GE Appliances: Order

  4. Utility: Order (2016-SE-42003) | Department of Energy

    Energy Savers [EERE]

    SE-42003) Utility: Order (2016-SE-42003) March 1, 2016 DOE ordered Utility Refrigerator to pay a $200 civil penalty after finding Utility manufactured and distributed in commerce in the U.S. 1 unit of a Utility brand commercial refrigerator, model PT-R-75-SS-3S-3S-N. The Order adopted a Compromise Agreement, which reflected settlement terms between DOE and Utility. Federal law subjects manufacturers and private labelers to civil penalties if those parties distribute in the U.S. products that do

  5. Sunshine Lighting: Order (2014-SE-54008) | Department of Energy

    Energy Savers [EERE]

    Sunshine Lighting: Order (2014-SE-54008) Sunshine Lighting: Order (2014-SE-54008) July 7, 2015 DOE ordered Lighting & Supplies, Inc. d/b/a Sunshine Lighting Company ("Sunshine") to pay a $150,000 civil penalty after finding Sunshine had manufactured and distributed in commerce in the U.S. 1780 units of Sunlite brand basic model 04937-SU and 1134 units of basic model 04952-SU, noncompliant metal halide lamp fixtures. The Order adopted a Compromise Agreement, which reflected

  6. Excited-State Relaxation in PbSe Quantum Dots

    SciTech Connect (OSTI)

    An, J. M.; Califano, M.; Franceschetti, A.; Zunger, A.

    2008-01-01

    In solids the phonon-assisted, nonradiative decay from high-energy electronic excited states to low-energy electronic excited states is picosecond fast. It was hoped that electron and hole relaxation could be slowed down in quantum dots, due to the unavailability of phonons energy matched to the large energy-level spacings ('phonon-bottleneck'). However, excited-state relaxation was observed to be rather fast ({le}1 ps) in InP, CdSe, and ZnO dots, and explained by an efficient Auger mechanism, whereby the excess energy of electrons is nonradiatively transferred to holes, which can then rapidly decay by phonon emission, by virtue of the densely spaced valence-band levels. The recent emergence of PbSe as a novel quantum-dot material has rekindled the hope for a slow down of excited-state relaxation because hole relaxation was deemed to be ineffective on account of the widely spaced hole levels. The assumption of sparse hole energy levels in PbSe was based on an effective-mass argument based on the light effective mass of the hole. Surprisingly, fast intraband relaxation times of 1-7 ps were observed in PbSe quantum dots and have been considered contradictory with the Auger cooling mechanism because of the assumed sparsity of the hole energy levels. Our pseudopotential calculations, however, do not support the scenario of sparse hole levels in PbSe: Because of the existence of three valence-band maxima in the bulk PbSe band structure, hole energy levels are densely spaced, in contradiction with simple effective-mass models. The remaining question is whether the Auger decay channel is sufficiently fast to account for the fast intraband relaxation. Using the atomistic pseudopotential wave functions of Pb{sub 2046}Se{sub 2117} and Pb{sub 260}Se{sub 249} quantum dots, we explicitly calculated the electron-hole Coulomb integrals and the P {yields} S electron Auger relaxation rate. We find that the Auger mechanism can explain the experimentally observed P {yields} S intraband decay time scale without the need to invoke any exotic relaxation mechanisms.

  7. Reverse Monte Carlo simulation of Se{sub 80}Te{sub 20} and Se{sub 80}Te{sub 15}Sb{sub 5} glasses

    SciTech Connect (OSTI)

    Abdel-Baset, A. M.; Rashad, M.; Moharram, A. H.

    2013-12-16

    Two-dimensional Monte Carlo of the total pair distribution functions g(r) is determined for Se{sub 80}Te{sub 20} and Se{sub 80}Te{sub 15}Sb{sub 5} alloys, and then it used to assemble the three-dimensional atomic configurations using the reverse Monte Carlo simulation. The partial pair distribution functions g{sub ij}(r) indicate that the basic structure unit in the Se{sub 80}Te{sub 15}Sb{sub 5} glass is di-antimony tri-selenide units connected together through Se-Se and Se-Te chain. The structure of Se{sub 80}Te{sub 20} alloys is a chain of Se-Te and Se-Se in addition to some rings of Se atoms.

  8. Orbitally-driven giant phonon anharmonicity in SnSe

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Li, Chen W.; Hong, Jiawang; May, Andrew F.; Bansal, Dipanshu; Chi, Songxue; Hong, Tao; Ehlers, Georg; Delaire, Olivier A.

    2015-10-19

    We understand that elementary excitations and their couplings in condensed matter systems is critical to develop better energy-conversion devices. In thermoelectric materials, the heat-to-electricity conversion efficiency is directly improved by suppressing the propagation of phonon quasiparticles responsible for macroscopic thermal transport. The material with the current record for thermoelectric conversion efficiency, SnSe, achieves an ultra-low thermal conductivity, but the mechanism enabling this strong phonon scattering remains largely unknown. Using inelastic neutron scattering measurements and first-principles simulations, we mapped the four-dimensional phonon dispersion surfaces of SnSe, and revealed the origin of ionic-potential anharmonicity responsible for the unique properties of SnSe. Wemore » show that the giant phonon scattering arises from an unstable electronic structure, with orbital interactions leading to a ferroelectric-like lattice instability. Our results provide a microscopic picture connecting electronic structure and phonon anharmonicity in SnSe, and offers precious insights on how electron-phonon and phononphonon interactions may lead to the realization of ultra-low thermal conductivity.« less

  9. Orbitally-driven giant phonon anharmonicity in SnSe

    SciTech Connect (OSTI)

    Li, Chen W.; Hong, Jiawang; May, Andrew F.; Bansal, Dipanshu; Chi, Songxue; Hong, Tao; Ehlers, Georg; Delaire, Olivier A.

    2015-10-19

    We understand that elementary excitations and their couplings in condensed matter systems is critical to develop better energy-conversion devices. In thermoelectric materials, the heat-to-electricity conversion efficiency is directly improved by suppressing the propagation of phonon quasiparticles responsible for macroscopic thermal transport. The material with the current record for thermoelectric conversion efficiency, SnSe, achieves an ultra-low thermal conductivity, but the mechanism enabling this strong phonon scattering remains largely unknown. Using inelastic neutron scattering measurements and first-principles simulations, we mapped the four-dimensional phonon dispersion surfaces of SnSe, and revealed the origin of ionic-potential anharmonicity responsible for the unique properties of SnSe. We show that the giant phonon scattering arises from an unstable electronic structure, with orbital interactions leading to a ferroelectric-like lattice instability. Our results provide a microscopic picture connecting electronic structure and phonon anharmonicity in SnSe, and offers precious insights on how electron-phonon and phononphonon interactions may lead to the realization of ultra-low thermal conductivity.

  10. filewNsAsN

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

  11. LANSCE-NS thrust areas

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    irradiations (ICE House, ICE II) High resolution gamma-ray measurements following nuclear reactions (GEANIE) Detector development Neutron radiography (FP05) Fission and...

  12. LANSCE-NS Block Schedule

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    LANSCE Planned Run Schedule - 2015/2016 run_schedule

  13. Analysis of the Salmonella regulatory network suggests involvement of SsrB and H-NS in σE-regulated SPI-2 gene expression

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Li, Jie; Overall, Christopher C.; Nakayasu, Ernesto S.; Kidwai, Afshan S.; Jones, Marcus B.; Johnson, Rudd; Nguyen, Nhu T.; McDermott, Jason E.; Ansong, Charles; Heffron, Fred; et al

    2015-02-10

    The extracytoplasmic functioning sigma factor ?E is known to play an essential role for Salmonella enterica serovar Typhimurium to survive and proliferate in macrophages and mice. However, its regulatory network is not well characterized, especially during infection. Here we used microarray to identify genes regulated by ?E in Salmonella grown in three conditions: a nutrient-rich condition and two others that mimic early and late intracellular infection. We found that in each condition ?E regulated different sets of genes, and notably, several global regulators. When comparing nutrient-rich and infection-like conditions, large changes were observed in the expression of genes involved inmoreSalmonella pathogenesis island (SPI)-1 type-three secretion system (TTSS), SPI-2 TTSS, protein synthesis, and stress responses. In total, the expression of 58% of Salmonella genes was affected by ?E in at least one of the three conditions. An important finding is that ?E up-regulates SPI-2 genes, which are essential for Salmonella intracellular survival, by up-regulating SPI-2 activator ssrB expression at the early stage of infection and down-regulating SPI-2 repressor hns expression at a later stage. Moreover, ?E is capable of countering the silencing of H-NS, releasing the expression of SPI-2 genes. This connection between ?E and SPI-2 genes, combined with the global regulatory effect of ?E, may account for the lethality of rpoE-deficient Salmonella in murine infection.less

  14. A new spectrometer design for the x-ray spectroscopy of laser-produced plasmas with high (sub-ns) time resolution

    SciTech Connect (OSTI)

    Bitter, M. Hill, K. W.; Efthimion, P. C.; Delgado-Aparicio, L.; Pablant, N.; Lu, Jian; Beiersdorfer, P.; Chen, Hui

    2014-11-15

    This paper describes a new type of x-ray crystal spectrometer, which can be used in combination with gated x-ray detectors to obtain spectra from laser-produced plasmas with a high (sub-ns) time resolution. The spectrometer consists of a convex, spherically bent crystal, which images individual spectral lines as perfectly straight lines across multiple, sequentially gated, strip detectors. Since the Bragg-reflected rays are divergent, the distance between detector and crystal is arbitrary, so that this distance can be appropriately chosen to optimize the experimental arrangement with respect to the detector parameters. The spectrometer concept was verified in proof-of-principle experiments by imaging the L?{sub 1}- and L?{sub 2}-lines of tungsten, at 9.6735 and 9.96150 keV, from a micro-focus x-ray tube with a tungsten target onto a two-dimensional pixilated Pilatus detector, using a convex, spherically bent Si-422 crystal with a radius of curvature of 500 mm.

  15. Giant piezoelectricity of monolayer group IV monochalcogenides: SnSe, SnS, GeSe, and GeS

    SciTech Connect (OSTI)

    Fei, Ruixiang; Yang, Li; Li, Wenbin; Li, Ju

    2015-10-26

    We predict enormous, anisotropic piezoelectric effects in intrinsic monolayer group IV monochalcogenides (MX, M=Sn or Ge, X=Se or S), including SnSe, SnS, GeSe, and GeS. Using first-principle simulations based on the modern theory of polarization, we find that their piezoelectric coefficients are about one to two orders of magnitude larger than those of other 2D materials, such as MoS{sub 2} and GaSe, and bulk quartz and AlN which are widely used in industry. This enhancement is a result of the unique “puckered” C{sub 2v} symmetry and electronic structure of monolayer group IV monochalcogenides. Given the achieved experimental advances in the fabrication of monolayers, their flexible character, and ability to withstand enormous strain, these 2D structures with giant piezoelectric effects may be promising for a broad range of applications such as nano-sized sensors, piezotronics, and energy harvesting in portable electronic devices.

  16. Epitaxial growth of CZT(S,Se) on silicon

    DOE Patents [OSTI]

    Bojarczuk, Nestor A.; Gershon, Talia S.; Guha, Supratik; Shin, Byungha; Zhu, Yu

    2016-03-15

    Techniques for epitaxial growth of CZT(S,Se) materials on Si are provided. In one aspect, a method of forming an epitaxial kesterite material is provided which includes the steps of: selecting a Si substrate based on a crystallographic orientation of the Si substrate; forming an epitaxial oxide interlayer on the Si substrate to enhance wettability of the epitaxial kesterite material on the Si substrate, wherein the epitaxial oxide interlayer is formed from a material that is lattice-matched to Si; and forming the epitaxial kesterite material on a side of the epitaxial oxide interlayer opposite the Si substrate, wherein the epitaxial kesterite material includes Cu, Zn, Sn, and at least one of S and Se, and wherein a crystallographic orientation of the epitaxial kesterite material is based on the crystallographic orientation of the Si substrate. A method of forming an epitaxial kesterite-based photovoltaic device and an epitaxial kesterite-based device are also provided.

  17. Deformation potentials of CdSe quantum dots

    SciTech Connect (OSTI)

    Li, Jingbo; Wang, Lin-Wang

    2004-06-02

    The size dependent deformation potentials of CdSe quantum dots are studied by first principle and semi-empirical pseudopotentials calculations. They find that the amplitude of the quantum dot deformation potential is only slightly larger than the bulk value, and this increase is mostly caused by the off {Lambda} point deformation potentials in the bulk, which are larger in amplitude than the {Lambda} point deformation potential.

  18. Quantum confined acceptors and donors in InSe nanosheets

    SciTech Connect (OSTI)

    Mudd, G. W.; Patan, A. Makarovsky, O.; Eaves, L.; Kudrynskyi, Z. R.; Kovalyuk, Z. D.; Fay, M. W.; Zlyomi, V.; Falko, V.

    2014-12-01

    We report on the radiative recombination of photo-excited carriers bound at native donors and acceptors in exfoliated nanoflakes of nominally undoped rhombohedral ?-polytype InSe. The binding energies of these states are found to increase with the decrease in flake thickness, L. We model their dependence on L using a two-dimensional hydrogenic model for impurities and show that they are strongly sensitive to the position of the impurities within the nanolayer.

  19. Analysis of the Salmonella regulatory network suggests involvement of SsrB and H-NS in σE-regulated SPI-2 gene expression

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Li, Jie; Overall, Christopher C.; Nakayasu, Ernesto S.; Kidwai, Afshan S.; Jones, Marcus B.; Johnson, Rudd; Nguyen, Nhu T.; McDermott, Jason E.; Ansong, Charles; Heffron, Fred; et al

    2015-02-10

    The extracytoplasmic functioning sigma factor σE is known to play an essential role for Salmonella enterica serovar Typhimurium to survive and proliferate in macrophages and mice. However, its regulatory network is not well characterized, especially during infection. Here we used microarray to identify genes regulated by σE in Salmonella grown in three conditions: a nutrient-rich condition and two others that mimic early and late intracellular infection. We found that in each condition σE regulated different sets of genes, and notably, several global regulators. When comparing nutrient-rich and infection-like conditions, large changes were observed in the expression of genes involved inmore » Salmonella pathogenesis island (SPI)-1 type-three secretion system (TTSS), SPI-2 TTSS, protein synthesis, and stress responses. In total, the expression of 58% of Salmonella genes was affected by σE in at least one of the three conditions. An important finding is that σE up-regulates SPI-2 genes, which are essential for Salmonella intracellular survival, by up-regulating SPI-2 activator ssrB expression at the early stage of infection and down-regulating SPI-2 repressor hns expression at a later stage. Moreover, σE is capable of countering the silencing of H-NS, releasing the expression of SPI-2 genes. This connection between σE and SPI-2 genes, combined with the global regulatory effect of σE, may account for the lethality of rpoE-deficient Salmonella in murine infection.« less

  20. American Ref-Fuel of SE CT Biomass Facility | Open Energy Information

    Open Energy Info (EERE)

    Ref-Fuel of SE CT Biomass Facility Jump to: navigation, search Name American Ref-Fuel of SE CT Biomass Facility Facility American Ref-Fuel of SE CT Sector Biomass Facility Type...

  1. V-181: Oracle Java SE Critical Patch Update Advisory - June 2013...

    Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site

    1: Oracle Java SE Critical Patch Update Advisory - June 2013 V-181: Oracle Java SE Critical Patch Update Advisory - June 2013 June 19, 2013 - 1:06am Addthis PROBLEM: Oracle Java SE...

  2. Bi-Se doped with Cu, p-type semiconductor

    DOE Patents [OSTI]

    Bhattacharya, Raghu Nath; Phok, Sovannary; Parilla, Philip Anthony

    2013-08-20

    A Bi--Se doped with Cu, p-type semiconductor, preferably used as an absorber material in a photovoltaic device. Preferably the semiconductor has at least 20 molar percent Cu. In a preferred embodiment, the semiconductor comprises at least 28 molar percent of Cu. In one embodiment, the semiconductor comprises a molar percentage of Cu and Bi whereby the molar percentage of Cu divided by the molar percentage of Bi is greater than 1.2. In a preferred embodiment, the semiconductor is manufactured as a thin film having a thickness less than 600 nm.

  3. Pressure-dependent Optical Behaviors of Colloidal CdSe Nanoplatelets...

    Office of Scientific and Technical Information (OSTI)

    dependent Optical Behaviors of Colloidal CdSe Nanoplatelets Citation Details In-Document Search Title: Pressure-dependent Optical Behaviors of Colloidal CdSe Nanoplatelets Authors: ...

  4. Thermodynamic properties of model CdTe/CdSe mixtures

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    van Swol, Frank; Zhou, Xiaowang W.; Challa, Sivakumar R.; Martin, James E.

    2015-02-20

    We report on the thermodynamic properties of binary compound mixtures of model groups II–VI semiconductors. We use the recently introduced Stillinger–Weber Hamiltonian to model binary mixtures of CdTe and CdSe. We use molecular dynamics simulations to calculate the volume and enthalpy of mixing as a function of mole fraction. The lattice parameter of the mixture closely follows Vegard's law: a linear relation. This implies that the excess volume is a cubic function of mole fraction. A connection is made with hard sphere models of mixed fcc and zincblende structures. We found that the potential energy exhibits a positive deviation frommore » ideal soluton behaviour; the excess enthalpy is nearly independent of temperatures studied (300 and 533 K) and is well described by a simple cubic function of the mole fraction. Using a regular solution approach (combining non-ideal behaviour for the enthalpy with ideal solution behaviour for the entropy of mixing), we arrive at the Gibbs free energy of the mixture. The Gibbs free energy results indicate that the CdTe and CdSe mixtures exhibit phase separation. The upper consolute temperature is found to be 335 K. Finally, we provide the surface energy as a function of composition. Moreover, it roughly follows ideal solution theory, but with a negative deviation (negative excess surface energy). This indicates that alloying increases the stability, even for nano-particles.« less

  5. Laser damage by ns and sub-ps pulses on hafnia/silica anti-reflection coatings on fused silica double-sided polished using zirconia or ceria and washed with or without an alumina wash step.

    SciTech Connect (OSTI)

    Bellum, John Curtis; Rambo, Patrick K.; Schwarz, Jens; Kletecka, Damon; Atherton, Briggs W.; Kimmel, Mark W.; Smith, Ian Craig; Smith, Douglas; Hobbs, Zachary

    2010-10-01

    Sandia's Large Optics Coating Operation has extensive results of laser induced damage threshold (LIDT) testing of its anti-reflection (AR) and high reflection coatings on substrates pitch polished using ceria and washed in a process that includes an alumina wash step. The purpose of the alumina wash step is to remove residual polishing compound to minimize its role in laser damage. These LIDT tests are for multi longitudinal mode, ns class pulses at 1064 nm and 532 nm (NIF-MEL protocol) and mode locked, sub-ps class pulses at 1054 nm (Sandia measurements), and show reasonably high and adequate laser damage resistance for coatings in the beam trains of Sandia's Z-Backlighter terawatt and petawatt lasers. An AR coating in addition to coatings of our previous reports confirms this with LIDTs of 33.0 J/cm{sup 2} for 3.5 ns pulses and 1.8 J/cm{sup 2} for 350 fs pulses. In this paper, we investigate both ceria and zirconia in doublesided polishing (common for large flat Z-Backlighter laser optics) as they affect LIDTs of an AR coating on fused silica substrates washed with or without the alumina wash step. For these AR coated, double-sided polished surfaces, ceria polishing in general affords better resistance to laser damage than zirconia polishing and laser damage is less likely with the alumina wash step than without it. This is supported by specific results of laser damage tests with 3.5 ns, multi longitudinal mode, single shot pulses at 1064 nm and 532 nm, with 7.0 ns, single and multi longitudinal mode, single and multi shot pulses at 532 nm, and with 350 fs, mode-locked, single shot pulses at 1054 nm.

  6. Magnetooptical study of CdSe/ZnMnSe semimagnetic quantum-dot ensembles with n-type modulation doping

    SciTech Connect (OSTI)

    Reshina, I. I. Ivanov, S. V.

    2014-12-15

    Magnetic and polarization investigations of the photoluminescence and resonant electron spin-flip Raman scattering in ensembles of self-organized CdSe/ZnMnSe semimagnetic quantum dots with n-type modulation doping are carried out. It is demonstrated that exciton transitions contribute to the photoluminescence band intensity, along with the transitions of trions in the singlet state. In the Hanle-effect measurements, negative circular polarization in zero magnetic field is observed, which is related to the optical orientation of a trion heavy hole. The lifetime and spin-relaxation time of a heavy hole are estimated as ?3 and ?1 ps, respectively. Such short times are assumed to be due to Auger recombination with the excitation of an intrinsic transition in a Mn{sup 2+} ion. Investigations of the photoluminescence-maximum intensity and shift in a longitudinal magnetic field at the ?{sup ?}?{sup +} and ?{sup ?}?{sup ?} polarizations reveal the pronounced spin polarization of electrons. Under resonant excitation conditions, a sharp increase in the photoluminescence-band maximum intensity at ?{sup ?} excitation polarization over the ?{sup +} one is observed. The Raman scattering peak at the electron spin-flip transition is observed upon resonant excitation in a transverse magnetic field in crossed linear polarizations. This peak is shown to be a Brillouin function of a magnetic field.

  7. Photoluminescence study of the substitution of Cd by Zn during the growth by atomic layer epitaxy of alternate CdSe and ZnSe monolayers

    SciTech Connect (OSTI)

    Hernndez-Caldern, I.; Salcedo-Reyes, J. C.

    2014-05-15

    We present a study of the substitution of Cd atoms by Zn atoms during the growth of alternate ZnSe and CdSe compound monolayers (ML) by atomic layer epitaxy (ALE) as a function of substrate temperature. Samples contained two quantum wells (QWs), each one made of alternate CdSe and ZnSe monolayers with total thickness of 12 ML but different growth parameters. The QWs were studied by low temperature photoluminescence (PL) spectroscopy. We show that the Cd content of underlying CdSe layers is affected by the exposure of the quantum well film to the Zn flux during the growth of ZnSe monolayers. The amount of Cd of the quantum well film decreases with higher exposures to the Zn flux. A brief discussion about the difficulties to grow the Zn{sub 0.5}Cd{sub 0.5}Se ordered alloy (CuAu-I type) by ALE is presented.

  8. Study of the recombination process at crystallite boundaries in CuIn{sub 1-x}Ga{sub x}Se{sub 2} (CIGS) films by microwave photoconductivity

    SciTech Connect (OSTI)

    Bocharov, K. V.; Novikov, G. F.; Hsieh, T. Y.; Gapanovich, M. V.; Jeng, M. J.

    2013-03-15

    The loss kinetics of photogenerated charge carriers in thin polycrystalline chalcopyrite CuIn{sub 1-x}Ga{sub x}Se{sub 2} (CIGS) films has been studied by microwave photoconductivity (at 36 GHz). The films were synthesized using the ampoule method and three variants of physical vapor deposition with subsequent selenization: magnetron sputtering, thermal deposition, and modified thermal deposition with intermetallic precursors. The photoconductivity was excited by 8-ns nitrogen laser pulses with maximum intensity of 4 Multiplication-Sign 10{sup 14} photons/cm per pulse. Measurements were performed in the temperature range 148-293 K. The photoresponse amplitude is found to depend linearly on the sizes of coherent-scattering regions in the film grains, which were calculated from X-ray diffraction data. The photoresponse decay obeys hyperbolic law. The photoresponse half-decay time increases with a decrease in both temperature and light intensity. It is shown that the recombination of free holes with trapped electrons is very efficient near the crystallite boundaries.

  9. Intersubband absorption in CdSe/Zn{sub x}Cd{sub y}Mg{sub 1-x-y}Se self-assembled quantum dot multilayers

    SciTech Connect (OSTI)

    Shen, A.; Lu, H.; Charles, W.; Yokomizo, I.; Tamargo, M. C.; Franz, K. J.; Gmachl, C.; Zhang, S. K.; Zhou, X.; Alfano, R. R.; Liu, H. C.

    2007-02-12

    The authors report the observation of intersubband absorption in multilayers of CdSe/Zn{sub x}Cd{sub y}Mg{sub 1-x-y}Se self-assembled quantum dots. The samples were grown by molecular beam epitaxy on InP substrates. For samples with the CdSe dot layers doped with Cl and with the deposited CdSe equivalent layer thickness between 5.2 and 6.9 ML, peak absorption between 2.5 and 3.5 {mu}m was observed. These materials are promising for intersubband devices operating in the mid- and near-infrared ranges.

  10. Expanding the Repertoire of Chalcogenide Nanocrystal Networks: Ag2Se Gels

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    and Aerogels by Cation Exchange Reactions | Energy Frontier Research Centers Expanding the Repertoire of Chalcogenide Nanocrystal Networks: Ag2Se Gels and Aerogels by Cation Exchange Reactions Home Author: Q. Yao, I. U. Arachchige, S. L. Brock Year: 2009 Abstract: Cation exchange is shown to be a simple and efficient method to prepare nanostructured Ag2Se gels and aerogels from CdSe gel precursors. Treatment of CdSe wet gels with AgNO3yields, for the first time, Ag2Se gels, and these are

  11. Elastic and surface energies: Two key parameters for CdSe quantum dot formation

    SciTech Connect (OSTI)

    Robin, Ivan-Christophe; Andre, Regis; Bougerol, Catherine; Aichele, Thomas; Tatarenko, Serge

    2006-06-05

    The two-dimensional-three-dimensional transition of a strained CdSe layer on (001) ZnSe induced by the use of amorphous selenium is studied. To precisely control the thickness of the CdSe layer, atomic layer epitaxy growth mode is used. Atomic force microscopy and reflection high-energy electron diffraction measurements reveal the formation of CdSe islands when 3 ML (monolayers) of CdSe, corresponding to the critical thickness, are deposited. When only 2.5 ML of CdSe are deposited another relaxation mechanism is observed, leading to the appearance of strong undulations on the surface. For a 3 ML thick CdSe layer, transmission electron microscopy images indicate that the formation of the islands occurs only after the amorphous selenium desorption.

  12. Method of synthesizing and growing copper-indium-diselenide (CuInSe.sub.2) crystals

    DOE Patents [OSTI]

    Ciszek, Theodore F.

    1987-01-01

    A process for preparing CuInSe.sub.2 crystals includes melting a sufficient quantity of B.sub.2 O.sub.3 along with stoichiometric quantities of Cu, In, and Se in a crucible in a high pressure atmosphere of inert gas to encapsulate the CuInSe.sub.2 melt and confine the Se to the crucible. Additional Se in the range of 1.8 to 2.2 percent over the stoichiometric quantity is preferred to make up for small amounts of Se lost in the process. The crystal is grown by inserting a seed crystal through the B.sub.2 O.sub.3 encapsulate into contact with the CuInSe.sub.2 melt and withdrawing the seed upwardly to grow the crystal thereon from the melt.

  13. Method of synthesizing and growing copper-indium-diselenide (CuInSe/sub 2/) crystals

    DOE Patents [OSTI]

    Ciszek, T.F.

    1984-11-29

    A process for preparing CuInSe/sub 2/ crystals includes melting a sufficient quantity of B/sub 2/O/sub 2/ along with stochiometric quantities of Cu, In, and Se in a crucible in a high-pressure atmosphere of inert gas to encapsulate the CuInSe/sub 2/ melt and confine the Se to the crucible. Additional Se in the range of 1.8 to 2.2% over the stochiometric quantity is preferred to make up for small amounts of Se lost in the process. The melt can then be cooled slowly to form the crystal as direct solidification, or the crystal can be grown by inserting a seed crystal through the B/sub 2/O/sub 3/ encapsulate into contact with the CuInSe/sub 2/ melt and withdrawing the seed upwardly to grow the crystal thereon from the melt.

  14. Electrical properties of In{sub 2}Se{sub 3} single crystals and photosensitivity of Al/In{sub 2}Se{sub 3} Schottky barriers

    SciTech Connect (OSTI)

    Bodnar, I. V.; Ilchuk, G. A.; Petrus', R. Yu.; Rud', V. Yu.; Rud', Yu. V.; Serginov, M.

    2009-09-15

    In{sub 2}Se{sub 3} single crystals {approx}40 mm long and 14 mm in diameter were grown by the Bridgman method. The composition of grown single crystals and their crystal structure were determined. The conductivity ({sigma}) and Hall constant (R) of grown single crystals were measured and the first Schottky barriers Al/n-In{sub 2}Se{sub 3} were fabricated. Rectification and photovoltaic effect were detected in the new structures. Based on the study of the photosensitivity spectra of Al/n-In{sub 2}Se{sub 3} structures, the nature of the interband transitions and band gap of In{sub 2}Se{sub 3} crystals were determined. It was concluded that the new structures can be applied to develop broadband photoconverters of optical radiation.

  15. Pulsed laser deposition of Mn doped CdSe quantum dots for improved solar cell performance

    SciTech Connect (OSTI)

    Dai, Qilin; Wang, Wenyong E-mail: jtang2@uwyo.edu; Tang, Jinke E-mail: jtang2@uwyo.edu; Sabio, Erwin M.

    2014-05-05

    In this work, we demonstrate (1) a facile method to prepare Mn doped CdSe quantum dots (QDs) on Zn{sub 2}SnO{sub 4} photoanodes by pulsed laser deposition and (2) improved device performance of quantum dot sensitized solar cells of the Mn doped QDs (CdSe:Mn) compared to the undoped QDs (CdSe). The band diagram of photoanode Zn{sub 2}SnO{sub 4} and sensitizer CdSe:Mn QD is proposed based on the incident-photon-to-electron conversion efficiency (IPCE) data. Mn-modified band structure leads to absorption at longer wavelengths than the undoped CdSe QDs, which is due to the exchange splitting of the CdSe:Mn conduction band by the Mn dopant. Three-fold increase in the IPCE efficiency has also been observed for the Mn doped samples.

  16. Ligand-Mediated Modification of the Electronic Structure of CdSe Quantum Dots

    SciTech Connect (OSTI)

    Lee, Jonathan R.; Whitley, Heather D.; Meulenberg, Robert W.; Wolcott, Abraham; Zhang, Jin Z.; Prendergast, Peter; Lovingood, Derek D.; Strouse, Geoffrey F.; Ogitsu, Tadashi; Schwegler, Eric; Terminello, Louis J.; Van Buuren, Tony W.

    2012-05-18

    X-ray absorption spectroscopy and ab initio modeling of the experimental spectra have been used to investigate the effects of surface passivation on the unoccupied electronic states of CdSe quantum dots (QDs). Significant differences are observed in the unoccupied electronic structure of the CdSe QDs, which are shown to arise from variations in specific ligand-surface bonding interactions.

  17. Development of a Low Cost Insulated Foil Substrate for Cu(InGaSe)2 Photovoltaics

    SciTech Connect (OSTI)

    ERTEN ESER

    2012-01-22

    The project validated the use of stainless steel flexible substrate coated with silicone-based resin dielectric, developed by Dow Corning Corporation, for Cu(InGa)Se2 based photovoltaics. The projects driving force was the high performance of Cu(InGa)Se2 based photovoltaics coupled with potential cost reduction that could be achieved with dielectric coated SS web substrate.

  18. Surface Plasmon Excitation via Au Nanoparticles in CdSe Semiconductor

    SciTech Connect (OSTI)

    Pradhan, A. K.; Konda, R. B.; Mundle, R.; Mustafa, H.; Bamiduro, O.; Roy, U. N.; Cui, Y.; Burger, A.

    2008-10-23

    We present experimental evidence for the large Raman and photoluminescence enhancement in CdSe semiconductor films grown on Si and glass substrates due to excitation of surface plasmon resonances in proximate gold metal nanoparticles deposited on the surface of CdSe film. Heterojunction diodes containing n-CdSe on p-Si semiconductor were fabricated and the surface of the diodes was in situ coated with Au nanoparticles using the ultra-high vacuum pulsed-laser deposition technique. A significant enhancement of the photocurrent was obtained in CdSe/p-Si containing Au nanoparticles on the surface compared to CdSe/p-Si due to the enhanced photo-absorption within the semiconductor by the phenomenon of surface plasmon resonance. These observations suggest a variety of approaches for improving the performance of devices such as photodetectors, photovoltaic, and related devices, including biosensors.

  19. Structural phase transitions in Bi2Se3 under high pressure

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Yu, Zhenhai; Gu, Genda; Wang, Lin; Hu, Qingyang; Zhao, Jinggeng; Yan, Shuai; Yang, Ke; Sinogeikin, Stanislav; Mao, Ho -kwang

    2015-11-02

    Raman spectroscopy and angle dispersive X-ray diffraction (XRD) experiments of bismuth selenide (Bi2Se3) have been carried out to pressures of 35.6 and 81.2 GPa, respectively, to explore its pressure-induced phase transformation. The experiments indicate that a progressive structural evolution occurs from an ambient rhombohedra phase (Space group (SG): R-3m) to monoclinic phase (SG: C2/m) and eventually to a high pressure body-centered tetragonal phase (SG: I4/mmm). Evidenced by our XRD data up to 81.2 GPa, the Bi2Se3 crystallizes into body-centered tetragonal structures rather than the recently reported disordered body-centered cubic (BCC) phase. Furthermore, first principles theoretical calculations favor the viewpoint thatmore » the I4/mmm phase Bi2Se3 can be stabilized under high pressure (>30 GPa). Remarkably, the Raman spectra of Bi2Se3 from this work (two independent runs) are still Raman active up to ~35 GPa. Furthermore, it is worthy to note that the disordered BCC phase at 27.8 GPa is not observed here. The remarkable difference in atomic radii of Bi and Se in Bi2Se3 may explain why Bi2Se3 shows different structural behavior than isocompounds Bi2Te3 and Sb2Te3.« less

  20. Probing the size and environment induced phase transformation in CdSe quantum dots

    SciTech Connect (OSTI)

    Karakoti, Ajay S.; Sanghavi, Shail P.; Nachimuthu, Ponnusamy; Yang, Ping; Thevuthasan, Suntharampillai

    2011-11-17

    The structural and electronic properties of CdSe quantum dots in toluene and drop-casted on Si wafer were investigated by in-situ micro X-ray diffraction, X-ray photoelectron spectroscopy and UV-Vis absorption and emission spectroscopy. The in-situ micro diffraction data show that the CdSe quantum dots capped with TOPO or hexadecylamine (HDA) in toluene exhibit predominantly wurtzite crystal structure, which undergoes a phase transformation to zinc blende crystal structure following drop casting on Si and this phase transition increases with decreasing the size of the CdSe quantum dots. Decreasing the size of quantum dots also increases the Se vacancies that facilitate the phase transformation. The X-ray photoelectron spectra show a systematic increase in the core level binding energies of Cd 3d and Se 3d, the band gap and the Cd/Se ratio as the size of the quantum dots decreases from 6.6nm to 2.1nm. This is attributed to the quantum confinement of CdSe crystallites by the capping ligands in toluene which increases with decreasing the size of the quantum dots. However, drop-casting quantum dots on Si alter the density and arrangement of capping ligands and solvent molecules on the quantum dots which causes significant phase transformation.

  1. Near-Unity Quantum Yields of Biexciton Emission from CdSe=CdS Nanocrystals

    Office of Scientific and Technical Information (OSTI)

    Measured Using Single-Particle Spectroscopy (Journal Article) | SciTech Connect Near-Unity Quantum Yields of Biexciton Emission from CdSe=CdS Nanocrystals Measured Using Single-Particle Spectroscopy Citation Details In-Document Search Title: Near-Unity Quantum Yields of Biexciton Emission from CdSe=CdS Nanocrystals Measured Using Single-Particle Spectroscopy Biexciton photoluminescence (PL) quantum yields (Q2X) of individual CdSe/CdS core-shell nanocrystal quantum dots with various shell

  2. Optimal packing size of non-ligated CdSe nanoclusters for microstructure synthesis

    SciTech Connect (OSTI)

    Tefera, Anteneh G.; Mochena, Mogus D.; Johnson, Elijah; Dickerson, James

    2014-09-14

    Structural and electrostatic properties of nanoclusters of CdSe of diameter 1–2 nm are studied with first principle calculations to determine the optimal size for synthesizing microstructures. Based on robustness of the core structure, i.e., the retention of tetrahedral geometry, hexagonal ring structure, and overall wu{sup ¨}rtzite structure to surface relaxations, we conclude that nanoclusters of ~2 nm diameter are the best candidates to form a dense microstructure with minimal interstitial space. Se-terminated surfaces retain a zigzag structure as Se atoms are pulled out and Cd atoms are pulled in due to relaxation, therefore, are best suited for inter-nanocluster formations.

  3. An oleic acid-capped CdSe quantum-dot sensitized solar cell

    SciTech Connect (OSTI)

    Chen Jing; Song, J. L.; Deng, W. Q.; Sun, X. W.; Jiang, C. Y.; Lei, W.; Huang, J. H.; Liu, R. S.

    2009-04-13

    In this letter, we report an oleic acid (OA)-capped CdSe quantum-dot sensitized solar cell (QDSSC) with an improved performance. The TiO{sub 2}/OA-CdSe photoanode in a two-electrode device exhibited a photon-to-current conversion efficiency of 17.5% at 400 nm. At AM1.5G irradiation with 100 mW/cm{sup 2} light intensity, the QDSSCs based on OA-capped CdSe showed a power conversion efficiency of about 1%. The function of OA was to increase QD loading, extend the absorption range and possibly suppress the surface recombination.

  4. Thickness-dependent coherent phonon frequency in ultrathin FeSe/SrTiO3

    Office of Scientific and Technical Information (OSTI)

    films (Journal Article) | SciTech Connect Thickness-dependent coherent phonon frequency in ultrathin FeSe/SrTiO3 films Citation Details In-Document Search Title: Thickness-dependent coherent phonon frequency in ultrathin FeSe/SrTiO3 films Ultrathin FeSe films grown on SrTiO3 substrates are a recent milestone in atomic material engineering due to their important role in understanding unconventional superconductivity in Fe-based materials. By using femtosecond time- and angle-resolved

  5. Population Pulsation Resonances of Excitons in Monolayer MoSe 2 with Sub- 1 μ eV Linewidths

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Schaibley, John R.; Karin, Todd; Yu, Hongyi; Ross, Jason S.; Rivera, Pasqual; Jones, Aaron M.; Scott, Marie E.; Yan, Jiaqiang; Mandrus, D. G.; Yao, Wang; et al

    2015-04-01

    Monolayer transition metal dichalcogenides, a new class of atomically thin semiconductors, possess optically coupled 2D valley excitons. The nature of exciton relaxation in these systems is currently poorly understood. Here, we investigate exciton relaxation in monolayer MoSe₂ using polarization-resolved coherent nonlinear optical spectroscopy with high spectral resolution. We report strikingly narrow population pulsation resonances with two different characteristic linewidths of 1 and <0.2 μeV at low temperature. These linewidths are more than 3 orders of magnitude narrower than the photoluminescence and absorption linewidth, and indicate that a component of the exciton relaxation dynamics occurs on time scales longer than 1more » ns. The ultranarrow resonance (<0.2 μeV) emerges with increasing excitation intensity, and implies the existence of a long-lived state whose lifetime exceeds 6 ns.« less

  6. Low-temperature ferromagnetic properties in Co-doped Ag{sub 2}Se nanoparticles

    SciTech Connect (OSTI)

    Yang, Fengxia E-mail: xia9020@hust.edu.cn; Yu, Gen; Han, Chong; Liu, Tingting; Zhang, Duanming; Xia, Zhengcai E-mail: xia9020@hust.edu.cn

    2014-01-06

    β-Ag{sub 2}Se is a topologically nontrivial insulator. The magnetic properties of Co-doped Ag{sub 2}Se nanoparticles with Co concentrations up to 40% were investigated. The cusp of zero-field-cooling magnetization curves and the low-temperature hysteresis loops were observed. With increasing concentration of Co{sup 2+} ions mainly substituting Ag{sub I} sites in the Ag{sub 2}Se structure, the resistivity, Curie temperature T{sub c}, and magnetization increased. At 10 T, a sharp drop of resistance near T{sub c} was detected due to Co dopants. The ferromagnetic behavior in Co-doped Ag{sub 2}Se might result from the intra-layer ferromagnetic coupling and surface spin. This magnetic semiconductor is a promising candidate in electronics and spintronics.

  7. Thermoelectric properties of polycrystalline In4Se3 and In4Te3

    SciTech Connect (OSTI)

    Shi, Xun; Cho, Jung Y; Salvador, James R.; Yang, Jihui; Wang, Hsin

    2010-01-01

    High thermoelectric performance of a single crystal layered compound In{sub 4}Se{sub 3} was reported recently. We present here an electrical and thermal transport property study over a wide temperature range for polycrystalline samples of In{sub 4}Se{sub 3} and In{sub 4}Te{sub 3}. Our data demonstrate that these materials are lightly doped semiconductors, leading to large thermopower and resistivity. Very low thermal conductivity, below 1 W/m K, is observed. The power factors for In{sub 4}Se{sub 3} and In{sub 4}Te{sub 3} are much smaller when compared with state-of-the-art thermoelectric materials. This combined with the very low thermal conductivity results in the maximum ZT value of less than 0.6 at 700 K for In{sub 4}Se{sub 3}.

  8. Enhanced spontaneous emission of CdSe quantum dots in monolithic II-VI pillar microcavities

    SciTech Connect (OSTI)

    Lohmeyer, H.; Kruse, C.; Sebald, K.; Gutowski, J.; Hommel, D.

    2006-08-28

    The emission properties of CdSe/ZnSe quantum dots in ZnSe-based pillar microcavities are studied. All-epitaxial cavities made of ZnSSe and MgS/ZnCdSe superlattices with a single quantum-dot sheet embedded have been grown by molecular beam epitaxy. Pillar structures with diameters down to 500 nm have been realized by focused-ion-beam etching. A pronounced enhancement of the spontaneous emission rate of quantum dots coupling to the fundamental mode of the cavities is found as evidence for the Purcell effect. The enhancement by a factor of up to 3.8 depends systematically on the pillar diameter and thus on the Purcell factor of the individual pillars.

  9. Phonon properties of BaFe?X? (X=S, Se) spin ladder compounds

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Popovicq, Z. V.; Petrovic, C.; Scepanovic, M.; Lazarevic, N.; Opacic, M.; Radonjic, M. M.; Tanaskovic, D.; Lei, Hechang

    2015-02-27

    We present the Raman scattering spectra of the S=2 spin ladder compounds BaFe?X? (X=S,Se) in a temperature range between 20 and 400 K. Although the crystal structures of these two compounds are both orthorhombic and very similar, they are not isostructural. The unit cell of BaFe?S? (BaFe?Se?) is base-centered Cmcm (primitive Pnma), giving 18 (36) modes to be observed in the Raman scattering experiment. We have detected almost all Raman active modes, predicted by factor group analysis, which can be observed from the cleavage planes of these compounds. Assignment of the observed Raman modes of BaFe?S(Se)? is supported by themorelattice dynamics calculations. The antiferromagnetic long-range spin ordering in BaFe?Se? below TN=255K leaves a fingerprint both in the A1g and B3g phonon mode linewidth and energy.less

  10. Super-Poissonian Statistics of Photon Emission from Single CdSe...

    Office of Scientific and Technical Information (OSTI)

    Statistics of Photon Emission from Single CdSe-CdS Core-Shell Nanocrystals Coupled to Metal Nanostructures Citation Details In-Document Search Title: Super-Poissonian Statistics of ...

  11. Flow of US/SE Program Funding to National Laboratories (FY 2014 Enacted)

    Broader source: Energy.gov [DOE]

    This figure illustrates the flow of funding to each of 17 DOE National Laboratories from five of the six US/SE program offices. IE does not directly fund program work at the National Laboratories.

  12. AeroSys: Noncompliance Determination (2010-SE-0302) | Department of Energy

    Energy Savers [EERE]

    Noncompliance Determination (2010-SE-0302) AeroSys: Noncompliance Determination (2010-SE-0302) April 13, 2010 DOE issued a Notice of Noncompliance Determination to AeroSys, Inc. finding that basic model THDC-24SG does not comport with the energy conservation standards. DOE determined the product was noncompliant based on DOE testing. AeroSys must immediately notify each person (or company) to whom AeroSys distributed the noncompliant product that the product does not meet Federal standards. In

  13. Unique Challenges Accompany Thick-Shell CdSe/nCdS (n > 10) Nanocrystal Synthesis

    SciTech Connect (OSTI)

    Guo, Y; Marchuk, K; Abraham, R; Sampat, S; Abraham, R.; Fang, N; Malko, AV; Vela, J

    2011-12-23

    Thick-shell CdSe/nCdS (n {ge} 10) nanocrystals were recently reported that show remarkably suppressed fluorescence intermittency or 'blinking' at the single-particle level as well as slow rates of Auger decay. Unfortunately, whereas CdSe/nCdS nanocrystal synthesis is well-developed up to n {le} 6 CdS monolayers (MLs), reproducible syntheses for n {ge} 10 MLs are less understood. Known procedures sometimes result in homogeneous CdS nucleation instead of heterogeneous, epitaxial CdS nucleation on CdSe, leading to broad and multimodal particle size distributions. Critically, obtained core/shell sizes are often below those desired. This article describes synthetic conditions specific to thick-shell growth (n {ge} 10 and n {ge} 20 MLs) on both small (sub2 nm) and large (>4.5 nm) CdSe cores. We find added secondary amine and low concentration of CdSe cores and molecular precursors give desired core/shell sizes. Amine-induced, partial etching of CdSe cores results in apparent shell-thicknesses slightly beyond those desired, especially for very-thick shells (n {ge} 20 MLs). Thermal ripening and fast precursor injection lead to undesired homogeneous CdS nucleation and incomplete shell growth. Core/shells derived from small CdSe (1.9 nm) have longer PL lifetimes and more pronounced blinking at single-particle level compared with those derived from large CdSe (4.7 nm). We expect our new synthetic approach will lead to a larger throughput of these materials, increasing their availability for fundamental studies and applications.

  14. Synthesis of CdSe quantum dots for quantum dot sensitized solar cell

    SciTech Connect (OSTI)

    Singh, Neetu Kapoor, Avinashi; Kumar, Vinod; Mehra, R. M.

    2014-04-24

    CdSe Quantum Dots (QDs) of size 0.85 nm were synthesized using chemical route. ZnO based Quantum Dot Sensitized Solar Cell (QDSSC) was fabricated using CdSe QDs as sensitizer. The Pre-synthesized QDs were found to be successfully adsorbed on front ZnO electrode and had potential to replace organic dyes in Dye Sensitized Solar Cells (DSSCs). The efficiency of QDSSC was obtained to be 2.06 % at AM 1.5.

  15. Supercharging a Superconductor: Understanding the Tc enhancement of FeSe |

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Stanford Synchrotron Radiation Lightsource Supercharging a Superconductor: Understanding the Tc enhancement of FeSe Wednesday, April 13, 2016 - 3:00pm SLAC, Redtail Hawk Conference Room 108A Speaker: Rob Moore, SIMES Program Description The recent synthesis of interfaces and heterostructures with atomic precision has revealed numerous new and unexpected phenomena. The order of magnitude enhancement of the superconducting properties of FeSe in the ultrathin 2D limit is an example of such a

  16. Super-Poissonian Statistics of Photon Emission from Single CdSe-CdS

    Office of Scientific and Technical Information (OSTI)

    Core-Shell Nanocrystals Coupled to Metal Nanostructures (Journal Article) | SciTech Connect Super-Poissonian Statistics of Photon Emission from Single CdSe-CdS Core-Shell Nanocrystals Coupled to Metal Nanostructures Citation Details In-Document Search Title: Super-Poissonian Statistics of Photon Emission from Single CdSe-CdS Core-Shell Nanocrystals Coupled to Metal Nanostructures Authors: Park, Young-Shin ; Ghosh, Yagnaseni ; Chen, Yongfen ; Piryatinski, Andrei ; Xu, Ping ; Mack, Nathan H. ;

  17. Advanced Precursor Reaction Processing for Cu(InGa)(SeS)2 Solar Cells

    SciTech Connect (OSTI)

    Shafarman, William N.

    2015-10-12

    This project “Advanced Precursor Reaction Processing for Cu(InGa)(SeS)2 Solar Cells”, completed by the Institute of Energy Conversion (IEC) at the University of Delaware in collaboration with the Department of Chemical Engineering at the University of Florida, developed the fundamental understanding and technology to increase module efficiency and improve the manufacturability of Cu(InGa)(SeS)2 films using the precursor reaction approach currently being developed by a number of companies. Key results included: (1) development of a three-step H2Se/Ar/H2S reaction process to control Ga distribution through the film and minimizes back contact MoSe2 formation; (2) Ag-alloying to improve precursor homogeneity by avoiding In phase agglomeration, faster reaction and improved adhesion to allow wider reaction process window; (3) addition of Sb, Bi, and Te interlayers at the Mo/precursor junction to produce more uniform precursor morphology and improve adhesion with reduced void formation in reacted films; (4) a precursor structure containing Se and a reaction process to reduce processing time to 5 minutes and eliminate H2Se usage, thereby increasing throughput and reducing costs. All these results were supported by detailed characterization of the film growth, reaction pathways, thermodynamic assessment and device behavior.

  18. Doping SrTiO3 supported FeSe by excess atoms and oxygen vacancies

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Shanavas, Kavungal Veedu; Singh, David J.

    2015-07-24

    Photoemission studies of FeSe monolayer films on SrTiO3 substrate have shown electronic structures that deviate from pristine FeSe, consistent with heavy electron doping. With the help of first-principles calculations we studied the effect of excess Fe and Se atoms on the monolayer and oxygen vacancies in the substrate in order to understand the reported Fermi surface in this system. We find that both excess Fe and Se atoms prefer the same adsorption site above the bottom Se atoms on the monolayer. The adsorbed Fe is strongly magnetic and contributes electrons to the monolayer, while excess Se hybridizes with the monolayermore » Fe-d states and partially opens a gap just above the Fermi energy. We also find that the two-dimensional electron gas generated by the oxygen vacancies is partly transferred to the monolayer and can potentially suppress the hole pockets around the Γ point. Furthermore, both O vacancies in the SrTiO3 substrate and excess Fe over the monolayer can provide high levels of electron doping.« less

  19. A comparative transport study of Bi{sub 2}Se{sub 3} and Bi{sub 2}Se{sub 3}/yttrium iron garnet

    SciTech Connect (OSTI)

    Jiang, Zilong; Tang, Chi; Shi, Jing; Katmis, Ferhat; Wei, Peng; Moodera, Jagadeesh S.

    2014-06-02

    Bilayers of 20 quintuple layer Bi{sub 2}Se{sub 3} on 30 nm thick yttrium iron garnet (YIG) have been grown with molecular beam epitaxy in conjunction with pulsed laser deposition. The presence of the ferri-magnetic insulator YIG causes additional scattering to the surface states of the Bi{sub 2}Se{sub 3} topological insulator layer, as indicated by the temperature dependence of the resistivity. From the two-channel analysis of the Hall data, we find that the surface contribution in the bilayer samples is greatly reduced. Furthermore, the weak antilocalization effect from the surface states is clearly suppressed due to the presence of the YIG layer.

  20. CdSe/ZnSe quantum dot with a single Mn{sup 2+} ionA new system for a single spin manipulation

    SciTech Connect (OSTI)

    Smole?ski, T.

    2015-03-21

    We present a magneto-optical study of individual self-assembled CdSe/ZnSe quantum dots doped with single Mn{sup 2+} ions. Properties of the studied dots are analyzed analogously to more explored system of Mn-doped CdTe/ZnTe dots. Characteristic sixfold splitting of the neutral exciton emission line as well as its evolution in the magnetic field are described using a spin Hamiltonian model. Dynamics of both exciton recombination and Mn{sup 2+} spin relaxation are extracted from a series of time-resolved experiments. Presence of a single dopant is shown not to affect the average excitonic lifetime measured for a number of nonmagnetic and Mn-doped dots. On the other hand, non-resonant pumping is demonstrated to depolarize the Mn{sup 2+} spin in a quantum dot placed in external magnetic field. This effect is utilized to determine the ion spin relaxation time in the dark.

  1. Hidden Superlattice in Tl2(SC6H4S) and Tl2(SeC6H4Se) Solved from Powder X-ray Diffraction

    SciTech Connect (OSTI)

    K Stone; D Turner; M Singh; T Vaid; P Stephens

    2011-12-31

    The crystal structures of the isostructural title compounds poly[({mu}-benzene-1,4-dithiolato)dithallium], Tl{sub 2}(SC{sub 6}H{sub 4}S), and poly[({mu}-benzene-1,4-diselenolato)dithallium], Tl{sub 2}(SeC{sub 6}H{sub 4}Se), were solved by simulated annealing from high-resolution synchrotron X-ray powder diffraction. Rietveld refinements of an initial structure with one formula unit per triclinic cell gave satisfactory agreement with the data, but led to a structure with impossibly close non-bonded contacts. A disordered model was proposed to alleviate this problem, but an alternative supercell structure leads to slightly improved agreement with the data. The isostructural superlattice structures were confirmed for both compounds through additional data collection, with substantially better counting statistics, which revealed the presence of very weak superlattice peaks not previously seen. Overall, each structure contains Tl-S or Tl-Se two-dimensional networks, connected by phenylene bridges. The sulfur (or selenium) coordination sphere around each thallium is a highly distorted square pyramid or a 'see-saw' shape, depending upon how many Tl-S or Tl-Se interactions are considered to be bonds. In addition, the two compounds contain pairs of Tl{sup I} ions that interact through a closed-shell 'thallophilic' interaction: in the sulfur compound there are two inequivalent pairs of Tl atoms with Tl-Tl distances of 3.49 and 3.58 {angstrom}, while in the selenium compound those Tl-Tl interactions are at 3.54 and 3.63 {angstrom}.

  2. Non-H{sub 2}Se, ultra-thin CuInSe{sub 2} devices. Annual subcontract report, November 10, 1992--November 9, 1993

    SciTech Connect (OSTI)

    Delahoy, A.E.; Britt, J.; Faras, F.; Kiss, Z.

    1994-09-01

    This report describes advances made during Phase II (November 10, 1992-November 9, 1993) of a three-phase, cost-shared subcontract whose ultimate goal is the demonstration of thin film CuInSe{sub 2} photovoltaic modules prepared by methods adaptable to safe, high yield, high volume manufacturing. At the end of Phase I, EPV became one of the first groups to clear the 10% efficiency barrier for CIS cells prepared by non-H{sub 2}Se selenization. During Phase II a total area efficiency of 12.5% was achieved for a 1 cm{sup 2} cell. The key achievement of Phase II was the production of square foot CIS modules without the use of H{sub 2}Se. This is seen as a crucial step towards the commercialization of CIS. Using a novel interconnect technology, EPV delivered an 8.0% aperture area efficiency mini-module and a 6.2% aperture area efficiency 720 cm{sub 2} module to NREL. On the processing side, advances were made in precursor formation and the selenization profile, both of which contributed to higher quality CIS. The higher band gap quaternary chalcopyrite material CuIn(S{sub x}, Se{sub 1{minus}X}){sub 2} was prepared and 8% cells were fabricated using this material. Device analysis revealed a correlation between long wavelength quantum efficiency and the CIS Cu/In ratio. Temperature dependent studies highlighted the need for high V{sub OC} devices to minimize the impact of the voltage drop at operating temperature. Numerical modeling of module performance was performed in order to identify the correct ZnO sheet resistance for modules. Efforts in Phase III will focus on increase of module efficiency to 9-10%, initiation of an outdoor testing program, preparation of completely uniform CIS plates using second generation selenization equipment, and exploration of alternative precursors for CIS formation.

  3. Persistent photoconductivity in two-dimensional Mo1-xW xSe2–MoSe2 van der Waals heterojunctions

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Puretzky, Alexander A.; Basile, Leonardo; Idrobo, Juan Carlos; Rouleau, Christopher M.; Geohegan, David B.; Xiao, Kai; Li, Xufan; Lin, Ming -Wei; Wang, Kei

    2016-02-16

    Van der Waals (vdW) heterojunctions consisting of vertically-stacked individual or multiple layers of two-dimensional (2D) layered semiconductors, especially the transition metal dichalcogenides (TMDs), are fascinating new artificial solids just nanometers-thin that promise novel optoelectronic functionalities due to the sensitivity of their electronic and optical properties to strong quantum confinement and interfacial interactions. Here, monolayers of n-type MoSe2 and p-type Mo1-xW xSe2–MoSe2 are grown by vapor transport methods, then transferred and stamped to form artificial vdW heterostructures with different interlayer orientations. Atomic-resolution Z-contrast electron microscopy and electron diffraction are used to characterize both the individual monolayers and the atomic registry betweenmore » layers in the bilayer vdW heterostructures. These measurements are compared with photoluminescence and low-frequency Raman spectroscopy, which indicates strong interlayer coupling in heterostructures. Remarkably, the heterojunctions exhibit an unprecedented photoconductivity effect that persists at room temperature for several days. This persistent photoconductivity is shown to be tunable by applying a gate bias that equilibrates the charge distribution. Furthermore, these measurements indicate that such ultrathin vdW heterojunctions can function as rewritable optoelectronic switches or memory elements under time-dependent photo-illumination, an effect which appears promising for new monolayer TMDs-based optoelectronic devices applications.« less

  4. Recrystallization method to selenization of thin-film Cu(In,Ga)Se.sub.2 for semiconductor device applications

    DOE Patents [OSTI]

    Albin, David S.; Carapella, Jeffrey J.; Tuttle, John R.; Contreras, Miguel A.; Gabor, Andrew M.; Noufi, Rommel; Tennant, Andrew L.

    1995-07-25

    A process for fabricating slightly Cu-poor thin-films of Cu(In,Ga)Se.sub.2 on a substrate for semiconductor device applications includes the steps of forming initially a slightly Cu-rich, phase separated, mixture of Cu(In,Ga)Se.sub.2 :Cu.sub.x Se on the substrate in solid form followed by exposure of the Cu(In,Ga)Se.sub.2 :Cu.sub.x Se solid mixture to an overpressure of Se vapor and (In,Ga) vapor for deposition on the Cu(In,Ga)Se.sub.2 :Cu.sub.x Se solid mixture while simultaneously increasing the temperature of the solid mixture toward a recrystallization temperature (about 550.degree. C.) at which Cu(In,Ga)Se.sub.2 is solid and Cu.sub.x Se is liquid. The (In,Ga) flux is terminated while the Se overpressure flux and the recrystallization temperature are maintained to recrystallize the Cu.sub.x Se with the (In, Ga) that was deposited during the temperature transition and with the Se vapor to form the thin-film of slightly Cu-poor Cu.sub.x (In,Ga).sub.y Se.sub.z. The initial Cu-rich, phase separated large grain mixture of Cu(In,Ga)Se.sub.2 :Cu.sub.x Se can be made by sequentially depositing or co-depositing the metal precursors, Cu and (In, Ga), on the substrate at room temperature, ramping up the thin-film temperature in the presence of Se overpressure to a moderate anneal temperature (about 450.degree. C.) and holding that temperature and the Se overpressure for an annealing period. A nonselenizing, low temperature anneal at about 100.degree. C. can also be used to homogenize the precursors on the substrates before the selenizing, moderate temperature anneal.

  5. Novel Approaches to Wide Bandgap CuInSe2 Based Absorbers

    SciTech Connect (OSTI)

    William N. Shafarman

    2011-04-28

    This project targeted the development of high performance wide bandgap solar cells based on thin film alloys of CuInSe2 to relax constraints on module design and enable tandem solar cell structures. This addressed goals of the Solar Energy Technologies Program for Next Generation PV to develop technology needed for higher thin film module efficiency as a means to reduce costs. Specific objectives of the research project were: 1) to develop the processes and materials required to improve the performance of wide bandgap thin film solar cells based on alloys of CuInSe2, and 2) to provide the fundamental science and engineering basis for the material, electronic, and device properties required to effectively apply these processes and materials to commercial manufacture. CuInSe2-based photovoltaics have established the highest efficiencies of the thin film materials at both the cell and module scales and are actively being scaled up to commercialization. In the highest efficiency cells and modules, the optical bandgap, a function of the CuInSe2-based alloy composition, is relatively low compared to the optimum match to the solar spectrum. Wider bandgap alloys of CuInSe2 produce higher cell voltages which can improve module performance and enable the development of tandem solar cells to boost the overall efficiency. A focus for the project was alloying with silver to form (AgCu)(InGa)Se2 pentenary thin films deposited by elemental co-evaporation which gives the broadest range of control of composition and material properties. This alloy has a lower melting temperature than Ag-free, Cu-based chalcopyrite compounds, which may enable films to be formed with lower defect densities and the (AgCu)(InGa)Se2 films give improved material properties and better device performance with increasing bandgap. A comprehensive characterization of optical, structural, and electronic properties of (AgCu)(InGa)Se2 was completed over the complete compositional range 0 ≤ Ga/(In+Ga) ≤ 1 and 0 ≤ Ag/(Ag+Cu) ≤ 1. Evidence of improved material quality includes reduced sub-bandgap optical absorption, sharper bandtails, and increased grain size with Ag addition. The Ag alloying was shown to increase the range of bandgaps over which solar cells can be fabricated without any drop-off in performance. With bandgap greater than 1.6 eV, in the range needed for tandem solar cells, (AgCu)(InGa)Se2 gave higher efficiency than other CuInSe2-based alloys. Using a simple single-stage co-evaporation process, a solar cell with 17.6% efficiency using a film with bandgap = 1.3 eV was achieved, demonstrating the viability of (AgCu)(InGa)Se2 for high efficiency devices. With a three-stage co-evaporation process for (AgCu)(InGa)Se2 deposition a device with efficiency = 13.0 % and VOC = 890 mV with JSC = 20.5 mA/cm2, FF = 71.3% was achieved. This surpasses the performance of other wide bandgap CuInSe2-based solar cells. Detailed characterization of the electronic properties of the materials and devices including the application of advanced admittance-based easements was completed.

  6. Superconductivity in strong spin orbital coupling compound Sb2Se3

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Kong, P. P.; Sun, F.; Xing, L. Y.; Zhu, J.; Zhang, S. J.; Li, W. M.; Liu, Q. Q.; Wang, X. C.; Feng, S. M.; Yu, X. H.; et al

    2014-10-20

    Recently, A2B3 type strong spin orbital coupling compounds such as Bi2Te3, Bi2Se3 and Sb2Te3 were theoretically predicated to be topological insulators and demonstrated through experimental efforts. The counterpart compound Sb2Se3 on the other hand was found to be topological trivial, but theoretical studies indicated that the pressure might induce Sb2Se3 into a topological nontrivial state. We report on the discovery of superconductivity in Sb2Se3 single crystal induced via pressure. Our experiments indicated that Sb2Se3 became superconductive at high pressures above 10 GPa proceeded by a pressure induced insulator to metal like transition at ~3 GPa which should be related tomore » the topological quantum transition. The superconducting transition temperature (TC) increased to around 8.0 K with pressure up to 40 GPa while it keeps ambient structure. As a result, high pressure Raman revealed that new modes appeared around 10 GPa and 20 GPa, respectively, which correspond to occurrence of superconductivity and to the change of TC slop as the function of high pressure in conjunction with the evolutions of structural parameters at high pressures.« less

  7. Electronic structure, irreversibility line and magnetoresistance of Cu0.3Bi2Se3 superconductor

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Hemian, Yi; Gu, Genda; Chen, Chao -Yu; Sun, Xuan; Xie, Zhuo -Jin; Feng, Ya; Liang, Ai -Ji; Peng, Ying -Ying; He, Shao -Long; Zhao, Lin; et al

    2015-06-01

    CuxBi2Se3 is a superconductor that is a potential candidate for topological superconductors. We report our laser-based angle-resolved photoemission measurement on the electronic structure of the CuxBi2Se3 superconductor, and a detailed magneto-resistance measurement in both normal and superconducting states. We find that the topological surface state of the pristine Bi2Se3 topological insulator remains robust after the Cu-intercalation, while the Dirac cone location moves downward due to electron doping. Detailed measurements on the magnetic field-dependence of the resistance in the superconducting state establishes an irreversibility line and gives a value of the upper critical field at zero temperature of ~4000 Oe formore » the Cu0.3Bi2Se3 superconductor with a middle point Tc of 1.9K. The relation between the upper critical field Hc2 and temperature T is different from the usual scaling relation found in cuprates and in other kinds of superconductors. Small positive magneto-resistance is observed in Cu0.3Bi2Se3 superconductors up to room temperature. As a result, these observations provide useful information for further study of this possible candidate for topological superconductors.« less

  8. In-situ surface composition measurements of CuGaSe{sub 2} thin films

    SciTech Connect (OSTI)

    Fons, P.; Yamada, A.; Niki, S.; Oyanagi, H.

    1998-12-31

    Two CuGaSe{sub 2} films were grown by molecular beam epitaxy onto GaAs (001) substrates with varying Cu/Ga flux ratios under Se overpressure conditions. Growth was interrupted at predetermined times and the surface composition was measured using Auger electron spectroscopy after which growth was continued. After growth, the film composition was analyzed using voltage dependent electron microprobe spectroscopy. Film structure and morphology were also analyzed using x-ray diffraction and atomic force microscopy. The film with a Cu/Ga ratio larger than unity showed evidence of surface segregation of a second Cu-rich phase with a Cu/Se composition ratio slightly greater than unity. A second CuGaSe{sub 2} film with a Cu/Ga ratio of less than unity showed no change in surface composition with time and was also consistent with bulk composition measurements. Diffraction measurements indicated a high concentration of twins as well as the presence of domains with mixed c and a axes in the Ga-rich film. The Cu-rich films by contrast were single domain and had a narrower mosaics. High sensitivity scans along the [001] reciprocal axis did not exhibit any new peaks not attributable to either the substrate or the CuGaSe{sub 2} thin film.

  9. Method of fabricating high-efficiency Cu(In,Ga)(Se,S){sub 2} thin films for solar cells

    DOE Patents [OSTI]

    Noufi, R.; Gabor, A.M.; Tuttle, J.R.; Tennant, A.L.; Contreras, M.A.; Albin, D.S.; Carapella, J.J.

    1995-08-15

    A process for producing a slightly Cu-poor thin film of Cu(In,Ga)(Se,S){sub 2} comprises depositing a first layer of (In,Ga){sub x} (Se,S){sub y} followed by depositing just enough Cu+(Se,S) or Cu{sub x} (Se,S) to produce the desired slightly Cu-poor material. In a variation, most, but not all, (about 90 to 99%) of the (In,Ga){sub x} (Se,S){sub y} is deposited first, followed by deposition of all the Cu+(Se,S) or Cu{sub x} (Se,S) to go near stoichiometric, possibly or even preferably slightly Cu-rich, and then in turn followed by deposition of the remainder (about 1 to 10%) of the (In,Ga){sub x} (Se,S){sub y} to end with a slightly Cu-poor composition. In yet another variation, a small portion (about 1 to 10%) of the (In,Ga){sub x} (Se,S){sub y} is first deposited as a seed layer, followed by deposition of all of the Cu+(Se,S) or Cu{sub x} (Se,S) to make a very Cu-rich mixture, and then followed deposition of the remainder of the (In,Ga){sub x} (Se,S){sub y} to go slightly Cu-poor in the final Cu(In,Ga)(Se,S){sub 2} thin film. 5 figs.

  10. Method of fabricating high-efficiency Cu(In,Ga)(SeS).sub.2 thin films for solar cells

    DOE Patents [OSTI]

    Noufi, Rommel; Gabor, Andrew M.; Tuttle, John R.; Tennant, Andrew L.; Contreras, Miguel A.; Albin, David S.; Carapella, Jeffrey J.

    1995-01-01

    A process for producing a slightly Cu-poor thin film of Cu(In,Ga)(Se,S).sub.2 comprises depositing a first layer of (In,Ga).sub.x (Se,S).sub.y followed by depositing just enough Cu+(Se,S) or Cu.sub.x (Se,S) to produce the desired slightly Cu-poor material. In a variation, most, but not all, (about 90 to 99%) of the (In,Ga).sub.x (Se,S).sub.y is deposited first, followed by deposition of all the Cu+(Se,S) or Cu.sub.x (Se,S) to go near stoichiometric, possibly or even preferably slightly Cu-rich, and then in turn followed by deposition of the remainder (about 1 to 10%) of the (In,Ga).sub.x (Se,S).sub.y to end with a slightly Cu-poor composition. In yet another variation, a small portion (about 1 to 10%) of the (In,Ga).sub.x (Se,S).sub.y is first deposited as a seed layer, followed by deposition of all of the Cu+(Se,S) or Cu.sub.x (Se,S) to make a very Cu-rich mixture, and then followed deposition of the remainder of the (In,Ga).sub.x (Se,S).sub.y to go slightly Cu-poor in the final Cu(In,Ga)(Se,S).sub.2 thin film.

  11. Charge-transfer dynamics in multilayered PbS and PbSe quantum dot architectures

    SciTech Connect (OSTI)

    Xu, F.; Ma, X.; Haughn, C. R.; Doty, M. F.; Cloutier, S. G.

    2014-02-03

    We demonstrate control of the charge transfer process in PbS and PbSe quantum dot assemblies. We first demonstrate efficient charge transfer from donor quantum dots to acceptor quantum dots in a multi-layer PbSe cascade structure. Then, we assemble type-I and type-II heterostructures using both PbS and PbSe quantum dots via careful control of the band alignment. In type-I structures, photo-generated carriers are transferred and localized in the smaller bandgap (acceptor) quantum dots, resulting in a significant luminescence enhancement. In contrast, a significant luminescence quenching and shorter emission lifetime confirms an efficient separation of photo-generated carriers in the type-II architecture.

  12. Luminescence of CdSe/ZnS quantum dots infiltrated into an opal matrix

    SciTech Connect (OSTI)

    Gruzintsev, A. N. Emelchenko, G. A.; Masalov, V. M.; Yakimov, E. E.; Barthou, C.; Maitre, A.

    2009-02-15

    The effect of the photonic band gap in the photonic crystal, the synthesized SiO{sub 2} opal with embedded CdSe/ZnS quantum dots, on its luminescence in the visible spectral region is studied. It is shown that the position of the photonic band gap in the luminescence and reflectance spectra for the infiltrated opal depends on the diameter of the constituent nanospheres and on the angle of recording the signal. The optimal conditions for embedding the CdSe/ZnS quantum dots from the solution into the opal matrix are determined. It is found that, for the opal-CdSe/ZnS nanocomposites, the emission intensity decreases and the luminescence decay time increases in the spatial directions, in which the spectral positions of the photonic band gap and the luminescence peak of the quantum dots coincide.

  13. Role of polycrystallinity in CdTe and CuInSe sub 2 photovoltaic cells

    SciTech Connect (OSTI)

    Sites, J.R. )

    1991-01-01

    The polycrystalline nature of thin-film CdTe and CuInSe{sub 2} solar cells continues to be a major factor in several individual losses that limit overall cell efficiency. This report describes progress in the quantitative separation of these losses, including both measurement and analysis procedures. It also applies these techniques to several individual cells to help document the overall progress with CdTe and CuInSe{sub 2} cells. Notably, CdTe cells from Photon Energy have reduced window photocurrent losses to 1 mA/Cm{sup 2}; those from the University of South Florida have achieved a maximum power voltage of 693 mV; and CuInSe{sub 2} cells from International Solar Electric Technology have shown a hole density as high as 7 {times} 10{sup 16} cm{sup {minus}3}, implying a significant reduction in compensation. 9 refs.

  14. A Novel and Functional Single Layer Sheet of ZnSe

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Zhou, Jia; Sumpter, Bobby G; Kent, Paul R; Huang, Jingsong

    2015-01-01

    In this Communication, we report a novel singlelayer sheet of ZnSe, with a three-atomic thickness, which demonstrates a strong quantum confinement effect by exhibiting a large blue shift of 2.0 eV in its absorption edge relative to the zinc blende (ZB) bulk phase. Theoretical optical absorbance shows that the largest absorption of this ultrathin single-layer sheet of ZnSe occurs at a wavelength similar to its four-atom-thick doublelayer counterpart but with higher photoabsorption efficiency, suggesting a superior behavior on incident photon-to-current conversion efficiency for solar water splitting, among other potential applications. The results presented herein for ZnSe may be generalized tomore » other group II-VI analogues.« less

  15. Two-step growth of two-dimensional WSe2/MoSe2 heterostructures

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Gong, Yongji; Lei, Sidong; Lou, Jun; Liu, Zheng; Vajtai, Robert; Zhou, Wu; Ajayan, Pullikel M.

    2015-08-03

    Two dimensional (2D) materials have attracted great attention due to their unique properties and atomic thickness. Although various 2D materials have been successfully synthesized with different optical and electrical properties, a strategy for fabricating 2D heterostructures must be developed in order to construct more complicated devices for practical applications. Here we demonstrate for the first time a two-step chemical vapor deposition (CVD) method for growing transition-metal dichalcogenide (TMD) heterostructures, where MoSe2 was synthesized first and followed by an epitaxial growth of WSe2 on the edge and on the top surface of MoSe2. Compared to previously reported one-step growth methods, thismore » two-step growth has the capability of spatial and size control of each 2D component, leading to much larger (up to 169 μm) heterostructure size, and cross-contamination can be effectively minimized. Furthermore, this two-step growth produces well-defined 2H and 3R stacking in the WSe2/MoSe2 bilayer regions and much sharper in-plane interfaces than the previously reported MoSe2/WSe2 heterojunctions obtained from one-step growth methods. The resultant heterostructures with WSe2/MoSe2 bilayer and the exposed MoSe2 monolayer display rectification characteristics of a p-n junction, as revealed by optoelectronic tests, and an internal quantum efficiency of 91% when functioning as a photodetector. As a result, a photovoltaic effect without any external gates was observed, showing incident photon to converted electron (IPCE) efficiencies of approximately 0.12%, providing application potential in electronics and energy harvesting.« less

  16. The prevalence of the pre-existing hepatitis C viral variants and the evolution of drug resistance in patients treated with the NS3-4a serine protease inhibitor telaprevir

    SciTech Connect (OSTI)

    Rong, Libin; Ribeiro, Ruy M; Perelson, Alan S

    2008-01-01

    Telaprevir (VX-950), a novel hepatitis C virus (HCV) NS3-4A serine protease inhibitor, has demonstrated substantial antiviral activity in patients infected with HCV genotype 1. Some patients experience viral breakthrough, which has been shown to be associated with emergence of telaprevir-resistant HCV variants during treatment. The exact mechanisms underlying the rapid selection of drug resistant viral variants during dosing are not fully understood. In this paper, we develop a two-strain model to study the pre-treatment prevalence of the mutant virus and derive an analytical solution of the mutant frequency after administration of the protease inhibitor. Our analysis suggests that the rapid increase of the mutant frequency during therapy is not due to mutant growth but rather due to the rapid and profound loss of wild-type virus, which uncovers the pre-existing mutant variants. We examine the effects of backward mutation and hepatocyte proliferation on the pre-existence of the mutant virus and the competition between wild-type and drug resistant virus during therapy. We then extend the simple model to a general model with multiple viral strains. Mutations during therapy do not play a significant role in the dynamics of various viral strains, although they are capable of generating low levels of HCV variants that would otherwise be completely suppressed because of fitness disadvantages. Hepatocyte proliferation may not affect the pretreatment frequency of mutant variants, but is able to influence the quasispecies dynamics during therapy. It is the relative fitness of each mutant strain compared with wild-type that determines which strain(s) will dominate the virus population. The study provides a theoretical framework for exploring the prevalence of pre-existing mutant variants and the evolution of drug resistance during treatment with other protease inhibitors or HCV polymerase inhibitors.

  17. Laser parametric instability experiments of a 3ω, 15 kJ, 6-ns laser pulse in gas-filled hohlraums at the Ligne d'Intégration Laser facility

    SciTech Connect (OSTI)

    Rousseaux, C.; Huser, G.; Loiseau, P.; Casanova, M.; Alozy, E.; Villette, B.; Wrobel, R.; Henry, O.; Raffestin, D.

    2015-02-15

    Experimental investigation of stimulated Raman (SRS) and Brillouin (SBS) scattering have been obtained at the Ligne-d'Intégration-Laser facility (LIL, CEA-Cesta, France). The parametric instabilities (LPI) are driven by firing four laser beamlets (one quad) into millimeter size, gas-filled hohlraum targets. A quad delivers energy on target of 15 kJ at 3ω in a 6-ns shaped laser pulse. The quad is focused by means of 3ω gratings and is optically smoothed with a kinoform phase plate and with smoothing by spectral dispersion-like 2 GHz and/or 14 GHz laser bandwidth. Open- and closed-geometry hohlraums have been used, all being filled with 1-atm, neo-pentane (C{sub 5}H{sub 12}) gas. For SRS and SBS studies, the light backscattered into the focusing optics is analyzed with spectral and time resolutions. Near-backscattered light at 3ω and transmitted light at 3ω are also monitored in the open geometry case. Depending on the target geometry (plasma length and hydrodynamic evolution of the plasma), it is shown that, at maximum laser intensity about 9 × 10{sup 14} W/cm{sup 2}, Raman reflectivity noticeably increases up to 30% in 4-mm long plasmas while SBS stays below 10%. Consequently, laser transmission through long plasmas drops to about 10% of incident energy. Adding 14 GHz bandwidth to the laser always reduces LPI reflectivities, although this reduction is not dramatic.

  18. Direct Observation of Energy-Gap Scaling Law in CdSe Quantum Dots with Positrons

    SciTech Connect (OSTI)

    Denison, Arthur Blanchard; Weber, M. H.; Lynn, K. G.; Barbiellini, B.; Sterne, P. A.

    2002-07-01

    CdSe quantum dot samples with sizes in the range of 1.8~6 nm in diameter were examined by positron annihilation spectroscopy. The results were compared to data obtained for single-crystal bulk CdSe. Evidence is provided that the positrons annihilate within the nanospheres. The annihilation line shape shows a smearing at the boundary of the Jones zone proportional to the widening of the band gap due to a reduction in the size of the quantum dots. The data confirm that the change in the band gap is inversely proportional to the square of the quantum dot diameter.

  19. Tuning thermoelectricity in a Bi2Se3 topological insulator via varied film thickness

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Guo, Minghua; Wang, Zhenyu; Xu, Yong; Huang, Huaqing; Zang, Yunyi; Liu, Chang; Duan, Wenhui; Gan, Zhongxue; Zhang, Shou-Cheng; He, Ke; et al

    2016-01-12

    We report thermoelectric transport studies on Bi2Se3 topological insulator thin films with varied thickness grown by molecular beam epitaxy. We find that the Seebeck coefficient and thermoelectric power factor decrease systematically with the reduction of film thickness. These experimental observations can be explained quantitatively by theoretical calculations based on realistic electronic band structure of the Bi2Se3 thin films. Lastly, this work illustrates the crucial role played by the topological surface states on the thermoelectric transport of topological insulators, and sheds new light on further improvement of their thermoelectric performance.

  20. Thickness-dependent coherent phonon frequency in ultrathin FeSe/SrTiO3

    Office of Scientific and Technical Information (OSTI)

    films (Journal Article) | SciTech Connect Thickness-dependent coherent phonon frequency in ultrathin FeSe/SrTiO3 films Citation Details In-Document Search Title: Thickness-dependent coherent phonon frequency in ultrathin FeSe/SrTiO3 films × You are accessing a document from the Department of Energy's (DOE) SciTech Connect. This site is a product of DOE's Office of Scientific and Technical Information (OSTI) and is provided as a public service. Visit OSTI to utilize additional information

  1. Ordering mechanism of stacked CdSe/ZnS{sub x}Se{sub 1-x} quantum dots: A combined reciprocal-space and real-space approach

    SciTech Connect (OSTI)

    Schmidt, Th.; Roventa, E.; Clausen, T.; Flege, J. I.; Alexe, G.; Rosenauer, A.; Hommel, D.; Falta, J.; Bernstorff, S.; Kuebel, C.

    2005-11-15

    The vertical and lateral ordering of stacked CdSe quantum dot layers embedded in ZnS{sub x}Se{sub 1-x} has been investigated by means of grazing incidence small angle x-ray scattering and transmission electron microscopy. Different growth parameters have been varied in order to elucidate the mechanisms leading to quantum dot correlation. From the results obtained for different numbers of quantum dot layers, we conclude on a self-organized process which leads to increasing ordering for progressive stacking. The dependence on the spacer layer thickness indicates that strain induced by lattice mismatch drives the ordering process, which starts to break down for too thick spacer layers in a thickness range from 45 to 80 A. Typical quantum dot distances in a range from about 110 to 160 A have been found. A pronounced anisotropy of the quantum dot correlation has been observed, with the strongest ordering along the [110] direction. Since an increased ordering is found with increasing growth temperature, the formation of stacking faults as an additional mechanism for quantum dot alignment can be ruled out.

  2. T-641: Oracle Java SE Critical Patch Update Advisory- June 2011

    Broader source: Energy.gov [DOE]

    This Critical Patch Update contains 17 new security fixes for Oracle Java SE - 5 apply to client and server deployments of Java SE, 11 apply to client deployments of Java SE only, and 1 applies to server deployments of Java SE only. All of these vulnerabilities may be remotely exploitable without authentication, i.e., may be exploited over a network without the need for a username and password. Oracle CVSS scores assume that a user running a Java applet or Java Web Start application has administrator privileges (typical on Windows). Where the user does not run with administrator privileges (typical on Solaris and Linux), the corresponding CVSS impact scores for Confidentiality, Integrity, and Availability are "Partial" instead of "Complete", and the corresponding CVSS Base score is 7.5 instead of 10 respectively. For issues in Deployment, fixes are only made available for JDK and JRE 6. Users should use the Java Web Start in JRE 6 and the new Java Plug-in introduced in 6 Update 10. CVE-2011-0862, CVE-2011-0873, CVE-2011-0815, CVE-2011-0817, CVE-2011-0863, CVE-2011-0864, CVE-2011-0802, CVE-2011-0814, CVE-2011-0871, CVE-2011-0786, CVE-2011-0788, CVE-2011-0866, CVE-2011-0868, CVE-2011-0872, CVE-2011-0867, CVE-2011-0869, and CVE-2011-0865

  3. Low-temperature photoluminescence analysis of CdTeSe crystals for radiation-detector applications

    SciTech Connect (OSTI)

    YANG G.; Roy, U. N.; Bolotnikov, A. E.; Cui, Y.; Camarda, G.S.; Hossain, A.; and James, R. B.

    2015-10-05

    Goal: Understanding the changes of material defects in CdTeSe following annealing. Experimental results and discussions: Infrared (IR) transmission microscopy; current-voltage measurements (Highlight: Improvement of resistivity of un-doped crystals after annealing); low-temperature photoluminescence (PL) spectrum of as-grown and annealed samples.

  4. Molecular beam epitaxial growth of Bi{sub 2}Se{sub 3} nanowires and nanoflakes

    SciTech Connect (OSTI)

    Knebl, G. M. Gessler, J. R.; Kamp, M.; Höfling, S.

    2014-09-29

    Topological Insulators are in focus of immense research efforts and rapid scientific progress is obtained in that field. Bi{sub 2}Se{sub 3} has proven to be a topological insulator material that provides a large band gap and a band structure with a single Dirac cone at the Γ-point. This makes Bi{sub 2}Se{sub 3} one of the most promising three dimensional topological insulator materials. While Bi{sub 2}Se{sub 3} nanowires and nanoflakes so far were fabricated with different methods and for different purposes, we here present the first Bi{sub 2}Se{sub 3} nanowires as well as nanoflakes grown by molecular beam epitaxy. The nanostructures were nucleated on pretreated, silicon (100) wafers. Altering the growth conditions nanoflakes could be fabricated instead of nanowires; both with high crystalline quality, confirmed by scanning electron microscopy as well as transmission electron microscopy. These nanostructures have promise for spintronic devices and Majorana fermion observation in contact to superconductor materials.

  5. Stability of S and Se induced reconstructions on GaP(001)(21) surface

    SciTech Connect (OSTI)

    Li , D. F.; Guo, Zhi C.; Xiao, Hai Yan; Zu, Xiaotao T.; Gao, Fei

    2010-10-15

    The structural and electronic properties of S- and Se- passivated GaP(001)(21) surfaces were studied using first-principles simulations. Our calculations showed that the most stable structure consists of a single chalcogen atom (S or Se) in the first crystal layer, which is bonded to two Ga atoms of the second layer, and the third P layer replaced by chalcogen atoms, similar to the passivation of GaAs(001)(21) surface by chalcogen atoms. The structural parameters were determined and the surface band characters and the local density of states were also analyzed. The results showed that the preferable structure has no surface states in the bulk band gap, but the energy band gaps of the S- and Se-adsorbed GaP(001) surfaces are 1.83eV and 1.63eV, respectively. The passivation effects for the S- and Se-adsorbed surfaces are similar to each other.

  6. T-558: Oracle Java SE and Java for Business Critical Patch Update Advisory- February 2011

    Broader source: Energy.gov [DOE]

    This Critical Patch Update contains 21 new security fixes for Oracle Java SE and Java for Business. 19 of these vulnerabilities may be remotely exploitable without authentication, i.e., may be exploited over a network without the need for a username and password.

  7. Manufacturable CuIn(Ga)Se{sub 2}-based solar cells via development of co-sputtered CuInSe{sub 2} absorber layers

    SciTech Connect (OSTI)

    Dr. Ingrid Eisgruber

    1999-03-20

    Yield and reproducibility remain issues in CuIn(Ga)Se{sub 2} (CIGS) photovoltaic module fabrication. While small-area cells (<1 cm{sup 2}) over 18% efficient have been reported, the best large-area manufactured devices (>1 ft{sup 2}) are 11% efficient with about 60% yield. If improvements in large-area manufacturing can accomplish 15% efficiency and 90% yield, the result is a doubling in throughput leading to a reduction in cost per watt of over 50%. The challenge now facing the photovoltaics industry is to bring the efficiencies of small-area cells and large-area industrial modules closer together and to raise manufacturing yields.

  8. Enhanced quality thin film Cu(In,Ga)Se[sub 2] for semiconductor device applications by vapor-phase recrystallization

    DOE Patents [OSTI]

    Tuttle, J.R.; Contreras, M.A.; Noufi, R.; Albin, D.S.

    1994-10-18

    Enhanced quality thin films of Cu[sub w](In,Ga[sub y])Se[sub z] for semiconductor device applications are fabricated by initially forming a Cu-rich, phase-separated compound mixture comprising Cu(In,Ga):Cu[sub x]Se on a substrate to form a large-grain precursor and then converting the excess Cu[sub x]Se to Cu(In,Ga)Se[sub 2] by exposing it to an activity of In and/or Ga, either in vapor In and/or Ga form or in solid (In,Ga)[sub y]Se[sub z]. Alternatively, the conversion can be made by sequential deposition of In and/or Ga and Se onto the phase-separated precursor. The conversion process is preferably performed in the temperature range of about 300--600 C, where the Cu(In,Ga)Se[sub 2] remains solid, while the excess Cu[sub x]Se is in a liquid flux. The characteristic of the resulting Cu[sub w](In,Ga)[sub y]Se[sub z] can be controlled by the temperature. Higher temperatures, such as 500--600 C, result in a nearly stoichiometric Cu(In,Ga)Se[sub 2], whereas lower temperatures, such as 300--400 C, result in a more Cu-poor compound, such as the Cu[sub z](In,Ga)[sub 4]Se[sub 7] phase. 7 figs.

  9. Enhanced quality thin film Cu(In,Ga)Se.sub.2 for semiconductor device applications by vapor-phase recrystallization

    DOE Patents [OSTI]

    Tuttle, John R.; Contreras, Miguel A.; Noufi, Rommel; Albin, David S.

    1994-01-01

    Enhanced quality thin films of Cu.sub.w (In,Ga.sub.y)Se.sub.z for semiconductor device applications are fabricated by initially forming a Cu-rich, phase-separated compound mixture comprising Cu(In,Ga):Cu.sub.x Se on a substrate to form a large-grain precursor and then converting the excess Cu.sub.x Se to Cu(In,Ga)Se.sub.2 by exposing it to an activity of In and/or Ga, either in vapor In and/or Ga form or in solid (In,Ga).sub.y Se.sub.z. Alternatively, the conversion can be made by sequential deposition of In and/or Ga and Se onto the phase-separated precursor. The conversion process is preferably performed in the temperature range of about 300.degree.-600.degree. C., where the Cu(In,Ga)Se.sub.2 remains solid, while the excess Cu.sub.x Se is in a liquid flux. The characteristic of the resulting Cu.sub.w (In,Ga).sub.y Se.sub.z can be controlled by the temperature. Higher temperatures, such as 500.degree.-600.degree. C., result in a nearly stoichiometric Cu(In,Ga)Se.sub.2, whereas lower temperatures, such as 300.degree.-400.degree. C., result in a more Cu-poor compound, such as the Cu.sub.z (In,Ga).sub.4 Se.sub.7 phase.

  10. Algorithmically scalable block preconditioner for fully implicit shallow water equations in CAM-SE

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Lott, P Aaron; Woodward, Carol; Evans, Katherine J

    2015-01-01

    Performing accurate and efficient numerical simulation of global atmospheric climate models is challenging due to the disparate length and time scales over which physical processes interact. Implicit solvers enable the physical system to be integrated with a time step commensurate with processes being studied. The dominant cost of an implicit time step is the ancillary linear system solves, so we have developed a preconditioner aimed at improving the efficiency of these linear system solves. Our preconditioner is based on an approximate block factorization of the linearized shallow-water equations and has been implemented within the spectral element dynamical core within themore » Community Atmospheric Model (CAM-SE). In this paper we discuss the development and scalability of the preconditioner for a suite of test cases with the implicit shallow-water solver within CAM-SE.« less

  11. Low-cost CuInSe[sub 2] submodule development

    SciTech Connect (OSTI)

    Basol, B.M.; Kapur, V.K.; Halani, A.; Leidholm, C. )

    1992-10-01

    Aim of this project is development and demonstration of processing steps necessary for fabrication of high efficiency CuInSe[sub 2] solar cells and sub-modules by the two-stage technique (also called the selenization method.) During this period, we have optimized the processing parameters of this method and demonstrated CuInSe[sub 2]/CdS/ZnO devices with a 1[endash]4 cm[sup 2] area and up to 12.4% active area efficiency. We have also developed a novel approach for the preparation of Cu/In precursors that improved the stoichiometric and morphological uniformity in these films. We have developed processing steps and tooling for handling up to 1 ft[sup 2] size substrates and as a result of these efforts demonstrated our first monolithically integrated sub-module of 1 ft[sup 2] area. 16 figs, 1 tab, 15 refs.

  12. CdS/PbSe heterojunction for high temperature mid-infrared photovoltaic detector applications

    SciTech Connect (OSTI)

    Weng, Binbin E-mail: shi@ou.edu; Qiu, Jijun; Zhao, Lihua; Chang, Caleb; Shi, Zhisheng E-mail: shi@ou.edu

    2014-03-24

    n-CdS/p-PbSe heterojunction is investigated. A thin CdS film is deposited by chemical bath deposition on top of epitaxial PbSe film by molecular beam epitaxy on Silicon. Current-voltage measurements demonstrate very good junction characteristics with rectifying ratio of ∼178 and ideality factor of 1.79 at 300 K. Detectors made with such structure exhibit mid-infrared spectral photoresponse at room temperature. The peak responsivity R{sub λ} and specific detectivity D{sup *} are 0.055 A/W and 5.482 × 10{sup 8} cm·Hz{sup 1/2}/W at λ = 4.7 μm under zero-bias photovoltaic mode. Temperature-dependent photoresponse measurements show abnormal intensity variation below ∼200 K. Possible reasons for this phenomenon are also discussed.

  13. Radiative lifetimes of zincblende CdSe/CdS quantum dots

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Gong, Ke; Martin, James E.; Shea-Rohwer, Lauren E.; Lu, Ping; Kelley, David F.

    2015-01-02

    Recent synthetic advances have made available very monodisperse zincblende CdSe/CdS quantum dots having near-unity photoluminescence quantum yields. Because of the absence of nonradiative decay pathways, accurate values of the radiative lifetimes can be obtained from time-resolved PL measurements. Radiative lifetimes can also be obtained from the Einstein relations, using the static absorption spectra and the relative thermal populations in the angular momentum sublevels. We found that one of the inputs into these calculations is the shell thickness, and it is useful to be able to determine shell thickness from spectroscopic measurements. We use an empirically corrected effective mass model tomore » produce a “map” of exciton wavelength as a function of core size and shell thickness. These calculations use an elastic continuum model and the known lattice and elastic constants to include the effect of lattice strain on the band gap energy. The map is in agreement with the known CdSe sizing curve and with the shell thicknesses of zincblende core/shell particles obtained from TEM images. Furthermore, if selenium–sulfur diffusion is included and lattice strain is omitted from the calculation then the resulting map is appropriate for wurtzite CdSe/CdS quantum dots synthesized at high temperatures, and this map is very similar to one previously reported (J. Am. Chem. Soc. 2009, 131, 14299). Radiative lifetimes determined from time-resolved measurements are compared to values obtained from the Einstein relations, and found to be in excellent agreement. For a specific core size (2.64 nm diameter, in the present case), radiative lifetimes are found to decrease with increasing shell thickness. Thus, this is similar to the size dependence of one-component CdSe quantum dots and in contrast to the size dependence in type-II quantum dots.« less

  14. Radiative lifetimes of zincblende CdSe/CdS quantum dots

    SciTech Connect (OSTI)

    Gong, Ke; Martin, James E.; Shea-Rohwer, Lauren E.; Lu, Ping; Kelley, David F.

    2015-01-02

    Recent synthetic advances have made available very monodisperse zincblende CdSe/CdS quantum dots having near-unity photoluminescence quantum yields. Because of the absence of nonradiative decay pathways, accurate values of the radiative lifetimes can be obtained from time-resolved PL measurements. Radiative lifetimes can also be obtained from the Einstein relations, using the static absorption spectra and the relative thermal populations in the angular momentum sublevels. We found that one of the inputs into these calculations is the shell thickness, and it is useful to be able to determine shell thickness from spectroscopic measurements. We use an empirically corrected effective mass model to produce a “map” of exciton wavelength as a function of core size and shell thickness. These calculations use an elastic continuum model and the known lattice and elastic constants to include the effect of lattice strain on the band gap energy. The map is in agreement with the known CdSe sizing curve and with the shell thicknesses of zincblende core/shell particles obtained from TEM images. Furthermore, if selenium–sulfur diffusion is included and lattice strain is omitted from the calculation then the resulting map is appropriate for wurtzite CdSe/CdS quantum dots synthesized at high temperatures, and this map is very similar to one previously reported (J. Am. Chem. Soc. 2009, 131, 14299). Radiative lifetimes determined from time-resolved measurements are compared to values obtained from the Einstein relations, and found to be in excellent agreement. For a specific core size (2.64 nm diameter, in the present case), radiative lifetimes are found to decrease with increasing shell thickness. Thus, this is similar to the size dependence of one-component CdSe quantum dots and in contrast to the size dependence in type-II quantum dots.

  15. Cr-doped TiSe2 - A layered dichalcogenide spin glass

    SciTech Connect (OSTI)

    Luo, Huixia; Tao, Jing; Krizan, Jason W.; Seibel, Elizabeth M.; Xie, Weiwei; Sahasrabudhe, Girija S.; Bergman, Susanna L.; Phelan, Brendan F.; Wang, Zhen; Zhang, Jiandi; Cava, R. J.

    2015-09-17

    We report the magnetic characterization of the Cr-doped layered dichalcogenide TiSe2. The temperature dependent magnetic susceptibilities are typical of those seen in geometrically frustrated insulating antiferromagnets. The Cr moment is close to the spin-only value, and the Curie–Weiss temperatures (θcw) are between –90 and –230 K. Freezing of the spin system, which is glassy, characterized by peaks in the ac and dc susceptibility and specific heat, does not occur until below T/θcw = 0.05. The CDW transition seen in the resistivity for pure TiSe2 is still present for 3% Cr substitution but is absent by 10% substitution, above which the materials are metallic and p-type. Structural refinements, magnetic characterization, and chemical considerations indicate that the materials are of the type Ti1–xCrxSe2-x/2 for 0 ≤ x ≤ 0.6.

  16. Blue and green electroluminescence from CdSe nanocrystal quantum-dot-quantum-wells

    SciTech Connect (OSTI)

    Lu, Y. F.; Cao, X. A.

    2014-11-17

    CdS/CdSe/ZnS quantum dot quantum well (QDQW) nanocrystals were synthesized using the successive ion layer adsorption and reaction technique, and their optical properties were tuned by bandgap and strain engineering. 3-monolayer (ML) CdSe QWs emitted blue photoluminescence at 467?nm with a spectral full-width-at-half-maximum of ?30?nm. With a 3 ML ZnS cladding layer, which also acts as a passivating and strain-compensating layer, the QDQWs acquired a ?35% quantum yield of the QW emission. Blue and green electroluminescence (EL) was obtained from QDQW light-emitting devices with 34.5 ML CdSe QWs. It was found that as the peak blueshifted, the overall EL was increasingly dominated by defect state emission due to poor hole injection into the QDQWs. The weak EL was also attributed to strong field-induced charge separation resulting from the unique QDQW geometry, weakening the oscillator strength of optical transitions.

  17. Cr-doped TiSe2 - A layered dichalcogenide spin glass

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Luo, Huixia; Tao, Jing; Krizan, Jason W.; Seibel, Elizabeth M.; Xie, Weiwei; Sahasrabudhe, Girija S.; Bergman, Susanna L.; Phelan, Brendan F.; Wang, Zhen; Zhang, Jiandi; et al

    2015-09-17

    We report the magnetic characterization of the Cr-doped layered dichalcogenide TiSe2. The temperature dependent magnetic susceptibilities are typical of those seen in geometrically frustrated insulating antiferromagnets. The Cr moment is close to the spin-only value, and the Curie–Weiss temperatures (θcw) are between –90 and –230 K. Freezing of the spin system, which is glassy, characterized by peaks in the ac and dc susceptibility and specific heat, does not occur until below T/θcw = 0.05. The CDW transition seen in the resistivity for pure TiSe2 is still present for 3% Cr substitution but is absent by 10% substitution, above which themore » materials are metallic and p-type. Structural refinements, magnetic characterization, and chemical considerations indicate that the materials are of the type Ti1–xCrxSe2-x/2 for 0 ≤ x ≤ 0.6.« less

  18. Novel thin-film CuInSe sub 2 fabrication

    SciTech Connect (OSTI)

    Mooney, G.D.; Hermann, A.M. )

    1992-03-01

    This report describes research in Rapid Thermal Processing (RTP), a process that allows the formation of CuInSe{sub 2} without the use of H{sub 2}Se. RTP is a well-established method of rapidly achieving temperatures necessary to melt and recrystallize materials such as Si and and silicides. RTP processes can rapidly and uniformly heat large surface areas to hundreds of degrees Celsius. RTP is the most promising method of rapid recrystallization studied to date, being readily scalable from the research to the production level. The approach to the experiment was divided into two sections: (1) fabricating the precursor film and (2) processing the precursor film. The objective of the first phase of the work was to fabricate the thin films by RTP, then fully characterize them, to demonstrate the viability of the process as a method by which to make device-quality CuInSe{sub 2}. The second phase was to demonstrate that material made by this method could be used to make an active photovoltaic device. 24 refs.

  19. High Compositional Homogeneity of CdTexSe1-x Crystals Grown by the Bridgman Method

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Roy, U. N.; Bolotnikov, A. E.; Camarda, G. S.; Cui, Y.; Hossain, A.; Lee, K.; Lee, W.; Tappero, R.; Yang, G.; Gul, R.; et al

    2015-02-03

    We obtained high-quality CdTexSe1-x (CdTeSe) crystals from ingots grown by the vertical Bridgman technique. The compositional uniformity of the ingots was evaluated by X-ray fluorescence at BNL’s National Synchrotron Light Source X27A beam line. The resulting compositional homogeneity was highly uniform throughout the ingot, and the effective segregation coefficient of Se was ~1.0. This uniformity offers potential opportunity to enhance the yield of the materials for both infrared substrate and radiation-detector applications, so greatly lowering the cost of production and also offering us the prospect to grow large-diameter ingots for use as large-area substrates and for producing higher efficiency gamma-raymore » detectors. The concentration of secondary phases was found to be much lower, by eight- to ten fold compared to that of conventional CdxZn1-xTe (CdZnTe or CZT).« less

  20. X-ray irradiation induced changes in electron transport in stabilized a-Se photoconductors

    SciTech Connect (OSTI)

    Walornyj, M.; Kasap, S. O.

    2013-12-07

    We have examined the effect of high-dose x-ray irradiation on electron transport in stabilized amorphous selenium (a-Se) x-ray photoconductive films (of the type used in x-ray image detectors) by measuring the electron lifetime ?{sub e} through interrupted-field time-of-flight experiments. X-ray induced effects have been examined through two types of experiments. In recovery experiments, the a-Se was preirradiated with and without an applied field (5 V/?m) during irradiation with sufficient dose (typically ?20 Gy at 21 C) to significantly reduce the electron lifetime by ?50%, and then the recovery of the lifetime was monitored as a function of time at three different temperatures, 10 C, 21 C, and 35 C. The lifetime recovery kinetics was exponential with a relaxation time ?{sub r} that is thermally activated with an activation energy of 1.66 eV. ?{sub r} is a few hours at 21 C and only a few minutes at 35 C. In experiments examining the irradiation induced effects, the a-Se film was repeatedly exposed to x-ray radiation and the changes in the drift mobility and lifetime were monitored as a function of accumulated dose D. There was no observable change in the drift mobility. At 21 C, the concentration of x-ray induced deep traps (or capture centers), N{sub d}, increases linearly with D (N{sub d} ? D) whereas at 35 C, the recovery process prevents a linear increase in N{sub d} with D, and N{sub d} saturates. In all cases, even under high dose irradiation (?50 Gy), the lifetime was recoverable to its original equilibrium (pre-exposure) value within a few relaxation times.

  1. Experimental study of the valence band of Bi2Se3

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Heremans, Joseph; Gao, Yibin; He, Bin; Androulakis, Yiannis; Parker, David S

    2014-01-01

    The valence band of Bi2Se3 is investigated with Shubnikov - de Haas measurements, galvanomagnetic and thermoelectric transport. At low hole concentration, the hole Fermi surface is closed and box-like, but at higher concentrations it develops tube-like extensions that are open. The experimentally determined density-of-states effective mass is lighter than density-functional theory calculations predict; while we cannot give a definitive explanation for this, we suspect that the theory may lack sufficient precision to compute room-temperature transport properties, such as the Seebeck coefficient, in solids in which there are Van der Waals interlayer bonds.

  2. Microsized structures assisted nanostructure formation on ZnSe wafer by femtosecond laser irradiation

    SciTech Connect (OSTI)

    Wang, Shutong; Feng, Guoying E-mail: zhoush@scu.edu.cn

    2014-12-22

    Micro/nano patterning of ZnSe wafer is demonstrated by femtosecond laser irradiation through a diffracting pinhole. The irradiation results obtained at fluences above the ablation threshold are characterized by scanning electron microscopy. The microsized structure with low spatial frequency has a good agreement with Fresnel diffraction theory. Laser induced periodic surface structures and laser-induced periodic curvelet surface structures with high spatial frequency have been found on the surfaces of microsized structures, such as spikes and valleys. We interpret its formation in terms of the interference between the reflected laser field on the surface of the valley and the incident laser pulse.

  3. Determination of the Exciton Binding Energy in CdSe Quantum Dots

    SciTech Connect (OSTI)

    Meulenberg, R; Lee, J; Wolcott, A; Zhang, J; Terminello, L; van Buuren, T

    2009-10-27

    The exciton binding energy (EBE) in CdSe quantum dots (QDs) has been determined using x-ray spectroscopy. Using x-ray absorption and photoemission spectroscopy, the conduction band (CB) and valence band (VB) edge shifts as a function of particle size have been determined and combined to obtain the true band gap of the QDs (i.e. without and exciton). These values can be compared to the excitonic gap obtained using optical spectroscopy to determine the EBE. The experimental EBE results are compared with theoretical calculations on the EBE and show excellent agreement.

  4. Multiband semimetallic electronic structure of superconducting Ta2PdSe5

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Singh, David Joseph

    2015-04-24

    We report the electronic structure and related properties of the superconductor Ta2PdSe5 as determined from density functional calculations. The Fermi surface has two disconnected sheets, both derived from bands of primarily chalcogenide p states. These are a corrugated hole cylinder and a heavier complex shaped electron sheet. The sheets contain 0.048 holes and a compensating number of electrons per formula unit, making the material a semimetallic superconductor. The results support the presence of two band superconductivity, although a discrepancy in the specific heat is noted. This discrepancy is discussed as a possible consequence of Pd deficiency in samples.

  5. ScanningTunneling Luminescence of Grain Boundaries in Cu(In,Ga)Se2

    SciTech Connect (OSTI)

    Romero, M. J.; Jiang, C.-S.; Al-Jassim, M. M.; Noufi, R.

    2005-01-01

    At the Laboratory, photon emission in semiconductors has been mapped in the nanoscale using scanning tunneling microscopy (STM). In this Solar Program Review Meeting, we report on the latest results obtained in Cu(In,Ga)Se2 (CIGS) thin films by this adapted STM. Scanning tunneling luminescence (STL) spectroscopy suggests that photons are emitted near the surface of CIGS. STL is excited either by (1) diffusion of tunneling electrons and subsequent recombination with available holes in CIGS or (2) impact ionization by hot electrons. Which process becomes predominant depends on the voltage applied to the STM tip. Photon mapping shows electronically active, extended defects near the surface of CIGS thin films.

  6. Local-moment magnetism in superconducting FeTe0.35Se0.65 as seen...

    Office of Scientific and Technical Information (OSTI)

    Local-moment magnetism in superconducting FeTe0.35Se0.65 as seen via inelastic neutron scattering Prev Next Title: Local-moment magnetism in superconducting FeTe0.35Se0.65 as ...

  7. Synthesis of monodispersed CdSe nanocrystals in poly(styrene-alt-maleic anhydride) at room temperature

    SciTech Connect (OSTI)

    Liu, S.H.; Qian, X.F.; Yuan, J.Y.; Yin, J.; He, R.; Zhu, Z.K

    2003-07-14

    Nanocomposite of CdSe/poly(styrene-alt-maleic anhydride) (PSM) was successfully prepared via an in situ reaction process at room temperature and ambient pressure. Transmission electron microscopy (TEM) analysis revealed that CdSe nanoparticles with a small size and narrow size distribution were obtained. The obtained nanocomposite was also characterized by FT-IR, XRD, ultraviolet-visible, and fluorescence spectroscopy.

  8. Tensile Strain Switched Ferromagnetism in Layered NbS2 and NbSe2

    SciTech Connect (OSTI)

    Zhou, Yungang; Wang, Zhiguo; Yang, Ping; Zu, Xiaotao; Yang, Li; Sun, Xin; Gao, Fei

    2012-11-01

    Developing approaches to effectively induce and control the magnetic states is critical to the use of magnetic nanostructures in quantum information devices but is still challenging. Here we have demonstrated, by employing the density functional theory calculations, an existence of infinite magnetic sheets with structural integrity and magnetic homogeneity. Examination from a series of transition metal dichalcogenides shows that the biaxial tensile strained NbS2 and NbSe2 structures can be magnetized with a ferromagnetic character due to the competitive effects of through-bond interaction and through-space interaction. The estimated Curie temperatures (387 and 542 K under the 10% strain for NbS2 and NbSe2 structures, respectively) suggest that the unique ferromagnetic character can be achieved above room temperature. The self-exchange of population between 4d orbitals of Nb atom that leads to the exchange splitting is the mechanism behind the transition of the spin moment. The induced magnetic moments can be significantly enhanced by the tensile strain, even giving rise to half-metallic character with the strong spin polarization around the Fermi level. Given the recent progress that the desired strain can be achieved on two-dimensional nanostructures, such as graphene and BN layer in a controlled way, we believe that our calculated results are suitable for experimental verification and implementation opening a new path to explore the spintronics in pristine two-dimensional nanostructures.

  9. Resonance photoelectron spectroscopy of TiX{sub 2} (X = S, Se, Te) titanium dichalcogenides

    SciTech Connect (OSTI)

    Shkvarin, A. S. Yarmoshenko, Yu. M.; Skorikov, N. A.; Yablonskikh, M. V.; Merentsov, A. I.; Shkvarina, E. G.; Titov, A. N.

    2012-11-15

    The photoelectron valence band spectra of TiS{sub 2}, TiSe{sub 2}, and TiTe{sub 2} dichalcogenides are investigated in the Ti 2p-3d resonance regime. Resonance bands in the vicinity of the Fermi energy are found for TiS{sub 2} and TiTe{sub 2}. The nature of these bands is analyzed based on model calculations of the density of electronic states in TiS{sub 2}, TiSe{sub 2}, and TiTe{sub 2} compounds intercalated by titanium atoms. Analysis of experimental data and their comparison with model calculations showed that these bands have different origins. It is found that the resonance enhancement of an additional band observed in TiS{sub 2} is explained by self-intercalation by titanium during the synthesis of this compound. The resonance enhancement in TiTe{sub 2} is caused by occupation of the 3d band in Ti.

  10. Electronic structure of titanium dichalcogenides TiX{sub 2} (X = S, Se, Te)

    SciTech Connect (OSTI)

    Shkvarin, A. S. Yarmoshenko, Yu. M.; Skorikov, N. A.; Yablonskikh, M. V.; Merentsov, A. I.; Shkvarina, E. G.; Titov, A. N.

    2012-01-15

    The electronic structure and the chemical bond in titanium dichalcogenides TiX{sub 2} (X = S, Se, Te), which are promising electrode materials for lithium batteries, are studied experimentally and theoretically. It is found that the X-ray photoelectron spectra of the valence bands and the core levels of titanium and its X-ray L{sub 2,3} absorption spectra demonstrate a change in the ionic and covalent components of the chemical bond in these compounds. The densities of states in these compounds are calculated by the full-potential augmented-plane-wave method, and multiplet calculations of the X-ray L{sub 2,3} absorption spectra of titanium are performed. It is shown that, in the row TiS{sub 2}-TiSe{sub 2}-TiTe{sub 2}, the covalence increases, the ionicity of the chemical bond decreases, and the effect of the crystal field of a ligand is weakened.

  11. Polytypism, polymorphism, and superconductivity in TaSe2-xTex

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Luo, Huixia; Tao, Jing; Xie, Weiwei; Inoue, Hiroyuki; Gyenis, Andras; Krizan, Jason W.; Yazdani, Ali; Zhu, Yimei; Cava, R. J.

    2015-03-17

    Polymorphism in materials often leads to significantly different physical properties - the rutile and anatase polymorphs of TiO? are a prime example. Polytypism is a special type of polymorphism, occurring in layered materials when the geometry of a repeating structural layer is maintained but the layer stacking sequence of the overall crystal structure can be varied; SiC is an example of a material with many polytypes. Although polymorphs can have radically different physical properties, it is much rarer for polytypism to impact physical properties in a dramatic fashion. Here we study the effects of polytypism and polymorphism on the superconductivitymoreof TaSe?, one of the archetypal members of the large family of layered dichalcogenides. We show that it is possible to access 2 stable polytypes and 2 stable polymorphs in the TaSe2-xTex solid solution, and find that the 3R polytype shows a superconducting transition temperature that is between 6 and 17 times higher than that of the much more commonly found 2H polytype. The reason for this dramatic change is not apparent, but we propose that it arises either from a remarkable dependence of Tc on subtle differences in the characteristics of the single layers present, or from a surprising effect of the layer stacking sequence on electronic properties that instead are expected to be dominated by the properties of a single layer in materials of this kind.less

  12. Dependence of superconductivity in CuxBi?Se? on quenching conditions

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Schneeloch, J. A.; Zhong, R. D.; Xu, Z. J.; Gu, G. D.; Tranquada, J. M.

    2015-04-20

    Topological superconductivity, implying gapless protected surface states, has recently been proposed to exist in the compound CuxBi?Se?. Unfortunately, low diamagnetic shielding fractions and considerable inhomogeneity have been reported in this compound. In an attempt to understand and improve on the finite superconducting volume fractions, we have investigated the effects of various growth and post-annealing conditions. With a melt-growth (MG) method, diamagnetic shielding fractions of up to 56% in Cu???Bi?Se? have been obtained, the highest value reported for this method. We investigate the efficacy of various quenching and annealing conditions, finding that quenching from temperatures above 560C is essential for superconductivity,morewhereas quenching from lower temperatures or not quenching at all is detrimental. A modified floating zone (FZ) method yielded large single crystals but little superconductivity. Even after annealing and quenching, FZ-grown samples had much less chance of being superconducting than MG-grown samples. From the low shielding fractions in FZ-grown samples and the quenching dependence, we suggest that a metastable secondary phase having a small volume fraction in most of the samples may be responsible for the superconductivity.less

  13. The role of ligands in the optical and electronic spectra of CdSe nanoclusters

    SciTech Connect (OSTI)

    Kilina, Svletana; Sergei, Ivanov A; Victor, Klimov I; Sergei, Tretiak

    2008-01-01

    We investigate the impact of ligands on morphology, electronic structure, and optical response of the Cd33Se33 cluster, which already overlapps in size with the smallest synthesized CdSe quantum dots (QDs). Our Density Functional Theory (DFT) calculations demonstrate significant surface reorganization both for the bare cluster and for the cluster capped by amine and phosphine oxide ligand models. We observe strong surface-ligand interactions leading to substantial charge redistribution and polarization effects on the surface. This effect results in the appearance of hybridized states, where the electronic density is spread over the cluster and the ligands. Neither the ligand's nor hybridized molecular orbitals appear as trap states inside or near the band gap of the QD. Instead, being optically dark, dense hybridized states from the edges of the valence and the conduction bands could open new relaxation channels for high energy photoexcitations. Comparing quantum dots passivated by different ligands, we found that hybridized states are denser in at the edge of the conduction band of the cluster ligated with phosphine oxide molecules than that with primary amines. Such a different manifestation of ligand binding may potentially lead to the faster electron relaxation in dots passivated by phosphine oxide than by amine ligands, which is in agreement with experimental data.

  14. Electronic Structure of Ligated CdSe Clusters: Dependence on DFT Methodology

    SciTech Connect (OSTI)

    Albert, VV; Ivanov, SA; Tretiak, S; Kilina, SV

    2011-07-07

    Simulations of ligated semiconductor quantum dots (QDs) and their physical properties, such as morphologies, QD-ligand interactions, electronic structures, and optical transitions, are expected to be very sensitive to computational methodology. We utilize Density Functional Theory (DFT) and systematically study how the choice of density functional, atom-localized basis set, and a solvent affects the physical properties of the Cd{sub 33}Se{sub 33} cluster ligated with a trimethyl phosphine oxide ligand. We have found that qualitative performance of all exchange-correlation (XC) functionals is relatively similar in predicting strong QD-ligand binding energy ({approx}1 eV). Additionally, all functionals predict shorter Cd-Se bond lengths on the QD surface than in its core, revealing the nature and degree of QD surface reconstruction. For proper modeling of geometries and QD-ligand interactions, however, augmentation of even a moderately sized basis set with polarization functions (e.g., LANL2DZ* and 6-31G*) is very important. A polar solvent has very significant implications for the ligand binding energy, decreasing it to 0.2-0.5 eV. However, the solvent model has a minor effect on the optoelectronic properties, resulting in persistent blue shifts up to {approx}0.3 eV of the low-energy optical transitions. For obtaining reasonable energy gaps and optical transition energies, hybrid XC functionals augmented by a long-range Hartree-Fock orbital exchange have to be applied.

  15. Effect of Ligands on Characteristics of (CdSe)13 Quantum Dot

    SciTech Connect (OSTI)

    Gao, Yang; Zhou, Bo; Kang, Seung-gu; Xin, Minsi; Yang, Ping; Dai, Xing; Wang, Zhigang; Zhou, Ruhong

    2014-01-01

    The widespread applications of quantum dots (QDs) have spurred an increasing interest in the study of their coating ligands, which can not only protect the electronic structures of the central QDs, but also control their permeability through biological membranes with both size and shape. In this work, we have used density functional theory (DFT) to investigate the electronic structures of (CdSe)13 passivated by OPMe2(CH2)nMe ligands with different lengths and various numbers of branches (Me=methyl group, n = 0, 1-3). Our results show that the absorption peak in the ultraviolet-visible (UV-vis) spectra displays a clear blue-shift, on the scale of ~100 nm, upon the binding of ligands. Once the total number of ligands bound with (CdSe)13 reached a saturated number (9 or 10), no more blue-shift occurred in the absorption peak in the UV-vis spectra. On the other hand, the aliphatic chain length of ligands has a negligible effect on the optical properties of the QD core. Analyses of the bonding characteristics confirm that optical transitions are dominantly governed by the central QD core rather than the organic passivation. Interestingly, the density of states (DOS) share similar characteristics as vibrational spectra, even though there is no coordination vibration mode between the ligands and the central QD. These findings might provide insights on the material design for the passivation of quantum dots for biomedical applications.

  16. Lattice dynamics of BaFe2X3(X=S,Se) compounds

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Popović, Z. V.; Šćepanović, M.; Lazarević, N.; Opačić, M.; Radonjić, M. M.; Tanasković, D.; Lei, Hechang; Petrovic, C.

    2015-02-27

    We present the Raman scattering spectra of the S=2 spin ladder compounds BaFe₂X₃ (X=S,Se) in a temperature range between 20 and 400 K. Although the crystal structures of these two compounds are both orthorhombic and very similar, they are not isostructural. The unit cell of BaFe₂S₃ (BaFe₂Se₃) is base-centered Cmcm (primitive Pnma), giving 18 (36) modes to be observed in the Raman scattering experiment. We have detected almost all Raman active modes, predicted by factor group analysis, which can be observed from the cleavage planes of these compounds. Assignment of the observed Raman modes of BaFe₂S(Se)₃ is supported by themore » lattice dynamics calculations. The antiferromagnetic long-range spin ordering in BaFe₂Se₃ below TN=255K leaves a fingerprint both in the A1g and B3g phonon mode linewidth and energy.« less

  17. Nonmonotonic pressure evolution of the upper critical field in superconducting FeSe

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Kaluarachchi, Udhara S.; Taufour, Valentin; Böhmer, Anna E.; Tanatar, Makariy A.; Bud'ko, Sergey L.; Kogan, Vladimir G.; Prozorov, Ruslan; Canfield, Paul C.

    2016-02-01

    The pressure dependence of the upper critical field, Hc2,c, of single crystalline FeSe was studied using measurements of the interplane resistivity, ρc, in magnetic fields parallel to tetragonal c axis. Hc2,c(T) curves obtained under hydrostatic pressures up to 1.56 GPa, the range over which the superconducting transition temperature, Tc, of FeSe exhibits a nonmonotonic dependence with local maximum at p1 ≈ 0.8 GPa and local minimum at p2 ≈ 1.2 GPa. The slope of the upper critical field at Tc,(dHc2,c/dT)Tc, also exhibits a nonmonotonic pressure dependence with distinct changes at p1 and p2. For p < p1 the slope canmore » be described within a multiband orbital model. For both p1 < p < p2 and p > p2 the slope is in good semiquantitative agreement with a single band, orbital Helfand-Werthamer theory with Fermi velocities determined from Shubnikov–de Haas measurements. Lastly, this finding indicates that Fermi surface changes are responsible for the local minimum of Tc(p) at p2 ≈ 1.2 GPa.« less

  18. Biexciton formation and exciton coherent coupling in layered GaSe

    SciTech Connect (OSTI)

    Dey, P.; Paul, J.; Stevens, C. E.; Glikin, N.; Karaiskaj, D.; Moody, G.; Kovalyuk, Z. D.; Kudrynskyi, Z. R.; Romero, A. H.; Cantarero, A.; Hilton, D. J.

    2015-06-07

    Nonlinear two-dimensional Fourier transform (2DFT) and linear absorption spectroscopy are used to study the electronic structure and optical properties of excitons in the layered semiconductor GaSe. At the 1s exciton resonance, two peaks are identified in the absorption spectra, which are assigned to splitting of the exciton ground state into the triplet and singlet states. 2DFT spectra acquired for co-linear polarization of the excitation pulses feature an additional peak originating from coherent energy transfer between the singlet and triplet. At cross-linear polarization of the excitation pulses, the 2DFT spectra expose a new peak likely originating from bound biexcitons. The polarization dependent 2DFT spectra are well reproduced by simulations using the optical Bloch equations for a four level system, where many-body effects are included phenomenologically. Although biexciton effects are thought to be strong in this material, only moderate contributions from bound biexciton creation can be observed. The biexciton binding energy of ?2 meV was estimated from the separation of the peaks in the 2DFT spectra. Temperature dependent absorption and 2DFT measurements, combined with ab initio theoretical calculations of the phonon spectra, indicate strong interaction with the A{sub 1}{sup ?} phonon mode. Excitation density dependent 2DFT measurements reveal excitation induced dephasing and provide a lower limit for the homogeneous linewidth of the excitons in the present GaSe crystal.

  19. Manufacturing technology development for CuInGaSe sub 2 solar cell modules

    SciTech Connect (OSTI)

    Stanbery, B.J. )

    1991-11-01

    The report describes research performed by Boeing Aerospace and Electronics under the Photovoltaic Manufacturing Technology project. We anticipate that implementing advanced semiconductor device fabrication techniques to the production of large-area CuIn{sub 1-x}Ga{sub x}Se{sub 2} (CIGS)/Cd{sub 1-y}Zn{sub y}S/ZnO monolithically integrated thin-film solar cell modules will enable 15% median efficiencies to be achieved in high-volume manufacturing. We do not believe that CuInSe{sub 2} (CIS) can achieve this efficiency in production without sufficient gallium to significantly increase the band gap, thereby matching it better to the solar spectrum (i.e., x{ge}0.2). Competing techniques for CIS film formation have not been successfully extended to CIGS devices with such high band gaps. The SERI-confirmed intrinsic stability of CIS-based photovoltaics renders them far superior to a-Si:H-based devices, making a 30-year module lifetime feasible. The minimal amounts of cadmium used in the structure we propose, compared to CdTe-based devices, makes them environmentally safer and more acceptable to both consumers and relevant regulatory agencies. Large-area integrated thin-film CIGS modules are the product most likely to supplant silicon modules by the end of this decade and enable the cost improvements which will lead to rapid market expansion.

  20. Probing Interfacial Electronic States in CdSe Quantum Dots using Second Harmonic Generation Spectroscopy

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Doughty, Benjamin L; Ma, Yingzhong; Shaw, Robert W

    2015-01-01

    Understanding and rationally controlling the properties of nanomaterial surfaces is a rapidly expanding field of research due to the dramatic role they play on the optical and electronic properties vital to light harvesting, emitting and detection technologies. This information is essential to the continued development of synthetic approaches designed to tailor interfaces for optimal nanomaterial based device performance. In this work, closely spaced electronic excited states in model CdSe quantum dots (QDs) are resolved using second harmonic generation (SHG) spectroscopy, and the corresponding contributions from surface species to these states are assessed. Two distinct spectral features are observed in themore » SHG spectra, which are not readily identified in linear absorption and photoluminescence excitation spectra. These features include a weak band at 395 6 nm, which coincides with transitions to the 2S1/2 1Se state, and a much more pronounced band at 423 4 nm arising from electronic transitions to the 1P3/2 1Pe state. Chemical modification of the QD surfaces through oxidation resulted in disappearance of the SHG band corresponding to the 1P3/2 1Pe state, indicating prominent surface contributions. Signatures of deep trap states localized on the surfaces of the QDs are also observed. We further find that the SHG signal intensities depend strongly on the electronic states being probed and their relative surface contributions, thereby offering additional insight into the surface specificity of SHG signals from QDs.« less

  1. Properties of Cu(In,Ga,Al)Se{sub 2} thin films fabricated by magnetron sputtering

    SciTech Connect (OSTI)

    Hameed, Talaat A.; Cao, Wei; Mansour, Bahiga A.; Elzawaway, Inas K.; Abdelrazek, El-Metwally M.; Elsayed-Ali, Hani E.

    2015-05-15

    Cu(In,Ga,Al)Se{sub 2} (CIGAS) thin films were studied as an alternative absorber layer material to Cu(In{sub x}Ga{sub 1?x})Se{sub 2}. CIGAS thin films with varying Al content were prepared by magnetron sputtering on Si(100) and soda-lime glass substrates at 350?C, followed by postdeposition annealing at 520?C for 5 h in vacuum. The film composition was measured by an electron probe microanalyzer while the elemental depth profiles were determined by secondary ion mass spectrometry. X-ray diffraction studies indicated that CIGAS films are single phase with chalcopyrite structure and that the (112) peak clearly shifts to higher 2? values with increasing Al content. Scanning electron microscopy images revealed dense and well-defined grains, as well as sharp CIGAS/Si(100) interfaces for all films. Atomic force microscopy analysis indicated that the roughness of CIGAS films decreases with increasing Al content. The bandgap of CIGAS films was determined from the optical transmittance and reflectance spectra and was found to increase as Al content increased.

  2. Characterization and device performance of (AgCu)(InGa)Se2 absorber layers

    SciTech Connect (OSTI)

    Hanket, Gregory; Boyle, Jonathan H.; Shafarman, William N.

    2009-06-08

    The study of (AgCu)(InGa)Se2 absorber layers is of interest in that Ag-chalcopyrites exhibit both wider bandgaps and lower melting points than their Cu counterparts. (AgCu)(InGa)Se2 absorber layers were deposited over the composition range 0 < Ag/(Ag+Cu) < 1 and 0.3 < Ga/(In+Ga) < 1.0 using a variety of elemental co-evaporation processes. Films were found to be singlephase over the entire composition range, in contrast to prior studies. Devices with Ga content 0.3 < Ga/(In+Ga) <0.5 tolerated Ag incorporation up to Ag/(Ag+Cu) = 0.5 without appreciable performance loss. Ag-containing films with Ga/(In+Ga) = 0.8 showed improved device characteristics over Cu-only control samples, in particular a 30-40% increase in short-circuit current. An absorber layer with composition Ag/(Ag+Cu) = 0.75 and Ga/(In+Ga) = 0.8 yielded a device with VOC = 890 mV, JSC = 20.5mA/cm2, fill factor = 71.3%, and ? = 13.0%.

  3. ZnO/Cu(InGa)Se.sub.2 solar cells prepared by vapor phase Zn doping

    DOE Patents [OSTI]

    Ramanathan, Kannan; Hasoon, Falah S.; Asher, Sarah E.; Dolan, James; Keane, James C.

    2007-02-20

    A process for making a thin film ZnO/Cu(InGa)Se.sub.2 solar cell without depositing a buffer layer and by Zn doping from a vapor phase, comprising: depositing Cu(InGa)Se.sub.2 layer on a metal back contact deposited on a glass substrate; heating the Cu(InGa)Se.sub.2 layer on the metal back contact on the glass substrate to a temperature range between about 100.degree. C. to about 250.degree. C.; subjecting the heated layer of Cu(InGa)Se.sub.2 to an evaporant species from a Zn compound; and sputter depositing ZnO on the Zn compound evaporant species treated layer of Cu(InGa)Se.sub.2.

  4. Migrating data from TcSE to DOORS : an evaluation of the T-Plan Integrator software application.

    SciTech Connect (OSTI)

    Post, Debra S.; Manzanares, David A.; Taylor, Jeffrey L.

    2011-02-01

    This report describes our evaluation of the T-Plan Integrator software application as it was used to transfer a real data set from the Teamcenter for Systems Engineering (TcSE) software application to the DOORS software application. The T-Plan Integrator was evaluated to determine if it would meet the needs of Sandia National Laboratories to migrate our existing data sets from TcSE to DOORS. This report presents the struggles of migrating data and focuses on how the Integrator can be used to map a data set and its data architecture from TcSE to DOORS. Finally, this report describes how the bulk of the migration can take place using the Integrator; however, about 20-30% of the data would need to be transferred from TcSE to DOORS manually. This report does not evaluate the transfer of data from DOORS to TcSE.

  5. Flowing versus Static Conditions for Measuring Multiple Exciton Generation in PbSe Quantum Dots

    SciTech Connect (OSTI)

    Midgett, Aaron G. [National Renewable Energy Lab. (NREL), Golden, CO (United States); Univ. of Colorado, Boulder, CO (United States); Hillhouse, Hugh W. [Univ. of Washington, Seattle, WA (United States); Hughes, Barbara K. [National Renewable Energy Lab. (NREL), Golden, CO (United States); Univ. of Colorado, Boulder, CO (United States); Nozik, Arthur J. [National Renewable Energy Lab. (NREL), Golden, CO (United States); Univ. of Colorado, Boulder, CO (United States); Beard, Matthew C. [Univ. of Colorado, Boulder, CO (United States)

    2010-09-22

    Recent reports question the validity of pulsed fs-laser experiments for measuring the photon-to-exciton quantum yields (QYs) that result from multiple exciton generation (MEG). The repetitive nature of these experiments opens up an alternative relaxation pathway that may produce artificially high results. We present transient-absorption (TA) data for 4.6 and 6.6 nm diameter PbSe quantum dots (QDs) at a variety of pump photon energies. The data are collected under laminar flow conditions with volumetric flow rates ranging from 0 to 150 mL/min (resulting in Reynolds numbers up to 460). The results are modeled with a spatially resolved population balance of generation, recombination, convective replacement, and accumulation of long-lived excited QDs. By comparing the simulations and experiments, the steady-state population of the long-lived QD-excited states and their kinetics are determined for different experimental conditions. We also improve upon reported photon-to-exciton QYs for PbSe QDs. We find differences in the observed TA dynamics between flowing and static conditions that depend upon photon fluence, pump photon energy, and quality of the QD surfaces. For excitation energies below 2 Eg, independent of QD size or photon fluence, we observe no flow rate dependence in the TA dynamics. At excitation energies of h? > 3 Eg, we observe differences between static and flowing conditions that are most pronounced for high photon fluences. At 3.7 Eg and for 4.6 nm PbSe QDs we find a QY of 1.2 0.1 and at 4.5 Eg the QY is 1.55 0.05. With 6.6 nm QDs excited at 4.7 Eg we observe no difference between static and flowing conditions and find a QY of 1.61 0.05. We also find that by treating the surface of QDs, we can decrease the charging probability (Pg ? 5 10-5) by a factor of 3-4. The observed variations suggest that different QD samples vary regarding their susceptibility to the creation of long-lived states.

  6. Apparent critical phenomena in the superionic phase transition of Cu2-xSe

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Kang, Stephen Dongmin; Danilkin, Sergey A.; Aydemir, Umut; Avdeev, Maxim; Studer, Andrew; Snyder, G. Jeffrey

    2016-01-11

    The superionic phase transition ofmore » $${\\mathrm{Cu}}_{2-x}\\mathrm{Se}$$ accompanies drastic changes in transport properties. The Seebeck coefficient increases sharply while the electrical conductivity and thermal diffusivity drops. Such behavior has previously been attributed to critical phenomena under the assumption of a continuous phase transition. However, applying Landau's criteria suggests that the transition should be first order. Using the phase diagram that is consistent with a first order transition, we show that the observed transport properties and heat capacity curves can be accounted for and modeled with good agreement. The apparent critical phenomena is shown to be a result of compositional degree-of-freedom. In conclusion, understanding of the phase transition allows to explain the enhancement in the thermoelectric figure-of-merit that is accompanied with the transition.« less

  7. Nuclear Structure Relevant to Neutrinoless Double {beta} Decay: {sup 76}Ge and {sup 76}Se

    SciTech Connect (OSTI)

    Schiffer, J. P.; Gros, S.; Jiang, C. L.; Rehm, K. E. [Physics Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Freeman, S. J.; Fitzpatrick, C. R.; Kay, B. P. [University of Manchester, Manchester M13 9PL (United Kingdom); Clark, J. A.; Deibel, C.; Heinz, A.; Parikh, A.; Parker, P. D.; Werner, V.; Wrede, C. [Yale University, New Haven, Connecticut 06520 (United States); Hirata, D. [GANIL (IN2P3/CNRS -DSM/CEA), B.P. 55027 14076 Caen Cedex 5 (France); Dept. of Physics and Astronomy, Open University, Milton Keynes, MK7 6AA (United Kingdom); Villari, A. C. C. [GANIL (IN2P3/CNRS -DSM/CEA), B.P. 55027 14076 Caen Cedex 5 (France)

    2008-03-21

    The possibility of observing neutrinoless double {beta} decay offers the opportunity of determining the effective neutrino mass if the nuclear matrix element were known. Theoretical calculations are uncertain, and measurements of the occupations of valence orbits by nucleons active in the decay can be important. The occupation of valence neutron orbits in the ground states of {sup 76}Ge (a candidate for such decay) and {sup 76}Se (the daughter nucleus) were determined by precisely measuring cross sections for both neutron-adding and removing transfer reactions. Our results indicate that the Fermi surface is much more diffuse than in theoretical calculations. We find that the populations of at least three orbits change significantly between these two ground states while in the calculations, the changes are confined primarily to one orbit.

  8. Stable n-CuInSe/sub 2/iodide-iodine photoelectrochemical cell

    DOE Patents [OSTI]

    Cahen, D.; Chen, Y.W.

    1984-09-20

    In a photoelectrochemical solar cell, stable output and solar efficiency in excess of 10% are achieved with a photoanode of n-CuInSe/sub 2/ electrode material and an iodine/iodide redox couple used in a liquid electrolyte. The photoanode is prepared by treating the electrode material by chemical etching, for example in Br/sub 2//MeOH; heating the etched electrode material in air or oxygen; depositing a surface film coating of indium on the electrode material after the initial heating; and thereafter again heating the electrode material in air or oxygen to oxidize the indium. The electrolyte is treated by the addition of Cu/sup +/ or Cu/sup 2 +/ salts and in In/sup 3 +/ salts.

  9. Stable N-CuInSe.sub.2 /iodide-iodine photoelectrochemical cell

    DOE Patents [OSTI]

    Cahen, David; Chen, Yih W.

    1985-01-01

    In a photoelectrochemical solar cell, stable output and solar efficiency in excess of 10% are achieved with a photoanode of n-CuInSe.sub.2 electrode material and an iodine/iodide redox couple used in a liquid electrolyte. The photoanode is prepared by treating the electrode material by chemical etching, for example in Br.sub.2 /MeOH; heating the etched electrode material in air or oxygen; depositing a surface film coating of indium on the electrode material after the initial heating; and thereafter again heating the electrode material in air or oxygen to oxidize the indium. The electrolyte is treated by the addition of Cu.sup.+ or Cu.sup.2+ salts and In.sup.3+ salts.

  10. Strain-dependent photoluminescence behavior in three geometries of CdSe/CdS nanocrystals

    SciTech Connect (OSTI)

    Choi, Charina L; Koski, Kristie J; Sivasankar, Sanjeevi; Alivisatos, A Paul

    2009-05-26

    In recent years, a new generation of quantum confined colloidal semiconductor structures has emerged, with more complex shapes than simple quantum dots1, 2. These include nanorods3 and tetrapods4. Beyond shape, it is also now possible to spatially vary the electron and hole potentials within these nanoparticles by varying the composition. Examples of these new structures include seeded dots, rods, and tetrapods, which contain a CdSe core embedded within a CdS shell5, 6. These structures may have many uses beyond those envisioned for simple quantum dots, which are frequently employed in luminescent applications7. This paper is concerned with changes in the optoelectronic properties of tetrapods when the arms are bent. We demonstrate that seeded tetrapods can serve as an optical strain gauge, capable of measuring forces on the order of nanonewtons. We anticipate that a nanocrystal strain gauge with optical readout will be useful for applications ranging from sensitive optomechanical devices to biological force investigations.

  11. Co-Evaporated Cu2ZnSnSe4 Films and Devices

    SciTech Connect (OSTI)

    Repins, I.; Beall, C.; Vora, N.; DeHart, C.; Kuciauskas, D.; Dippo, P.; To, B.; Mann, J.; Hsu, W. C.; Goodrich, A.; Noufi, R.

    2012-06-01

    The use of vacuum co-evaporation to produce Cu2ZnSnSe4 photovoltaic devices with 9.15% total-area efficiency is described. These new results suggest that the early success of the atmospheric techniques for kesterite photovoltaics may be related to the ease with which one can control film composition and volatile phases, rather than a fundamental benefit of atmospheric conditions for film properties. The co-evaporation growth recipe is documented, as is the motivation for various features of the recipe. Characteristics of the resulting kesterite films and devices are shown in scanning electron micrographs, including photoluminescence, current-voltage, and quantum efficiency. Current-voltage curves demonstrate low series resistance without the light-dark cross-over seen in many devices in the literature. Band gap indicated by quantum efficiency and photoluminescence is roughly consistent with that expected from first principles calculation.

  12. Development and characterization of PCDTBT:CdSe QDs hybrid solar cell

    SciTech Connect (OSTI)

    Dixit, Shiv Kumar Bhatnagar, Chhavi Kumari, Anita Madhwal, Devinder Bhatnagar, P. K. Mathur, P. C.

    2014-10-15

    Solar cell consisting of low band gap polymer poly[N-900-hepta-decanyl-2,7-carbazole-alt-5,5-(40,70-di-2-thienyl-20,10, 30-benzothiadiazole)] (PCDTBT) as donor and cadmium selenide/zinc sulphide (CdSe/ZnS) core shell quantum dots (QDs) as an acceptor has been developed. The absorption measurements show that the absorption coefficient increases in bulk heterojunction (BHJ) structure covering broad absorption spectrum (200nm–700nm). Also, the photoluminescence (PL) of the PCDTBT:QDs film is found to decrease by an order of magnitude showing a significant transfer of electrons to the QDs. With this approach and under broadband white light with an irradiance of 8.19 mW/cm{sup 2}, we have been able to achieve a power conversion efficiency (PCE) of 3.1 % with fill factor 0.42 for our typical solar cell.

  13. Photo-instability of CdSe/ZnS quantum dots in poly(methylmethacrylate) film

    SciTech Connect (OSTI)

    Zhang, Hongyi; Liu, Yu; Ye, Xiaoling; Chen, Yonghai

    2013-12-28

    The photo-instability of CdSe/ZnS quantum dots (QDs) has been studied under varied conditions. We discussed the main features of the evolution of photoluminescence (PL) intensity and energy at different laser powers, which showed critical dependences on the environment. The PL red shift in a vacuum showed strong temperature dependence, from which we concluded that the thermal activation energy for trapping states of the charge carriers was about 14.7 meV. Furthermore, the PL spectra showed asymmetric evolution during the laser irradiation, for which two possible explanations were discussed. Those results provided a comprehensive picture for the photo-instability of the colloidal QDs under different conditions.

  14. Optical and quantum efficiency analysis of (Ag,Cu)(In,Ga)Se2 absorber layers

    SciTech Connect (OSTI)

    Boyle, Jonathan; Hanket, Gregory; Shafarman, William

    2009-06-09

    (Ag,Cu)(In,Ga)Se2 thin films have been deposited by elemental co-evaporation over a wide range of compositions and their optical properties characterized by transmission and reflection measurements and by relative shift analysis of quantum efficiency device measurements. The optical bandgaps were determined by performing linear fits of (?h?)2 vs. h?, and the quantum efficiency bandgaps were determined by relative shift analysis of device curves with fixed Ga/(In+Ga) composition, but varying Ag/(Cu+Ag) composition. The determined experimental optical bandgap ranges of the Ga/(In+Ga) = 0.31, 0.52, and 0.82 groups, with Ag/(Cu+Ag) ranging from 0 to 1, were 1.19-1.45 eV, 1.32-1.56 eV, and 1.52-1.76 eV, respectively. The optical bowing parameter of the different Ga/(In+Ga) groups was also determined.

  15. Time-resolved terahertz dynamics in thin films of the topological insulator Bi2Se3

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Valdés Aguilar, R.; Qi, J.; Brahlek, M.; Bansal, N.; Azad, A.; Bowlan, J.; Oh, S.; Taylor, A. J.; Prasankumar, R. P.; Yarotski, D. A.

    2015-01-07

    We use optical pump–THz probe spectroscopy at low temperatures to study the hot carrier response in thin Bi2Se3 films of several thicknesses, allowing us to separate the bulk from the surface transient response. We find that for thinner films the photoexcitation changes the transport scattering rate and reduces the THz conductivity, which relaxes within 10 picoseconds (ps). For thicker films, the conductivity increases upon photoexcitation and scales with increasing both the film thickness and the optical fluence, with a decay time of approximately 5 ps as well as a much higher scattering rate. Furthermore, these different dynamics are attributed tomore » the surface and bulk electrons, respectively, and demonstrate that long-lived mobile surface photo-carriers can be accessed independently below certain film thicknesses for possible optoelectronic applications.« less

  16. Green route synthesis of high quality CdSe quantum dots for applications in light emitting devices

    SciTech Connect (OSTI)

    Bera, Susnata, E-mail: susnata.bera@gmail.com [Department of Physics and Meteorology, Indian Institute of Technology Kharagpur, Kharagpur 721302 (India); Singh, Shashi B. [Department of Physics and Meteorology, Indian Institute of Technology Kharagpur, Kharagpur 721302 (India); Ray, S.K., E-mail: physkr@phy.iitkgp.ernet.in [Department of Physics and Meteorology, Indian Institute of Technology Kharagpur, Kharagpur 721302 (India)

    2012-05-15

    Investigation was made on light emitting diodes fabricated using CdSe quantum dots. CdSe quantum dots were synthesized chemically using olive oil as the capping agent, instead of toxic phosphine. Room temperature photoluminescence investigation showed sharp 1st excitonic emission peak at 568 nm. Bi-layer organic/inorganic (P3HT/CdSe) hybrid light emitting devices were fabricated by solution process. The electroluminescence study showed low turn on voltage ({approx}2.2 V) .The EL peak intensity was found to increase by increasing the operating current. - Graphical abstract: Light emitting diode was fabricated using CdSe quantum dots using olive oil as the capping agent, instead of toxic phosphine. Bi-layer organic/inorganic (P3HT/CdSe) hybrid light emitting device shows strong electroluminescence in the range 630-661 nm. Highlights: Black-Right-Pointing-Pointer CdSe Quantum dots were synthesized using olive oil as the capping agent. Black-Right-Pointing-Pointer Light emitting device was fabricated using CdSe QDs/P3HT polymer heterojunction. Black-Right-Pointing-Pointer The I-V characteristics study showed low turn on voltage at {approx}2.2 V. Black-Right-Pointing-Pointer The EL peak intensity increases with increasing the operating current.

  17. Investigation of size dependent structural and optical properties of thin films of CdSe quantum dots

    SciTech Connect (OSTI)

    Sharma, Madhulika; Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology, Bombay, Powai, Mumbai 400076 ; Sharma, A.B.; Mishra, N.; Pandey, R.K.

    2011-03-15

    Research highlights: {yields} CdSe q-dots have been synthesized using simple chemical synthesis route. {yields} Thin film of CdSe quantum dots exhibited self-organized growth. {yields} Size dependent blue shift observed in the absorption edge of CdSe nanocrystallites. {yields} PL emission band corresponds to band edge luminescence and defect luminescence. {yields} Organized growth led to enhancement in luminescence yield of smaller size Q-dots. -- Abstract: Cadmium selenide (CdSe) quantum dots were grown on indium tin oxide substrate using wet chemical technique for possible application as light emitting devices. The structural, morphological and luminescence properties of the as deposited thin films of CdSe Q-dot have been investigated, using X-ray diffraction, transmission electron microscopy, atomic force microscopy and optical and luminescence spectroscopy. The quantum dots have been shown to deposit in an organized array on ITO/glass substrate. The as grown Q-dots exhibited size dependent blue shift in the absorption edge. The effect of quantum confinement also manifested as a blue shift of photoluminescence emission. It is shown that the nanocrystalline CdSe exhibits intense photoluminescence as compared to the large grained polycrystalline CdSe films.

  18. Single-step in-situ synthesis and optical properties of ZnSe nanostructured dielectric nanocomposites

    SciTech Connect (OSTI)

    Dey, Chirantan; Rahaman Molla, Atiar; Tarafder, Anal; Karmakar, Basudeb; Kr Mishra, Manish; De, Goutam; Goswami, Madhumita; Kothiyal, G. P.

    2014-04-07

    This work provides the evidence of visible red photoluminescent light emission from ZnSe nanocrystals (NCs) grown within a dielectric (borosilicate glass) matrix synthesized by a single step in-situ technique for the first time and the NC sizes were controlled by varying only the concentration of ZnSe in glass matrix. The ZnSe NCs were investigated by UV-Vis optical absorption spectroscopy, Raman spectroscopy, and transmission electron microscopy (TEM). The sizes of the ZnSe NCs estimated from the TEM images are found to alter in the range of 2–53 nm. Their smaller sizes of the NCs were also calculated by using the optical absorption spectra and the effective mass approximation model. The band gap enlargements both for carrier and exciton confinements were evaluated and found to be changed in the range of 0–1.0 eV. The Raman spectroscopic studies showed blue shifted Raman peaks of ZnSe at 295 and 315 cm{sup −1} indicating phonon confinement effect as well as compressive stress effect on the surface atoms of the NCs. Red photoluminescence in ZnSe-glass nanocomposite reveals a broad multiple-peak structure due to overlapping of emission from NC size related electron-hole recombination (∼707 nm) and emissions from defects to traps, which were formed due to Se and Zn vacancies signifying potential application in photonics.

  19. Effects of competing magnetic interactions on the electronic transport properties of CuCrSe{sub 2}

    SciTech Connect (OSTI)

    Tewari, Girish C.; Jawaharlal Nehru University, New Delhi 110067 ; Karppinen, Maarit; Rastogi, Ashok K.

    2013-02-15

    We have synthesized single-phase samples of the CuCrSe{sub 2} phase that exhibits hexagonal-rhombohedral layered crystal structure with space group R3m. Here we present a detailed study of electronic transport and magnetic properties of CuCrSe{sub 2}. We moreover investigate the heat capacity of CuCrSe{sub 2} in comparison to that of CuCrS{sub 2}. The electrical resistivity of CuCrSe{sub 2} shows metallic-like behavior down to 2 K, while the thermoelectric power is large around 100 {mu}V K{sup -1} at 300 K. A weak anomaly in resistivity and a rounded maximum in magnetic susceptibility are observed around 55 K. No sharp transition at 55 K is observed in the heat capacity of CuCrSe{sub 2}, rather a visible maximum is seen. At low temperatures from 2 to 14 K, the magnetic heat capacity follows T{sup 2}-dependence. We tentatively believe this behavior of CuCrSe{sub 2} to be due to competing magnetic interactions between intralayer Cr atoms. The ferromagnetic Cr-Se-Cr indirect exchange among intralayer Cr atoms is enhanced in the selenide compound (that is more metallic than the sulfide compound), and competes with the antiferromagnetic Cr-Cr direct interactions. The interlayer antiferromagnetic exchange through Cu atoms leads to magnetic ordering at low temperature at T{sub N}=55 K. - Graphical abstract: Comparison of magnetic properties of CuCrSe{sub 2} and CuCrS{sub 2} indicates a sharp cusp-like anomaly in magnetic susceptibility at the antiferromagnetic transition of CuCrS{sub 2} while the maximum of CuCrSe{sub 2} is well rounded. Magnetization is reversible after field-cooling (FC) and zero-field-cooling (ZFC) for both compounds. Highlights: Black-Right-Pointing-Pointer Layered CuCrSe{sub 2} can be synthesized in both fully and partially cation-ordered forms. Black-Right-Pointing-Pointer Contrary to previously believed insulating nature the cation-ordered phase is metallic. Black-Right-Pointing-Pointer Magnetic property of CuCrSe{sub 2} is somewhat different from that of CuCrS{sub 2}. Black-Right-Pointing-Pointer Magnetization and heat capacity data suggest complex short-range ordering for CuCrSe{sub 2}.

  20. Molecular beam epitaxial growth and characterization of Bi{sub 2}Se{sub 3}/II-VI semiconductor heterostructures

    SciTech Connect (OSTI)

    Chen, Zhiyi Zhao, Lukas; Krusin-Elbaum, Lia; Garcia, Thor Axtmann; Tamargo, Maria C.; Hernandez-Mainet, Luis C.; Deng, Haiming

    2014-12-15

    Surfaces of three-dimensional topological insulators (TIs) have been proposed to host quantum phases at the interfaces with other types of materials, provided that the topological properties of interfacial regions remain unperturbed. Here, we report on the molecular beam epitaxy growth of II-VI semiconductorTI heterostructures using c-plane sapphire substrates. Our studies demonstrate that Zn{sub 0.49}Cd{sub 0.51}Se and Zn{sub 0.23}Cd{sub 0.25}Mg{sub 0.52}Se layers have improved quality relative to ZnSe. The structures exhibit a large relative upward shift of the TI bulk quantum levels when the TI layers are very thin (?6nm), consistent with quantum confinement imposed by the wide bandgap II-VI layers. Our transport measurements show that the characteristic topological signatures of the Bi{sub 2}Se{sub 3} layers are preserved.

  1. CdSe/CdTe type-II superlattices grown on GaSb (001) substrates by molecular beam epitaxy

    SciTech Connect (OSTI)

    Li Jingjing; Liu Shi; Wang Shumin; Ding Ding; Johnson, Shane R.; Zhang Yonghang; Liu Xinyu; Furdyna, Jacek K.; Smith, David J.

    2012-03-19

    CdSe/CdTe superlattices are grown on GaSb substrates using molecular beam epitaxy. X-ray diffraction measurements and cross-sectional transmission electron microscopy images indicate high crystalline quality. Photoluminescence (PL) measurements show the effective bandgap varies with the superlattice layer thicknesses and confirm the CdSe/CdTe heterostructure has a type-II band edge alignment. The valence band offset between unstrained CdTe and CdSe is determined as 0.63 {+-} 0.06 eV by fitting the measured PL peak positions using the envelope function approximation and the Kronig-Penney model. These results suggest that CdSe/CdTe superlattices are promising candidates for multi-junction solar cells and other optoelectronic devices based on GaSb substrates.

  2. Enhanced photorefractive performance in CdSe quantum-dot-dispersed poly(styrene-co-acrylonitrile) polymers

    SciTech Connect (OSTI)

    Li Xiangping; Embden, Joel van; Chon, James W. M.; Gu Min; Evans, Richard A.

    2010-06-21

    This paper reports on the enhanced photorefractive behavior of a CdSe quantum-dot-dispersed less expensive polymer of poly(styrene-co-acrylonitrile). The capability of CdSe quantum dots used as photosensitizers and the associated photorefractive performance are characterized through a photocurrent experiment and a two-beam coupling experiment, respectively. An enhanced two-beam coupling gain coefficient of 12.2 cm{sup -1} at 46 V/mum was observed owning to the reduced potential barrier. The photorefractive performance per CdSe quantum dot is three orders of magnitude higher than that in the sample sensitized by trinitrofluorenone in poly(styrene-co-acrylonitrile), and almost ten times higher than that in the CdSe quantum-dot-sensitized poly(N-vinylcarbazole) polymers.

  3. Photodeposition of Pt on Colloidal CdS and CdSe/CdS Semiconductor Nanostructures

    SciTech Connect (OSTI)

    Dukovic, Gordana; Merkle, Maxwell G.; Nelson, James H.; Hughes, Steven M.; Alivisatos, A. Paul

    2008-08-06

    Semiconductor photocatalysis has been identified as a promising avenue for the conversion of solar energy into environmentally friendly fuels, most notably by the production of hydrogen from water.[1-5] Nanometer-scale materials in particular have attracted considerable scientific attention as the building blocks for light-harvesting applications.[6,7] Their desirable attributes include tunability of the optical properties with size, amenability to relatively inexpensive low-temperature processing, and a high degree of synthetic sophistication leading to increasingly complex and multi-functional architectures. For photocatalysis in particular, the high surface-to-volume ratios in nanoscale materials should lead to an increased availability of carriers for redox reactions on the nanoparticle surface. Recombination of photoexcited carriers directly competes with photocatalytic activity.[3] Charge separation is often achieved with multi-component heterostructures. An early example is the case of TiO2 powders functionalized with Pt and RuO2 particles, where photoexcited electrons are transferred to Pt (the reduction site) and holes to RuO2 (the oxidation site).[8] More recently, many colloidally synthesized nanometer-scale metal-semiconductor heterostructures have been reported.[7,9,10] A majority of these structures are made by thermal methods.[7,10] We have chosen to study photochemical formation of metal-semiconductor heterostructures. The detailed understanding of the mechanisms involved in photodeposition of metals on nanometer-scale semiconductors is necessary to enable a high degree of synthetic control. At the same time, because the results of metal deposition can be directly observed by electron microscopy, it can be used to understand how factors such as nanocrystal composition, shape, carrier dynamics, and surface chemistry influence the photochemical properties of semiconductor nanocrystals. In this communication, we report on the photodeposition of Pt on colloidal CdS and CdSe/CdS core/shell nanocrystals. Among the II-VI semiconductors, CdS is of particular interest because it has the correct band alignment for water photolysis[2] and has been demonstrated to be photocatalytically active.[11-16] We have found that the photoexcitation of CdS and CdSe/CdS in the presence of an organometallic Pt precursor leads to deposition of Pt nanoparticles on the semiconductor surface. Stark differences are observed in the Pt nanoparticle location on the two substrates, and the photodeposition can be completely inhibited by the modification of the semiconductor surface. Our results suggest that tuning of the semiconductor band structure, spatial organization and surface chemistry should be crucial in the design of photocatalytic nanostructures.

  4. Large single crystal quaternary alloys of IB-IIIA-SE.sub.2 and methods of synthesizing the same

    DOE Patents [OSTI]

    Ciszek, Theodore F.

    1988-01-01

    New alloys of Cu.sub.x Ag.sub.(1-x) InSe.sub.2 (where x ranges between 0 and 1 and preferably has a value of about 0.75) and CuIn.sub.y Ga.sub.(1-y) Se.sub.2 (where y ranges between 0 and 1 and preferably has a value of about 0.90) in the form of single crystals with enhanced structure perfection, which crystals are substantially free of fissures are disclosed. Processes are disclosed for preparing the new alloys of Cu.sub.x Ag.sub.(1-x) InSe.sub.2. The process includes placing stoichiometric quantities of a Cu, Ag, In, and Se reaction mixture or stoichiometric quantities of a Cu, In, Ga, and Se reaction mixture in a refractory crucible in such a manner that the reaction mixture is surrounded by B.sub.2 O.sub.3, placing the thus loaded crucible in a chamber under a high pressure atmosphere of inert gas to confine the volatile Se to the crucible, and heating the reaction mixture to its melting point. The melt can then be cooled slowly to form, by direct solidification, a single crystal with enhanced structure perfection, which crystal is substantially free of fissures.

  5. Large single crystal quaternary alloys of IB-IIIA-Se/sub 2/ and methods of synthesizing the same

    DOE Patents [OSTI]

    Ciszek, T.F.

    1986-07-15

    New alloys of Cu/sub x/Ag/sub (1-x)/InSe/sub 2/ (where x ranges between 0 and 1 and preferably has a value of about 0.75) and CuIn/sub y/Ga/sub (1-y)/Se/sub 2/ (where y ranges between 0 and 1 and preferably has a value of about 0.90) in the form of single crystals with enhanced structure perfection, which crystals are substantially free of fissures, are disclosed. Processes are disclosed for preparing the new alloys of Cu/sub x/Ag/sub (1-x)/InSe/sub 2/. The process includes placing stoichiometric quantities of a Cu, Ag, In, and Se reaction mixture or stoichiometric quantities of a Cu, In, Ga, and Se reaction mixture in a refractory crucible in such a manner that the reaction mixture is surrounded by B/sub 2/O/sub 3/, placing the thus loaded crucible in a chamber under a high pressure atmosphere of inert gas to confine the volatile Se to the crucible, and heating the reaction mixture to its melting point. The melt can then be cooled slowly to form, by direct solidification, a single crystal with enhanced structure perfection, which crystal is substantially free of fissures.

  6. Processing approach towards the formation of thin-film Cu(In,Ga)Se2

    DOE Patents [OSTI]

    Beck, Markus E.; Noufi, Rommel

    2003-01-01

    A two-stage method of producing thin-films of group IB-IIIA-VIA on a substrate for semiconductor device applications includes a first stage of depositing an amorphous group IB-IIIA-VIA precursor onto an unheated substrate, wherein the precursor contains all of the group IB and group IIIA constituents of the semiconductor thin-film to be produced in the stoichiometric amounts desired for the final product, and a second stage which involves subjecting the precursor to a short thermal treatment at 420.degree. C.-550.degree. C. in a vacuum or under an inert atmosphere to produce a single-phase, group IB-III-VIA film. Preferably the precursor also comprises the group VIA element in the stoichiometric amount desired for the final semiconductor thin-film. The group IB-IIIA-VIA semiconductor films may be, for example, Cu(In,Ga)(Se,S).sub.2 mixed-metal chalcogenides. The resultant supported group IB-IIIA-VIA semiconductor film is suitable for use in photovoltaic applications.

  7. Performance Characterization and Remedy of Experimental CuInGaSe2 Mini-Modules: Preprint

    SciTech Connect (OSTI)

    Pern, F. J.; Yan, F.; Mansfield, L.; Glynn, S.; Rekow, M.; Murion, R.

    2011-07-01

    We employed current-voltage (I-V), quantum efficiency (QE), photoluminescence (PL), electroluminescence (EL), lock-in thermography (LIT), and (electrochemical) impedance spectroscopy (ECIS) to complementarily characterize the performance and remedy for two pairs of experimental CuInGaSe2 (CIGS) mini-modules. One pair had the three scribe-lines (P1/P2/P3) done by a single pulse-programmable laser, and the other had the P2/P3 lines by mechanical scribe. Localized QE measurements for each cell strip on all four mini-modules showed non-uniform distributions that correlated well with the presence of performance-degrading strips or spots revealed by PL, EL, and LIT imaging. Performance of the all-laser-scribed mini-modules improved significantly by adding a thicker Al-doped ZnO layer and reworking the P3 line. The efficiency on one of the all-laser-scribed mini-modules increased notably from 7.80% to 8.56% after the performance-degrading spots on the side regions along the cell array were isolated by manual scribes.

  8. CdSe Quantum-Dot-Sensitized Solar Cell with ~100% Internal Quantum Efficiency

    SciTech Connect (OSTI)

    Fuke, Nobuhiro; Hoch, Laura B.; Koposov, Alexey Y.; Manner, Virginia W.; Werder, Donald J.; Fukui, Atsushi; Koide, Naoki; Katayama, Hiroyuki; Sykora, Milan

    2010-10-20

    We have constructed and studied photoelectrochemical solar cells (PECs) consisting of a photoanode prepared by direct deposition of independently synthesized CdSe nanocrystal quantum dots (NQDs) onto a nanocrystalline TiO2 film (NQD/TiO2), aqueous Na2S or Li2S electrolyte, and a Pt counter electrode. We show that light harvesting efficiency (LHE) of the NQD/TiO2 photoanode is significantly enhanced when the NQD surface passivation is changed from tri-n-octylphosphine oxide (TOPO) to 4-butylamine (BA). In the PEC the use of NQDs with a shorter passivating ligand, BA, leads to a significant enhancement in both the electron injection efficiency at the NQD/TiO2 interface and charge collection efficiency at the NQD/electrolyte interface, with the latter attributed mostly to a more efficient diffusion of the electrolyte through the pores of the photoanode. We show that by utilizing BA-capped NQDs and aqueous Li2S as an electrolyte, it is possible to achieve ~100% internal quantum efficiency of photon-to-electron conversion, matching the performance of dye-sensitized solar cells.

  9. Anomalously Large Polarization Effect Responsible for Excitonic Red Shifts in PbSe Quantum Dot Solids

    SciTech Connect (OSTI)

    A Wolcott; V Doyeux; C Nelson; R Gearba; K Lei; K Yager; A dolocan; K Williams; D Nguyen; X Zhu

    2011-12-31

    The formation of solid thin films from colloidal semiconductor quantum dots (QDs) is often accompanied by red shifts in excitonic transitions, but the mechanisms responsible for the red shifts are under debate. We quantitatively address this issue using optical absorption spectroscopy of two-dimensional (2D) and three-dimensional (3D) arrays of PbSe QDs with controlled inter-QD distance, which was determined by the length of alkanedithiol linking molecules. With decreasing inter-QD distance, the first and second exciton absorption peaks show increasing red shifts. Using thin films consisting of large and isolated QDs embedded in a matrix of small QDs, we determine that a dominant contribution to the observed red shift is due to changes in polarization of the dielectric environment surrounding each QD ({approx}88%), while electronic or transition dipole coupling plays a lesser role. However, the observed red shifts are more than 1 order of magnitude larger than theoretical predictions based on the dielectric polarization effect for spherical QDs. We attribute this anomalously large polarization effect to deviations of the exciton wave functions from eigenfunctions of the idealized spherical quantum well model.

  10. Characterization of Cu(In,Ga)Se2 (CIGS) films with varying gallium ratios

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Claypoole, Jesse; Peace, Bernadette; Sun, Neville; Dwyer, Dan; Eisaman, Matthew D.; Haldar, Pradeep; Efstathiadis, Harry

    2015-09-05

    Cu(In1-x,Gax)Se2 (CIGS) absorber layers were deposited on molybdenum (Mo) coated soda-lime glass substrates with varying Ga content (described as Ga/(In+Ga) ratios) with respect to depth. As the responsible mechanisms for the limitation of the performance of the CIGS solar cells with high Ga contents are not well understood, the goal of this work was to investigate different properties of CIGS absorber films with Ga/(In+Ga) ratios varied between 0.29 and 0.41 (as determined by X-ray florescence spectroscopy (XRF)) in order to better understand the role that the Ga content has on film quality. The Ga grading in the CIGS layer hasmore » the effect causing a higher bandgap toward the surface and Mo contact while the band gap in the middle of the CIGS layer is lower. Also, a wider and larger Ga/(In+Ga) grading dip located deeper in the CIGS absorber layers tend to produce larger grains in the regions of the films that have lower Ga/(In+Ga) ratios. It was found that surface roughness decreases from 51.2 nm to 41.0 nm with increasing Ga/(In+Ga) ratios. However, the surface roughness generally decreases if the Ga grading occurs deeper in the absorber layer.« less

  11. Monte Carlo modeling of transport in PbSe nanocrystal films

    SciTech Connect (OSTI)

    Carbone, I. Carter, S. A.; Zimanyi, G. T.

    2013-11-21

    A Monte Carlo hopping model was developed to simulate electron and hole transport in nanocrystalline PbSe films. Transport is carried out as a series of thermally activated hopping events between neighboring sites on a cubic lattice. Each site, representing an individual nanocrystal, is assigned a size-dependent electronic structure, and the effects of particle size, charging, interparticle coupling, and energetic disorder on electron and hole mobilities were investigated. Results of simulated field-effect measurements confirm that electron mobilities and conductivities at constant carrier densities increase with particle diameter by an order of magnitude up to 5?nm and begin to decrease above 6?nm. We find that as particle size increases, fewer hops are required to traverse the same distance and that site energy disorder significantly inhibits transport in films composed of smaller nanoparticles. The dip in mobilities and conductivities at larger particle sizes can be explained by a decrease in tunneling amplitudes and by charging penalties that are incurred more frequently when carriers are confined to fewer, larger nanoparticles. Using a nearly identical set of parameter values as the electron simulations, hole mobility simulations confirm measurements that increase monotonically with particle size over two orders of magnitude.

  12. Characterization of Cu(In,Ga)Se2 (CIGS) films with varying gallium ratios

    SciTech Connect (OSTI)

    Claypoole, Jesse; Peace, Bernadette; Sun, Neville; Dwyer, Dan; Eisaman, Matthew D.; Haldar, Pradeep; Efstathiadis, Harry

    2015-09-05

    Cu(In1-x,Gax)Se2 (CIGS) absorber layers were deposited on molybdenum (Mo) coated soda-lime glass substrates with varying Ga content (described as Ga/(In+Ga) ratios) with respect to depth. As the responsible mechanisms for the limitation of the performance of the CIGS solar cells with high Ga contents are not well understood, the goal of this work was to investigate different properties of CIGS absorber films with Ga/(In+Ga) ratios varied between 0.29 and 0.41 (as determined by X-ray florescence spectroscopy (XRF)) in order to better understand the role that the Ga content has on film quality. The Ga grading in the CIGS layer has the effect causing a higher bandgap toward the surface and Mo contact while the band gap in the middle of the CIGS layer is lower. Also, a wider and larger Ga/(In+Ga) grading dip located deeper in the CIGS absorber layers tend to produce larger grains in the regions of the films that have lower Ga/(In+Ga) ratios. It was found that surface roughness decreases from 51.2 nm to 41.0 nm with increasing Ga/(In+Ga) ratios. However, the surface roughness generally decreases if the Ga grading occurs deeper in the absorber layer.

  13. Temperature-driven band inversion in Pb?.??Sn?.??Se: Optical and Hall-effect studies

    SciTech Connect (OSTI)

    Anand, Naween; Gu, Genda; Buvaev, Sanal; Hebard, A. F.; Tanner, D. B.; Chen, Zhiguo; Li, Zhiqiang; Choudhary, Kamal; Sinnott, S. B.; Martin, C.

    2014-12-23

    Optical and Hall-effect measurements have been performed on single crystals of Pb?.??Sn?.??Se, a IV-VI mixed chalcogenide. The temperature dependent (10300 K) reflectance was measured over 407000 cm? (5870 meV) with an extension to 15,500 cm? (1.92 eV) at room temperature. The reflectance was fit to the Drude-Lorentz model using a single Drude component and several Lorentz oscillators. The optical properties at the measured temperatures were estimated via Kramers-Kronig analysis as well as by the Drude-Lorentz fit. The carriers were p-type with the carrier density determined by Hall measurements. A signature of valence intraband transition is found in the low-energy optical spectra. It is found that the valence-conduction band transition energy as well as the free carrier effective mass reach minimum values at 100 K, suggesting temperature-driven band inversion in the material. Density function theory calculation for the electronic band structure also make similar predictions.

  14. Temperature-driven band inversion in Pb?.??Sn?.??Se: Optical and Hall-effect studies

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Anand, Naween; Gu, Genda; Buvaev, Sanal; Hebard, A. F.; Tanner, D. B.; Chen, Zhiguo; Li, Zhiqiang; Choudhary, Kamal; Sinnott, S. B.; Martin, C.

    2014-12-23

    Optical and Hall-effect measurements have been performed on single crystals of Pb?.??Sn?.??Se, a IV-VI mixed chalcogenide. The temperature dependent (10300 K) reflectance was measured over 407000 cm? (5870 meV) with an extension to 15,500 cm? (1.92 eV) at room temperature. The reflectance was fit to the Drude-Lorentz model using a single Drude component and several Lorentz oscillators. The optical properties at the measured temperatures were estimated via Kramers-Kronig analysis as well as by the Drude-Lorentz fit. The carriers were p-type with the carrier density determined by Hall measurements. A signature of valence intraband transition is found in the low-energy opticalmorespectra. It is found that the valence-conduction band transition energy as well as the free carrier effective mass reach minimum values at 100 K, suggesting temperature-driven band inversion in the material. Density function theory calculation for the electronic band structure also make similar predictions.less

  15. Polytypism, polymorphism, and superconductivity in TaSe2–xTex

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Luo, Huixia; Xie, Weiwei; Tao, Jing; Inoue, Hiroyuki; Gyenis, András; Krizan, Jason W.; Yazdani, Ali; Zhu, Yimei; Cava, Robert Joseph

    2015-03-03

    Polymorphism in materials often leads to significantly different physical properties - the rutile and anatase polymorphs of TiO₂ are a prime example. Polytypism is a special type of polymorphism, occurring in layered materials when the geometry of a repeating structural layer is maintained but the layer stacking sequence of the overall crystal structure can be varied; SiC is an example of a material with many polytypes. Although polymorphs can have radically different physical properties, it is much rarer for polytypism to impact physical properties in a dramatic fashion. Here we study the effects of polytypism and polymorphism on the superconductivitymore » of TaSe₂, one of the archetypal members of the large family of layered dichalcogenides. We show that it is possible to access 2 stable polytypes and 2 stable polymorphs in the TaSe2-xTex solid solution, and find that the 3R polytype shows a superconducting transition temperature that is between 6 and 17 times higher than that of the much more commonly found 2H polytype. Thus, the reason for this dramatic change is not apparent, but we propose that it arises either from a remarkable dependence of Tc on subtle differences in the characteristics of the single layers present, or from a surprising effect of the layer stacking sequence on electronic properties that instead are expected to be dominated by the properties of a single layer in materials of this kind.« less

  16. Structural phase transitions in Bi2Se3 under high pressure

    SciTech Connect (OSTI)

    Yu, Zhenhai; Gu, Genda; Wang, Lin; Hu, Qingyang; Zhao, Jinggeng; Yan, Shuai; Yang, Ke; Sinogeikin, Stanislav; Mao, Ho -kwang

    2015-11-02

    Raman spectroscopy and angle dispersive X-ray diffraction (XRD) experiments of bismuth selenide (Bi2Se3) have been carried out to pressures of 35.6 and 81.2 GPa, respectively, to explore its pressure-induced phase transformation. The experiments indicate that a progressive structural evolution occurs from an ambient rhombohedra phase (Space group (SG): R-3m) to monoclinic phase (SG: C2/m) and eventually to a high pressure body-centered tetragonal phase (SG: I4/mmm). Evidenced by our XRD data up to 81.2 GPa, the Bi2Se3 crystallizes into body-centered tetragonal structures rather than the recently reported disordered body-centered cubic (BCC) phase. Furthermore, first principles theoretical calculations favor the viewpoint that the I4/mmm phase Bi2Se3 can be stabilized under high pressure (>30 GPa). Remarkably, the Raman spectra of Bi2Se3 from this work (two independent runs) are still Raman active up to ~35 GPa. Furthermore, it is worthy to note that the disordered BCC phase at 27.8 GPa is not observed here. The remarkable difference in atomic radii of Bi and Se in Bi2Se3 may explain why Bi2Se3 shows different structural behavior than isocompounds Bi2Te3 and Sb2Te3.

  17. Determination of Grain Boundary Charging in Cu(In,Ga)Se2 Thin Films: Preprint

    SciTech Connect (OSTI)

    Jiang, C. S.; Contreras, M. A.; Repins, I.; Moutinho, H. R.; Noufi, R.; Al-Jassim, M. M.

    2012-06-01

    Surface potential mapping of Cu(In,Ga)Se2 (CIGS) thin films using scanning Kelvin probe force microscopy (SKPFM) aims to understand the minority-carrier recombination at the grain boundaries (GBs) of this polycrystalline material by examining GB charging, which has resulted in a number of publications. However, the reported results are highly inconsistent. In this paper, we report on the potential mapping by measuring wide-bandgap or high-Ga-content films and by using a complementary atomic force microscopy-based electrical technique of scanning capacitance microscopy (SCM). The results demonstrate consistent, positively charged GBs on our high-quality films with minimal surface defects/charges. The potential image taken on a low-quality film with a 1.2-eV bandgap shows significantly degraded potential contrast on the GBs and degraded potential uniformity on grain surfaces, resulting from the surface defects/charges of the low-quality film. In contrast, the potential image on an improved high-quality film with the same wide bandgap shows significantly improved GB potential contrast and surface potential uniformity, indicating that the effect of surface defects is critical when examining GB charging using surface potential data. In addition, we discuss the effect of the SKPFM setup on the validity of potential measurement, to exclude possible artifacts due to improper SKPFM setups. The SKPFM results were corroborated by using SCM measurements on the films with a CdS buffer layer. The SCM image shows clear GB contrast, indicating different electrical impedance on the GB from the grain surface. Further, we found that the GB contrast disappeared when the CdS window layer was deposited after the CIGS film was exposed extensively to ambient, which was caused by the creation of CIGS surface defects by the ambient exposure.

  18. Biological investigations of the Sandia National Laboratories Sol se Mete Aerial Cable Facility

    SciTech Connect (OSTI)

    Sullivan, R.M.

    1994-10-01

    This report provides results of a comprehensive biological field survey performed on the Sandia National Laboratories Aerial Cable Facility, at the east end of Kirtland Air Force Base (KAFB), Bernalillo County, New Mexico. This survey was conducted late September through October, 1991. ACF occupies a 440-acre tract of land withdrawn by the US Forest Service (USFS) for use by KAFB, and in turn placed under operational control of SNL by the Department of Energy (DOE). All land used by SNL for ACF is part of a 15,851-acre tract of land withdrawn by the US Forest Service. In addition, a number of different organizations use the 15,851-acre area. The project area used by SNL encompasses portions of approximately six sections (3,840 acres) of US Forest Service land located within the foothills of the west side of the Manzano Mountains (East Mesa). The biological study area is used by the KAFB, the US Department of Interior, and SNL. This area includes: (1) Sol se Mete Springs and Canyon, (2) East Anchor Access Road, (3) East Anchor Site, (4) Rocket Sled Track, (5) North Arena, (6) East Instrumentation Site and Access Road, (7) West Anchor Access Road, (8) West Anchor Site, (9) South Arena, (10) Winch Sites, (11) West Instrumentation Sites, (12) Explosive Assembly Building, (13) Control Building, (14) Lurance Canyon Road and vicinity. Although portions of approximately 960 acres of withdrawn US Forest Service land have been altered, only 700 acres have been disturbed by activities associated with ACF; approximately 2,880 acres consist of natural habitat. Absence of grazing by livestock and possibly native ungulates, and relative lack of human disturbance have allowed this area to remain in a more natural vegetative state relative to the condition of private range lands throughout New Mexico. This report evaluates threatened and endangered species found on ACF, as well as a comprehensive assessment of biological habitats.

  19. High field magnetotransport and point contact Andreev reflection measurements on CuCr{sub 2}Se{sub 4} and CuCr{sub 2}Se{sub 3}BrDegenerate magnetic semiconductor single crystals

    SciTech Connect (OSTI)

    Borisov, K. Coey, J. M. D.; Stamenov, P.; Alaria, J.

    2014-05-07

    Single crystals of the metallically degenerate fully magnetic semiconductors CuCr{sub 2}Se{sub 4} and CuCr{sub 2}Se{sub 3}Br have been prepared by the Chemical Vapour Transport method, using either Se or Br as transport agents. The high-quality, millimetre-sized, octahedrally faceted, needle- and platelet-shaped crystals are characterised by means of high field magnetotransport (?{sub 0}H? 14?T) and Point Contact Andreev Reflection. The relatively high spin polarisation observed |P|>0.56, together with the relatively low minority carrier effective mass of 0.25 m{sub e}, and long scattering time 10{sup ?13}?s, could poise these materials for integration in low- and close-to-room temperature minority injection bipolar heterojunction transistor demonstrations.

  20. Superconductivity in strong spin orbital coupling compound Sb2Se3

    SciTech Connect (OSTI)

    Kong, P. P.; Sun, F.; Xing, L. Y.; Zhu, J.; Zhang, S. J.; Li, W. M.; Liu, Q. Q.; Wang, X. C.; Feng, S. M.; Yu, X. H.; Zhu, J. L.; Yu, R. C.; Yang, W. G.; Shen, G. Y.; Zhao, Y. S.; Ahuja, R.; Mao, H. K.; Jin, C. Q.

    2014-10-20

    Recently, A2B3 type strong spin orbital coupling compounds such as Bi2Te3, Bi2Se3 and Sb2Te3 were theoretically predicated to be topological insulators and demonstrated through experimental efforts. The counterpart compound Sb2Se3 on the other hand was found to be topological trivial, but theoretical studies indicated that the pressure might induce Sb2Se3 into a topological nontrivial state. We report on the discovery of superconductivity in Sb2Se3 single crystal induced via pressure. Our experiments indicated that Sb2Se3 became superconductive at high pressures above 10 GPa proceeded by a pressure induced insulator to metal like transition at ~3 GPa which should be related to the topological quantum transition. The superconducting transition temperature (TC) increased to around 8.0 K with pressure up to 40 GPa while it keeps ambient structure. As a result, high pressure Raman revealed that new modes appeared around 10 GPa and 20 GPa, respectively, which correspond to occurrence of superconductivity and to the change of TC slop as the function of high pressure in conjunction with the evolutions of structural parameters at high pressures.

  1. Sustained phase separation and spin glass in Co-doped KxFe2-ySe2 single crystals

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Ryu, Hyejin; Wang, Kefeng; Opacic, M.; Lazarevic, N.; Warren, J. B.; Popovic, Z. V.; Bozin, Emil S.; Petrovic, C.

    2015-11-19

    We describe Co substitution effects in KxFe2-y-zCozSe2 (0.06 ≤ z ≤ 1.73) single crystal alloys. By 3.5% of Co doping superconductivity is suppressed whereas phase separation of semiconducting K2Fe4Se5 and superconducting/metallic KxFe2Se2 is still present. We show that the arrangement and distribution of superconducting phase (stripe phase) is connected with the arrangement of K, Fe and Co atoms. Semiconducting spin glass is found in proximity to superconducting state, persisting for large Co concentrations. At high Co concentrations ferromagnetic metallic state emerges above the spin glass. This is coincident with changes of the unit cell, arrangement and connectivity of stripemore » conducting phase.« less

  2. Quasiparticle interference, quasiparticle interactions, and the origin of the charge density wave in 2H-NbSe?

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Arguello, C. J.; Valla, T.; Rosenthal, E. P.; Andrade, E. F.; Jin, W.; Yeh, P. C.; Zaki, N.; Jia, S.; Cava, R. J.; Fernandes, R. M.; et al

    2015-01-20

    We show that a small number of intentionally introduced defects can be used as a spectroscopic tool to amplify quasiparticle interference in 2H-NbSe?, that we measure by scanning tunneling spectroscopic imaging. We show from the momentum and energy dependence of the quasiparticle interference that Fermi surface nesting is inconsequential to charge density wave formation in 2H-NbSe?. We demonstrate that by combining quasiparticle interference data with additional knowledge of the quasiparticle band structure from angle resolved photoemission measurements, one can extract the wavevector and energy dependence of the important electronic scattering processes thereby obtaining direct information both about the fermiology andmorethe interactions. In 2H-NbSe?, we use this combination to show that the important near-Fermi-surface electronic physics is dominated by the coupling of the quasiparticles to soft mode phonons at a wave vector different from the CDW ordering wave vector.less

  3. Sustained phase separation and spin glass in Co-doped KxFe2?ySe2 single crystals

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Ryu, Hyejin; Wang, Kefeng; Opacic, M.; Lazarevic, N.; Warren, J. B.; Popovic, Z. V.; Bozin, Emil S.; Petrovic, C.

    2015-11-19

    We describe Co substitution effects in KxFe2-y-zCozSe2 (0.06 ? z ? 1.73) single crystal alloys. By 3.5% of Co doping superconductivity is suppressed whereas phase separation of semiconducting K2Fe4Se5 and superconducting/metallic KxFe2Se2 is still present. We show that the arrangement and distribution of superconducting phase (stripe phase) is connected with the arrangement of K, Fe and Co atoms. Semiconducting spin glass is found in proximity to superconducting state, persisting for large Co concentrations. At high Co concentrations ferromagnetic metallic state emerges above the spin glass. This is coincident with changes of the unit cell, arrangement and connectivity of stripemoreconducting phase.less

  4. Van der Waals epitaxial growth of two-dimensional single-crystalline GaSe domains on graphene

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Li, Xufan; Basile, Leonardo; Huang, Bing; Ma, Cheng; Lee, Jaekwang; Vlassiouk, Ivan V.; Puretzky, Alexander A.; Lin, Ming -Wei; Chi, Miaofang; Idrobo Tapia, Juan Carlos; et al

    2015-07-22

    Two-dimensional (2D) van der Waals (vdW) heterostructures are a family of artificially-structured materials that promise tunable optoelectronic properties for devices with enhanced functionalities. Compared to stamping, direct epitaxy of vdW heterostructures is ideal for clean interlayer interfaces and scalable device fabrication. Here, we explore the synthesis and preferred orientations of 2D GaSe atomic layers on graphene (Gr) by vdW epitaxy. Guided by the wrinkles on graphene, GaSe nuclei form that share a predominant lattice orientation. Due to vdW epitaxial growth many nuclei grow as perfectly aligned crystals and coalesce to form large (tens of microns), single-crystal flakes. Through theoretical investigationsmore » of interlayer energetics, and measurements of preferred orientations by atomic-resolution STEM and electron diffraction, a 10.9 interlayer rotation of the GaSe lattice with respect to the underlying graphene is found to be the most energetically preferred vdW heterostructure with the largest binding energy and the longest-range ordering. These GaSe/Gr vdW heterostructures exhibit an enhanced Raman E21g band of monolayer GaSe along with highly-quenched photoluminescence due to strong charge transfer. Despite the very large lattice mismatch of GaSe/Gr through vdW epitaxy, the predominant orientation control and convergent formation of large single-crystal flakes demonstrated here is promising for the scalable synthesis of large-area vdW heterostructures for the development of new optical and optoelectronic devices.« less

  5. Van der Waals epitaxial growth of two-dimensional single-crystalline GaSe domains on graphene

    SciTech Connect (OSTI)

    Li, Xufan; Basile, Leonardo; Huang, Bing; Ma, Cheng; Lee, Jaekwang; Vlassiouk, Ivan V.; Puretzky, Alexander A.; Lin, Ming -Wei; Chi, Miaofang; Idrobo Tapia, Juan Carlos; Rouleau, Christopher M.; Sumpter, Bobby G.; Yoon, Mina; Geohegan, David B.; Xiao, Kai

    2015-07-22

    Two-dimensional (2D) van der Waals (vdW) heterostructures are a family of artificially-structured materials that promise tunable optoelectronic properties for devices with enhanced functionalities. Compared to stamping, direct epitaxy of vdW heterostructures is ideal for clean interlayer interfaces and scalable device fabrication. Here, we explore the synthesis and preferred orientations of 2D GaSe atomic layers on graphene (Gr) by vdW epitaxy. Guided by the wrinkles on graphene, GaSe nuclei form that share a predominant lattice orientation. Due to vdW epitaxial growth many nuclei grow as perfectly aligned crystals and coalesce to form large (tens of microns), single-crystal flakes. Through theoretical investigations of interlayer energetics, and measurements of preferred orientations by atomic-resolution STEM and electron diffraction, a 10.9 interlayer rotation of the GaSe lattice with respect to the underlying graphene is found to be the most energetically preferred vdW heterostructure with the largest binding energy and the longest-range ordering. These GaSe/Gr vdW heterostructures exhibit an enhanced Raman E21g band of monolayer GaSe along with highly-quenched photoluminescence due to strong charge transfer. Despite the very large lattice mismatch of GaSe/Gr through vdW epitaxy, the predominant orientation control and convergent formation of large single-crystal flakes demonstrated here is promising for the scalable synthesis of large-area vdW heterostructures for the development of new optical and optoelectronic devices.

  6. Van der Waals Epitaxial Growth of Single-Crystal Two-Dimensional GaSe on Graphene

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Li, Xufan; Basile, Leonardo; Huang, Bing; Ma, Cheng; Lee, Jaekwang; Vlassiouk, Ivan V.; Puretzky, Alexander A.; Lin, Ming-Wei; Chi, Miaofang; Idrobo Tapia, Juan Carlos; et al

    2015-07-22

    Two-dimensional (2D) van der Waals (vdW) heterostructures are a family of artificially-structured materials that promise tunable optoelectronic properties for devices with enhanced functionalities. Compared to stamping, direct epitaxy of vdW heterostructures is ideal for clean interlayer interfaces and scalable device fabrication. Here, we explore the synthesis and preferred orientations of 2D GaSe atomic layers on graphene (Gr) by vdW epitaxy. Guided by the wrinkles on graphene, GaSe nuclei form that share a predominant lattice orientation. Due to vdW epitaxial growth many nuclei grow as perfectly aligned crystals and coalesce to form large (tens of microns), single-crystal flakes. Through theoretical investigationsmoreof interlayer energetics, and measurements of preferred orientations by atomic-resolution STEM and electron diffraction, a 10.9 interlayer rotation of the GaSe lattice with respect to the underlying graphene is found to be the most energetically preferred vdW heterostructure with the largest binding energy and the longest-range ordering. These GaSe/Gr vdW heterostructures exhibit an enhanced Raman E21g band of monolayer GaSe along with highly-quenched photoluminescence due to strong charge transfer. Despite the very large lattice mismatch of GaSe/Gr through vdW epitaxy, the predominant orientation control and convergent formation of large single-crystal flakes demonstrated here is promising for the scalable synthesis of large-area vdW heterostructures for the development of new optical and optoelectronic devices.less

  7. Enhancement of surface phonon modes in the Raman spectrum of ZnSe nanoparticles on adsorption of 4-mercaptopyridine

    SciTech Connect (OSTI)

    Islam, Syed K.; Lombardi, John R.

    2014-02-21

    By chemically etching a thin film of crystalline ZnSe with acid, we observe a strong Raman enhancement of the surface phonon modes of ZnSe on adsorption of a molecule (4-mercaptopyridine). The surface is composed of oblate hemi-ellipsoids, which has a large surface-to-bulk ratio. The assignment of the observed modes (at 248 and 492 cm{sup ?1}) to a fundamental and first overtone of the surface optical mode is consistent with observations from high-resolution electron energy loss spectroscopy as well as calculations.

  8. Polarization-Driven Stark Shifts in Quantum Dot Luminescence from Single CdSe/oligo-PPV Nanoparticles

    SciTech Connect (OSTI)

    Early, K. T.; Sudeep, P. K.; Emrick, Todd; Barnes, M. D.

    2010-05-12

    We demonstrate polarization-induced spectral shifts and associated linearly polarized absorption and emission in single CdSe/oligo-(phenylene vinylene) (CdSe/OPV) nanoparticles. A mechanism for these observations is presented in which charge separation from photoexcited ligands results in a significant Stark distortion of the quantum dot electron/hole wavefunctions. This distortion results in an induced linear polarization and an associated red shift in band-edge photoluminescence. These studies suggest the use of single quantum dots as local charge mobility probes.

  9. Role of double Ti O 2 layers at the interface of FeSe/ SrTi O 3

    Office of Scientific and Technical Information (OSTI)

    superconductors (Journal Article) | SciTech Connect SciTech Connect Search Results Journal Article: Role of double Ti O 2 layers at the interface of FeSe/ SrTi O 3 superconductors Citation Details In-Document Search This content will become publicly available on May 16, 2017 Title: Role of double Ti O 2 layers at the interface of FeSe/ SrTi O 3 superconductors Authors: Zou, Ke ; Mandal, Subhasish ; Albright, Stephen D. ; Peng, Rui ; Pu, Yujia ; Kumah, Divine ; Lau, Claudia ; Simon, Georg H.

  10. Electro-optical and dielectric properties of CdSe quantum dots and 6CHBT liquid crystals composites

    SciTech Connect (OSTI)

    Singh, U. B.; Pandey, M. B.; Dhar, R; Pandey, A. S.; Kumar, S.; Dabrowski, R.

    2014-11-15

    We have prepared the composites of a room temperature nematic liquid crystal namely 4-(trans-4-n-hexylcyclohexyl) isothiocyanatobenzoate (6CHBT) and Cadmium Selenide Quantum Dots (CdSe-QDs) and investigated their electro-optical and dielectric properties. Effect of dispersion of CdSe-QDs on various electro-optical and display parameters of host liquid crystalline material have been studied. Physical parameters, such as switching threshold voltage and splay elastic constant have been altered drastically for composites. Dispersion of QDs in a liquid crystals medium destabilizes nematic ordering of the host and decreases the nematic-to-isotropic transition temperature.

  11. Role of double Ti O 2 layers at the interface of FeSe/ SrTi O 3

    Office of Scientific and Technical Information (OSTI)

    superconductors (Journal Article) | DOE PAGES Publisher's Accepted Manuscript: Role of double Ti O 2 layers at the interface of FeSe/ SrTi O 3 superconductors This content will become publicly available on May 16, 2017 « Prev Next » Title: Role of double Ti O 2 layers at the interface of FeSe/ SrTi O 3 superconductors Authors: Zou, Ke ; Mandal, Subhasish ; Albright, Stephen D. ; Peng, Rui ; Pu, Yujia ; Kumah, Divine ; Lau, Claudia ; Simon, Georg H. ; Dagdeviren, Omur E. ; He, Xi ;

  12. Reduced Cu(InGa)Se2 Thickness in Solar Cells Using a Superstrate Configuration

    SciTech Connect (OSTI)

    Shafarman, William N.

    2015-03-30

    This project by the Institute of Energy Conversion (IEC) and the Department of Electrical and Computer Engineering at the University of Delaware sought to develop the technology and underlying science to enable reduced cost of Cu(InGa)Se2 manufacturing by reducing the thickness of the Cu(InGa)Se2 absorber layer by half compared to typical production. The approach to achieve this was to use the superstrate cell configuration in which light is incident on the cell through the glass. This structure facilitates optical enhancement approaches needed to achieve high efficiency with Cu(InGa)Se2 thicknesses less than 1 µm. The primary objective was to demonstrate a Cu(InGa)Se2 cell with absorber thickness 0.5 - 0.7 µm and 17% efficiency, along with a quantitative loss analysis to define a pathway to 20% efficiency. Additional objectives were the development of stable TCO and buffer layers or contact layers to withstand the Cu(InGa)Se2 deposition temperature and of advanced optical enhancement methods. The underlying fundamental science needed to effectively transition these outcomes to large scale was addressed by extensive materials and device characterization and by development of comprehensive optical models. Two different superstrate configurations have been investigated. A frontwall cell is illuminated through the glass to the primary front junction of the device. This configuration has been used for previous efforts on superstrate Cu(InGa)Se2 but performance has been limited by interdiffusion or reaction with CdS or other buffer layers. In this project, several approaches to overcome these limitations were explored using CdS, ZnO and ZnSe buffer layers. In each case, mechanisms that limit device performance were identified using detailed characterization of the materials and junctions. Due to the junction formation difficulties, efforts were concentrated on a new backwall configuration in which light is incident through the substrate into the back of the absorber layer. The primary junction is then formed after Cu(InGa)Se2 deposition. This allows the potential benefits of superstrate cells for optical enhancement while maintaining processing advantages of the substrate configuration and avoiding the harmful effects of high temperature deposition on p-n junction formation. Backwall devices have outperformed substrate cells at absorber thicknesses of 0.1-0.5 µm through enhanced JSC due to easy incorporation of a Ag reflector and, with light incident on the absorber, the elimination of parasitic absorption in the CdS buffer. An efficiency of 9.7% has been achieved for a backwall Cu(InGa)Se2 device with absorber thickness ~0.4 μm. A critical achievement that enabled implementation of the backwall cell was the development of a transparent back contact using MoO3 or WO3. Processes for controlled deposition of each material by reactive rf sputtering from metal targets were developed. These contacts have wide bandgaps making them well-suited for application as contacts for backwall devices as well as potential use in bifacial cells and as the top cell of tandem CuInSe2-based devices. Optical enhancement will be critical for further improvements. Wet chemical texturing of ZnO films has been developed for a simple, low cost light-trapping scheme for backwall superstrate devices to enhance long wavelength quantum efficiency. An aqueous oxalic acid etch was developed and found to strongly texture sputtered ZnO with high haze ≈ 0.9 observed across the whole spectrum. And finally, advanced optical models have been developed to assist the characterization and optimization of Cu(InGa)Se2 cells with thin absorbers

  13. Photoluminescence Enhancement in CdSe/ZnSDNA linkedAu Nanoparticle Heterodimers Probed by Single Molecule Spectroscopy

    SciTech Connect (OSTI)

    Cotlet, M.; Maye, M.M.; Gang, O.

    2010-07-26

    Photoluminescence enhancement of up to 20 fold is demonstrated at the single molecule level for heterodimers composed of a core/shell CdSe/ZnS semiconductive quantum dot and a gold nanoparticle of 60 nm size separated by a 32 nm-long dsDNA linker when employing optical excitation at wavelengths near the surface plasmon resonance of the gold nanoparticle.

  14. Benefits of Carrier Pocket Anisotropy to Thermoelectric Performance: The case of p-type AgBiSe2

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Parker, David S; May, Andrew F; Singh, David J

    2015-01-01

    We study theoretically the effects of anisotropy on the thermoelectric performance of p-type AgBiSe2. We present an apparent realization of the thermoelectric benefits of one-dimensional plate-like carrier pocket anisotropy in the valence band of this material. Based on first principles calculations we find a substantial anisotropy in the electronic structure, likely favorable for thermoelectric performance, in the valence bands of the hexagonal phase of the silver chalcogenide thermoelectric AgBiSe2, while the conduction bands are more isotropic, and in our experiments do not attain high performance. AgBiSe2 has already exhibited a ZT value of 1.5 in a high-temperature disordered fcc phase,more » but room-temperature performance has not been demonstrated. We develop a theory for the ability of anisotropy to decouple the density-of-states and conductivity effective masses, pointing out the influence of this effect in the high performance thermoelectrics Bi2Te3 and PbTe. From our first principles and Boltzmann transport calculations we find that p-type AgBiSe2 has substantial promise as a room temperature thermoelectric, and estimate its performance.« less

  15. Benefits of Carrier Pocket Anisotropy to Thermoelectric Performance: The case of p-type AgBiSe2

    SciTech Connect (OSTI)

    Parker, David S; May, Andrew F; Singh, David J

    2015-01-01

    We study theoretically the effects of anisotropy on the thermoelectric performance of p-type AgBiSe2. We present an apparent realization of the thermoelectric benefits of one-dimensional plate-like carrier pocket anisotropy in the valence band of this material. Based on first principles calculations we find a substantial anisotropy in the electronic structure, likely favorable for thermoelectric performance, in the valence bands of the hexagonal phase of the silver chalcogenide thermoelectric AgBiSe2, while the conduction bands are more isotropic, and in our experiments do not attain high performance. AgBiSe2 has already exhibited a ZT value of 1.5 in a high-temperature disordered fcc phase, but room-temperature performance has not been demonstrated. We develop a theory for the ability of anisotropy to decouple the density-of-states and conductivity effective masses, pointing out the influence of this effect in the high performance thermoelectrics Bi2Te3 and PbTe. From our first principles and Boltzmann transport calculations we find that p-type AgBiSe2 has substantial promise as a room temperature thermoelectric, and estimate its performance.

  16. Comparative Study of the Defect Point Physics and Luminescence of the Kesterites Cu2ZnSnS4 and Cu2ZnSnSe4 and Chalcopyrite Cu(In,Ga)Se2: Preprint

    SciTech Connect (OSTI)

    Romero, M. J.; Repins, I.; Teeter, G.; Contreras, M.; Al-Jassim, M.; Noufi, R.

    2012-08-01

    In this contribution, we present a comparative study of the luminescence of the kesterites Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) and their related chalcopyrite Cu(In,Ga)Se2 (CIGSe). Luminescence spectroscopy suggests that the electronic properties of Zn-rich, Cu-poor kesterites (both CZTS and CZTSe) and Cu-poor CIGSe are dictated by fluctuations of the electrostatic and chemical potentials. The large redshift in the luminescence of grain boundaries in CIGSe, associated with the formation of a neutral barrier is clearly observed in CZTSe, and, to some extent, in CZTS. Kesterites can therefore replicate the fundamental electronic properties of CIGSe.

  17. Seeded Growth of Highly Luminescent CdSe/CdS Nano-Heterostructures with Rod and Tetrapod Morphologies

    SciTech Connect (OSTI)

    Talapin, Dmitri; Talapin, Dmitri V.; Nelson, James H.; Shevchenko, Elena V.; Aloni, Shaul; Sadtler, Bryce; Alivisatos, A. Paul

    2007-08-09

    We have demonstrated that seeded growth of nanocrystals offers a convenient way to design nanoheterostructures with complex shapes and morphologies by changing the crystalline structure of the seed. By using Use nanocrystals with wurtzite and zinc blende structure as seeds for growth of US nanorods, we synthesized CdSe/CdS heterostructure nanorods and nanotetrapods, respectively. Both of these structures showed excellent luminescentproperties, combining high photoluminescence efficiency (similar to 80 and similar to 50percent for nanorods and nanotetrapods, correspondingly), giant extinction coefficients (similar to 2 x 10(7) and similar to 1.5 x 10(8) M-1 cm (-1) at 350 nm for nanorods and nanotetrapods, correspondingly), and efficient energy transfer from the US arms into the emitting CdSe Core.

  18. Magneto-optical characterizations of FeTe???Se??? thin films with critical current density over 1 MA/cm

    SciTech Connect (OSTI)

    Sun, Yue; Li, Qiang; Tsuchiya, Yuji; Pyon, Sunseng; Tamegai, Tsuyoshi; Zhang, Cheng; Ozaki, Toshinori

    2015-01-01

    We performed magneto-optical (MO) measurements on FeTe???Se??? thin films grown on LaAlO? (LAO) and Yttria-stabilized zirconia (YSZ) single-crystalline substrates. These thin films show superconducting transition temperature Tc ~19 K, 4 K higher than the bulk sample. Typical roof-top patterns can be observed in the MO images of thin films grown on LAO and YSZ, from which a large and homogeneous critical current density Jc ~ 3 - 4 x 10? A/cm at 5 K was obtained. Magnetic flux penetration measurement reveals that the current is almost isotropically distributed in the two thin films. Compared with bulk crystals, FeTe???Se??? thin film demonstrates not only higher Tc, but also much larger Jc, which is attractive for applications.

  19. Properties of the 0{sub 2}{sup +} state and isospin excitation in the N=Z nucleus {sup 68}Se

    SciTech Connect (OSTI)

    Al-Khudair, Falih H.; Li, Y. S.; Long, G. L. [Key Laboratory for Quantum Information and Measurements and Department of Physics, Tsinghua University, Beijing 100084 (China); Center of Nuclear Theory, Lanzhou National Laboratory of Accelerators, Lanzhou 730000 (China)

    2007-05-15

    Band structure and electromagnetic transition properties of the low-lying states in the N=Z {sup 68}Se nucleus were studied within the framework of interacting boson model 3. The isospin excitation states with T>T{sub Z} are identified. The M1 and E2 matrix elements for low-lying states have been investigated and were used to identify the low-lying mixed symmetry states. Special attention is given to the occurrence of 0{sub 2}{sup +} state, recently predicted by the projected shell-model (PSM) calculation. The present predicted spectrum for {sup 68}Se is close to the recent PSM results and confirms the results for the 0{sub 2}{sup +} state. The calculated results are compared with available experimental data, and they are in general good agreement.

  20. All-metallic electrically gated 2H-TaSe{sub 2} thin-film switches and logic circuits

    SciTech Connect (OSTI)

    Renteria, J.; Jiang, C.; Yan, Z.; Samnakay, R.; Goli, P.; Pope, T. R.; Salguero, T. T.; Wickramaratne, D.; Lake, R. K.; Khitun, A. G.; Balandin, A. A.

    2014-01-21

    We report the fabrication and performance of all-metallic three-terminal devices with tantalum diselenide thin-film conducting channels. For this proof-of-concept demonstration, the layers of 2H-TaSe{sub 2} were exfoliated mechanically from single crystals grown by the chemical vapor transport method. Devices with nanometer-scale thicknesses exhibit strongly non-linear current-voltage characteristics, unusual optical response, and electrical gating at room temperature. We have found that the drain-source current in thin-film 2H-TaSe{sub 2}Ti/Au devices reproducibly shows an abrupt transition from a highly resistive to a conductive state, with the threshold tunable via the gate voltage. Such current-voltage characteristics can be used, in principle, for implementing radiation-hard all-metallic logic circuits. These results may open new application space for thin films of van der Waals materials.

  1. JacketSE: An Offshore Wind Turbine Jacket Sizing Tool: Theory Manual and Sample Usage with Preliminary Validation

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    JacketSE: An Offshore Wind Turbine Jacket Sizing Tool Theory Manual and Sample Usage with Preliminary Validation Rick Damiani National Renewable Energy Laboratory Technical Report NREL/TP-5000-65417 February 2016 NREL is a national laboratory of the U.S. Department of Energy Office of Energy Efficiency & Renewable Energy Operated by the Alliance for Sustainable Energy, LLC This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

  2. Direct imaging of enhanced current collection on grain boundaries of Cu(In,Ga)Se{sub 2} solar cells

    SciTech Connect (OSTI)

    Kim, JunHo; Kim, SeongYeon; Jiang, Chun-Sheng; Ramanathan, Kannan; Al-Jassim, Mowafak M.

    2014-02-10

    We report on direct imaging of current collection by performing conductive atomic force microscopy (C-AFM) measurement on a complete Cu(In,Ga)Se{sub 2} solar cell. The localized current was imaged by milling away the top conductive layer of the device by repeated C-AFM scans. The result exhibits enhanced photocurrent collection on grain boundaries (GBs) of CIGS films, consistent with the argument for electric-field-assisted carrier collection on the GBs.

  3. Structural and optical properties of (Ag,Cu)(In,Ga)Se{sub 2} polycrystalline thin film alloys

    SciTech Connect (OSTI)

    Boyle, J. H.; Shafarman, W. N.; Birkmire, R. W.; McCandless, B. E.

    2014-06-14

    The structural and optical properties of pentenary alloy (Ag,Cu)(In,Ga)Se{sub 2} polycrystalline thin films were characterized over the entire compositional range at a fixed (Cu + Ag)/(In + Ga) ratio. Films deposited at 550 °C on bare and molybdenum coated soda-lime glass by elemental co-evaporation in a single-stage process with constant incident fluxes exhibit single phase chalcopyrite structure, corresponding to 122 spacegroup (I-42d) over the entire compositional space. Unit cell refinement of the diffraction patterns show that increasing Ag substitution for Cu, the refined a{sub o} lattice constant, (Ag,Cu)-Se bond length, and anion displacement increase in accordance with the theoretical model proposed by Jaffe, Wei, and Zunger. However, the refined c{sub o} lattice constant and (In,Ga)-Se bond length deviated from theoretical expectations for films with mid-range Ag and Ga compositions and are attributed to influences from crystallographic bond chain ordering or cation electronegativity. The optical band gap, derived from transmission and reflection measurements, widened with increasing Ag and Ga content, due to influences from anion displacement and cation electronegativity, as expected from theoretical considerations for pseudo-binary chalcopyrite compounds.

  4. Tunable inverse topological heterostructure utilizing (Bi1−xInx)2Se3 and multichannel weak-antilocalization effect

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Brahlek, Matthew J.; Koirala, Nikesh; Liu, Jianpeng; Yusufaly, Tahir I.; Salehi, Maryam; Han, Myung-Geun; Zhu, Yimei; Vanderbilt, David; Oh, Seongshik

    2016-03-10

    In typical topological insulator (TI) systems the TI is bordered by a non-TI insulator, and the surrounding conventional insulators, including vacuum, are not generally treated as part of the TI system. Here, we implement a material system where the roles are reversed, and the topological surface states form around the non-TI (instead of the TI) layers. This is realized by growing a layer of the tunable non-TI (Bi1-xInx)2Se3 in between two layers of the TI Bi2Se3 using the atomically precise molecular beam epitaxy technique. On this tunable inverse topological platform, we systematically vary the thickness and the composition of themore » (Bi1-xInx)2Se3 layer and show that this tunes the coupling between the TI layers from strongly coupled metallic to weakly coupled, and finally to a fully decoupled insulating regime. This system can be used to probe the fundamental nature of coupling in TI materials and provides a tunable insulating layer for TI devices.« less

  5. Acoustic phonon dynamics in thin-films of the topological insulator Bi{sub 2}Se{sub 3}

    SciTech Connect (OSTI)

    Glinka, Yuri D.; Babakiray, Sercan; Johnson, Trent A.; Holcomb, Mikel B.; Lederman, David

    2015-04-28

    Transient reflectivity traces measured for nanometer-sized films (6–40 nm) of the topological insulator Bi{sub 2}Se{sub 3} revealed GHz-range oscillations driven within the relaxation of hot carriers photoexcited with ultrashort (∼100 fs) laser pulses of 1.51 eV photon energy. These oscillations have been suggested to result from acoustic phonon dynamics, including coherent longitudinal acoustic phonons in the form of standing acoustic waves. An increase of oscillation frequency from ∼35 to ∼70 GHz with decreasing film thickness from 40 to 15 nm was attributed to the interplay between two different regimes employing traveling-acoustic-waves for films thicker than 40 nm and the film bulk acoustic wave resonator (FBAWR) modes for films thinner than 40 nm. The amplitude of oscillations decays rapidly for films below 15 nm thick when the indirect intersurface coupling in Bi{sub 2}Se{sub 3} films switches the FBAWR regime to that of the Lamb wave excitation. The frequency range of coherent longitudinal acoustic phonons is in good agreement with elastic properties of Bi{sub 2}Se{sub 3}.

  6. Mo{sub 6}Se{sub 8}-cluster-based superconducting compounds Cs{sub 2}Mo{sub 12}Se{sub 14} and Rb{sub 4}Mo{sub 18}Se{sub 20}: Evidence for a strongly correlated and anisotropic electron system

    SciTech Connect (OSTI)

    Brusetti, R.; Laborde, O.; Sulpice, A.; Calemczuk, R.; Potel, M.; Gougeon, P.

    1995-08-01

    We studied the normal and superconducting states of the title compounds by measuring the conductivity and magnetization of single crystals and powder samples. From the upper and lower critical fields we deduced the characteristic lengths and thermodynamical fields. These results are borne out by our specific-heat measurements. We recognize in these compounds many features of the Chevrel-phase superconductors, including very small coherence lengths and strong-coupling-like effects. However, we show that the electron system is much more anisotropic and still less delocalized in these materials where the Mo{sub 6}Se{sub 8} clusters have condensed in Mo{sub 6{ital n}}Se{sub 6{ital n}+2} finite chains. This condensation is accompanied by an enhancement of the magnetic response whereas the lengthening of the chains leads to a counteracting reduction of the density of carriers. This indicates that superconductivity is built upon highly correlated molecular states. Reviewing the available data on the other Chevrel-cluster-based superconductors confirms this picture and suggests that the small coherence lengths reflect the local character of the electron pairing. This comparison also shows that forming finite chains of Mo{sub 6}Se{sub 8} clusters makes the electron correlations more repulsive and pushes the electron system near the borderline between superconductivity and magnetism. In this respect these compounds could provide valuable complementary information on issues which are at the center of the research upon high-{ital Y}{sub {ital c}} superconductivity.

  7. Quantifying electron-phonon coupling in CdTe{sub 1−x}Se{sub x} nanocrystals via coherent phonon manipulation

    SciTech Connect (OSTI)

    Spann, B. T.; Xu, X.

    2014-08-25

    We employ ultrafast transient absorption spectroscopy with temporal pulse shaping to manipulate coherent phonon excitation and quantify the strength of electron-phonon coupling in CdTe{sub 1−x}Se{sub x} nanocrystals (NCs). Raman active CdSe and CdTe longitudinal optical phonon (LO) modes are excited and probed in the time domain. By temporally controlling pump pulse pairs to coherently excite and cancel coherent phonons in the CdTe{sub 1−x}Se{sub x} NCs, we estimate the relative amount of optical energy that is coupled to the coherent CdSe LO mode.

  8. Photo-crystallization in a-Se layer structures: Effects of film-substrate interface-rigidity

    SciTech Connect (OSTI)

    Lindberg, G. P.; Gross, N.; Weinstein, B. A.; O'Loughlin, T.; Mishchenko, A.; Reznik, A.; Abbaszadeh, S.; Karim, K. S.; Belev, G.

    2014-11-21

    Amorphous selenium (a-Se) films deposited on rigid substrates can undergo photo-induced crystallization (PC) even at temperatures (T) well below the glass transition, T{sub g}???313?K. Substrate-generated shear strain is known to promote the PC process. In the present work, we explore the influence of different substrates (Si and glass), and different film-layer-substrate combinations, on the PC in a variety of a-Se films and film-structures. The intermediate layers (indium tin oxide and polyimide) are chosen to promote conductivity and/or to be a buffer against interface strain in structures of interest for digital imaging applications. The PC characteristics in these samples are evaluated and compared using optical microscopy, atomic-force microscopy, Raman mapping, and T-dependent Raman spectroscopy. Both the presence of a soft intermediate layer, and the thermal softening that occurs for T increasing through T{sub g}, inhibit the tendency for the onset of PC. The extensive PC mapping results in the wide range of samples studied here, as well as the suppression of PC near T{sub g} in this array of samples, strongly support the generality of this behavior. As a consequence, one may expect that the stability of a-Se films against PC can be enhanced by decreasing the rigidity of the film-substrate interface. In this regard, advanced film structures that employ flexible substrates, soft intermediate layers, and/or are designed to be operated near T{sub g} should be explored.

  9. Enhanced excitonic photoconductivity due to built-in internal electric field in TlGaSe{sub 2} layered semiconductor

    SciTech Connect (OSTI)

    Seyidov, MirHasan Yu. Suleymanov, Rauf A.; ?ale, Yasin; Balaban, Ertan

    2014-12-07

    The strong enhancement, by several orders of magnitude, of the excitonic peak within the photoconductivity spectrum of TlGaSe{sub 2} semiconductor was observed. The samples were polarized in external dc electric field, which was applied prior to the measurements. Due to the accumulation of charges near the surface, an internal electric field was formed. Electron-hole pairs that were created after the absorption of light are fallen in and then separated by the built-in electric field, which prevents radiative recombination process.

  10. Electronic structure, transport, and phonons of SrAgChF (Ch = S,Se,Te): Bulk superlattice thermoelectrics

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Gudelli, Vijay Kumar; Kanchana, V.; Vaitheeswaran, G.; Singh, David J.; Svane, Axel; Christensen, Niels Egede; Mahanti, Subhendra D.

    2015-07-15

    Here, we report calculations of the electronic structure, vibrational properties, and transport for the p-type semiconductors, SrAgChF (Ch = S, Se, and Te). We find soft phonons with low frequency optical branches intersecting the acoustic modes below 50 cm–1, indicative of a material with low thermal conductivity. The bands at and near the valence-band maxima are highly two-dimensional, which leads to high thermopowers even at high carrier concentrations, which is a combination that suggests good thermoelectric performance. These materials may be regarded as bulk realizations of superlattice thermoelectrics.

  11. Strain-Dependent Photoluminescence Behavior of CdSe/CdS Nanocrystals with Spherical, Linear, and Branched Topologies

    SciTech Connect (OSTI)

    Choi, Charina L.; Koski, Kristie J.; Sivasankar, Sanjeevi; Alivisatos, A. Paul

    2009-08-13

    The photoluminescence of CdSe/CdS core/shell quantum dots, nanorods, and tetrapods is investigated as a function of applied hydrostatic and non-hydrostatic pressure. The optoelectronic properties of all three nanocrystal morphologies are affected by strain. Furthermore, it is demonstrated that the unique morphology of a tetrapod is highly sensitive to non-isotropic stress environments. Seeded tetrapods can thereby serve as an optical strain gauge, capable of measuring forces on the order of nanonewtons. We anticipate that a nanocrystal strain gauge with optical readout will be useful for applications ranging from sensitive optomechanical devices to investigations of biomechanical processes.

  12. Properties of electrospun CdS and CdSe filled poly(methyl methacrylate) (PMMA) nanofibres

    SciTech Connect (OSTI)

    Mthethwa, T.P.; Moloto, M.J.; De Vries, A.; Matabola, K.P.

    2011-04-15

    Graphical abstract: SEM images of CdS/PMMA showing coiling as loading of CdS nanoparticles is increased. Thermal stability is increased with increase in %loading of both CdS and CdSe nanoparticles. Research highlights: {yields} TOPO-capped CdS and HDA-capped CdSe nanoparticles were synthesized and fully characterized. {yields} The nanoparticles were mixed with the polymer, PMMA using electrospinning technique using 2, 5 and 10% weight loadings. {yields} The mixture was spun to produce fibres with optical and thermal properties showing significant change and also the increase in loading causing bending or spiraling. {yields} Both TEM images for nanoparticles and SEM for fibres shows the morphology and sizes of the particles. -- Abstract: Electrospinning technique was used to fabricate poly(methyl methacrylate) (PMMA) fibres incorporating CdS and CdSe quantum dots (nanoparticles). Different nanoparticle loadings (2, 5 and 10 wt% with respect to PMMA) were used and the effect of the quantum dots on the properties of the fibres was studied. The optical properties of the hybrid composite fibres were investigated by photoluminescence and UV-vis spectrophotometry. Scanning electron microscopy (SEM), X-ray diffraction and FTIR spectrophotometry were also used to investigate the morphology and structure of the fibres. The optical studies showed that the size-tunable optical properties can be achieved in the polymer fibres by addition of quantum dots. SEM images showed that the morphologies of the fibres were dependent on the added amounts of quantum dots. A spiral type of morphology was observed with an increase in the concentration of CdS and CdSe nanoparticles. Less beaded structures and bigger diameter fibres were obtained at higher quantum dot concentrations. X-ray diffractometry detected the amorphous peaks of the polymer and even after the quantum dots were added and the FTIR analysis shows that there was no considerable interaction between the quantum dots and the polymer fibres at low concentration of quantum dots however at higher concentrations some interactions were observed which shows that QDs were present on the surfaces of the fibres.

  13. Electrically driven single photon emission from a CdSe/ZnSSe single quantum dot at 200?K

    SciTech Connect (OSTI)

    Quitsch, Wolf; Kmmell, Tilmar; Bacher, Gerd; Gust, Arne; Kruse, Carsten; Hommel, Detlef

    2014-09-01

    High temperature operation of an electrically driven single photon emitter based on a single epitaxial quantum dot is reported. CdSe/ZnSSe/MgS quantum dots are embedded into a p-i-n diode architecture providing almost background free excitonic and biexcitonic electroluminescence from individual quantum dots through apertures in the top contacts. Clear antibunching with g{sup 2}(??=?0)?=?0.28??0.20 can be tracked up to T?=?200?K, representing the highest temperature for electrically triggered single photon emission from a single quantum dot device.

  14. Elastic Scattering Of {sup 6,7}Li+{sup 80}Se At Near And Above Barrier Energies

    SciTech Connect (OSTI)

    Fimiani, L.; Marti, G. V.; Capurro, O. A.; Barbara, E. de; Testoni, J. E.; Zalazar, L.; Arazi, A.; Cardona, M. A.; Carnelli, P.; Figueira, J. M.; Hojman, D.; Martinez Heimann, D.; Negri, A. E.; Pacheco, A. J.; Fernandez Niello, J. O.

    2010-08-04

    In this work we propose to study the elastic scattering of the weakly bound projectiles {sup 6,7}Li on an intermediate mass target {sup 80}Se. From the experimental results presented here, precise angular distributions at energies below, around and above the nominal Coulomb barriers of the systems were obtained. The final goal of our work is to determine the characteristic parameters of the optical potential and use them to address the question of whether the usual threshold anomaly or the breakup threshold anomaly are present or not in these systems.

  15. Density functional theory calculations of the turbostratically disordered compound [(SnSe)1+y]m(VSe2)n

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Rudin, Sven P.; Johnson, David C.

    2015-04-30

    Among composite materials that layer constituent substances of nanoscale thicknesses, [(SnSe)1+y ]m(VSe2)n emerges as an example where the constituents retain incommensurate lattice structures. Perpendicular to the stacking direction, the system exhibits random translations and random rotations on average, i.e., turbostratic disorder, with local regions showing twelvefold diffraction patterns. Earlier theoretical work on these structures showed that combining density functional theory with an empirical treatment of the van der Waals interaction gave structural parameters in good agreement with experiment, but no attempt was made to examine the relative orientations. Here we approximate the extended system with one extended constituent and onemore » finite constituent, which allows the treatment of all relative orientations on equal footing. Furthermore, the calculations show how the twelvefold periodicity follows from how the ions of the SnSe layer lock in with favored positions relative to the VSe2 layer, and the associated energy scale supports arguments for the overall turbostratic disorder.« less

  16. Visible Light Photoreduction of CO{sub 2} Using CdSe/Pt/TiO{sub 2} Heterostructured Catalysts

    SciTech Connect (OSTI)

    Wang, Congjun; Thompson, Robert L.; Baltrus, John; Matranga, Christopher

    2010-08-01

    A series of CdSe quantum dot (QD)-sensitized TiO{sub 2} heterostructures have been synthesized, characterized, and tested for the photocatalytic reduction of CO{sub 2} in the presence of H{sub 2}O. Our results show that these heterostructured materials are capable of catalyzing the photoreduction of CO{sub 2} using visible light illumination (? > 420 nm) only. The effect of removing surfactant caps from the CdSe QDs by annealing and using a hydrazine chemical treatment have also been investigated. The photocatalytic reduction process is followed using infrared spectroscopy to probe the gas-phase reactants and gas chromatography to detect the products. Gas chromatographic analysis shows that the primary reaction product is CH{sub 4}, with CH{sub 3}OH, H{sub 2}, and CO observed as secondary products. Typical yields of the gas-phase products after visible light illumination (?>420 nm) were 48 ppm g{sup -1} h{sup -1} of CH{sub 4}, 3.3 ppm g{sup -1} h{sup -1} of CH{sub 3}OH (vapor), and trace amounts of CO and H{sub 2}.

  17. Magnetic anisotropy in ultrathin Fe films on GaAs, ZnSe, and Ge (001) substrates

    SciTech Connect (OSTI)

    Tivakornsasithorn, K.; Liu, X.; Li, X.; Dobrowolska, M.; Furdyna, J. K.

    2014-07-28

    We discuss magnetic anisotropy parameters of ferromagnetic body-centered cubic (bcc) Fe films grown by molecular beam epitaxy (MBE) on (001) substrates of face-centered cubic (fcc) GaAs, ZnSe, and Ge. High-quality MBE growth of these metal/semiconductor combinations is made possible by the fortuitous atomic relationship between the bcc Fe and the underlying fcc semiconductor surfaces, resulting in excellent lattice match. Magnetization measurements by superconducting quantum interference device (SQUID) indicate that the Fe films grown on (001) GaAs surfaces are characterized by a very strong uniaxial in-plane anisotropy; those grown on (001) Ge surfaces have a fully cubic anisotropy; and Fe films grown on ZnSe represent an intermediate case between the preceding two combinations. Ferromagnetic resonance measurements carried out on these three systems provide a strikingly clear quantitative picture of the anisotropy parameters, in excellent agreement with the SQUID results. Based on these results, we propose that the observed anisotropy of cubic Fe films grown in this way results from the surface reconstruction of the specific semiconductor substrate on which the Fe film is deposited. These results suggest that, by controlling surface reconstruction of the substrate during the MBE growth, one may be able to engineer the magnetic anisotropy in Fe, and possibly also in other MBE-grown ferromagnetic films.

  18. Midea: Order (2010-SE-0110, 2012-SE-1402, 2012-SE-1404, 2013-SE-1401)

    Broader source: Energy.gov [DOE]

    DOE ordered Midea America Corp., Hefei Hualing Co., Ltd., and China Refrigeration Industry Co., Ltd., to pay a $4,579,949 ($4,562,838 plus one percent interest) civil penalty after finding Midea had manufactured and distributed in commerce in the U.S. a large quantity of basic models HD-146F, HS-390C, UL-WD145-D, and UL-WD195-D of noncompliant refrigerator-freezers and freezers.

  19. PHaSe-EFRC

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    cell fabrication, interlayer adjustment of active layer to electrode work function control for better power conversion, environmentally transformational strategies for...

  20. Nuclear structure relevant to neutrinoless double {beta} decay : the valence protons in {sup 76}Ge and {sup 76}Se.

    SciTech Connect (OSTI)

    Kay, B. P.; Schiffer, J. P.; Freeman, S. J.; Adachi, T.; Clark, J. A.; Deibel, C. M.; Fujita, H.; Fujita, Y.; Grabmayr, P.; Hatanaka, K.; Ishikawa, D.; Matsubara, H.; Meada, Y.; Okamura, H.; Rehm, K. E.; Sakemi, T.; Shimizu, Y.; Shimoda, H.; Suda, K.; Tameshige, Y.; Tamii, A.; Wrede, C.; Univ. of Manchester; Osaka Univ.; Yale Univ.; Univ. of Tuebingen; Miyazaki Univ.; Tohoku Univ.; Univ. of Tokyo; Kyushu Univ.

    2009-01-01

    The possibility of observing neutrinoless double {beta} decay offers the opportunity of determining the effective neutrino mass if the nuclear matrix element were known. Theoretical calculations are uncertain, and the occupation of valence orbits by nucleons active in the decay is likely to be important. The occupation of valence proton orbits in the ground states of {sup 76}Ge, a candidate for such decay, and {sup 76}Se, the corresponding daughter nucleus, is determined by precisely measuring cross sections for proton-removing transfer reactions. As in previous work on neutron occupation, we find that the Fermi surface for protons is much more diffuse than previously thought, and the occupancies of at least three orbits change significantly between the two 0{sup +} ground states.

  1. Nuclear structure relevant to neutrinoless double {beta} decay: The valence protons in {sup 76}Ge and {sup 76}Se

    SciTech Connect (OSTI)

    Kay, B. P.; Schiffer, J. P.; Rehm, K. E. [Physics Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Freeman, S. J. [University of Manchester, Manchester M13 9PL (United Kingdom); Adachi, T.; Fujita, H.; Hatanaka, K.; Ishikawa, D.; Matsubara, H.; Okamura, H.; Suda, K.; Tameshige, Y.; Tamii, A. [Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047 (Japan); Clark, J. A.; Deibel, C. M.; Wrede, C. [Yale University, New Haven, Connecticut 06520 (United States); Fujita, Y. [Department of Physics, Osaka University, Toyonaka, Osaka 567-0043 (Japan); Grabmayr, P. [Physikalisches Institut, Universitaet Tuebingen, D-72076 Tuebingen (Germany); Meada, Y. [Department of Applied Physics, Miyazaki University, Miyazaki 889-2192 (Japan); Sakemi, Y. [Cyclotron Radioisotope Center, Tohoku University, Sendai, Miyagi 980-8578 (Japan)] (and others)

    2009-02-15

    The possibility of observing neutrinoless double {beta} decay offers the opportunity of determining the effective neutrino mass if the nuclear matrix element were known. Theoretical calculations are uncertain, and the occupation of valence orbits by nucleons active in the decay is likely to be important. The occupation of valence proton orbits in the ground states of {sup 76}Ge, a candidate for such decay, and {sup 76}Se, the corresponding daughter nucleus, is determined by precisely measuring cross sections for proton-removing transfer reactions. As in previous work on neutron occupation, we find that the Fermi surface for protons is much more diffuse than previously thought, and the occupancies of at least three orbits change significantly between the two 0{sup +} ground states.

  2. Insulating and metallic spin glass in Ni-doped KxFe2-ySe? single crystals

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Ryu, Hyejin; Abeykoon, Milinda; Wang, Kefeng; Lei, Hechang; Lazarevic, N.; Warren, J. B.; Bozin, E. S.; Popovic, Z. V.; Petrovic, C.

    2015-05-04

    We report electron doping effects by Ni in KxFe2-?-yNiySe? (0.06 ? y ? 1.44) single crystal alloys. A rich ground state phase diagram is observed. A small amount of Ni (~ 4%) suppressed superconductivity below 1.8 K, inducing insulating spin glass magnetic ground state for higher Ni content. With further Ni substitution, metallic resistivity is restored. For high Ni concentration in the lattice the unit cell symmetry is high symmetry I4/mmm with no phase separation whereas both I4/m + I4/mmm space groups were detected in the phase separated crystals when concentration of Ni morewith the absence of crystalline Fe vacancy order.less

  3. Temperature-dependent carrier–phonon coupling in topological insulator Bi{sub 2}Se{sub 3}

    SciTech Connect (OSTI)

    Lai, Yi-Ping; Liu, Jia-Ming; Chen, Hsueh-Ju; Wu, Kuang-Hsiung

    2014-12-08

    Temperature-dependent (11.0 K−294.5 K) carrier–phonon coupling in Bi{sub 2}Se{sub 3} is investigated by ultrafast pump−probe spectroscopy. The rise time of the differential reflectivity is interpreted by a combined effect of electron temperature relaxation and hot-phonon lifetime. The electron−phonon coupling constant of the bulk state (λ=0.63±0.05) is deduced from theoretical fitting. Increasing hot-phonon lifetime with decreasing temperature is attributed to a decreasing phonon−phonon collision rate. A complete analysis of the thermalization process is presented. Understanding carrier and phonon dynamics is essential for future optoelectronic and spintronic applications of topological insulators.

  4. CdS and CdS/CdSe sensitized ZnO nanorod array solar cells prepared by a solution ions exchange process

    SciTech Connect (OSTI)

    Chen, Ling; Gong, Haibo; Zheng, Xiaopeng; Zhu, Min; Zhang, Jun; Yang, Shikuan; Cao, Bingqiang

    2013-10-15

    Graphical abstract: - Highlights: CdS and CdS/CdSe quantum dots are assembled on ZnO nanorods by ion exchange process. The CdS/CdSe sensitization of ZnO effectively extends the absorption spectrum. The performance of ZnO/CdS/CdSe cell is improved by extending absorption spectrum. - Abstract: In this paper, cadmium sulfide (CdS) and cadmium sulfide/cadmium selenide (CdS/CdSe) quantum dots (QDs) are assembled onto ZnO nanorod arrays by a solution ion exchange process for QD-sensitized solar cell application. The morphology, composition and absorption properties of different photoanodes were characterized with scanning electron microscope, transmission electron microscope, energy-dispersive X-ray spectrum and Raman spectrum in detail. It is shown that conformal and uniform CdS and CdS/CdSe shells can grow on ZnO nanorod cores. Quantum dot sensitized solar cells based on ZnO/CdS and ZnO/CdS/CdSe nanocable arrays were assembled with gold counter electrode and polysulfide electrolyte solution. The CdS/CdSe sensitization of ZnO can effectively extend the absorption spectrum up to 650 nm, which has a remarkable impact on the performance of a photovoltaic device by extending the absorption spectrum. Preliminary results show one fourth improvement in solar cell efficiency.

  5. First-principles studies of the structural, electronic, and optical properties of a novel thorium compound Rb{sub 2}Th{sub 7}Se{sub 15}

    SciTech Connect (OSTI)

    Brik, M.G.

    2014-04-01

    The structural, electronic, and optical properties of a recently synthesized thorium compound Rb{sub 2}Th{sub 7}Se{sub 15} have been calculated in the density functional theory framework for the first time. The calculated direct band gap was 1.471 eV (generalized gradient approximation) and 1.171 eV (local density approximation), with both results being close to the experimental result of 1.83 eV. High covalency/iconicity of the Th–Se/Rb–Se bonds was demonstrated by calculating effective Mulliken charges of all ions. The polarized calculations of the complex dielectric function are presented; dependence of the calculated index of refraction was fitted to the Sellmeyer equation in the wavelength range from 500 to 2500 nm. - Graphical abstract: Calculated band structure of Rb{sub 2}Th{sub 7}Se{sub 15}. - Highlights: • The first theoretical analysis of the Rb{sub 2}Th{sub 7}Se{sub 15} properties is reported. • Structural, electronic and optical properties of Rb{sub 2}Th{sub 7}Se{sub 15} were calculated. • An indirect character of Rb{sub 2}Th{sub 7}Se{sub 15} band gap was confirmed. • Dependence of the refractive index on the wavelength was calculated.

  6. Characterization of few-layer 1T-MoSe{sub 2} and its superior performance in the visible-light induced hydrogen evolution reaction

    SciTech Connect (OSTI)

    Gupta, Uttam; Naidu, B. S.; Maitra, Urmimala; Rao, C. N. R.; Singh, Anjali; Shirodkar, Sharmila N.; Waghmare, Umesh V.

    2014-09-01

    Based on earlier results on the photocatalytic properties of MoS{sub 2}, the 1T form of MoSe{sub 2}, prepared by lithium intercalation and exfoliation of bulk MoSe{sub 2}, has been employed for the visible-light induced generation of hydrogen. 1T-MoSe{sub 2} is found to be superior to both 2H and 1T MoS{sub 2} as well as 2H-MoSe{sub 2} in producing hydrogen from water, the yield being in the 6075 mmol?h{sup ?1}?g{sup ?1} range with a turn over frequency of 1519 h{sup ?1}. First principles calculations reveal that 1T-MoSe{sub 2} has a lower work function than 2H-MoSe{sub 2} as well as 1T and 2H-MoS{sub 2}, making it easier to transfer an electron from 1T-MoSe{sub 2} for the production of H{sub 2}.

  7. Influence of defects on the charge density wave of ([SnSe]1+δ)1(VSe2)1 ferecrystals

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Falmbigl, Matthias; Putzky, Daniel; Ditto, Jeffrey; Esters, Marco; Bauers, Sage R.; Ronning, Filip; Johnson, David C.

    2015-07-14

    A series of ferecrystalline compounds ([SnSe]1+δ)1(VSe2)1 with varying Sn/V ratios were synthesized using the modulated elemental reactant technique. Temperature-dependent specific heat data reveal a phase transition at 102 K, where the heat capacity changes abruptly. An abrupt increase in electrical resistivity occurs at the same temperature, correlated with an abrupt increase in the Hall coefficient. Combined with the magnitude and nature of the specific heat discontinuity, this suggests that the transition is similar to the charge density wave transitions in transition metal dichalcogenides. An ordered intergrowth was formed over a surprisingly wide compositional range of Sn/V ratios of 0.89 ≤more » 1 + δ ≤ 1.37. X-ray diffraction and transmission electron microscopy reveal the formation of various volume defects in the compounds in response to the nonstoichiometry. The electrical resistivity and Hall coefficient data of samples with different Sn/V ratios show systematic variation in the carrier concentration with the Sn/V ratio. There is no significant change in the onset temperature of the charge density wave transition, only a variation in the carrier densities before and after the transition. Given the sensitivity of the charge density wave transitions of transition metal dichalcogenides to variations in composition, it is very surprising that the charge density wave transition observed at 102 K for ([SnSe]1.15)1(VSe2)1 is barely influenced by the nonstoichiometry and structural defects. As a result, this might be a consequence of the two-dimensional nature of the structurally independent VSe2 layers.« less

  8. Effect of argon gas flow rate on properties of film electrodes prepared by thermal vacuum evaporation from synthesized Cu{sub 2}SnSe{sub 3} source

    SciTech Connect (OSTI)

    Sabli, Nordin; Talib, Zainal Abidin; Yunus, Wan Mahmood Mat; Zainal, Zulkarnain; Hilal, Hikmat S.; Fujii, Masatoshi

    2014-03-05

    This work describes a new technique to enhance photoresponse of metal chalcogenide-based semiconductor film electrodes deposited by thermal vacuum evaporation under argon gas flow from synthesized Cu{sub 2}SnSe{sub 3} sources. SnSe formation with Cu-doped was obtained under higher argon gas flow rate (V{sub A} = 25 cm{sup 3}/min). Higher value of photoresponse was observed for films deposited under V{sub A} = 25 cm{sup 3}/min which was 9.1%. This finding indicates that Cu atoms inside the SnSe film were important to increase carrier concentrations that promote higher photoresponse.

  9. Bright three-band white light generated from CdSe/ZnSe quantum dot-assisted Sr{sub 3}SiO{sub 5}:Ce{sup 3+},Li{sup +}-based white light-emitting diode with high color rendering index

    SciTech Connect (OSTI)

    Jang, Ho Seong; Kwon, Byoung-Hwa; Jeon, Duk Young; Yang, Heesun

    2009-10-19

    In this study, bright three-band white light was generated from the CdSe/ZnSe quantum dot (QD)-assisted Sr{sub 3}SiO{sub 5}:Ce{sup 3+},Li{sup +}-based white light-emitting diode (WLED). The CdSe/ZnSe core/shell structure was confirmed by energy dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy. The CdSe/ZnSe QDs showed high quantum efficiency (79%) and contributed to the high luminous efficiency ({eta}{sub L}) of the fabricated WLED. The WLED showed bright natural white with excellent color rendering property ({eta}{sub L}=26.8 lm/W, color temperature=6140 K, and color rendering index=85) and high stability against the increase in forward bias currents from 20 to 70 mA.

  10. Atomic arrangement at ZnTe/CdSe interfaces determined by high resolution scanning transmission electron microscopy and atom probe tomography

    SciTech Connect (OSTI)

    Bonef, Bastien; Rouvire, Jean-Luc; Jouneau, Pierre-Henri; Bellet-Amalric, Edith; Grard, Lionel; Mariette, Henri; Andr, Rgis; Bougerol, Catherine; Grenier, Adeline

    2015-02-02

    High resolution scanning transmission electron microscopy and atom probe tomography experiments reveal the presence of an intermediate layer at the interface between two binary compounds with no common atom, namely, ZnTe and CdSe for samples grown by Molecular Beam Epitaxy under standard conditions. This thin transition layer, of the order of 1 to 3 atomic planes, contains typically one monolayer of ZnSe. Even if it occurs at each interface, the direct interface, i.e., ZnTe on CdSe, is sharper than the reverse one, where the ZnSe layer is likely surrounded by alloyed layers. On the other hand, a CdTe-like interface was never observed. This interface knowledge is crucial to properly design superlattices for optoelectronic applications and to master band-gap engineering.

  11. NMR characterization of sulphur substitution effects in the KxFe2-ySe2-zSz high-Tc superconductor

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Torchetti, D. A.; Imai, T.; Lei, H. C.; Petrovic, C.

    2012-04-17

    We present a⁷⁷ Se NMR study of the effect of S substitution in the high-Tc superconductor KxFe2-ySe2-zSz in a temperature range up to 250 K. We examine two S concentrations, with z=0.8 (Tc~ 26 K) and z=1.6 (nonsuperconducting). The samples containing sulphur exhibit broader NMR line shapes than the KxFe₂Se₂ sample due to local disorder in the Se environment. Our Knight shift ⁷⁷K data indicate that in all samples, uniform spin susceptibility decreases with temperature, and that the magnitude of the Knight shift itself decreases with increased S concentration. In addition, S substitution progressively suppresses low-frequency spin fluctuations. None ofmore » the samples exhibit an enhancement of low-frequency antiferromagnetic spin fluctuations near Tc in 1/T₁T, as seen in FeSe.« less

  12. Limitation of the Open-Circuit Voltage Due to Metastable Intrinsic Defects in Cu(In,Ga)Se2 and Strategies to Avoid These Defects: Preprint

    SciTech Connect (OSTI)

    Lany, S.; Zunger, A.

    2008-05-01

    This paper summarizes using first-principles defect theory to investigate the role of intrinsic point defects in the limitation of the open-circuit voltage (VOC) in Cu(In,Ga)Se2 solar cells.

  13. Alternative fabrication techniques for high-efficiency CuInSe{sub 2} and CuInSe{sub 2}-alloy films and cells. Final subcontract report, 1 March 1990--31 August 1992

    SciTech Connect (OSTI)

    Rockett, A.; Yang, L.C.; Kenshole, G.; Banda, E.; Feen, A.

    1994-07-01

    Work performed during the course of this subcontract has led to improved CuInSe{sub 2} (CIS) processing techniques and materials resulting in improved solar cell performance (up to 10% active area efficiency) based on a thick conductive evaporated CdS window layer and an indium-tin-oxide transparent conductor. Modeling of the device performance has indicated that an optimal CdS thickness should exist if pinholes occur in the CIS layer (for example, due to adhesion failures) leading to shunts between the CdS and the back contact. Pinholes in the CIS layer have been dramatically reduced by the use of a Cu-Mo two-phase back contact metallization resulting from significant increases in adhesion between the CIS and the back contact. Controlled leaching of the Cu from the back contact apparently contributes to this improvement without degradation of the solar cells. Finally, CIS has been grown epitaxially on GaAs. Preliminary results suggest explanations for the morphology and defect structures of polycrystalline layers used in devices as well as indicating the general mechanism for growth of CIS by vapor phase methods.

  14. Arrays of ZnO/CuIn{sub x}Ga{sub 1?x}Se{sub 2} nanocables with tunable shell composition for efficient photovoltaics

    SciTech Connect (OSTI)

    Akram, Muhammad Aftab; Javed, Sofia; Xu, Jun; Mujahid, Mohammad; Lee, Chun-Sing

    2015-05-28

    Arrays of one-dimensional (1D) nanostructure are receiving much attention for their optoelectronic and photovoltaic applications due to their advantages in light absorption, charge separation, and transportation. In this work, arrays of ZnO/CuIn{sub x}Ga{sub 1?x}Se{sub 2} core/shell nanocables with tunable shell compositions over the full range of 0???x???1 have been controllably synthesized. Chemical conversions of ZnO nanorods to a series of ZnO-based nanocables, including ZnO/ZnSe, ZnO/CuSe, ZnO/CuSe/In{sub x}Ga{sub 1?x}, ZnO/CuSe/(In{sub x}Ga{sub 1?x}){sub 2}Se{sub 3}, and ZnO/CuIn{sub x}Ga{sub 1?x}Se{sub 2}, are well designed and successfully achieved. Composition-dependent influences of the CuIn{sub x}Ga{sub 1?x}Se{sub 2} shells on photovoltaic performance are investigated. It is found that the increase in indium content (x) leads to an increase in short-circuit current density (J{sub SC}) but a decrease in open-circuit voltage (V{sub OC}) for the ZnO/CuIn{sub x}Ga{sub 1?x}Se{sub 2} nanocable solar cells. An array of ZnO/CuIn{sub 0.67}Ga{sub 0.33}Se{sub 2} nanocables with a length of ?1??m and a shell thickness of ?10?nm exhibits a bandgap of 1.20?eV, and yields a maximum power conversion efficiency of 1.74% under AM 1.5?G illumination at an intensity of 100 mW/cm{sup 2}. It dramatically surpasses that (0.22%) of the ZnO/CuIn{sub 0.67}Ga{sub 0.33}Se{sub 2} planar thin-film device. Our work reveals that 1D nanoarray allows efficient photovoltaics without using toxic CdS buffer layer.

  15. Dispersion of the linear and nonlinear optical susceptibilities of the CuAl(S{sub 1x}Se{sub x})? mixed chaclcopyrite compounds

    SciTech Connect (OSTI)

    Reshak, A. H.; Brik, M. G.; Auluck, S.

    2014-09-14

    Based on the electronic band structure, we have calculated the dispersion of the linear and nonlinear optical susceptibilities for the mixed CuAl(S{sub 1x}Se{sub x})? chaclcopyrite compounds with x=0.0, 0.25, 0.5, 0.75, and 1.0. Calculations are performed within the Perdew-Becke-Ernzerhof general gradient approximation. The investigated compounds possess a direct band gap of about 2.2 eV (CuAlS?), 1.9 eV (CuAl(S?.??Se?.??)?), 1.7 eV (CuAl(S?.?Se?.?)?), 1.5 eV (CuAl(S?.??Se?.??)?), and 1.4 eV (CuAlSe?) which tuned to make them optically active for the optoelectronics and photovoltaic applications. These results confirm that substituting S by Se causes significant band gaps' reduction. The optical function's dispersion ??{sup xx}(?) and ??{sup zz}(?)/??{sup xx}(?), ??{sup yy}(?), and ??{sup zz}(?) was calculated and discussed in detail. To demonstrate the effect of substituting S by Se on the complex second-order nonlinear optical susceptibility tensors, we performed detailed calculations for the complex second-order nonlinear optical susceptibility tensors, which show that the neat parents compounds CuAlS? and CuAlSe? exhibit | ????}(-2?;?;?) | as the dominant component, while the mixed alloys exhibit | ????(-2?;?;?) | as the dominant component. The features of | ????}(-2?;?;?) | and | ?{sub 111}}(-2?;?;?) | spectra were analyzed on the basis of the absorptive part of the corresponding dielectric function ??(?) as a function of both ?/2 and ?.

  16. Surface structure of CdSe Nanorods revealed by combined X-rayabsorption fine structure measurements and ab-initio calculations

    SciTech Connect (OSTI)

    Aruguete, Deborah A.; Marcus, Matthew A.; Li, Liang-shi; Williamson, Andrew; Fakra, Sirine; Gygi, Francois; Galli, Giulia; Alivisatos, A. Paul

    2006-01-27

    We report orientation-specific, surface-sensitive structural characterization of colloidal CdSe nanorods with extended X-ray absorption fine structure spectroscopy and ab-initio density functional theory calculations. Our measurements of crystallographically-aligned CdSe nanorods show that they have reconstructed Cd-rich surfaces. They exhibit orientation-dependent changes in interatomic distances which are qualitatively reproduced by our calculations. These calculations reveal that the measured interatomic distance anisotropy originates from the nanorod surface.

  17. Recombination luminescence and trap levels in undoped and Al-doped ZnO thin films on quartz and GaSe (0 0 0 1) substrates

    SciTech Connect (OSTI)

    Evtodiev, I.; Caraman, I.; Leontie, L.; Rusu, D.-I.; Dafinei, A.; Nedeff, V.; Lazar, G.

    2012-03-15

    Highlights: Black-Right-Pointing-Pointer ZnO films on GaSe create electron trapping states and PL recombination levels. Black-Right-Pointing-Pointer Zn and Al diffusion in GaSe produces low-energy widening of its PL emission. Black-Right-Pointing-Pointer ZnO:Al films on GaSe lamellas are suitable for gas-discharge lamp applications. -- Abstract: Photoluminescence spectra of ZnO and ZnO:Al (1.00, 2.00 and 5.00 at.%) films on GaSe (0 0 0 1) lamellas and amorphous quartz substrates, obtained by annealing, at 700 K, of undoped and Al-doped metal films, are investigated. For all samples, the nonequilibrium charge carriers recombine by radiative band-to-band transitions with energy of 3.27 eV, via recombination levels created by the monoionized oxygen atoms, forming the impurity band laying in the region 2.00 - 2.70 eV. Al doping induces an additional recombination level at 1.13 eV above the top of the valence band of ZnO films on GaSe substrates. As a result of thermal diffusion of Zn and Al into the GaSe interface layer from ZnO:Al/GaSe heterojunction, electron trap levels located at 0.22 eV and 0.26 eV below the conduction band edge of GaSe, as well as a deep recombination level, responsible for the luminescent emission in the region 1.10 - 1.40 eV, are created.

  18. Polytypism, polymorphism, and superconductivity in TaSe2–xTex

    SciTech Connect (OSTI)

    Luo, Huixia; Xie, Weiwei; Tao, Jing; Inoue, Hiroyuki; Gyenis, András; Krizan, Jason W.; Yazdani, Ali; Zhu, Yimei; Cava, Robert Joseph

    2015-03-03

    Polymorphism in materials often leads to significantly different physical properties - the rutile and anatase polymorphs of TiO₂ are a prime example. Polytypism is a special type of polymorphism, occurring in layered materials when the geometry of a repeating structural layer is maintained but the layer stacking sequence of the overall crystal structure can be varied; SiC is an example of a material with many polytypes. Although polymorphs can have radically different physical properties, it is much rarer for polytypism to impact physical properties in a dramatic fashion. Here we study the effects of polytypism and polymorphism on the superconductivity of TaSe₂, one of the archetypal members of the large family of layered dichalcogenides. We show that it is possible to access 2 stable polytypes and 2 stable polymorphs in the TaSe2-xTex solid solution, and find that the 3R polytype shows a superconducting transition temperature that is between 6 and 17 times higher than that of the much more commonly found 2H polytype. Thus, the reason for this dramatic change is not apparent, but we propose that it arises either from a remarkable dependence of Tc on subtle differences in the characteristics of the single layers present, or from a surprising effect of the layer stacking sequence on electronic properties that instead are expected to be dominated by the properties of a single layer in materials of this kind.

  19. Temperature-driven band inversion in Pb0.77Sn0.23Se: Optical and Hall effect studies

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Anand, Naween; Buvaev, Sanal; Hebard, A. F.; Tanner, D. B.; Chen, Zhiguo; Li, Zhiqiang; Choudhary, Kamal; Sinnott, S. B.; Gu, Genda; Martin, C.

    2014-12-23

    Optical and Hall-effect measurements have been performed on single crystals of Pb₀.₇₇Sn₀.₂₃Se, a IV-VI mixed chalcogenide. The temperature dependent (10–300 K) reflectance was measured over 40–7000 cm⁻¹ (5–870 meV) with an extension to 15,500 cm⁻¹ (1.92 eV) at room temperature. The reflectance was fit to the Drude-Lorentz model using a single Drude component and several Lorentz oscillators. The optical properties at the measured temperatures were estimated via Kramers-Kronig analysis as well as by the Drude-Lorentz fit. The carriers were p-type with the carrier density determined by Hall measurements. A signature of valence intraband transition is found in the low-energy opticalmore » spectra. It is found that the valence-conduction band transition energy as well as the free carrier effective mass reach minimum values at 100 K, suggesting temperature-driven band inversion in the material. Thus, density function theory calculation for the electronic band structure also make similar predictions.« less

  20. Highly Emissive Multiexcitons in Steady-State Photoluminescence of Individual Giant CdSe/CdS Core/Shell Nanocrystals

    SciTech Connect (OSTI)

    Htoon, Han; Malko, Anton V.; Bussian, David A.; Vela, Javier; Chen, Yongfen; Hollingsworth, Jennifer A.; Klimov, Victor I.

    2010-06-01

    The development of nanocrystal quantum dots (NQDs) with suppressed nonradiative Auger recombination has been an important goal in colloidal nanostructure research motivated by the needs of prospective applications in lasing devices, light-emitting diodes, and photovoltaic cells. Here, we conduct single-nanocrystal spectroscopic studies of recently developed core-shell NQDs (so-called giant NQDs) that comprise a small CdSe core surrounded by a 16-monolayer-thick CdS shell. Using both continuous-wave and pulsed excitation, we observe strong emission features due both to neutral and charged biexcitons, as well as multiexcitons of higher order. The development of pronounced multiexcitonic peaks in steady-state photoluminescence of individual nanocrystals, as well as continuous growth of the emission intensity in the range of high pump levels, point toward a significant suppression of nonradiative Auger decay that normally renders multiexcitons nonemissive. The unusually high multiexciton emission efficiencies in these systems open interesting opportunities for studies of multiexciton phenomena using well-established methods of single-dot spectroscopy, as well as new exciting prospects for applications, that have previously been hampered by nonradiative Auger decay.

  1. Lifetime and Polarization of the Radiative Decay of Excitons, Biexcitons, and Trions in CdSe Nanocrystal Quantum Dots

    SciTech Connect (OSTI)

    Califano, M.; Franceschetti, A.; Zunger, A.

    2007-01-01

    Using the pseudopotential configuration-interaction method, we calculate the intrinsic lifetime and polarization of the radiative decay of single excitons (X), positive and negative trions (X{sup +} and X{sup -}), and biexcitons (XX) in CdSe nanocrystal quantum dots. We investigate the effects of the inclusion of increasingly more complex many-body treatments, starting from the single-particle approach and culminating with the configuration-interaction scheme. Our configuration-interaction results for the size dependence of the single-exciton radiative lifetime at room temperature are in excellent agreement with recent experimental data. We also find the following. (i) Whereas the polarization of the bright exciton emission is always perpendicular to the hexagonal c axis, the polarization of the dark exciton switches from perpendicular to parallel to the hexagonal c axis in large dots, in agreement with experiment. (ii) The ratio of the radiative lifetimes of mono- and biexcitons (X):(XX) is {approx}1:1 in large dots (R=19.2 {angstrom}). This ratio increases with decreasing nanocrystal size, approaching 2 in small dots (R=10.3 {angstrom}). (iii) The calculated ratio (X{sup +}):(X{sup -}) between positive and negative trion lifetimes is close to 2 for all dot sizes considered.

  2. CdSe/ZnS quantum dots based electrochemical immunoassay for the detection of phosphorylated bovine serum albumin

    SciTech Connect (OSTI)

    Pinwattana, Kulwadee; Wang, Jun; Lin, Chiann Tso; Wu, Hong; Du, Dan; Lin, Yuehe; Chailapakul, Orawon

    2010-11-15

    A CdSe/ZnS quantum dot (QD) based electrochemical immunoassay of phosphorylated bovine serum albumin as a protein biomarker is presented. The QDs were used as labels and were conjugated with the secondary anti-phosphoserine antibody in a heterogeneous sandwich immunoassay. First, the primary BSA antibody was immobilized on polystyrene microwells, followed by the addition of BSA-OP. After that, the QD-labeled anti-phosphoserine antibody was added into microwells for immunorecognition. Finally, the bound QD was dissolved in an acid-dissolution step and was detected by electrochemical stripping analysis. The measured current responses were proportional to the concentration of BSA-OP. Under optimal conditions, the voltammetric response was linear over the range of 0.5 - 500 ng mL-1 of BSA-OP, with a detection limit of 0.5 ng mL-1 at a deposition potential of -1.2 V for 120 s. It also shows good reproducibility with a relative standard deviation of 8.6% of six times determination of 25 ng mL-1 of BSA-OP. This QD-based electrochemical immunoassay offers great promise for simple and cost-effective analysis of protein biomarkers.

  3. Emergence of coherence in the charge-density wave state of 2H-NbSe2

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Chatterjee, U.; Zhao, J.; Iavarone, M.; Di Capua, R.; Castellan, J. P.; Karapetrov, G.; Malliakas, C. D.; Kanatzidis, M. G.; Claus, H.; Ruff, J. P. C.; et al

    2015-02-17

    A charge-density wave (CDW) state has a broken symmetry described by a complex order parameter with an amplitude and a phase. The conventional view, based on clean, weak-coupling systems, is that a finite amplitude and long-range phase coherence set in simultaneously at the CDW transition temperature Tcdw. Here we investigate, using photoemission, X-ray scattering and scanning tunnelling microscopy, the canonical CDW compound 2H-NbSe2 intercalated with Mn and Co, and show that the conventional view is untenable. We find that, either at high temperature or at large intercalation, CDW order becomes short-ranged with a well-defined amplitude, which has impacts on themoreelectronic dispersion, giving rise to an energy gap. The phase transition at Tcdw marks the onset of long-range order with global phase coherence, leading to sharp electronic excitations. Our observations emphasize the importance of phase fluctuations in strongly coupled CDW systems and provide insights into the significance of phase incoherence in pseudogap states.less

  4. Twisted MoSe2 bilayers with variable local stacking and interlayer coupling revealed by low-frequency Raman spectroscopy

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Puretzky, Alexander A.; Liang, Liangbo; Li, Xufan; Xiao, Kai; Sumpter, Bobby G.; Meunier, Vincent; Geohegan, David B.

    2016-01-14

    Unique twisted bilayers of MoSe2 with multiple stacking orientations and interlayer couplings in the narrow range of twist angles, 60 ± 3°, are revealed by low-frequency Raman spectroscopy and theoretical analysis. The slight deviation from 60 allows the concomitant presence of patches featuring all three high-symmetry stacking configurations (2H or AA', AB', A'B) in one unique bilayer system. In this case, the periodic arrangement of the patches and their size strongly depend on the twist angle. Ab initio modeling predicts significant changes in frequencies and intensities of low-frequency modes versus stacking and twist angle. Experimentally, the variable stacking and couplingmore » across the interface is revealed by the appearance of two breathing modes corresponding to the mixture of the high-symmetry stacking configurations and unaligned regions of monolayers. Only one breathing mode is observed outside the narrow range of twist angles. This indicates a stacking transition to unaligned monolayers with mismatched atom registry without the in-plane restoring force required to generate a shear mode. As a result, the variable interlayer coupling and spacing in transition metal dichalcogenide bilayers revealed in this study may provide a new platform for optoelectronic applications of these materials.« less

  5. Emergence of coherence in the charge-density wave state of 2H-NbSe2

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Chatterjee, U.; Zhao, J.; Iavarone, M.; Di Capua, R.; Castellan, J. P.; Karapetrov, G.; Malliakas, C. D.; Kanatzidis, M. G.; Claus, H.; Ruff, J. P. C.; et al

    2015-02-17

    A charge-density wave (CDW) state has a broken symmetry described by a complex order parameter with an amplitude and a phase. The conventional view, based on clean, weak-coupling systems, is that a finite amplitude and long-range phase coherence set in simultaneously at the CDW transition temperature Tcdw. Here we investigate, using photoemission, X-ray scattering and scanning tunnelling microscopy, the canonical CDW compound 2H-NbSe2 intercalated with Mn and Co, and show that the conventional view is untenable. We find that, either at high temperature or at large intercalation, CDW order becomes short-ranged with a well-defined amplitude, which has impacts on themore » electronic dispersion, giving rise to an energy gap. The phase transition at Tcdw marks the onset of long-range order with global phase coherence, leading to sharp electronic excitations. As a result, our observations emphasize the importance of phase fluctuations in strongly coupled CDW systems and provide insights into the significance of phase incoherence in ‘pseudogap’ states.« less

  6. Electron-beam induced variation of surface profile in amorphous As{sub 20}Se{sub 80} films

    SciTech Connect (OSTI)

    Kaganovskii, Yu. E-mail: trunov.m@gmail.com; Trunov, M. L. E-mail: trunov.m@gmail.com; Cserhati, C.; Beke, D. L.; Kknyesi, S.

    2014-05-14

    Unusual profile variation of holographic surface relief gratings is detected in thin (2??m) As{sub 20}Se{sub 80} chalcogenide films under e-beam irradiation: gratings of small periods were smoothed, whereas the gratings of larger periods increased their amplitudes. Irradiation was carried out in SEM, with 20?kV voltage and 8?nA current; the profiles of the irradiated areas were analyzed both by AFM and SEM. It is found that the kinetics of both flattening and growth followed by exponential law and took place due to lateral mass transport accelerated by e-irradiation. It is shown that the profile variation is mainly caused by competition between capillary forces and chemical forces induced by broken and deformed atomic bonds under e-beam irradiation. The kinetics of profile variation was calculated assuming that the mechanism of e-beam induced mass transfer is volume diffusion. The diffusion coefficients were estimated from the experimental data using theoretical expressions derived.

  7. Exploring the electronic structure and optical properties of the quaternary selenide compound, Ba{sub 4}Ga{sub 4}SnSe{sub 12}: For photovoltaic applications

    SciTech Connect (OSTI)

    Azam, Sikander; Khan, Saleem Ayaz; Goumri-Said, Souraya

    2015-09-15

    Due to huge demand on discovering new materials for energy, we used first-principle calculations to explore the electronic structure and optical properties of a recent quaternary selenide, namely Ba{sub 4}Ga{sub 4}SnSe{sub 12}. The electronic structure and the optical properties of Ba{sub 4}Ga{sub 4}SnSe{sub 12} were calculated through a reliable approach of Engle Vosko-GGA (EV-GGA). We found that Ba{sub 4}Ga{sub 4}SnSe{sub 12} has a direct band gap of 2.14 eV positioned at Γ. Acquiring the fundamental characteristics of Ba{sub 4}Ga{sub 4}SnSe{sub 12,} we studied the linear optical properties like dielectric function in the energy range of 0–14 eV. From the dielectric function we noticed a weak directional anisotropy for the two components. The absorption spectrum indicates the possibility of greater multiple direct and indirect inter-band transitions in the visible regions and shows similar behavior with experimental spectrum. Ba{sub 4}Ga{sub 4}SnSe{sub 12} can be used as shielding material from UV radiations. Present study predicts that the Ba{sub 4}Ga{sub 4}SnSe{sub 12} is promising for photovoltaic applications due to their high absorption of solar radiations and photoconductivity in the visible range. - Graphical abstract: Interesting quaternary selenide compound, Ba{sub 4}Ga{sub 4}SnSe{sub 12}, for photovoltaic applications. - Highlights: • Ba{sub 4}Ga{sub 4}SnSe{sub 12} is a quaternary selenide designed for PV and thermoelectric. • Ba{sub 4}Ga{sub 4}SnSe{sub 12} has a direct band gap of 2.14 eV. • Ba{sub 4}Ga{sub 4}SnSe{sub 12,} has a maximum reflectivity in the visible and UV regions.

  8. Hydrogenated indium oxide window layers for high-efficiency Cu(In,Ga)Se{sub 2} solar cells

    SciTech Connect (OSTI)

    Jäger, Timo Romanyuk, Yaroslav E.; Nishiwaki, Shiro; Bissig, Benjamin; Pianezzi, Fabian; Fuchs, Peter; Gretener, Christina; Tiwari, Ayodhya N.; Döbeli, Max

    2015-05-28

    High mobility hydrogenated indium oxide is investigated as a transparent contact for thin film Cu(In,Ga)Se{sub 2} (CIGS) solar cells. Hydrogen doping of In{sub 2}O{sub 3} thin films is achieved by injection of H{sub 2}O water vapor or H{sub 2} gas during the sputter process. As-deposited amorphous In{sub 2}O{sub 3}:H films exhibit a high electron mobility of ∼50 cm{sup 2}/Vs at room temperature. A bulk hydrogen concentration of ∼4 at. % was measured for both optimized H{sub 2}O and H{sub 2}-processed films, although the H{sub 2}O-derived film exhibits a doping gradient as detected by elastic recoil detection analysis. Amorphous IOH films are implemented as front contacts in CIGS based solar cells, and their performance is compared with the reference ZnO:Al electrodes. The most significant feature of IOH containing devices is an enhanced open circuit voltage (V{sub OC}) of ∼20 mV regardless of the doping approach, whereas the short circuit current and fill factor remain the same for the H{sub 2}O case or slightly decrease for H{sub 2}. The overall power conversion efficiency is improved from 15.7% to 16.2% by substituting ZnO:Al with IOH (H{sub 2}O) as front contacts. Finally, stability tests of non-encapsulated solar cells in dry air at 80 °C and constant illumination for 500 h demonstrate a higher stability for IOH-containing devices.

  9. Effect of sintering in ball-milled K{sub 2}Bi{sub 8}Se{sub 13} thermoelectric nano-composites

    SciTech Connect (OSTI)

    Hatzikraniotis, E.; Ioannou, M.; Chrissafis, K.; Chung, D.Y.; Paraskevopoulos, K.M.; Kyratsi, Th.

    2012-09-15

    K{sub 2}Bi{sub 8}Se{sub 13} has many attractive features for thermoelectric applications. Recently, K{sub 2}Bi{sub 8}Se{sub 13}-based nanocomposite materials, consisting of nano-crystalline, micro-crystalline and amorphous phases, have been fabricated based on powder technology techniques. The Seebeck coefficient has been enhanced while the thermal conductivity has been decreased presenting, thus, interesting behavior. The behavior of the materials under heat treatment conditions is now of interest, as the application of sintering process is necessary for the development of thermoelectric modules. In this work, the crystallization of the K{sub 2}Bi{sub 8}Se{sub 13}-based nano-composites is studied using Differential Scanning Calorimetry. The results show that crystallization follows a multiple-step process with different activation energies. The thermoelectric properties are also discussed in the range that crystallization occurs. - Graphical Abstract: {beta}-K{sub 2}Bi{sub 8}Se{sub 13}-based nanocomposites follow a multiple-step crystallization process. Highlights: Black-Right-Pointing-Pointer K{sub 2}Bi{sub 8}Se{sub 13}-based composites consisting of nanocrystalline and amorphous phases. Black-Right-Pointing-Pointer Sintering results multiple-step crystallization with variable activation energies. Black-Right-Pointing-Pointer Thermoelectric properties follow a step-like behavior during sintering. Black-Right-Pointing-Pointer Properties are attributed to the strain relaxation, nucleation and grain growth.

  10. Correlation between morphology, chemical environment, and ferromagnetism in the intrinsic-vacancy dilute magnetic semiconductor Cr-doped Ga2Se3/Si(001)

    SciTech Connect (OSTI)

    Yitamben, E.N.; Arena, D.; Lovejoy, T.C.; Pakhomov, A.B.; Heald, S.M.; Negusse, E.; Ohuchi, F.S.; Olmstead, M.A.

    2011-01-28

    Chromium-doped gallium sesquiselenide, Cr:Ga{sub 2}Se{sub 3}, is a member of a new class of dilute magnetic semiconductors exploiting intrinsic vacancies in the host material. The correlation among room-temperature ferromagnetism, surface morphology, electronic structure, chromium concentration, and local chemical and structural environments in Cr:Ga{sub 2}Se{sub 3} films grown epitaxially on silicon is investigated with magnetometry, scanning tunneling microscopy, photoemission spectroscopy, and x-ray absorption spectroscopy. Inclusion of a few percent chromium in Ga{sub 2}Se{sub 3} results in laminar, semiconducting films that are ferromagnetic at room temperature with a magnetic moment 4{micro}{sub B}/Cr. The intrinsic-vacancy structure of defected-zinc-blende {beta}-Ga{sub 2}Se{sub 3} enables Cr incorporation in a locally octahedral site without disrupting long-range order, determined by x-ray absorption spectroscopy, as well as strong overlap between Cr 3d states and the Se 4p states lining the intrinsic-vacancy rows, observed with photoemission. The highest magnetic moment per Cr is observed near the solubility limit of roughly one Cr per three vacancies. At higher Cr concentrations, islanded, metallic films result, with a magnetic moment that depends strongly on surface morphology. The effective valence is Cr{sup 3+} in laminar films, with introduction of Cr{sup 0} upon islanding. A mechanism is proposed for laminar films whereby ordered intrinsic vacancies mediate ferromagnetism.

  11. Electronic structure, irreversibility line and magnetoresistance of Cu0.3Bi2Se3 superconductor

    SciTech Connect (OSTI)

    Hemian, Yi; Gu, Genda; Chen, Chao -Yu; Sun, Xuan; Xie, Zhuo -Jin; Feng, Ya; Liang, Ai -Ji; Peng, Ying -Ying; He, Shao -Long; Zhao, Lin; Liu, Guo -Dong; Dong, Xiao -Li; Zhang, Jun; Chen, Chuang -Tian; Xu, Zu -Yan; Zhou, X. -J.

    2015-06-01

    CuxBi2Se3 is a superconductor that is a potential candidate for topological superconductors. We report our laser-based angle-resolved photoemission measurement on the electronic structure of the CuxBi2Se3 superconductor, and a detailed magneto-resistance measurement in both normal and superconducting states. We find that the topological surface state of the pristine Bi2Se3 topological insulator remains robust after the Cu-intercalation, while the Dirac cone location moves downward due to electron doping. Detailed measurements on the magnetic field-dependence of the resistance in the superconducting state establishes an irreversibility line and gives a value of the upper critical field at zero temperature of ~4000 Oe for the Cu0.3Bi2Se3 superconductor with a middle point Tc of 1.9K. The relation between the upper critical field Hc2 and temperature T is different from the usual scaling relation found in cuprates and in other kinds of superconductors. Small positive magneto-resistance is observed in Cu0.3Bi2Se3 superconductors up to room temperature. As a result, these observations provide useful information for further study of this possible candidate for topological superconductors.

  12. Understanding the electronic structure of CdSe quantum dot-fullerene (C{sub 60}) hybrid nanostructure for photovoltaic applications

    SciTech Connect (OSTI)

    Sarkar, Sunandan; Rajbanshi, Biplab; Sarkar, Pranab

    2014-09-21

    By using the density-functional tight binding method, we studied the electronic structure of CdSe quantum dot(QD)-buckminsterfullerene (C{sub 60}) hybrid systems as a function of both the size of the QD and concentration of the fullerene molecule. Our calculation reveals that the lowest unoccupied molecular orbital energy level of the hybrid CdSeQD-C{sub 60} systems lies on the fullerene moiety, whereas the highest occupied molecular orbital (HOMO) energy level lies either on the QD or the fullerene depending on size of the CdSe QD. We explored the possibility of engineering the energy level alignment by varying the size of the CdSe QD. With increase in size of the QD, the HOMO level is shifted upward and crosses the HOMO level of the C{sub 60}-thiol molecule resulting transition from the type-I to type-II band energy alignment. The density of states and charge density plot support these types of band gap engineering of the CdSe-C{sub 60} hybrid systems. This type II band alignment indicates the possibility of application of this nanohybrid for photovoltaic purpose.

  13. ZnCuInS/ZnSe/ZnS Quantum Dot-Based Downconversion Light-Emitting Diodes and Their Thermal Effect

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Liu, Wenyan; Zhang, Yu; Ruan, Cheng; Wang, Dan; Zhang, Tieqiang; Feng, Yi; Gao, Wenzhu; Yin, Jingzhi; Wang, Yiding; Riley, Alexis P.; et al

    2015-01-01

    The quantum dot-based light-emitting diodes (QD-LEDs) were fabricated using blue GaN chips and red-, yellow-, and green-emitting ZnCuInS/ZnSe/ZnS QDs. The power efficiencies were measured as 14.0 lm/W for red, 47.1 lm/W for yellow, and 62.4 lm/W for green LEDs at 2.6 V. The temperature effect of ZnCuInS/ZnSe/ZnS QDs on these LEDs was investigated using CIE chromaticity coordinates, spectral wavelength, full width at half maximum (FWHM), and power efficiency (PE). The thermal quenching induced by the increased surface temperature of the device was confirmed to be one of the important factors to decrease power efficiencies while the CIE chromaticity coordinates changed little due to themore » low emission temperature coefficients of 0.022, 0.050, and 0.068 nm/°C for red-, yellow-, and green-emitting ZnCuInS/ZnSe/ZnS QDs. These indicate that ZnCuInS/ZnSe/ZnS QDs are more suitable for downconversion LEDs compared to CdSe QDs.« less

  14. Role of polycrystallinity in CdTe and CuInSe{sub 2} photovoltaic cells. Annual subcontract report, 1 April 1990--31 March 1991

    SciTech Connect (OSTI)

    Sites, J.R.

    1991-12-31

    The polycrystalline nature of thin-film CdTe and CuInSe{sub 2} solar cells continues to be a major factor in several individual losses that limit overall cell efficiency. This report describes progress in the quantitative separation of these losses, including both measurement and analysis procedures. It also applies these techniques to several individual cells to help document the overall progress with CdTe and CuInSe{sub 2} cells. Notably, CdTe cells from Photon Energy have reduced window photocurrent losses to 1 mA/Cm{sup 2}; those from the University of South Florida have achieved a maximum power voltage of 693 mV; and CuInSe{sub 2} cells from International Solar Electric Technology have shown a hole density as high as 7 {times} 10{sup 16} cm{sup {minus}3}, implying a significant reduction in compensation. 9 refs.

  15. Linear and nonlinear transmission of Fe{sup 2+}-doped ZnSe crystals at a wavelength of 2940 nm in the temperature range 20220 C

    SciTech Connect (OSTI)

    Il'ichev, N N; Pashinin, P P; Gulyamova, E S; Bufetova, G A; Shapkin, P V; Nasibov, A S

    2014-03-28

    The linear and nonlinear transmission of Fe{sup 2+}:ZnSe crystals is measured at a wavelength of 2940 nm in the temperature range 20 220 C. It is found that, with increasing temperature from 20 C to 150 220 C, the transmission of Fe{sup 2+}:ZnSe crystals decreases in the case of incident radiation with an intensity of ?5.5 MW cm{sup -2} and increases in the case of radiation with an intensity of 28 kW cm{sup -2}. At a temperature of 220 C, the linear transmission almost coincides with the nonlinear transmission. The transmission spectra of Fe{sup 2+}:ZnSe crystals at temperatures of 22 and 220 C in the wavelength range 500 7000 nm are presented. (active media)

  16. The impact of oxygen incorporation during intrinsic ZnO sputtering on the performance of Cu(In,Ga)Se{sub 2} thin film solar cells

    SciTech Connect (OSTI)

    Lee, Kkotnim; Ok, Eun-A; Park, Jong-Keuk; Kim, Won Mok; Baik, Young-Joon; Jeong, Jeung-hyun; Kim, Donghwan

    2014-08-25

    We investigated the impact of incorporating 2% oxygen during intrinsic ZnO sputtering on the efficiency of Cu(In,Ga)Se{sub 2} solar cells. The added oxygen not only reduced the optical absorption loss of the Al-doped ZnO overlaying layer but also improved the electronic properties of the underlying CdS/Cu(In,Ga)Se{sub 2} by increasing carrier density, lowering defect level, and increasing diffusion length, eventually enhancing J{sub SC}, V{sub OC}, and fill factor. It was found that the Na doping concentration was significantly increased around the CdS/Cu(In,Ga)Se{sub 2} junction due to the plasma-activated oxygen. The improved electronic properties are better explained by the increased Na concentration than simply the oxygen-related defect passivation.

  17. The influence of air temperature inversions on snowmelt and glacier mass-balance simulations, Ammassalik island, SE Greenland

    SciTech Connect (OSTI)

    Mernild, Sebastian Haugard [Los Alamos National Laboratory; Liston, Glen [COLORADO STATE UNIV.

    2009-01-01

    In many applications, a realistic description of air temperature inversions is essential for accurate snow and glacier ice melt, and glacier mass-balance simulations. A physically based snow-evolution modeling system (SnowModel) was used to simulate eight years (1998/99 to 2005/06) of snow accumulation and snow and glacier ice ablation from numerous small coastal marginal glaciers on the SW-part of Ammassalik Island in SE Greenland. These glaciers are regularly influenced by inversions and sea breezes associated with the adjacent relatively low temperature and frequently ice-choked fjords and ocean. To account for the influence of these inversions on the spatiotemporal variation of air temperature and snow and glacier melt rates, temperature inversion routines were added to MircoMet, the meteorological distribution sub-model used in SnowModel. The inversions were observed and modeled to occur during 84% of the simulation period. Modeled inversions were defined not to occur during days with strong winds and high precipitation rates due to the potential of inversion break-up. Field observations showed inversions to extend from sea level to approximately 300 m a.s.l., and this inversion level was prescribed in the model simulations. Simulations with and without the inversion routines were compared. The inversion model produced air temperature distributions with warmer lower elevation areas and cooler higher elevation areas than without inversion routines due to the use of cold sea-breeze base temperature data from underneath the inversion. This yielded an up to 2 weeks earlier snowmelt in the lower areas and up to 1 to 3 weeks later snowmelt in the higher elevation areas of the simulation domain. Averaged mean annual modeled surface mass-balance for all glaciers (mainly located above the inversion layer) was -720 {+-} 620 mm w.eq. y{sup -1} for inversion simulations, and -880 {+-} 620 mm w.eq. y{sup -1} without the inversion routines, a difference of 160 mm w.eq. y{sup -1}. The annual glacier loss for the two simulations was 50.7 x 10{sup 6} m{sup 3} y{sup -1} and 64.4 x 10{sup 6} m{sup 3} y{sup -1} for all glaciers - a difference of {approx}21%. The average equilibrium line altitude (ELA) for all glaciers in the simulation domain was located at 875 m a.s.l. and at 900 m a.s.l. for simulations with or without inversion routines, respectively.

  18. Molecular Control of the Nanoscale: Effect of PhosphineChalcogenide Reactivity on CdSCdSe Nanocrystal Composition and Morphology

    SciTech Connect (OSTI)

    Ruberu, T. Purnima A.; Albright, Haley R.; Callis, Brandon; Ward, Brittney; Cisneros, Joana; Fan, Hua-Jun; Vela, Javier

    2012-04-22

    We demonstrate molecular control of nanoscale composition, alloying, and morphology (aspect ratio) in CdSCdSe nanocrystal dots and rods by modulating the chemical reactivity of phosphinechalcogenide precursors. Specific molecular precursors studied were sulfides and selenides of triphenylphosphite (TPP), diphenylpropylphosphine (DPP), tributylphosphine (TBP), trioctylphosphine (TOP), and hexaethylphosphorustriamide (HPT). Computational (DFT), NMR (31P and 77Se), and high-temperature crossover studies unambiguously confirm a chemical bonding interaction between phosphorus and chalcogen atoms in all precursors. Phosphinechalcogenide precursor reactivity increases in the order: TPPE < DPPE < TBPE < TOPE < HPTE (E = S, Se). For a given phosphine, the selenide is always more reactive than the sulfide. CdS1xSex quantum dots were synthesized via single injection of a R3PSR3PSe mixture to cadmium oleate at 250 C. X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV/Vis and PL optical spectroscopy reveal that relative R3PS and R3PSe reactivity dictates CdS1xSex dot chalcogen content and the extent of radial alloying (alloys vs core/shells). CdS, CdSe, and CdS1xSex quantum rods were synthesized by injection of a single R3PE (E = S or Se) precursor or a R3PSR3PSe mixture to cadmiumphosphonate at 320 or 250 C. XRD and TEM reveal that the length-to-diameter aspect ratio of CdS and CdSe nanorods is inversely proportional to R3PE precursor reactivity. Purposely matching or mismatching R3PSR3PSe precursor reactivity leads to CdS1xSex nanorods without or with axial composition gradients, respectively. We expect these observations will lead to scalable and highly predictable bottom-up programmed syntheses of finely heterostructured nanomaterials with well-defined architectures and properties that are tailored for precise applications.

  19. Solar-energy conversion by combined photovoltaic converters with CdTe and CuInSe{sub 2} base layers

    SciTech Connect (OSTI)

    Khrypunov, G. S. Sokol, E. I.; Yakimenko, Yu. I.; Meriuts, A. V.; Ivashuk, A. V.; Shelest, T. N.

    2014-12-15

    The possibility of the combined use of bifacial thin-film solar cells based on CdTe and frontal solar cells with a CuInSe{sub 2} base layer in tandem structures is experimentally confirmed. It is found that, for the use of bifacial solar cells based on cadmium telluride in a tandem structure, the optimal thickness of their base layer should be 1 ?m. The gain in the efficiency of the tandem structure, compared with an individual CuInSe{sub 2}-based solar cell, is 1.8% in the case of series-connected solar cells and 1.3%, for parallel-connected.

  20. Observation of an electron band above the Fermi level in FeTe?.??Se?.?? from in-situ surface doping

    SciTech Connect (OSTI)

    Zhang, P.; Richard, P.; Xu, N.; Xu, Y. -M.; Ma, J.; Qian, T.; Fedorov, A. V.; Denlinger, J. D.; Gu, G. D.; Ding, H.

    2014-10-27

    We used in-situ potassium (K) evaporation to dope the surface of the iron-based superconductor FeTe?.??Se?.??. The systematic study of the bands near the Fermi level confirms that electrons are doped into the system, allowing us to tune the Fermi level of this material and to access otherwise unoccupied electronic states. In particular, we observe an electron band located above the Fermi level before doping that shares similarities with a small three-dimensional pocket observed in the cousin, heavily-electron-doped KFe??xSe? compound.

  1. Wavelengths, transition probabilities, and oscillator strengths for M-shell transitions in Co-, Ni-, Cu-, Zn-, Ga-, Ge-, and Se-like Au ions

    SciTech Connect (OSTI)

    Xu, Min; Jiang, Gang; Deng, Banglin; Bian, Guojie

    2014-11-15

    Wavelengths, transition probabilities, and oscillator strengths have been calculated for M-shell electric dipole transitions in Co-, Ni-, Cu-, Zn-, Ga-, Ge-, and Se-like Au ions. The fully relativistic multiconfiguration Dirac–Fock method, taking quantum electrodynamical effects and the Breit correction into account, was used in the calculations. Calculated energy levels of M-shell excited states for Cu-, Zn-, Ga-, Ge-, and Se-like Au ions from the method were compared with available theoretical and experimental results, and good agreement with them was achieved.

  2. Effect of thermal annealing on structure and optical band gap of Se{sub 66}Te{sub 25}In{sub 9} thin films

    SciTech Connect (OSTI)

    Dwivedi, D. K.; Pathak, H. P.; Shukla, Nitesh; Kumar, Vipin

    2015-05-15

    Thin films of a-Se{sub 66}Te{sub 25}In{sub 9} have been deposited onto a chemically cleaned glass substrate by thermal evaporation technique under vacuum. Glassy nature of the films has been ascertained by X-ray diffraction pattern. The analysis of absorption spectra, measured at normal incidence, in the spectral range 400-1100 nm has been used for the optical characterization of thin films under investigation. The effect of thermal annealing on structure and optical band gap (E{sub g}) of a-Se{sub 66}Te{sub 25}In{sub 9} have been studied.

  3. Synthesis and X-ray diffraction study of Cu{sub 2}ZnSn(S{sub x}Se{sub 1-x}){sub 4} solid solutions

    SciTech Connect (OSTI)

    Sheleg, A. U. Hurtavy, V. G.; Chumak, V. A.

    2015-09-15

    Quaternary compounds Cu{sub 2}ZnSnS{sub 4} and Cu{sub 2}ZnSnSe{sub 4} and solid solutions on their basis have been fabricated by one-temperature synthesis from elementary components: Cu, Zn, Sn, S, and Se. Single crystals of these compounds have been grown by the method of chemical gas-transport reactions from polycrystalline samples. The compositional dependence of the unit-cell parameters of Cu{sub 2}ZnSn(S{sub x}Se{sub 1–x}){sub 4} has been investigated by X-ray diffraction. It is found that parameters a and c linearly decrease with an increase in sulfur concentration in accordance with Vegard’s law. The temperature dependences of parameters a and thermalexpansion coefficients α{sub a} of Cu{sub 2}ZnSnS{sub 4} and Cu{sub 2}ZnSnSe{sub 4} single crystals in the range of 100–300 K are determined.

  4. Interfacial mode coupling as the origin of the enhancement of Tc in FeSe films on SrTiO3

    SciTech Connect (OSTI)

    Lee, J. J.; Schmitt, F. T.; Moore, R. G.; Johnston, S.; Cui, Y. -T.; Li, W.; Yi, M.; Liu, Z. K.; Hashimoto, M.; Zhang, Y.; Lu, D. H.; Devereaux, T. P.; Lee, D. -H.; Shen, Z. -X.; /SIMES, Stanford /SLAC /Stanford U., Geballe Lab.

    2014-11-12

    Films of iron selenide (FeSe) one unit cell thick grown on strontium titanate (SrTiO3 or STO) substrates have recently shown superconducting energy gaps opening at temperatures close to the boiling point of liquid nitrogen (77 K), which is a record for the iron-based superconductors. The gap opening temperature usually sets the superconducting transition temperature Tc, as the gap signals the formation of Cooper pairs, the bound electron states responsible for superconductivity. To understand why Cooper pairs form at such high temperatures, we examine the role of the SrTiO3 substrate. Here we report high-resolution angle-resolved photoemission spectroscopy results that reveal an unexpected characteristic of the single-unit-cell FeSe/SrTiO3 system: shake-off bands suggesting the presence of bosonic modes, most probably oxygen optical phonons in SrTiO3, which couple to the FeSe electrons with only a small momentum transfer. Such interfacial coupling assists superconductivity in most channels, including those mediated by spin fluctuations. Our calculations suggest that this coupling is responsible for raising the superconducting gap opening temperature in single-unit-cell FeSe/SrTiO3.

  5. Atomic and electronic structures of single-layer FeSe on SrTiO3(001): The role of oxygen deficiency

    SciTech Connect (OSTI)

    Bang, Junhyeok; Li, Zhi; Sun, Y. Y.; Samanta, Amit; Zhang, Y. Y.; Zhang, Wenhao; Wang, Lili; Chen, X.; Ma, Xucun; Xue, Q.-K.; Zhang, S. B.

    2013-06-06

    Using first-principles calculation, we propose an interface structure for single triple-layer FeSe on the SrTiO3(001) surface, a high-Tc superconductor found recently. The key component of this structure is the oxygen deficiency on the top layer of the SrTiO3 substrate, as a result of Se etching used in preparing the high-Tc samples. The O vacancies strongly bind the FeSe triple layer to the substrate giving rise to a (21) reconstruction, as observed by scanning tunneling microscopy. The enhanced binding correlates to the significant increase of Tc observed in experiment. The O vacancies also serve as the source of electron doping, which modifies the Fermi surface of the first FeSe layer by filling the hole pocket near the center of the surface Brillouin zone, as suggested from angle-resolved photoemission spectroscopy measurement.

  6. Atomic and electronic structures of single-layer FeSe on SrTiO3(001): The role of oxygen deficiency

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Bang, Junhyeok; Li, Zhi; Sun, Y. Y.; Samanta, Amit; Zhang, Y. Y.; Zhang, Wenhao; Wang, Lili; Chen, X.; Ma, Xucun; Xue, Q.-K.; et al

    2013-06-06

    Using first-principles calculation, we propose an interface structure for single triple-layer FeSe on the SrTiO3(001) surface, a high-Tc superconductor found recently. The key component of this structure is the oxygen deficiency on the top layer of the SrTiO3 substrate, as a result of Se etching used in preparing the high-Tc samples. The O vacancies strongly bind the FeSe triple layer to the substrate giving rise to a (2×1) reconstruction, as observed by scanning tunneling microscopy. The enhanced binding correlates to the significant increase of Tc observed in experiment. The O vacancies also serve as the source of electron doping, whichmore » modifies the Fermi surface of the first FeSe layer by filling the hole pocket near the center of the surface Brillouin zone, as suggested from angle-resolved photoemission spectroscopy measurement.« less

  7. Plasma-Assisted Coevaporation of S and Se for Wide Band Gap Chalcopyrite Photovoltaics: Phase I Annual Report; December 2001-December 2002

    SciTech Connect (OSTI)

    Repins, I.; Wolden, C.

    2003-01-01

    In this work, ITN Energy Systems (ITN) and lower-tier subcontractor Colorado School of Mines (CSM) explore the replacement of the molecular chalcogen precursors during deposition (e.g., Se2 or H2Se) with more reactive chalcogen monomers or radicals (e.g., Se). Molecular species will be converted to atomic species in a low-pressure inductively coupled plasma. The non-equilibrium environment created by the plasma will allow control over the S/Se ratio in these films. Tasks of the proposed program center on developing and validating monoatomic chalcogen chemistry, tuning of low-pressure monomer chalcogen sources, and evaluating plasma-assisted coevaporation (PACE) for CIGS coevaporation. Likely advantages of deposition by plasma-enhanced coevaporation include: (a)provides potential for lower deposition temperature and/or for better film quality at higher deposition temperature; (b) provide potential for decreased deposition times; (c) provides high material utilization efficiency ({approx}90%) that results in less deposition on other parts of the reactor, leading to lower clean-up and maintenance costs, as well as longer equipment lifetime; (d) high material utilization efficiency also reduces the total operating pressure, which is beneficial for the design and control of metal coevaporation (advantages include minimal metal-vapor beam spread and lower source operating temperatures); (e) enables deposition of wide-bandgap copper indium gallium sulfur-selenide (CIGSS) films with controlled stoichiometry.

  8. Characterization of Damp-Heat Degradation of CuInGaSe2 Solar Cell Components and Devices by (Electrochemical) Impedance Spectroscopy: Preprint

    SciTech Connect (OSTI)

    Pern, F. J. J.; Noufi, R.

    2011-09-01

    This work evaluated the capability of (electrochemical) impedance spectroscopy (IS, or ECIS as used here) to monitor damp heat (DH) stability of contact materials, CuInGaSe2 (CIGS) solar cell components, and devices. Cell characteristics and its variation of the CIGS devices were also examined by the ECIS.

  9. Synthesis, characterization, and anomalous dielectric and conductivity performance of one-dimensional (bdaH)InSe{sub 2} (bda = 1,4-butanediamine)

    SciTech Connect (OSTI)

    Du, Ke-Zhao; Hu, Wan-Biao; Graduate School of the Chinese Academy of Sciences, Beijing 100049 ; Hu, Bing; Guan, Xiang-Feng; Huang, Xiao-Ying

    2011-11-15

    Graphical abstract: Anomalous dielectric and conductivity performance have been observed in the organic-containing indium selenide (bdaH)InSe{sub 2}, which are attributed to the water molecules existing in the crystal boundary rather than phase transition. Highlights: {yields} The title compound is the first example of organic-containing one-dimensional indium selenide. {yields} The anomalous dielectric peak is attributed to water molecules in crystal boundary. {yields} The inorganic and organic components of the title compound are connected via hydrogen bonding to form a supramolecular three-dimensional network. -- Abstract: A new indium selenide, namely (bdaH)InSe{sub 2} (1) (bda = 1,4-butanediamine) has been solvothermally synthesized and structurally characterized. It belongs to the non-centrosymmetric space group Fdd2. Its structure features an infinite one-dimensional anionic chain of [InSe{sub 2}]{sub n}{sup n-} with monoprotonated [bdaH]{sup +} as charge compensating cation. The organic [bdaH]{sup +} cations are joined into a supramolecular one-dimensional chain via N-H...N hydrogen bonding, which further interacts with the inorganic chain via N-H...Se and C-H...Se hydrogen bonding, forming a supramolecular three-dimensional network. Based on such a well-defined structure, the thermal stability, optical, conductivity, and dielectric properties were systematically investigated, showing that dielectric constant, as well as conductivity, had a hump at about 95 {sup o}C, which could be attributed to water molecules in the crystal boundary.

  10. Palladium site ordering and the occurrence of superconductivity in Bi{sub 2}Pd{sub 3}Se{sub 2-x}S{sub x}

    SciTech Connect (OSTI)

    Weihrich, R.; Matar, S.F.; Anusca, I.; Pielnhofer, F.; Peter, P.; Bachhuber, F.; Eyert, V.

    2011-04-15

    The crystallographic and electronic structures of compounds related to parkerite (Bi{sub 2}Ni{sub 3}S{sub 2}) are investigated with respect to the recently reported occurrence (Bi{sub 2}Pd{sub 3}Se{sub 2}) and absence (Bi{sub 2}Pd{sub 3}S{sub 2}) of superconductivity. Similarities and differences of the crystal structures are discussed within the series of solid solutions Bi{sub 2}Pd{sub 3}S{sub 2-x}Se{sub x} from powder and single crystal diffraction data. From crystal structure refinements, the question of different structures and settings of parkerite is discussed. Similar and different 2D and 3D partial Pd-Ch (Ch=S, Se) structures are related to half antiperovskite ordering schemes. To investigate the relation of low dimensional structures and the occurrence of superconductivity, electronic structures are analyzed by scalar-relativistic DFT calculations, including site projected DOS, ECOV and Fermi surfaces. -- Graphical abstract: Structure relations for perovskite type BiPd{sub 3}C, BiPd{sub 3/2}Se and BiPd{sub 3/2}S. Display Omitted Research highlights: {yields} Merging crystallographic and electronic structures studies to understand chalcogenides related to parkerite (Bi{sub 2}Ni{sub 3}S{sub 2}). {yields} Investigation in view of recently reported occurrence (Bi{sub 2}Pd{sub 3}Se{sub 2}) and absence (Bi{sub 2}Pd{sub 3}S{sub 2}) of superconductivity. {yields} Relationship of half perovskites with perovskites.

  11. Low-cost CuInSe{sub 2} submodule development. Final subcontract report, 9 July 1990--31 January 1992

    SciTech Connect (OSTI)

    Basol, B.M.; Kapur, V.K.; Halani, A.; Leidholm, C.

    1992-10-01

    Aim of this project is development and demonstration of processing steps necessary for fabrication of high efficiency CuInSe{sub 2} solar cells and sub-modules by the two-stage technique (also called the selenization method.) During this period, we have optimized the processing parameters of this method and demonstrated CuInSe{sub 2}/CdS/ZnO devices with a 1{endash}4 cm{sup 2} area and up to 12.4% active area efficiency. We have also developed a novel approach for the preparation of Cu/In precursors that improved the stoichiometric and morphological uniformity in these films. We have developed processing steps and tooling for handling up to 1 ft{sup 2} size substrates and as a result of these efforts demonstrated our first monolithically integrated sub-module of 1 ft{sup 2} area. 16 figs, 1 tab, 15 refs.

  12. Measurement of the valence band-offset in a PbSe/ZnO heterojunction by x-ray photoelectron spectroscopy

    SciTech Connect (OSTI)

    Li Lin; Qiu Jijun; Weng Binbin; Yuan Zijian; Shi Zhisheng; Li Xiaomin; Gan Xiaoyan; Sellers, Ian R.

    2012-12-24

    A heterojunction of PbSe/ZnO has been grown by molecular beam epitaxy. X-ray photoelectron spectroscopy was used to directly measure the valence-band offset (VBO) of the heterojunction. The VBO, {Delta}E{sub V}, was determined as 2.51 {+-} 0.05 eV using the Pb 4p{sup 3/2} and Zn 2p{sup 3/2} core levels as a reference. The conduction-band offset, {Delta}E{sub C}, was, therefore, determined to be 0.59 {+-} 0.05 eV based on the above {Delta}E{sub V} value. This analysis indicates that the PbSe/ZnO heterojunction forms a type I (Straddling Gap) heterostructure.

  13. Surface half-metallicity of CrS thin films and perfect spin filtering and spin diode effects of CrS/ZnSe heterostructure

    SciTech Connect (OSTI)

    Gao, G. Y. Yao, K. L.

    2014-11-03

    Recently, ferromagnetic zinc-blende Mn{sub 1−x}Cr{sub x}S thin films (above x = 0.5) were fabricated experimentally on ZnSe substrate, which confirmed the previous theoretical prediction of half-metallic ferromagnetism in zinc-blende CrS. Here, we theoretically reveal that both Cr- and S-terminated (001) surfaces of the CrS thin films retain the half-metallicity. The CrS/ZnSe(001) heterogeneous junction exhibits excellent spin filtering and spin diode effects, which are explained by the calculated band structure and transmission spectra. The perfect spin transport properties indicate the potential applications of half-metallic CrS in spintronic devices. All computational results are obtained by using the density functional theory combined with nonequilibrium Green's function.

  14. Spectral behavior of the optical constants in the visible/near infrared of GeSbSe chalcogenide thin films grown at glancing angle

    SciTech Connect (OSTI)

    Martin-Palma, R. J.; Ryan, Joseph V.; Pantano, C. G.

    2007-04-23

    GeSbSe chalcogenide thin films were deposited using glancing angle deposition onto transparent glass substrates for the determination of the spectral behavior of the optical constants (index of refraction n and extinction coefficient k) in the visible and near infrared ranges (400-2500 nm) as a function of the deposition angle. Computational simulations based on the matrix method were employed to determine the values of the optical constants of the different films from the experimental reflectance and transmittance spectra. A significant dependence of the overall optical behavior on the deposition angle is found. Furthermore, the band gap of the GeSbSe thin films was calculated. The accurate determination of the optical constants of films grown at glancing angle will enable the development of sculptured thin film fiber-optic chemical sensors and biosensors.

  15. Defects in {sup 6}LiInSe{sub 2} neutron detector investigated by photo-induced current transient spectroscopy and photoluminescence

    SciTech Connect (OSTI)

    Cui, Yunlong; Bhattacharya, Pijush; Buliga, Vladimir; Tupitsyn, Eugene; Rowe, Emmanuel; Wiggins, Brenden; Johnstone, Daniel; Stowe, Ashley; Burger, Arnold; Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235

    2013-08-26

    {sup 6}LiInSe{sub 2} is a promising thermal neutron semiconductor detector material. The performance of the detector is affected by the carrier mobility-lifetime products. Therefore, defects that function as carrier recombination centers need to be identified. In this letter, characterization of defect levels in {sup 6}LiInSe{sub 2} by photo-induced current transient spectroscopy (PICTS) and photoluminescence is reported. PICTS measurements revealed electron-related defects located at 0.22, 0.36, and 0.55 eV and hole-related defects at 0.19, 0.30, and 0.73 eV. Free exciton and donor-acceptor pairs (DAP) emissions were observed. The PICTS defect level values are consistent with those extracted from DAP transitions.

  16. Density of electronic states and dispersion of optical functions of defect chalcopyrite CdGa{sub 2}X{sub 4} (X = S, Se): DFT study

    SciTech Connect (OSTI)

    Reshak, A.H.; Khan, Saleem Ayaz

    2013-11-15

    Graphical abstract: - Highlights: FPLAPW method is used for calculating the electronic and optical properties of CdGa{sub 2}X{sub 4}. Electronic and optical properties were calculated using LDA, GGA, EVGGA and mBJ. Band gap conformed that CdGa{sub 2}X{sub 4} are semiconductors fit for UV and visible light. The ECD shows that change in the bond length and bond nature affect the band gap. The dielectric tensor components and its derivatives show considerable anisotropy. - Abstract: A density functional theory (DFT) based on full potential linear augmented plane wave (FPLAPW) was used for calculating the electronic structure, charge density and optical properties of CdGa{sub 2}X{sub 4} (X = S, Se) compounds. Local density approximation (LDA), generalized gradient approximation (GGA), Engle Vasko generalized gradient approximation (EVGGA) and recently modified BeckeJohnson (mBJ) were applied to calculate the band structure, total and partial density of states. The investigation of band structures and density of states of CdGa{sub 2}X{sub 4} (X = S, Se) elucidate that mBJ potential show close agreement to the experimental results. The mBJ potential was selected for further explanation of optical properties of CdGa{sub 2}X{sub 4} (X = S, Se). The study of electronic charge density contours shows that change in the bond lengths and bond nature affect the band gap of the compounds. The two non-zero dielectric tensor components and its derivatives show considerable anisotropy between the perpendicular and parallel components. The present work provide accurate information about the combination (hybridization) of orbital, formation of bands and dispersion of non-zero tensor components of CdGa{sub 2}X{sub 4} (X = S, Se)

  17. Plasma-Assisted Coevaporation of S and Se for Wide Band Gap Chalcopyrite Photovoltaics: Phase II Annual Report, December 2002--December 2003

    SciTech Connect (OSTI)

    Repins, I.; Wolden, C.

    2004-01-01

    In this work, ITN Energy Systems (ITN) and lower-tier subcontractor Colorado School of Mines (CSM) explore the replacement of the molecular chalcogen precursors during deposition (e.g., Se2 or H2Se) with more reactive chalcogen monomers or radicals (e.g., Se). Molecular species are converted to atomic species in a low-pressure inductively coupled plasma (ICP). Tasks of the proposed program center on development and validation of monatomic chalcogen chemistry, tuning of low-pressure monomer chalcogen sources, and evaluation of plasma-assisted co-evaporation (PACE) for CIGS co-evaporation. Likely advantages of deposition by plasma-enhanced co-evaporation include: (1) Providing potential for lower deposition temperature and/or for better film quality at higher deposition temperature. (2) Providing potential for decreased deposition times. (3) Providing high material utilization efficiency ({approx}90%) that results in less deposition on other parts of the reactor, leading to lower clean up and maintenance costs, as well as longer equipment lifetime. High material utilization efficiency also reduces the total operating pressure, which is beneficial for the design and control of metal co-evaporation. Advantages include minimal metal-vapor beam spread and lower source operating temperatures. (4) Enabling deposition of wide-bandgap copper indium gallium disulfur-selenide (CIGSS) films with controlled stoichiometry. University researchers at CSM are developing and testing the fundamental chemistry and engineering principles. Industrial researchers at ITN are adapting PACE technology to CIGSS co-evaporation and validating PACE process for fabrication of thin-film photovoltaics. In2Se3 films, which are used as precursor layers in high-efficiency CIGS depositions, were used this year as the first test case for examining the advantages of PACE listed above. Gradually, the investigation is being extended to the complete high-efficiency three-stage co-evaporation process.

  18. EVIDENCE FROM THE VERY LONG BASELINE ARRAY THAT J1502SE/SW ARE DOUBLE HOTSPOTS, NOT A SUPERMASSIVE BINARY BLACK HOLE

    SciTech Connect (OSTI)

    Wrobel, J. M.; Walker, R. C.; Fu, H. E-mail: cwalker@nrao.edu

    2014-09-01

    SDSS J150243.09+111557.3 is a merging system at z = 0.39 that hosts two confirmed active galactic nuclei (AGNs), one unobscured and one dust-obscured, offset by several kiloparsecs. Deane et al. recently reported evidence from the European VLBI Network (EVN) that the dust-obscured AGN exhibits two flat-spectrum radio sources, J1502SE/SW, offset by 26 mas (140 pc), with each source being energized by its own supermassive black hole (BH). This intriguing interpretation of a close binary BH was reached after ruling out a double-hotspot scenario, wherein both hotspots are energized by a single, central BH, a configuration occurring in the well-studied compact symmetric objects. When observed with sufficient sensitivity and resolution, an object with double hotspots should have an edge-brightened structure. We report evidence from the Very Long Baseline Array (VLBA) for just such a structure in an image of the obscured AGN with higher sensitivity and resolution than the EVN images. We thus conclude that a double-hotspot scenario should be reconsidered as a viable interpretation for J1502SE/SW, and suggest further VLBA tests of that scenario. A double-hotspot scenario could have broad implications for feedback in obscured AGNs. We also report a VLBA detection of high-brightness-temperature emission from the unobscured AGN that is offset several kiloparsecs from J1502SE/SW.

  19. Novel thin-film CuInSe{sub 2} fabrication. Annual subcontract report, 1 March 1990--30 April 1991

    SciTech Connect (OSTI)

    Mooney, G.D.; Hermann, A.M.

    1992-03-01

    This report describes research in Rapid Thermal Processing (RTP), a process that allows the formation of CuInSe{sub 2} without the use of H{sub 2}Se. RTP is a well-established method of rapidly achieving temperatures necessary to melt and recrystallize materials such as Si and and silicides. RTP processes can rapidly and uniformly heat large surface areas to hundreds of degrees Celsius. RTP is the most promising method of rapid recrystallization studied to date, being readily scalable from the research to the production level. The approach to the experiment was divided into two sections: (1) fabricating the precursor film and (2) processing the precursor film. The objective of the first phase of the work was to fabricate the thin films by RTP, then fully characterize them, to demonstrate the viability of the process as a method by which to make device-quality CuInSe{sub 2}. The second phase was to demonstrate that material made by this method could be used to make an active photovoltaic device. 24 refs.

  20. Density Profiles in Sputtered Molybdenum Thin Films and Their Effects on Sodium Diffusion in Cu(InxGa1-x)Se2 Photovoltaics

    SciTech Connect (OSTI)

    Li, J.; Glynn, S.; Mansfield, L.; Young, M.; Yan, Y.; Contreras, M.; Noufi, R.; Terry Jr., F. L.; Levi, D.

    2011-01-01

    Molybdenum (Mo) thin films were sputtered onto soda lime glass (SLG) substrates. The main variable in the deposition parameters, the argon (Ar) pressure p{sub Ar}, was varied in the range of 6-20 mTorr. Ex situ spectroscopic ellipsometry (SE) was performed to find out that the dielectric functions {var_epsilon} of the Mo films were strongly dependent on p{sub Ar}, indicating a consistent and significant decrease in the Mo film density {rho}{sub Mo} with increasing p{sub Ar}. This trend was confirmed by high-angle-annular-dark-field scanning transmission electron microscopy. {var_epsilon} of Mo was then found to be correlated with secondary ion mass spectroscopy profiles of Sodium (Na) in the Cu(In{sub x}Ga{sub 1-x})Se{sub 2} (CIGS) layer grown on top of Mo/SLG. Therefore, in situ optical diagnostics can be applied for process monitoring and optimization in the deposition of Mo for CIGS solar cells. Such capability is demonstrated with simulated optical transmission and reflectance of variously polarized incident light, using {var_epsilon} deduced from SE.

  1. Zinc concentration effect on structural, optical and electrical properties of Cd{sub 1?x}Zn{sub x}Se thin films

    SciTech Connect (OSTI)

    Akaltun, Yunus; Y?ld?r?m, M. Ali; Ate?, Aytun; Y?ld?r?m, Muhammet

    2012-11-15

    Highlights: ? Cd{sub 1?x}Zn{sub x}Se thin films were deposited using SILAR method. ? The electron effective mass, refractive index, dielectric constant values were calculated by using the energy bandgap values as a function of the zinc concentration (x). ? The resistivity and activation energy changed as a function of the zinc concentration (x). -- Abstract: Cd{sub 1?x}Zn{sub x}Se thin films with different compositions (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) were deposited on glass substrates using successive ionic layer adsorption and reaction (SILAR) method at room temperature and ambient pressure. The zinc concentration (x) effect on the structural, morphological, optical and electrical properties of Cd{sub 1?x}Zn{sub x}Se thin films were investigated. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies showed that all the films exhibited polycrystalline nature and were covered well on glass substrates. The energy dispersive X-ray (EDAX) analysis confirmed nearly stoichiometric deposition of the films. The energy bandgap values were changed from 1.99 to 2.82 eV depending on the zinc concentration. Bowing parameter was calculated as 0.08 eV. The electron effective mass (m{sub e}*/m{sub o}), refractive index (n), optical static and high frequency dielectric constants (?{sub o}, ?{sub ?}) values were calculated by using the energy bandgap values as a function of the zinc concentration. The resistivity values of the films changed between 10{sup 5} and 10{sup 7} ? cm with increasing zinc concentration at room temperature.

  2. CuAl{sub x}Ga{sub 1?x}Se{sub 2} thin films for photovoltaic applications: Optical and compositional analysis

    SciTech Connect (OSTI)

    Lpez-Garca, J.; Maffiotte, C.; Guilln, C.; Herrero, J.

    2013-03-15

    Highlights: ? Wide band gap CAGS thin films have been obtained by selenization of evaporated metallic precursors. ? Direct nonlinear dependence of the band gap energy with the Al/(Al + Ga) ratio is found. ? The bowing parameter decreases when the CAGS film thickness increases. ? The Cu at% remains constant in depth, together with some Al, Ga and Se gradients. ? Surface is strongly oxidized but the oxidation is relatively low in bulk. - Abstract: Wide-band gap chalcopyrite semiconductors have a great interest due to their potential application in multi-junction thin film solar cells or as window layers. Polycrystalline CuAl{sub x}Ga{sub 1?x}Se{sub 2} (CAGS) thin films have been prepared by selenization of evaporated metallic precursor layers on bare and Mo-coated soda lime glass substrates. The optical properties of CAGS films of 2 thicknesses have been analyzed by spectrophotometry in the visible-infrared (VIS-IR) and the compositional characteristics have been studied by energy dispersive analysis of X-rays (EDAX) and X-ray photoelectron spectroscopy (XPS). The optical transmission increases and the band gap energy shifts toward higher values as the Al content increases, which indicates the partial substitution of Ga by Al. The dependence of the band gap with the composition has resulted to be nonlinear and a bowing parameter of b = 0.62 and b = 0.54 for 0.6 ?m and 1.1 ?m-CAGS samples, respectively, has been obtained. XPS data have shown an Al, Ga and Se composition gradient in depth and a surface strongly oxidized. However, XPS reveals that the Cu composition remains constant in depth and the oxidation is relatively low in bulk increasing slightly in the interface with Mo/SLG. Moreover, samples with high Al content reveal a higher contribution of CuO in depth.

  3. Preparation of water soluble L-arginine capped CdSe/ZnS QDs and their interaction with synthetic DNA: Picosecond-resolved FRET study

    SciTech Connect (OSTI)

    Giri, Anupam; Goswami, Nirmal; Lemmens, Peter; Pal, Samir Kumar

    2012-08-15

    Graphical abstract: Frster resonance energy transfer (FRET) studies on the interaction of water soluble arginine-capped CdSe/ZnS QDs with ethidium bromide (EB) labeled synthetic dodecamer DNA. Highlights: ? We have solubilized CdSe/ZnS QD in water replacing their TOPO ligand by L-arginine. ? We have studied arginine@QDDNA interaction using FRET technique. ? Arginine@QDs act as energy donor and ethidium bromide-DNA acts as energy acceptor. ? We have applied a kinetic model to understand the kinetics of energy transfer. ? Circular dichroism studies revealed negligible perturbation in the DNA B-form in the arg@QD-DNA complex. -- Abstract: We have exchanged TOPO (trioctylphosphine oxide) ligand of CdSe/ZnS core/shell quantum dots (QDs) with an amino acid L-arginine (Arg) at the toluene/water interface and eventually rendered the QDs from toluene to aqueous phase. We have studied the interaction of the water soluble Arg-capped QDs (energy donor) with ethidium (EB) labeled synthetic dodecamer DNA (energy acceptor) using picoseconds resolved Frster resonance energy transfer (FRET) technique. Furthermore, we have applied a model developed by M. Tachiya to understand the kinetics of energy transfer and the distribution of acceptor (EB-DNA) molecules around the donor QDs. Circular dichroism (CD) studies revealed a negligible perturbation in the native B-form structure of the DNA upon interaction with Arg-capped QDs. The melting and the rehybridization pathways of the DNA attached to the QDs have been monitored by the CD which reveals hydrogen bonding is the associative mechanism for interaction between Arg-capped QDs and DNA.

  4. Charge trapping and de-trapping in isolated CdSe/ZnS nanocrystals under an external electric field: Indirect evidence for a permanent dipole moment

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Zang, Huidong; Cristea, Mihail; Shen, Xuan; Liu, Mingzhao; Camino, Fernando; Cotlet, Mircea

    2015-08-05

    Single nanoparticle studies of charge trapping and de-trapping in core/shell CdSe/ZnS nanocrystals incorporated into an insulating matrix and subjected to an external electric field demonstrate the ability to reversibly modulate the exciton dynamics and photoluminescence blinking while providing indirect evidence for the existence of a permanent ground state dipole moment in such nanocrystals. A model assuming the presence of energetically deep charge traps physically aligned along the direction of the permanent dipole is proposed in order to explain the dynamics of nanocrystal blinking in the presence of a permanent dipole moment.

  5. TiO2 Nanotubes with a ZnO Thin Energy Barrier for Improved Current Efficiency of CdSe Quantum-Dot-Sensitized Solar Cells

    SciTech Connect (OSTI)

    Lee, W.; Kang, S. H.; Kim, J. Y.; Kolekar, G. B.; Sung, Y. E.; Han, S. H.

    2009-01-01

    This paper reports the formation of a thin ZnO energy barrier between a CdSe quantum dot (Q dots) sensitizer and TiO{sub 2} nanotubes (TONTs) for improved current efficiency of Q dot-sensitized solar cells. The formation of a ZnO barrier between TONTs and the Q dot sensitizer increased the short-circuit current under illumination and also reduced the dark current in a dark environment. The power conversion efficiency of Q dot-sensitized TONT solar cells increased by 25.9% in the presence of the ZnO thin layer due to improved charge-collecting efficiency and reduced recombination.

  6. Quantum-dot light-emitting diodes utilizing CdSe/ZnS nanocrystals embedded in TiO{sub 2} thin film

    SciTech Connect (OSTI)

    Kang, Seung-Hee; Kumar, Ch. Kiran; Kim, Eui-Tae; Lee, Zonghoon; Kim, Kyung-Hyun; Huh, Chul

    2008-11-10

    Quantum-dot (QD) light-emitting diodes (LEDs) are demonstrated on Si wafers by embedding core-shell CdSe/ZnS nanocrystals in TiO{sub 2} thin films via plasma-enhanced metallorganic chemical vapor deposition. The n-TiO{sub 2}/QDs/p-Si LED devices show typical p-n diode current-voltage and efficient electroluminescence characteristics, which are critically affected by the removal of QD surface ligands. The TiO{sub 2}/QDs/Si system we presented can offer promising Si-based optoelectronic and electronic device applications utilizing numerous nanocrystals synthesized by colloidal solution chemistry.

  7. Fluorescent CdSe/ZnS nanocrystal-peptide conjugates for long-term, nontoxic imaging and nuclear targeting in living cells

    SciTech Connect (OSTI)

    Chen, Fanqing; Gerion, Daniele

    2004-06-14

    One of the biggest challenges in cell biology is the imaging of living cells. For this purpose, the most commonly used visualization tool is fluorescent markers. However, conventional labels, such as organic fluorescent dyes or green fluorescent proteins (GFP), lack the photostability to allow the tracking of cellular events that happen over minutes to days. In addition, they are either toxic to cells (dyes), or difficult to construct and manipulate (GFP). We report here the use of a new class of fluorescent labels, silanized CdSe/ZnS nanocrystal-peptide conjugates, for imaging the nuclei of living cells. CdSe/ZnS nanocrystals, or so called quantum dots (qdots), are extremely photostable, and have been used extensively in cellular imaging of fixed cells. However, most of the studies about living cells so far have been concerned only with particle entry into the cytoplasm or the localization of receptors on the cell membrane. Specific targeting of qdots to the nucleus of living cells ha s not been reported in previous studies, due to the lack of a targeting mechanism and proper particle size. Here we demonstrate for the first time the construction of a CdSe/ZnS nanocrystal-peptide conjugate that carries the SV40 large T antigen nuclear localization signal (NLS), and the transfection of the complex into living cells. By a novel adaptation of commonly used cell transfection techniques for qdots, we were able to introduce and retain the NLS-qdots conjugate in living cells for up to a week without detectable negative cellular effects. Moreover, we can visualize the movement of the CdSe/ZnS nanocrystal-peptide conjugates from cytoplasm to the nucleus, and the accumulation of the complex in the cell nucleus, over a long observation time period. This report opens the door for using qdots to visualize long-term biological events that happen in the cell nucleus, and provides a new nontoxic, long-term imaging platform for cell nuclear processes.

  8. Midea: Amended Noncompliance Determination (2010-SE-0110, 2012-SE-1402)

    Broader source: Energy.gov [DOE]

    DOE issued an Amended Notice of Noncompliance Determination to Midea America Corp., Hefei Hualing Co., Ltd., and China Refrigeration Industry Co., Ltd. finding that basic model HD-146F, a refrigerator-freezer, and basic model HS-390C, a freezer, do not comport with the energy conservation standards.

  9. Effect of dietary fat on plasma glutathione peroxidase levels and intestinal absorption of /sup 75/Se-labeled sodium selenite in chicks

    SciTech Connect (OSTI)

    Mutanen, M.L.; Mykkaenen, H.M.

    1984-05-01

    The effect of dietary fat on the availability of selenium was investigated in chicks fed either 4 or 20% butter, olive oil, rape oil, corn oil or sunflower oil in the diet for 3 weeks after hatching. Plasma glutathione peroxidase (GSH-Px) activity was used as an indicator of the body selenium status. In addition, the intestinal absorption of sodium selenite (/sup 75/Se-labeled) was determined by using both the in vivo ligated loop procedure and oral administration of the isotope. The plasma GSH-Px levels increased with increasing proportion of the polyunsaturated fatty acids in the diet. Increasing the amount of fat from 4 to 20% significantly enhanced the GSH-Px activity in the groups receiving butter or olive oil, but had no effect in animals fed the unsaturated fats. The absorption of (/sup 75/Se)selenite from the ligated duodenal loops tended to be reduced in chicks fed corn oil or sunflower oil as compared to the animals receiving butter in their diet. On the other hand, the type of dietary fat did not appear to affect the absorption of the orally administered selenite. The present study demonstrates that the type of dietary fat can affect the plasma GSH-Px levels in chicks without altering the intestinal absorption of selenite. However, the results on the absorption of the intraduodenally injected sodium selenite suggest that dietary fat plays some role in the intestinal transport of selenium.

  10. Fabrication and testing of diamond-machined gratings in ZnSe, GaP, and bismuth germanate for the near infrared and visible

    SciTech Connect (OSTI)

    Kuzmenko, P J; Little, S L; Ikeda, Y; Kobayashi, N

    2008-06-22

    High quality immersion gratings for infrared applications have been demonstrated in silicon and germanium. To extend this technology to shorter wavelengths other materials must be investigated. We selected three materials, zinc selenide, gallium phosphide and bismuth germanate (Bi{sub 4}Ge{sub 3}O{sub 12}), based on high refractive index, good visible transmission and commercial availability in useful sizes. Crystal samples were diamond turned on an ultra-precision lathe to identify preferred cutting directions. Using this information we diamond-flycut test gratings over a range of feed rates to determine the optimal cutting conditions. For both ZnSe and GaP good surface quality was achieved at feed rates up to 1.0 cm/minute using a special compound angle diamond tool with negative rake angles on both cutting surfaces. The surface roughness of the groove facets was about 4 nm. A Zygo interferometer measured grating wavefront errors in reflection. For the ZnSe the RMS error was < {lambda}/20 at 633nm. More extensive testing was performed with a HeNe laser source and a cooled CCD camera. These measurements demonstrated high relative diffraction efficiency (> 80%), low random groove error (2.0 nm rms), and Rowland ghost intensities at < 0.1%. Preliminary tests on bismuth germanate show high tool wear.

  11. Thermal Aging Study of a Dow Corning SE 1700 Porous Structure Made by Direct Ink Writing: 1-Year Results and Long-Term Predictions

    SciTech Connect (OSTI)

    Small, Ward; Pearson, Mark A.; Maiti, Amitesh; Metz, Thomas R.; Duoss, Eric B.; Wilson, Thomas S.

    2015-11-13

    Dow Corning SE 1700 (reinforced polydimethylsiloxane) porous structures were made by direct ink writing (DIW). The specimens (~50% porosity) were subjected to various compressive strains (15, 30, 45%) and temperatures (room temperature, 35, 50, 70°C) in a nitrogen atmosphere (active purge) for 1 year. Compression set and load retention of the aged specimens were measured periodically during the study. Compression set increased with strain and temperature. After 1 year, specimens aged at room temperature, 35, and 50°C showed ~10% compression set (relative to the applied compressive deflection), while those aged at 70°C showed 20-40%. Due to the increasing compression set, load retention decreased with temperature, ranging from ~90% at room temperature to ~60-80% at 70°C. Long-term compression set and load retention at room temperature were predicted by applying time-temperature superposition (TTS). The predictions show compression set relative to the compressive deflection will be ~10-15% with ~70-90% load retention after 50 years at 15-45% strain, suggesting the material will continue to be mechanically functional. Comparison of the results to previously acquired data for cellular (M97*, M9760, M9763) and RTV (S5370) silicone foams suggests that the SE 1700 DIW porous specimens are on par with, or outperform, the legacy foams.

  12. Optimum composition of a Bi{sub 2}Te{sub 3-x}Se{sub x} alloy for the n-type leg of a thermoelectric generator

    SciTech Connect (OSTI)

    Prokofieva, L. V. Pshenay-Severin, D. A.; Konstantinov, P. P.; Shabaldin, A. A.

    2009-08-15

    The reliability of determination of model parameters for the Bi{sub 2}Te{sub 3-x}Se{sub x} alloys is improved by extending the concentration and temperature ranges in experimental studies and, correspondingly, in calculations of kinetic coefficients based on the two-band model of the electronic spectrum. The obtained results served as a motivation for a study of the thermoelectric figure of merit for the above-mentioned alloys with x = 0.3, 0.45, and 0.6 and with the electron concentration varied in the range (1-50) x 10{sup 18} cm{sup -3} at temperatures 300-550 K. Comparison of the results showed that the highest efficiency is exhibited by the Bi{sub 2}Te{sub 2.7}Se{sub 0.3} alloy with the absolute value of the thermoelectric power of about 165 {mu}VK{sup -1} at 300 K, and the dimensionless efficiency is equal to 1.2 at 410 K. An appreciable decrease in thermal conductivity in alloys with x = 0.6 at 410 K is related to a larger band gap and could beneficially affect the figure of merit. However, the magnitude of this effect is found to be too small to compensate a decrease in electrical conductivity due to a large fraction of heavy electrons in the concentration and to a high content of selenium.

  13. Magnetic properties of Ce{sup 3+} in Pb{sub 1{minus}x}Ce{sub x}Se: Kondo and crystal-field effect

    SciTech Connect (OSTI)

    Gratens, X.; Charar, S.; Averous, M.; Isber, S.; Deportes, J.; Golacki, Z.

    1997-10-01

    Electron paramagnetic resonance (EPR) experiments were performed on a Pb{sub 1{minus}x}Ce{sub x}Se crystal at liquid-helium temperatures and show very clearly that the doublet {Gamma}{sub 7} is the ground state for cerium ions. The cubic symmetry is shown and the effective Land{acute e} factor for the Ce{sup 3+} is determined to be 1.354{plus_minus}0.003. An orbital reduction factor is introduced to explain the g experimental value. High-field magnetization results are in good agreement with the EPR results. The nominal Ce composition in PbSe deduced from saturation of the magnetization, x=0.0405{plus_minus}0.0003, is very closed to the value determined by microprobe analysis (x=0.04). At 1.5 K, an antiferromagnetic interaction between the nearest-neighbor cerium atoms is found, J{sub ex}/k{sub B}={minus}0.715thinspK. The low-field magnetic-susceptibility results show that the magnetic moment of cerium impurities is strongly temperature dependent, explained by the presence of the crystal-field effect and the Kondo effect. {copyright} {ital 1997} {ital The American Physical Society}

  14. Visible Light Photoreduction of CO2 Using CdSe/Pt/TiO2 Heterostructured Catalysts

    SciTech Connect (OSTI)

    Wang, Congjun; Thompson, Robert L.; Baltrus, John; Matranga, Christopher

    2010-01-07

    A series of CdSe quantum dot (QD)-sensitized TiO2 heterostructures have been synthesized, characterized, and tested for the photocatalytic reduction of CO2 in the presence of H2O. Our results show that these heterostructuredmaterials are capable of catalyzing the photoreduction of CO2 using visible light illumination (? > 420 nm) only. The effect of removing surfactant caps from the CdSe QDs by annealing and using a hydrazine chemical treatment have also been investigated. The photocatalytic reduction process is followed using infrared spectroscopy to probe the gas-phase reactants and gas chromatography to detect the products. Gas chromatographic analysis shows that the primary reaction product is CH4, with CH3OH, H2, and CO observed as secondary products. Typical yields of the gas-phase products after visible light illumination (? > 420 nm) were 48 ppm g-1 h-1 of CH4, 3.3 ppm g-1 h-1 of CH3OH (vapor), and trace amounts of CO and H2.

  15. Synchrotron X-ray 2D and 3D Elemental Imaging of CdSe/ZnS Quantum dot Nanoparticles in Daphnia Magna

    SciTech Connect (OSTI)

    Jackson, B.; Pace, H; Lanzirotti, A; Smith, R; Ranville, J

    2009-01-01

    The potential toxicity of nanoparticles to aquatic organisms is of interest given that increased commercialization will inevitably lead to some instances of inadvertent environmental exposures. Cadmium selenide quantum dots (QDs) capped with zinc sulfide are used in the semiconductor industry and in cellular imaging. Their small size (<10 nm) suggests that they may be readily assimilated by exposed organisms. We exposed Daphnia magna to both red and green QDs and used synchrotron X-ray fluorescence to study the distribution of Zn and Se in the organism over a time period of 36 h. The QDs appeared to be confined to the gut, and there was no evidence of further assimilation into the organism. Zinc and Se fluorescence signals were highly correlated, suggesting that the QDs had not dissolved to any extent. There was no apparent difference between red or green QDs, i.e., there was no effect of QD size. 3D tomography confirmed that the QDs were exclusively in the gut area of the organism. It is possible that the QDs aggregated and were therefore too large to cross the gut wall.

  16. Photophysics of (CdSe)ZnS Colloidal Quantum Dots in an Aqueous Environment Stabilized with Amino Acids and Genetically-Modified Proteins

    SciTech Connect (OSTI)

    Ai, X.; Xu, Q.; Jones, M.; Song, Q.; Ding, S.-Y.; Ellingson, R. J.; Himmel, M.; Rumbles, G.

    2007-01-01

    Using a combination of two amino acids, histidine and N-acetyl-cysteine, to replace the original organic capping groups of (CdSe)ZnS quantum dots, water-soluble and highly luminescent (CdSe)ZnS quantum dots have been successfully prepared at pH 8. Characterization by steady-state and time-resolved photoluminescence spectroscopy, and transient absorption spectroscopy, demonstrate that the electronic properties of these quantum dots exceed those of the original as-synthesized samples dissolved in a more-conventional organic solvent. Furthermore, these amino acid-stabilized quantum dots have been assembled onto a cellulose substrate via cellulose binding proteins that specifically bind to cellulose and was genetically engineered to harbor dual hexahistidine tags at the N- and C-termini to confer binding with the zinc(II) on the quantum dot surface. The spectroscopic measurements show that the protein-bound quantum dots continue to retain their desirable electronic properties when bound on the substrate. Meanwhile, the specific and very selective binding properties of the proteins have remained effective. (1)Select optimal greenhouse gas (GHG) and petroleum reduction strategies for each fleet location, (2)Meet or exceed Federal fleet GHG and petroleum reduction requirements outlined in the Guidance, (3)Acquire vehicles to support these strategies while minimizing fleet size and vehicle miles traveled (VMT), (4)Refine strategies based on agency performance.

  17. Electronic structure of antifluorite Cu{sub 2}X (X = S, Se, Te) within the modified Becke-Johnson potential plus an on-site Coulomb U

    SciTech Connect (OSTI)

    Zhang, Yubo; Wang, Youwei; Xi, Lili; Qiu, Ruihao; Shi, Xun; Zhang, Peihong E-mail: pzhang3@buffalo.edu; Beijing Computational Science Research Center, Beijing 100084 ; Zhang, Wenqing E-mail: pzhang3@buffalo.edu; School of Chemistry and Chemical Engineering, and Sate Key Laboratory of Coordination Chemistry, Nanjing University, Jiangsu 210093

    2014-02-21

    The traditional photon absorbers Cu{sub 2?x}X (X = S, Se, and Te) have regained significant research attention in the search of earth-abundant photovoltaic materials. These moderate- and narrow-gap materials have also been shown to exhibit excellent thermoelectric properties recently. However, semimetallic band structures with inverted band orderings are predicted for antifluorite structure Cu{sub 2}X using density functional theory with the local density approximation or the generalized gradient approximation. We find that semiconducting band structures and normal band orderings can be obtained using the modified Becke-Johnson potential plus an on-site Coulomb U (the mBJ+U approach), which is consistent with our earlier finding for diamond-like Cu-based multinary semiconductors [Y. Zhang, J. Zhang, W. Gao, T. A. Abtew, Y. Wang, P. Zhang, and W. Zhang, J. Chem. Phys. 139, 184706 (2013)]. The trend of the chemical bonding of Cu{sub 2}X is analyzed, which shows that the positions of the valence band maximum and conduction band minimum are strongly affected by the inter-site pd and intra-site sp hybridizations, respectively. The calculated gaps of Cu{sub 2}S and Cu{sub 2}Se still seem to be underestimated compared with experimental results. We also discuss the effects of different structural phases and Cu disordering and deficiency on the bandgaps of these materials.

  18. Publications-PHaSe-EFRC

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Publications Publications of 2014 Publications of 2013 Publications of 2012 Publications of 2011 Publications of 2010 Publications of 2009 2015 Last update 30 April 2015. Jung, Jae Woong; Liu, Feng;Russel, Thomas P.; Ho Jo, Won "Anthracene-Based Medium Bandgap Conjugated Polymers for High Performance Polymer Solar Cells Exceeding 8% PCE Without Additive and Annealing Process", Adv. Energy, Mater., [early view], (2015). DOI: 10.1002/aenm.201500065 Karak, Supravat; Page, Zachariah A;

  19. Research-PHaSe-EFRC

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Research This webpage is provided for legacy archive purposes only, as of 30 April 2015. However, this research continues in the groups of many UMass Amherst groups listed on this site. Organic photovoltaics (OPVs) hold the promise of delivering efficient low-cost, lightweight, flexible, and portable solar cells. Driven by this promise, the last decade has witnessed an explosive growth in this area resulting in dramatic increases in power conversion efficiencies (PCEs). Yet the challenge framed

  20. Whirlpool: Order (2013-SE-1420)

    Broader source: Energy.gov [DOE]

    DOE ordered Whirlpool Corporation to pay a $5,329,800 civil penalty after finding Whirlpool had manufactured and distributed in commerce in the U.S. at least 26,649 units of basic model 8TAR81 noncompliant refrigerator-freezer.

  1. Teddico: Order (2012-SE-5409)

    Broader source: Energy.gov [DOE]

    DOE ordered The Electrical Design, Development and Implementation Company d/b/a Teddico to pay a $18,994 civil penalty after finding Teddico had manufactured and distributed in commerce in the U.S. 218 units of a variety of noncompliant metal halide lamp fixtures basic models.

  2. Midea: Order (2013-SE-1505)

    Broader source: Energy.gov [DOE]

    DOE ordered GD Midea Air-Conditioning Equipment Co. Ltd. to pay a $416,800 civil penalty after finding Midea had manufactured and distributed in commerce in the U.S. atleast 14,968 units of basic model MWJ1-08ERN1-BI8, a noncompliant room air conditioner.

  3. Bigwall: Order (2014-SE-15006)

    Broader source: Energy.gov [DOE]

    DOE ordered Bigwall Enterprises, Inc. to abide by the terms of the Notice of Noncompliance Determination, issued on February 11, 2014, after finding Bigwall Enterprises, Inc. had privately labeled and distributed in commerce in the U.S. at least 600 units of PerfectAire brand room air conditioner model PACH8000.

  4. AHT: Order (2015-SE-42031)

    Broader source: Energy.gov [DOE]

    DOE ordered AHT Cooling Systems, Inc. to pay a $179,040 civil penalty after finding AHT had manufactured and distributed in commerce in the U.S. at least 1,032 units of commercial refrigeration equipment model RIO S 68 L F, a noncompliant product.

  5. Perlick: Order (2011-SE-1401)

    Broader source: Energy.gov [DOE]

    DOE ordered Perlick Corporation to pay a $400 civil penalty after finding Perlick had manufactured and distributed in commerce in the U.S. at least two noncompliant model HP48RO, electric refrigerators.

  6. Hicon: Order (2013-SE-1426)

    Broader source: Energy.gov [DOE]

    DOE ordered Ningbo Hicon International Industry Company, Ltd. to pay a $1,912,714 civil penalty after finding Hicon had manufactured and distributed in commerce in the U.S. 115,126 units of basic model BD-200, a noncompliant freezer.

  7. Cooper: Order (2012-SE-4701)

    Broader source: Energy.gov [DOE]

    DOE ordered Cooper Power Systems, LLC to abide by the Compromise Agreement, which waived the civil penalty after finding Cooper had inadvertently distributed in commerce in the U.S. three models (total of five units) of distribution transformers. Cooper agrees to abide by the terms of a Notice of Noncompliance Determination to be issued pursuant to 10 C.F.R. § 429.114.

  8. Perlick: Order (2013-SE-14002)

    Broader source: Energy.gov [DOE]

    DOE ordered Perlick Corporation to pay a $60,725 civil penalty after finding Perlick had manufactured and distributed in commerce in the U.S. 347 units of basic model HP48RR, a noncompliant refrigerator.

  9. Target: Subpoena (2010-SE-2001)

    Broader source: Energy.gov [DOE]

    DOE issued a Subpoena for Information and Production of Documents to Target Corporation requesting information regarding the compliance of various torchieres Target has distributed in commerce in the U.S.

  10. Philips: Order (2012-SE-2605)

    Broader source: Energy.gov [DOE]

    DOE ordered Philips Lighting Electronics N. A. to pay a $82,478 civil penalty after finding Philips had manufactured and distributed in commerce in the U.S. 7,498 units of basic model VEL-1S40-SC, noncompliant fluorescent lamp ballasts.

  11. Adesso: Subpoena (2010-SE-2002)

    Broader source: Energy.gov [DOE]

    DOE issued a Subpoena for Information and Production of Documents to Adesso, Inc., requesting information regarding the compliance of various torchieres Adesso has distributed in commerce in the U.S.

  12. Simkar: Order (2012-SE-5408)

    Broader source: Energy.gov [DOE]

    DOE ordered Simkar Corporation to pay a $28,193 civil penalty after finding Simkar had manufactured and distributed in commerce in the U.S. 326 units of a variety of noncompliant metal halide lamp fixtures basic models.

  13. About-PHaSe-EFRC

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    of faculty from four different departments at the University - Chemical Engineering, Chemistry, Physics, Polymer Science & Engineering - with those of partner investigators from...

  14. LG: Order (2014-SE-15011)

    Broader source: Energy.gov [DOE]

    DOE ordered LG Electronics USA, Inc. to pay a $1,479,860 civil penalty after finding LG had manufactured and distributed in commerce in the U.S. at least 7,438 units of basic model LT143CNR, a noncompliant room air conditioner.

  15. Universal: Order (2013-SE-26004)

    Broader source: Energy.gov [DOE]

    DOE ordered Universal Lighting Technologies, Inc. to pay a $7,264 civil penalty after finding Universal had manufactured and distributed in commerce in the U.S. 454 units of model B140R277HP, a noncompliant fluorescent lamp ballast.

  16. ELCO: Order (2014-SE-54005)

    Broader source: Energy.gov [DOE]

    DOE ordered ELCO Lighting to pay a $14,000 civil penalty after finding ELCO had failed to certify that certain models of illuminated exit signs and metal halide lamp fixtures comply with the applicable energy conservation standards and had failed to provide requested test data.

  17. Friedrich: Order (2014-SE-15010)

    Broader source: Energy.gov [DOE]

    DOE ordered Friedrich Air Conditioning Co. to pay a $1.5 million civil penalty after finding Friedrich had manufactured and distributed in commerce in the U.S. 8,241 units of Friedrich model SQ10N10, a noncompliant room air conditioner.

  18. Hydac: Order (2012-SE-4107)

    Broader source: Energy.gov [DOE]

    DOE ordered Hydac Technology Corporation to pay a $29,000 civil penalty after finding Hydac had manufactured and distributed in commerce in the U.S. noncompliant electric motors.

  19. Perlick: Agreement (2010-SE-0109)

    Broader source: Energy.gov [DOE]

    DOE and Perlick Residential & Hospitality Products entered into a Compromise Agreement in which Perlick agreed to pay a $5,000 civil penalty after DOE found that Perlick had manufactured and distributed in commerce in the U.S. model HP72ROO-S, a noncompliant refrigerator.

  20. Investigation of scanning tunneling spectra on iron-based superconductor FeSe0.5Te0.5(in Chinese)

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Du, Z. -Y.; Fang, D. -L.; Wang, Z. -Y.; Du, G.; Yang, X.; Yang, H.; Gu, G.; -H, Wen H.

    2015-05-05

    FeSe0.5Te0.5 single crystals with superconducting critical temperature of 13.5 K are investigated by scanning tunneling microscopy/spectroscopy (STM/STS) measureflents in detail. STM image on the top surface shows an atomically resolved square lattice consisted by white and dark spots with a constant of about 3.73± 0.03 Å which is consistent with the lattice constant 3.78 Å. The Se and Te atoms with a height difference of about 0.35 Å are successfully identified since the sizes of the two kinds of atoms are different. The tunneling spectra show very large zero-bias conductance value and asymmetric coherent peaks in the superconducting state. Accordingmore » to the positions of coherence peaks, we determine the superconducting gap 2Δ = 5.5 meV, and the reduced gap 2Δ/kBTc = 4.9 is larger than the value predicted by the weak-coupling BCS theory. The zero-bias conductance at 1.7 K only have a decrease of about 40% compared with the normal state conductance, which may originate from some scattering and broadening mechanism in the material. This broadening effect will also make the superconducting gap determined by the distance between the coherence peaks larger than the exact gap value. The asymmetric structure of the tunneling spectra near the superconducting gap is induced by the hump on the background. This hump appears at temperature more than twice the superconducting critical temperature. This kind of hump has also been observed in other iron pnictides and needs further investigation. A possible bosonic mode outside the coherence peak with a mode energy Ω of about 5.5 meV is observed in some tunneling spectra, and the ratio between the mode energy and superconducting transition temperature Ω/kBTc ≈ 4.7 is roughly consistent with the universal ratio 4.3 in iron-based superconductors. The high-energy background of the spectra beyond the superconducting gaps shows a V-shape feature. The slopes of the differential conductance spectra at high energy are very different in the areas of Te-atom cluster and Se-atom cluster, and the difference extends to the energy of more than 300 meV. The differential conductance mapping has very little information about the quasi-particle interference of the superconducting state, which may result from the other strong scattering mechanism in the sample.« less

  1. Midea: Proposed Penalty (2010-SE-0110, 2012-SE-1402, 2012-SE-1404)

    Broader source: Energy.gov [DOE]

    DOE alleged in a Notice of Proposed Civil Penalty that Midea America Corp., Hefei Hualing Co., Ltd., and China Refrigeration Industry Co., Ltd. manufactured and distributed noncompliant refrigerator-freezers and freezers in the U.S.

  2. Employing time-resolved terahertz spectroscopy to analyze carrier dynamics in thin-film Cu{sub 2}ZnSn(S,Se){sub 4} absorber layers

    SciTech Connect (OSTI)

    Guglietta, Glenn W.; Baxter, Jason B.; Choudhury, Kaushik Roy; Caspar, Jonathan V.

    2014-06-23

    We report the application of time-resolved terahertz spectroscopy (TRTS) to measure photoexcited carrier lifetimes and mobility, and to determine recombination mechanisms in Cu{sub 2}ZnSn(S,Se){sub 4} (CZTSSe) thin films fabricated from nanocrystal inks. Ultrafast time resolution permits tracking the evolution of carrier density to determine recombination rates and mechanisms. The carrier generation profile was manipulated by varying the photoexcitation wavelength and fluence to distinguish between surface, Shockley-Read-Hall (SRH), radiative, and Auger recombination mechanisms and determine rate constants. Surface and SRH recombination are the dominant mechanisms for the air/CZTSSe/SiO{sub 2}/Si film stack. Diffusion to, and then recombination at, the air-CZTSSe interface occurred on the order of 100 picoseconds, while SRH recombination lifetimes were 1–2 nanoseconds. TRTS measurements can provide information that is complementary to conventional time-resolved photoluminescence measurements and can direct the design of efficient thin film photovoltaics.

  3. Effect of carrier recombination on ultrafast carrier dynamics in thin films of the topological insulator Bi{sub 2}Se{sub 3}

    SciTech Connect (OSTI)

    Glinka, Yuri D.; Babakiray, Sercan; Johnson, Trent A.; Holcomb, Mikel B.; Lederman, David

    2014-10-27

    Transient reflectivity (TR) from thin films (6–40 nm thick) of the topological insulator Bi{sub 2}Se{sub 3} revealed ultrafast carrier dynamics, which suggest the existence of both radiative and non-radiative recombination between electrons residing in the upper cone of initially unoccupied high energy Dirac surface states (SS) and holes residing in the lower cone of occupied low energy Dirac SS. The modeling of measured TR traces allowed us to conclude that recombination is induced by the depletion of bulk electrons in films below ∼20 nm thick due to the charge captured on the surface defects. We predict that such recombination processes can be observed using time-resolved photoluminescence techniques.

  4. Substitution of Ni for Fe in superconducting Fe?.??Te?.?Se?.? depresses the normal-state conductivity but not the magnetic spectral weight

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Wang, Jinghui; Tranquada, J. M.; Zhong, Ruidan; Li, Shichao; Gan, Yuan; Xu, Zhijun; Zhang, Cheng; Ozaki, T.; Matsuda, M.; Zhao, Yang; et al

    2015-01-05

    We have performed systematic resistivity and inelastic neutron scattering measurements on Fe?.???zNizTe?.?Se?.? samples to study the impact of Ni substitution on the transport properties and the low-energy (? 12 meV) magnetic excitations. It is found that, with increasing Ni doping, both the conductivity and superconductivity are gradually suppressed; in contrast, the low-energy magnetic spectral weight changes little. Comparing with the impact of Co and Cu substitution, we find that the effects on conductivity and superconductivity for the same degree of substitution grow systematically as the atomic number of the substituent deviates from that of Fe. The impact of the substituentsmoreas scattering centers appears to be greater than any contribution to carrier concentration. The fact that low-energy magnetic spectral weight is not reduced by increased electron scattering indicates that the existence of antiferromagnetic correlations does not depend on electronic states close to the Fermi energy.less

  5. Giant increase in critical current density of KxFe2-ySe? single crystals

    SciTech Connect (OSTI)

    Lei, Hechang; Petrovic, C.

    2011-12-28

    The critical current density Jabc of KxFe2-ySe? single crystals can be enhanced by more than one order of magnitude, up to ~2.110? A/cm by the post annealing and quenching technique. A scaling analysis reveals the universal behavior of the normalized pinning force as a function of the reduced field for all temperatures, indicating the presence of a single vortex pinning mechanism. The main pinning sources are three-dimensional (3D) point-like normal cores. The dominant vortex interaction with pinning centers is via spatial variations in critical temperature Tc (?Tc pinning).

  6. Fluorescence resonance energy transfer measured by spatial photon migration in CdSe-ZnS quantum dots colloidal systems as a function of concentration

    SciTech Connect (OSTI)

    Azevedo, G.; Monte, A. F. G.; Reis, A. F.; Messias, D. N.

    2014-11-17

    The study of the spatial photon migration as a function of the concentration brings into attention the problem of the energy transfer in quantum dot embedded systems. By measuring the photon propagation and its spatial dependence, it is possible to understand the whole dynamics in a quantum dot system, and also improve their concentration dependence to maximize energy propagation due to radiative and non-radiative processes. In this work, a confocal microscope was adapted to scan the spatial distribution of photoluminescence from CdSe-ZnS core-shell quantum dots in colloidal solutions. The energy migration between the quantum dots was monitored by the direct measurement of the photon diffusion length, according to the diffusion theory. We observed that the photon migration length decreases by increasing the quantum dot concentration, this kind of behavior has been regarded as a signature of Frster resonance energy transfer in the system.

  7. Structural, dynamic, electronic, and vibrational properties of flexible, intermediate, and stressed rigid As-Se glasses and liquids from first principles molecular dynamics

    SciTech Connect (OSTI)

    Bauchy, M.; Kachmar, A.; Micoulaut, M.

    2014-11-21

    The structural, vibrational, electronic, and dynamic properties of amorphous and liquid As{sub x}Se{sub 1-x} (0.10

  8. Improved Ga grading of sequentially produced Cu(In,Ga)Se{sub 2} solar cells studied by high resolution X-ray fluorescence

    SciTech Connect (OSTI)

    Schöppe, Philipp; Schnohr, Claudia S.; Oertel, Michael; Kusch, Alexander; Johannes, Andreas; Eckner, Stefanie; Reislöhner, Udo; Ronning, Carsten; Burghammer, Manfred; Martínez-Criado, Gema

    2015-01-05

    There is particular interest to investigate compositional inhomogeneity of Cu(In,Ga)Se{sub 2} solar cell absorbers. We introduce an approach in which focused ion beam prepared thin lamellas of complete solar cell devices are scanned with a highly focused synchrotron X-ray beam. Analyzing the resulting fluorescence radiation ensures high resolution compositional analysis combined with high spatial resolution. Thus, we are able to detect subtle variations of the Ga/(Ga + In) ratio down to 0.01 on a submicrometer scale. We observed that for sequentially processed solar cells a higher selenization temperature leads to absorbers with almost homogenous Ga/(Ga + In) ratio, which significantly improved the conversion efficiency.

  9. Point defects in CdTexSe1-x crystals grown from a Te-rich solution for applications in detecting radiation

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Gul, R.; Roy, U. N.; Bolotnikov, A. E.; Camarda, G. S.; Cui, Y.; Hossain, A.; Lee, W.; Yang, G.; Burger, A.; James, R. B.; et al

    2015-04-15

    We investigated cadmium telluride selenide (CdTeSe) crystals, newly grown by the Traveling Heater Method (THM), for the presence and abundance of point defects. Deep Level Transient spectroscopy (I-DLTS) was used to determine the energies of the traps, their capture cross sections, and densities. The bias across the detectors was varied from (1–30) V. Four types of point defects were identified, ranging from 10 meV to 0.35 eV. Two dominant traps at energies of 0.18 eV and 0.14 eV were studied in depth. Cd vacancies are found at lower concentrations than other point defects present in the material.

  10. Properties of Sb{sub 2}S{sub 3} and Sb{sub 2}Se{sub 3} thin films obtained by pulsed laser ablation

    SciTech Connect (OSTI)

    Virt, I. S.; Rudyj, I. O.; Kurilo, I. V.; Lopatynskyi, I. Ye.; Linnik, L. F.; Tetyorkin, V. V.; Potera, P.; Luka, G.

    2013-07-15

    The properties of Sb{sub 2}S{sub 3} and Sb{sub 2}Se{sub 3} thin films of variable thickness deposited onto Al{sub 2}O{sub 3}, Si, and KCl substrates are investigated by the method of pulsed laser ablation. The samples are obtained at a substrate temperature of 180 Degree-Sign C in a vacuum chamber with a residual pressure of 10{sup -5} Torr. The thickness of the films amounted to 40-1500 nm. The structure of the bulk material of the targets and films is investigated by the methods of X-ray diffraction and transmission high-energy electron diffraction, respectively. The electrical properties of the films are investigated in the temperature range of 253-310 K. It is shown that the films have semiconductor properties. The structural features of the films determine their optical parameters.

  11. Synthesis and characterization of bulk Cu{sub 2}ZnSnX{sub 4} (X: S, Se) via thermodynamically supported mechano-chemical process

    SciTech Connect (OSTI)

    Pareek, Devendra Balasubramaniam, K.R.; Sharma, Pratibha

    2015-05-15

    Materials with the general formula, Cu{sub 2}ZnSnX{sub 4} (CZTX; X: Group 16 elements), with X being S/Se, have been receiving considerable attention due to their utility as an absorber layer in solar photovoltaics (PV). This paper reports on the synthesis of CZTSe and CZTS nanocrystalline powders at low temperatures, starting from elemental metal and chalcogen powders, via the low cost, scalable technique of ball milling. The prepared samples were well characterized using the different characterization tools. XRD, Raman, SEM and TEM studies confirm the formation of single-phase, stoichiometric, nano-crystalline kesterite CZTS and CZTSe powders. The low temperature phase selection of the complex quaternary compound in this system is seen as a direct consequence of the thermodynamic facilitation, coupled with the capability of mechano-chemical synthesis to aid in overcoming kinetic constraints. The optical bandgap of the various samples of CZTS was observed in the range of 1.4–1.6 eV and corresponding values for CZTSe was observed to be in the range of 1.08–1.18 eV. Our work provides a pathway for developing cheap, scalable, and ink-based techniques for low cost solar PV. - Graphical abstract: Display Omitted - Highlights: • A scalable route for synthesis of near phase pure CZTS/Se nano-crystals has been demonstrated. • Stoichiometric CZTS and CZTSe were synthesized via mechano-chemical synthesis route. • Synthesis at near room temperature is supported by thermodynamic calculations.

  12. Formation mechanism of superconducting phase and its three-dimensional architecture in pseudo-single-crystal KxFe2-ySe2

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Liu, Yong; Xing, Qingfeng; Straszheim, Warren E.; Marshman, Jeff; Pedersen, Pal; McLaughlin, Richard; Lograsso, Thomas A.

    2016-02-11

    Here, we report how the superconducting phase forms in pseudo-single-crystal KxFe2-ySe2. In situ scanning electron microscopy (SEM) observation reveals that, as an order-disorder transition occurs, on cooling, most of the high-temperature iron-vacancy-disordered phase gradually changes into the iron-vacancy-ordered phase whereas a small quantity of the high-temperature phase retains its structure and aggregates to the stripes with more iron concentration but less potassium concentration compared to the iron-vacancy-ordered phase. The stripes that are generally recognized as the superconducting phase are actually formed as a remnant of the high-temperature phase with a compositional change after an “imperfect” order-disorder transition. It should bemore » emphasized that the phase separation in pseudo-single-crystal KxFe2-ySe2 is caused by the iron-vacancy order-disorder transition. The shrinkage of the high-temperature phase and the expansion of the newly created iron-vacancy-ordered phase during the phase separation rule out the mechanism of spinodal decomposition proposed in an early report [Wang et al, Phys. Rev. B 91, 064513 (2015)]. Since the formation of the superconducting phase relies on the occurrence of the iron-vacancy order-disorder transition, it is impossible to synthesize a pure superconducting phase by a conventional solid state reaction or melt growth. By focused ion beam-scanning electron microscopy, we further demonstrate that the superconducting phase forms a contiguous three-dimensional architecture composed of parallelepipeds that have a coherent orientation relationship with the iron-vacancy-ordered phase.« less

  13. Spatiotemporal Monte Carlo transport methods in x-ray semiconductor detectors: Application to pulse-height spectroscopy in a-Se

    SciTech Connect (OSTI)

    Fang Yuan; Badal, Andreu; Allec, Nicholas; Karim, Karim S.; Badano, Aldo

    2012-01-15

    Purpose: The authors describe a detailed Monte Carlo (MC) method for the coupled transport of ionizing particles and charge carriers in amorphous selenium (a-Se) semiconductor x-ray detectors, and model the effect of statistical variations on the detected signal. Methods: A detailed transport code was developed for modeling the signal formation process in semiconductor x-ray detectors. The charge transport routines include three-dimensional spatial and temporal models of electron-hole pair transport taking into account recombination and trapping. Many electron-hole pairs are created simultaneously in bursts from energy deposition events. Carrier transport processes include drift due to external field and Coulombic interactions, and diffusion due to Brownian motion. Results: Pulse-height spectra (PHS) have been simulated with different transport conditions for a range of monoenergetic incident x-ray energies and mammography radiation beam qualities. Two methods for calculating Swank factors from simulated PHS are shown, one using the entire PHS distribution, and the other using the photopeak. The latter ignores contributions from Compton scattering and K-fluorescence. Comparisons differ by approximately 2% between experimental measurements and simulations. Conclusions: The a-Se x-ray detector PHS responses simulated in this work include three-dimensional spatial and temporal transport of electron-hole pairs. These PHS were used to calculate the Swank factor and compare it with experimental measurements. The Swank factor was shown to be a function of x-ray energy and applied electric field. Trapping and recombination models are all shown to affect the Swank factor.

  14. Processing of CuInSe{sub 2}-based solar cells: Characterization of deposition processes in terms of chemical reaction analyses. Phase I annual report, 6 May 1995--5 May 1996

    SciTech Connect (OSTI)

    Anderson, T.

    1997-04-01

    An interdisciplinary team of five graduate students and four faculty have made considerable progress during Phase I of this program. The objective of this initiative is to develop a high-rate processing sequence to produce device-quality thin films of CI(G)S(Se). A comprehensive CI(G)S(Se) device fabrication capability is being established that includes thermal evaporation and plasma assisted deposition of CI(G)S(Se), rapid thermal processing, DC sputtering of both undoped and doped ZnO, CBD and MOCVD of CdS, and rf sputtering of Mo. Insight into the materials processing issues is being addressed through assessment of the thermochemistry and phase equilibria of the CI(G)S(Se) system, single crystal growth studies, investigation of Na effects on the growth, and detailed materials characterization.

  15. Probing structure-induced optical behavior in a new class of self-activated luminescent 0D/1D CaWO? metal oxide CdSe nanocrystal composite heterostructures

    SciTech Connect (OSTI)

    Han, Jinkyu; McBean, Coray; Wang, Lei; Hoy, Jessica; Jaye, Cherno; Liu, Haiqing; Li, Zhuo-Qun; Sfeir, Matthew Y.; Fischer, Daniel A.; Taylor, Gordon T.; Misewich, James A.; Wong, Stanislaus S.

    2015-01-30

    In this report, we synthesize and characterize the structural and optical properties of novel heterostructures composed of (i) semiconducting nanocrystalline CdSe quantum dot (QDs) coupled with (ii) both one and zero-dimensional (1D and 0D) motifs of self-activated luminescence CaWO? metal oxides. Specifically, ~4 nm CdSe QDs have been anchored onto (i) high-aspect ratio 1D nanowires, measuring ~230 nm in diameter and ~3 ?m in length, as well as onto (ii) crystalline 0D nanoparticles (possessing an average diameter of ~ 80 nm) of CaWO? through the mediation of 3-mercaptopropionic acid (MPA) as a connecting linker. Composite formation was confirmed by complementary electron microscopy and spectroscopy (i.e. IR and Raman) data. In terms of luminescent properties, our results show that our 1D and 0D heterostructures evince photoluminescence (PL) quenching and shortened PL lifetimes of CaWO? as compared with unbound CaWO?. We propose that a photo-induced electron transfer process occurs from CaWO? to CdSe QDs, a scenario which has been confirmed by NEXAFS measurements and which highlights a decrease in the number of unoccupied orbitals in the conduction bands of CdSe QDs. By contrast, the PL signature and lifetimes of MPA-capped CdSe QDs within these heterostructures do not exhibit noticeable changes as compared with unbound MPA-capped CdSe QDs. The striking difference in optical behavior between CaWO? nanostructures and CdSe QDs within our heterostructures can be correlated with the relative positions of their conduction and valence energy band levels. In addition, the PL quenching behaviors for CaWO? within the heterostructure configuration were examined by systematically varying (i) the quantities and coverage densities of CdSe QDs as well as (ii) the intrinsic morphology (and by extension, the inherent crystallite size) of CaWO? itself.

  16. Effect of burst and recombination models for Monte Carlo transport of interacting carriers in a-Se x-ray detectors on Swank noise

    SciTech Connect (OSTI)

    Fang, Yuan; Karim, Karim S.; Badano, Aldo

    2014-01-15

    Purpose: The authors describe the modification to a previously developed Monte Carlo model of semiconductor direct x-ray detector required for studying the effect of burst and recombination algorithms on detector performance. This work provides insight into the effect of different charge generation models for a-Se detectors on Swank noise and recombination fraction. Methods: The proposed burst and recombination models are implemented in the Monte Carlo simulation package, ARTEMIS, developed byFang et al. [Spatiotemporal Monte Carlo transport methods in x-ray semiconductor detectors: Application to pulse-height spectroscopy in a-Se, Med. Phys. 39(1), 308319 (2012)]. The burst model generates a cloud of electron-hole pairs based on electron velocity, energy deposition, and material parameters distributed within a spherical uniform volume (SUV) or on a spherical surface area (SSA). A simple first-hit (FH) and a more detailed but computationally expensive nearest-neighbor (NN) recombination algorithms are also described and compared. Results: Simulated recombination fractions for a single electron-hole pair show good agreement with Onsager model for a wide range of electric field, thermalization distance, and temperature. The recombination fraction and Swank noise exhibit a dependence on the burst model for generation of many electron-hole pairs from a single x ray. The Swank noise decreased for the SSA compared to the SUV model at 4 V/?m, while the recombination fraction decreased for SSA compared to the SUV model at 30 V/?m. The NN and FH recombination results were comparable. Conclusions: Results obtained with the ARTEMIS Monte Carlo transport model incorporating drift and diffusion are validated with the Onsager model for a single electron-hole pair as a function of electric field, thermalization distance, and temperature. For x-ray interactions, the authors demonstrate that the choice of burst model can affect the simulation results for the generation of many electron-hole pairs. The SSA model is more sensitive to the effect of electric field compared to the SUV model and that the NN and FH recombination algorithms did not significantly affect simulation results.

  17. High temperature redox reactions with uranium: Synthesis and characterization of Cs(UO{sub 2})Cl(SeO{sub 3}), Rb{sub 2}(UO{sub 2}){sub 3}O{sub 2}(SeO{sub 3}){sub 2}, and RbNa{sub 5}U{sub 2}(SO{sub 4}){sub 7}

    SciTech Connect (OSTI)

    Babo, Jean-Marie; Albrecht-Schmitt, Thomas E.

    2013-10-15

    Cs(UO{sub 2})Cl(SeO{sub 3}) (1), Rb{sub 2}(UO{sub 2}){sub 3}O{sub 2}(SeO{sub 3}){sub 3} (2), and RbNa{sub 5}U{sub 2}(SO{sub 4}){sub 7} (3) single crystals were synthesized using CsCl, RbCl, and a CuCl/NaCl eutectic mixture as fluxes, respectively. Their lattice parameters and space groups are as follows: P2{sub 1}/n (a=6.548(1) Å, b=11.052(2) Å, c=10.666(2) Å and β=93.897(3)°), P1{sup ¯} (a=7.051(2) Å, b=7.198(2) Å, c=8.314(2) Å, α=107.897(3)°, β=102.687(3)° and γ=100.564(3)°) and C2/c (a=17.862(4) Å, b=6.931(1) Å, c=20.133(4) Å and β=109.737(6)°. The small anionic building units found in these compounds are SeO{sub 3}{sup 2−} and SO{sub 4}{sup 2−} tetrahedra, oxide, and chloride. The crystal structure of the first compound is composed of [(UO{sub 2}){sub 2}Cl{sub 2}(SeO{sub 3}){sub 2}]{sup 2−} chains separated by Cs{sup +} cations. The structure of (2) is constructed from [(UO{sub 2}){sub 3}O{sub 11}]{sup 16−} chains further connected through selenite units into layers stacked perpendicularly to the [0 1 0] direction, with Rb{sup +} cations intercalating between them. The structure of compound (3) is made of uranyl sulfate layers formed by edge and vertex connections between dimeric [U{sub 2}O{sub 16}] and [SO{sub 4}] polyhedra. These layers contain unusual sulfate–metal connectivity as well as large voids. - Graphical abstract: A new family of uranyl selenites and sulfates has been prepared by high-temperature redox reactions. This compounds display new bonding motifs. Display Omitted - Highlights: • Low-dimensional Uranyl Oxoanion compounds. • Conversion of U(IV) to U(VI) at high temperatures. • Dimensional reduction by both halides and stereochemically active lone-pairs.

  18. Thickness Effect of Al-Doped ZnO Window Layer on Damp Heat Stability of CuInGaSe2 Solar Cells: Preprint

    SciTech Connect (OSTI)

    Pern, F. J.; Mansfield, L.; DeHart, C.; Glick, S. H.; Yan, F.; Noufi, R.

    2011-07-01

    We investigated the damp heat (DH) stability of CuInGaSe2 (CIGS) solar cells as a function of thickness of the Al-doped ZnO (AZO) window layer from the 'standard' 0.12 μm to a modest 0.50 μm over an underlying 0.10-μm intrinsic ZnO buffer layer. The CIGS cells were prepared with external electrical contact using fine Au wire to the tiny 'standard' Ni/Al (0.05 μm/3 μm) metal grid contact pads. Bare cell coupons and sample sets encapsulated in a specially designed, Al-frame test structure with an opening for moisture ingress control using a TPT backsheet were exposed to DH at 85oC and 85% relative humidity, and characterized by current-voltage (I-V), quantum efficiency (QE), and (electrochemical) impedance spectroscopy (ECIS). The results show that bare cells exhibited rapid degradation within 50-100 h, accompanied by film wrinkling and delamination and corrosion of Mo and AlNi grid, regardless of AZO thickness. In contrast, the encapsulated cells did not show film wrinkling, delamination, and Mo corrosion after 168 h DH exposure; but the trend of efficiency degradation rate showed a weak correlation to the AZO thickness.

  19. Thickness Effect of Al-Doped ZnO Window Layer on Damp-Heat Stability of CuInGaSe2 Solar Cells

    SciTech Connect (OSTI)

    Pern, F. J.; Mansfield, L.; DeHart, C.; Glick, S. H.; Yan, F.; Noufi, R.

    2011-01-01

    We investigated the damp heat (DH) stability of CuInGaSe{sub 2} (CIGS) solar cells as a function of thickness of the Al-doped ZnO (AZO) window layer from the 'standard' 0.12 {micro}m to a modest 0.50 {micro}m over an underlying 0.10-{micro}m intrinsic ZnO buffer layer. The CIGS cells were prepared with external electrical contact using fine Au wire to the tiny 'standard' Ni/Al (0.05 {micro}m/3 {micro}m) metal grid contact pads. Bare cell coupons and sample sets encapsulated in a specially designed, Al-frame test structure with an opening for moisture ingress control using a TPT backsheet were exposed to DH at 85 C and 85% relative humidity, and characterized by current-voltage (I-V), quantum efficiency (QE), and (electrochemical) impedance spectroscopy (ECIS). The results show that bare cells exhibited rapid degradation within 50-100 h, accompanied by film wrinkling and delamination and corrosion of Mo and AlNi grid, regardless of AZO thickness. In contrast, the encapsulated cells did not show film wrinkling, delamination, and Mo corrosion after 168 h DH exposure; but the trend of efficiency degradation rate showed a weak correlation to the AZO thickness.

  20. X-ray magnetic spectroscopy of MBE-grown Mn-doped Bi{sub 2}Se{sub 3} thin films

    SciTech Connect (OSTI)

    Collins-McIntyre, L. J.; Watson, M. D.; Zhang, S. L.; Coldea, A. I.; Hesjedal, T.; Baker, A. A.; Harrison, S. E.; Pushp, A.; Kellock, A. J.; Parkin, S. S. P.; Laan, G. van der

    2014-12-15

    We report the growth of Mn-doped Bi{sub 2}Se{sub 3} thin films by molecular beam epitaxy (MBE), investigated by x-ray diffraction (XRD), atomic force microscopy (AFM), SQUID magnetometry and x-ray magnetic circular dichroism (XMCD). Epitaxial films were deposited on c-plane sapphire substrates by co-evaporation. The films exhibit a spiral growth mechanism typical of this material class, as revealed by AFM. The XRD measurements demonstrate a good crystalline structure which is retained upon doping up to ?7.5 atomic-% Mn, determined by Rutherford backscattering spectrometry (RBS), and show no evidence of the formation of parasitic phases. However an increasing interstitial incorporation of Mn is observed with increasing doping concentration. A magnetic moment of 5.1 ?{sub B}/Mn is obtained from bulk-sensitive SQUID measurements, and a much lower moment of 1.6 ?{sub B}/Mn from surface-sensitive XMCD. At ?2.5 K, XMCD at the Mn L{sub 2,3} edge, reveals short-range magnetic order in the films and indicates ferromagnetic order below 1.5 K.

  1. Probing the Role of Interlayer Coupling and Coulomb Interactions on Electronic Structure in Few-Layer MoSe 2 Nanostructures

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Bradley, Aaron J.; M. Ugeda, Miguel; da Jornada, Felipe H.; Qiu, Diana Y.; Ruan, Wei; Zhang, Yi; Wickenburg, Sebastian; Riss, Alexander; Lu, Jiong; Mo, Sung-Kwan; et al

    2015-03-16

    Despite the weak nature of interlayer forces in transition metal dichalcogenide (TMD) materials, their properties are highly dependent on the number of layers in the few-layer two-dimensional (2D) limit. Here, we present a combined scanning tunneling microscopy/spectroscopy and GW theoretical study of the electronic structure of high quality single- and few-layer MoSe2 grown on bilayer graphene. We find that the electronic (quasiparticle) bandgap, a fundamental parameter for transport and optical phenomena, decreases by nearly one electronvolt when going from one layer to three due to interlayer coupling and screening effects. Our results paint a clear picture of the evolution ofmore » the electronic wave function hybridization in the valleys of both the valence and conduction bands as the number of layers is changed. This demonstrates the importance of layer number and electron-electron interactions on van der Waals heterostructures and helps to clarify how their electronic properties might be tuned in future 2D nanodevices.« less

  2. Excited state carrier dynamics in CdS{sub x}Se{sub 1-x} semisconductor alloys as studied by ultrafast fluorescence spectroscopy

    SciTech Connect (OSTI)

    Gadd, S.E.

    1995-08-01

    This dissertation discusses studies of the electron-hole pair dynamics of CdS{sub x}Se{sub 1-x} semiconductor alloys for the entire compositional range from x = 1 to x = 0 as examined by the ultrafast fluorescence techniques of time correlated single photon counting and fluorescence upconversion. Specifically, samples with x = 1, .75, .5, .25, and 0 were studied each at a spread of wavelengths about its respective emission maximum which varies according to {lambda} = 718nm - 210x nm. The decays of these samples were found to obey a Kohlrausch distribution, exp [(t/{tau}){sup {beta}}], with the exponent 3 in the range .5-.7 for the alloys. These results are in agreement with those expected for localization due to local potential variations resulting from the random distribution of sulfur and selenium atoms on the element VI A sub-lattice. This localization can be understood in terms of Anderson localization of the holes in states whose energy distribution tails into the forbidden energy band-gap. Because these states have energy dependent lifetimes, the carriers can decay via many parallel channels. This distribution of channels is the ultimate source of the Kohlrausch form of the fluorescence decays.

  3. Determining the exact number of dye molecules attached to colloidal CdSe/ZnS quantum dots in Frster resonant energy transfer assemblies

    SciTech Connect (OSTI)

    Kaiser, Uwe; Jimenez de Aberasturi, Dorleta; Vzquez-Gonzlez, Margarita; Carrillo-Carrion, Carolina; Niebling, Tobias; Parak, Wofgang J.; Heimbrodt, Wolfram

    2015-01-14

    Semiconductor quantum dots functionalized with organic dye molecules are important tools for biological sensor applications. Energy transfer between the quantum dot and the attached dyes can be utilized for sensing. Though important, the determination of the real number of dye molecules attached per quantum dot is rather difficult. In this work, a method will be presented to determine the number of ATTO-590 dye molecules attached to CdSe/ZnS quantum dots based on time resolved spectral analysis. The energy transfer from the excited quantum dot to the attached ATTO-590 dye leads to a reduced lifetime of the quantum dot's excitons. The higher the concentration of dye molecules, the shorter the excitonic lifetime becomes. However, the number of dye molecules attached per quantum dot will vary. Therefore, for correctly explaining the decay of the luminescence upon photoexcitation of the quantum dot, it is necessary to take into account the distribution of the number of dyes attached per quantum dot. A Poisson distribution of the ATTO-590 dye molecules not only leads to excellent agreement between experimental and theoretical decay curves but also additionally yields the average number of dye molecules attached per quantum dot. In this way, the number of dyes per quantum dot can be conveniently determined.

  4. 'Giant' multishell CdSe nanocrystal quantum dots with supporessed blinking: novel fluorescent probes for real-time detection of single-molecule events

    SciTech Connect (OSTI)

    Hollingsworth, Jennifer A; Vela, Javier; Htoon, Han; Klimov, Victor I; Casson, Amy R; Chen, Yongfen

    2009-01-01

    We reported for the first time that key nanocrystal quantum dot (NQD) optical properties-quantum yield, photobleaching and blinking-can be rendered independent ofNQD surface chemistry and environment by growth of a very thick, defect-free inorganic shell. Here, we show the precise shell-thickness dependence of these effects. We demonstrate that 'giant-shell' NQDs can be largely non-blinking for observation times as long as 54 minutes and lhat on-time fractions are independent of experimental time-resolution from 1-200 ms. These effects are primarily demonstrated on (CdSe)CdS (core)shell NQDs, but we also show that alloyed shells comprising Cd.Znl.'S and terminated with a non-cytotoxic ZnS layer exhibit similar properties. The mechanism for suppressed blinking and dramatically enhanced stability is attributed to both effective isolation of the NQD core excitonic wavefunction from the NQD surface, as well as a quasi-Type II electronic structure. The unusual electronic structure provides for effective spatial separation of the electron and hole into the shell and core, respectively, and, thereby, for reduced efficiencies in non-radiative Auger recombination.

  5. Surface collective modes in the topological insulators Bi2Se3 and Bi0.5Sb1.5Te3-xSex

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Kogar, A.; Gu, G.; Vig, S.; Thaler, A.; Wong, M. H.; Xiao, Y.; Reig-i-Plessis, D.; Cho, G. Y.; Valla, T.; Pan, Z.; et al

    2015-12-15

    In this study, we used low-energy, momentum-resolved inelastic electron scattering to study surface collective modes of the three-dimensional topological insulators Bi2Se3 and Bi0.5Sb1.5Te3-xSex. Our goal was to identify the “spin plasmon” predicted by Raghu and co-workers [Phys. Rev. Lett. 104, 116401 (2010)]. Instead, we found that the primary collective mode is a surface plasmon arising from the bulk, free carriers in these materials. This excitation dominates the spectral weight in the bosonic function of the surface χ''(q,ω) at THz energy scales, and is the most likely origin of a quasiparticle dispersion kink observed in previous photoemission experiments. Our study suggestsmore » that the spin plasmon may mix with this other surface mode, calling for a more nuanced understanding of optical experiments in which the spin plasmon is reported to play a role.« less

  6. Determining conductivity and mobility values of individual components in multiphase composite Cu{sub 1.97}Ag{sub 0.03}Se

    SciTech Connect (OSTI)

    Day, Tristan W.; Brown, David R.; Snyder, G. Jeffrey; Zeier, Wolfgang G.; Melot, Brent C.

    2014-10-27

    The intense interest in phase segregation in thermoelectrics as a means to reduce the lattice thermal conductivity and to modify the electronic properties from nanoscale size effects has not been met with a method for separately measuring the properties of each phase assuming a classical mixture. Here, we apply effective medium theory for measurements of the in-line and Hall resistivity of a multiphase composite, in this case Cu{sub 1.97}Ag{sub 0.03}Se. The behavior of these properties with magnetic field as analyzed by effective medium theory allows us to separate the conductivity and charge carrier mobility of each phase. This powerful technique can be used to determine the matrix properties in the presence of an unwanted impurity phase, to control each phase in an engineered composite, and to determine the maximum carrier concentration change by a given dopant, making it the first step toward a full optimization of a multiphase thermoelectric material and distinguishing nanoscale effects from those of a classical mixture.

  7. Investigation of deep-level defects in Cu(In,Ga)Se{sub 2} thin films by a steady-state photocapacitance method

    SciTech Connect (OSTI)

    Hu, Xiaobo, E-mail: hxb1314@gmail.com; Sakurai, Takeaki; Akimoto, Katsuhiro [Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573 (Japan); Yamada, Akimasa; Ishizuka, Shogo; Niki, Sigeru [National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan)

    2014-10-28

    The properties of defect levels located 0.8?eV above the valence band in Cu(In{sub 1?x},Ga{sub x})Se{sub 2} thin films were investigated by a steady-state photocapacitance method. When illuminated by light with a photon energy of 0.8?eV at 60?K, a fast increase, followed by a slow increase, was observed in the photocapacitance transients of all samples. Upon being re-exposed, samples with a low bandgap energy showed a slow decrease in photocapacitance transients. These observations were interpreted using a configuration coordinate model assuming two states for the 0.8?eV defect: a stable state D and its metastable state D* with a large lattice relaxation. The difference in the evolution mechanisms of the photocapacitance transients was attributed to the difference in the optical transition of carriers between the two states of the 0.8?eV defect and the valence and conduction bands.

  8. Electronic Structure and Optical Properties of Cu2ZnGeSe4. First-Principles Calculations and Vacuum-Ultraviolet Spectroscopic Ellipsometric Studies

    SciTech Connect (OSTI)

    Choi, Sukgeun; Park, Ji-Sang; Donohue, Andrea; Christensen, Steven T.; To, Bobby; Beall, Carolyn; Wei, Su-Huai; Repins, Ingid L.

    2015-11-19

    Cu2ZnGeSe4 is of interest for the development of next-generation thin-film photovoltaic technologies. To understand its electronic structure and related fundamental optical properties, we perform first-principles calculations for three structural variations: kesterite, stannite, and primitive-mixed CuAu phases. The calculated data are compared with the room-temperature dielectric function?=?1+i?2 spectrum of polycrystalline Cu2ZnGeSe4 determined by vacuum-ultraviolet spectroscopic ellipsometry in the photon-energy range of 0.7 to 9.0 eV. Ellipsometric data are modeled with the sum of eight Tauc-Lorentz oscillators, and the best-fit model yields the band-gap and Tauc-gap energies of 1.25 and 1.19 eV, respectively. A comparison of overall peak shapes and relative intensities between experimental spectra and the calculated ? data for three structural variations suggests that the sample may not have a pure (ordered) kesterite phase. We found that the complex refractive index N=n+ik, normal-incidence reflectivity R, and absorption coefficients ? are calculated from the modeled ? spectrum, which are also compared with those of Cu2ZnSnSe4 . The spectral features for Cu2ZnGeSe4 appear to be weaker and broader than those for Cu2ZnSnSe4 , which is possibly due to more structural imperfections presented in Cu2ZnGeSe4 than Cu2ZnSnSe4 .

  9. Seed-mediated synthesis, properties and application of {gamma}-Fe{sub 2}O{sub 3}-CdSe magnetic quantum dots

    SciTech Connect (OSTI)

    Lin, Alex W.H.; Ang, Chung Yen; Patra, Pranab K.; Han Yu; Gu Hongwei; Le Breton, Jean-Marie; Juraszek, Jean; Chiron, Hubert; Papaefthymiou, Georgia C.; Tamil Selvan, Subramanian; Ying, Jackie Y.

    2011-08-15

    Seed-mediated growth of fluorescent CdSe quantum dots (QDs) around {gamma}-Fe{sub 2}O{sub 3} magnetic cores was performed at high temperature (300 deg. C) in the presence of organic surfactants. Bi-functional magnetic quantum dots (MQDs) with tunable emission properties were successfully prepared. The as-synthesized MQDs were characterized by high-resolution transmission electron microscopy (HRTEM) and dynamic light scattering (DLS), which confirmed the assembly of heterodimers. When a longer growth period was employed, a homogeneous dispersion of QDs around a magnetic nanoparticle was obtained. The magnetic properties of these nanocomposites were examined. The MQDs were superparamagnetic with a saturation magnetization of 0.40 emu/g and a coercivity of 138 Oe at 5 K. To demonstrate their potential application in bio-labeling, these MQDs were coated with a thin silica shell, and functionalized with a polyethylene glycol (PEG) derivative. The functionalized MQDs were effectively used for the labeling of live cell membranes of 4T1 mouse breast cancer cells and HepG2 human liver cancer cells. - Graphical abstract: (a) HRTEM image of oleic acid capped MPs. The size of MPs ranges from 8 to 10 nm. (b) XRD pattern of {gamma}-Fe{sub 2}O{sub 3} MPs. Highlights: > The fabrication of MQDs through a seed-mediated approach has been demonstrated. > The formation and assembly of these bi-functional nanocomposites have been elucidated. > The MQDs exhibit superparamagnetism and tunable emissions characteristic of the components. > MQDs with thin silica coating were successfully employed in the labeling of cancer cell membranes.

  10. Comparison of Sn-doped and nonstoichiometric vertical-Bridgman-grown crystals of the topological insulator Bi{sub 2}Te{sub 2}Se

    SciTech Connect (OSTI)

    Kushwaha, S. K. Gibson, Q. D.; Cava, R. J.; Xiong, J.; Ong, N. P.; Pletikosic, I.; Weber, A. P.; Fedorov, A. V.; Valla, T.

    2014-04-14

    A comparative study of the properties of topological insulator Bi{sub 2}Te{sub 2}Se (BTS) crystals grown by the vertical Bridgeman method is described. Two defect mechanisms that create acceptor impurities to compensate for the native n-type carriers are compared: Bi excess, and light Sn doping. Both methods yield low carrier concentrations and an n-p crossover over the length of the grown crystal boules, but lower carrier concentrations and higher resistivities are obtained for the Sn-doped crystals, which reach carrier concentrations as low as 8??10{sup 14}?cm{sup ?3}. Further, the temperature dependent resistivities for the Sn-doped crystals display strongly activated behavior at high temperatures, with a characteristic energy of half the bulk band gap. The (001) cleaved Sn-doped BTS crystals display high quality Shubnikov de Haas (SdH) quantum oscillations due to the topological surface state electrons. Angle resolved photoelectron spectroscopy (ARPES) characterization shows that the Fermi energy (E{sub F}) for the Sn-doped crystals falls cleanly in the surface states with no interference from the bulk bands, which the Dirac point for the surface states lies approximately 60?meV below the top of the bulk valence band maximum, and allows for a determination of the bulk and surface state carrier concentrations as a function of Energy near E{sub F}. Electronic structure calculations that compare Bi excess and Sn dopants in BTS demonstrate that Sn acts as a special impurity, with a localized impurity band that acts as a charge buffer occurring inside the bulk band gap. We propose that the special resonant level character of Sn in BTS gives rise to the exceptionally low carrier concentrations and activated resistivities observed.

  11. Reliable wet-chemical cleaning of natively oxidized high-efficiency Cu(In,Ga)Se{sub 2} thin-film solar cell absorbers

    SciTech Connect (OSTI)

    Lehmann, Jascha; Lehmann, Sebastian; Lauermann, Iver; Rissom, Thorsten; Kaufmann, Christian A.; Lux-Steiner, Martha Ch.; Br, Marcus; Sadewasser, Sascha

    2014-12-21

    Currently, Cu-containing chalcopyrite-based solar cells provide the highest conversion efficiencies among all thin-film photovoltaic (PV) technologies. They have reached efficiency values above 20%, the same performance level as multi-crystalline silicon-wafer technology that dominates the commercial PV market. Chalcopyrite thin-film heterostructures consist of a layer stack with a variety of interfaces between different materials. It is the chalcopyrite/buffer region (forming the p-n junction), which is of crucial importance and therefore frequently investigated using surface and interface science tools, such as photoelectron spectroscopy and scanning probe microscopy. To ensure comparability and validity of the results, a general preparation guide for realistic surfaces of polycrystalline chalcopyrite thin films is highly desirable. We present results on wet-chemical cleaning procedures of polycrystalline Cu(In{sub 1-x}Ga{sub x})Se{sub 2} thin films with an average x?=?[Ga]/([In]?+?[Ga])?=?0.29, which were exposed to ambient conditions for different times. The hence natively oxidized sample surfaces were etched in KCN- or NH{sub 3}-based aqueous solutions. By x-ray photoelectron spectroscopy, we find that the KCN treatment results in a chemical surface structure which is apart from a slight change in surface composition identical to a pristine as-received sample surface. Additionally, we discover a different oxidation behavior of In and Ga, in agreement with thermodynamic reference data, and we find indications for the segregation and removal of copper selenide surface phases from the polycrystalline material.

  12. Phase stabilities of pyrite-related MTCh compounds (M=Ni, Pd, Pt; T=Si, Ge, Sn, Pb; Ch=S, Se, Te): A systematic DFT study

    SciTech Connect (OSTI)

    Bachhuber, Frederik; Krach, Alexander; Furtner, Andrea; Söhnel, Tilo; Peter, Philipp; Rothballer, Jan; Weihrich, Richard

    2015-03-15

    Pyrite-type and related systems appear for a wide range of binary and ternary combinations of transition metals and main group elements that form Zintl type dumbbell anion units. Those representatives with 20 valence electrons exhibit an extraordinary structural flexibility and interesting properties as low-gap semiconductors or thermoelectric and electrode materials. This work is devoted to the systematic exploration of novel compounds within the class of MTCh compounds (M=Ni, Pd, Pt; T=Si, Ge, Sn, Pb; Ch=S, Se, Te) by means of density functional calculations. Their preferred structures are predicted from an extended scheme of colored pyrites and marcasites. To determine their stabilities, competing binary MT{sub 2} and MCh{sub 2} boundary phases are taken into account as well as ternary M{sub 3}T{sub 2}Ch{sub 2} and M{sub 2}T{sub 3}Ch{sub 3} systems. Recently established stability diagrams are presented to account for MTCh ordering phenomena with a focus on a not-yet-reported ordering variant of the NiAs{sub 2} type. Due to the good agreement with experimental data available for several PtTCh systems, the predictions for the residual systems are considered sufficiently accurate. - Graphical abstract: Compositional and structural stability of MTCh compounds is investigated from first principle calculations. A conceptional approach is presented to study and predict novel stable and metastable compounds and structures of low gap semiconductors with TCh dumbbell units that are isoelectronic and structurally related to pyrite (FeS{sub 2}). - Highlights: • Study of compositional stability of MTCh vs. M{sub 3}T{sub 2}Ch{sub 2} and M{sub 2}T{sub 3}Ch{sub 3} compounds. • Study of structural stability of known and novel MTCh compounds. • Prediction of novel stable and metastable structures and compounds isoelectronic to pyrite, FeS{sub 2}.

  13. Enhanced performance of branched TiO{sub 2} nanorod based Mn-doped CdS and Mn-doped CdSe quantum dot-sensitized solar cell

    SciTech Connect (OSTI)

    Kim, Soo-Kyoung; Gopi, Chandu V. V. M.; Lee, Jae-Cheol; Kim, Hee-Je

    2015-04-28

    TiO{sub 2} branched nanostructures could be efficient as photoanodes for quantum dot-sensitized solar cells (QDSCs) due to their large surface area for QD deposition. In this study, Mn-doped CdS/Mn-doped CdSe deposited branched TiO{sub 2} nanorods were fabricated to enhance the photovoltaic performance of QDSCs. Mn doping in CdS and CdSe retards the recombination losses of electrons, while branched TiO{sub 2} nanorods facilitate effective electron transport and compensate for the low surface area of the nanorod structure. As a result, the charge-transfer resistance (R{sub CT}), electron lifetime (?{sub e}), and the amount of QD deposition were significantly improved with branched TiO{sub 2} nanorod based Mn-doped CdS/Mn-doped CdSe quantum dot-sensitized solar cell.

  14. Effect of annealing on the kinetic properties and band parameters of Hg{sub 1?x?y}Cd{sub x}Eu{sub y}Se semiconductor crystals

    SciTech Connect (OSTI)

    Kovalyuk, T. T. Maistruk, E. V.; Maryanchuk, P. D.

    2014-12-15

    The results of studies of the kinetic properties of Hg{sub 1?x?y}Cd{sub x}Eu{sub y}Se semiconductor crystals in the ranges of temperatures T = 77300 K and magnetic fields H = 0.55 kOe before and after heat treatment of the samples in Se vapors are reported. It is established that annealing of the samples in Se vapors induces a decrease in the electron concentration. From the concentration dependence of the electron effective mass at the Fermi level, the band gap, the matrix element of interband interaction, and the electron effective mass at the bottom of the conduction band are determined.

  15. Observation of an electron band above the Fermi level in FeTe{sub 0.55}Se{sub 0.45} from in-situ surface doping

    SciTech Connect (OSTI)

    Zhang, P.; Ma, J.; Qian, T.; Richard, P. Ding, H.; Xu, N.; Xu, Y.-M.; Fedorov, A. V.; Denlinger, J. D.; Gu, G. D.

    2014-10-27

    We used in-situ potassium (K) evaporation to dope the surface of the iron-based superconductor FeTe{sub 0.55}Se{sub 0.45}. The systematic study of the bands near the Fermi level confirms that electrons are doped into the system, allowing us to tune the Fermi level of this material and to access otherwise unoccupied electronic states. In particular, we observe an electron band located above the Fermi level before doping that shares similarities with a small three-dimensional pocket observed in the cousin, heavily electron-doped KFe{sub 2?x}Se{sub 2} compound.

  16. Controlled peak wavelength shift of Ca{sub 1-} {sub x} Sr {sub x} (S {sub y} Se{sub 1-} {sub y} ):Eu{sup 2+} phosphor for LED application

    SciTech Connect (OSTI)

    Nazarov, Mihail . E-mail: nazarov.mihail@samsung.com; Yoon, Chulsoo

    2006-08-15

    The highly efficient red-orange-yellow-emitting phosphor (Ca{sub 1-} {sub x} Sr {sub x} )(S{sub 1-} {sub y} Se {sub y} ):Eu{sup 2+} in combination with commercial green phosphor SrGa{sub 2}S{sub 4}:Eu{sup 2+} and blue LED are proposed for a three-band white LED. The luminescence mechanism and optimization parameters are discussed on the basis of proposed peak wavelength diagram. - Graphical abstract: 'Peak wavelength diagram for (Ca{sub 1-} {sub x} Sr {sub x} )(S{sub 1-} {sub y} Se {sub y} ):Eu{sup 2+}'.

  17. Probing structure-induced optical behavior in a new class of self-activated luminescent 0D/1D CaWO₄ metal oxide – CdSe nanocrystal composite heterostructures

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Han, Jinkyu; McBean, Coray; Wang, Lei; Hoy, Jessica; Jaye, Cherno; Liu, Haiqing; Li, Zhuo-Qun; Sfeir, Matthew Y.; Fischer, Daniel A.; Taylor, Gordon T.; et al

    2015-01-30

    In this report, we synthesize and characterize the structural and optical properties of novel heterostructures composed of (i) semiconducting nanocrystalline CdSe quantum dot (QDs) coupled with (ii) both one and zero-dimensional (1D and 0D) motifs of self-activated luminescence CaWO₄ metal oxides. Specifically, ~4 nm CdSe QDs have been anchored onto (i) high-aspect ratio 1D nanowires, measuring ~230 nm in diameter and ~3 μm in length, as well as onto (ii) crystalline 0D nanoparticles (possessing an average diameter of ~ 80 nm) of CaWO₄ through the mediation of 3-mercaptopropionic acid (MPA) as a connecting linker. Composite formation was confirmed by complementarymore » electron microscopy and spectroscopy (i.e. IR and Raman) data. In terms of luminescent properties, our results show that our 1D and 0D heterostructures evince photoluminescence (PL) quenching and shortened PL lifetimes of CaWO₄ as compared with unbound CaWO₄. We propose that a photo-induced electron transfer process occurs from CaWO₄ to CdSe QDs, a scenario which has been confirmed by NEXAFS measurements and which highlights a decrease in the number of unoccupied orbitals in the conduction bands of CdSe QDs. By contrast, the PL signature and lifetimes of MPA-capped CdSe QDs within these heterostructures do not exhibit noticeable changes as compared with unbound MPA-capped CdSe QDs. The striking difference in optical behavior between CaWO₄ nanostructures and CdSe QDs within our heterostructures can be correlated with the relative positions of their conduction and valence energy band levels. In addition, the PL quenching behaviors for CaWO₄ within the heterostructure configuration were examined by systematically varying (i) the quantities and coverage densities of CdSe QDs as well as (ii) the intrinsic morphology (and by extension, the inherent crystallite size) of CaWO₄ itself.« less

  18. Laser parametric instability experiments of a 3ω, 15 kJ, 6-ns...

    Office of Scientific and Technical Information (OSTI)

    For SRS and SBS studies, the light backscattered into the focusing optics is analyzed with ... LASER TARGETS; LASERS; LENGTH; OPTICS; PARAMETRIC INSTABILITIES; PENTANE; ...

  19. Analysis of reliable sub-ns spin-torque switching under transverse bias magnetic fields

    SciTech Connect (OSTI)

    D'Aquino, M.; Perna, S.; Serpico, C.; Bertotti, G.; Mayergoyz, I. D.

    2015-05-07

    The switching process of a magnetic spin-valve nanosystem subject to spin-polarized current pulses is considered. The dependence of the switching probability on the current pulse duration is investigated. The further application of a transverse field along the intermediate anisotropy axis of the particle is used to control the quasi-random relaxation of magnetization to the reversed magnetization state. The critical current amplitudes to realize the switching are determined by studying the phase portrait of the Landau-Lifshtz-Slonczewski dynamics. Macrospin numerical simulations are in good agreement with the theoretical prediction and demonstrate reliable switching even for very short (below 100 ps) current pulses.

  20. Complete genome sequence of Dyadobacter fermentans type strain (NS114T)

    SciTech Connect (OSTI)

    Lang, Elke; Lapidus, Alla; Chertkov, Olga; Brettin, Thomas; Detter, John C.; Han, Cliff; Copeland, Alex; Glavina Del Rio, Tijana; Nolan, Matt; Chen, Feng; Lucas, Susan; Tice, Hope; Cheng, Jan-Fang; Land, Miriam; Hauser, Loren; Chang, Yun-Juan; Jeffries, Cynthia; Bruce, David; Goodwin, Lynne; Pitluck, Sam; Ovchinnikova, Galina; Pati, Amrita; Ivanova, Natalia; Mavromatis, Konstantinos; Chen, Amy; Chain, Patrick; Bristow, Jim; Eisen, Jonathan A.; Markowitz, Victor; Hugenholtz, Philip; Goker, Markus; Rohde, Manfred; Kyrpides, Nikos C; Klenk, Hans-Peter

    2009-05-20

    Dyadobacter fermentans (Chelius MK and Triplett EW, 2000) is the type species of the genus Dyadobacter. It is of phylogenetic interest because of its location in the Cytophagaceae, a very diverse family within the order 'Sphingobacteriales'. D. fermentans has a mainly respiratory metabolism, stains Gram-negative, is non-motile and oxidase and catalase positive. It is characterized by the production of cell filaments in ageing cultures, a flexirubin-like pigment and its ability to ferment glucose, which is almost unique in the aerobically living members of this taxonomically difficult family. Here we describe the features of this organism, together with the complete genome sequence, and annotation. This is the first complete genome sequence of the 'sphingobacterial' genus Dyadobacter, and this 6,967,790 bp long single replicon genome with its 5804 protein-coding and 50 RNA genes is part of the Genomic Encyclopedia of Bacteria and Archaea project.

  1. THE CHANDRA PLANETARY NEBULA SURVEY (ChanPlaNS). III. X-RAY EMISSION...

    Office of Scientific and Technical Information (OSTI)

    X-ray emission components that are unlikely to be due to photospheric emission from the hot central stars (CSPN). Instead, we demonstrate that these sources are well modeled by...

  2. THE CHANDRA PLANETARY NEBULA SURVEY (ChanPlaNS). III. X-RAY EMISSION...

    Office of Scientific and Technical Information (OSTI)

    cases this conclusion is supported by corroborative multiwavelength evidence for the wind and binary properties of the PN central stars. By thus honing in on the origins of...

  3. Influence of different sulfur to selenium ratios on the structural and electronic properties of Cu(In,Ga)(S,Se){sub 2} thin films and solar cells formed by the stacked elemental layer process

    SciTech Connect (OSTI)

    Mueller, B. J.; Zimmermann, C.; Haug, V. Koehler, T.; Zweigart, S.; Hergert, F.; Herr, U.

    2014-11-07

    In this study, we investigate the effect of different elemental selenium to elemental sulfur ratios on the chalcopyrite phase formation in Cu(In,Ga)(S,Se){sub 2} thin films. The films are formed by the stacked elemental layer process. The structural and electronic properties of the thin films and solar cells are analyzed by means of scanning electron microscopy, glow discharge optical emission spectrometry, X-ray diffraction, X-ray fluorescence, Raman spectroscopy, spectral photoluminescence as well as current-voltage, and quantum efficiency measurements. The influence of different S/(S+Se) ratios on the anion incorporation and on the Ga/In distribution is investigated. We find a homogenous sulfur concentration profile inside the film from the top surface to the bottom. External quantum efficiency measurements show that the band edge of the solar cell device is shifted to shorter wavelength, which enhances the open-circuit voltages. The relative increase of the open-circuit voltage with S/(S+Se) ratio is lower than expected from the band gap energy trend, which is attributed to the presence of S-induced defects. We also observe a linear decrease of the short-circuit current density with increasing S/(S+Se) ratio which can be explained by a reduced absorption. Above a critical S/(S+Se) ratio of around 0.61, the fill factor drops drastically, which is accompanied by a strong series resistance increase which may be attributed to changes in the back contact or p-n junction properties.

  4. Crystalline electric field at the rare-earth site in Chevrel-phase RMo/sub 6/S/sub 8/ and RMo/sub 6/Se/sub 8/ from Moessbauer spectroscopy

    SciTech Connect (OSTI)

    Noakes, D.R.; Shenoy, G.K.; Hinks, D.G.

    1985-05-01

    The /sup 155/Gd Moessbauer-effect measurements in GdMo/sub 6/S/sub 8/ and GdMo/sub 6/Se/sub 8/ are reported. A quadrupole interaction of 545 +- 40 and 470 +- 60 MHz is measured at /sup 155/Gd in GdMo/sub 6/S/sub 8/ and GdMo/sub 6/Se/sub 8/, respectively. This indicates the presence of a large B/sub 2//sup 0/O /sub 2//sup 0/ term in the crystalline-electric-field (CEF) Hamiltonian in all rare-earth Chevrel-phase sulfides and selenides. The results imply that the previous analyses of CEF effects in these materials based on a cubic Hamiltonian are not valid. The importance of the CEF in understanding various measured magnetic and superconducting properties of the RMo/sub 6/S/sub 8/ compounds, where R denotes rare earth, is discussed.

  5. Voltage-induced electroluminescence characteristics of hybrid light-emitting diodes with CdSe/Cd/ZnS core-shell nanoparticles embedded in a conducting polymer on plastic substrates

    SciTech Connect (OSTI)

    Kwak, Kiyeol; Cho, Kyoungah, E-mail: chochem@korea.ac.kr, E-mail: sangsig@korea.ac.kr; Kim, Sangsig, E-mail: chochem@korea.ac.kr, E-mail: sangsig@korea.ac.kr [Department of Electrical Engineering, Korea University, Seoul 136-713 (Korea, Republic of)] [Department of Electrical Engineering, Korea University, Seoul 136-713 (Korea, Republic of)

    2014-03-10

    We investigate the electroluminescence (EL) characteristics of a hybrid light-emitting diode (HyLED) with an emissive layer comprised of CdSe/Cd/ZnS core-shell nanoparticles (NPs) embedded in poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) on a plastic substrate. The EL characteristics change dramatically with increasing of the biased voltage. At low voltages, recombination of electrons and holes occurs only in the PFO film because of poor charge transfer in the PFO-CdSe/Cd/ZnS NPs composite film, while the color of the light-emitting from the HyLED changes from blue to red as the biased voltage increases from 7.5 to 17.5?V. We examine and discuss the mechanism of this color tunability.

  6. Erratum: Evolution of precipitate morphology during heat treatment and its implications for the superconductivity in KxFe1.6+ySe2 single crystals [Phys. Rev. B 86 , 144507 (2012)

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Liu, Y.; Xing, Q.; Dennis, K. W.; McCallum, R. W.; Lograsso, T. A.

    2015-08-14

    In this article, we study the relationship between precipitate morphology and superconductivity in KxFe1.6+ySe2 single crystals grown by self-flux method. Scanning electron microscopy (SEM) measurements revealed that the superconducting phase forms a network in the samples quenched above iron vacancy order-disorder transition temperature Ts, whereas it aggregates into micrometer-sized rectangular bars and aligns as disconnected chains in the furnace-cooled samples.

  7. Structural and conductivity studies of CsK(SO{sub 4}){sub 0.32}(SeO{sub 4}){sub 0.68}Te(OH){sub 6}

    SciTech Connect (OSTI)

    Djemel, M.; Abdelhedi, M.; Dammak, M.; Kolsi, A.W.

    2012-12-15

    The compound CsK(SO{sub 4}){sub 0.32}(SeO{sub 4}){sub 0.68}Te(OH){sub 6} crystallizes in the monoclinic P2{sub 1}/n space group. It was analyzed, at room temperature, using X-ray diffractometer data. The main feature of these atomic arrangements is the coexistence of three and different anions (SO{sub 4}{sup 2-}, SeO{sub 4}{sup 2-} and TeO{sub 6}{sup 6-}groups) in the unit cell, connected by hydrogen bonds which make the building of the crystal. The thermal analysis of the title compound shows three distinct endothermal peaks at 435, 460 and 475 K. Complex impedance measurements are performed on this material as a function of both temperature and frequency. The electric conduction has been studied. The temperature dependence on the conductivity indicates that the sample became an ionic conductor at high temperature. - Graphical abstract: Projection of crystal structure CsK(SO{sub 4}){sub 0.32}(SeO{sub 4}){sub 0.68}Te(OH){sub 6} on the ab plane. Highlights: Black-Right-Pointing-Pointer We have studied the results of the crystal structure of the new mixed compound. Black-Right-Pointing-Pointer We have characterized the phase transition observed in DSC curve. Black-Right-Pointing-Pointer The protonic conduction in our material is probably due to a hopping mechanism.

  8. Solar Cells from Plastics? Mission Possible at the PHaSE Energy Research Center, UMass Amherst (A "Life at the Frontiers of Energy Research" contest entry from the 2011 Energy Frontier Research Centers (EFRCs) Summit and Forum)

    SciTech Connect (OSTI)

    Russell, Thomas P; Lahti, Paul M.; PHaSE Staff

    2011-05-01

    'Solar Cells from Plastics? Mission Possible at the PHaSE Energy Research Center, UMass Amherst' was submitted by the Polymer-Based Materials for Harvesting Solar Energy (PHaSE) EFRC to the 'Life at the Frontiers of Energy Research' video contest at the 2011 Science for Our Nation's Energy Future: Energy Frontier Research Centers (EFRCs) Summit and Forum. Twenty-six EFRCs created short videos to highlight their mission and their work. PHaSE, an EFRC co-directed by Thomas P. Russell and Paul M. Lahti at the University of Massachusetts, Amherst, is a partnership of scientists from six institutions: UMass (lead), Oak Ridge National Laboratory, Pennyslvania State University, Rensselaer Polytechnic Institute, and the University of Pittsburgh. The Office of Basic Energy Sciences in the U.S. Department of Energy's Office of Science established the 46 Energy Frontier Research Centers (EFRCs) in 2009. These collaboratively-organized centers conduct fundamental research focused on 'grand challenges' and use-inspired 'basic research needs' recently identified in major strategic planning efforts by the scientific community. The overall purpose is to accelerate scientific progress toward meeting the nation's critical energy challenges.

  9. Solar Cells from Plastics? Mission Possible at the PHaSE Energy Research Center, UMass Amherst (A "Life at the Frontiers of Energy Research" contest entry from the 2011 Energy Frontier Research Centers (EFRCs) Summit and Forum)

    ScienceCinema (OSTI)

    Russell, Thomas P; Lahti, Paul M. (PHaSE - Polymer-Based Materials for Harvesting Solar Energy); PHaSE Staff

    2011-11-03

    'Solar Cells from Plastics? Mission Possible at the PHaSE Energy Research Center, UMass Amherst' was submitted by the Polymer-Based Materials for Harvesting Solar Energy (PHaSE) EFRC to the 'Life at the Frontiers of Energy Research' video contest at the 2011 Science for Our Nation's Energy Future: Energy Frontier Research Centers (EFRCs) Summit and Forum. Twenty-six EFRCs created short videos to highlight their mission and their work. PHaSE, an EFRC co-directed by Thomas P. Russell and Paul M. Lahti at the University of Massachusetts, Amherst, is a partnership of scientists from six institutions: UMass (lead), Oak Ridge National Laboratory, Pennyslvania State University, Rensselaer Polytechnic Institute, and the University of Pittsburgh. The Office of Basic Energy Sciences in the U.S. Department of Energy's Office of Science established the 46 Energy Frontier Research Centers (EFRCs) in 2009. These collaboratively-organized centers conduct fundamental research focused on 'grand challenges' and use-inspired 'basic research needs' recently identified in major strategic planning efforts by the scientific community. The overall purpose is to accelerate scientific progress toward meeting the nation's critical energy challenges.

  10. Temperature and composition phase diagram in the iron-based ladder compounds Ba 1 - x Cs x Fe 2 Se 3

    SciTech Connect (OSTI)

    Hawai, Takafumi; Nambu, Yusuke; Ohgushi, Kenya; Du, Fei; Hirata, Yasuyuki; Avdeev, Maxim; Uwatoko, Yoshiya; Sekine, Yurina; Fukazawa, Hiroshi; Ma, Jie; Chi, Songxue; Ueda, Yutaka; Yoshizawa, Hideki; Sato, Taku J.

    2015-05-28

    We investigated the iron-based ladder compounds (Ba,Cs)Fe?Se?. Their parent compounds BaFe?Se? and CsFe?Se? have different space groups, formal valences of Fe, and magnetic structures. Electrical resistivity, specific heat, magnetic susceptibility, x-ray diffraction, and powder neutron diffraction measurements were conducted to obtain a temperature and composition phase diagram of this system. Block magnetism observed in BaFe?Se? is drastically suppressed with Cs doping. In contrast, stripe magnetism observed in CsFe?Se? is not so fragile against Ba doping. A new type of magnetic structure appears in intermediate compositions, which is similar to stripe magnetism of CsFe?Se?, but interladder spin configuration is different. Intermediate compounds show insulating behavior, nevertheless a finite T-linear contribution in specific heat was obtained at low temperatures.

  11. Liquid precursor inks for deposition of In--Se, Ga--Se and In--Ga--Se

    DOE Patents [OSTI]

    Curtis, Calvin J.; Hersh, Peter A.; Miedaner, Alexander; Habas, Susan; van Hest, Maikel; Ginley, David S.

    2015-08-11

    An ink includes a solution of selenium in ethylene diamine solvent and a solution of at least one metal salt selected from the group consisting of an indium salt or a gallium salt in at least one solvent including an organic amide. The organic amide can include dimethylformamide. The organic amide can include N-methylpyrrolidone.

  12. Comparison of crystal growth and thermoelectric properties of n-type Bi-Se-Te and p-type Bi-Sb-Te nanocrystalline thin films: Effects of homogeneous irradiation with an electron beam

    SciTech Connect (OSTI)

    Takashiri, Masayuki, E-mail: takashiri@tokai-u.jp; Imai, Kazuo; Uyama, Masato; Nishi, Yoshitake [Department of Materials Science, Tokai University, 4-1-1 Kitakaname, Hiratsuka, Kanagawa 259-1292 (Japan); Hagino, Harutoshi; Miyazaki, Koji [Department of Mechanical and Control Engineering, Kyushu Institute of Technology, 1-1 Sensui, Tobata-ku, Kitakyushu 804-8550 (Japan); Tanaka, Saburo [Department of Mechanical Engineering, College of Engineering, Nihon University, Nakagawara, Tokusada, Tamuramachi, Koriyama, Fukushima 963-8642 (Japan)

    2014-06-07

    The effects of homogenous electron beam (EB) irradiation on the crystal growth and thermoelectric properties of n-type Bi-Se-Te and p-type Bi-Sb-Te thin films were investigated. Both types of thin films were prepared by flash evaporation, after which homogeneous EB irradiation was performed at an acceleration voltage of 0.17?MeV. For the n-type thin films, nanodots with a diameter of less than 10?nm were observed on the surface of rice-like nanostructures, and crystallization and crystal orientation were improved by EB irradiation. The resulting enhancement of mobility led to increased electrical conductivity and thermoelectric power factor for the n-type thin films. In contrast, the crystallization and crystal orientation of the p-type thin films were not influenced by EB irradiation. The carrier concentration increased and mobility decreased with increased EB irradiation dose, possibly because of the generation of defects. As a result, the thermoelectric power factor of p-type thin films was not improved by EB irradiation. The different crystallization behavior of the n-type and p-type thin films is attributed to atomic rearrangement during EB irradiation. Selenium in the n-type thin films is more likely to undergo atomic rearrangement than the other atoms present, so only the crystallinity of the n-type Bi-Se-Te thin films was enhanced.

  13. Structural, electrical, and thermoelectrical properties of (Bi{sub 1-x}Sb{sub x}){sub 2}Se{sub 3} alloys prepared by a conventional melting technique

    SciTech Connect (OSTI)

    Shokr, E. Kh.; Ibrahim, E. M. M. Abdel Hakeem, A. M.; Adam, A. M.

    2013-01-15

    Polycrystalline solid solutions of (Bi{sub 1-x}Sb{sub x}){sub 2}Se{sub 3} (x = 0, 0.025, 0.050, 0.075, 0.100) were prepared using a facile method based on the conventional melting technique followed by annealing process. X-ray analysis and Raman spectroscopical measurements revealed formation of Bi{sub 2}Se{sub 3} in single phase. The electrical and thermoelectric properties have been studied on the bulk samples in the temperature range 100-420 K. The electrical conductivity measurements show that the activation energy and room-temperature electrical conductivity dependences on the Sb content respectively exhibit minimum and maximum values at x = 0.05. The thermoelectric power exhibited a maximum value near the room temperature suggesting promising materials for room-temperature applications. The highest power factor value was found to be 13.53 {mu}W K{sup -2} cm{sup -1} and recorded for the x = 0.05 compound.

  14. Grainger: Compromise Agreement (2013-SE-1411)

    Broader source: Energy.gov [DOE]

    DOE and Grainger International Inc. entered into a Compromise Agreement to resolve a case involving the distribution in commerce of noncompliant freezers.

  15. Haier: Noncompliance Determination (2011-SE-1408)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Haier America Trading, L.L.C. finding that model number HNCM070, a chest freezer, does not comport with the energy conservation standards.

  16. Pax Global: Compromise Agreement (2013-SE-1413)

    Broader source: Energy.gov [DOE]

    DOE and Pax Global, Inc., entered into a Compromise Agreement to resolve a case involving the distribution in commerce of noncompliant freezers.

  17. Central Moloney: Proposed Penalty (2013-SE-4702)

    Broader source: Energy.gov [DOE]

    DOE alleged in a Notice of Proposed Civil Penalty that Central Moloney, Inc. manufactured and distributed a variety of noncompliant liquid-immersed distribution transformers in the U.S.

  18. Central Moloney: Noncompliance Determination (2013-SE-4702)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Central Moloney, Inc. finding that liquid-immersed distribution transformer basic models 30300150 and 32500095 do not comport with the energy conservation standards.

  19. Perlick: Noncompliance Determination (2013-SE-14001)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Perlick Corporation finding that freezer basic model HP24F does not comport with the energy conservation standards.

  20. Islandaire: Noncompliance Determination (2015-SE-43008)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Islandaire, Inc. finding that the Islandaire package terminal air conditioner basic model CPZ-129ANR1-B, which includes models EZDR12B and EZD4212B, does not comport with the applicable energy conservation standards.

  1. Everest Refrigeration: Noncompliance Determination (2015-SE-42001)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Bu Sung America Corporation (dba Everest Refrigeration) finding that commercial refrigeration equipment model number ESGR3 does not comport with the energy conservation standards.

  2. Universal: Noncompliance Determination (2013-SE-26004)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Universal Lighting Technologies, Inc. finding that fluorescent lamp ballast model B140R277HP does not comport with the energy conservation standards.

  3. Cooper: Noncompliance Determination (2012-SE-4701)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Cooper Power Systems, LLC finding that basic models 277-99.28, 277-99.26, and 277-99.22 of distribution transformers do not comport with the energy conservation standards.

  4. Teddico: Noncompliance Determination (2012-SE-5409)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to The Electrical Design, Development and Implementation Company d/b/a Teddico finding that a variety of basic models of magnetic probe-start metal halide lamp fixtures do not comport with the energy conservation standards.

  5. Whirlpool: Compliance Determination (2010-SE-0103)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Compliance Determination to Whirlpool Corporation after DOE testing confirmed that the Maytag refrigerator-freezer model MSD2578VE comports with the applicable energy conservation standard.

  6. Islandaire: Noncompliance Determination (2015-SE-43009)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Islandaire, Inc. finding that the Islandaire package terminal air conditioner basic model CPZ-07ANR1-B, which includes model EZDR07B, does not comport with the applicable energy conservation standards.

  7. Heat Controller: Noncompliance Determination (2014-SE-15004)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Heat Controller, Inc. finding that the room air conditioner distributed in commerce by Heat Controller as Comfort Aire brand models CGREG-81H and REG-81J does not comport with the energy conservation standards.

  8. Utility: Noncompliance Determination (2016-SE-42003)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Utility Refrigerator finding that commercial refrigeration equipment basic model number PT-R-75-SS-3S-3S-N does not comport with the energy conservation standards.

  9. Bigwall: Noncompliance Determination (2014-SE-15006)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Bigwall Enterprises, Inc. finding that PerfectAire brand model PACH8000 ("Bigwall model PACH8000") of room air conditioners do not comport with the energy conservation standards.

  10. Mile High: Noncompliance Determination (2012-SE-4501)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Mile High Equipment, LLC finding that Ice-O-Matic brand automatic commercial ice maker basic model ICE2106 FW, HW does not comport with the energy conservation standards.

  11. Perlick: Noncompliance Determination (2013-SE-14002)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Perlick Corporation finding that refrigerator basic model HP48RR does not comport with the energy conservation standards.

  12. Hydac: Noncompliance Determination (2012-SE-4107)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Hydac Technology Corporation finding that a variety of electric motor basic models do not comport with the energy conservation standards.

  13. Midea: Noncompliance Determination (2013-SE-1505)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to GD Midea Air-Conditioning Equipment Co. Ltd. finding that Arctic King brand room air conditioner basic model MWJ1-08ERN1-BI8, manufactured by Midea, does not comport with the energy conservation standards.

  14. Sunshine Lighting: Noncompliance Determination (2014-SE-54008)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Sunshine Lighting Company finding that Sunlite brand metal halide lamp fixture basic models 04937-SU, 04938-SU, 04952 SU, and 04956 SU do not comport with the energy conservation standards.

  15. Engineered Products: Noncompliance Determination (2012-SE-5401)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Engineered Products Company finding that basic model 15701 of metal halide lamp fixture does not comport with the energy conservation standards.

  16. Whirlpool: Noncompliance Determination (2013-SE-1420)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Whirlpool Corporation finding that refrigerator-freezer basic model 8TAR81 does not comport with the energy conservation standards.

  17. SeWave | Open Energy Information

    Open Energy Info (EERE)

    50:50 JV between UK's Wavegen and Faroese electricity company SEV to to design and build a tunnelled demonstration wave power plant in the Faroes Islands. References:...

  18. Leader Electronics: Noncompliance Determination (2010-SE-2301)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Leader Electronics, Inc. finding that "NU50-2093400-I3(NU50-21090-300F)" and "MU03-F050040-A1(MU03-Fl050-AKOS)" of external power supplies do not comport with the energy conservation standards.

  19. Leader Electronics: Data Request (2010-SE-2301)

    Broader source: Energy.gov [DOE]

    DOE requested test data from Leader Electronics Inc. for various models of external power supplies after Leader Electronics certified energy values that did not meet federal energy conservation standards.

  20. Equipment-Resources-PHaSe-EFRC

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Equipment Equipment photo Last update 30 April 2015. People wishing to use equipment listed below must first receive training and permission from the Facility Director, or present instrument contact person, who can provide basic training and information from an experienced user. Training and access must be arranged in advance of first use. Reservation of usage time for a number of instruments requires you to set up an account on the Facilities Online Manager (FOM) service! Connect to the

  1. GE Lighting Solutions: Order (2013-SE-4901)

    Broader source: Energy.gov [DOE]

    DOE ordered General Electric Lighting Solutions, LLC to pay a $5,360 civil penalty after finding GE Lighting Solutions had manufactured and distributed in commerce in the U.S. 30 units of basic model DR4-RTFB-23B and 177 units (of which 85 units remain in inventory) of basic model DR4-RTFB-77A-002, noncompliant traffic signal modules.

  2. Fuzhou Sunlight: Noncompliance Determination (2010-SE-1402)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Fuzhou Sunlight Lighting Electrical Appliance Co., Ltd. finding that a variety of models of incandescent reflector lamps do not comport with the energy conservation standards.

  3. Haier: Noncompliance Determination (2011-SE-1428)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Haier America Trading, LLC finding that Haier model HMCM106EA, a freezer, does not comport with the energy conservation standards.

  4. HKC-US: Order (2013-SE-33002)

    Office of Energy Efficiency and Renewable Energy (EERE)

    DOE ordered HKC-US, LLC to pay a $6,500 civil penalty after finding HKC-US had failed to certify that one basic model of ceiling fan light kit complies with the applicable energy conservation standards.

  5. Aspen: Noncompliance Determination (2011-SE-1602)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Aspen Manufacturing finding that indoor unit model AEW244 and outdoor unit model NCPC-424-3010 of residential split system central air conditioning system do not comport with the energy conservation standards.

  6. Aspen: Noncompliance Determination (2010-SE-0305)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Aspen Manufacturing finding that a variety of basic models of split-system air conditioning heat pumps do not comport with the energy conservation standards.

  7. Mile High: Proposed Penalty (2012-SE-4501)

    Broader source: Energy.gov [DOE]

    DOE alleged in a Notice of Proposed Civil Penalty that Mile High Equipment, LLC manufactured and distributed noncompliant Ice-O-Matic brand automatic commercial ice maker basic model ICE2106 FW, HW in the U.S.

  8. Engineered Products: Proposed Penalty (2012-SE-5401)

    Broader source: Energy.gov [DOE]

    DOE alleged in a Notice of Proposed Civil Penalty that Engineered Products Company manufactured/privately-labeled and distributed a number of units of noncompliant basic model 15701, a metal halide lamp fixture with a magnetic probe-start ballast in the U.S.

  9. Maxx: Proposed Penalty (2012-SE-4506)

    Broader source: Energy.gov [DOE]

    DOE alleged in a Notice of Proposed Civil Penalty that Maxx Cold Food Service manufactured and distributed a noncompliant Maxx Ice brand automatic commercial ice maker basic model MIM450 in the U.S.

  10. Solar Power Potential in SE New Mexico

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Solar Power Potential in Southeast New Mexico Solar Power Project Opportunities Abound in the Region The WIPP site is receives abundant solar energy with 6-7 kWhsq meter power ...

  11. Wind Energy Potential in SE New Mexico

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    click to return to the Renewable Energy page Return to Renewable Energy Page Wind Energy in Southeast New Mexico Several Ongoing and New Wind Power Projects are Contributing to Making Renewable Energy Sources an Important Economic and Environmental Mainstay of the Region As the accompanying map of New Mexico shows, the best wind power generation potential near WIPP is along the Delaware Mountain ridge line of the southern Guadalupe Mountains, about 50-60 miles southwest. The numeric grid values

  12. Neptun Light: Order (2012-SE-3504)

    Broader source: Energy.gov [DOE]

    DOE ordered Neptun Light, Inc. to pay a $13,000 civil penalty after finding Neptun Light had failed to certify that certain models of medium base compact fluorescent lamps comply with the applicable energy conservation standards.

  13. Islandaire: Noncompliance Determination (2015-SE-43007)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Islandaire, Inc. finding that the Islandaire package terminal air conditioner basic model CPZ-09ANR1-B, which includes models EZ4209B and EZDR09B, does not comport with the applicable energy conservation standards.

  14. Sears: Noncompliance Determination (2011-SE-1418)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Sears, Roebuck & Co. finding that Kenmore-brand model number 255.19502010 ("19502") and Kenmore-brand model number 255.19702010 ("19702"), compact chest freezers, do not comport with the energy conservation standards.

  15. Sears: Compromise Agreement (2011-SE-1418)

    Broader source: Energy.gov [DOE]

    DOE and Sears, Roebuck & Co. entered into a Compromise Agreement to resolve a case involving the distribution in commerce of noncompliant freezers.

  16. Central Moloney: Order (2013-SE-4702)

    Broader source: Energy.gov [DOE]

    DOE ordered Central Moloney, Inc. to pay a $2,500 civil penalty after finding Central Moloney had manufactured and distributed noncompliant liquid-immersed distribution transformers in commerce in the U.S.

  17. CNA: Proposed Penalty (2013-SE-1430)

    Broader source: Energy.gov [DOE]

    DOE alleged in a Notice of Proposed Civil Penalty that CNA International, Inc., d/b/a MC Appliance Corp. privately labeled and distributed noncompliant freezer Magic Chef model number HMCF7W in the U.S.

  18. CNA: Noncompliance Determination (2013-SE-1430)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to CNA International, Inc., d/b/a MC Appliance Corp. finding that Magic Chef-brand model HMCF7W ("CNA model HMCF7W") does not comport with the energy conservation standards.

  19. Felix Storch: Noncompliance Determination (2011-SE-1420)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Felix Storch, Inc., finding that model number CF11ES, a chest freezer does not comport with the energy conservation standards.

  20. Sanyo: Notice of Allowance (2013-SE-1428)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Allowance to Sanyo E & E Corporation, allowing Sanyo to resume distribution of refrigerator model SBC-500 after Sanyo provided documentation showing that it had modified the model to be in compliance with the applicable energy conservation standard.

  1. Morris: Noncompliance Determination (2013-SE-5403)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Morris Products, Inc. finding that various models of metal halide lamp fixtures do not comport with the energy conservation standards.

  2. Morris: Proposed Penalty (2013-SE-5403)

    Broader source: Energy.gov [DOE]

    DOE alleged in a Notice of Proposed Civil Penalty that Morris Products, Inc. manufactured and distributed noncompliant metal halide lamp fixtures in the U.S.

  3. ERG 1-Research-PHaSe-EFRC

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    1-Energy Research Group 1 Polymer-based Architectures, Design & Synthesis Three students lab photo rainbow vials This webpage is provided for legacy archive purposes only, as of 30 April 2015. ERG 1 was coordinated by Prof. Todd Emrick (PSE), with Prof. Paul M. Lahti (Chemistry) as co-coordinator. Researchers associated with ERG 1 synthesize new polymers and nanocomposite materials with well-defined structures and architectures, that are capable of harvesting light and generating

  4. ERG 2-Research-PHaSe-EFRC

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    2-Energy Research Group 2 Controlled Assemblies and Morphologies This webpage is provided for legacy archive purposes only, as of 30 April 2015. ERG2 was coordinated by Prof. Dhandapani Venkataraman (Chemistry), with Prof. Tom Russell (PSE) as co-coordinator. This ERG has the largest number of participants, all of whom work to control the assembly and morphology of photovoltaic materials in order to improve charge transport. Multiple strategies are being pursued, including templated nanoscopic

  5. ERG 3-Research-PHaSe-EFRC

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    3-Energy Research Group 3 Photophysical Characterization, Device Design and Integration ERG3 diagram This webpage is provided for legacy archive purposes only, as of 30 April 2015. ERG 3 was coordinated by Profs. Mike Barnes (Chemistry) and Dimitrios Maroudas (Chemical Engineering). The primary goal of ERG 3 is to elucidate photophysical details of charge transport and energy transfer within nanostructured photovoltaic composite films. Single-molecule spectroscopy and ultrafast optical

  6. National Comfort Products: Order (2014-SE-16014)

    Broader source: Energy.gov [DOE]

    DOE ordered National Comfort Products to pay a $16,000 civil penalty after finding National Comfort Products had failed to certify that certain models of central air conditioners and heat pumps comply with the applicable energy conservation standards.

  7. Sanden Vendo America: Order (2014-SE-52002)

    Broader source: Energy.gov [DOE]

    DOE ordered Sanden Vendo America Inc. to pay a $6,200 civil penalty after finding Sanden Vendo America had manufactured and distributed in commerce in the U.S. 31 units of Class A refrigerated bottled or canned beverage vending machine model Vue30 (with 1128127 cassette refrigeration deck), a noncompliant product.

  8. Royal Pacific: Proposed Penalty (2013-SE-33004)

    Broader source: Energy.gov [DOE]

    DOE alleged in a Notice of Proposed Civil Penalty that Royal Pacific, Ltd. failed to certify ceiling fans, ceiling fan light kits, medium base compact fluorescent lamps, and illuminated exit signs as compliant with the applicable energy conservation standards.

  9. Royal Pacific: Order (2013-SE-33004)

    Broader source: Energy.gov [DOE]

    DOE ordered Royal Pacific, Ltd. to pay a $8,000 civil penalty after finding Royal Pacific had failed to certify that various basic models of medium base compact fluorescent lamps, ceiling fans, ceiling fan light kits, and illuminated exit signs comply with the applicable energy conservation standards.

  10. ASKO Appliances: Compliance Determination (2010-SE-0601)

    Broader source: Energy.gov [DOE]

    DOE tested four units dishwasher manufactured by ASKO Appliances, Inc. Applying statistical analysis, DOE found that the dishwasher meets the federal energy standards for maximum energy use.

  11. Lutron Electronics: Order (2012-SE-3796)

    Broader source: Energy.gov [DOE]

    DOE ordered Lutron Electronics Co., Inc. to pay a $13,000 civil penalty after finding Lutron Electronics had manufactured and distributed in commerce in the U.S. at least 79,000 units of various basic models, noncompliant Class A external power supplies.

  12. Lutron Electronics: Noncompliance Determination (2012-SE-3796)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Lutron Electronics Co., Inc. finding that a variety of Class A external power supply basic models do not comport with the energy conservation standards.

  13. Hicon: Proposed Penalty (2013-SE-1426)

    Broader source: Energy.gov [DOE]

    DOE alleged in a Notice of Proposed Civil Penalty that Ningbo Hicon International Industry Company, Ltd. manufactured and distributed noncompliant freezer basic model BD-200 in the U.S.

  14. Hicon: Noncompliance Determination (2013-SE-1426)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Ningbo Hicon International Industry Company, Ltd. finding that model number BD-200, a compact chest freezer, does not comport with the energy conservation standards.

  15. Precision: Noncompliance Determination (2013-SE-1410)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Noncompliance Determination to Precision Trading Corp. finding that Precision brand model Premium PFR515M, a freezer, does not comport with the energy conservation standards.

  16. Precision: Compromise Agreement (2013-SE-1410)

    Broader source: Energy.gov [DOE]

    DOE and Precision Trading Corp. entered into a Compromise Agreement to resolve a case involving the distribution in commerce of noncompliant freezers.

  17. Engineered Products: Order (2012-SE-5401)

    Broader source: Energy.gov [DOE]

    DOE ordered Engineered Products Company to pay a $480 civil penalty after finding EPCO had manufactured/privately labeled and distributed in commerce in the U.S. 19 units of basic model 15701, a metal halide lamp fixture.

  18. Midea: Penalty Notice Withdrawal (2010-SE-0110)

    Broader source: Energy.gov [DOE]

    DOE withdrew its January 26, 2012 Notice of Proposed Civil Penalty, but retained the right to take further enforcement actions.

  19. Whirlpool: Data Request (2010-SE-0103)

    Office of Energy Efficiency and Renewable Energy (EERE)

    DOE requested test data underlying Whirlpool Corporation's certification that one model of refrigerator-freezer complies with the applicable energy conservation standard.

  20. Arelik A.?: Compliance Determination (2010-SE-0105)

    Broader source: Energy.gov [DOE]

    DOE issued a Notice of Compliance Determination after test results revealed that Arelik's Blomberg BRFB1450 refrigerator-freezer complies with the applicable energy conservation standards.