skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Core level excitations—A fingerprint of structural and electronic properties of epitaxial silicene

Abstract

From the analysis of high-resolution Si 2p photoelectron and near-edge x-ray absorption fine structure (NEXAFS) spectra, we show that core level excitations of epitaxial silicene on ZrB{sub 2}(0001) thin films are characteristically different from those of sp{sup 3}-hybridized silicon. In particular, it is revealed that the lower Si 2p binding energies and the low onset in the NEXAFS spectra as well as the occurrence of satellite features in the core level spectra are attributed to the screening by low-energy valence electrons and interband transitions between π bands, respectively. The analysis of observed Si 2p intensities related to chemically distinct Si atoms indicates the presence of at least one previously unidentified component. The presence of this component suggests that the observation of stress-related stripe domains in scanning tunnelling microscopy images is intrinsically linked to the relaxation of Si atoms away from energetically unfavourable positions.

Authors:
; ; ;  [1]; ; ;  [2]; ; ; ; ; ;  [3]
  1. School of Materials Science, Japan Advanced Institute of Science and Technology (JAIST), 1-1, Asahidai, Nomi, Ishikawa 923-1292 (Japan)
  2. MESA Institute for Nanotechnology, University of Twente, 7500 AE Enschede (Netherlands)
  3. The Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581 (Japan)
Publication Date:
OSTI Identifier:
22252864
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 140; Journal Issue: 18; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ABSORPTION; ABSORPTION SPECTROSCOPY; BINDING ENERGY; ELECTRONS; EPITAXY; EXCITATION; FINE STRUCTURE; SCANNING TUNNELING MICROSCOPY; SILICON; SPECTRA; THIN FILMS; X RADIATION; X-RAY SPECTROSCOPY; ZIRCONIUM BORIDES

Citation Formats

Friedlein, R., E-mail: friedl@jaist.ac.jp, Fleurence, A., Aoyagi, K., Yamada-Takamura, Y., Jong, M. P. de, Van Bui, H., Wiggers, F. B., Yoshimoto, S., Koitaya, T., Shimizu, S., Noritake, H., Mukai, K., and Yoshinobu, J.. Core level excitations—A fingerprint of structural and electronic properties of epitaxial silicene. United States: N. p., 2014. Web. doi:10.1063/1.4875075.
Friedlein, R., E-mail: friedl@jaist.ac.jp, Fleurence, A., Aoyagi, K., Yamada-Takamura, Y., Jong, M. P. de, Van Bui, H., Wiggers, F. B., Yoshimoto, S., Koitaya, T., Shimizu, S., Noritake, H., Mukai, K., & Yoshinobu, J.. Core level excitations—A fingerprint of structural and electronic properties of epitaxial silicene. United States. doi:10.1063/1.4875075.
Friedlein, R., E-mail: friedl@jaist.ac.jp, Fleurence, A., Aoyagi, K., Yamada-Takamura, Y., Jong, M. P. de, Van Bui, H., Wiggers, F. B., Yoshimoto, S., Koitaya, T., Shimizu, S., Noritake, H., Mukai, K., and Yoshinobu, J.. Wed . "Core level excitations—A fingerprint of structural and electronic properties of epitaxial silicene". United States. doi:10.1063/1.4875075.
@article{osti_22252864,
title = {Core level excitations—A fingerprint of structural and electronic properties of epitaxial silicene},
author = {Friedlein, R., E-mail: friedl@jaist.ac.jp and Fleurence, A. and Aoyagi, K. and Yamada-Takamura, Y. and Jong, M. P. de and Van Bui, H. and Wiggers, F. B. and Yoshimoto, S. and Koitaya, T. and Shimizu, S. and Noritake, H. and Mukai, K. and Yoshinobu, J.},
abstractNote = {From the analysis of high-resolution Si 2p photoelectron and near-edge x-ray absorption fine structure (NEXAFS) spectra, we show that core level excitations of epitaxial silicene on ZrB{sub 2}(0001) thin films are characteristically different from those of sp{sup 3}-hybridized silicon. In particular, it is revealed that the lower Si 2p binding energies and the low onset in the NEXAFS spectra as well as the occurrence of satellite features in the core level spectra are attributed to the screening by low-energy valence electrons and interband transitions between π bands, respectively. The analysis of observed Si 2p intensities related to chemically distinct Si atoms indicates the presence of at least one previously unidentified component. The presence of this component suggests that the observation of stress-related stripe domains in scanning tunnelling microscopy images is intrinsically linked to the relaxation of Si atoms away from energetically unfavourable positions.},
doi = {10.1063/1.4875075},
journal = {Journal of Chemical Physics},
number = 18,
volume = 140,
place = {United States},
year = {Wed May 14 00:00:00 EDT 2014},
month = {Wed May 14 00:00:00 EDT 2014}
}
  • We performed first-principle study of the structural and electronic properties of two-dimensional hydrogenated silicene for two configurations; one is hydrogenation along one side of silicene sheet and second is hydrogenation in both sides of silicene sheet. The one-side hydrogenated silicene is found stable at planar geometry while increased buckling of 0.725 Å is found for both-side hydrogenated silicene. The result shows that the hydrogenation occupy the extended π-bonding network of silicene, and thus it exhibits semi-conducting behaviour with a band gap of 1.77 eV and 2.19 eV for one-side hydrogenated silicene and both-side hydrogenated silicene respectively. However, both-side hydrogenated silicenemore » of binding energy 4.56 eV is more stable than one-side hydrogenated silicene of binding energy 4.30 eV, but experimentally silicene is synthesized on substrates which interacts one side of silicene layer and only other side is available for H-atoms. Therefore, practically one-side hydrogenation is also important.« less
  • We report on the changes in structural, morphological, and optical properties of sol-gel derived ZnO and ZnO:Fe nanoparticles due to dense electronic excitations produced by heavy ion irradiations using 200 MeV Ag{sup +15} ion beams. X-ray diffraction studies with Rietveld refinement show that the samples are single phase and tensile strain has been developed in the ion-irradiated samples. The Raman spectroscopy measurements show that ion-irradiation results in microscopic structural disorders and breaking of translational symmetry giving rise to local distortions in the lattice. Atomic force microscopy studies show that roughness of the pellets increases strongly for pure ZnO as comparedmore » with Fe-doped ZnO due to ion-irradiation. Fourier transform infrared analysis confirms tetrahedral coordination of O ions surrounding the Zn-ions and surface modification of the nanoparticles. The UV-Vis spectroscopy measurements show that the band gap increases on Fe doping which may be due to 4s–3d and 2p–3d interactions and the Burstein-Moss band filling effect. The band gap decreases after irradiation which can be interpreted on the basis of creation of some new localized energy states above the valence band. Photoluminescence (PL) intensity is enhanced and two new emission bands viz. a blue band at ∼480 nm (related to surface defects) and a green band at ∼525 nm (related to O vacancies) are observed in ion-irradiated nanoparticles. The enhancement of PL-intensity in irradiated samples is attributed to the increase of different defect states and Zn−O bonds on the surfaces of the irradiated nanoparticles arising from surface modification.« less
  • We study the ionization energy, electron affinity, and the π → π{sup ∗} ({sup 1}L{sub a}) excitation energy of the anthracene molecule, by means of variational quantum Monte Carlo (QMC) methods based on a Jastrow correlated antisymmetrized geminal power (JAGP) wave function, developed on molecular orbitals (MOs). The MO-based JAGP ansatz allows one to rigorously treat electron transitions, such as the HOMO → LUMO one, which underlies the {sup 1}L{sub a} excited state. We present a QMC optimization scheme able to preserve the rank of the antisymmetrized geminal power matrix, thanks to a constrained minimization with projectors built upon symmetrymore » selected MOs. We show that this approach leads to stable energy minimization and geometry relaxation of both ground and excited states, performed consistently within the correlated QMC framework. Geometry optimization of excited states is needed to make a reliable and direct comparison with experimental adiabatic excitation energies. This is particularly important in π-conjugated and polycyclic aromatic hydrocarbons, where there is a strong interplay between low-lying energy excitations and structural modifications, playing a functional role in many photochemical processes. Anthracene is an ideal benchmark to test these effects. Its geometry relaxation energies upon electron excitation are of up to 0.3 eV in the neutral {sup 1}L{sub a} excited state, while they are of the order of 0.1 eV in electron addition and removal processes. Significant modifications of the ground state bond length alternation are revealed in the QMC excited state geometry optimizations. Our QMC study yields benchmark results for both geometries and energies, with values below chemical accuracy if compared to experiments, once zero point energy effects are taken into account.« less
  • Homoepitaxial and heteroepitaxial ZnO, ZnO:Al, and Zn{sub 1-x}Mg{sub x}O:Al films have been grown by magnetron sputtering from ceramic targets at substrate temperatures between 200 °C and 500 °C. We studied the relation between the electronic transport and structural properties for the epitaxially grown films and compared it to the properties of polycrystalline films by means of X-ray diffraction, transmission electron microscopy and optical reflectance and transmittance measurements. The results show that the epitaxial growth of ZnO:Al and Zn{sub 1-x}Mg{sub x}O:Al thin films, which has been observed for nearly all films prepared on single crystalline substrates, will not significantly improve themore » electronic transport properties in comparison to polycrystalline films unless the grain boundaries are eliminated completely. The grain boundary defect densities of about 3 × 10{sup 13} cm{sup −2} are nearly independent on the structural quality of the different polycrystalline, hetero- and homoepitaxial films. This clearly proves that the grain boundary defects are not caused by crystallographic defects, but, most probably, by the dopant aluminium.« less
  • Growth of InN epilayers on c-plane sapphire substrate by chemical vapor deposition technique using pure indium metal and ammonia as precursors has been systematically explored. It has been found that [0001] oriented indium nitride epitaxial layers with smooth surface morphology can be grown on c-plane sapphire substrates by optimizing the growth conditions. Bandgap of the film is observed to be Burstein–Moss shifted likely to be due to high background electron concentration. It has been found that the concentration of this unintentional doping decreases with the increase in the growth temperature and the ammonia flux. Epitaxial quality on the other handmore » deteriorates as the growth temperature increases. Moreover, the morphology of the deposited layer has been found to change from flat top islands to faceted mounds as the flow rate of ammonia increases. This phenomenon is expected to be related to the difference in surface termination character at low and high ammonia flow rates.« less