bluuebunny/crossref_metadata_2025_split huggingface dataset:
Penn‐like model calculations application to hydrogenated amorphous silicon films prepared by glow discharge
Authors: Ravindra N. M. , Ance C. , Ferraton J. P. , Donnadieu A. , Robin S. 
Published: July 2007

AbstractRecent model calculations are studied of Ance et al. concerning the valence electron density and hydrogen concentration in hydrogenated amorphous silicon films prepared by glow discharge decomposition of silane. This study is essentially necessitated by the fact that the model of Ance et al. yields values of Penn gap which are fairly large when compared to energies corresponding to peaks in the spectra of the imaginary part of the dielectric constant. Also a method is proposed to evaluate the density of the films. The densities hence determined are shown to be in accord with available experimental data. In the passing, results of the electronic polarizability of these films are also reported.
Study of energy band parameters in p‐type Ge0.9Si0.1 alloys
Authors: Takeda K. , Maeda Y. , Ohta E. , Sakata M. , Kido G. , Miura N. 
Published: July 2007

AbstractThe electronic properties of Ge0.9Si0.1 are investigated by cyclotron resonance, optical absorption, and galvanomagnetic measurements. The cyclotron effective masses are determined for light and heavy holes and interpreted using the band structure theories of group IV semiconductors including the subband interaction. The temperature dependence of the mobility of holes is obtained both by Hall effect and cyclotron resonance. The optical phonon energy involved in the indirect transition is also obtained by intrinsic absorption spectra.
Intrinsic recombination in dependence on doping concentration and excitation level application to lead chalcogenides
Authors: Mocker M. , Ziep O. 
Published: July 2007

AbstractOn the base of anisotropic and parabolic band structure recombination rates are calculated for the mixed crystals Pb0.78Sn0.22Te and PbS0.1Se0.9 in dependence on non‐equilibrium carrier concentration δn up to 1020 cm−3 in a wide range of temperatures and doping levels. Degeneracy causes different changes of lifetimes or recombination rates for material with different activation energies of the recombination process. Both, weakening or strengthening of the known n2p‐law of the Auger transition rate can occur at beginning degeneracy. At δn > 1019 cm−3 always sublinear behaviour should be observed. For radiative recombination a weakening of the np‐law is obtained generally; in the limit δn > 1019 cm−3 the rate behaves like (δn)4/3.
Study of thermophysical and anharmonic properties of fluorite compounds
Authors: Singh R. K. , Pandey N. K. 
Published: July 2007

AbstractAn extensive study is made of thermophysical and anharmonic properties of fluorite compounds using an interionic potential, which consists of a long‐range Coulomb and three‐body interactions and the short‐range overlap repulsion and van der Waals attraction. The agreement achieved between experimental and the theoretical results on third‐order elastic constants and pressure derivatives of second order elastic constants are generally better than those obtained by others. This potential succeeds in predicting various thermophysical properties, like compressibility and its pressure and temperature derivatives, thermal expansion and Grüneisen parameters of seven crystals of fluorite structure.
Role of the electron scattering processes in the Hubbard model in the insulator‐to‐metal transition
Authors: Kalra M. L. 
Published: July 2007

AbstractThe role of the spin disorder scattering and dynamical processes in the Hubbard model in the insulator‐to‐metal transition is investigated at finite temperatures. An explicit expression for the dc conductivity is obtained by studying the two particle double time retarded Green function by the equation of motion method. Frequency and temperature dependence of the conductivity is discussed in detail. It is found that the system exhibits a continuous insulator‐to‐metal transition with increasing temperature. The conductivity changes by a considerable factor around transition temperature. The results obtained can be applied to explain the electrical properties of transition metal oxides and other compounds which show the continuous insulator‐to‐metal transition.
Absorption, fluorescence, and excitation spectra of thallium‐activated rubidium bromide
Authors: Sharan V. B. 
Published: July 2007

AbstractAbsorption, excitation, and fluorescence spectra of polycrystalline RbBr: Tl phosphors are presented at various thallium concentrations. For very low thallium content two absorption bands are obtained peaking at 224 and 260 nm. Additional absorption bands appear around 230, 244 267, and 278 nm with rise of thallium content. An asymmetric fluorescence band in the ultraviolet region is obtained at low thallium concentration which can be resolved into two Gaussian emission bands peaking at 317 and 365 nm. Two additional visible fluorescence bands appear at 440 and 535 nm with rise of thallium content. The excitation spectra for the ultraviolet and visible emission bands are found to be different. Accordingly the ultraviolet emission band is attributed to the characteristic A‐emission in Tl+ monomer entering substitutionally and the visible bands are attributed to dimer centers having D4h site symmetry.
Study of electronic structure of reduced TiO2 and VxTi1−xO2 crystals by ESCA and optical absorption
Authors: Sakata K. 
Published: July 2007

AbstractAn analysis is made of optical absorption spectra and electron spectroscopy for chemical analysis (ESCA) on pure TiO2, reduced TiO2, and VxTi1−xO2. It is found that in the reduced TiO2, the Ti ion takes the variable valence states, Ti4+, Ti3+, and Ti2+, and they form a broad donor band, which overlaps with the conduction band originating from Ti4s levels. 3d–4s mixing results in a large change of the conductivity of TiO2 from insulator to metal depending upon the degree of reduction. In TiO2 doped with V, which behaves like a free ion, the excess 3d electrons of the V ions form impurity level just above the O2p valence band. In the reduced VxTi1−xO2, four different valence states, Ti4+, Ti3+, Ti2+, and V4+, are found and this accounts for the narrow optical gap of this material.
On the elastic anisotropy of ferroelectric triglycine selenate
Authors: Khanna S. K. 
Published: July 2007

AbstractThe numerical values of the elastic constants C11, C22, C33, C15, C35, C55 are determined experimentally by using an acousto‐optical method. Results are reported of the anisotropy of the velocity of 10 MHz ultrasonic waves in the direct vicinity of the phase transition temperature. It is observed that in the ferroelectric phase the velocity rises with a rotation of the sound wave vector by 2 to 4° with respect to the z‐axis in the Y–Z plane. On the other hand these critical anomalies of velocity are found to follow an identical logarithmic behaviour in the paraelectric phase. The results are discussed on the basis of Landau theory but at the same time taking into account the long range dipole–dipole interactions as well as the fluctuations of the order parameter. The correlation parameter is estimated from the temperature dependence of the elastic coefficient in the paraelectric phase (δ = 0.2 × 10−16 cm2).
Generalized pseudoatom model of inhomogeneous systems and its application to a simple‐metal surface
Authors: Streitenberger P. 
Published: July 2007

AbstractGeneral expressions in real‐space representation are derived for charge density, total energy, and Hellmann‐Feynman forces on an ion. They represent a uniform and systematic extension of the pseudoatom or pair‐potential model to highly inhomogeneous electron–ion systems. Modifications appear in form of non‐central pair potentials and additional one‐body potentials arising from the screening in the inhomogeneous electron gas. The corresponding self‐consistent charge density results from the superposition of overlapping non‐spherical pseudoatoms and an additional charge density that is mainly localized in the defect region. A first application to the simple‐metal surface is given where some general results within the jellium model are obtained.
Reaction field approximation for inhomogeneous ferromagnets
Authors: Wojtczak L. , Balcerzak T. 
Published: July 2007

AbstractThe reaction field approximation method for inhomogeneous magnetic systems is extended. The Curie temperature of inhomogeneous samples is calculated on the basis of the perturbation theory. As a result the shift of the Curie temperature is obtained with respect to the value of the Curie temperature for an effective crystalline structure. A comparison of the results with those following from other methods shows that the accuracy of the presented method is the same as the cluster method and is much better than the molecular field approximation.
Determination of the correlation between the crystal field axis system and the crystallographic axes in chromium‐doped β‐Ga2O3 by EPR
Authors: Gunsser W. , Rohwer K. 
Published: July 2007

AbstractThe correct relationship is found between the crystal field axes and crystallographic axes in β‐Ga2O3 by application of a simplified orientation method. A computer program is set up, which is able to calculate and to plot the angular variation of the resonance field strengths and of the energy levels involved in EPR. In this way, the strange angular dependence of the EPR lines can be explained and the correctness of the stated correlation between the two axis systems can be verified. From the measured resonance fields a set of spin Hamiltonian parameters is calculated.
Exciton–phonon interaction in crystalline and vitreous SiO2
Authors: Godmanis I. T. , Trukhin A. N. , Hübner K. 
Published: July 2007

AbstractAn investigation of the Urbach rule in crystalline SiO2 (α‐quartz), crystalline SiO2Ge, and vitreous SiO2 in the framework of the models of Dow and Redfield and of Toyozawa shows that the fundamental optical absorption edge of SiO2 is determined by strong exciton–phonon interactions. In the crystalline and vitreous SiO2 low‐energy excitons with E = 9.1 eV (α‐quartz) and E = 8.7 eV (glass) interact mainly with longitudinal optical phonons. In the crystalline SiO2Ge alloy the interaction with phonons is realized by excitons localized on germanium impurities. The exciton–phonon interaction in SiO2Ge and vitreous SiO2 is stronger than in crystalline SiO2 due to the higher degree of localization of low‐energy excitons in these disturbed SiO2 forms. The strong exciton–phonon interaction leads to a momentary self‐trapping of the low‐energy excitons in crystalline and non‐crystalline SiO2 and to a corresponding relaxation of the SiO2Ge excitons localized on Ge impurities. Numerical values of the fundamental exciton parameters are deduced and discussed.
Low‐frequency secondary radiation in polar semiconductors at finite temperature
Authors: Comas F. , Giner C. Trallero 
Published: July 2007

AbstractSecondary radiation in polar direct–gap semiconductors is considered for finite, but not too large, temperatures. For sufficiently pure and perfect samples, photoexcited electrons (holes) relax via phonon scattering. Assuming an infinite recombination time, the differential cross‐section for photon emission is calculated in the low‐frequency region of the spectra. Rather intense secondary radiation is predicted for high temperatures. The general shape of emission and excitation spectra is discussed in detail.
Investigation of asymmetrical grain boundaries and their coincidence site lattices
Authors: An Nguyen , Herrmann R. , Worm G. 
Published: July 2007

AbstractThe subject of this paper is a method for the examination of asymmetrical grain boundaries with randomly directed axes of rotation. In so far as the axis of rotation lies in a plane of symmetry of the crystal the geometrical relation between symmetrical and asymmetrical grain boundaries is shown. The CSL Bravais cells corresponding to asymmetrical grain boundaries and the facet angles for the considered grain boundaries are calculated.
Decay behaviour of high‐excitation luminescence in GaP:N. I. Model for the decay of two coexisting phases
Authors: Weinert H. 
Published: July 2007

AbstractThe time behaviour of the radiative recombination of nitrogen‐doped GaP is investigated at pulsed intense optical excitations and low temperatures (T = 2 and 27 K). The decay behaviour of the luminescence intensities corresponding to the electron–hole liquid (EHL) and the coexisting lowdensity phase (LDP) is found for all nitrogen concentrations (nN = 2 × 1017 to 2.9 × 1018 cm−3) to be nonexponential. It is interpreted as a consequence of interactions between both coexisting phases. A model is introduced where the EHL is fed by the LDP continuously. It describes the observed decay of the luminescence very well, even for different nitrogen concentrations and different excitation intensities.
Theory of the verwey transition in the mixed valence compound Eu3S4
Authors: Ihle D. , Lorenz B. 
Published: July 2007

AbstractThe Verwey transition in Eu3S4 at TV = 186 K is explained on the basis of a model which takes into account the Coulomb interaction of the extra 4f electrons at the Eu2+ ions and the formation of small polarons due to the interaction with phonons. This model is treated in the Hartree and cluster variation approximations. At TV a first‐order Verwey transition is obtained. The magnitude of the observed entropy change at TV is explained. Above TV the polarons are found to be considerably short‐range ordered.
The electrical resistivity of short‐range ordered alloys and its temperature dependence
Authors: Richter J. , Schubert G. 
Published: July 2007

AbstractThe electrical resistivity R of short‐range ordered binary alloys with b.c.c. structure is calculated using the force‐force correlation function scheme in the weak‐scattering limit. For the description of short‐range order for temperatures above the critical temperature the theory of Clapp and Moss is applied yielding the Fourier transform of the Cowley short‐range order parameters in dependence on the interatomic potential, the concentration and the temperature. In AB ordering alloys the short‐range order causes a decrease of the resistivity R in comparison with the totally stochastic alloy and a positive temperature coefficient (1/R) dR/dT. In clustering alloys the atomic short‐range order increases the resistivity and yields negative (1/R) dR/dT. This qualitative relation between R and (1/R) dR/dT is in agreement with Mooij's rule. Furthermore the short‐range ordering causes characteristic deviations from the Nordheim behaviour.
On the role of the soliton mechanism in the electron transfer along the quasi‐one‐dimensional molecular structures
Authors: Satarić M. , Žakula R. 
Published: July 2007

AbstractAn expression for the probability of electron transfer from a donor molecule (D) to an acceptor molecule (A) along a quasi‐linear molecular chain (biopolymer), to which D and A are attached is derived. Investigated is the case with an indirect interaction caused by modification of Coulomb interaction due to electron transition from D to A and vice versa via a periodical structure, in addition to the direct, resonant interaction of D and A. The indirect interaction may lead to the electron capture by a soliton wave. The one‐way transfer of an electron caused by relaxation phenomena for the dynamical system in contact with a thermostat (T = 0 K) is discussed.
Raman scattering in GeS single crystals at low temperatures
Authors: Vorlíček V. , Gregora I. , Chvostová D. 
Published: July 2007

AbstractThe Raman spectra of GeS single crystals are investigated in the temperature interval 20 to 300 K. The possible origin of new features observed at low temperatures is discussed. A new assignment of the off‐diagonal B1g and B3g modes is proposed.
Optical properties of K2SeO4 in the vicinity of phase transitions
Authors: Pačesová S. , Březina B. , Jastrabík L. 
Published: July 2007

AbstractThe temperature dependence of the absorption edge of K2SeO4 is measured in the range 300 to 4.2 K. In this temperature range the dependence of the absorption coefficient on the energy of photons and temperature is described by Urbach's rule. The magnitudes of the band gap obtained are E∥ = 6.06 and E⟂ = 6.14 eV for light polarized parallel and perpendicular to the a‐axis. The temperature gradient of the band gap (∂E/∂T)∥, ⟂ reveals a jump at the paraelectric‐incommensurate phase transition T2 = 129.5 K for both polarizations of incident light in agreement with the second‐order nature of the phase transition. In the paraelectric phase, phonons with eigenfrequencies ω∥ = 218 cm−1 and ω⟂ = 181 cm−1 are interacting with the optical transitions. A switch‐over to the optical phonon of frequency ω∥,⟂ = 92 cm−1 is observed at T2 together with the change of the electron‐optical‐phonon coupling constants indicating the increase of the ionic character of the bonds in the incommensurate phase between the K+ ions and the (SeO4)2− tetrahedral groups.
On the two‐site spinless Falicov‐Kimball model with hybridization
Authors: Zieliński J. , Kowalska J. 
Published: July 2007

AbstractThe exactly solvable two‐site extended Falicov‐Kimball model is considered. It is shown that the increase of hopping energy lowers the tendency to an abrupt change of the average occupation number of f‐electrons. Some thermodynamic quantities are evaluated. The results are used for the alloy analogy coherent potential approximation treatment of the periodic model.
Far ultraviolet photoelectric study of thin SnSe evaporated films
Authors: Bennouna A. , Tessier P. Y. , Priol M. , Dang Tran Q. , Robin S. 
Published: July 2007

AbstractEnergy distribution curves of photoemitted electrons are obtained for SnSe thin polycrystalline films in the 10 to 40 eV energy range. The method of preparation of the sample under ultrahigh vacuum conditions is described and the synthesis of the initial material. The quality of the sample is checked by Auger analysis which reveals a weak reactivity of the material. The EDC's show structures appearing at 0.9, 2.1 to 2.7, 3.9, 7.4 eV below the top of the valence band. Also the Sn 4d levels are investigated. The 4d(5/2) is found at 24.3 eV and the 4d(3/2) at 25.3 eV below the top of the valence band. Structures in the EDC's are compared with those of existing similar works and are interpreted by means of theoretical bands scheme.
Screening of electrostatic fields in crystalline semiconductors by electrons hopping over defects
Authors: Poklonski N. A. , Stelmakh V. F. 
Published: July 2007

AbstractThe expression for the electrostatic field screening length is obtained and it is shown that the effective concentration of electrons hopping via defects is included both into the screening length and electrical conductivity. The quotient of the diffusion coefficient to the drift mobility for hopping electrons is found.
Self‐consistent embedded‐cluster calculations of the electronic structure of alkaline earth fluorides in the hartree‐fock‐slater approximation
Authors: Amaral N. C. , Maffeo B. , Guenzburger Diana 
Published: July 2007

AbstractMolecular orbital calculations are performed for clusters representing the CaF2, SrF2, and BaF2 ionic crystals. The discrete variational method is employed, with the Xα approximation for the exchange interaction; a detailed investigation of different models for embedding the clusters in the solids led to a realistic description of the effect of the neighbour ions in the infinite crystal. The results obtained are used to interpret optical and photoelectron data reported in the literature. In the case of CaF2, comparisons are made with existing band structure calculations.
Picosecond reflectivity measurements on glow discharge a‐Si: H
Authors: Bergner H. , Brückner V. , Dietrich D. , Kerstan F. , Nowick W. 
Published: July 2007

AbstractThe temporal behaviour of photoinduced charge carriers in amorphous hydrogenated silicon films is studied by means of time‐resolved reflectivity measurements using a Nd:YAG laser. The investigated a‐Si:H films, deposited by the glow discharge technique under systematic variation of the silane—hydrogen pressure, show different structures and defects. The temporal behaviour of the non‐equilibrium charge carriers of all samples is determined by a two‐step relaxation process. In accordance with the model the photoexcited carriers relax from the conduction band to an intermediate state in the mobility gap and than to the ground state. The characteristic times of these relaxation processes are 30 to 85 ps and 0.75 to 2.5 ns, respectively. The influence of the structure of the a‐Si:H films on the relaxation times is discussed.
Model for optical absorption in transition metals containing d impurities
Authors: Parlebas J. C. 
Published: July 2007

AbstractThe effect of a ‘d’ impurity is investigated on the contribution to the optical absorption in a transition metal from electronic intra‐ and interband transitions. Within a tight‐binding approximation a previous calculation of the imaginary part ϵ2(ω) of the dielectric constant in simple models is extended to realistic multiband dilute alloys. The possibility is shown of exploring critical points in nickel host band structure, for example, by wave‐vector non‐conserving transitions induced by impurities, in relation with recent experimental data.
Amorphous problem in exafs data analysis
Authors: Ageev A. L. , Babanov Yu. A. , Vasin V. V. , Ershov N. V. , Serikov A. V. 
Published: July 2007

AbstractIt is shown that the radial atomic distribution function for disordered systems can, in principle, be determined from the oscillating extended fine structure of X‐ray absorption spectra using the regular algorithms of solution of incorrect problems. The radial atomic distribution function for Fe80B20, obtained from experimental EXAFS data and corresponding to the results of diffraction studies, is presented.
Polarized light absorption of the magnetic semiconductor CdCr2Se4
Authors: Edelman I. S. , Dustmuradov G. , Kononov V. P. 
Published: July 2007

AbstractThe absorption of polarized light in CdCr2Se4 thin films in the spectral region 10000 to 22000 cm−1 at different temperatures is investigated. Through the whole spectral region the absorption intensity differs for right‐handed and left‐handed circularly polarized light or for parallel and perpendicular linearly polarized light. The character of the temperature and polarization dependence of the absorption intensity is different for different parts of the spectrum. The observed absorption is considered as a sum of the interband transitions and the transitions between localized states.
Orthoferrite Dynamical Properties in the Vicinity of the Tricritical Point
Authors: Tarasenko S. V. , Medvedovskaya O. G. 
Published: July 2007

AbstractThe peculiarities are investigated of the behaviour characteristic of the components of the high‐frequency magnetic susceptibility tensor of the electronic spin subsystem considering and not considering the nuclear spin subsystem and also the amplification coefficient of the nuclear magnetic resonance and the shape of the curves of the resonance absorption of the electromagnetic energy in the vicinity of the NMR frequency.
Influence of Interaction Range on Computed Peierls Stress and Dislocation Displacement in B.C.C. Lithium
Authors: Beauchamp P. , Prevost J. 
Published: July 2007

AbstractThe simple form of interaction between [111] rows deduced from pseudo‐potential theory is used to compute the core structure, the Peierls stress and the glide plane of a a/2 [111] screw dislocation at 0 K in b.c.c. lithium. Particular attention is given to the influence of the cut‐off radius of the row interaction. It is found that the unstressed core structure and the stresses producing a movement of the dislocation are only weakly dependent on the cut‐off radius. The glide plane is either {112} twinning or {112} antitwinning depending on the range of row interaction so that one cannot forecast what it could be if interactions are taken into account completely.