Showing papers on "Electronic band structure published in 1976"
TL;DR: In this paper, the adiabatic approximation and perturbation theory to second order in atomic displacement are used to construct a theory of thermal-electron energy shifts, including both intraband and interband'self-energy' and 'Debye-Waller' corrections.
Abstract: The adiabatic approximation and perturbation theory to second order in atomic displacement are used to construct a theory of thermal-electron energy shifts. Both intraband and interband 'self-energy' and 'Debye-Waller' corrections are included. A sum rule based on translational invariance clarified the intimate relation between these two types of correction. Various kinds of cancellation between the terms can be seen explicitly for the two limiting cases of a very narrow band and a small gap in a nearly-free-electron band structure.
283 citations
TL;DR: In this article, an anomalous temperature dependence of the Urbach exponential absorption edge for intramolecular electronic excitation is noted and interpreted in terms of the perturbation of the lone-pair valence band by hydrogen bonding.
Abstract: We approximate liquid water as a lone‐pair amorphous semiconductor. Since electronic orbital times are short compared to the periods of atomic and molecular motion, properties dependent on electronic states can be interpreted to determine short‐time intermediate range order. An anomalous temperature dependence of the Urbach exponential absorption edge for intramolecular electronic excitation is noted and interpreted in terms of the perturbation of the lone‐pair valence band by hydrogen bonding. The extrinsic optical absorptions with I− and Br− doped water are observed to have Urbach tails. An approximate electronic band structure for pure and doped liquid water is presented.
197 citations
TL;DR: In this paper, the optical properties of Au and Ag are measured between 0.5 and 5.4 eV for temperatures ranging from 40 to 840 K. The analysis of these spectra-also extended to the case of Cu-permits the assessment of energy separations associated with interconduction-band transitions in the vicinity of L over a wide temperature range.
Abstract: The optical properties of Au and Ag are measured between 0.5 and 5.4 eV for temperatures ranging from 40 to 840K. The analysis of these spectra-also extended to the case of Cu-permits the assessment of energy separations associated with interconduction-band transitions in the vicinity of L over a wide temperature range. Notably the L4- to L4+ (nonrelativistic: L2' to L1) energy gap at 295K is found to be 4.81 eV for Cu, 4.11 eV for Ag and 4.20 eV for Au. The temperature dependence of this gap (around 295K) typically is -6.5*10-4 eV K-1 for all noble metals, i.e., considerably larger than predicted on the basis of band calculations. The present analysis also shows the interband absorption edge of Ag to arise from transitions in extended regions of the Brillouin zone. A comparison of experimental and theoretical spectra suggests lattice expansion to be the major source of temperature dependence of the band structure. It also yields information regarding the influence of dipole matrix elements on the epsilon 2 spectra.
195 citations
[...]
TL;DR: In this article, a review of the electronic properties of pure bismuth is given, and the validity of the Cohen model as a first approximation to the electron spectrum is established, and deviations from this model are described.
Abstract: A review of the electronic properties of pure bismuth is given. Theoretical ideas on the band structure of bismuth and the dispersion relation for electrons near the bottom of the conduction band are briefly outlined. The experiments considered are those which give the most precise information on the Fermi surface (quantum effects in conductivity, cyclotron resonance, size effects, magnetoplasma waves, etc.) and on the electron energy spectrum near the bottom of the conduction band (studies in the quantum limit, infra-red magneto-reflection). The validity of the Cohen model as a first approximation to the electron spectrum in bismuth is established, and deviations from this model are described. Experiments are proposed which may give additional information on electrons in bismuth.
170 citations
TL;DR: In this article, an energy band model of amorphous GexSe1-x films has been proposed for consistent explanations of experimental data, and measurements of the photoconductivity and the absorption spectra have been made at room temperature.
Abstract: Measurements of electrical and optical properties have been made on GexSe1-x amorphous thin films of about 1 µm thickness. From the experiment of electrical conductivity at various temperatures, two processes of the d.c. conductivity in GexSe1-x films are observed in plots of ln σ against 1/T. The thermoelectric power exhibits a maximum value of p-type conduction at pure Se and a change of the sign from positive to negative at 0.4
165 citations
PARC1
TL;DR: In this article, it was shown that lattice dynamical properties of insulators can be calculated directly from the electronic band structure using the "special points" method, and the shear modulii and zone boundary transverse acoustic phonon frequencies of C, Si and Ge were calculated with no adjustable parameters.
111 citations
TL;DR: The mixed-basis method has been used to compute the energy bands of an idealized ''ensuremath{\beta}$-cristobalite form of silicon dioxide''.
Abstract: The mixed-basis method has been used to compute the energy bands of an idealized $\ensuremath{\beta}$-cristobalite form of silicon dioxide. A direct-forbidden optical-absorption edge is predicted. Peaks in observed x-ray emission and optical-absorption spectra identified with critical points in the densities of states.
109 citations
TL;DR: In this paper, the authors used Extended Huckel method to study hydrogen chemisorption on nickel surfaces and found that the stability of adsorption decreases in the order (110 > (100) > (111) and Atop > Bridge > Centred.
107 citations
TL;DR: In this paper, the exciton absorption peak in a III-V ternary alloy was observed and the most accurate determination of both the composition dependence of the Γ band gap and the position of the X crossover was made.
102 citations
TL;DR: In this paper, the atomic volumes, the bulk moduli, the magnetizations, the gain susceptibilities and the derivatives of these quantities with respect to pressure have been obtained from first principles for Fe, Ni, Rh, Pd, Ir and Pt at 0K using canonical band theory and the local spin-density approximation for exchange and correlation.
Abstract: The atomic volumes, the bulk moduli, the magnetizations, the gain susceptibilities and the derivatives of these quantities with respect to pressure have been obtained from first principles for Fe, Ni, Rh, Pd, Ir and Pt at 0K using canonical band theory and the local spin-density approximation for exchange and correlation. The agreement with experiment is surprisingly good. For Fe the calculated ferromagnetic contribution to the pressure is nearly large enough to account for the relative softness and large volume in the BCC phase and it creates an instability in the FCC phase.
101 citations
TL;DR: In this paper, the theory of electron energy losses is discussed in terms of the electronic band structure of a solid and the relationship between the observed plasmon energies, the average interband energy gap and the background dielectric constant of the solid is developed.
Abstract: The theory of characteristic electron energy losses is discussed in terms of the electronic band structure of a solid. The relationship between the observed plasmon energies, the average interband energy gap and the background dielectric constant of the solid is developed. The transmission energy loss spectra of a number of the layer-type transition metal dichalcogenides, MX2, where M=Zr, Hf, Nb, Ta, Mo and W and X=S and Se, have been measured in the range of 0–50 eV. In the experiments, a beam of 50 keV electrons is incident along the c-axis of the crystals and electrons inelastically scattered through an angle of 1 m radian are selected for energy analysis. This ensures that the momentum transfer and hence the electric vector for the excitations lies in the basal plane of the crystal (E⊥c). Kramers-Kronig analysis has been applied to the energy loss data to deduce the complex dielectric function of each material. From this function, all other ‘optical’ constants, such as the reflectivity, and t...
TL;DR: In this paper, the electronic structure of Hg has been studied by means of high resolution ESCA, using monochromatized AlKα excitation, and the atomic spectrum from the gas phase is compared with the solid state spectrum from frozen Hg.
TL;DR: Theoretical studies and numerical calculations of bound state resonances (selective adsorption) in the elastic scattering of low-energy light atoms from a perfect crystalline surface are made in this article.
TL;DR: In this paper, the x-ray photo-electron spectra of transition-metal carbides with the rock-salt structure were analyzed and the band structures and densities of states (DOSs) of ZrC, HfC, and TaC were calculated by the augmented plane-wave method.
Abstract: The band structures and densities of states (DOSs) of ZrC, HfC, and TaC were calculated by the augmented-plane-wave method, and the x-ray photoelectron spectra of valence bands of these compounds were observed. The theoretical energy distribution curves (EDCs) were in good agreement with the experimental EDCs. These band structures resemble each other and also those of TiC obtained by our previous work. This fact suggests that the rigid-band model is applicable to the transition-metal carbides with the rock-salt structure. Their DOSs are divided into three parts. Peak I derived from the $\mathrm{C} 2s$ state is isolated from the higher valence-band peak II arising from the $\mathrm{C} 2p$ and the valence electrons of the metal atom. Peak III derived from the $d$ and $s$ states of the metal atom is separated by the Fermi level from peak II. The Fermi level lies at the minimum point of the DOS for the group IV carbides, but for TaC it lies at a relatively large DOS point. The DOS at the Fermi level of ZrC, HfC, and TaC are 0.18, 0.16, and 0.65 electrons/(eV primitive cell), respectively. The characteristic mutual differences among these compounds are a stronger localization of $d$ electrons in ZrC and HfC compared with TiC and an enhancement of the photoelectron spectrum intensity of TaC around the Fermi level.
TL;DR: In this paper, a Green's-function approach, closely related to that of Koster and Slater, is developed, within the one-electron pseudopotential formalism, for single vacancies, the divacancy and vacancyoxygen pairs in GaAs, and single vacancies in GaP and InSb.
Abstract: A Green's-function approach, closely related to that of Koster and Slater, is developed, within the one-electron pseudopotential formalism. This is applied to single vacancies, the divacancy and vacancy-oxygen pairs in GaAs, and single vacancies in GaP and InSb. A number of localized states are found. It is shown that the properties of the host-crystal band structure, the electron-electron interaction, and lattice relaxation play an important part in the formation of these states. In contrast with the Koster-Slater calculations, our results are not very sensitive to the strength of the vacancy potential. Our calculations indicate that As and Ga vacancies in GaAs should behave as single donors and acceptors, respectively. The ${V}_{\mathrm{Ga}}\ensuremath{-}\mathrm{O}$ complex behaves as a deep neutral center. The wave functions associated with the levels introduced into the band gap are highly localized. Since they contain admixtures of both valence- and conduction-band functions, and exhibit large lattice distortion, they are likely to take part in nonradiative recombination processes. Finally, we note that nonradiative recombination via some deep neutral centers is likely to be very efficient since our calculation also indicates a possibility of localized excited states introduced by these centers.
TL;DR: In this paper, a method for pinning the Fermi level of insulators to that of a metal calibrant is described, resulting in the ability to obtain absolute binding energies of the electronic levels in wide bandgap insulators.
Abstract: Fourier deconvolved X-ray photoelectron spectroscopy (XPS) valence band spectra obtained from crystalline and amorphous silica, used in conjuction with the results of quantum chemical calculations of the SiO4 tetrahedral unit and other spectrometric measurements (soft X-ray emission, UV absorption and reflectivity, photoconductivity, photoinjection and energy loss spectroscopy), suggest a reinterpretation of the electronic band structure of silica that is consistent with all the data. A unique method for pinning the Fermi level of insulators to that of a metal calibrant is described, resulting in the ability to obtain absolute binding energies of the electronic levels in wide bandgap insulators. Observe peaks in UV reflectivity and energy loss spectra of silica are all assigned to direct interband transitions, and no excitonic states need be involved to explain the data. Upper and lower limits for the bandgap of dry crystalline (α-quartz) and amorphous (Corning Code 7940 glass) silica are adjusted downward from the 8.9 eV bandgap proposed by DiStefano and Eastman [1] to 7.8–5.55 eV for α-quartz and 7.3–5.05 eV for fused silica, respectively. This in no way compromises the obvious insulating properties of silica in MOS devices, since the conductivity is governed by the high barrier height (∼3.8 eV in the case of gold) for metal-insulator electron transfer. The lowered bandgap results from increased low-energy electron density in the valence band, which we ascribe to the 1t1 molecular orbital predicted by various quantum formalisms, but heretofore not detected experimentally in bulk (thick) silica. Disappearances of this orbital and rearrangement of the non-binding 5t2 and 1e orbitals in silicas rich in silanols (OH), as may be the case for thin-film silica on Si metals, would increase the bandgap to 8.3 eV, in better agreement with previous determinations.
TL;DR: In this paper, the surface dipole barriers for transition metals have been deduced using calculated internal Fermi levels and experimental electron workfunctions from a survey of band structure calculations and a theorem which relates the pressure on a solid to the wavefunctions, their derivatives and energies at the Wigner-Seitz cell boundary.
Abstract: Surface dipole barriers for transition metals have been deduced using calculated internal Fermi levels and experimental electron workfunctions. The internal Fermi levels are estimated from a survey of band structure calculations. They have been checked using a theorem which relates the pressure on a solid to the wavefunctions, their derivatives and energies at the Wigner-Seitz cell boundary. This theorem represents a generalization of a relation previously derived using statistical theory, which was used to provide an independent check on internal Fermi levels in simple metals by imposing the equilibrium, zero pressure condition. Reasonable agreement between band structure and pressure cell-boundary estimates for the transition metal internal Fermi level was obtained. The surface dipole barriers range from 0.2-0.44 Ryd (2.5-6 eV). Their large magnitude is a reflection of the large cell boundary electron densities for these metals.
TL;DR: In this paper, the authors presented a detailed calculation of the transition temperature of a model filamentary excitonic superconductor, consisting of a linear chain of transition-metal atoms to which is complexed a ligand system of highly polarizable dyelike molecules.
Abstract: We present a detailed calculation of the transition temperature of a model filamentary excitonic superconductor. The proposed structure consists of a linear chain of transition-metal atoms to which is complexed a ligand system of highly polarizable dyelike molecules. Calculations of the electronic properties and experimental data on related materials are used to estimate the strength of the excitonic interaction, Coulomb repulsion, and band structure. From this the superconducting transition temperature was calculated by integration of the gap equation. For the particular structure proposed, transition temperatures of several hundred degrees are calculated. However, we find superconductivity only in those systems where the excitonic medium is within a covalent bond length of, and completely surrounds, the conductive spine. This imposes severe constraints on the structure of any excitonic superconductor. We show that for the structure proposed the momentum dependence of the exciton interaction results in the superconducting state being favored over the Peierls state and in vertex corrections to the electron-exciton interaction which are small.
TL;DR: In this paper, double source differentiated photocapacitance (DSDP) is proposed to detect hole and electron optical emission in a single spectrum. But the authors do not consider the effects of long time constants which could be masked by slow drifts.
Abstract: A photocapacitance technique which allows rapid characterization of deep traps in a semiconductor is described. Continuous illumination with light of photon energy slightly below the band gap provides for the occupation of a trap level by both holes and electrons, and at the same time reduces the time constants associated with population changes to typically 0.1 sec. The first feature enables both hole‐emission and electron‐emission processes to be detected in a single spectrum and the second eliminates the effects of long time constants which could be masked by slow drifts. Sharp features due to individual traps are displayed by electronic differentiation with respect to energy of the photocapacitance signal. Thus we refer to the technique as double source differentiated photocapacitance (DSDP). Our data for deep levels in GaAs show that the variation of cross section with respect to energy is much more rapid than described by the frequently applied Lucovsky theory. This effect can be understood in terms of band structure throughout the reduced zone, as is more appropriately considered for very deep levels. Characteristic differences of the trap distribution for GaAs grown under different conditions are described. A series of traps less than 0.6 eV above the valence band in vapor‐phase epitaxial material are not observed in liquid‐phase epitaxial material. A strong feature representing a trap ∼0.65 eV below the conduction band mainly in vapor epitaxial material is associated with chromium. It clearly demonstrated that the transitions detected in this optical cross‐section DSDP experiment relate not precisely to the band edge, but to points higher in the bands, influenced by the detailed density of states. We find the complementary energies, of peak hole and electron optical‐emission processes in the derivative spectra of a given very deep level, total ∼1.9 eV, considerably greater than the minimum (direct) band gap of GaAs and expected value from the Lucovsky model.
TL;DR: In this paper, the γ-decay of high-spin levels in 190, 192, 194 Pt is observed when Os targets are bombarded with α-particles with energies between 23 and 51 MeV.
TL;DR: In this article, an electronic band structure model for the organic charge transfer complex HMTSeF-TCNQ was constructed for the semi-metallic under pressure down to the lowest investigated temperatures.
TL;DR: In this article, the energy loss spectra of 75 keV electrons transmitted through thin evaporated foils of heavy rare earths (Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) in three different chemical states (metal, hydride and oxide) exhibit two main peaks due to collective plasmon excitations in the 10-17 eV energy range and to inner 5p excitations between 30 and 40 eV.
Abstract: 2014 The energy loss spectra of 75 keV electrons transmitted through thin evaporated foils of heavy rare earths (Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) in three different chemical states (metal, hydride and oxide) exhibit two main peaks due to collective « plasmon » excitations in the 10-17 eV energy range and to inner 5p excitations between 30 and 40 eV. A quantitative analysis of the intensity spectral distribution allows one to calculate the energy loss function and, through a KramersKrönig inversion, the dielectric constant and the dipole oscillator strength. Various results are then explained in terms of band structure, so that we are lead to propose a simple model for the interband transitions occuring in oxides. LE JOURNAL DE PHYSIQUE TOME 37, AVRIL 1976, Classification Physics Abstracts 2.820 8.800 8.120
TL;DR: In this article, angle-resolved uv photoemission spectra (UPS) of the (110) surface of GaAs were used to study the dispersion information about occupied states and thus to discriminate between surface and bulk transitions.
Abstract: Synchrotron radiation was used to study the angle‐resolved uv photoemission spectra (UPS) of the (110) surface of GaAs. The wide photon energy continuum (hν<30 eV) coupled with 40 angular resolution permitted the identification of two occupied surface states, centered at ∠−1 and ∠−7 eV measured from the valence band (VB) maximum. These states have not previously been observed in photoemission experiments due to their degeneracy with the bulk VB emission. The relatively new technique of angle‐resolved UPS enables one to obtain dispersion information about occupied states and thus lends itself to discriminating between surface and bulk transitions. Since the parallel component of the electron’s momentum is conserved upon leaving the sample, portions of the occupied surface band structure could be identified and mapped out. These were found to be in qualitative agreement with the dispersions predicted by Joannopoulos and Cohen. Sensitivity of the emission to surface contamination served as a test of their su...
TL;DR: In this paper, the magnetic entropy of NiS 2 is shown to be smaller than that of a localized spin 1 and is in good agreement with that expected for the magnetic moment observed by neutron diffraction.
Abstract: Specific heats of FeS 2 -CoS 2 -NiS 2 Solid solutions and of Ni 0.95 Cu 0.05 S 2 have been measured from 10 K to 350 K. Debye temperatures, coefficients of electronic contribution γ, magnetic ordering temperatures, and magnetic entropies have been determined. The magnetic entropy of ferromagnetic Fe 1- x Co x S 2 is proportional to cobalt concentration and is 40% of that expected for a localized spin 1/2 per Co atom, suggesting an itinerant character of e g electrons. The magnetic entropy of NiS 2 is smaller than that of a localized spin 1 and is in good agreement with that expected for the magnetic moment observed by neutron diffraction. The magnetic entropy of antiferromagnetic Co 1- x Ni x S 2 Suggests that only Ni atoms have magnetic moment in Ni-rich phase. The density-of-states curve of e g band for NiS 2 has been constructed from γ values assuming a rigid band. The band width of lower half of e g band is 0.6 eV. The Debye temperature decreases monotonously from 605 K of FeS 2 to 455 K of NiS 2 .
TL;DR: In this article, the energy bands of an ordered alloy Fe 3 Al both in paramagnetic and ferromagnetic state are calculated by the symmetrized augmented plane wave (SAPW) method.
Abstract: The energy bands of an ordered alloy Fe 3 Al both in paramagnetic and ferromagnetic state are calculated by the symmetrized augmented plane wave (SAPW) method. There are two types of iron atoms (Fe(I) and Fe(II)) in ferromagnetic state with a different value of the magnetic moment. The density-of-states of Fe(I) which has eight iron atoms as its nearest neighbors is different from that of Fe(II) which is surrounded by four iron atoms and four aluminum atoms. The former density is quite similar to that of iron metal, but the latter is considerably different. The d -bands of majority spin electrons mostly lie below the Fermi level, whereas those of minority spin electrons are extended across the Fermi level. The values of magnetic moments calculated for Fe(I) and Fe(II) are in good agreement with experimental values. The difference between magnetic moments on the atom Fe(II) and on Fe atom in iron metal seems to be attributed to the change of the density-of-states near the top of the d -bands. It is evident...
TL;DR: In this article, the elastic constants of metallic (Ti1-xVx)2O3 differ from those of semiconducting (Ti2-O3) Ti1-Vx 2O3 due to vanadium impurity.
TL;DR: In this article, a Hartree-Fock treatment of the regular chemisorption of hydrogen on a graphite monolayer in a crystalline orbital NOO approximation is presented.
Abstract: A Hartree–Fock treatment of the regular chemisorption of hydrogen on a graphite monolayer in a crystalline orbital NOO approximation is presented. The computational problems concerning the full exploitation of the point symmetry of the lattice, as well as the integration procedures are the same as encountered in a corresponding ab initio treatment. Three different cases have been considered, corresponding to the chemisorption of one hydrogen atom per unit cell: (A) above alternate carbon atoms; (B) above the center of a C–C bond; (C) at the center of a carbon ring. Bound states are found to occur only for cases A and B. The electronic features of the adsorbent–adsorbate system are appreciably differentiated. Such differences are discussed by using energy band structures and total and partial density of states spectra.
TL;DR: In this paper, the role of charge transfer in the order-disorder transition of CsCl type structure transitional alloys such as VMn, TiFe and ScCo is investigated.
Abstract: Intra- and inter-atomic Coulomb interactions have been accounted for in the band theory of the order-disorder transition in binary alloys. The variation of the energy levels of the two kinds of atoms on the two sublattices is determined self-consistently using an extension of the coherent potential approximation (CPA). As an application, the authors investigate the role of the charge transfer in the order-disorder transition of CsCl type structure transitional alloys such as VMn, TiFe and ScCo.