National Library of Energy BETA

Sample records for lighting phonons thermal

  1. Contributions of anharmonic phonon interactions to thermal boundary conductance.

    SciTech Connect (OSTI)

    Hopkins, Patrick E.; Norris, Pamela M.; Duda, John C.

    2010-05-01

    Continued reduction of characteristic dimensions in nanosystems has given rise to increasing importance of material interfaces on the overall system performance. With regard to thermal transport, this increases the need for a better fundamental understanding of the processes affecting interfacial thermal transport, as characterized by the thermal boundary conductance. When thermal boundary conductance is driven by phononic scattering events, accurate predictions of interfacial transport must account for anharmonic phononic coupling as this affects the thermal transmission. In this paper, a new model for phononic thermal boundary conductance is developed that takes into account anharonic coupling, or inelastic scattering events, at the interface between two materials. Previous models for thermal boundary conductance are first reviewed, including the Diffuse Mismatch Model, which only consdiers elastic phonon scattering events, and earlier attempts to account for inelastic phonon scattering, namely, the Maximum Transmission Model and the Higher Harmonic Inelastic model. A new model is derived, the Anharmonic Inelastic Model, which provides a more physical consideration of the effects of inelastic scattering on thermal boundary conductance. This is accomplished by considering specific ranges of phonon frequency interactions and phonon number density conservation. Thus, this model considers the contributions of anharmonic, inelastically scattered phonons to thermal boundary conductance. This new Anharmonic Inelastic Model shows excellent agreement between model predictions and experimental data at the Pb/diamond interface due to its ability to account for the temperature dependent changing phonon population in diamond, which can couple anharmonically with multiple phonons in Pb.

  2. First-principles prediction of phononic thermal conductivity of silicene: A comparison with graphene

    SciTech Connect (OSTI)

    Gu, Xiaokun; Yang, Ronggui

    2015-01-14

    There has been great interest in two-dimensional materials, beyond graphene, for both fundamental sciences and technological applications. Silicene, a silicon counterpart of graphene, has been shown to possess some better electronic properties than graphene. However, its thermal transport properties have not been fully studied. In this paper, we apply the first-principles-based phonon Boltzmann transport equation to investigate the thermal conductivity of silicene as well as the phonon scattering mechanisms. Although both graphene and silicene are two-dimensional crystals with similar crystal structure, we find that phonon transport in silicene is quite different from that in graphene. The thermal conductivity of silicene shows a logarithmic increase with respect to the sample size due to the small scattering rates of acoustic in-plane phonon modes, while that of graphene is finite. Detailed analysis of phonon scattering channels shows that the linear dispersion of the acoustic out-of-plane (ZA) phonon modes, which is induced by the buckled structure, makes the long-wavelength longitudinal acoustic phonon modes in silicene not as efficiently scattered as that in graphene. Compared with graphene, where most of the heat is carried by the acoustic out-of-plane (ZA) phonon modes, the ZA phonon modes in silicene only have ?10% contribution to the total thermal conductivity, which can also be attributed to the buckled structure. This systematic comparison of phonon transport and thermal conductivity of silicene and graphene using the first-principle-based calculations shed some light on other two-dimensional materials, such as two-dimensional transition metal dichalcogenides.

  3. Acoustic phonon spectrum and thermal transport in nanoporous alumina arrays

    SciTech Connect (OSTI)

    Kargar, Fariborz; Ramirez, Sylvester; Debnath, Bishwajit; Malekpour, Hoda; Lake, Roger; Balandin, Alexander A.

    2015-10-28

    We report results of a combined investigation of thermal conductivity and acoustic phonon spectra in nanoporous alumina membranes with the pore diameter decreasing from D=180 nm to 25 nm. The samples with the hexagonally arranged pores were selected to have the same porosity Ø ≈13%. The Brillouin-Mandelstam spectroscopy measurements revealed bulk-like phonon spectrum in the samples with D=180-nm pores and spectral features, which were attributed to spatial confinement, in the samples with 25-nm and 40-nm pores. The velocity of the longitudinal acoustic phonons was reduced in the samples with smaller pores. As a result, analysis of the experimental data and calculated phonon dispersion suggests that both phonon-boundary scattering and phonon spatial confinement affect heat conduction in membranes with the feature sizes D<40 nm.

  4. Acoustic phonon spectrum and thermal transport in nanoporous alumina arrays

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

    Kargar, Fariborz; Ramirez, Sylvester; Debnath, Bishwajit; Malekpour, Hoda; Lake, Roger; Balandin, Alexander A.

    2015-10-28

    We report results of a combined investigation of thermal conductivity and acoustic phonon spectra in nanoporous alumina membranes with the pore diameter decreasing from D=180 nm to 25 nm. The samples with the hexagonally arranged pores were selected to have the same porosity Ø ≈13%. The Brillouin-Mandelstam spectroscopy measurements revealed bulk-like phonon spectrum in the samples with D=180-nm pores and spectral features, which were attributed to spatial confinement, in the samples with 25-nm and 40-nm pores. The velocity of the longitudinal acoustic phonons was reduced in the samples with smaller pores. As a result, analysis of the experimental data andmore » calculated phonon dispersion suggests that both phonon-boundary scattering and phonon spatial confinement affect heat conduction in membranes with the feature sizes D<40 nm.« less

  5. Phonon anharmonicity and negative thermal expansion in SnSe

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

    Bansal, Dipanshu; Hong, Jiawang; Li, Chen W.; May, Andrew F.; Porter, Wallace; Hu, Michael Y.; Abernathy, Douglas L.; Delaire, Olivier

    2016-08-09

    In this paper, the anharmonic phonon properties of SnSe in the Pnma phase were investigated with a combination of experiments and first-principles simulations. Using inelastic neutron scattering (INS) and nuclear resonant inelastic X-ray scattering (NRIXS), we have measured the phonon dispersions and density of states (DOS) and their temperature dependence, which revealed a strong, inhomogeneous shift and broadening of the spectrum on warming. First-principles simulations were performed to rationalize these measurements, and to explain the previously reported anisotropic thermal expansion, in particular the negative thermal expansion within the Sn-Se bilayers. Including the anisotropic strain dependence of the phonon free energy,more » in addition to the electronic ground state energy, is essential to reproduce the negative thermal expansion. From the phonon DOS obtained with INS and additional calorimetry measurements, we quantify the harmonic, dilational, and anharmonic components of the phonon entropy, heat capacity, and free energy. Finally, the origin of the anharmonic phonon thermodynamics is linked to the electronic structure.« less

  6. Giant Anaharmonic Phonon Scattering in PbTe (Journal Article...

    Office of Scientific and Technical Information (OSTI)

    Country of Publication: United States Language: English Subject: solar (photovoltaic), solar (thermal), solid state lighting, phonons, thermal conductivity, thermoelectric, ...

  7. Thermally triggered phononic gaps in liquids at THz scale

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

    Bolmatov, Dima; Zhernenkov, Mikhail; Zavyalov, Dmitry; Stoupin, Stanislav; Cunsolo, Alessandro; Cai, Yong Q.

    2016-01-14

    In this study we present inelastic X-ray scattering experiments in a diamond anvil cell and molecular dynamic simulations to investigate the behavior of phononic excitations in liquid Ar. The spectra calculated using molecular dynamics were found to be in a good agreement with the experimental data. Furthermore, we observe that, upon temperature increases, a low-frequency transverse phononic gap emerges while high-frequency propagating modes become evanescent at the THz scale. The effect of strong localization of a longitudinal phononic mode in the supercritical phase is observed for the first time. The evidence for the high-frequency transverse phononic gap due to themore » transition from an oscillatory to a ballistic dynamic regimes of motion is presented and supported by molecular dynamics simulations. This transition takes place across the Frenkel line thermodynamic limit which demarcates compressed liquid and non-compressed fluid domains on the phase diagram and is supported by calculations within the Green-Kubo phenomenological formalism. These results are crucial to advance the development of novel terahertz thermal devices, phononic lenses, mirrors, and other THz metamaterials.« less

  8. Temperature dependence of Brillouin light scattering spectra of acoustic phonons in silicon

    SciTech Connect (OSTI)

    Olsson, Kevin S.; Klimovich, Nikita; An, Kyongmo; Sullivan, Sean; Weathers, Annie; Shi, Li E-mail: elaineli@physics.utexas.edu; Li, Xiaoqin E-mail: elaineli@physics.utexas.edu

    2015-02-02

    Electrons, optical phonons, and acoustic phonons are often driven out of local equilibrium in electronic devices or during laser-material interaction processes. The need for a better understanding of such non-equilibrium transport processes has motivated the development of Raman spectroscopy as a local temperature sensor of optical phonons and intermediate frequency acoustic phonons, whereas Brillouin light scattering (BLS) has recently been explored as a temperature sensor of low-frequency acoustic phonons. Here, we report the measured BLS spectra of silicon at different temperatures. The origins of the observed temperature dependence of the BLS peak position, linewidth, and intensity are examined in order to evaluate their potential use as temperature sensors for acoustic phonons.

  9. Electrical and thermal properties of polycrystalline Si thin films with phononic crystal nanopatterning for thermoelectric applications

    SciTech Connect (OSTI)

    Nomura, Masahiro; Kage, Yuta; Mller, David; Moser, Dominik; Paul, Oliver

    2015-06-01

    Electrical and thermal properties of polycrystalline Si thin films with two-dimensional phononic patterning were investigated at room temperature. Electrical and thermal conductivities for the phononic crystal nanostructures with a variety of radii of the circular holes were measured to systematically investigate the impact of the nanopatterning. The concept of phonon-glass and electron-crystal is valid in the investigated electron and phonon transport systems with the neck size of 80?nm. The thermal conductivity is more sensitive than the electrical conductivity to the nanopatterning due to the longer mean free path of the thermal phonons than that of the charge carriers. The values of the figure of merit ZT were 0.065 and 0.035, and the enhancement factors were 2 and 4 for the p-doped and n-doped phononic crystals compared to the unpatterned thin films, respectively, when the characteristic size of the phononic crystal nanostructure is below 100?nm. The greater enhancement factor of ZT for the n-doped sample seems to result from the strong phonon scattering by heavy phosphorus atoms at the grain boundaries.

  10. Thermally stimulated 315 THz emission at plasmon-phonon frequencies in polar semiconductors

    SciTech Connect (OSTI)

    Poela, J., E-mail: pozela@pfi.lt; Poela, K.; il?nas, A.; irmulis, E.; Kaalynas, I.; Jucien?, V.; Venckevi?ius, R. [Center for Physical Sciences and Technology, Semiconductor Physics Institute (Lithuania)

    2014-12-15

    The possibilities of distinguishing highly coherent terahertz emission at a specified frequency from the incoherent thermal emission of a hot body are considered. It is experimentally shown that the smooth planar surface (with no diffraction guides) of heated GaAs and AlGaAs wafers emits directed continuous-wave (cw) terahertz radiation at coupled surface plasmon-phonon vibrational frequencies. The recording of terahertz reflectance spectra is demonstrated as a method for the identification of plasmons, optical phonons, and coupled plasmon-phonon vibrations in semiconductors.

  11. Electron-phonon coupling and thermal transport in the thermoelectric compound Mo3Sb7–xTex

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

    Bansal, Dipanshu; Li, Chen W.; Said, Ayman H.; Abernathy, Douglas L.; Yan, Jiaqiang; Delaire, Olivier A.

    2015-12-07

    Phonon properties of Mo3Sb7–xTex (x = 0, 1.5, 1.7), a potential high-temperature thermoelectric material, have been studied with inelastic neutron and x-ray scattering, and with first-principles simulations. The substitution of Te for Sb leads to pronounced changes in the electronic struc- ture, local bonding, phonon density of states (DOS), dispersions, and phonon lifetimes. Alloying with tellurium shifts the Fermi level upward, near the top of the valence band, resulting in a strong suppression of electron-phonon screening, and a large overall stiffening of interatomic force- constants. The suppression in electron-phonon coupling concomitantly increases group velocities and suppresses phonon scattering rates, surpassingmore » the effects of alloy-disorder scattering, and re- sulting in a surprising increased lattice thermal conductivity in the alloy. We also identify that the local bonding environment changes non-uniformly around different atoms, leading to variable perturbation strengths for different optical phonon branches. The respective roles of changes in phonon group velocities and phonon lifetimes on the lattice thermal conductivity are quantified. Lastly, our results highlight the importance of the electron-phonon coupling on phonon mean-free-paths in this compound, and also estimates the contributions from boundary scattering, umklapp scattering, and point-defect scattering.« less

  12. Phononic crystal devices

    SciTech Connect (OSTI)

    El-Kady, Ihab F.; Olsson, Roy H.

    2012-01-10

    Phononic crystals that have the ability to modify and control the thermal black body phonon distribution and the phonon component of heat transport in a solid. In particular, the thermal conductivity and heat capacity can be modified by altering the phonon density of states in a phononic crystal. The present invention is directed to phononic crystal devices and materials such as radio frequency (RF) tags powered from ambient heat, dielectrics with extremely low thermal conductivity, thermoelectric materials with a higher ratio of electrical-to-thermal conductivity, materials with phononically engineered heat capacity, phononic crystal waveguides that enable accelerated cooling, and a variety of low temperature application devices.

  13. Thermal Conductivity in Nanoporous Gold Films during Electron-Phonon Nonequilibrium

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

    Hopkins, Patrick E.; Norris, Pamela M.; Phinney, Leslie M.; Policastro, Steven A.; Kelly, Robert G.

    2008-01-01

    The reduction of nanodevices has given recent attention to nanoporous materials due to their structure and geometry. However, the thermophysical properties of these materials are relatively unknown. In this article, an expression for thermal conductivity of nanoporous structures is derived based on the assumption that the finite size of the ligaments leads to electron-ligament wall scattering. This expression is then used to analyze the thermal conductivity of nanoporous structures in the event of electron-phonon nonequilibrium.

  14. Electron-phonon coupling and thermal conductance at a metal-semiconductor interface: First-principles analysis

    SciTech Connect (OSTI)

    Sadasivam, Sridhar; Fisher, Timothy S.; Waghmare, Umesh V.

    2015-04-07

    The mechanism of heat transfer and the contribution of electron-phonon coupling to thermal conductance of a metal-semiconductor interface remains unclear in the present literature. We report ab initio simulations of a technologically important titanium silicide (metal)–silicon (semiconductor) interface to estimate the Schottky barrier height, and the strength of electron-phonon and phonon-phonon heat transfer across the interface. The electron and phonon dispersion relations of TiSi{sub 2} with C49 structure and the TiSi{sub 2}-Si interface are obtained using first-principles calculations within the density functional theory framework. These are used to estimate electron-phonon linewidths and the associated Eliashberg function that quantifies coupling. We show that the coupling strength of electrons with interfacial phonon modes is of the same order of magnitude as coupling of electrons to phonon modes in the bulk metal, and its contribution to electron-phonon interfacial conductance is comparable to the harmonic phonon-phonon conductance across the interface.

  15. Thermal conductivity in large-J two-dimensional antiferromagnets: Role of phonon scattering

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

    Chernyshev, A. L.; Brenig, Wolfram

    2015-08-05

    Different types of relaxation processes for magnon heat current are discussed, with a particular focus on coupling to three-dimensional phonons. There is thermal conductivity by these in-plane magnetic excitations using two distinct techniques: Boltzmann formalism within the relaxation-time approximation and memory-function approach. Also considered are the scattering of magnons by both acoustic and optical branches of phonons. We demonstrate an accord between the two methods, regarding the asymptotic behavior of the effective relaxation rates. It is strongly suggested that scattering from optical or zone-boundary phonons is important for magnon heat current relaxation in a high-temperature window of ΘD≲T<< J.

  16. First-principles prediction of phononic thermal conductivity...

    Office of Scientific and Technical Information (OSTI)

    There has been great interest in two-dimensional materials, beyond graphene, for both ... SILICENE; THERMAL CONDUCTIVITY; TRANSPORT THEORY; TWO-DIMENSIONAL SYSTEMS; VISIBLE ...

  17. Optic phonon bandwidth and lattice thermal conductivity: The case of Li2X ( X=O , S, Se, Te)

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

    Mukhopadhyay, S.; Lindsay, L.; Parker, D. S.

    2016-06-07

    Here, we examine the lattice thermal conductivities ( l) of Li2X (X=O, S, Se, Te) using a first-principles Peierls-Boltzmann transport methodology. We find low l values ranging between 12 and 30 W/m-K despite light Li atoms, a large mass difference between constituent atoms and tightly bunched acoustic branches, all features that give high l in other materials including BeSe (630 W/m-1K-1), BeTe (370 W/m-1K-1) and cubic BAs (3150 W/m-1K-1). Together these results suggest a missing ingredient in the basic guidelines commonly used to understand and predict l. Unlike typical simple systems (e.g., Si, GaAs, SiC), the dominant resistance to heat-carryingmore » acoustic phonons in Li2Se and Li2Te comes from interactions of these modes with two optic phonons. These interactions require significant bandwidth and dispersion of the optic branches, both present in Li2X materials. Finally, these considerations are important for the discovery and design of new materials for thermal management applications, and give a more comprehensive understanding of thermal transport in crystalline solids.« less

  18. First approximations of phonon thermal transport at solid-graphite interfaces.

    SciTech Connect (OSTI)

    Hopkins, Patrick E.; Norris, Pamela M.; Beechem, Thomas Edwin, Iii; Smoyer, Justin L.; Duda, John C.

    2010-04-01

    This model predicts thermal boundary conductance at interfaces where one material comprising the junction is characterized by high elastic anisotropy (i.e, graphite). The thermal properties of graphite are determined through a simplified vibrational model, where the bulk structure is treated as an linear assembly of two-dimensional systems. This model is validated at temperatures above cryogenic through comparison to experimentally determined values of specific heat. Elastic processes are accounted for through traditional diffuse transport theory. Inelastic contributions due to multi-phonon processes are also addressed and quantified.

  19. Introducing thermally stable inter-tube defects to assist off-axial phonon transport in carbon nanotube films

    SciTech Connect (OSTI)

    Wang, Jing; Chen, Di; Wallace, Joseph; Gigax, Jonathan; Wang, Xuemei; Shao, Lin

    2014-05-12

    Through integrated molecular dynamics (MD) simulations and experimental studies, we demonstrated the feasibility of an ion-irradiation-and-annealing based phonon engineering technique to enhance thermal conductivity of carbon nanotube (CNT) films. Upon ion irradiation of CNT films, both inter-tube defects and intra-tube defects are introduced. Our MD simulations show that inter-tube defects created between neighboring tubes are much more stable than intra-tube defects created on tube graphitic planes. Upon thermal annealing, intra-tube defects are preferentially removed but inter-tube defects stay. Consequently, axial phonon transport increases due to reduced phonon scattering and off-axial phonon transport is sustained due to the high stability of inter-tube defects, leading to a conductivity enhancement upon annealing. The modeling predictions agree with experimental observations that thermal conductivities of CNT films were enhanced after 2 MeV hydrogen ion irradiations and conductivities were further enhanced upon post irradiation annealing.

  20. Phonon-assisted transient electroluminescence in Si

    SciTech Connect (OSTI)

    Cheng, Tzu-Huan, E-mail: f94943139@ntu.edu.tw [Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei, Taiwan (China); Chu-Su, Yu [Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan and Department of Laboratory Medicine, National Taiwan University Hospital, Taipei, Taiwan (China); Liu, Chien-Sheng [Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan (China); Lin, Chii-Wann [Institute of Biomedical Engineering and Institute of Electrical Engineering, National Taiwan University, Taipei, Taiwan (China)

    2014-06-30

    The phonon-replica infrared emission is observed at room temperature from indirect band gap Si light-emitting diode under forward bias. With increasing injection current density, the broadened electroluminescence spectrum and band gap reduction are observed due to joule heating. The spectral-resolved temporal response of electroluminescence reveals the competitiveness between single (TO) and dual (TO?+?TA) phonon-assisted indirect band gap transitions. As compared to infrared emission with TO phonon-replica, the retarder of radiative recombination at long wavelength region (?1.2??m) indicates lower transition probability of dual phonon-replica before thermal equivalent.

  1. Lighting system with thermal management system

    DOE Patents [OSTI]

    Arik, Mehmet; Weaver, Stanton; Stecher, Thomas; Seeley, Charles; Kuenzler, Glenn; Wolfe, Jr., Charles; Utturkar, Yogen; Sharma, Rajdeep; Prabhakaran, Satish; Icoz, Tunc

    2013-05-07

    Lighting systems having unique configurations are provided. For instance, the lighting system may include a light source, a thermal management system and driver electronics, each contained within a housing structure. The light source is configured to provide illumination visible through an opening in the housing structure. The thermal management system is configured to provide an air flow, such as a unidirectional air flow, through the housing structure in order to cool the light source. The driver electronics are configured to provide power to each of the light source and the thermal management system.

  2. Lighting system with thermal management system

    DOE Patents [OSTI]

    Arik, Mehmet; Weaver, Stanton Earl; Stecher, Thomas Elliot; Seeley, Charles Erklin; Kuenzler, Glenn Howard; Wolfe, Jr., Charles Franklin; Utturkar, Yogen Vishwas; Sharma, Rajdeep; Prabhakaran, Satish; Icoz, Tunc

    2015-08-25

    Lighting systems having unique configurations are provided. For instance, the lighting system may include a light source, a thermal management system and driver electronics, each contained within a housing structure. The light source is configured to provide illumination visible through an opening in the housing structure. The thermal management system is configured to provide an air flow, such as a unidirectional air flow, through the housing structure in order to cool the light source. The driver electronics are configured to provide power to each of the light source and the thermal management system.

  3. Lighting system with thermal management system

    DOE Patents [OSTI]

    Arik, Mehmet; Weaver, Stanton Earl; Stecher, Thomas Elliot; Seeley, Charles Erklin; Kuenzler, Glenn Howard; Wolfe, Jr., Charles Franklin; Utturkar, Yogen Vishwas; Sharma, Rajdeep; Prabhakaran, Satish; Icoz, Tunc

    2015-02-24

    Lighting systems having unique configurations are provided. For instance, the lighting system may include a light source, a thermal management system and driver electronics, each contained within a housing structure. The light source is configured to provide illumination visible through an opening in the housing structure. The thermal management system is configured to provide an air flow, such as a unidirectional air flow, through the housing structure in order to cool the light source. The driver electronics are configured to provide power to each of the light source and the thermal management system.

  4. Nonlinear vs. bolometric radiation response and phonon thermal conductance in graphene-superconductor junctions

    SciTech Connect (OSTI)

    Vora, Heli; Nielsen, Bent; Du, Xu [Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York (United States)

    2014-02-21

    Graphene is a promising candidate for building fast and ultra-sensitive bolometric detectors due to its weak electron-phonon coupling and low heat capacity. In order to realize a practical graphene-based bolometer, several important issues, including the nature of radiation response, coupling efficiency to the radiation and the thermal conductance need to be carefully studied. Addressing these issues, we present graphene-superconductor junctions as a viable option to achieve efficient and sensitive bolometers, with the superconductor contacts serving as hot electron barriers. For a graphene-superconductor device with highly transparent interfaces, the resistance readout in the presence of radio frequency radiation is dominated by non-linear response. On the other hand, a graphene-superconductor tunnel device shows dominantly bolometric response to radiation. For graphene devices fabricated on SiO{sub 2} substrates, we confirm recent theoretical predictions of T{sup 2} temperature dependence of phonon thermal conductance in the presence of disorder in the graphene channel at low temperatures.

  5. Reflection thermal diffuse x-ray scattering for quantitative determination of phonon dispersion relations

    SciTech Connect (OSTI)

    Mei, A. B.; Hellman, O.; Schlepuetz, C. M.; Rockett, A.; Chiang, T. -C.; Hultman, L.; Petrov, I.; Greene, J. E.

    2015-11-03

    Synchrotron reflection x-ray thermal diffuse scattering (TDS) measurements, rather than previously reported transmission TDS, are carried out at room temperature and analyzed using a formalism based upon second-order interatomic force constants and long-range Coulomb interactions to obtain quantitative determinations of MgO phonon dispersion relations (h) over bar omega(j) (q), phonon densities of states g((h) over bar omega), and isochoric temperature-dependent vibrational heat capacities cv (T). We use MgO as a model system for investigating reflection TDS due to its harmonic behavior as well as its mechanical and dynamic stability. Resulting phonon dispersion relations and densities of states are found to be in good agreement with independent reports from inelastic neutron and x-ray scattering experiments. Temperature-dependent isochoric heat capacities cv (T), computed within the harmonic approximation from (h) over bar omega(j) (q) values, increase with temperature from 0.4 x 10-4 eV/atom K at 100 K to 1.4 x 10-4 eV/atom K at 200 K and 1.9 x 10-4 eV/atom K at 300 K, in excellent agreement with isobaric heat capacity values cp (T) between 4 and 300 K. We anticipate that the experimental approach developed here will be valuable for determining vibrational properties of heteroepitaxial thin films since the use of grazing-incidence (θ ≲ θc where θc is the density-dependent critical angle) allows selective tuning of x-ray penetration depths to ≲ 10 nm.

  6. Reflection thermal diffuse x-ray scattering for quantitative determination of phonon dispersion relations

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

    Mei, A. B.; Hellman, O.; Schlepuetz, C. M.; Rockett, A.; Chiang, T. -C.; Hultman, L.; Petrov, I.; Greene, J. E.

    2015-11-03

    Synchrotron reflection x-ray thermal diffuse scattering (TDS) measurements, rather than previously reported transmission TDS, are carried out at room temperature and analyzed using a formalism based upon second-order interatomic force constants and long-range Coulomb interactions to obtain quantitative determinations of MgO phonon dispersion relations (h) over bar omega(j) (q), phonon densities of states g((h) over bar omega), and isochoric temperature-dependent vibrational heat capacities cv (T). We use MgO as a model system for investigating reflection TDS due to its harmonic behavior as well as its mechanical and dynamic stability. Resulting phonon dispersion relations and densities of states are found tomore » be in good agreement with independent reports from inelastic neutron and x-ray scattering experiments. Temperature-dependent isochoric heat capacities cv (T), computed within the harmonic approximation from (h) over bar omega(j) (q) values, increase with temperature from 0.4 x 10-4 eV/atom K at 100 K to 1.4 x 10-4 eV/atom K at 200 K and 1.9 x 10-4 eV/atom K at 300 K, in excellent agreement with isobaric heat capacity values cp (T) between 4 and 300 K. We anticipate that the experimental approach developed here will be valuable for determining vibrational properties of heteroepitaxial thin films since the use of grazing-incidence (θ ≲ θc where θc is the density-dependent critical angle) allows selective tuning of x-ray penetration depths to ≲ 10 nm.« less

  7. Electron-phonon coupling and thermal transport in the thermoelectric compound Mo3Sb7–xTex

    SciTech Connect (OSTI)

    Bansal, Dipanshu; Li, Chen W.; Said, Ayman H.; Abernathy, Douglas L.; Yan, Jiaqiang; Delaire, Olivier A.

    2015-12-07

    Phonon properties of Mo3Sb7–xTex (x = 0, 1.5, 1.7), a potential high-temperature thermoelectric material, have been studied with inelastic neutron and x-ray scattering, and with first-principles simulations. The substitution of Te for Sb leads to pronounced changes in the electronic struc- ture, local bonding, phonon density of states (DOS), dispersions, and phonon lifetimes. Alloying with tellurium shifts the Fermi level upward, near the top of the valence band, resulting in a strong suppression of electron-phonon screening, and a large overall stiffening of interatomic force- constants. The suppression in electron-phonon coupling concomitantly increases group velocities and suppresses phonon scattering rates, surpassing the effects of alloy-disorder scattering, and re- sulting in a surprising increased lattice thermal conductivity in the alloy. We also identify that the local bonding environment changes non-uniformly around different atoms, leading to variable perturbation strengths for different optical phonon branches. The respective roles of changes in phonon group velocities and phonon lifetimes on the lattice thermal conductivity are quantified. Lastly, our results highlight the importance of the electron-phonon coupling on phonon mean-free-paths in this compound, and also estimates the contributions from boundary scattering, umklapp scattering, and point-defect scattering.

  8. Optimal electron, phonon, and magnetic characteristics for low energy thermally induced magnetization switching

    SciTech Connect (OSTI)

    Atxitia, U.; Ostler, T. A.; Chantrell, R. W.; Chubykalo-Fesenko, O.

    2015-11-09

    Using large-scale computer simulations, we thoroughly study the minimum energy required to thermally induced magnetization switching (TIMS) after the application of a femtosecond heat pulse in transition metal-rare earth ferrimagnetic alloys. We find that for an energy efficient TIMS, a low ferrimagnetic net magnetization with a strong temperature dependence is the relevant factor for the magnetic system. For the lattice and electron systems, the key physics for efficient TIMS is a large electron-phonon relaxation time. Importantly, we show that as the cooling time of the heated electrons is increased, the minimum power required to produce TIMS can be reduced by an order of magnitude. Our results show the way to low power TIMS by appropriate engineering of magnetic heterostructures.

  9. Atomistic study of porosity impact on phonon driven thermal conductivity: Application to uranium dioxide

    SciTech Connect (OSTI)

    Colbert, Mehdi; Ribeiro, Fabienne; Trglia, Guy

    2014-01-21

    We present here an analytical method, based on the kinetic theory, to determine the impact of defects such as cavities on the thermal conductivity of a solid. This approach, which explicitly takes into account the effects of internal pore surfaces, will be referred to as the Phonon Interface THermal cONductivity (PITHON) model. Once exposed in the general case, this method is then illustrated in the case of uranium dioxide. It appears that taking properly into account these interface effects significantly modifies the temperature and porosity dependence of thermal conductivity with respect to that issued from either micromechanical models or more recent approaches, in particular, for small cavity sizes. More precisely, it is found that if the mean free path appears to have a major effect in this system in the temperature and porosity distribution range of interest, the variation of the specific heat at the surface of the cavity is predicted to be essential at very low temperature and small sizes for sufficiently large porosity.

  10. Role of direct electron-phonon coupling across metal-semiconductor interfaces in thermal transport via molecular dynamics

    SciTech Connect (OSTI)

    Lin, Keng-Hua; Strachan, Alejandro

    2015-07-21

    Motivated by significant interest in metal-semiconductor and metal-insulator interfaces and superlattices for energy conversion applications, we developed a molecular dynamics-based model that captures the thermal transport role of conduction electrons in metals and heat transport across these types of interface. Key features of our model, denoted eleDID (electronic version of dynamics with implicit degrees of freedom), are the natural description of interfaces and free surfaces and the ability to control the spatial extent of electron-phonon (e-ph) coupling. Non-local e-ph coupling enables the energy of conduction electrons to be transferred directly to the semiconductor/insulator phonons (as opposed to having to first couple to the phonons in the metal). We characterize the effect of the spatial e-ph coupling range on interface resistance by simulating heat transport through a metal-semiconductor interface to mimic the conditions of ultrafast laser heating experiments. Direct energy transfer from the conduction electrons to the semiconductor phonons not only decreases interfacial resistance but also increases the ballistic transport behavior in the semiconductor layer. These results provide new insight for experiments designed to characterize e-ph coupling and thermal transport at the metal-semiconductor/insulator interfaces.

  11. Energy distribution of nonequilibrium electrons and optical phonons in GaAs under band-to-band pumping by intense short pulses of light

    SciTech Connect (OSTI)

    Altybaev, G. S.; Kumekov, S. E. Mahmudov, A. A.

    2009-03-15

    Deviation from the Fermi distribution of nonequilibrium electrons and distribution of 'hot' optical phonons in GaAs under band-to-band pumping by picosecond pulses of light are calculated.

  12. Phonon manipulation with phononic crystals.

    SciTech Connect (OSTI)

    Kim Bongsang; Hopkins, Patrick Edward; Leseman, Zayd C.; Goettler, Drew F.; Su, Mehmet F.; El-Kady, Ihab Fathy; Reinke, Charles M.; Olsson, Roy H., III

    2012-01-01

    In this work, we demonstrated engineered modification of propagation of thermal phonons, i.e. at THz frequencies, using phononic crystals. This work combined theoretical work at Sandia National Laboratories, the University of New Mexico, the University of Colorado Boulder, and Carnegie Mellon University; the MESA fabrication facilities at Sandia; and the microfabrication facilities at UNM to produce world-leading control of phonon propagation in silicon at frequencies up to 3 THz. These efforts culminated in a dramatic reduction in the thermal conductivity of silicon using phononic crystals by a factor of almost 30 as compared with the bulk value, and about 6 as compared with an unpatterned slab of the same thickness. This work represents a revolutionary advance in the engineering of thermoelectric materials for optimal, high-ZT performance. We have demonstrated the significant reduction of the thermal conductivity of silicon using phononic crystal structuring using MEMS-compatible fabrication techniques and in a planar platform that is amenable to integration with typical microelectronic systems. The measured reduction in thermal conductivity as compared to bulk silicon was about a factor of 20 in the cross-plane direction [26], and a factor of 6 in the in-plane direction. Since the electrical conductivity was only reduced by a corresponding factor of about 3 due to the removal of conductive material (i.e., porosity), and the Seebeck coefficient should remain constant as an intrinsic material property, this corresponds to an effective enhancement in ZT by a factor of 2. Given the number of papers in literature devoted to only a small, incremental change in ZT, the ability to boost the ZT of a material by a factor of 2 simply by reducing thermal conductivity is groundbreaking. The results in this work were obtained using silicon, a material that has benefitted from enormous interest in the microelectronics industry and that has a fairly large thermoelectric power

  13. Strong Energy-momentum Dispersion of Phonon Dressed Carriers in the Lightly Doped Band Insulator SrTiO3

    SciTech Connect (OSTI)

    Meevasana, Warawat

    2010-05-26

    Much progress has been made recently in the study of the effects of electron-phonon (el-ph) coupling in doped insulators using angle resolved photoemission (ARPES), yielding evidence for the dominant role of el-ph interactions in underdoped cuprates. As these studies have been limited to doped Mott insulators, the important question arises how this compares with doped band insulators where similar el-ph couplings should be at work. The archetypical case is the perovskite SrTiO{sub 3} (STO), well known for its giant dielectric constant of 10000 at low temperature, exceeding that of La{sub 2}CuO{sub 4} by a factor of 500. Based on this fact, it has been suggested that doped STO should be the archetypical bipolaron superconductor. Here we report an ARPES study from high-quality surfaces of lightly doped SrTiO{sub 3}. Comparing to lightly doped Mott insulators, we find the signatures of only moderate electron-phonon coupling: a dispersion anomaly associated with the low frequency optical phonon with a {lambda}{prime} {approx} 0.3 and an overall bandwidth renormalization suggesting an overall {lambda}{prime} {approx} 0.7 coming from the higher frequency phonons. Further, we find no clear signatures of the large pseudogap or small polaron phenomena. These findings demonstrate that a large dielectric constant itself is not a good indicator of el-ph coupling and highlight the unusually strong effects of the el-ph coupling in doped Mott insulators.

  14. Thermal conductivity in large-J two-dimensional antiferromagnets: Role of phonon scattering

    SciTech Connect (OSTI)

    Chernyshev, A. L.; Brenig, Wolfram

    2015-08-05

    Different types of relaxation processes for magnon heat current are discussed, with a particular focus on coupling to three-dimensional phonons. There is thermal conductivity by these in-plane magnetic excitations using two distinct techniques: Boltzmann formalism within the relaxation-time approximation and memory-function approach. Also considered are the scattering of magnons by both acoustic and optical branches of phonons. We demonstrate an accord between the two methods, regarding the asymptotic behavior of the effective relaxation rates.

    It is strongly suggested that scattering from optical or zone-boundary phonons is important for magnon heat current relaxation in a high-temperature window of ΘD≲T<< J.

  15. NREL: Transportation Research - Light-Duty Vehicle Thermal Management

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

    Light-Duty Vehicle Thermal Management Image of a semi-transparent car with parts of the engine highlighted in green. NREL evaluates technologies and methods such as advanced window glazing, cooling heat-pipe systems, parked car ventilation, and direct energy recovery. Illustration by Josh Bauer, NREL National Renewable Energy Laboratory (NREL) researchers are focused on improving the thermal efficiency of light-duty vehicles (LDVs) while maintaining the thermal comfort that drivers expect.

  16. Light mixed sneutrinos as thermal dark matter

    SciTech Connect (OSTI)

    Bélanger, G.; Kakizaki, M.; Park, E.K.; Kraml, S.

    2010-11-01

    In supersymmetric models with Dirac neutrino masses, a left-right mixed sneutrino can be a viable dark matter candidate. We examine the MSSM+ν-tilde {sub R} parameter space where this is the case with particular emphasis on light sneutrinos with masses below 10 GeV. We discuss implications for direct and indirect dark matter searches, including the relevant uncertainties, as well as consequences for collider phenomenology.

  17. A comment on the thermal conductivity of (U,Pu)O2 and (U,Th)O2 by molecular dynamics with adjustment for phonon-spin scattering

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

    Cooper, Michael William D.; Liu, Xiang -Yang; Stanek, Christopher Richard; Andersson, David Anders

    2016-07-15

    In this study, a new approach for adjusting molecular dynamics results on UO2 thermal conductivity to include phonon-spin scattering has been used to improve calculations on Ux Pu1–x O2 and UxTh1xO2. We demonstrate that by including spin scattering a strong asymmetry as a function of uranium actinide fraction, x, is obtained. Greater degradation is shown for UxTh1–xO2 than UxPu1-xO2. Minimum thermal conductivities are predicted at U0.97Pu0.03O2 and U0.58Th0.42O2, although the degradation in UxPu1–xO2 is negligible relative to pure UO2.

  18. Phonon coherence in isotopic silicon superlattices

    SciTech Connect (OSTI)

    Frieling, R.; Radek, M.; Eon, S.; Bracht, H.; Wolf, D. E.

    2014-09-29

    Recent experimental and theoretical investigations have confirmed that a reduction in thermal conductivity of silicon is achieved by isotopic silicon superlattices. In the present study, non-equilibrium molecular dynamics simulations are performed to identify the isotope doping and isotope layer ordering with minimum thermal conductivity. Furthermore, the impact of isotopic intermixing at the superlattice interfaces on phonon transport is investigated. Our results reveal that the coherence of phonons in isotopic Si superlattices is prevented if interfacial mixing of isotopes is considered.

  19. Toward quantitative modeling of silicon phononic thermocrystals

    SciTech Connect (OSTI)

    Lacatena, V.; Haras, M.; Robillard, J.-F. Dubois, E.; Monfray, S.; Skotnicki, T.

    2015-03-16

    The wealth of technological patterning technologies of deca-nanometer resolution brings opportunities to artificially modulate thermal transport properties. A promising example is given by the recent concepts of 'thermocrystals' or 'nanophononic crystals' that introduce regular nano-scale inclusions using a pitch scale in between the thermal phonons mean free path and the electron mean free path. In such structures, the lattice thermal conductivity is reduced down to two orders of magnitude with respect to its bulk value. Beyond the promise held by these materials to overcome the well-known “electron crystal-phonon glass” dilemma faced in thermoelectrics, the quantitative prediction of their thermal conductivity poses a challenge. This work paves the way toward understanding and designing silicon nanophononic membranes by means of molecular dynamics simulation. Several systems are studied in order to distinguish the shape contribution from bulk, ultra-thin membranes (8 to 15 nm), 2D phononic crystals, and finally 2D phononic membranes. After having discussed the equilibrium properties of these structures from 300 K to 400 K, the Green-Kubo methodology is used to quantify the thermal conductivity. The results account for several experimental trends and models. It is confirmed that the thin-film geometry as well as the phononic structure act towards a reduction of the thermal conductivity. The further decrease in the phononic engineered membrane clearly demonstrates that both phenomena are cumulative. Finally, limitations of the model and further perspectives are discussed.

  20. Lighting system with thermal management system having point contact synthetic jets

    DOE Patents [OSTI]

    Arik, Mehmet; Weaver, Stanton Earl; Kuenzler, Glenn Howard; Wolfe, Jr, Charles Franklin; Sharma, Rajdeep

    2016-08-30

    Lighting systems having unique configurations are provided. For instance, the lighting system may include a light source, a thermal management system and driver electronics, each contained within a housing structure. The light source is configured to provide illumination visible through an opening in the housing structure. The thermal management system includes a plurality of synthetic jets. The synthetic jets are arranged within the lighting system such that they are secured at contact points.

  1. Lighting system with thermal management system having point contact synthetic jets

    SciTech Connect (OSTI)

    Arik, Mehmet; Weaver, Stanton Earl; Kuenzler, Glenn Howard; Wolfe, Jr., Charles Franklin; Sharma, Rajdeep

    2013-12-10

    Lighting system having unique configurations are provided. For instance, the lighting system may include a light source, a thermal management system and driver electronics, each contained within a housing structure. The light source is configured to provide illumination visible through an opening in the housing structure. The thermal management system includes a plurality of synthetic jets. The synthetic jets are arranged within the lighting system such that they are secured at contact points.

  2. Lighting system with thermal management system having point contact synthetic jets

    DOE Patents [OSTI]

    Arik, Mehmet; Weaver, Stanton Earl; Kuenzler, Glenn Howard; Wolfe, Jr., Charles Franklin; Sharma, Rajdeep

    2016-08-23

    Lighting systems having unique configurations are provided. For instance, the lighting system may include a light source, a thermal management system and driver electronics, each contained within a housing structure. The light source is configured to provide illumination visible through an opening in the housing structure. The thermal management system includes a plurality of synthetic jets. The synthetic jets are arranged within the lighting system such that they are secured at contact points.

  3. Manipulation of Phonons with Phononic Crystals

    SciTech Connect (OSTI)

    Leseman, Zayd Chad

    2015-07-09

    There were three research goals associated with this project. First, was to experimentally demonstrate phonon spectrum control at THz frequencies using Phononic Crystals (PnCs), i.e. demonstrate coherent phonon scattering with PnCs. Second, was to experimentally demonstrate analog PnC circuitry components at GHz frequencies. The final research goal was to gain a fundamental understanding of phonon interaction using computational methods. As a result of this work, 7 journal papers have been published, 1 patent awarded, 14 conference presentations given, 4 conference publications, and 2 poster presentations given.

  4. Thermoelectric HVAC and Thermal Comfort Enablers for Light-Duty...

    Broader source: Energy.gov (indexed) [DOE]

    More Documents & Publications Thermoelectric HVAC for Light-Duty Vehicle Applications Improving efficiency of a vehicle HVAC system with comfort modeling, zonal design, and ...

  5. Phonon interference effects in molecular junctions

    SciTech Connect (OSTI)

    Markussen, Troels

    2013-12-28

    We study coherent phonon transport through organic, ?-conjugated molecules. Using first principles calculations and Green's function methods, we find that the phonon transmission function in cross-conjugated molecules, like meta-connected benzene, exhibits destructive quantum interference features very analogous to those observed theoretically and experimentally for electron transport in similar molecules. The destructive interference features observed in four different cross-conjugated molecules significantly reduce the thermal conductance with respect to linear conjugated analogues. Such control of the thermal conductance by chemical modifications could be important for thermoelectric applications of molecular junctions.

  6. Lifetime of the phonons in the PLT ceramic

    SciTech Connect (OSTI)

    Barba-Ortega, J. Joya, M. R.; Londoo, F. A.

    2014-11-05

    The lifetimes at higher temperatures on lanthanum-modified lead titanate (PLT) are mainly due to the anharmonic decay of optical phonons into low-energy phonons. The temperature-independent contributions from inherent crystal defects and from boundary scattering become comparable to the phonon scattering contribution at lower temperatures. The thermal interaction is large at higher temperatures which decreases the phonon mean free path, and so the decay lifetime decreases as the temperature of the system is increased. This leads to the increased line width at higher temperatures. We made an estimate of the lifetimes for different concentrations and temperatures in PLT.

  7. Glass-like thermal conductivity in high efficiency thermoelectric materials

    Broader source: Energy.gov [DOE]

    Discusses strategies to design thermoelectric materials with extremely low lattice thermal conductivity through modifications of the phonon band structure and phonon relaxation time.

  8. Synthetic thermoelectric materials comprising phononic crystals

    DOE Patents [OSTI]

    El-Kady, Ihab F; Olsson, Roy H; Hopkins, Patrick; Reinke, Charles; Kim, Bongsang

    2013-08-13

    Synthetic thermoelectric materials comprising phononic crystals can simultaneously have a large Seebeck coefficient, high electrical conductivity, and low thermal conductivity. Such synthetic thermoelectric materials can enable improved thermoelectric devices, such as thermoelectric generators and coolers, with improved performance. Such synthetic thermoelectric materials and devices can be fabricated using techniques that are compatible with standard microelectronics.

  9. Measuring phonon mean free path distributions by probing quasiballistic phonon transport in grating nanostructures

    SciTech Connect (OSTI)

    Zeng, Lingping; Collins, Kimberlee C.; Hu, Yongjie; Luckyanova, Maria N.; Maznev, Alexei A.; Huberman, Samuel; Chiloyan, Vazrik; Zhou, Jiawei; Huang, Xiaopeng; Nelson, Keith A.; Chen, Gang

    2015-11-27

    Heat conduction in semiconductors and dielectrics depends upon their phonon mean free paths that describe the average travelling distance between two consecutive phonon scattering events. Nondiffusive phonon transport is being exploited to extract phonon mean free path distributions. Here, we describe an implementation of a nanoscale thermal conductivity spectroscopy technique that allows for the study of mean free path distributions in optically absorbing materials with relatively simple fabrication and a straightforward analysis scheme. We pattern 1D metallic grating of various line widths but fixed gap size on sample surfaces. The metal lines serve as both heaters and thermometers in time-domain thermoreflectance measurements and simultaneously act as wiregrid polarizers that protect the underlying substrate from direct optical excitation and heating. We demonstrate the viability of this technique by studying length-dependent thermal conductivities of silicon at various temperatures. The thermal conductivities measured with different metal line widths are analyzed using suppression functions calculated from the Boltzmann transport equation to extract the phonon mean free path distributions with no calibration required. Furthermore, this table-top ultrafast thermal transport spectroscopy technique enables the study of mean free path spectra in a wide range of technologically important materials.

  10. Measuring phonon mean free path distributions by probing quasiballistic phonon transport in grating nanostructures

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

    Zeng, Lingping; Collins, Kimberlee C.; Hu, Yongjie; Luckyanova, Maria N.; Maznev, Alexei A.; Huberman, Samuel; Chiloyan, Vazrik; Zhou, Jiawei; Huang, Xiaopeng; Nelson, Keith A.; et al

    2015-11-27

    Heat conduction in semiconductors and dielectrics depends upon their phonon mean free paths that describe the average travelling distance between two consecutive phonon scattering events. Nondiffusive phonon transport is being exploited to extract phonon mean free path distributions. Here, we describe an implementation of a nanoscale thermal conductivity spectroscopy technique that allows for the study of mean free path distributions in optically absorbing materials with relatively simple fabrication and a straightforward analysis scheme. We pattern 1D metallic grating of various line widths but fixed gap size on sample surfaces. The metal lines serve as both heaters and thermometers in time-domainmore » thermoreflectance measurements and simultaneously act as wiregrid polarizers that protect the underlying substrate from direct optical excitation and heating. We demonstrate the viability of this technique by studying length-dependent thermal conductivities of silicon at various temperatures. The thermal conductivities measured with different metal line widths are analyzed using suppression functions calculated from the Boltzmann transport equation to extract the phonon mean free path distributions with no calibration required. Furthermore, this table-top ultrafast thermal transport spectroscopy technique enables the study of mean free path spectra in a wide range of technologically important materials.« less

  11. Wide Area Thermal Processing of Light Emitting Materials

    SciTech Connect (OSTI)

    Duty, Chad E; Joshi, Pooran C; Jellison Jr, Gerald Earle; Angelini, Joseph Attilio; Sabau, Adrian S

    2011-10-01

    Laboratory laser materials synthesis of wide bandgap materials has been successfully used to create white light emitting materials (LEMs). This technology development has progressed to the exploration on design and construction of apparatus for wide area doping and phase transformation of wide bandgap material substrates. The objective of this proposal is to develop concepts for wide area doping and phase transformation based on AppliCote Associates, LLC laser technology and ORNL high density pulsed plasma arc technology.

  12. Phonon scattering in graphene over substrate steps

    SciTech Connect (OSTI)

    Sevinçli, H.; Brandbyge, M.

    2014-10-13

    We calculate the effect on phonon transport of substrate-induced bends in graphene. We consider bending induced by an abrupt kink in the substrate, and provide results for different step-heights and substrate interaction strengths. We find that individual substrate steps reduce thermal conductance in the range between 5% and 47%. We also consider the transmission across linear kinks formed by adsorption of atomic hydrogen at the bends and find that individual kinks suppress thermal conduction substantially, especially at high temperatures. Our analysis show that substrate irregularities can be detrimental for thermal conduction even for small step heights.

  13. Visible-Wavelength Polarized-Light Emission with Small-Diameter...

    Office of Scientific and Technical Information (OSTI)

    Subject: solar (photovoltaic), solar (thermal), phonons, thermal conductivity, thermoelectric, electrodes - solar, defects, charge transport, materials and chemistry by design, ...

  14. ThermoPhonon

    Energy Science and Technology Software Center (OSTI)

    2014-11-24

    ThermoPhonon is a stand-alone code, which can be integrated into other software packages. Typically, it is used together with a density functional theory (DFT) code (such as VASP, Wien2k, AbInit, SIESTA) and a phonon code (such as Phonopy or Phon). The workflow is the following. Molecular dynamics (MD) in a supercell at a given temperature T is performed using another code. After sufficient equilibration, the output in the form of atomic positions and forces formore » a large number of selected MD steps is recorded into a file. If needed, one can modify this file by applying additional constraints, such as enforced crystal symmetry or subtracted motion of the center of mass. ThermoPhonon reads the file with atomic positions and forces and writes a new file with the force constants. Force constants can be used by another code (such as Phonopy or Phon) to produce phonon spectrum for plotting, in the assumption of known equilibrium atomic positions provided in a separate file.« less

  15. 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

  16. 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.

  17. High-efficiency white organic light-emitting diodes using thermally activated delayed fluorescence

    SciTech Connect (OSTI)

    Nishide, Jun-ichi; Hiraga, Yasuhide; Nakanotani, Hajime; Adachi, Chihaya

    2014-06-09

    White organic light-emitting diodes (WOLEDs) have attracted much attention recently, aimed for next-generation lighting sources because of their high potential to realize high electroluminescence efficiency, flexibility, and low-cost manufacture. Here, we demonstrate high-efficiency WOLED using red, green, and blue thermally activated delayed fluorescence materials as emissive dopants to generate white electroluminescence. The WOLED has a maximum external quantum efficiency of over 17% with Commission Internationale de l'Eclairage coordinates of (0.30, 0.38).

  18. Phonon mean free path of graphite along the c-axis

    SciTech Connect (OSTI)

    Wei, Zhiyong; Yang, Juekuan; Chen, Weiyu; Bi, Kedong; Chen, Yunfei, E-mail: yunfeichen@seu.edu.cn [Jiangsu Key Laboratory for Design and Manufacture of Micro/Nano Biomedical Instruments and School of Mechanical Engineering, Southeast University, Nanjing 210096 (China); Li, Deyu, E-mail: deyu.li@vanderbilt.edu [Department of Mechanical Engineering, Vanderbilt University, Nashville, Tennessee 37235-1592 (United States)

    2014-02-24

    Phonon transport in the c-axis direction of graphite thin films has been studied using non-equilibrium molecular dynamics (MD) simulation. The simulation results show that the c-axis thermal conductivities for films of thickness ranging from 20 to 500 atomic layers are significantly lower than the bulk value. Based on the MD data, a method is developed to construct the c-axis thermal conductivity as an accumulation function of phonon mean free path (MFP), from which we show that phonons with MFPs from 2 to 2000?nm contribute ?80% of the graphite c-axis thermal conductivity at room temperature, and phonons with MFPs larger than 100?nm contribute over 40% to the c-axis thermal conductivity. These findings indicate that the commonly believed value of just a few nanometers from the simple kinetic theory drastically underestimates the c-axis phonon MFP of graphite.

  19. Thermal equation of state and spin transition of magnesiosiderite...

    Office of Scientific and Technical Information (OSTI)

    Citation Details In-Document Search Title: Thermal equation of ... Subject: catalysis (heterogeneous), solar (photovoltaic), phonons, thermoelectric, energy storage (including ...

  20. Phonons with orbital angular momentum

    SciTech Connect (OSTI)

    Ayub, M. K.; Ali, S.; Mendonca, J. T.

    2011-10-15

    Ion accoustic waves or phonon modes are studied with orbital angular momentum (OAM) in an unmagnetized collissionless uniform plasma, whose constituents are the Boltzmann electrons and inertial ions. For this purpose, we have employed the fluid equations to obtain a paraxial equation in terms of ion density perturbations and discussed its Gaussian beam and Laguerre-Gauss (LG) beam solutions. Furthermore, an approximate solution for the electrostatic potential problem is presented, allowing to express the components of the electric field in terms of LG potential perturbations. The energy flux due to phonons is also calculated and the corresponding OAM is derived. Numerically, it is shown that the parameters such as azimuthal angle, radial and angular mode numbers, and beam waist, strongly modify the profiles of the phonon LG potential. The present results should be helpful in understanding the phonon mode excitations produced by Brillouin backscattering of laser beams in a uniform plasma.

  1. Thermal boundary conductance accumulation and interfacial phonon...

    Office of Scientific and Technical Information (OSTI)

    GrantContract Number: AC04-94AL85000 Type: Publisher's Accepted Manuscript Journal Name: Physical Review B Additional Journal Information: Journal Volume: 91; Journal Issue: 3; ...

  2. Thermal boundary conductance accumulation and spectral phonon...

    Office of Scientific and Technical Information (OSTI)

    DOE Contract Number: AC04-94AL85000 Resource Type: Journal Article Resource Relation: Journal Name: Nature Communications Research Org: Sandia National Laboratories (SNL-NM), ...

  3. Probing Light Thermal Dark-Matter With a Higgs Portal Mediator

    SciTech Connect (OSTI)

    Krnjaic, Gordan

    2015-12-13

    We systematically study light (< few GeV) Dark Matter (DM) models that thermalize with visible matter through the Higgs portal and identify the remaining gaps in the viable parameter space. Such models require a comparably light scalar mediator that mixes with the Higgs to avoid DM overproduction and can be classified according to whether this mediator decays (in)visibly. In a representative benchmark model with Dirac fermion DM, we find that, even with conservative assumptions about the DM-mediator coupling and mass ratio, the regime in which the mediator is heavier than the DM is fully ruled out by a combination of collider, rare meson decay, and direct detection limits; future and planned experiments including NA62 can further improve sensitivity to scenarios in which the Higgs portal interaction does not determine the DM abundance. The opposite, regime in which the mediator is lighter than the DM and the latter annihilates to pairs of visibly-decaying mediators is still viable, but much of the parameter space is covered by rare meson decay, supernova cooling, beam dump, and direct detection constraints. Nearly all of these conclusions apply broadly to the simplest variations (e.g. scalar or asymmetric DM). Future experiments including SHiP, NEWS, and Super-CDMS SNOLAB can greatly improve coverage to this class of models.

  4. Thermal upgrading of residual oil to light product and heavy residual fuel

    SciTech Connect (OSTI)

    Yan, T.Y.; Shu, P.

    1986-08-05

    The method is described of upgrading residual oil boiling in the range of 1050/sup 0/F+ comprising: thermally cracking the residual oil at a temperature of 650/sup 0/-900/sup 0/F, a pressure of 0-100 psig, and a residence time of 0.1 to 5 hours at the highest severity in the range between about 1,000-18,000 seconds, as expressed in equivalent reaction time at 800/sup 0/F, sufficient to convert at least about 50 wt% of the residual oil to light products, substantially without the formation of solid coke; recovering separate fractions of light product and emulsifiable heavy bottom product which has a fusion temperature below about 150/sup 0/C and a quinoline-insoluble content between about 10 wt% and 30 wt% and wherein the highest severity is determined by a functional relationship between the asphaltene content of the residual oil feedstock and the heavy bottom product yield and quinoline-insoluble content.

  5. Lighting

    Broader source: Energy.gov [DOE]

    One of the simplest ways to save energy and money is to switch to energy-efficient lights. Learn about your lighting choices that can save you money.

  6. Structure of crystalline oxide ceramics studied by phonon spectroscopy

    SciTech Connect (OSTI)

    Kaminskii, Alexandr A; Taranov, A V; Khazanov, E N

    2013-03-31

    This paper describes a method for gaining detailed insight into the structure and phonon spectrum of polycrystalline oxide ceramics. We examine how the diffusion coefficient of subterahertz phonons is related to the properties of a system of grain boundaries and to the grain size and structure and demonstrate that the temperature dependence of the phonon diffusion coefficient at liquid-helium temperatures is determined by the spectral properties of the intergranular layer, which allows one to estimate the volumeaveraged intergranular layer thickness and acoustic impedance. We also analyse the effect of plastic deformation via twinning on the formation of the structure of grains and intergranular layers, which determine the thermophysical, acoustic and optical properties of ceramic materials. (extreme light fields and their applications)

  7. Intensity Pattern of Diffuse X-Ray Scattering From Thermally...

    Office of Scientific and Technical Information (OSTI)

    Populated Phonons in Fcc d-Pu-Ga Citation Details In-Document Search Title: Intensity Pattern of Diffuse X-Ray Scattering From Thermally Populated Phonons in Fcc d-Pu-Ga ...

  8. Demand Shifting with Thermal Mass in Light and Heavy Mass Commercial Buildings

    SciTech Connect (OSTI)

    Xu, Peng; Zagreus, Leah

    2009-05-01

    The potential for utilizing building thermal mass for load shifting and peak demand reduction has been demonstrated in a number of simulation, laboratory, and field studies. This project studied the potential of pre-cooling and demand limiting in a heavy mass and a light mass building in the Bay Area of California. The conclusion of the work to date is that pre-cooling has the potential to improve the demand responsiveness of commercial buildings while maintaining acceptable comfort conditions. Results indicate that pre-cooling increases the depth (kW) and duration (kWh) of the shed capacity of a given building, all other factors being equal. Due to the time necessary for pre-cooling, it is only applicable to day-ahead demand response programs. Pre-cooling can be very effective if the building mass is relatively heavy. The effectiveness of night pre-cooling under hot weather conditions has not been tested. Further work is required to quantify and demonstrate the effectiveness of pre-cooling in different climates. Research is also needed to develop screening tools that can be used to select suitable buildings and customers, identify the most appropriate pre-cooling strategies, and estimate the benefits to the customer and the utility.

  9. 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.

  10. Direct evaluation of ballistic phonon transport in a multi-walled carbon nanotube

    SciTech Connect (OSTI)

    Hayashi, Hiroyuki; Takahashi, Koji; Ikuta, Tatsuya; Nishiyama, Takashi; Takata, Yasuyuki; Zhang, Xing

    2014-03-17

    Phonon confinement and in situ thermal conductance measurements in an individual multi-walled carbon nanotube (MWNT) are reported. Focused ion beam (FIB) irradiation was used to successively shorten a 4.8??m long MWNT, eventually yielding a 0.3??m long MWNT. After the first FIB irradiation, a 41% reduction in conductance was achieved, compared with that of the pristine MWNT. This was because the contributions from phonons with long free paths were excluded by scattering at FIB-induced defects. Phonon transport in linked multiple-length nanotubes was also investigated.

  11. Phonon quarticity induced by changes in phonon-tracked hybridization during lattice expansion and its stabilization of rutile TiO2

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

    Lan, Tian; Li, Chen W.; Hellman, O.; Kim, D. S.; Muñoz, Jorge A.; Smith, Hillary; Abernathy, Douglas L.; Fultz, B.

    2015-08-11

    Although the rutile structure of TiO2 is stable at high temperatures, the conventional quasiharmonic approximation predicts that several acoustic phonons decrease anomalously to zero frequency with thermal expansion, incorrectly predicting a structural collapse at temperatures well below 1000 K. In this paper, inelastic neutron scattering was used to measure the temperature dependence of the phonon density of states (DOS) of rutile TiO2 from 300 to 1373 K. Surprisingly, these anomalous acoustic phonons were found to increase in frequency with temperature. First-principles calculations showed that with lattice expansion, the potentials for the anomalous acoustic phonons transform from quadratic to quartic, stabilizingmore » the rutile phase at high temperatures. In these modes, the vibrational displacements of adjacent Ti and O atoms cause variations in hybridization of 3d electrons of Ti and 2p electrons of O atoms. Finally, with thermal expansion, the energy variation in this “phonon-tracked hybridization” flattens the bottom of the interatomic potential well between Ti and O atoms, and induces a quarticity in the phonon potential.« less

  12. Thermal conductivity of graphene mediated by strain and size

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

    Kuang, Youdi; Shi, Sanqiang; Wang, Xinjiang; Huang, Baoling; Lindsay, Lucas

    2016-06-09

    Based on first-principles calculations and full iterative solution of the linearized Boltzmann–Peierls transport equation for phonons, we systematically investigate effects of strain, size and temperature on the thermal conductivity k of suspended graphene. The calculated size-dependent and temperature-dependent k for finite samples agree well with experimental data. The results show that, contrast to the convergent room-temperature k = 5450 W/m-K of unstrained graphene at a sample size ~8 cm, k of strained graphene diverges with increasing the sample size even at high temperature. Out-of-plane acoustic phonons are responsible for the significant size effect in unstrained and strained graphene due tomore » their ultralong mean free path and acoustic phonons with wavelength smaller than 10 nm contribute 80% to the intrinsic room temperature k of unstrained graphene. Tensile strain hardens the flexural modes and increases their lifetimes, causing interesting dependence of k on sample size and strain due to the competition between boundary scattering and intrinsic phonon–phonon scattering. k of graphene can be tuned within a large range by strain for the size larger than 500 μm. These findings shed light on the nature of thermal transport in two-dimensional materials and may guide predicting and engineering k of graphene by varying strain and size.« less

  13. Neutron Scattering Investigation of Phonon Scattering Rates in Ag1-xSb1+xTe2+x (x = 0, 0.1, and 0.2)

    SciTech Connect (OSTI)

    Abernathy, Douglas L [ORNL; Budai, John D [ORNL; Delaire, Olivier A [ORNL; Ehlers, Georg [ORNL; Hong, Tao [ORNL; Karapetrova, Evguenia A. [Argonne National Laboratory (ANL); Ma, Jie [ORNL; May, Andrew F [ORNL; McGuire, Michael A [ORNL; Specht, Eliot D [ORNL

    2014-01-01

    The phonon dispersions and scattering rates of the thermoelectric material AgSbTe$_{2}$ were measured as a function of temperature with inelastic neutron scattering. The results show that phonon scattering rates are large and weakly dependent on temperature. The lattice thermal conductivity was calculated from the measured phonon lifetimes and group velocities, providing good agreement with bulk transport measurements. The measured phonon scattering rates and their temperature dependence are compared with models of phonon scattering by anharmonicity and point defect. We find that these processes cannot account for the large total phonon scattering rates observed, and their lack of temperature dependence. Neutron and synchrotron diffraction measurements on single crystals revealed an extensive nanostructure from cation ordering, which is likely responsible for the strong phonon scattering.

  14. Thermal Issues Associated with the Lighting Systems, Electronics Racks, and Pre-Amplifier Modules in the National Ignition System

    SciTech Connect (OSTI)

    A. C. Owen; J. D. Bernardin; K. L. Lam

    1998-08-01

    This report summarizes an investigation of the thermal issues related to the National Ignition Facility. The influence of heat sources such as lighting fixtures, electronics racks, and pre-amplifier modules (PAMs) on the operational performance of the laser guide beam tubes and optical alignment hardware in the NE laser bays were investigated with experiments and numerical models. In particular, empirical heat transfer data was used to establish representative and meaningful boundary conditions and also serve as bench marks for computational fluid dynamics (CFD) models. Numerical models, constructed with a commercial CFD code, were developed to investigate the extent of thermal plumes and radiation heat transfer from the heat sources. From these studies, several design modifications were recommended including reducing the size of all fluorescent lights in the NIF laser bays to single 32 W bulb fixtures, maintaining minimum separation distances between light fixtures/electronics racks and beam transport hardware, adding motion sensors in areas of the laser bay to control light fixture operation during maintenance procedures, properly cooling all electronics racks with air-water heat exchangers with heat losses greater than 25 W/rack to the M1 laser bay, ensuring that the electronics racks are not overcooked and thus maintain their surface temperatures to within a few degrees centigrade of the mean air temperature, and insulating the electronic bays and optical support structures on the PAMs.

  15. Nanoscale transport of phonons: Dimensionality, subdiffusion, molecular damping, and interference effects

    SciTech Connect (OSTI)

    Walczak, Kamil; Yerkes, Kirk L.

    2014-05-07

    We examine heat transport carried by acoustic phonons in the systems composed of nanoscale chains of masses coupled to two thermal baths of different temperatures. Thermal conductance is obtained by using linearized Landauer-type formula for heat flux with phonon transmission probability calculated within atomistic Green's functions (AGF) method. AGF formalism is extended onto dissipative chains of masses with harmonic coupling beyond nearest-neighbor approximation, while atomistic description of heat reservoirs is also included into computational scheme. In particular, the phonon lifetimes and the phonon frequency shifts are discussed for harmonic lattices of different dimensions. Further, resonant structure of phonon transmission spectrum is analyzed with respect to reservoir-induced effects, molecular damping, and mass-to-mass harmonic coupling. Analysis of transmission zeros (antiresonances) and their accompanied Fano-shape resonances are discussed as a result of interference effects between different vibrational modes. Finally, we also predict subdiffusive transport regime for low-frequency ballistic phonons propagated along a linear chain of harmonically coupled masses.

  16. Optical-phonon-mediated photocurrent in terahertz quantum-well photodetectors

    SciTech Connect (OSTI)

    Gu, L. L.; Guo, X. G. Fu, Z. L.; Wan, W. J.; Zhang, R.; Tan, Z. Y.; Cao, J. C.

    2015-03-16

    Strong and sharp photocurrent peak at longitudinal optical (LO) phonon frequency (8.87 THz) is found in GaAs/(Al,Ga)As terahertz quantum-well photodetectors (QWPs). Two mesa-structure terahertz QWPs with and without one-dimensional metal grating are fabricated to investigate the behavior of such photoresponse peak. The experimental and simulation results indicate that the photocurrent peak originates from a two-step process. First, at the LO phonon frequency, a large number of non-equilibrium LO phonons are excited by the incident electromagnetic field, and the electromagnetic energy is localized and enhanced in the thin multi-quantum-well layer. Second, through the Frohlich interaction, the localized electrons are excited to continuum states by absorbing the non-equilibrium LO phonons, which leads to the strong photoresponse peak. This finding is useful for exploring strong light-matter interaction and realizing high sensitive terahertz photodetectors.

  17. Phonon Polariton Behavior in 2D Materials

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

    Phonon Polariton Behavior in 2D Materials Phonon Polariton Behavior in 2D Materials Print Tuesday, 19 January 2016 09:57 In a crystal, collective excitations can be treated as if they are quasiparticles. For example, an excited electron and its associated hole are an exciton; oscillations of conduction electrons in a metal are plasmons; and different modes of lattice vibrations are phonons. Furthermore, when such excitations interact strongly with photons, a new form of quasiparticle emerges:

  18. Imaging carrier and phonon transport in Si using ultrashort optical pulses

    SciTech Connect (OSTI)

    David H. Hurley; O. B. Wright; O. Matsuda; B. E. McCandless; S. Shinde

    2009-01-01

    A series of experiments have been conducted that microscopically image thermal diffusion and surface acoustic phonon propagation within a single crystallite of a polycrystalline Si sample. The experimental approach employs ultrashort optical pulses to generate an electron-hole plasma and a second probe pulse is used to image the evolution of the plasma. By decomposing the signal into a component that varies with delay time and a steady state component that varies with pump modulation frequency, the respective influence of carrier recombination and thermal diffusion are identified. Additionally, the coherent surface acoustic phonon component to the signal is imaged using a Sagnac interferometer to monitor optical phase.

  19. Thermoelectric HVAC and Thermal Comfort Enablers for Light-Duty Vehicle

    Broader source: Energy.gov (indexed) [DOE]

    Applications | Department of Energy 2 DOE Hydrogen and Fuel Cells Program and Vehicle Technologies Program Annual Merit Review and Peer Evaluation Meeting ace047_maranville_2012_o.pdf (1.03 MB) More Documents & Publications Thermoelectric HVAC for Light-Duty Vehicle Applications Improving efficiency of a vehicle HVAC system with comfort modeling, zonal design, and thermoelectric devices

  20. Structural, thermal, optical properties and simulation of white light of titanium-tungstate-tellurite glasses doped with dysprosium

    SciTech Connect (OSTI)

    Jyothi, L. [School of Physics, University of Hyderabad, Hyderabad 500046 (India); Upender, G. [Glass Science and Technology Section, Glass Division, CSIR-CGCRI, Kolkata 700032 (India); Kuladeep, R. [School of Physics, University of Hyderabad, Hyderabad 500046 (India); Rao, D. Narayana, E-mail: dnrsp@uohyd.ernet.in [School of Physics, University of Hyderabad, Hyderabad 500046 (India)

    2014-02-01

    Graphical abstract: CIE coordinate diagram of different concentrations of the Dy{sup 3+}-doped TTWD glasses with coordinates in the white light region. - Highlights: Radiative lifetime of {sup 4}F{sub 9/2} level of Dy{sup 3+} ions is longer in the tellurite glass. Quantum efficiency is found to be high. These glasses are suitable materials for generating white light. - Abstract: Structural, thermal, optical properties and simulation of white light of Dy{sup 3+}-doped tellurite glasses of composition TTWD: (75 ? x)TeO{sub 2} ? 10TiO{sub 2} ? 15WO{sub 3} ? xDy{sub 2}O{sub 3} (x = 0, 0.1, 0.5, 1.0 and 2.0 mol%) were investigated. Raman spectra revealed that the glass contains TeO{sub 4}, TeO{sub 3}, WO{sub 4} and WO{sub 6} units. Differential scanning calorimetry (DSC) measurements were carried out to measure the glass transition temperature of all the glasses. From the optical absorption spectra, luminescence spectra and using the JuddOfelt (JO) analysis, we estimated the radiative transition probabilities, emission cross-sections, branching ratios and radiative lifetimes. The decay curves at lower concentrations are exponential while they show a non-exponential behavior at higher concentrations (?0.5 mol%) due to energy transfer processes. The effective lifetime for the {sup 4}F{sub 9/2} level decreases with increase in Dy{sub 2}O{sub 3} concentration for the glasses under investigation. The non-exponential decay curves could fit well to the InokutiHirayama (IH) model with S = 6, indicating that the nature of interaction responsible for energy transfer is of dipoledipole type. Simulation of white light is examined with varying concentration and the results indicate that these glasses are suitable for white light emitting diode applications.

  1. Twisting phonons in complex crystals with quasi-one-dimensional...

    Office of Scientific and Technical Information (OSTI)

    Twisting phonons in complex crystals with quasi-one-dimensional substructures Twisting Phonons in Higher Manganese Silicides with a Complex Nowotny Chimney Ladder Structure ...

  2. Phonon Bottleneck in Graphene-Based Josephson Junctions at Millikelvin...

    Office of Scientific and Technical Information (OSTI)

    Phonon Bottleneck in Graphene-Based Josephson Junctions at Millikelvin Temperatures Title: Phonon Bottleneck in Graphene-Based Josephson Junctions at Millikelvin Temperatures ...

  3. Effects of temperature and pressure on phonons in FeSi1–xAlx

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

    Delaire, O.; Al-Qasir, I. I.; Ma, J.; dos Santos, A. M.; Sales, B. C.; Mauger, L.; Stone, M. B.; Abernathy, D. L.; Xiao, Y.; Somayazulu, M.

    2013-05-31

    The effects of temperature and pressure on phonons in B20 compounds FeSi1–xAlx were measured using inelastic neutron scattering and nuclear-resonant inelastic x-ray scattering. The effect of hole doping through Al substitution is compared to results of alloying with Co (electron doping) in Fe₁₋xCoxSi. While the temperature dependence of phonons in FeSi is highly anomalous, doping with either type of carriers leads to a recovery of the normal quasiharmonic behavior. Density functional theory (DFT) computations of the electronic band structure and phonons were performed. The anomaly in the temperature dependence of the phonons in undoped FeSi was related to the narrowmore » band gap, and its sensitivity to the effect of thermal disordering by phonons. On the other hand, the pressure dependence of phonons at room temperature in undoped FeSi follows the quasiharmonic behavior and is well reproduced by the DFT calculations.« less

  4. METHOD FOR REMOVAL OF LIGHT ISOTOPE PRODUCT FROM LIQUID THERMAL DIFFUSION UNITS

    DOE Patents [OSTI]

    Hoffman, J.D.; Ballou, J.K.

    1957-11-19

    A method and apparatus are described for removing the lighter isotope of a gaseous-liquid product from a number of diffusion columns of a liquid thermal diffusion system in two stages by the use of freeze valves. The subject liquid flows from the diffusion columns into a heated sloping capsule where the liquid is vaporized by the action of steam in a heated jacket surrounding the capsule. When the capsule is filled the gas flows into a collector. Flow between the various stages is controlled by freeze valves which are opened and closed by the passage of gas and cool water respectively through coils surrounding portions of the pipes through which the process liquid is passed. The use of the dual stage remover-collector and the freeze valves is an improvement on the thermal diffusion separation process whereby the fraction containing the lighter isotope many be removed from the tops of the diffusion columns without intercolumn flow, or prior stage flow while the contents of the capsule is removed to the final receiver.

  5. Thermal neutron steady-state spectra in light water reactor fuel assemblies poisoned with various non-1/v absorbers of different concentrations

    SciTech Connect (OSTI)

    Swaminathan, K.; Chandra, S.; Jha, R.C.; Tewari, S.P. )

    1991-07-01

    This paper reports on the thermal neutron scattering kernel that explicitly incorporates the presence of chemical binding energy and the collective oscillations in the dynamics of water, the steady-state thermal neutron spectra in light water reactor fuel assemblies poisoned with non-1/v absorbers, such as cadmium, samarium, erbium, and gadolinium, in various concentrations have been computed at 298 K. The calculated spectra are in reasonable agreement with the corresponding experimental spectra for realistic source terms.

  6. Phonon quarticity induced by changes in phonon-tracked hybridization during lattice expansion and its stabilization of rutile TiO2

    SciTech Connect (OSTI)

    Lan, Tian; Li, Chen W.; Hellman, O.; Kim, D. S.; Muñoz, Jorge A.; Smith, Hillary; Abernathy, Douglas L.; Fultz, B.

    2015-08-11

    Although the rutile structure of TiO2 is stable at high temperatures, the conventional quasiharmonic approximation predicts that several acoustic phonons decrease anomalously to zero frequency with thermal expansion, incorrectly predicting a structural collapse at temperatures well below 1000 K. In this paper, inelastic neutron scattering was used to measure the temperature dependence of the phonon density of states (DOS) of rutile TiO2 from 300 to 1373 K. Surprisingly, these anomalous acoustic phonons were found to increase in frequency with temperature. First-principles calculations showed that with lattice expansion, the potentials for the anomalous acoustic phonons transform from quadratic to quartic, stabilizing the rutile phase at high temperatures. In these modes, the vibrational displacements of adjacent Ti and O atoms cause variations in hybridization of 3d electrons of Ti and 2p electrons of O atoms. Finally, with thermal expansion, the energy variation in this “phonon-tracked hybridization” flattens the bottom of the interatomic potential well between Ti and O atoms, and induces a quarticity in the phonon potential.

  7. Phonon Polariton Behavior in 2D Materials

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

    Phonon Polariton Behavior in 2D Materials Print In a crystal, collective excitations can be treated as if they are quasiparticles. For example, an excited electron and its associated hole are an exciton; oscillations of conduction electrons in a metal are plasmons; and different modes of lattice vibrations are phonons. Furthermore, when such excitations interact strongly with photons, a new form of quasiparticle emerges: the "polariton." The ability to excite and control polaritons in

  8. Phonon Polariton Behavior in 2D Materials

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

    Phonon Polariton Behavior in 2D Materials Print In a crystal, collective excitations can be treated as if they are quasiparticles. For example, an excited electron and its associated hole are an exciton; oscillations of conduction electrons in a metal are plasmons; and different modes of lattice vibrations are phonons. Furthermore, when such excitations interact strongly with photons, a new form of quasiparticle emerges: the "polariton." The ability to excite and control polaritons in

  9. Phonon Polariton Behavior in 2D Materials

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

    Phonon Polariton Behavior in 2D Materials Print In a crystal, collective excitations can be treated as if they are quasiparticles. For example, an excited electron and its associated hole are an exciton; oscillations of conduction electrons in a metal are plasmons; and different modes of lattice vibrations are phonons. Furthermore, when such excitations interact strongly with photons, a new form of quasiparticle emerges: the "polariton." The ability to excite and control polaritons in

  10. Phonon Polariton Behavior in 2D Materials

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

    Phonon Polariton Behavior in 2D Materials Print In a crystal, collective excitations can be treated as if they are quasiparticles. For example, an excited electron and its associated hole are an exciton; oscillations of conduction electrons in a metal are plasmons; and different modes of lattice vibrations are phonons. Furthermore, when such excitations interact strongly with photons, a new form of quasiparticle emerges: the "polariton." The ability to excite and control polaritons in

  11. Phonon Polariton Behavior in 2D Materials

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

    Phonon Polariton Behavior in 2D Materials Print In a crystal, collective excitations can be treated as if they are quasiparticles. For example, an excited electron and its associated hole are an exciton; oscillations of conduction electrons in a metal are plasmons; and different modes of lattice vibrations are phonons. Furthermore, when such excitations interact strongly with photons, a new form of quasiparticle emerges: the "polariton." The ability to excite and control polaritons in

  12. Calculation of energy relaxation rates of fast particles by phonons in crystals

    SciTech Connect (OSTI)

    Prange, Micah P.; Campbell, Luke W.; Wu, Dangxin; Gao, Fei; Kerisit, Sebastien N.

    2015-03-01

    We present ab initio calculations of the temperature-dependent exchange of energy between a classical charged point-particle and the phonons of a crystalline material. The phonons, which are computed using density functional perturbation theory (DFPT) methods, interact with the mov- ing particle via the Coulomb interaction between the density induced in the material by phonon excitation and the charge of the classical particle. Energy relaxation rates are computed using time- dependent perturbation theory. The method, which is applicable wherever DFPT is, is illustrated with results for CsI, an important scintillator whose performance is affected by electron thermal- ization. We discuss the influence of the form assumed for quasiparticle dispersion on theoretical estimates of electron cooling rates.

  13. Phonon Spectrum Engineering in Rolled-up Micro- and Nano-Architectures

    SciTech Connect (OSTI)

    Fomin, Vladimir M.; Balandin, Alexander A.

    2015-10-10

    We report on a possibility of efficient engineering of the acoustic phonon energy spectrum in multishell tubular structures produced by a novel high-tech method of self-organization of micro- and nano-architectures. The strain-driven roll-up procedure paved the way for novel classes of metamaterials such as single semiconductor radial micro- and nano-crystals and multi-layer spiral micro- and nano-superlattices. The acoustic phonon dispersion is determined by solving the equations of elastodynamics for InAs and GaAs material systems. It is shown that the number of shells is an important control parameter of the phonon dispersion together with the structure dimensions and acoustic impedance mismatch between the superlattice layers. The obtained results suggest that rolled up nano-architectures are promising for thermoelectric applications owing to a possibility of significant reduction of the thermal conductivity without degradation of the electronic transport.

  14. Phonon Spectrum Engineering in Rolled-up Micro- and Nano-Architectures

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

    Fomin, Vladimir M.; Balandin, Alexander A.

    2015-10-10

    We report on a possibility of efficient engineering of the acoustic phonon energy spectrum in multishell tubular structures produced by a novel high-tech method of self-organization of micro- and nano-architectures. The strain-driven roll-up procedure paved the way for novel classes of metamaterials such as single semiconductor radial micro- and nano-crystals and multi-layer spiral micro- and nano-superlattices. The acoustic phonon dispersion is determined by solving the equations of elastodynamics for InAs and GaAs material systems. It is shown that the number of shells is an important control parameter of the phonon dispersion together with the structure dimensions and acoustic impedance mismatchmore » between the superlattice layers. The obtained results suggest that rolled up nano-architectures are promising for thermoelectric applications owing to a possibility of significant reduction of the thermal conductivity without degradation of the electronic transport.« less

  15. Specific heat of twisted bilayer graphene: Engineering phonons by atomic plane rotations

    SciTech Connect (OSTI)

    Nika, Denis L. [E. Pokatilov Laboratory of Physics and Engineering of Nanomaterials, Department of Physics and Engineering, Moldova State University, Chisinau MD-2009, Republic of Moldova (Moldova, Republic of); Nano-Device Laboratory, Department of Electrical Engineering and Materials Science and Engineering Program, Bourns College of Engineering, University of CaliforniaRiverside, Riverside, California, 92521 (United States); Cocemasov, Alexandr I. [E. Pokatilov Laboratory of Physics and Engineering of Nanomaterials, Department of Physics and Engineering, Moldova State University, Chisinau MD-2009, Republic of Moldova (Moldova, Republic of); Balandin, Alexander A., E-mail: balandin@ee.ucr.edu [Nano-Device Laboratory, Department of Electrical Engineering and Materials Science and Engineering Program, Bourns College of Engineering, University of CaliforniaRiverside, Riverside, California, 92521 (United States)

    2014-07-21

    We have studied the phonon specific heat in single-layer, bilayer, and twisted bilayer graphene. The calculations were performed using the Born-von Karman model of lattice dynamics for intralayer atomic interactions and spherically symmetric interatomic potential for interlayer interactions. We found that at temperature T?phonon specific heat reveals an intriguing dependence on the twist angle in bilayer graphene, which is particularly pronounced at low temperature. The results suggest a possibility of phonon engineering of thermal properties of layered materials by twisting the atomic planes.

  16. Twisting phonons in complex crystals with quasi-one-dimensional substructures [Twisting Phonons in Higher Manganese Silicides with a Complex Nowotny Chimney Ladder Structure

    SciTech Connect (OSTI)

    Abernathy, Douglas L.; Ma, Jie; Yan, Jiaqiang; Delaire, Olivier A.; Chen, Xi; Weathers, Annie; Mukhopadhyay, Saikat; Shi, Li

    2015-04-15

    A variety of crystals contain quasi-one-dimensional substructures, which yield distinctive electronic, spintronic, optical and thermoelectric properties. There is a lack of understanding of the lattice dynamics that influences the properties of such complex crystals. Here we employ inelastic neutron scatting measurements and density functional theory calculations to show that numerous low-energy optical vibrational modes exist in higher manganese silicides, an example of such crystals. These optical modes, including unusually low-frequency twisting motions of the Si ladders inside the Mn chimneys, provide a large phase space for scattering acoustic phonons. A hybrid phonon and diffuson model is proposed to explain the low and anisotropic thermal conductivity of higher manganese silicides and to evaluate nanostructuring as an approach to further suppress the thermal conductivity and enhance the thermoelectric energy conversion efficiency. This discovery offers new insights into the structure-property relationships of a broad class of materials with quasi-one-dimensional substructures for various applications.

  17. Progress from DOE EF RC: Solid-State Solar-Thermal Energy Conversion...

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

    Introduction to the solid-state solar-thermal energy conversion center plus discussion on phonon transport and solar thermoelectric energy conversion PDF icon chen.pdf More ...

  18. First-principles calculations of phonons and Raman spectra in...

    Office of Scientific and Technical Information (OSTI)

    First-principles calculations of phonons and Raman spectra in monoclinic CsSnCl 3 Citation Details In-Document Search Title: First-principles calculations of phonons and Raman ...

  19. Electronic, phononic, and thermoelectric properties of graphyne sheets

    SciTech Connect (OSTI)

    Sevinli, Hldun; Sevik, Cem

    2014-12-01

    Electron, phonon, and thermoelectric transport properties of ?-, ?-, ?-, and 6,6,12-graphyne sheets are compared and contrasted with those of graphene. ?-, ?-, and 6,6,12-graphynes, with direction dependent Dirac dispersions, have higher electronic transmittance than graphene. ?-graphyne also attains better electrical conduction than graphene except at its band gap. Vibrationally, graphene conducts heat much more efficiently than graphynes, a behavior beyond an atomic density differences explanation. Seebeck coefficients of the considered Dirac materials are similar but thermoelectric power factors decrease with increasing effective speeds of light. ?-graphyne yields the highest thermoelectric efficiency with a thermoelectric figure of merit as high as ZT?=?0.45, almost an order of magnitude higher than that of graphene.

  20. Frequency stabilization of the zero-phonon line of a quantum dot via phonon-assisted active feedback

    SciTech Connect (OSTI)

    Hansom, Jack; Schulte, Carsten H. H.; Matthiesen, Clemens; Stanley, Megan J.; Atatre, Mete

    2014-10-27

    We report on the feedback stabilization of the zero-phonon emission frequency of a single InAs quantum dot. The spectral separation of the phonon-assisted component of the resonance fluorescence provides a probe of the detuning between the zero-phonon transition and the resonant driving laser. Using this probe in combination with active feedback, we stabilize the zero-phonon transition frequency against environmental fluctuations. This protocol reduces the zero-phonon fluorescence intensity noise by a factor of 22 by correcting for environmental noise with a bandwidth of 191?Hz, limited by the experimental collection efficiency. The associated sub-Hz fluctuations in the zero-phonon central frequency are reduced by a factor of 7. This technique provides a means of stabilizing the quantum dot emission frequency without requiring access to the zero-phonon emission.

  1. Electron-phonon interaction and scattering in Si and Ge: Implications for phonon engineering

    SciTech Connect (OSTI)

    Tandon, Nandan; Albrecht, J. D.; Ram-Mohan, L. R.

    2015-07-28

    We report ab-initio results for electron-phonon (e-ph) coupling and display the existence of a large variation in the coupling parameter as a function of electron and phonon dispersion. This variation is observed for all phonon modes in Si and Ge, and we show this for representative cases where the initial electron states are at the band gap edges. Using these e-ph matrix elements, which include all possible phonon modes and electron bands within a relevant energy range, we evaluate the imaginary part of the electron self-energy in order to obtain the associated scattering rates. The temperature dependence is seen through calculations of the scattering rates at 0 K and 300 K. The results provide a basis for understanding the impacts of phonon scattering vs. orientation and geometry in the design of devices, and in analysis of transport phenomena. This provides an additional tool for engineering the transfer of energy from carriers to the lattice.

  2. Phonon Transport at the Interfaces of Vertically Stacked Graphene and Hexagonal Boron Nitride Heterostructures

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

    Yan, Zhequan; Chen, Liang; Yoon, Mina; Kumar, Satish

    2016-01-12

    Hexagonal boron nitride (h-BN) is a substrate for graphene based nano-electronic devices. We investigate the ballistic phonon transport at the interface of vertically stacked graphene and h-BN heterostructures using first principles density functional theory and atomistic Green's function simulations considering the influence of lattice stacking. We compute the frequency and wave-vector dependent transmission function and observe distinct stacking-dependent phonon transmission features for the h-BN/graphene/h-BN sandwiched systems. We find that the in-plane acoustic modes have the dominant contributions to the phonon transmission and thermal boundary conductance (TBC) for the interfaces with the carbon atom located directly on top of the boronmore » atom (C–B matched) because of low interfacial spacing. The low interfacial spacing is a consequence of the differences in the effective atomic volume of N and B and the difference in the local electron density around N and B. For the structures with the carbon atom directly on top of the nitrogen atom (C–N matched), the spatial distance increases and the contribution of in-plane modes to the TBC decreases leading to higher contributions by out-of-plane acoustic modes. We find that the C–B matched interfaces have stronger phonon–phonon coupling than the C–N matched interfaces, which results in significantly higher TBC (more than 50%) in the C–B matched interface. The findings in this study will provide insights to understand the mechanism of phonon transport at h-BN/graphene/h-BN interfaces, to better explain the experimental observations and to engineer these interfaces to enhance heat dissipation in graphene based electronic devices.« less

  3. A study of the structure and scattering mechanisms of subterahertz phonons in lithium fluoride single crystals and optical ceramics

    SciTech Connect (OSTI)

    Khazanov, E. N. Taranov, A. V.; Gainutdinov, R. V.; Akchurin, M. Sh.; Basiev, T. T.; Konyushkin, V. A.; Fedorov, P. P.; Kuznetsov, S. V.; Osiko, V. V.

    2010-06-15

    The methods of optical, electron, and atomic force microscopy (AFM) are applied to the study of the real structure of optical lithium fluoride ceramic obtained by hot deformation of single crystals. A comparative analysis is carried out of the scattering mechanisms of weakly nonequilibrium thermal phonons at liquid helium temperatures in LiF single crystals and ceramics. It is demonstrated that the phonon scattering in the original single crystals is determined by the forced vibrations of dislocations in the stress field of an elastic plane wave (a phonon), i.e., by the flutter mechanism. As the degree of deformation of the original material increases, the ceramics exhibit a change in the plastic deformation mechanisms, which leads to a decrease in the average size of grains and to an ordered structure. In this case, the dominant scattering is that by intergrain boundaries. The thickness and the acoustic impedance of these boundaries are evaluated.

  4. Evidence of superconductivity-induced phonon spectra renormalization in alkali-doped iron selenides

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

    Opačić, M.; Lazarević, N.; Šćepanović, M.; Ryu, Hyejin; Lei, Hechang; Petrovic, C.; Popović, Z. V.

    2015-11-16

    Polarized Raman scattering spectra of superconducting KxFe2-ySe2 and nonsuperconducting K0.8Fe1.8Co0.2Se2 single crystals were measured in a temperature range from 10 K up to 300 K. Two Raman active modes from the I4/mmm phase and seven from the I4/m phase are observed in frequency range from 150 to 325 cm -1 in both compounds, suggesting that K0.8Fe1.8Co0.2Se2 single crystal also has two-phase nature. Temperature dependence of Raman mode energy is analyzed in terms of lattice thermal expansion and phonon-phonon interaction. Temperature dependence of Raman mode linewidth is considered as temperature-induced anharmonic effects. It is shown that change of Raman mode energymore » with temperature is dominantly driven by thermal expansion of the crystal lattice. Abrupt change of the A1g mode energy near TC was observed in KxFe2-ySe2 , whereas it is absent in K0.8Fe1.8Co0.2Se2. Phonon energy hardening at low temperatures in the superconducting sample is a consequence of superconductivity-induced redistribution of the electronic states below critical temperature.« less

  5. Enhancing phonon flow through one-dimensional interfaces by impedance matching

    SciTech Connect (OSTI)

    Polanco, Carlos A. Ghosh, Avik W.

    2014-08-28

    We extend concepts from microwave engineering to thermal interfaces and explore the principles of impedance matching in 1D. The extension is based on the generalization of acoustic impedance to nonlinear dispersions using the contact broadening matrix ?(?), extracted from the phonon self energy. For a single junction, we find that for coherent and incoherent phonons, the optimal thermal conductance occurs when the matching ?(?) equals the Geometric Mean of the contact broadenings. This criterion favors the transmission of both low and high frequency phonons by requiring that (1) the low frequency acoustic impedance of the junction matches that of the two contacts by minimizing the sum of interfacial resistances and (2) the cut-off frequency is near the minimum of the two contacts, thereby reducing the spillage of the states into the tunneling regime. For an ultimately scaled single atom/spring junction, the matching criterion transforms to the arithmetic mean for mass and the harmonic mean for spring constant. The matching can be further improved using a composite graded junction with an exponential varying broadening that functions like a broadband antireflection coating. There is, however, a trade off as the increased length of the interface brings in additional intrinsic sources of scattering.

  6. Reactor Pressure Vessel Task of Light Water Reactor Sustainability Program: Initial Assessment of Thermal Annealing Needs and Challenges

    Broader source: Energy.gov [DOE]

    The most life-limiting structural component in light-water reactors (LWR) is the reactor pressure vessel (RPV) because replacement of the RPV is not considered a viable option at this time. LWR...

  7. Tunable ultrasonic phononic crystal controlled by infrared radiation

    SciTech Connect (OSTI)

    Walker, Ezekiel; Neogi, Arup, E-mail: zhmwang@gmail.com, E-mail: arup@unt.edu [Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu 610054 (China); University of North Texas, Department of Physics, Denton, Texas 76201 (United States); Reyes, Delfino [University of North Texas, Department of Physics, Denton, Texas 76201 (United States); Universidad Autnoma del Estado de Mxico, Toluca 50120 (Mexico); Rojas, Miguel Mayorga [Universidad Autnoma del Estado de Mxico, Toluca 50120 (Mexico); Krokhin, Arkadii [University of North Texas, Department of Physics, Denton, Texas 76201 (United States); Wang, Zhiming, E-mail: zhmwang@gmail.com, E-mail: arup@unt.edu [Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu 610054 (China)

    2014-10-06

    A tunable phononic crystal based ultrasonic filter was designed by stimulating the phase of the polymeric material embedded in a periodic structure using infrared radiation. The acoustic filter can be tuned remotely using thermal stimulation induced by the infrared radiation. The filter is composed of steel cylinder scatterers arranged periodically in a background of bulk poly (N-isopropylacrylamide) polymer hydrogel. The lattice structure creates forbidden bands for certain sets of mechanical waves that cause it to behave as an ultrasonic filter. Since the bandstructure is determined by not only the arrangement of the scatterers but also the physical properties of the materials composing the scatterers and background, modulating either the arrangement or physical properties will alter the effect of the crystal on propagating mechanical waves. Here, the physical properties of the filter are varied by inducing changes in the polymer hydrogel using an electromagnetic thermal stimulus. With particular focus on the k{sub 00}-wave, the transmission of ultrasonic wave changes by as much as 20 dBm, and band widths by 22% for select bands.

  8. Phonon anharmonicity of monoclinic zirconia and yttrium-stabilized...

    Office of Scientific and Technical Information (OSTI)

    Title: Phonon anharmonicity of monoclinic zirconia and yttrium-stabilized zirconia Authors: Li, Chen 1 ; Smith, Hillary 2 ; Lan, Tian 2 ; Niedziela, Jennifer L 1 ; Munoz, ...

  9. Evidence for coupling between collective state and phonons in...

    Office of Scientific and Technical Information (OSTI)

    for coupling between collective state and phonons in two-dimensional charge-density-wave systems Citation Details In-Document Search Title: Evidence for coupling between...

  10. Phonon Bottleneck in Graphene-Based Josephson Junctions at Millikelvin

    Office of Scientific and Technical Information (OSTI)

    Phonon Bottleneck in Graphene-Based Josephson Junctions at Millikelvin Temperatures Borzenets, I. V.; Coskun, U. C.; Mebrahtu, H. T.; Bomze, Yu. V.; Smirnov, A. I.; Finkelstein, G....

  11. Implementation and testing of the on-the-fly thermal scattering Monte Carlo sampling method for graphite and light water in MCNP6

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

    Pavlou, Andrew T.; Ji, Wei; Brown, Forrest B.

    2016-01-23

    Here, a proper treatment of thermal neutron scattering requires accounting for chemical binding through a scattering law S(α,β,T). Monte Carlo codes sample the secondary neutron energy and angle after a thermal scattering event from probability tables generated from S(α,β,T) tables at discrete temperatures, requiring a large amount of data for multiscale and multiphysics problems with detailed temperature gradients. We have previously developed a method to handle this temperature dependence on-the-fly during the Monte Carlo random walk using polynomial expansions in 1/T to directly sample the secondary energy and angle. In this paper, the on-the-fly method is implemented into MCNP6 andmore » tested in both graphite-moderated and light water-moderated systems. The on-the-fly method is compared with the thermal ACE libraries that come standard with MCNP6, yielding good agreement with integral reactor quantities like k-eigenvalue and differential quantities like single-scatter secondary energy and angle distributions. The simulation runtimes are comparable between the two methods (on the order of 5–15% difference for the problems tested) and the on-the-fly fit coefficients only require 5–15 MB of total data storage.« less

  12. Phonon anomalies in some iron telluride materials

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

    C. C. Homes; Dai, Y. M.; Schneeloch, J.; Zhong, R. D.; Gu, G. D.

    2016-03-21

    In this paper, the detailed temperature dependence of the infrared-active mode in Fe1.03Te (TN ≃ 68 K) and Fe1.13Te (TN ≃ 56 K) has been examined, and the position, width, strength, and asymmetry parameter have been determined using an asymmetric Fano profile superimposed on an electronic background. In both materials the frequency of the mode increases as the temperature is reduced; however, there is also a slight asymmetry in the line shape, indicating that the mode is coupled to either spin or charge excitations. Below TN there is an anomalous decrease in frequency, and the mode shows little temperature dependence,more » at the same time becoming more symmetric, suggesting a reduction in spin- or electron-phonon coupling. The frequency of the infrared-active mode and the magnitude of the shift below TN are predicted reasonably well by first-principles calculations; however, the predicted splitting of the mode is not observed. In superconducting FeTe0.55Se0.45 (Tc ≃ 14 K) the infrared-active Eu mode displays asymmetric line shape at all temperatures, which is most pronounced between 100 – 200 K, indicating the presence of either spin- or electron-phonon coupling, which may be a necessary prerequisite for superconductivity in this class of materials.« less

  13. Twisting phonons in complex crystals with quasi-one-dimensional substructures [Twisting Phonons in Higher Manganese Silicides with a Complex Nowotny Chimney Ladder Structure

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

    Abernathy, Douglas L.; Ma, Jie; Yan, Jiaqiang; Delaire, Olivier A.; Chen, Xi; Weathers, Annie; Mukhopadhyay, Saikat; Shi, Li

    2015-04-15

    A variety of crystals contain quasi-one-dimensional substructures, which yield distinctive electronic, spintronic, optical and thermoelectric properties. There is a lack of understanding of the lattice dynamics that influences the properties of such complex crystals. Here we employ inelastic neutron scatting measurements and density functional theory calculations to show that numerous low-energy optical vibrational modes exist in higher manganese silicides, an example of such crystals. These optical modes, including unusually low-frequency twisting motions of the Si ladders inside the Mn chimneys, provide a large phase space for scattering acoustic phonons. A hybrid phonon and diffuson model is proposed to explain themore » low and anisotropic thermal conductivity of higher manganese silicides and to evaluate nanostructuring as an approach to further suppress the thermal conductivity and enhance the thermoelectric energy conversion efficiency. This discovery offers new insights into the structure-property relationships of a broad class of materials with quasi-one-dimensional substructures for various applications.« less

  14. Phonon anharmonicity of monoclinic zirconia and yttrium-stabilized zirconia

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

    Li, Chen W.; Smith, Hillary L.; Lan, Tian; Niedziela, Jennifer L.; Munoz, Jorge A.; Keith, J. Brian; Mauger, L.; Abernathy, Douglas L; Fultz, B.

    2015-04-13

    Inelastic neutron scattering measurements on monoclinic zirconia (ZrO2) and 8 mol% yttrium-stabilized zirconia were performed at temperatures from 300 to 1373 ωK. We reported temperature-dependent phonon densities of states (DOS) and Raman spectra obtained at elevated temperatures. First-principles lattice dynamics calculations with density functional theory gave total and partial phonon DOS curves and mode Grüneisen parameters. These mode Grüneisen parameters were used to predict the experimental temperature dependence of the phonon DOS with partial success. However, substantial anharmonicity was found at elevated temperatures, especially for phonon modes dominated by the motions of oxygen atoms. Yttrium-stabilized zirconia (YSZ) was somewhat moremore » anharmonic and had a broader phonon spectrum at low temperatures, owing in part to defects in its structure. YSZ also has a larger vibrational entropy than monoclinic zirconia.« less

  15. Phonon anharmonicity of monoclinic zirconia and yttrium-stabilized zirconia

    SciTech Connect (OSTI)

    Li, Chen W.; Smith, Hillary L.; Lan, Tian; Niedziela, Jennifer L.; Munoz, Jorge A.; Keith, J. Brian; Mauger, L.; Abernathy, Douglas L; Fultz, B.

    2015-04-13

    Inelastic neutron scattering measurements on monoclinic zirconia (ZrO2) and 8 mol% yttrium-stabilized zirconia were performed at temperatures from 300 to 1373 ωK. We reported temperature-dependent phonon densities of states (DOS) and Raman spectra obtained at elevated temperatures. First-principles lattice dynamics calculations with density functional theory gave total and partial phonon DOS curves and mode Grüneisen parameters. These mode Grüneisen parameters were used to predict the experimental temperature dependence of the phonon DOS with partial success. However, substantial anharmonicity was found at elevated temperatures, especially for phonon modes dominated by the motions of oxygen atoms. Yttrium-stabilized zirconia (YSZ) was somewhat more anharmonic and had a broader phonon spectrum at low temperatures, owing in part to defects in its structure. YSZ also has a larger vibrational entropy than monoclinic zirconia.

  16. Role of low-energy phonons with mean-free-paths >0.8 μm in heat conduction in silicon

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

    Jiang, Puqing; Lindsay, Lucas R.; Koh, Yee Kan

    2016-06-30

    Despite recent progress in the first-principles calculations and measurements of phonon mean-free-paths (ℓ), contribution of low-energy phonons to heat conduction in silicon is still inconclusive, as exemplified by the discrepancies as large as 30% between different first-principles calculations. In this study, we investigate the contribution of low-energy phonons with ℓ>0.8 μm by accurately measuring the cross-plane thermal conductivity (Λcross) of crystalline silicon films by time-domain thermoreflectance (TDTR), over a wide range of film thicknesses 1≤ hf ≤ 10 μm and temperatures 100 ≤ T ≤ 300 K. We employ a dual-frequency TDTR approach to improve the accuracy of our Λcrossmore » measurements. We find from our Λcross measurements that phonons with ℓ>0.8 μm contribute 53 W m-1 K-1 (37%) to heat conduction in natural Si at 300 K while phonons with ℓ>3 μm contribute 523 W m-1 K-1 (61%) at 100 K, >20% lower than first-principles predictions of 68 W m-1 K-1 (47%) and 717 W m-1 K-1 (76%), respectively. Using a relaxation time approximation (RTA) model, we demonstrate that macroscopic damping (e.g., Akhieser s damping) eliminates the contribution of phonons with mean-free-paths >20 μm at 300 K, which contributes 15 W m-1 K-1 (10%) to calculated heat conduction in Si. Thus, we propose that omission of the macroscopic damping for low-energy phonons in the first-principles calculations could be one of the possible explanations for the observed differences between our measurements and calculations. Finally, our work provides an important benchmark for future measurements and calculations of the distribution of phonon mean-free-paths in crystalline silicon.« less

  17. Thermally activated delayed fluorescence from {sup 3}n?* to {sup 1}n?* up-conversion and its application to organic light-emitting diodes

    SciTech Connect (OSTI)

    Li, Jie; Zhang, Qisheng; Nomura, Hiroko [Department of Chemistry and Biochemistry, and Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395 (Japan); Miyazaki, Hiroshi [Department of Chemistry and Biochemistry, and Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395 (Japan); Functional Materials Laboratory, Nippon Steel and Sumikin Chemical Co., Ltd, 4680 Nakabaru, Sakinohama, Tobata, Kitakyushu, Fukuoka 8048503 (Japan); Adachi, Chihaya, E-mail: adachi@cstf.kyushu-u.ac.jp [Department of Chemistry and Biochemistry, and Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395 (Japan); International Institute for Carbon Neutral Energy Research (WPI-I2CNER), Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395 (Japan)

    2014-07-07

    Intense n?* fluorescence from a nitrogen-rich heterocyclic compound, 2,5,8-tris(4-fluoro-3-methylphenyl)-1,3,4,6,7,9,9b-heptaazaphenalene (HAP-3MF), is demonstrated. The overlap-forbidden nature of the n?* transition and the higher energy of the {sup 3}??* state than the {sup 3}n?* one lead to a small energy difference between the lowest singlet (S{sub 1}) and triplet (T{sub 1}) excited states of HAP-3MF. Green-emitting HAP-3MF has a moderate photoluminescence quantum yield of 0.26 in both toluene and doped film. However, an organic light-emitting diode containing HAP-3MF achieved a high external quantum efficiency of 6.0%, indicating that HAP-3MF harvests singlet excitons through a thermally activated T{sub 1} ? S{sub 1} pathway in the electroluminescent process.

  18. Los Alamos probes mysteries of uranium dioxide's thermal conductivity

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

    Mysteries of uranium dioxide's thermal conductivity Los Alamos probes mysteries of uranium dioxide's thermal conductivity New research is showing that the thermal conductivity of cubic uranium dioxide is strongly affected by interactions between phonons carrying heat and magnetic spins. August 4, 2014 Illustration of anisotropic thermal conductivity in uranium dioxide (UO2). Scientists are studying the thermal conductivity related to the material's different crystallographic directions, hoping

  19. Phonon Quasidiffusion in Cryogenic Dark Matter Search Large Germanium Detectors

    SciTech Connect (OSTI)

    Leman, S.W.; /MIT, MKI; Cabrera, B.; /Stanford U., Phys. Dept.; McCarthy, K.A.; /MIT, MKI; Pyle, M.; /Stanford U., Phys. Dept.; Resch, R.; /SLAC; Sadoulet, B.; Sundqvist, K.M.; /LBL, Berkeley; Brink, P.L.; Cherry, M.; /Stanford U., Phys. Dept.; Do Couto E Silva, E.; /SLAC; Figueroa-Feliciano, E.; /MIT, MKI; Mirabolfathi, N.; Serfass, B.; /UC, Berkeley; Tomada, A.; /Stanford U., Phys. Dept.

    2012-06-04

    We present results on quasidiffusion studies in large, 3 inch diameter, 1 inch thick [100] high purity germanium crystals, cooled to 50 mK in the vacuum of a dilution refrigerator, and exposed with 59.5 keV gamma-rays from an Am-241 calibration source. We compare data obtained in two different detector types, with different phonon sensor area coverage, with results from a Monte Carlo. The Monte Carlo includes phonon quasidiffusion and the generation of phonons created by charge carriers as they are drifted across the detector by ionization readout channels.

  20. Mode dependent lattice thermal conductivity of single layer graphene

    SciTech Connect (OSTI)

    Wei, Zhiyong; Yang, Juekuan; Bi, Kedong; Chen, Yunfei

    2014-10-21

    Molecular dynamics simulation is performed to extract the phonon dispersion and phonon lifetime of single layer graphene. The mode dependent thermal conductivity is calculated from the phonon kinetic theory. The predicted thermal conductivity at room temperature exhibits important quantum effects due to the high Debye temperature of graphene. But the quantum effects are reduced significantly when the simulated temperature is as high as 1000 K. Our calculations show that out-of-plane modes contribute about 41.1% to the total thermal conductivity at room temperature. The relative contribution of out-of-plane modes has a little decrease with the increase of temperature. Contact with substrate can reduce both the total thermal conductivity of graphene and the relative contribution of out-of-plane modes, in agreement with previous experiments and theories. Increasing the coupling strength between graphene and substrate can further reduce the relative contribution of out-of-plane modes. The present investigations also show that the relative contribution of different mode phonons is not sensitive to the grain size of graphene. The obtained phonon relaxation time provides useful insight for understanding the phonon mean free path and the size effects in graphene.

  1. Evidence of superconductivity-induced phonon spectra renormalization in alkali-doped iron selenides

    SciTech Connect (OSTI)

    Opačić, M.; Lazarević, N.; Šćepanović, M.; Ryu, Hyejin; Lei, Hechang; Petrovic, C.; Popović, Z. V.

    2015-11-16

    Polarized Raman scattering spectra of superconducting KxFe2-ySe2 and nonsuperconducting K0.8Fe1.8Co0.2Se2 single crystals were measured in a temperature range from 10 K up to 300 K. Two Raman active modes from the I4/mmm phase and seven from the I4/m phase are observed in frequency range from 150 to 325 cm -1 in both compounds, suggesting that K0.8Fe1.8Co0.2Se2 single crystal also has two-phase nature. Temperature dependence of Raman mode energy is analyzed in terms of lattice thermal expansion and phonon-phonon interaction. Temperature dependence of Raman mode linewidth is considered as temperature-induced anharmonic effects. It is shown that change of Raman mode energy with temperature is dominantly driven by thermal expansion of the crystal lattice. Abrupt change of the A1g mode energy near TC was observed in KxFe2-ySe2 , whereas it is absent in K0.8Fe1.8Co0.2Se2. Phonon energy hardening at low temperatures in the superconducting sample is a consequence of superconductivity-induced redistribution of the electronic states below critical temperature.

  2. Electronic Structure, Phonon Dynamical Properties, and CO2 Capture...

    Office of Scientific and Technical Information (OSTI)

    Journal Article: Electronic Structure, Phonon Dynamical Properties, and CO2 Capture Capability of Na2-xMxZrO3 ( MLi ,K): Density-Functional Calculations and Experimental...

  3. Interfacial Electron-Phonon Coupling as the Cause of Enhanced...

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

    Interfacial Electron-Phonon Coupling as the Cause of Enhanced Tc in Single-layer FeSe Films on SrTiO3 Friday, February 27, 2015 In the past several years, multiple studies have...

  4. Twisting phonons in complex crystals with quasi-one-dimensional...

    Office of Scientific and Technical Information (OSTI)

    ... phonon branches at energy up to about 20 meV, above ... in the following simple analytical form: t 1 (o) ... In addition, previous first principle calculations of Si and ...

  5. The Electron-Phonon Interaction as Studied by Photoelectron Spectroscopy

    SciTech Connect (OSTI)

    D.W. Lynch

    2004-09-30

    With recent advances in energy and angle resolution, the effects of electron-phonon interactions are manifest in many valence-band photoelectron spectra (PES) for states near the Fermi level in metals.

  6. Phonon densities of states and related thermodynamic properties of high temperature ceramics.

    SciTech Connect (OSTI)

    Loong, C.-K.

    1998-08-28

    Structural components and semiconductor devices based on silicon nitride, aluminum nitride and gallium nitride are expected to function more reliably at elevated temperatures and at higher levels of performance because of the strong atomic bonding in these materials. The degree of covalency, lattice specific heat, and thermal conductivity are important design factors for the realization of advanced applications. We have determined the phonon densities of states of these ceramics by the method of neutron scattering. The results provide a microscopic interpretation of the mechanical and thermal properties. Moreover, experimental data of the static, structures, and dynamic excitations of atoms are essential to the validation of interparticle potentials employed for molecular-dynamics simulations of high-temperature properties of multi-component ceramic systems. We present an overview of neutron-scattering investigations of the atomic organization, phonon excitations, as well as calculations of related thermodynamic properties of Si{sub 3}N{sub 4}, {beta}-sialon, AlN and GaN. The results are compared with those of the oxide analogs such as SiO{sub 2} and Al{sub 2}O{sub 3}.

  7. 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

  8. Temperature and compression effects on electron heat capacity and electron-phonon coupling in aluminum and beryllium: Insights from ab initio simulations

    SciTech Connect (OSTI)

    Li, Zi; Li, Chuanying; Wang, Cong; Zhang, Ping; Kang, Wei

    2015-11-15

    Ultrafast laser experiments on metals usually induce a high electron temperature and a low ion temperature and, thus, an energy relaxation process. The electron heat capacity and electron-phonon coupling factor are crucial thermal quantities to describe this process. We perform ab initio theoretical studies to determine these thermal quantities and their dependence on density and electron temperature for the metals aluminum and beryllium. The heat capacity shows an approximately linear dependence on the temperature, similar to free electron gas, and the compression only slightly affects the capacity. The electron-phonon coupling factor increases with both temperature and density, and the change observed for beryllium is more obvious than that for aluminum. The connections between thermal quantities and electronic/atomic structures are discussed in detail, and the different behaviors of aluminum and beryllium are well explained.

  9. Thermal transport across graphene and single layer hexagonal boron nitride

    SciTech Connect (OSTI)

    Zhang, Jingchao E-mail: yyue@whu.edu.cn; Hong, Yang; Yue, Yanan E-mail: yyue@whu.edu.cn

    2015-04-07

    As the dimensions of nanocircuits and nanoelectronics shrink, thermal energies are being generated in more confined spaces, making it extremely important and urgent to explore for efficient heat dissipation pathways. In this work, the phonon energy transport across graphene and hexagonal boron-nitride (h-BN) interface is studied using classic molecular dynamics simulations. Effects of temperature, interatomic bond strength, heat flux direction, and functionalization on interfacial thermal transport are investigated. It is found out that by hydrogenating graphene in the hybrid structure, the interfacial thermal resistance (R) between graphene and h-BN can be reduced by 76.3%, indicating an effective approach to manipulate the interfacial thermal transport. Improved in-plane/out-of-plane phonon couplings and broadened phonon channels are observed in the hydrogenated graphene system by analyzing its phonon power spectra. The reported R results monotonically decrease with temperature and interatomic bond strengths. No thermal rectification phenomenon is observed in this interfacial thermal transport. Results reported in this work give the fundamental knowledge on graphene and h-BN thermal transport and provide rational guidelines for next generation thermal interface material designs.

  10. High efficiency incandescent lighting

    DOE Patents [OSTI]

    Bermel, Peter; Ilic, Ognjen; Chan, Walker R.; Musabeyoglu, Ahmet; Cukierman, Aviv Ruben; Harradon, Michael Robert; Celanovic, Ivan; Soljacic, Marin

    2014-09-02

    Incandescent lighting structure. The structure includes a thermal emitter that can, but does not have to, include a first photonic crystal on its surface to tailor thermal emission coupled to, in a high-view-factor geometry, a second photonic filter selected to reflect infrared radiation back to the emitter while passing visible light. This structure is highly efficient as compared to standard incandescent light bulbs.

  11. Thermal conductivity of configurable two-dimensional carbon nanotube architecture and strain modulation

    SciTech Connect (OSTI)

    Zhan, H. F.; Bell, J. M.; Gu, Y. T., E-mail: yuantong.gu@qut.edu.au [School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, 2 George St., Brisbane, Queensland 4000 (Australia); Zhang, G. [Institute of High Performance Computing, Agency for Science, Technology and Research, 1 Fusionopolis Way, Singapore 138632 (Singapore)

    2014-10-13

    We reported the thermal conductivity of the two-dimensional carbon nanotube (CNT)-based architecture, which can be constructed through welding of single-wall CNTs by electron beam. Using large-scale nonequilibrium molecular dynamics simulations, the thermal conductivity is found to vary with different junction types due to their different phonon scatterings at the junction. The strong length and strain dependence of the thermal conductivity suggests an effective avenue to tune the thermal transport properties of the CNT-based architecture, benefiting the design of nanoscale thermal rectifiers or phonon engineering.

  12. Phonon dispersion curves determination in (delta)-phase Pu-Ga alloys

    SciTech Connect (OSTI)

    Wong, J; Clatterbuck, D; Occelli, F; Farber, D; Schwartz, A; Wall, M; Boro, C; Krisch, M; Beraud, A; Chiang, T; Xu, R; Hong, H; Zschack, P; Tamura, N

    2006-02-07

    We have designed and successfully employed a novel microbeam on large grain sample concept to conduct high resolution inelastic x-ray scattering (HRIXS) experiments to map the full phonon dispersion curves of an fcc {delta}-phase Pu-Ga alloy. This approach obviates experimental difficulties with conventional inelastic neutron scattering due to the high absorption cross section of the common {sup 239}Pu isotope and the non-availability of large (mm size) single crystal materials for Pu and its alloys. A classical Born von-Karman force constant model was used to model the experimental results, and no less than 4th nearest neighbor interactions had to be included to account for the observation. Several unusual features including, a large elastic anisotropy, a small shear elastic modulus, (C{sub 11}-C{sub 12})/2, a Kohn-like anomaly in the T{sub 1}[011] branch, and a pronounced softening of the T[111] branch towards the L point in the Brillouin are found. These features may be related to the phase transitions of plutonium and to strong coupling between the crystal structure and the 5f valence instabilities. Our results represent the first full phonon dispersions ever obtained for any Pu-bearing material, thus ending a 40-year quest for this fundamental data. The phonon data also provide a critical test for theoretical treatments of highly correlated 5f electron systems as exemplified by recent dynamical mean field theory (DMFT) calculations for {delta}-plutonium. We also conducted thermal diffuse scattering experiments to study the T(111) dispersion at low temperatures with an attempt to gain insight into bending of the T(111) branch in relationship to the {delta} {yields} {alpha}{prime} transformation.

  13. Study of the thermodynamic properties of CeO{sub 2} from ab initio calculations: The effect of phonon-phonon interaction

    SciTech Connect (OSTI)

    Niu, Zhen-Wei; Zeng, Zhao-Yi; Hu, Cui-E; Cai, Ling-Cang; Chen, Xiang-Rong

    2015-01-07

    The thermodynamic properties of CeO{sub 2} have been reevaluated by a simple but accurate scheme. All our calculations are based on the self-consistent ab initio lattice dynamical (SCAILD) method that goes beyond the quasiharmonic approximation. Through this method, the effects of phonon-phonon interactions are included. The obtained thermodynamic properties and phonon dispersion relations are in good agreement with experimental data when considering the correction of phonon-phonon interaction. We find that the correction of phonon-phonon interaction is equally important and should not be neglected. At last, by comparing with quasiharmonic approximation, the present scheme based on SCAILD method is probably more suitable for high temperature systems.

  14. Phonon anharmonicity in silicon from 100 to 1500 K

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

    Kim, D. S.; Smith, Hillary L.; Niedziela, Jennifer L.; Li, Chen W.; Abernathy, Douglas L.; Fultz, B.

    2015-01-21

    Inelastic neutron scattering was performed on silicon powder to measure the phonon density of states (DOS) from 100 to 1500 K. The mean fractional energy shifts with temperature of the modes weremore » $$\\langle$$Δεi/εiΔT$$\\rangle$$=₋0.07, giving a mean isobaric Grüneisen parameter of +6.95±0.67, which is significantly different from the isothermal parameter of +0.98. These large effects are beyond the predictions from quasiharmonic models using density functional theory or experimental data, demonstrating large effects from phonon anharmonicity. At 1500 K the anharmonicity contributes 0.15kB/atom to the vibrational entropy, compared to 0.03kB/atom from quasiharmonicity. Lastly, excellent agreement was found between the entropy from phonon DOS measurements and the reference NIST-JANAF thermodynamic entropy from calorimetric measurements.« less

  15. Phonon anharmonicity in silicon from 100 to 1500 K

    SciTech Connect (OSTI)

    Kim, D. S.; Smith, Hillary L.; Niedziela, Jennifer L.; Li, Chen W.; Abernathy, Douglas L.; Fultz, B.

    2015-01-21

    Inelastic neutron scattering was performed on silicon powder to measure the phonon density of states (DOS) from 100 to 1500 K. The mean fractional energy shifts with temperature of the modes were $\\langle$ΔεiiΔT$\\rangle$=₋0.07, giving a mean isobaric Grüneisen parameter of +6.95±0.67, which is significantly different from the isothermal parameter of +0.98. These large effects are beyond the predictions from quasiharmonic models using density functional theory or experimental data, demonstrating large effects from phonon anharmonicity. At 1500 K the anharmonicity contributes 0.15kB/atom to the vibrational entropy, compared to 0.03kB/atom from quasiharmonicity. Lastly, excellent agreement was found between the entropy from phonon DOS measurements and the reference NIST-JANAF thermodynamic entropy from calorimetric measurements.

  16. Structural phase transition and phonon instabilities in Cu12Sb4S13

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

    May, Andrew F.; Delaire, Olivier A.; Niedziela, Jennifer L.; Lara-Curzio, Edgar; Susner, Michael A.; Abernathy, Douglas L.; Kirkham, Melanie J.; McGuire, Michael A.

    2016-02-08

    In this study, a structural phase transition has been discovered in the synthetic tetrahedrite Cu12Sb4S13 at approximately 88 K. Upon cooling, the material transforms from its known cubic symmetry to a tetragonal unit cell that is characterized by an in-plane ordering that leads to a doubling of the unit cell volume. Specific heat capacity measurements demonstrate a hysteresis of more than two degrees in the associated anomaly. A similar hysteresis was observed in powder x-ray diffraction measurements, which also indicate a coexistence of the two phases, and together these results suggest a first-order transition. This structural transition coincides with amore » recently-reported metal-insulator transition, and the structural instability is related to the very low thermal conductivity κ in these materials. Inelastic neutron scattering was used to measure the phonon density of states in Cu12Sb4S13 and Cu10Zn2Sb4S13, both of which possess a localized, low-energy phonon mode associated with strongly anharmonic copper displacements that suppress κ. In Cu12Sb4S13, signatures of the phase transition are observed in the temperature dependence of the localized mode, which disappears at the structural transition. In contrast, in the cubic Zn-doped material, the mode is at slightly higher-energy but observable for all temperatures, though it softens upon cooling.« less

  17. Structural phase transition and phonon instability in Cu12Sb4S13

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

    May, Andrew F.; Delaire, Olivier A.; Niedziela, Jennifer L.; Lara-Curzio, Edgar; Susner, Michael A.; Abernathy, Douglas L.; Kirkham, Melanie J.; McGuire, Michael A.

    2016-02-08

    In this study, a structural phase transition has been discovered in the synthetic tetrahedrite Cu12Sb4S13 at approximately 88 K. Upon cooling, the material transforms from its known cubic symmetry to a tetragonal unit cell that is characterized by an in-plane ordering that leads to a doubling of the unit cell volume. Specific heat capacity measurements demonstrate a hysteresis of more than two degrees in the associated anomaly. A similar hysteresis was observed in powder x-ray diffraction measurements, which also indicate a coexistence of the two phases, and together these results suggest a first-order transition. This structural transition coincides with amore » recently-reported metal-insulator transition, and the structural instability is related to the very low thermal conductivity κ in these materials. Inelastic neutron scattering was used to measure the phonon density of states in Cu12Sb4S13 and Cu10Zn2Sb4S13, both of which possess a localized, low-energy phonon mode associated with strongly anharmonic copper displacements that suppress κ. In Cu12Sb4S13, signatures of the phase transition are observed in the temperature dependence of the localized mode, which disappears at the structural transition. In contrast, in the cubic Zn-doped material, the mode is at slightly higher-energy but observable for all temperatures, though it softens upon cooling.« less

  18. Evolution of the phonon density of states of LaCoO3 over the...

    Office of Scientific and Technical Information (OSTI)

    Evolution of the phonon density of states of LaCoO3 over the spin state transition Citation Details In-Document Search Title: Evolution of the phonon density of states of LaCoO3 ...

  19. Preface to special topic: Selected articles from phononics 2013: The second international conference on phononic crystals/metamaterials, phonon transport and optomechanics, 2-7 June 2013, Sharm El-Sheikh, Egypt

    SciTech Connect (OSTI)

    Hussein, Mahmoud I.; El-Kady, Ihab; Li, Baowen; Snchez-Dehesa, Jos

    2014-12-31

    Phononics is an interdisciplinary branch of physics and engineering that deals with the behavior of phonons, and more broadly elastic and acoustic waves in similar context, and their manipulation in solids and/or fluids to benefit technological applications. Compared to resembling disciplines, such as electronics and photonics, phononics is a youthful field. It is growing at a remarkable rate, especially when viewed liberally with no limiting constraints on any particular length scale, discipline or application.

  20. 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.

  1. Optical phonons in PbTe/CdTe multilayer heterostructures

    SciTech Connect (OSTI)

    Novikova, N. N.; Yakovlev, V. A.; Kucherenko, I. V.; Karczewski, G.; Aleshchenko, Yu. A.; Muratov, A. V.; Zavaritskaya, T. N.; Melnik, N. N.

    2015-05-15

    The infrared reflection spectra of PbTe/CdTe multilayer nanostructures grown by molecular-beam epitaxy are measured in the frequency range of 20–5000 cm{sup −1} at room temperature. The thicknesses and high-frequency dielectric constants of the PbTe and CdTe layers and the frequencies of the transverse optical (TO) phonons in these structures are determined from dispersion analysis of the spectra. It is found that the samples under study are characterized by two TO phonon frequencies, equal to 28 and 47 cm{sup −1}. The first frequency is close to that of TO phonons in bulk PbTe, and the second is assigned to the optical mode in structurally distorted interface layers. The Raman-scattering spectra upon excitation with the radiation of an Ar{sup +} laser at 514.5 nm are measured at room and liquid-nitrogen temperatures. The weak line at 106 cm{sup −1} observed in these spectra is attributed to longitudinal optical phonons in the interface layers.

  2. Coupling Between An Optical Phonon and the Kondo Effect

    SciTech Connect (OSTI)

    Burch, Kenneth; Chia, Elbert E. M.; Talbayev, D.; Sales, Brian C; Mandrus, David; Taylor, A. J.; Averitt, R. D.

    2008-01-01

    We explore the ultrafast optical response of Yb14MnSb11, providing further evidence that this Zintl compound is one of the first examples of a ferromagnetic under-screened Kondo lattice. These experiments also provide the first demonstration of coupling between an optical phonon and the Kondo effect.

  3. Phonon-enhanced crystal growth and lattice healing

    DOE Patents [OSTI]

    Buonassisi, Anthony; Bertoni, Mariana; Newman, Bonna

    2013-05-28

    A system for modifying dislocation distributions in semiconductor materials is provided. The system includes one or more vibrational sources for producing at least one excitation of vibrational mode having phonon frequencies so as to enhance dislocation motion through a crystal lattice.

  4. 3D Printing of Interdigitated Li-Ion Microbattery Architectures...

    Office of Scientific and Technical Information (OSTI)

    of Publication: United States Language: English Subject: solar (photovoltaic), solid state lighting, phonons, thermal conductivity, electrodes - solar, materials and chemistry...

  5. Device fabrication: Three-dimensional printed electronics (Journal...

    Office of Scientific and Technical Information (OSTI)

    of Publication: United States Language: English Subject: solar (photovoltaic), solid state lighting, phonons, thermal conductivity, electrodes - solar, materials and chemistry...

  6. 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.

  7. Phonon dispersion and quantization tuning of strained carbon nanotubes for flexible electronics

    SciTech Connect (OSTI)

    Gautreau, Pierre; Chu, Yanbiao; Basaran, Cemal; Ragab, Tarek

    2014-06-28

    Graphene and carbon nanotubes are materials with large potentials for applications in flexible electronics. Such devices require a high level of sustainable strain and an understanding of the materials electrical properties under strain. Using supercell theory in conjunction with a comprehensive molecular mechanics model, the full band phonon dispersion of carbon nanotubes under uniaxial strain is studied. The results suggest an overall phonon softening and open up the possibility of phonon quantization tuning with uniaxial strain. The change in phonon quantization and the resulting increase in electron-phonon and phonon-phonon scattering rates offer further explanation and theoretical basis to the experimental observation of electrical properties degradation for carbon nanotubes under uniaxial strain.

  8. Thermal trim for luminaire

    DOE Patents [OSTI]

    Bazydola, Sarah; Ghiu, Camil-Daniel; Harrison, Robert; Jeswani, Anil

    2013-11-19

    A luminaire with a thermal pathway to reduce the junction temperature of the luminaire's light source, and methods for so doing, are disclosed. The luminaire includes a can, a light engine, and a trim, that define a substantially continuous thermal pathway from the light engine to a surrounding environment. The can defines a can cavity and includes a can end region. The light engine is within the can cavity and includes a light source and a heat sink, including a heat sink end region, coupled thereto. The trim is at least partially disposed within the can cavity and includes a first trim end region coupled to the heat sink end region and a second trim end region coupled to the can end region. Thermal interface material may be located between: the heat sink and the trim, the trim and the can, and/or the heat sink and the light source.

  9. A new regime of nanoscale thermal transport: Collective diffusion increases dissipation efficiency

    SciTech Connect (OSTI)

    Hoogeboom-Pot, Kathleen M.; Hernandez-Charpak, Jorge N.; Gu, Xiaokun; Frazer, Travis D.; Anderson, Erik H.; Chao, Weilun; Falcone, Roger W.; Yang, Ronggui; Murnane, Margaret M.; Kapteyn, Henry C.; Nardi, Damiano

    2015-03-23

    Understanding thermal transport from nanoscale heat sources is important for a fundamental description of energy flow in materials, as well as for many technological applications including thermal management in nanoelectronics and optoelectronics, thermoelectric devices, nanoenhanced photovoltaics, and nanoparticle-mediated thermal therapies. Thermal transport at the nanoscale is fundamentally different from that at the macroscale and is determined by the distribution of carrier mean free paths and energy dispersion in a material, the length scales of the heat sources, and the distance over which heat is transported. Past work has shown that Fourier’s law for heat conduction dramatically overpredicts the rate of heat dissipation from heat sources with dimensions smaller than the mean free path of the dominant heat-carrying phonons. In this work, we uncover a new regime of nanoscale thermal transport that dominates when the separation between nanoscale heat sources is small compared with the dominant phonon mean free paths. Surprisingly, the interaction of phonons originating from neighboring heat sources enables more efficient diffusive-like heat dissipation, even from nanoscale heat sources much smaller than the dominant phonon mean free paths. This finding suggests that thermal management in nanoscale systems including integrated circuits might not be as challenging as previously projected. In conclusion, we demonstrate a unique capability to extract differential conductivity as a function of phonon mean free path in materials, allowing the first (to our knowledge) experimental validation of predictions from the recently developed first-principles calculations.

  10. A new regime of nanoscale thermal transport: Collective diffusion increases dissipation efficiency

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

    Hoogeboom-Pot, Kathleen M.; Hernandez-Charpak, Jorge N.; Gu, Xiaokun; Frazer, Travis D.; Anderson, Erik H.; Chao, Weilun; Falcone, Roger W.; Yang, Ronggui; Murnane, Margaret M.; Kapteyn, Henry C.; et al

    2015-03-23

    Understanding thermal transport from nanoscale heat sources is important for a fundamental description of energy flow in materials, as well as for many technological applications including thermal management in nanoelectronics and optoelectronics, thermoelectric devices, nanoenhanced photovoltaics, and nanoparticle-mediated thermal therapies. Thermal transport at the nanoscale is fundamentally different from that at the macroscale and is determined by the distribution of carrier mean free paths and energy dispersion in a material, the length scales of the heat sources, and the distance over which heat is transported. Past work has shown that Fourier’s law for heat conduction dramatically overpredicts the rate ofmore » heat dissipation from heat sources with dimensions smaller than the mean free path of the dominant heat-carrying phonons. In this work, we uncover a new regime of nanoscale thermal transport that dominates when the separation between nanoscale heat sources is small compared with the dominant phonon mean free paths. Surprisingly, the interaction of phonons originating from neighboring heat sources enables more efficient diffusive-like heat dissipation, even from nanoscale heat sources much smaller than the dominant phonon mean free paths. This finding suggests that thermal management in nanoscale systems including integrated circuits might not be as challenging as previously projected. In conclusion, we demonstrate a unique capability to extract differential conductivity as a function of phonon mean free path in materials, allowing the first (to our knowledge) experimental validation of predictions from the recently developed first-principles calculations.« less

  11. Dynamics of Excitons and Phonons in Disordered Nanoscale Materials |

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

    MIT-Harvard Center for Excitonics Excitons and Phonons in Disordered Nanoscale Materials December 15, 2009 at 3pm/36-428 Sergei Tretiak Los Alamos National Laboratory trekiak.003 abstract: Prediction of the optical response and photoinduced processes of molecular and nanomaterials is fundamental to a myriad of technological applications, ranging from sensing, imaging, solar energy harvesting, to future optoelectronic devices. In this talk I will overview several applications of emerging

  12. Basal-plane thermal conductivity of few-layer molybdenum disulfide

    SciTech Connect (OSTI)

    Jo, Insun; Ou, Eric; Shi, Li; Pettes, Michael Thompson; Wu, Wei

    2014-05-19

    We report the in-plane thermal conductivity of suspended exfoliated few-layer molybdenum disulfide (MoS{sub 2}) samples that were measured by suspended micro-devices with integrated resistance thermometers. The obtained room-temperature thermal conductivity values are (4450) and (4852) W m{sup ?1} K{sup ?1} for two samples that are 4 and 7 layers thick, respectively. For both samples, the peak thermal conductivity occurs at a temperature close to 120?K, above which the thermal conductivity is dominated by intrinsic phonon-phonon scattering although phonon scattering by surface disorders can still play an important role in these samples especially at low temperatures.

  13. Structural and phonon transmission study of Ge-Au-Ge eutectically bonded interfaces

    SciTech Connect (OSTI)

    Knowlton, W.B. |

    1995-07-01

    This thesis presents a structural analysis and phonon transparency investigation of the Ge-Au-Ge eutectic bond interface. Interface development was intended to maximize the interfacial ballistic phonon transparency to enhance the detection of the dark matter candidate WIMPs. The process which was developed provides an interface which produces minimal stress, low amounts of impurities, and insures Ge lattice continuity through the interface. For initial Au thicknesses of greater than 1,000 {angstrom} Au per substrate side, eutectic epitaxial growth resulted in a Au dendritic structure with 95% cross sectional and 90% planar Au interfacial area coverages. In sections in which Ge bridged the interface, lattice continuity across the interface was apparent. Epitaxial solidification of the eutectic interface with initial Au thicknesses < 500 A per substrate side produced Au agglomerations thereby reducing the Au planar interfacial area coverage to as little as 30%. The mechanism for Au coalescence was attributed to lateral diffusion of Ge and Au in the liquid phase during solidification. Phonon transmission studies were performed on eutectic interfaces with initial Au thicknesses of 1,000 {angstrom}, 500 {angstrom}, and 300 {angstrom} per substrate side. Phonon imaging of eutectically bonded samples with initial Au thicknesses of 300 {angstrom}/side revealed reproducible interfacial percent phonon transmissions from 60% to 70%. Line scan phonon imaging verified the results. Phonon propagation TOF spectra distinctly showed the predominant phonon propagation mode was ballistic. This was substantiated by phonon focusing effects apparent in the phonon imaging data. The degree of interface transparency to phonons and resulting phonon propagation modes correlate with the structure of the interface following eutectic solidification. Structural studies of samples with initial Au thickness of 1,000 {angstrom}/side appear to correspond with the phonon transmission study.

  14. Spin-phonon coupling in scandium doped gallium ferrite

    SciTech Connect (OSTI)

    Chakraborty, Keka R. E-mail: smyusuf@barc.gov.in; Mukadam, M. D.; Basu, S.; Yusuf, S. M. E-mail: smyusuf@barc.gov.in; Paul, Barnita; Roy, Anushree; Grover, Vinita; Tyagi, A. K.

    2015-03-28

    We embarked on a study of Scandium (Sc) doped (onto Ga site) gallium ferrite (GaFeO{sub 3}) and found remarkable magnetic properties. In both doped as well as parent compounds, there were three types of Fe{sup 3+} ions (depending on the symmetry) with the structure conforming to space group Pna2{sub 1} (Sp. Grp. No. 33) below room temperature down to 5?K. We also found that all Fe{sup 3+} ions occupy octahedral sites, and carry high spin moment. For the higher Sc substituted sample (Ga{sub 1?x}Sc{sub x}FeO{sub 3}: x?=?0.3), a canted magnetic ordered state is found. Spin-phonon coupling below Nel temperature was observed in doped compounds. Our results indicated that Sc doping in octahedral site modifies spin-phonon interactions of the parent compound. The spin-phonon coupling strength was estimated for the first time in these Sc substituted compounds.

  15. Battle against Phonons (A "Life at the Frontiers of Energy Research" contest entry from the 2011 Energy Frontier Research Centers (EFRCs) Summit and Forum

    SciTech Connect (OSTI)

    Chen, Gang; S3TEC Staff

    2011-05-01

    'Battle against Phonons' was submitted by the Solid-State Solar-Thermal Energy Conversion (S3TEC) 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. This video was selected as one of five winners by a distinguished panel of judges for the special award, 'Best with Popcorn'. S3TEC, an EFRC directed by Gang Chen at the Massachusetts Institute of Technology is a partnership of scientists from four research institutions: MIT (lead), Oak Ridge National Laboratory, Boston College, and Rensselaer Polytechnic Institute. 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. The mission of the Solid-State Solar Thermal Energy Conversion Center is 'to create novel, solid-state materials for the conversion of sunlight into electricity using thermal and photovoltaic processes.' Research topics are: solar photovoltaic, photonic, metamaterial, optics, solar thermal, thermoelectric, phonons, thermal conductivity, defects, ultrafast physics, interfacial characterization, matter by design, novel materials synthesis, charge transport, defect tolerant materials, and scalable processing.

  16. Battle against Phonons (A "Life at the Frontiers of Energy Research" contest entry from the 2011 Energy Frontier Research Centers (EFRCs) Summit and Forum

    ScienceCinema (OSTI)

    Chen, Gang (Director, Solid-State Solar-Thermal Energy Conversion Center); S3TEC Staff

    2011-11-02

    'Battle against Phonons' was submitted by the Solid-State Solar-Thermal Energy Conversion (S3TEC) 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. This video was selected as one of five winners by a distinguished panel of judges for the special award, 'Best with Popcorn'. S3TEC, an EFRC directed by Gang Chen at the Massachusetts Institute of Technology is a partnership of scientists from four research institutions: MIT (lead), Oak Ridge National Laboratory, Boston College, and Rensselaer Polytechnic Institute. 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. The mission of the Solid-State Solar Thermal Energy Conversion Center is 'to create novel, solid-state materials for the conversion of sunlight into electricity using thermal and photovoltaic processes.' Research topics are: solar photovoltaic, photonic, metamaterial, optics, solar thermal, thermoelectric, phonons, thermal conductivity, defects, ultrafast physics, interfacial characterization, matter by design, novel materials synthesis, charge transport, defect tolerant materials, and scalable processing.

  17. Multi-phonon-assisted absorption and emission in semiconductors and its potential for laser refrigeration

    SciTech Connect (OSTI)

    Khurgin, Jacob B.

    2014-06-02

    Laser cooling of semiconductors has been an elusive goal for many years, and while attempts to cool the narrow gap semiconductors such as GaAs are yet to succeed, recently, net cooling has been attained in a wider gap CdS. This raises the question of whether wider gap semiconductors with higher phonon energies and stronger electron-phonon coupling are better suitable for laser cooling. In this work, we develop a straightforward theory of phonon-assisted absorption and photoluminescence of semiconductors that involves more than one phonon and use to examine wide gap materials, such as GaN and CdS and compare them with GaAs. The results indicate that while strong electron-phonon coupling in both GaN and CdS definitely improves the prospects of laser cooling, large phonon energy in GaN may be a limitation, which makes CdS a better prospect for laser cooling.

  18. Phonon-deficit effect in superconductors in a strong microwave field

    SciTech Connect (OSTI)

    Gulyan, A.M.; Zharkov, G.F.

    1981-08-20

    The phonon flux from a thin superconducting film irradiated by a microwave field is derived. It is shown that in intense microwave fields, as in the case of weak fields, studied previously )A. M. Gulian (Gulyan) and G. F. Zharkov, Phys. Lett. 80A, 79 (1980); Zh. Eksp. Teor. Fiz. 80, 303 (1981) (Sov. Phys. JETP 53, 154 (1981))), phonons are not emitted in a narrow spectral interval of phonon frequencies and are instead absorbed from the heat reservoir by the film.

  19. Direct evaluation of ballistic phonon transport in a multi-walled...

    Office of Scientific and Technical Information (OSTI)

    of Publication: United States Language: English Subject: 77 NANOSCIENCE AND NANOTECHNOLOGY; CARBON NANOTUBES; ION BEAMS; IRRADIATION; PHONONS Word Cloud More Like This Full...

  20. Electron-phonon coupling in a system with broken symmetry: Surface...

    Office of Scientific and Technical Information (OSTI)

    Electron-phonon coupling in a system with broken symmetry: Surface of Be ( 0001 ) Citation ... Country of Publication: United States Language: English Word Cloud More Like This Free ...

  1. Aspects of Electron-Phonon Self-Energy Revealed From Angle-Resolved...

    Office of Scientific and Technical Information (OSTI)

    Subject: 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; PHOTOEMISSION; SELF-ENERGY; EMISSION SPECTROSCOPY; ELECTRONS; PHONONS Other,OTHER Word Cloud More Like This Full Text ...

  2. Plasmon losses due to electron-phonon scattering: The case of...

    Office of Scientific and Technical Information (OSTI)

    Plasmon losses due to electron-phonon scattering: The case of graphene encapsulated in hexagonal boron nitride Citation Details In-Document Search Title: Plasmon losses due to ...

  3. Heavy ion Coulomb excitation and gamma decay studies of the one and two phonon giant dipole resonances in {sup 208}Pb and {sup 209}Bi

    SciTech Connect (OSTI)

    Mueller, P.E.; Beene, J.R.; Bertrand, F.E.

    1993-12-01

    Projectile -- photon coincidences were measured for the scattering of an 80 MeV/nucleon {sup 64}Zn beam from {sup 208}Pb and {sup 209}Bi targets at the GANIL heavy ion accelerator facility. Projectile-like particles between 0.5{degrees} and 4.5{degrees} relative to the incident beam direction were detected in the SPEG energy loss spectrometer where their momentum, charge, and mass were determined. Photons were detected in the BaF{sub 2} scintillation detector array TAPS. Light charged particles produced in the reaction were detected in the KVI Forward Wall. The analysis of the data acquired in this experiment is focused on three different phenomena: (1) the two phonon giant dipole resonance, (2) time dependence of the decay of the one phonon giant dipole resonance, and (3) giant resonance strength in projectile nuclei.

  4. Thermometry and thermal management of carbon nanotube circuits

    SciTech Connect (OSTI)

    Mayle, Scott; Gupta, Tanuj; Davis, Sam; Chandrasekhar, Venkat; Shafraniuk, Serhii

    2015-05-21

    Monitoring of the intrinsic temperature and the thermal management is discussed for the carbon nanotube nano-circuits. The experimental results concerning fabricating and testing of a thermometer able to monitor the intrinsic temperature on nanoscale are reported. We also suggest a model which describes a bi-metal multilayer system able to filter the heat flow, based on separating the electron and phonon components one from another. The bi-metal multilayer structure minimizes the phonon component of the heat flow, while retaining the electronic part. The method allows one to improve the overall performance of the electronic nano-circuits due to minimizing the energy dissipation.

  5. Preface to special topic: Selected articles from phononics 2013: The second international conference on phononic crystals/metamaterials, phonon transport and optomechanics, 2-7 June 2013, Sharm El-Sheikh, Egypt

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

    Hussein, Mahmoud I.; El-Kady, Ihab; Li, Baowen; Sánchez-Dehesa, José

    2014-12-31

    “Phononics” is an interdisciplinary branch of physics and engineering that deals with the behavior of phonons, and more broadly elastic and acoustic waves in similar context, and their manipulation in solids and/or fluids to benefit technological applications. Compared to resembling disciplines, such as electronics and photonics, phononics is a youthful field. It is growing at a remarkable rate, especially when viewed liberally with no limiting constraints on any particular length scale, discipline or application.

  6. Direct Conversion of Light into Work - Energy Innovation Portal

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

    concentrated sunlight or laser light focused on a highly absorptive material capable of converting light energy into heat generates thermal surface tension gradients that move ...

  7. Thermal conductivity of III-V semiconductor superlattices

    SciTech Connect (OSTI)

    Mei, S. Knezevic, I.

    2015-11-07

    This paper presents a semiclassical model for the anisotropic thermal transport in III-V semiconductor superlattices (SLs). An effective interface rms roughness is the only adjustable parameter. Thermal transport inside a layer is described by the Boltzmann transport equation in the relaxation time approximation and is affected by the relevant scattering mechanisms (three-phonon, mass-difference, and dopant and electron scattering of phonons), as well as by diffuse scattering from the interfaces captured via an effective interface scattering rate. The in-plane thermal conductivity is obtained from the layer conductivities connected in parallel. The cross-plane thermal conductivity is calculated from the layer thermal conductivities in series with one another and with thermal boundary resistances (TBRs) associated with each interface; the TBRs dominate cross-plane transport. The TBR of each interface is calculated from the transmission coefficient obtained by interpolating between the acoustic mismatch model (AMM) and the diffuse mismatch model (DMM), where the weight of the AMM transmission coefficient is the same wavelength-dependent specularity parameter related to the effective interface rms roughness that is commonly used to describe diffuse interface scattering. The model is applied to multiple III-arsenide superlattices, and the results are in very good agreement with experimental findings. The method is both simple and accurate, easy to implement, and applicable to complicated SL systems, such as the active regions of quantum cascade lasers. It is also valid for other SL material systems with high-quality interfaces and predominantly incoherent phonon transport.

  8. Cross-plane thermal properties of transition metal dichalcogenides

    SciTech Connect (OSTI)

    Muratore, C.; Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433 ; Varshney, V.; Universal Technology Corporation, Dayton, Ohio 45432 ; Gengler, J. J.; Spectral Energies LLC, Dayton, Ohio 45431 ; Hu, J. J.; Bultman, J. E.; University of Dayton Research Institute, Dayton, Ohio 45469 ; Smith, T. M.; Shamberger, P. J.; Roy, A. K.; Voevodin, A. A.; Qiu, B.; Ruan, X.

    2013-02-25

    In this work, we explore the thermal properties of hexagonal transition metal dichalcogenide compounds with different average atomic masses but equivalent microstructures. Thermal conductivity values of sputtered thin films were compared to bulk crystals. The comparison revealed a >10 fold reduction in thin film thermal conductivity. Structural analysis of the films revealed a turbostratic structure with domain sizes on the order of 5-10 nm. Estimates of phonon scattering lengths at domain boundaries based on computationally derived group velocities were consistent with the observed film microstructure, and accounted for the reduction in thermal conductivity compared to values for bulk crystals.

  9. Voltage tunability of thermal conductivity in ferroelectric materials

    DOE Patents [OSTI]

    Ihlefeld, Jon; Hopkins, Patrick Edward

    2016-02-09

    A method to control thermal energy transport uses mobile coherent interfaces in nanoscale ferroelectric films to scatter phonons. The thermal conductivity can be actively tuned, simply by applying an electrical potential across the ferroelectric material and thereby altering the density of these coherent boundaries to directly impact thermal transport at room temperature and above. The invention eliminates the necessity of using moving components or poor efficiency methods to control heat transfer, enabling a means of thermal energy control at the micro- and nano-scales.

  10. The change of microstructure and thermal properties in ion irradiated carbon nanotube mats as a function of ion penetration depth

    SciTech Connect (OSTI)

    Aitkaliyeva, A. [Materials Science and Engineering Program, Texas A and M University, College Station, Texas 77843 (United States)] [Materials Science and Engineering Program, Texas A and M University, College Station, Texas 77843 (United States); Shao, L. [Materials Science and Engineering Program, Texas A and M University, College Station, Texas 77843 (United States) [Materials Science and Engineering Program, Texas A and M University, College Station, Texas 77843 (United States); Department of Nuclear Engineering, Texas A and M University, College Station, Texas 77843 (United States)

    2013-02-11

    A stack of three carbon nanotube (CNT) mats was irradiated with 3 MeV He ions. The change in structural and thermal properties of individual mats as a function of ion penetration depth was characterized using electron microscopy and laser flash techniques. Ion irradiation can enhance thermal conductivity of the mats by introducing inter-tube displacements, which improve phonon transport across adjacent nanotubes. The enhancement, however, is reduced at higher damage levels due to the increasing phonon-defect scattering within the tubes. This study demonstrates the feasibility of using ion irradiation to manipulate thermal transport in carbon nanotubes.

  11. Elastic scattering by hot electrons and apparent lifetime of longitudinal optical phonons in gallium nitride

    SciTech Connect (OSTI)

    Khurgin, Jacob B.; Bajaj, Sanyam; Rajan, Siddharth

    2015-12-28

    Longitudinal optical (LO) phonons in GaN generated in the channel of high electron mobility transistors (HEMT) are shown to undergo nearly elastic scattering via collisions with hot electrons. The net result of these collisions is the diffusion of LO phonons in the Brillouin zone causing reduction of phonon and electron temperatures. This previously unexplored diffusion mechanism explicates how an increase in electron density causes reduction of the apparent lifetime of LO phonons, obtained from the time resolved Raman studies and microwave noise measurements, while the actual decay rate of the LO phonons remains unaffected by the carrier density. Therefore, the saturation velocity in GaN HEMT steadily declines with increased carrier density, in a qualitative agreement with experimental results.

  12. Solid state lighting component

    DOE Patents [OSTI]

    Yuan, Thomas; Keller, Bernd; Ibbetson, James; Tarsa, Eric; Negley, Gerald

    2010-10-26

    An LED component comprising an array of LED chips mounted on a planar surface of a submount with the LED chips capable of emitting light in response to an electrical signal. The LED chips comprise respective groups emitting at different colors of light, with each of the groups interconnected in a series circuit. A lens is included over the LED chips. Other embodiments can comprise thermal spreading structures included integral to the submount and arranged to dissipate heat from the LED chips.

  13. Solid state lighting component

    DOE Patents [OSTI]

    Keller, Bernd; Ibbetson, James; Tarsa, Eric; Negley, Gerald; Yuan, Thomas

    2012-07-10

    An LED component comprising an array of LED chips mounted on a planar surface of a submount with the LED chips capable of emitting light in response to an electrical signal. The LED chips comprise respective groups emitting at different colors of light, with each of the groups interconnected in a series circuit. A lens is included over the LED chips. Other embodiments can comprise thermal spreading structures included integral to the submount and arranged to dissipate heat from the LED chips.

  14. Search for: All records | SciTech Connect

    Office of Scientific and Technical Information (OSTI)

    Text1 Citations11 Multimedia0 Datasets0 Filter Results Filter by Subject solar (photovoltaic), solar (thermal), solid state lighting, phonons, thermal conductivity,...

  15. Catalytic thermal barrier coatings

    DOE Patents [OSTI]

    Kulkarni, Anand A.; Campbell, Christian X.; Subramanian, Ramesh

    2009-06-02

    A catalyst element (30) for high temperature applications such as a gas turbine engine. The catalyst element includes a metal substrate such as a tube (32) having a layer of ceramic thermal barrier coating material (34) disposed on the substrate for thermally insulating the metal substrate from a high temperature fuel/air mixture. The ceramic thermal barrier coating material is formed of a crystal structure populated with base elements but with selected sites of the crystal structure being populated by substitute ions selected to allow the ceramic thermal barrier coating material to catalytically react the fuel-air mixture at a higher rate than would the base compound without the ionic substitutions. Precious metal crystallites may be disposed within the crystal structure to allow the ceramic thermal barrier coating material to catalytically react the fuel-air mixture at a lower light-off temperature than would the ceramic thermal barrier coating material without the precious metal crystallites.

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

    SciTech Connect (OSTI)

    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.

  17. Visible light plasmonic heating of Au-ZnO for the catalytic reduction of CO2

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

    Wang, Congjun; Ranasingha, Oshadha; Natesakhawat, Sittichai; Ohodnicki, Paul R.; Andio, Mark; Lewis, James P.; Matranga, Christopher

    2013-01-01

    Plasmonic excitation of Au nanoparticles attached to the surface of ZnO catalysts using low power 532 nm laser illumination leads to significant heating of the catalyst and the conversion of CO2 and H2 reactants to CH4 and CO products. Temperature-calibrated Raman spectra of ZnO phonons show that intensity-dependent plasmonic excitation can controllably heat Au–ZnO from 30 to ~600 °C and simultaneously tune the CH4 : CO product ratio. The laser induced heating and resulting CH4 : CO product distribution agrees well with predictions from thermodynamic models and temperature-programmed reaction experiments indicating that the reaction is a thermally driven process resultingmore » from the plasmonic heating of the Au-ZnO. The apparent quantum yield for CO2 conversion under continuous wave (cw) 532 nm laser illumination is 0.030%. The Au-ZnO catalysts are robust and remain active after repeated laser exposure and cycling. The light intensity required to initiate CO2 reduction is low ( ~2.5 x 105 W m-2) and achievable with solar concentrators. Our results illustrate the viability of plasmonic heating approaches for CO2 utilization and other practical thermal catalytic applications.« less

  18. Lighting system with heat distribution face plate

    DOE Patents [OSTI]

    Arik, Mehmet; Weaver, Stanton Earl; Stecher, Thomas Elliot; Kuenzler, Glenn Howard; Wolfe, Jr., Charles Franklin; Li, Ri

    2013-09-10

    Lighting systems having a light source and a thermal management system are provided. The thermal management system includes synthetic jet devices, a heat sink and a heat distribution face plate. The synthetic jet devices are arranged in parallel to one and other and are configured to actively cool the lighting system. The heat distribution face plate is configured to radially transfer heat from the light source into the ambient air.

  19. Thermal trim for a luminaire

    DOE Patents [OSTI]

    Bazydola, Sarah; Ghiu, Camil-Daniel; Harrison, Robert; Jeswani, Anil

    2013-02-19

    A luminaire with a thermal pathway to reduce the junction temperature of the luminaire's light source, and methods for so doing, are disclosed. The luminaire includes a can, a light engine, and a trim, that define a substantially continuous thermal pathway from the light engine to a surrounding environment. The can defines a can cavity and includes a can end region. The light engine is within the can cavity and includes a light source and a heat sink, including a heat sink end region, coupled thereto. The trim is at least partially disposed within the can cavity and includes a first trim end region coupled to the heat sink end region and a second trim end region coupled to the can end region. Thermal interface material may be located between: the heat sink and the trim, the trim and the can, and/or the heat sink and the light source.

  20. Nanoscale size dependence parameters on lattice thermal conductivity of Wurtzite GaN nanowires

    SciTech Connect (OSTI)

    Mamand, S.M.; Omar, M.S.; Muhammad, A.J.

    2012-05-15

    Graphical abstract: Temperature dependence of calculated lattice thermal conductivity of Wurtzite GaN nanowires. Highlights: Black-Right-Pointing-Pointer A modified Callaway model is used to calculate lattice thermal conductivity of Wurtzite GaN nanowires. Black-Right-Pointing-Pointer A direct method is used to calculate phonon group velocity for these nanowires. Black-Right-Pointing-Pointer 3-Gruneisen parameter, surface roughness, and dislocations are successfully investigated. Black-Right-Pointing-Pointer Dislocation densities are decreases with the decrease of wires diameter. -- Abstract: A detailed calculation of lattice thermal conductivity of freestanding Wurtzite GaN nanowires with diameter ranging from 97 to 160 nm in the temperature range 2-300 K, was performed using a modified Callaway model. Both longitudinal and transverse modes are taken into account explicitly in the model. A method is used to calculate the Debye and phonon group velocities for different nanowire diameters from their related melting points. Effect of Gruneisen parameter, surface roughness, and dislocations as structure dependent parameters are successfully used to correlate the calculated values of lattice thermal conductivity to that of the experimentally measured curves. It was observed that Gruneisen parameter will decrease with decreasing nanowire diameters. Scattering of phonons is assumed to be by nanowire boundaries, imperfections, dislocations, electrons, and other phonons via both normal and Umklapp processes. Phonon confinement and size effects as well as the role of dislocation in limiting thermal conductivity are investigated. At high temperatures and for dislocation densities greater than 10{sup 14} m{sup -2} the lattice thermal conductivity would be limited by dislocation density, but for dislocation densities less than 10{sup 14} m{sup -2}, lattice thermal conductivity would be independent of that.

  1. Phonon-magnon interactions in body centered cubic iron: A combined molecular and spin dynamics study

    SciTech Connect (OSTI)

    Perera, Dilina Landau, David P.; Nicholson, Don M.; Malcolm Stocks, G.; Eisenbach, Markus; Yin, Junqi; Brown, Gregory

    2014-05-07

    Combining an atomistic many-body potential with a classical spin Hamiltonian parameterized by first principles calculations, molecular-spin dynamics computer simulations were performed to investigate phonon-magnon interactions in body centered cubic iron. Results obtained for spin-spin and density-density dynamic structure factors show that noticeable softening and damping of magnon modes occur due to the presence of lattice vibrations. Furthermore, as a result of the phonon-magnon coupling, additional longitudinal spin wave excitations are observed, with the same frequencies as the longitudinal phonon modes.

  2. Phonon densities of states of face-centered-cubic Ni-Fe alloys

    SciTech Connect (OSTI)

    Lucas, Matthew; Mauger, L; Munoz, Jorge A.; Halevy, I; Horwath, J; Semiatin, S L; Leontsev, S. O.; Stone, Matthew B; Abernathy, Douglas L; Xiao, Yuming; Chow, P; Fultz, B.

    2013-01-01

    Inelastic neutron scattering and nuclear resonant inelastic x-ray scattering were used to determine the phonon densities of states of face-centered-cubic Ni-Fe alloys. Increasing Fe concentration results in an average softening of the phonon modes. Chemical ordering of the Ni0.72Fe0.28 alloy results in a reduction of the partial vibrational entropy of the Fe atoms but does not significantly change the partial vibrational entropy of the Ni atoms. Changes in the phonon densities of states with composition and chemical ordering are discussed and analyzed with a cluster expansion method.

  3. Commercial Lighting

    Broader source: Energy.gov [DOE]

    Commercial lighting accounts for more than 20 percent of total commercial building energy use. The Energy Department works to reduce lighting energy use through research and deployment.

  4. NREL: Transportation Research - Vehicle Thermal Management Facilities

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

    a test pad to conduct vehicle thermal soak testing and stationary heating, ventilation, and air conditioning (HVAC) load testing on light-, medium-, and heavy-duty vehicles. ...

  5. The manifestation of spin-phonon coupling in CaMnO{sub 3}

    SciTech Connect (OSTI)

    Goian, V. Kamba, S.; Borodavka, F.; Nuzhnyy, D.; Savinov, M.; Belik, A. A.

    2015-04-28

    Recently predicted presence of spin-phonon coupling in the CaMnO{sub 3} is experimentally confirmed in infrared (IR), Raman and time-domain THz spectra. Most of phonon frequencies seen below 350?cm{sup ?1} exhibit significant shifts on cooling below antiferromagnetic phase transition at T{sub N}???120?K. Moreover, several new modes activate in the IR and Raman spectra on cooling below T{sub N}. Sum of phonon contributions to static permittivity exhibits small but reliable anomaly at T{sub N}. On the other hand, the spin-phonon coupling is not manifested in temperature dependence of radio-frequency permittivity, because intrinsic permittivity is screened by extrinsic contribution from conductivity, which enhances the permittivity to giant values.

  6. Phonon anharmonicity in silicon from 100 to 1500 K (Journal Article...

    Office of Scientific and Technical Information (OSTI)

    Citation Details In-Document Search Title: Phonon anharmonicity in silicon from 100 to 1500 K Authors: Kim, D. S. 1 ; Smith, Hillary 1 ; Niedziela, Jennifer L 2 ; Li, Chen ...

  7. Wave-vector-dependent electron-phonon coupling and the charge...

    Office of Scientific and Technical Information (OSTI)

    Wave-vector-dependent electron-phonon coupling and the charge-density-wave transition in ... Sponsoring Org: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22) Country ...

  8. Phonon anomalies and superconductivity in the Heusler compound YPd?Sn

    SciTech Connect (OSTI)

    Ttnc, H. M. [Sakarya niversitesi, Fen-Edebiyat Fakltesi, Fizik Blm, 54187, Adapazar? (Turkey); Srivastava, G. P. [School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom)

    2014-07-07

    We have studied the structural and electronic properties of YPd?Sn in the Heusler structure using a generalized gradient approximation of the density functional theory and the ab initio pseudopotential method. The electronic results indicate that the density of states at the Fermi level is primarily derived from Pd d states, which hybridize with Y d and Sn p states. Using our structural and electronic results, phonons and electron-phonon interactions have been studied by employing a linear response approach based on the density functional theory. Phonon anomalies have been observed for transverse acoustic branches along the [110] direction. This anomalous dispersion is merely a consequence of the strong coupling. By integrating the Eliashberg spectral function, the average electron-phonon coupling parameter is found to be ?=0.99. Using this value, the superconducting critical temperature is calculated to be 4.12 K, in good accordance with the recent experimental value of 4.7 K.

  9. Phonon spectroscopy with sub-meV resolution by femtosecond x...

    Office of Scientific and Technical Information (OSTI)

    Phonon spectroscopy with sub-meV resolution by femtosecond x-ray diffuse scattering Citation Details In-Document Search This content will become publicly available on August 9,...

  10. Giant two-phonon Raman scattering from nanoscale NbC precipitates...

    Office of Scientific and Technical Information (OSTI)

    Giant two-phonon Raman scattering from nanoscale NbC precipitates in Nb Not Available Temp HTML Storage 2: Cao, C.; Tao, R.; Ford, D. C.; Klie, R. F.; Proslier, T.; Cooley, L. D.; ...

  11. Giant phonon anomaly associated with superconducting fluctuations in the pseudogap phase of cuprates

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

    Liu, Ye-Hua; Konik, Robert M.; Rice, T. M.; Zhang, Fu-Chun

    2016-01-20

    The pseudogap in underdoped cuprates leads to significant changes in the electronic structure, and was later found to be accompanied by anomalous fluctuations of superconductivity and certain lattice phonons. Here we propose that the Fermi surface breakup due to the pseudogap, leads to a breakup of the pairing order into two weakly coupled sub-band amplitudes, and a concomitant low energy Leggett mode due to phase fluctuations between them. This increases the temperature range of superconducting fluctuations containing an overdamped Leggett mode. In this range inter-sub-band phonons show strong damping due to resonant scattering into an intermediate state with a pairmore » of overdamped Leggett modes. In the ordered state, the Leggett mode develops a finite energy, changing the anomalous phonon damping into an anomaly in the dispersion. Finally, this proposal explains the intrinsic connection between the anomalous pseudogap phase, enhanced superconducting fluctuations and giant anomalies in the phonon spectra.« less

  12. Parity conservation in electron-phonon scattering in zigzag graphene nanoribbon

    SciTech Connect (OSTI)

    Chu, Yanbiao; Gautreau, Pierre; Basaran, Cemal

    2014-09-15

    In contrast with carbon nanotubes, the absence of translational symmetry (or periodical boundary condition) in the restricted direction of zigzag graphene nanoribbon removes the selection rule of subband number conservation. However, zigzag graphene nanoribbons with even dimers do have the inversion symmetry. We, therefore, propose a selection rule of parity conservation for electron-phonon interactions. The electron-phonon scattering matrix in zigzag graphene nanoribbons is developed using the tight-binging model within the deformation potential approximation.

  13. Lattice thermal conductivity of filled skutterudites: An anharmonicity perspective

    SciTech Connect (OSTI)

    Geng, Huiyuan, E-mail: genghuiyuan@hit.edu.cn; Meng, Xianfu; Zhang, Hao; Zhang, Jian [State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001 (China)

    2014-10-28

    We report a phenomenological model to calculate the high-temperature lattice thermal conductivity of filled skutterudite antimonides. The model needs no phonon resonant scattering terms. Instead, we assume that umklapp processes dominate the high-temperature phonon scattering. In order to represent the anharmonicity introduced by the filling atom, we introduce a Gaussian term into the relaxation time of the umklapp process. The developed model agrees remarkably well with the experimental results of RE{sub f}Co{sub 4}Sb{sub 12} and RE{sub f}Fe{sub 4}Sb{sub 12} (RE?=?Yb, Ba, and Ca) alloys. To further test the validity of our model, we calculate the lattice thermal conductivity of nanostructured or multi-filled skutterudites. The calculation results are also in good agreement with experiment, increasing our confidence in the developed anharmonicity model.

  14. Progress from DOE EF RC: Solid-State Solar-Thermal Energy Conversion Center

    Broader source: Energy.gov (indexed) [DOE]

    (S3TEC ) | Department of Energy Introduction to the solid-state solar-thermal energy conversion center plus discussion on phonon transport and solar thermoelectric energy conversion chen.pdf (2.01 MB) More Documents & Publications Solar Thermoelectric Energy Conversion Solar Thermoelectric Energy Conversion DOE Office of Basic Sciences: An Overview of Basic Research Activities on Thermoelectrics

  15. Quasi-two-dimensional spin and phonon excitations in La1.965Ba0.035CuO4

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

    Wagman, J. J.; Parshall, D.; Stone, Matthew B.; Savici, Andrei T.; Zhao, Yang; Dabkowska, H. A.; Gaulin, B. D.

    2015-06-03

    Here, we present time-of-fight inelastic neutron scattering measurements of La1.965Ba0.035CuO4 (LBCO), a lightly doped member of the high temperature superconducting La-based cuprate family. By using time-of-flight neutron instrumentation coupled with single crystal sample rotation we obtain a four-dimensional data set (three Q and one energy) that is both comprehensive and spans a large region of reciprocal space. Our measurements identify rich structure in the energy dependence of the highly dispersive spin excitations, which are centered at equivalent (1/2, 1/2, L) wave-vectors. These structures correlate strongly with several crossings of the spin excitations with the lightly dispersive phonons found in thismore » system. These eects are signicant and account for on the order of 25% of the total inelastic scattering for energies between ≈5 and 40meV at low |Q|. Interestingly, this scattering also presents little or no L-dependence. As the phonons and dispersive spin excitations centred at equivalent (1/2, 1/2, L) wave-vectors are common to all members of La-based 214 copper oxides, we conclude such strong quasi-two dimensional scattering enhancements are likely to occur in all such 214 families of materials, including those concentrations corresponding to superconducting ground states. Such a phenomenon appears to be a fundamental characteristic of these materials and is potentially related to superconducting pairing.« less

  16. Quasi-two dimensional spin and phonon excitations in La1.965Ba0.035CuO4

    SciTech Connect (OSTI)

    Wagman, J.; Parshall, D.; Stone, Matthew B; Savici, Andrei T; Zhao, Yang; Dabkowska, H. A.; Gaulin, B. D.

    2015-01-01

    We present time-of-fight inelastic neutron scattering measurements of La1:965Ba0:035CuO4 (LBCO), a lightly doped member of the high temperature superconducting La-based cuprate family. By using time-of-flight neutron instrumentation coupled with single crystal sample rotation we obtain a four-dimensional data set (three Q and one energy) that is both comprehensive and spans a large region of reciprocal space. Our measurements identify rich structure in the energy dependence of the highly dispersive spin excitations, which are centered at equivalent ( 1/2 ; 1/2 ;L) wave-vectors. These structures correlate strongly with several crossings of the spin excitations with the lightly dispersive phonons found in this system. These eects are signicant and account for on the order of 25% of the total inelastic scattering for energies between 5 and 40meV at low jQj. Interestingly, this scattering also presents little or no L-dependence. As the phonons and dispersive spin excitations centred at equivalent ( 1/2 ; 1/2 ;L) wave-vectors are common to all members of La-based 214 copper oxides, we conclude such strong quasi-two dimensional scattering enhancements are likely to occur in all such 214 families of materials, including those concentrations corresponding to superconducting ground states. Such a phenomenon appears to be a fundamental characteristic of these materials and is potentially related to superconducting pairing.

  17. Heat meets light on the nanoscale

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

    Boriskina, Svetlana V.; Tong, Jonathan K.; Hsu, Wei -Chun; Liao, Bolin; Huang, Yi; Chiloyan, Vazrik; Chen, Gang

    2016-06-11

    We discuss the state-of-the-art and remaining challenges in the fundamental understanding and technology development for controlling light-matter interactions in nanophotonic environments in and away from thermal equilibrium. Furthermore, the topics covered range from the basics of the thermodynamics of light emission and absorption to applications in solar thermal energy generation, thermophotovoltaics, optical refrigeration, personalized cooling technologies, development of coherent incandescent light sources, and spinoptics.

  18. Visible light plasmonic heating of Au-ZnO for the catalytic reduction of CO{sub 2}

    SciTech Connect (OSTI)

    Wang, Congjun; Ranasingha, Oshadha; Natesakhawat, Sittichai; Ohodnicki, Paul R.; Ohodnicki, Andio, Mark; Lewis, James; P Matranga, Christopher

    2013-05-01

    Plasmonic excitation of Au nanoparticles attached to the surface of ZnO catalysts using low power 532 nm laser illumination leads to significant heating of the catalyst and the conversion of CO{sub 2} and H{sub 2} reactants to CH{sub 4} and CO products. Temperature-calibrated Raman spectra of ZnO phonons show that intensity-dependent plasmonic excitation can controllably heat AuZnO from 30 to #1;~600 {degrees}#3;C and simultaneously tune the CH{sub 4} : CO product ratio. The laser induced heating and resulting CH{sub 4} : CO product distribution agrees well with predictions from thermodynamic models and temperatureprogrammed reaction experiments indicating that the reaction is a thermally driven process resulting from the plasmonic heating of the AuZnO. The apparent quantum yield for CO{sub 2} conversion under continuous wave (cw) 532 nm laser illumination is 0.030%. The AuZnO catalysts are robust and remain active after repeated laser exposure and cycling. The light intensity required to initiate CO{sub 2} reduction is low (#1;~2.5 x#4; 10{sup 5} W m{sup #5;-2}) and achievable with solar concentrators. Our results illustrate the viability of plasmonic heating approaches for CO{sub 2} utilization and other practical thermal catalytic applications.

  19. The role of screening of the electron-phonon interaction in relaxation of photoexcited electron-hole plasma in semiconductors

    SciTech Connect (OSTI)

    Kumekov, S. E.

    2008-08-15

    The role of screening of the interaction of the electron-hole plasma with optical phonons is analytically evaluated by the example of gallium arsenide.

  20. Anisotropic in-plane thermal conductivity of black phosphorus nanoribbons at temperatures higher than 100 K

    SciTech Connect (OSTI)

    Lee, Sangwook; Yang, Fan; Suh, Joonki; Yang, Sijie; Lee, Yeonbae; Li, Guo; Sung Choe, Hwan; Suslu, Aslihan; Chen, Yabin; Ko, Changhyun; Park, Joonsuk; Liu, Kai; Li, Jingbo; Hippalgaonkar, Kedar; Urban, Jeffrey J.; Tongay, Sefaattin; Wu, Junqiao

    2015-10-16

    Black phosphorus attracts enormous attention as a promising layered material for electronic, optoelectronic and thermoelectric applications. Here we report large anisotropy in in-plane thermal conductivity of single-crystal black phosphorus nanoribbons along the zigzag and armchair lattice directions at variable temperatures. Thermal conductivity measurements were carried out under the condition of steady-state longitudinal heat flow using suspended-pad micro-devices. We discovered increasing thermal conductivity anisotropy, up to a factor of two, with temperatures above 100 K. A size effect in thermal conductivity was also observed in which thinner nanoribbons show lower thermal conductivity. Analysed with the relaxation time approximation model using phonon dispersions obtained based on density function perturbation theory, the high anisotropy is attributed mainly to direction-dependent phonon dispersion and partially to phonon–phonon scattering. Lastly, our results revealing the intrinsic, orientation-dependent thermal conductivity of black phosphorus are useful for designing devices, as well as understanding fundamental physical properties of layered materials.

  1. Formation of Bragg band gaps in anisotropic phononic crystals analyzed with the empty lattice model

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

    Wang, Yan -Feng; Maznev, Alexei; Laude, Vincent

    2016-05-11

    Bragg band gaps of phononic crystals generally, but not always, open at Brillouin zone boundaries. The commonly accepted explanation stems from the empty lattice model: assuming a small material contrast between the constituents of the unit cell, avoided crossings in the phononic band structure appear at frequencies and wavenumbers corresponding to band intersections; for scalar waves the lowest intersections coincide with boundaries of the first Brillouin zone. However, if a phononic crystal contains elastically anisotropic materials, its overall symmetry is not dictated solely by the lattice symmetry. We construct an empty lattice model for phononic crystals made of isotropic andmore » anisotropic materials, based on their slowness curves. We find that, in the anisotropic case, avoided crossings generally do not appear at the boundaries of traditionally defined Brillouin zones. Furthermore, the Bragg "planes" which give rise to phononic band gaps, are generally not flat planes but curved surfaces. Lastly, the same is found to be the case for avoided crossings between shear (transverse) and longitudinal bands in the isotropic case.« less

  2. Semiclassical multi-phonon theory for atom-surface scattering: Application to the Cu(111) system

    SciTech Connect (OSTI)

    Daon, Shauli; Pollak, Eli

    2015-05-07

    The semiclassical perturbation theory of Hubbard and Miller [J. Chem. Phys. 80, 5827 (1984)] is further developed to include the full multi-phonon transitions in atom-surface scattering. A practically applicable expression is developed for the angular scattering distribution by utilising a discretized bath of oscillators, instead of the continuum limit. At sufficiently low surface temperature good agreement is found between the present multi-phonon theory and the previous one-, and two-phonon theory derived in the continuum limit in our previous study [Daon, Pollak, and Miret-Arts, J. Chem. Phys. 137, 201103 (2012)]. The theory is applied to the measured angular distributions of Ne, Ar, and Kr scattered from a Cu(111) surface. We find that the present multi-phonon theory substantially improves the agreement between experiment and theory, especially at the higher surface temperatures. This provides evidence for the importance of multi-phonon transitions in determining the angular distribution as the surface temperature is increased.

  3. Phonon characteristics of high {Tc} superconductors from neutron Doppler broadening measurements

    SciTech Connect (OSTI)

    Trela, W.J.; Kwei, G.H.; Lynn, J.E.; Meggers, K.

    1994-12-01

    Statistical information on the phonon frequency spectrum of materials can be measured by neutron transmission techniques if they contain nuclei with low energy resonances, narrow enough to be Doppler-broadened, in their neutron cross sections. The authors have carried out some measurements using this technique for materials of the lanthanum barium cuprate class, La{sub 2{minus}x}Ba{sub x}CuO{sub 4}. Two samples with slightly different concentrations of oxygen, one being superconductive, the other not, were examined. Pure lanthanum cuprate was also measured. Lanthanum, barium and copper all have relatively low energy narrow resonances. Thus it should be possible to detect differences in the phonons carried by different kinds of atom in the lattice. Neutron cross section measurements have been made with high energy resolution and statistical precision on the 59m flight path of LANSCE, the pulsed spallation neutron source at Los Alamos National Laboratory. Measurements on all three materials were made over a range of temperatures from 15K to 300K, with small steps through the critical temperature region near 27K. No significant changes in the mean phonon energy of the lanthanum atoms were observed near the critical temperature of the super-conducting material. It appears however that the mean phonon energy of lanthanum in the superconductor is considerably higher than that in the non-superconductors. The samples used in this series of experiments were too thin in barium and copper to determine anything significant about their phonon spectra.

  4. Interaction of electrons with optical phonons localized in a quantum well

    SciTech Connect (OSTI)

    Pozela, J. Pozela, K.; Juciene, V.; Suziedelis, A.; Shkolnik, A. S.; Mikhrin, S. S.; Mikhrin, V. S.

    2009-12-15

    The scattering rate of electrons in a quantum well by localized polar optical and interface phonons is considered. The dependence of the force of the electron-phonon interaction on the frequency of optical phonons in materials of the heterostructure forming the electron and phonon quantum wells is determined. It is shown that, by varying the composition of semiconductors forming the quantum well and its barriers, it is possible to vary the scattering rates of electrons by a factor of several times. The scattering rates of electrons by polar optical phonons are calculated depending on the fractions In{sub x} and In{sub y} in the composition of semiconductors forming the In{sub x}Al{sub 1-x}As/In{sub y}Ga{sub 1-y}As quantum wells. Dependences of the mobility and saturated drift velocity of electrons in high electric fields and quantum wells In{sub y}Ga{sub 1-y}As on the composition of the In{sub x}Al{sub 1-x}As barriers introduced into quantum wells are determined experimentally. The electron mobility increases, while the saturated drift velocity decreases as the fraction of In{sub x} in the composition of barriers is increased.

  5. Improving the Efficiency of Light-Duty Vehicle HVAC Systems using...

    Broader source: Energy.gov (indexed) [DOE]

    More Documents & Publications Thermoelectric HVAC for Light-Duty Vehicle Applications Thermoelectric HVAC and Thermal Comfort Enablers for Light-Duty Vehicle Applications ...

  6. Tensile strains give rise to strong size effects for thermal conductivities of silicene, germanene and stanene

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

    Kuang, Youdi D.; Lindsay, Lucas R.; Shi, Sanqiang Q.; Zhen, Guangping P.

    2016-01-11

    Based on first principles calculations and self-consistent solution of linearized Boltzmann-Peierls equation for phonon transport approach within a three-phonon scattering framework, we characterize lattice thermal conductivities k of freestanding silicene, germanene and stanene under different isotropic tensile strains and temperatures. We find a strong size dependence of k for silicene with tensile strain, i.e., divergent k with increasing system size, in contrast, the intrinsic room temperature k for unstrained silicene converges with system size to 19.34 W/m–1 K–1 by 178 nm. The room temperature k of strained silicene becomes as large as that of bulk silicon by 84 m, indicatingmore » the possibility of using strain in silicene to manipulate k for thermal management. The relative contribution to the intrinsic k from out-of-plane acoustic modes is largest for unstrained silicene, –39% at room temperature. The single mode relaxation time approximation, which works reasonably well for bulk silicon, fails to appropriately describe phonon thermal transport in silicene, germanene and stanene within the temperature range considered. For large samples of silicene, k increases with tensile strain, peaks at –7% strain and then decreases with further strain. In germanene and stanene increasing strain hardens and stabilizes long wavelength out-of-plane acoustic phonons, and leads to similar k behaviors to those of silicene. As a result, these findings further our understanding of phonon dynamics in group-IV buckled monolayers and may guide transfer and fabrication techniques of these freestanding samples and engineering k by size and strain for applications of thermal management and thermoelectricity.« less

  7. Light Source

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

    a Light Source Data and Analysis Framework at NERSC Jack Deslippe, Shane Canon, Eli Dart, Abdelilah Essiari, Alexander Hexemer, Dula Parkinson, Simon Patton, Craig Tull + Many More The ALS Data Needs September 21, 2010 - NIST (MD) Light source data volumes are growing many times faster than Moore's law. ● Light source luminosity ● Detector resolution & rep-rates ● Sample automation BES user facilities serve 10,000 scientists and engineers every year. Mostly composed of many small

  8. Cerenkov Light

    ScienceCinema (OSTI)

    Slifer, Karl

    2014-05-22

    The bright blue glow from nuclear reactors is Cerenkov light. Karl Slifer describes how nuclear physicists can use this phenomenon to study the nucleus of the atom.

  9. Lighting Renovations

    Broader source: Energy.gov [DOE]

    When undertaking a lighting renovation in a Federal building, daylighting is the primary renewable energy opportunity. Photovoltaics (PV) also present an excellent opportunity. While this guide...

  10. Cerenkov Light

    SciTech Connect (OSTI)

    Slifer, Karl

    2013-06-13

    The bright blue glow from nuclear reactors is Cerenkov light. Karl Slifer describes how nuclear physicists can use this phenomenon to study the nucleus of the atom.

  11. Residential Lighting

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

    & Events Expand News & Events Skip navigation links Residential Residential Lighting Energy Star Appliances Consumer Electronics Heat Pump Water Heaters Electric Storage Water...

  12. Reasons for high-temperature superconductivity in the electron–phonon system of hydrogen sulfide

    SciTech Connect (OSTI)

    Degtyarenko, N. N.; Mazur, E. A.

    2015-08-15

    We have calculated the electron and phonon spectra, as well as the densities of the electron and phonon states, of the stable orthorhombic structure of hydrogen sulfide SH{sub 2} in the pressure interval 100–180 GPa. It is found that at a pressure of 175 GPa, a set of parallel planes of hydrogen atoms is formed due to a structural modification of the unit cell under pressure with complete accumulation of all hydrogen atoms in these planes. As a result, the electronic properties of the system become quasi-two-dimensional. We have also analyzed the collective synphase and antiphase vibrations of hydrogen atoms in these planes, leading to the occurrence of two high-energy peaks in the phonon density of states.

  13. Phonon and magnetic structure in δ-plutonium from density-functional theory

    SciTech Connect (OSTI)

    Söderlind, Per; Zhou, F.; Landa, A.; Klepeis, J. E.

    2015-10-30

    We present phonon properties of plutonium metal obtained from a combination of density-functional-theory (DFT) electronic structure and the recently developed compressive sensing lattice dynamics (CSLD). The CSLD model is here trained on DFT total energies of several hundreds of quasi-random atomic configurations for best possible accuracy of the phonon properties. The calculated phonon dispersions compare better with experiment than earlier results obtained from dynamical mean-field theory. The density-functional model of the electronic structure consists of disordered magnetic moments with all relativistic effects and explicit orbital-orbital correlations. The magnetic disorder is approximated in two ways: (i) a special quasi-random structure and (ii) the disordered-local-moment (DLM) method within the coherent potential approximation. Magnetism in plutonium has been debated intensely, However, the present magnetic approach for plutonium is validated by the close agreement between the predicted magnetic form factor and that of recent neutron-scattering experiments.

  14. Thermal Sciences

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

    Thermal Sciences NETL's Thermal Sciences competency provides the scientific, engineering, and technology development community with innovative and efficient approaches to measure, harness, and convert thermal energy. Research includes sensors, advanced energy concepts, and thermodynamic optimization, specifically: Sensors and Diagnostics Advanced sensor and diagnostic technology to develop and evaluate advanced methods for non-intrusive measurement and measurement in extreme environments.

  15. Molecular Solid EOS based on Quasi-Harmonic Oscillator approximation for phonons

    SciTech Connect (OSTI)

    Menikoff, Ralph

    2014-09-02

    A complete equation of state (EOS) for a molecular solid is derived utilizing a Helmholtz free energy. Assuming that the solid is nonconducting, phonon excitations dominate the specific heat. Phonons are approximated as independent quasi-harmonic oscillators with vibrational frequencies depending on the specific volume. The model is suitable for calibrating an EOS based on isothermal compression data and infrared/Raman spectroscopy data from high pressure measurements utilizing a diamond anvil cell. In contrast to a Mie-Gr ̈uneisen EOS developed for an atomic solid, the specific heat and Gr ̈uneisen coefficient depend on both density and temperature.

  16. Isotope effect on electron-phonon interaction in the multiband superconductor MgB2

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

    Mou, Daixiang; Manni, Soham; Taufour, Valentin; Wu, Yun; Huang, Lunan; Bud'ko, S. L.; Canfield, P. C.; Kaminski, Adam

    2016-04-07

    We investigate the effect of isotope substitution on the electron-phonon interaction in the multiband superconductor MgB2 using tunable laser-based angle-resolved photoemission spectroscopy. The kink structure around 70 meV in the σ band, which is caused by electron coupling to the E2g phonon mode, is shifted to higher binding energy by ~3.5 meV in Mg10B2 and the shift is not affected by superconducting transition. Furthermore, these results serve as the benchmark for investigations of isotope effects in known, unconventional superconductors and newly discovered superconductors where the origin of pairing is unknown.

  17. Interface nano-confined acoustic waves in polymeric surface phononic crystals

    SciTech Connect (OSTI)

    Travagliati, Marco; Nardi, Damiano; Giannetti, Claudio; Ferrini, Gabriele; Banfi, Francesco; Gusev, Vitalyi; Pingue, Pasqualantonio; Piazza, Vincenzo

    2015-01-12

    The impulsive acoustic dynamics of soft polymeric surface phononic crystals is investigated here in the hypersonic frequency range by near-IR time-resolved optical diffraction. The acoustic response is analysed by means of wavelet spectral methods and finite element modeling. An unprecedented class of acoustic modes propagating within the polymer surface phononic crystal and confined within 100 nm of the nano-patterned interface is revealed. The present finding opens the path to an alternative paradigm for characterizing the mechanical properties of soft polymers at interfaces and for sensing schemes exploiting polymers as embedding materials.

  18. Search for: All records | SciTech Connect

    Office of Scientific and Technical Information (OSTI)

    Everything8 Electronic Full Text0 Citations8 Multimedia0 Datasets0 Software0 Filter Results Filter by Subject solar (photovoltaic), solar (thermal), solid state lighting, phonons, ...

  19. Search for: All records | SciTech Connect

    Office of Scientific and Technical Information (OSTI)

    Everything2 Electronic Full Text0 Citations2 Multimedia0 Datasets0 Software0 Filter Results Filter by Subject solar (photovoltaic), solar (thermal), solid state lighting, phonons, ...

  20. Lighting Control Energy Savings

    Energy Science and Technology Software Center (OSTI)

    1985-01-01

    CONTROLITE 1.0 is a lighting energy analysis program designed to calculate the energy savings and cost benefits obtainable using lighting controls in buildings. The program can compute the lighting energy reductions that result from using daylighting, scheduling, and other control strategies. When modeling daylight control systems, the program uses QUICKLITE to compute the daylight illuminances at specified points 5 times a day, 12 days a year (the 21st of each month), and for two skymore » conditions (clear and overcast skies). Fourier series techniques are used to fit a continuous curve through the computed illuminance points. The energy use for each of the 12 days is then computed given user-specified power-in/light-out characteristics of the modeled control system. The monthly and annual energy usage for overcast and clear conditions are found separately by fitting two long-term Fourier series curves to the energy use computed for each of the 12 days. Finally, the monthly energy use is calculated by taking a weighted average for the monthly energy use computed for the overcast and clear sky conditions. The program only treats the energy use directly attributable to lighting. The impact of lighting control strategies on building thermal loads is not computed. The program allows input of different control schedules (i.e., on/off times for the lighting system) for each day of the week, but every week of the year is treated the same; thus, holidays cannot be modeled explicitly. When used for daylighting purposes, CONTROLITE1.0 understands only clear and overcast conditions. User-supplied values for the proportion of clear and overcast hours for each month of the year are required to accommodate different climatic conditions.« less

  1. Light Matters (A "Life at the Frontiers of Energy Research" contest entry from the 2011 Energy Frontier Research Centers (EFRCs) Summit and Forum)

    SciTech Connect (OSTI)

    Atwater, Harry , California Institute of Technology); LMI Staff

    2011-05-01

    'Light Matters' was submitted by the Center for Light-Material Interactions in Energy Conversion (LMI) 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. This video was selected as one of five winners by a distinguished panel of judges for its 'striking photography and visual impact'. LMI, an EFRC directed by Harry Atwater at the California Institute of Technology is a partnership of scientists from three institutions: CalTech (lead), University of California, Berkeley, and the University of Illinois at Urbana-Champaign. 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. The mission of Light-Material Interactions in Energy Conversion is 'to tailor the morphology, complex dielectric structure, and electronic properties of matter to sculpt the flow of sunlight, enabling light conversion to electrical and chemical energy with unprecedented efficiency.' Research topics are: catalysis (imines hydrocarbons), solar photovoltaic, solar fuels, photonic, solid state lighting, metamaterial, optics, phonons, thermal conductivity, solar electrodes, photsynthesis, CO{sub 2} (convert), greenhouse gas, and matter by design.

  2. Light Matters (A "Life at the Frontiers of Energy Research" contest entry from the 2011 Energy Frontier Research Centers (EFRCs) Summit and Forum)

    ScienceCinema (OSTI)

    Atwater, Harry (Director, Light-Material Interactions in Energy Conversion (LMI), California Institute of Technology); LMI Staff

    2011-11-02

    'Light Matters' was submitted by the Center for Light-Material Interactions in Energy Conversion (LMI) 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. This video was selected as one of five winners by a distinguished panel of judges for its 'striking photography and visual impact'. LMI, an EFRC directed by Harry Atwater at the California Institute of Technology is a partnership of scientists from three institutions: CalTech (lead), University of California, Berkeley, and the University of Illinois at Urbana-Champaign. 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. The mission of Light-Material Interactions in Energy Conversion is 'to tailor the morphology, complex dielectric structure, and electronic properties of matter to sculpt the flow of sunlight, enabling light conversion to electrical and chemical energy with unprecedented efficiency.' Research topics are: catalysis (imines hydrocarbons), solar photovoltaic, solar fuels, photonic, solid state lighting, metamaterial, optics, phonons, thermal conductivity, solar electrodes, photsynthesis, CO{sub 2} (convert), greenhouse gas, and matter by design.

  3. Integrated LED-based luminare for general lighting

    DOE Patents [OSTI]

    Dowling, Kevin J.; Lys, Ihor A.; Roberge, Brian; Williamson, Ryan C.; Roberts, Ron; Datta, Michael; Mollnow, Tomas; Morgan, Frederick M.

    2013-03-05

    Lighting apparatus and methods employing LED light sources are described. The LED light sources are integrated with other components in the form of a luminaire or other general purpose lighting structure. Some of the lighting structures are formed as Parabolic Aluminum Reflector (PAR) luminaires, allowing them to be inserted into conventional sockets. The lighting structures display beneficial operating characteristics, such as efficient operation, high thermal dissipation, high output, and good color mixing.

  4. Integrated LED-based luminaire for general lighting

    DOE Patents [OSTI]

    Dowling, Kevin J.; Lys, Ihor A.; Williamson, Ryan C.; Roberge, Brian; Roberts, Ron; Morgan, Frederick; Datta, Michael Jay; Mollnow, Tomas Jonathan

    2016-08-30

    Lighting apparatus and methods employing LED light sources are described. The LED light sources are integrated with other components in the form of a luminaire or other general purpose lighting structure. Some of the lighting structures are formed as Parabolic Aluminum Reflector (PAR) luminaires, allowing them to be inserted into conventional sockets. The lighting structures display beneficial operating characteristics, such as efficient operation, high thermal dissipation, high output, and good color mixing.

  5. Strain induced modification in phonon dispersion curves of monolayer boron pnictides

    SciTech Connect (OSTI)

    Jha, Prafulla K. E-mail: prafullaj@yahoo.com; Soni, Himadri R.

    2014-01-14

    In the frame work of density functional theory, the biaxial strain induced phonon dispersion curves of monolayer boron pnictides (BX, X = N, P, As, and Sb) have been investigated. The electron-ion interactions have been modelled using ultrasoft pseudopotentials while exchange-correlation energies have been approximated by the method of local density approximation in the parameterization of Perdew-Zunger. The longitudinal and transverse acoustic phonon modes of boron pnictide sheets show linear dependency on wave vector k{sup →} while out of plane mode varies as k{sup 2}. The in-plane longitudinal and out of plane transverse optical modes in boron nitride displaying significant dispersion similar to graphene. We have analyzed the biaxial strain dependent behaviour of out of plane acoustic phonon mode which is linked to ripple for four BX sheets using a model equation with shell elasticity theory. The strain induces the hardening of this mode with tendency to become more linear with increase in strain percentage. The strain induced hardening of out of plane acoustic phonon mode indicates the absence of rippling in these compounds. Our band structure calculations for both unstrained and strained 2D h-BX are consistent with previous calculations.

  6. Control of coherent information via on-chip photonic–phononic emitter–receivers

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

    Shin, Heedeuk; Cox, Jonathan A.; Jarecki, Robert; Starbuck, Andrew; Wang, Zheng; Rakich, Peter T.

    2015-03-05

    We report that rapid progress in integrated photonics has fostered numerous chip-scale sensing, computing and signal processing technologies. However, many crucial filtering and signal delay operations are difficult to perform with all-optical devices. Unlike photons propagating at luminal speeds, GHz-acoustic phonons moving at slower velocities allow information to be stored, filtered and delayed over comparatively smaller length-scales with remarkable fidelity. Hence, controllable and efficient coupling between coherent photons and phonons enables new signal processing technologies that greatly enhance the performance and potential impact of integrated photonics. Here we demonstrate a mechanism for coherent information processing based on travelling-wave photon–phonon transduction,more » which achieves a phonon emit-and-receive process between distinct nanophotonic waveguides. Using this device, physics—which supports GHz frequencies—we create wavelength-insensitive radiofrequency photonic filters with frequency selectivity, narrow-linewidth and high power-handling in silicon. More generally, this emit-receive concept is the impetus for enabling new signal processing schemes.« less

  7. Point defect weakened thermal contraction in monolayer graphene

    SciTech Connect (OSTI)

    Zha, Xian-Hu; Zhang, Rui-Qin; Lin, Zijing

    2014-08-14

    We investigate the thermal expansion behaviors of monolayer graphene and three configurations of graphene with point defects, namely the replacement of one carbon atom with a boron or nitrogen atom, or of two neighboring carbon atoms by boron-nitrogen atoms, based on calculations using first-principles density functional theory. It is found that the thermal contraction of monolayer graphene is significantly decreased by point defects. Moreover, the corresponding temperature for negative linear thermal expansion coefficient with the maximum absolute value is reduced. The cause is determined to be point defects that enhance the mechanical strength of graphene and then reduce the amplitude and phonon frequency of the out-of-plane acoustic vibration mode. Such defect weakening of graphene thermal contraction will be useful in nanotechnology to diminish the mismatching or strain between the graphene and its substrate.

  8. Reexamination of Basal Plane Thermal Conductivity of Suspended Graphene Samples Measured by Electro-Thermal Micro-Bridge Methods

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

    Jo, Insun; Pettes, Michael; Lindsay, Lucas R.; Ou, Eric; Weathers, Annie; Moore, Arden; Yao, Zhen; Shi, Li

    2015-05-18

    Thermal transport in suspended graphene samples has been measured in prior works and this work with the use of a suspended electro-thermal micro-bridge method. These measurement results are analyzed here to evaluate and eliminate the errors caused by the extrinsic thermal contact resistance. It is noted that the thermal resistance measured in a recent work increases linearly with the suspended length of the single-layer graphene samples synthesized by chemical vapor deposition (CVD), and that such a feature does not reveal the failure of Fourier s law despite the increase in the apparent thermal conductivity with length. The re-analyzed thermal conductivitymore » of a single-layer CVD graphene sample reaches about ( 1680 180 )Wm-1K-1 at room temperature, which is close to the highest value reported for highly oriented pyrolytic graphite. In comparison, the thermal conductivity values measured for two suspended exfoliated bi-layer graphene samples are about ( 880 60 ) and ( 730 60 ) Wm-1K-1 at room temperature, and approach that of the natural graphite source above room temperature. However, the low-temperature thermal conductivities of these suspended graphene samples are still considerably lower than the graphite values, with the peak thermal conductivities shifted to much higher temperatures. Analysis of the thermal conductivity data reveals that the low temperature behavior is dominated by phonon scattering by polymer residue instead of by the lateral boundary.« less

  9. Reexamination of Basal Plane Thermal Conductivity of Suspended Graphene Samples Measured by Electro-Thermal Micro-Bridge Methods

    SciTech Connect (OSTI)

    Jo, Insun; Pettes, Michael; Lindsay, Lucas R; Ou, Eric; Weathers, Annie; Moore, Arden; Yao, Zhen; Shi, Li

    2015-01-01

    Thermal transport in suspended graphene samples has been measured in prior works and this work with the use of a suspended electro-thermal micro-bridge method. These measurement results are analyzed here to evaluate and eliminate the errors caused by the extrinsic thermal contact resistance. It is noted that the thermal resistance measured in a recent work increases linearly with the suspended length of the single-layer graphene samples synthesized by chemical vapor deposition (CVD), and that such a feature does not reveal the failure of Fourier s law despite the increase in the apparent thermal conductivity with length. The re-analyzed thermal conductivity of a single-layer CVD graphene sample reaches about ( 1680 180 )Wm-1K-1 at room temperature, which is close to the highest value reported for highly oriented pyrolytic graphite. In comparison, the thermal conductivity values measured for two suspended exfoliated bi-layer graphene samples are about ( 880 60 ) and ( 730 60 ) Wm-1K-1 at room temperature, and approach that of the natural graphite source above room temperature. However, the low-temperature thermal conductivities of these suspended graphene samples are still considerably lower than the graphite values, with the peak thermal conductivities shifted to much higher temperatures. Analysis of the thermal conductivity data reveals that the low temperature behavior is dominated by phonon scattering by polymer residue instead of by the lateral boundary.

  10. Resonance laser-plasma excitation of coherent terahertz phonons in the bulk of fluorine-bearing crystals under high-intensity femtosecond laser irradiation

    SciTech Connect (OSTI)

    Potemkin, F V; Mareev, E I; Khodakovskii, N G; Mikheev, P M

    2013-08-31

    The dynamics of coherent phonons in fluorine-containing crystals was investigated by pump-probe technique in the plasma production regime. Several phonon modes, whose frequencies are overtones of the 0.38-THz fundamental frequency, were simultaneously observed in a lithium fluoride crystal. Phonons with frequencies of 1 and 0.1 THz were discovered in a calcium fluoride crystal and coherent phonons with frequencies of 1 THz and 67 GHz were observed in a barium fluoride crystal. Furthermore, in the latter case the amplitudes of phonon mode oscillations were found to significantly increase 15 ps after laser irradiation. (interaction of laser radiation with matter)

  11. Thermal Enhancer - Airless Exhaust Thermal Management Device | Department

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

    of Energy Enhancer - Airless Exhaust Thermal Management Device Thermal Enhancer - Airless Exhaust Thermal Management Device Presentation given at DEER 2006, August 20-24, 2006, Detroit, Michigan. Sponsored by the U.S. DOE's EERE FreedomCar and Fuel Partnership and 21st Century Truck Programs. 2006_deer_coker.pdf (1.85 MB) More Documents & Publications Heavy Duty Vehicle In-Use Emission Performance Why Light Duty Diesels Make Sense in the North American Market Scalable, Low-Cost, High

  12. Electric thermal storage demonstration program

    SciTech Connect (OSTI)

    Not Available

    1992-02-01

    In early 1989, MMWEC, a joint action agency comprised of 30 municipal light departments in Massachusetts and one affiliate in Rhode Island, responded to a Department of Energy request to proposal for the Least Cost Utility Planning program. The MMWEC submission was for the development of a program, focused on small rural electric utilities, to promote the use of electric thermal storage heating systems in residential applications. In this progress report, cost savings at Bolyston light department is discussed. (JL)

  13. Electric thermal storage demonstration program

    SciTech Connect (OSTI)

    Not Available

    1992-01-01

    In early 1989, MMWEC, a joint action agency comprised of 30 municipal light departments in Massachusetts and one affiliate in Rhode Island, responded to a Department of Energy request to proposal for the Least Cost Utility Planning program. The MMWEC submission was for the development of a program, focused on small rural electric utilities, to promote the use of electric thermal storage heating systems in residential applications. In this progress report, cost savings at Bolyston light department is discussed. (JL)

  14. Commercial Lighting and LED Lighting Incentives | Department...

    Broader source: Energy.gov (indexed) [DOE]

    Schools Institutional Savings Category Lighting Lighting ControlsSensors Other EE LED Lighting Maximum Rebate Up to 100% of cost; incentives that exceed 5,000 should be...

  15. In-situ optical transmission electron microscope study of exciton phonon replicas in ZnO nanowires by cathodoluminescence

    SciTech Connect (OSTI)

    Yang, Shize; Tian, Xuezeng; Wang, Lifen; Wei, Jiake; Qi, Kuo; Li, Xiaomin; Xu, Zhi E-mail: xdbai@iphy.ac.cn Wang, Wenlong; Zhao, Jimin; Bai, Xuedong E-mail: xdbai@iphy.ac.cn; Wang, Enge E-mail: xdbai@iphy.ac.cn

    2014-08-18

    The cathodoluminescence spectrum of single zinc oxide (ZnO) nanowires is measured by in-situ optical Transmission Electron Microscope. The coupling between exciton and longitudinal optical phonon is studied. The band edge emission varies for different excitation spots. This effect is attributed to the exciton propagation along the c axis of the nanowire. Contrary to free exciton emission, the phonon replicas are well confined in ZnO nanowire. They travel along the c axis and emit at the end surface. Bending strain increases the relative intensity of second order phonon replicas when excitons travel along the c-axis.

  16. Light's Darkness

    ScienceCinema (OSTI)

    Padgett, Miles [University of Glasgow, Glasgow, Scotland

    2010-01-08

    Optical vortices and orbital angular momentum are currently topical subjects in the optics literature. Although seemingly esoteric, they are, in fact, the generic state of light and arise whenever three or more plane waves interfere. To be observed by eye the light must be monochromatic. Laser speckle is one such example, where the optical energy circulates around each black spot, giving a local orbital angular momentum. This talk with report three on-going studies. First, when considering a volume of interfering waves, the laser specs map out threads of complete darkness embedded in the light. Do these threads form loops? Links? Or even knots? Second, when looking through a rapidly spinning window, the image of the world on the other side is rotated: true or false? Finally, the entanglement of orbital angular momentum states means measuring how the angular position of one photons sets the angular momentum of another: is this an angular version of the EPR (Einstein, Podolsky, and Rosen) paradox?

  17. Thermal Signatures of The Kondo Volume Collapse in Cerium (Journal...

    Office of Scientific and Technical Information (OSTI)

    fit by the Kondo volume collapse model plus a quasiharmonic representation of the phonons. ... CERIUM; FLUCTUATIONS; FREE ENERGY; PHONONS; SPIN; THERMODYNAMICS; X-RAY DIFFRACTION ...

  18. Electron - polar acoustical phonon interactions in nitride based diluted magnetic semiconductor quantum well via hot electron magnetotransport

    SciTech Connect (OSTI)

    Pandya, Ankur; Shinde, Satyam; Jha, Prafulla K.

    2015-05-15

    In this paper the hot electron transport properties like carrier energy and momentum scattering rates and electron energy loss rates are calculated via interactions of electrons with polar acoustical phonons for Mn doped BN quantum well in BN nanosheets via piezoelectric scattering and deformation potential mechanisms at low temperatures with high electric field. Electron energy loss rate increases with the electric field. It is observed that at low temperatures and for low electric field the phonon absorption is taking place whereas, for sufficient large electric field, phonon emission takes place. Under the piezoelectric (polar acoustical phonon) scattering mechanism, the carrier scattering rate decreases with the reduction of electric field at low temperatures wherein, the scattering rate variation with electric field is limited by a specific temperature beyond which there is no any impact of electric field on such scattering.

  19. Phonon self-energy and origin of anomalous neutron scattering spectra in SnTe and PbTe thermoelectrics

    SciTech Connect (OSTI)

    Li, Chen [ORNL] [ORNL; Ma, Jie [ORNL] [ORNL; May, Andrew F [ORNL] [ORNL; Cao, Huibo [ORNL] [ORNL; Christianson, Andrew D [ORNL] [ORNL; Ehlers, Georg [ORNL] [ORNL; Singh, David J [ORNL] [ORNL; Sales, Brian C [ORNL] [ORNL; Delaire, Olivier A [ORNL] [ORNL

    2014-01-01

    The anharmonic lattice dynamics of rock-salt thermoelectric compounds SnTe and PbTe are investigated with inelastic neutron scattering (INS) and first-principles calculations. The experiments show that, surprisingly, although SnTe is closer to the ferroelectric instability, phonon spectra in PbTe exhibit a more anharmonic character. This behavior is reproduced in first-principles calculations of the temperature-dependent phonon self-energy. Our simulations reveal how the nesting of phonon dispersions induces prominent features in the self-energy, which account for the measured INS spectra and their temperature dependence. We establish that the phase-space for three-phonon scattering processes, rather than just the proximity to the lattice instability, is the mechanism determining the complex spectrum of the transverse-optical ferroelectric mode.

  20. National Lighting Energy Consumption

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

    Lighting Energy National Lighting Energy Consumption Consumption 390 Billion kWh used for lighting in all 390 Billion kWh used for lighting in all commercial buildings in commercial buildings in 2001 2001 LED (<.1% ) Incandescent 40% HID 22% Fluorescent 38% Lighting Energy Consumption by Lighting Energy Consumption by Breakdown of Lighting Energy Breakdown of Lighting Energy Major Sector and Light Source Type Major Sector and Light Source Type Source: Navigant Consulting, Inc., U.S. Lighting

  1. Phonon-assisted tunneling and two-channel Kondo physics in molecular junctions

    SciTech Connect (OSTI)

    Dias Da Silva, Luis G; Dagotto, Elbio R

    2009-01-01

    The interplay between vibrational modes and Kondo physics is a fundamental aspect of transport properties of correlated molecular conductors. We present theoretical results for a single molecule in the Kondo regime connected to left and right metallic leads, creating the usual coupling to a conduction channel with left-right parity even. A center-of-mass vibrational mode introduces an additional phonon-assisted tunneling through the antisymmetric odd channel. A non-Fermi-liquid fixed point, reminiscent of the two-channel Kondo effect, appears at a critical value of the phonon-mediated coupling strength. Our numerical renormalization-group calculations for this system reveal non-Fermi-liquid behavior at low temperatures over lines of critical points. Signatures of this strongly correlated state are prominent in the thermodynamic properties and in the linear conductance.

  2. Covariant density functional theory with two-phonon coupling in nuclei

    SciTech Connect (OSTI)

    Ring, P.; Litvinova, E.; Tselyaev, V.

    2012-10-20

    A full description of excited states within the framework of density functional theory requires energy dependent self energies. We present a new class of many-body models. It allows a parameter free description of the fragmentation of nuclear states induced by mode coupling of two-quasiparticle and two-phonon configurations. The method is applied for an investigation of low-lying dipole excitations in Sn isotopes with large neutron excess.

  3. Phonons and magnetic excitation correlations in weak ferromagnetic YCrO{sub 3}

    SciTech Connect (OSTI)

    Sharma, Yogesh; Sahoo, Satyaprakash E-mail: guptaraj@iitk.ac.in Perez, William; Katiyar, Ram S. E-mail: guptaraj@iitk.ac.in; Mukherjee, Somdutta; Gupta, Rajeev E-mail: guptaraj@iitk.ac.in; Garg, Ashish; Chatterjee, Ratnamala

    2014-05-14

    Here, we report the temperature dependent Raman spectroscopic studies on orthorhombically distorted perovskite YCrO{sub 3} over a temperature range of 20–300 K. Temperature dependence of DC-magnetization measurements under field cooled and zero field cooled protocols confirmed a Néel transition at T{sub N} ∼ 142 K. Magnetization isotherms recorded at 125 K show a clear loop opening without any magnetization saturation up to 20 kOe, indicating a coexistence of antiferromagnetic (AFM) and weak ferromagnetic (WFM) phases. Estimation of exchange constants using mean-field approximation further confirm the presence of a complex magnetic phase below T{sub N}. Temperature evolution of Raman line-shape parameters of the selected modes (associated with the octahedral rotation and A(Y)-shift in the unit-cell) reveal an anomalous phonon shift near T{sub N}. An additional phonon anomaly was identified at T{sup *} ∼ 60 K, which could possibly be attributed to the change in the spin dynamics. Moreover, the positive and negative shifts in Raman frequencies between T{sub N} and T{sup *} suggest competing WFM and AFM interactions. A close match between the phonon frequency of B{sub 3g} (3)-octahedral rotation mode with the square of sublattice magnetization between T{sub N} and T{sup *} is indicative of the presence of spin-phonon coupling in multiferroic YCrO{sub 3}.

  4. Light Show

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

    9 Lightning - Nature's Light Show Lightning provides one of nature's most spectacular displays of energy. Though fascinating to observe, lightning can be dangerous and deadly. Protecting ARM instruments from lightning damage is vital. Putting equipment worth millions of dollars into open fields (Photo: NOAA) ARM Facilities Newsletter is published by Argonne National Laboratory, a multiprogram laboratory operated by The University of Chicago under contract W-31-109-Eng-38 with the U.S. Department

  5. Enhanced spin-phonon-electronic coupling in a 5d oxide

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

    Calder, Stuart A.; Yamaura, K.; Tsujimoto, Y.; Sun, Y. S.; Stone, Matthew B.; Shi, Y. G.; Lang, Jonathan; Christianson, Andrew D.; Lumsden, Mark D.; Lee, Jun Hee; et al

    2015-11-26

    Enhanced coupling of material properties offers new fundamental insights and routes to multifunctional devices. In this context 5d oxides provide new paradigms of cooperative interactions that drive novel emergent behaviour. This is exemplified in osmates that host metal insulator transitions where magnetic order appears intimately entwined. Here we consider such a material, the 5d perovskite NaOsO3, and observe a coupling between spin and phonon manifested in a frequency shift of 40 cm 1, the largest measured in any material. The anomalous modes are shown to involve solely Os O interactions and magnetism is revealed as the driving microscopic mechanism formore » the phonon renormalization. The magnitude of the coupling in NaOsO3 is primarily due to a property common to all 5d materials: the large spatial extent of the ion. This allows magnetism to couple to phonons on an unprecedented scale and in general offers multiple new routes to enhanced coupled phenomena in 5d materials.« less

  6. Flexocoupling impact on the generalized susceptibility and soft phonon modes in the ordered phase of ferroics

    SciTech Connect (OSTI)

    Morozovska, Anna N.; Vysochanskii, Yulian M.; Varenyk, Oleksandr V.; Silibin, Maxim V.; Kalinin, Sergei V.; Eliseev, Eugene A.

    2015-09-29

    The impact of the flexoelectric effect on the generalized susceptibility and soft phonon dispersion is not well known in the long-range-ordered phases of ferroics. Within the Landau-Ginzburg-Devonshire approach we obtained analytical expressions for the generalized susceptibility and phonon dispersion relations in the ferroelectric phase. The joint action of the static and dynamic flexoelectric effects induces nondiagonal components of the generalized susceptibility, whose amplitude is proportional to the convolution of the spontaneous polarization with the flexocoupling constants. The flexocoupling essentially broadens the k spectrum of the generalized susceptibility and leads to an additional “pushing away” of the optical and acoustic soft mode phonon branches. The degeneracy of the transverse optical and acoustic modes disappears in the ferroelectric phase in comparison with the paraelectric phase due to the joint action of flexoelectric coupling and ferroelectric nonlinearity. Lastly, the results obtained might be mainly important for theoretical analyses of a broad spectrum of experimental data, including neutron and Brillouin scattering.

  7. The effect of driven electron-phonon coupling on the electronic conductance of a polar nanowire

    SciTech Connect (OSTI)

    Mardaani, Mohammad Rabani, Hassan; Esmaili, Esmat; Shariati, Ashrafalsadat

    2015-08-07

    A semi-classical model is proposed to explore the effect of electron-phonon coupling on the coherent electronic transport of a polar chain which is confined between two rigid leads in the presence of an external electric field. To this end, we construct the model by means of Green's function technique within the nearest neighbor tight-binding and harmonic approximations. For a time-periodic electric field, the atomic displacements from the equilibrium positions are obtained precisely. The result is then used to compute the electronic transport properties of the chain within the Peierls-type model. The numerical results indicate that the conductance of the system shows interesting behavior in some special frequencies. For each special frequency, there is an electronic quasi-state in which the scattering of electrons by vibrating atoms reaches maximum. The system electronic conductance decreases dramatically at the strong electron-phonon couplings and low electron energies. In the presence of damping forces, the electron-phonon interaction has a less significant effect on the conductance.

  8. Lattice vibrations in the Frenkel-Kontorova model. I. Phonon dispersion, number density, and energy

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

    Meng, Qingping; Wu, Lijun; Welch, David O.; Zhu, Yimei

    2015-06-17

    We studied the lattice vibrations of two inter-penetrating atomic sublattices via the Frenkel-Kontorova (FK) model of a linear chain of harmonically interacting atoms subjected to an on-site potential, using the technique of thermodynamic Green's functions based on quantum field-theoretical methods. General expressions were deduced for the phonon frequency-wave-vector dispersion relations, number density, and energy of the FK model system. In addition, as the application of the theory, we investigated in detail cases of linear chains with various periods of the on-site potential of the FK model. Some unusual but interesting features for different amplitudes of the on-site potential of themore » FK model are discussed. In the commensurate structure, the phonon spectrum always starts at a finite frequency, and the gaps of the spectrum are true ones with a zero density of modes. In the incommensurate structure, the phonon spectrum starts from zero frequency, but at a non-zero wave vector; there are some modes inside these gap regions, but their density is very low. In our approximation, the energy of a higher-order commensurate state of the one-dimensional system at a finite temperature may become indefinitely close to the energy of an incommensurate state. This finding implies that the higher-order incommensurate-commensurate transitions are continuous ones and that the phase transition may exhibit a “devil's staircase” behavior at a finite temperature.« less

  9. Enhanced spin-phonon-electronic coupling in a 5d oxide

    SciTech Connect (OSTI)

    Calder, Stuart A.; Yamaura, K.; Tsujimoto, Y.; Sun, Y. S.; Stone, Matthew B.; Shi, Y. G.; Lang, Jonathan; Christianson, Andrew D.; Lumsden, Mark D.; Lee, Jun Hee; Feygenson, Mikhail; Zhao, Zhiying; Yan, Jiaqiang

    2015-11-26

    Enhanced coupling of material properties offers new fundamental insights and routes to multifunctional devices. In this context 5d oxides provide new paradigms of cooperative interactions that drive novel emergent behaviour. This is exemplified in osmates that host metal insulator transitions where magnetic order appears intimately entwined. Here we consider such a material, the 5d perovskite NaOsO3, and observe a coupling between spin and phonon manifested in a frequency shift of 40 cm 1, the largest measured in any material. The anomalous modes are shown to involve solely Os O interactions and magnetism is revealed as the driving microscopic mechanism for the phonon renormalization. The magnitude of the coupling in NaOsO3 is primarily due to a property common to all 5d materials: the large spatial extent of the ion. This allows magnetism to couple to phonons on an unprecedented scale and in general offers multiple new routes to enhanced coupled phenomena in 5d materials.

  10. Photoluminescent and thermal properties of (Sr{sub 0.995?x?y?z}Ca{sub x}Ba{sub y}Mg{sub z}){sub 2}SiO{sub 4}:0.01Eu{sup 2+} phosphors for warm white light-emitting diodes

    SciTech Connect (OSTI)

    Li, Yao; Ci, Zhipeng; Peng, Yingquan; Wang, Yuhua; Liu, Chunjuan

    2015-01-15

    Highlights: The photoluminescent property of Sr{sub 2}SiO{sub 4}:Eu{sup 2+} is improved by doping Ca{sup 2+} and Ba{sup 2+}. The emission spectra red-shift obviously by doping Ca{sup 2+} into Sr{sub 2}SiO{sub 4}:Eu{sup 2+}. The thermal stability is enhanced by doping Ba{sup 2+} into (Sr,Ca){sub 2}SiO{sub 4}:Eu{sup 2+}. The improved phosphors can combine blue-LED chips to generate warm white light. - Abstract: A series of phosphors (Sr{sub 0.995?x?y?z}Ca{sub x}Ba{sub y}Mg{sub z}){sub 2}SiO{sub 4}:0.01Eu{sup 2+} (0 ? x ? 0.45, 0 ? y ? 0.015, 0 ? z ? 0.35) were synthesized by solid state reaction. Their phase compositions and photoluminescent properties were investigated in detail. The X-ray diffraction analysis indicates the impurity phase of SrSiO{sub 3} is formed only when z ? 0.25. A photoluminescence investigation shows, with x increasing the emission spectra of the phosphors (0 ? x ? 0.45, 0 ? y ? 0.015, z = 0) obviously red-shift, the corresponding color tones shift from yellow to orangeyellow and their CCTs reduce from 2875 to 2237 K. All the results are beneficial for the phosphors to combining blue light-emitting diode chips to generate warm white light. Besides, the thermal stability of the phosphor (x = 0.36, y = z = 0) is enhanced by doping Ba{sup 2+}, due to the greater activation energy for the compounds containing barium.