Search results for "Electronic band structure"
showing 10 items of 206 documents
Electronic Band Transitions in γ-Ge3N4
2021
This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. Support from Estonian Research Council grant PUT PRG 619 is gratefully acknowledged. The multi-anvil experiments at LMV were supported by the French Government Laboratory of Excellence initiative no ANR-10-LABX-0006, the Région Auvergne and the European Regional Development Fund (ClerVolc Contribution Number 478).
Structural and electronic properties ofβ-FeSi2nanoparticles: The role of stacking fault domains
2014
We use conventional and aberration-corrected transmission electron microscopy (TEM) and ab initio calculations to investigate the structural and electronic properties of \ensuremath{\beta}-FeSi${}_{2}$ nanoparticles, which are a promising material for photovoltaic applications due to a band gap of 1 eV and a high absorption coefficient. The nanoparticles have average sizes of \ensuremath{\sim}20 nm, form aggregates, and are prepared by gas-phase synthesis. Amorphous SiO${}_{x}$ shells with thicknesses of \ensuremath{\sim}1.7 nm around \ensuremath{\beta}-FeSi${}_{2}$ cores are identified on individual nanoparticles using electron energy-loss spectroscopy, while stacking fault domains in the …
Pressure-induced band anticrossing in two adamantine ordered-vacancy compounds: CdGa2S4 and HgGa2S4
2021
Abstract This paper reports a joint experimental and theoretical study of the electronic band structure of two ordered-vacancy compounds with defect-chalcopyrite structure: CdGa2S4 and HgGa2S4. High-pressure optical-absorption experiments (up to around 17 GPa) combined with first-principles electronic band-structure calculations provide compelling evidence of strong nonlinear pressure dependence of the bandgap in both compounds. The nonlinear pressure dependence is well accounted for by the band anticrossing model that was previously established mostly for selenides with defect chalcopyrite structure. Therefore, our results on two sulfides with defect chalcopyrite structure under compressio…
First-principles study of the electronic structure of cubicGaS: Metallic versus insulating polymorphs
2007
The electronic structure of different polymorphs of gallium sulphide $(\mathrm{GaS})$ with cubic structure is investigated by means of first-principles band structure calculations in connection with experimental reports on a metastable semiconducting cubic form of this material. The expected metallic character of simple cubic phases containing one $\mathrm{GaS}$ group per unit cell (rocksalt or zinc-blende) is confirmed by the calculations. A cubane-based zinc-blende structure is found to exhibit a band gap which is compatible with experimental results but the unit cell parameter is much larger than the reported ones. We have also studied cubic phases containing hydrogen. It is found that t…
Resonant Raman characterization of InAlGaN/GaN heterostructures
2006
InAlGaN/GaN heterostructures and thin films with In composition ranging from 0.03 to 0.1 are characterized by means of Raman scattering excited at various energies in the ultra violet range, tuning the laser excitation energy through the band gap of In x Al y Ga 1-x-y N. It is shown that the addition of In to the Al y Ga 1-y N alloy diminishes considerably the vibration energy of the A 1 (LO) phonon mode. The phonon line is asymmetric on the low energy side, and the asymmetry increases with In content, while the main peak shifts to lower energies. A shift of the phonon energy has also been observed when the excitation energy is close to the absorption edge of the In x Al y Ga 1-x-y N layer.…
Photonic band gaps in highly ionic medium: CuCl, CuBr, CuI
2003
Abstract Using the transfer-matrix-method, we have studied the propagation of electromagnetic waves through two-dimensional (2D) and three-dimensional (3D) dispersive photonic band gap (PBG) structures constructed from copper halides materials, especially from CuCl compounds. A special attention has been paid to the effect of the polariton gap on the PBG properties. This study reveals that “Twin gaps” and “Twin brothers” concepts and the flattened bands phenomena in both polarizations and for both structures (i.e. 2D and 3D) are all consequences of the strong photon–phonon coupling, particularly near the long wave length transverse optical phonon frequency. Furthermore, results for comparis…
Band convergence in the non-cubic chalcopyrite compounds Cu_2MGeSe_4
2014
Inspired by recent theoretical predictions on band convergence in the tetragonal chalcopyrite compounds, we have explored the influence of the crystal structure on the transport and bandstructure of different quaternary chalcopyrites. In theory, a changing lattice parameter ratio of c/2a towards unity should lead to band convergence due to a more cubic and higher symmetry structure. In accordance with this prediction, the different solid solutions explored in this manuscript show a significant impact on the electronic transport depending on the ratio of the lattice parameters. An increasing lattice parameter ratio results in an increase of the carrier effective masses which can be explained…
Observation of quantized subband states and evidence for surface electron accumulation in CdO from angle-resolved photoemission spectroscopy
2008
The electronic structure of well-ordered single-crystal thin films of CdO100 has been studied using angleresolved photoemission spectroscopy. Quantized electron subbands are observed above the valence-band maximum. The existence of these states provides evidence of an intrinsic electron accumulation space-charge layer near the CdO surface, an interpretation supported by coupled Poisson-Schrodinger calculations. The origin of the accumulation layer result is discussed in terms of the bulk band structure of CdO calculated using quasiparticle-corrected density-functional theory, which reveals that the conduction-band minimum at the Brillouin-zone center lies below the charge neutrality level.
Optimum Carrier Concentration in n-Type PbTe Thermoelectrics
2014
Taking La- and I-doped PbTe as an example, the current work shows the effects of optimizing the thermoelectric figure of merit, zT, by controlling the doping level. The high doping effectiveness allows the carrier concentration to be precisely designed and prepared to control the Fermi level. In addition to the Fermi energy tuning, La-doping modifies the conduction band, leading to an increase in the density of states effective mass that is confirmed by transport, infrared reflectance and hard X-ray photoelectron spectroscopy measurements. Taking such a band structure modification effect into account, the electrical transport properties can then be well-described by a self-consistent single…
Electronic Shell Structure and the Crystal Field Splitting in Simple Metals Clusters
1991
An upper limit for the number of atoms in metal clusters capable of exhibiting electronic shell structure has been estimated by comparing the energy difference between the highest occupied and the lowest unoccupied state with the crystal field splitting. The former is obtained by solving the Schrodinger equation for a spherical potential well with hard walls while the latter is obtained from the band structure of the solid. The results indicate that shell structures may persist in clusters containing as many as a million atoms.