bluuebunny/crossref_metadata_2025_split huggingface dataset:
On Theoretical Modelling of Continuously Inhomogeneous Semiconductor Structures
Authors: Henniger U. , Keiper R. 
Published: July 2007

AbstractStarting from Boltzmann's equation the system of particle and energy rate equations is derived und discussed for describing the carrier transport in continuously inhomogeneous semiconductors. Special attention is paid to the dependence of the Shockley‐Read‐Hall recombination rate on the carrier temperatures. The so obtained generalization of the net recombination rate takes into consideration the effects of local carrier heating or cooling. A comment to the standard conception of field dependent mobilities is given.
Effect of Magnetic Field on a Phase Slip Centre
Authors: Chashoo G. J. , Singh Y. 
Published: July 2007

AbstractThe effect of a magnetic field on nonequilibrium quasiparticle relaxation processes in superconductors is investigated. It is observed that the normal‐like length of the first phase slip centre (PSC) in an indium whisker gets much reduced under the influence of magnetic field for temperature near the critical temperature. This suggests that the number of PSC's in a whisker increases in presence of the magnetic field for I > Ic. The results are in agreement with the experimental data for tin.
Low‐Frequency Dielectric Response Function of Sodium Nitrate
Authors: Wyncke B. , Brehat F. , Kozlov G. V. 
Published: July 2007

AbstractThe far infrared and submillimeter dielectric function of sodium nitrate single crystal is determined by means of precise transmission spectroscopy (7 to 18 cm−1) and reflexion spectroscopy (10 to 600 cm−1) over the temperature range 20 to 275 °C, parallel and perpendicular to the crystallographic c‐axis. All the infrared active lattice modes are observed and their parameters calculated using the factorized form of the dielectric function. A relaxation is introduced to explain the low‐frequency dielectric function in the two directions.
Simple Dynamical Model for the Vibrations of the Halogen Crystals
Authors: Higgs J. F. , Anderson A. 
Published: July 2007

AbstractA simple force constant model is developed and applied to the vibrations of the chorine, bromine, and iodine crystals. Fundamental frequencies are calculated and compared to those observed by infrared absorption, Raman scattering, and inelastic neutron scattering. The dependence of the halogen–halogen force constants on atomic separation is investigated.
On the Interaction between a Screw Dislocation and Point Defects in B.C.C. Transition Metals
Authors: Masuda‐Jindo K. 
Published: July 2007

AbstractThe interaction energy Eint between a (1/2) 〈111〉 screw dislocation and point defects (both substitutional solutes and vacancies) in b.c.c. transition metals is investigated using a tight‐binding electronic theory. It is shown that the “chemical interaction” (d‐band energy contribution) plays a central role in determining the Eint values for the substitutional solutes in b.c.c. transition metals. The solid solution hardening of the dilute b.c.c. transition metal alloys is also discussed in the light of the present electronic theory; particular attention is paid to the solid solution hardening due to the transition metal impurities and due to sp impurities (such as Al, Si, Ge and Be) in α‐Fe.
The Para‐ and Ortho‐Phases of High‐Density Excitons in Cu2O
Authors: Moskalenko S. A. , Russu S. S. , Baltaga V. V. , Bobrysheva A. I. , Lelyakov A. V. 
Published: July 2007

AbstractThe quasiequilibrium state of the two‐component non‐linear ortho‐para‐exciton gas is investigated. The concentration shifts of the exciton levels are taken into account at high densities of quasiparticles. Three exciton phases appear at any value of the chemical potential, due to the effect of optical bistability: the para‐phase, the ortho‐phase and the mixed ortho‐para‐phase. It is pointed out that Bose‐Einstein condensation (BEC) in the para‐ and ortho‐phase is possible, in spite of the fact that the initial level of ortho‐excitons is situated higher on the energetic scale than the initial level of para‐excitons.
Influence of Magnetic Quantization on the Effective Electron Mass in Ternary Semiconductors
Authors: Mondal M. , Ghatak K. P. 
Published: July 2007

AbstractAn attempt is made to study the effect of a quantizing magnetic field on the effective mass in degenerate n‐type ternary semiconductors at low temperatures taking n‐Hg1−xCdxTe as an example. It is found on the basis of the three‐band Kane model, which is the most valid model for n‐Hg1−xCdxTe, that the effective electron mass at the Fermi level shows an oscillatory magnetic field dependence as expected since the origin of the oscillations in the effective mass in small gap semiconductors is the same as that of the Shubnikov‐de Hass oscillations. Besides, the amplitude of oscillations is significantly influenced by the alloy composition whereas the period is found to be independent of the compositional parameters in ternary semiconductors. The corresponding results for parabolic energy bands are also obtained from the expressions derived.
Thermal Stability of Fe+ Centres and Thermoluminescence of ZnS Single Crystals
Authors: Tarkpea K. E. , Ots A. 
Published: July 2007

AbstractESR and TL methods are used to investigate cubic ZnS single crystals. At 104 to 153 K in iron containing ZnS crystals, the TL is shown to be connected with the thermal ionization of Fe+ centres according to the reaction Fe+ + kT → Fe2+ + e−. Various thermal stabilities of Fe+ centres are supposed to be conditioned by crystal field distortions around the Fe+ ion. The character of the distortion is determined by the high‐temperature heating conditions and the cooling rate of ZnS crystals. The activation energy of Fe+ centres is estimated.
Harmonics of Cyclotron and Cyclotron–Phonon Resonances in Semiconductors with Superlattice
Authors: Polyanovskii V. M. 
Published: July 2007

AbstractThe harmonics of cyclotron and cyclotron–phonon resonances (CR and CPR, respectively) in semiconductors with a superlattice (SL) in the presence of strong magnetic field, H, arranged parallel to SL axis, are studied based on quantum kinetic equation. The peculiarities of CR and CPR reveal themselves most explicitly with electromagnetic wave E(t) polarized transversely to H. This leads to sudden changes in the dependence of the absorption coefficient against incident light frequency. These sudden changes are shifted relative to the peaks of respective resonances by a miniband‐width. At E(t) ∥︁ H the sudden changes are absent and maxima of CR and CPR are defined less explicitly. In SL the maxima of CR and CPR as well as the sudden changes can manifest themselves in a rather weak magnetic field, while the respective quantum oscillations in conventional semiconductors are not revealed.
Raman and Infrared Spectra of Tellurium Sub‐Bromide (Te2Br)
Authors: Anastassakis E. , Raptis J. S. , Richter W. 
Published: July 2007

AbstractRaman and IR spectroscopic techniques are used to study the long‐wavelength optical phonons of tellurium sub‐bromide (orthorhombic structure). By use of an appropriate range of temperatures and excitation wavelengths the frequencies for nearly all of the A2 and B2 q ≈︁ 0 optical phonons are determined. Oscillator strengths and LO‐frequencies for these phonons are obtained from the fitting of IR reflection spectra with a multiple oscillator model. The temperature dependence of the frequency and damping constant for some of these phonons is discussed. A remarkable feature of this material is the existence of low frequency (≈︁ 20 cm−1) phonons with extremely large polarizabilities (Δχ up to 150).
Energy Spectrum of the Cross Motion of Excitons in a Superlattice
Authors: Guseinov R. R. 
Published: July 2007

AbstractOn the basis of the exact expression for the potential of a point charge in a superlattice, consisting of alternating layers with two different values of the dielectric constant, the energy spectrum is found of an exciton motion, perpendicular to the superlattice layer direction, at small values of the exciton quasi‐momentum component parallel to the layer plane. An evident form of an exciton energy dependence on the cross component of quasi‐momentum which is perpendicular to the layer plane is adduced. The exciton energy has a maximum at the centre of the Brillouin zone of the cross quasi‐momentum and a minimum at its boundaries.
On the Microscopic Theory of the Resonant Nonlinear Refractive Index of InSb
Authors: Dat Nguyen Nhu , Van Hieu Nguyen 
Published: July 2007

AbstractA new version is presented for the microscopic theory of the resonant intensity dependence of the refractive index of a narrow gap zincblende semiconductor InSb. A general formula is derived to include the contributions from both the mechanisms: the free charge carrier plasma and the dynamical Burstein‐Moss effect. The electron and hole distribution functions are determined by means of the transport equation.
Resonance Interaction between Impurities and Crystal Molecules. Application to Benzselenophene in Naphthalene
Authors: Brovchenko I. V. , Ostapenko N. I. , Shpak M. T. , Valkunas L. L. , Vektaris G. B. 
Published: July 2007

AbstractTheoretical and experimental investigations of resonance hybridization between impurity and local states are carried out in naphthalene with benzselenophene impurities. The analysis of the vibron regions of the luminescence and absorption spectra of this system shows that the hybridization effect really takes part in such a system and there are two centres with impurities being in non‐equivalent positions. Moreover each impurity perturbs two molecules of the crystal. The matrix elements of the resonance interaction between impurity and crystal molecules are given.
The Energy of Shallow Donor States in CdTe, GaAs, AgCl, AgBr Semiconductors
Authors: Grinberg M. , Łęgowski S. , Męczyńska H. 
Published: July 2007

AbstractThe model given by Bajaj of the energy levels of shallow point defects is modified introducing wave‐vector dependent dielectric functions. In the coupled polaron Hamiltonian the electron–ion interaction is described by the potential screened by the dielectric function. The electron–phonon interaction depends on the dielectric function too. The obtained energies of the ground and first excited states reproduce quite well the experimental data.
Photostimulated Reorientation of AsO Centres in Alkali Halides
Authors: Lohmeier F. J. 
Published: July 2007

AbstractMolecular arsenite centres in alkali halides show a photostimulated reorientation after excitation to different excited electronic states. The temperature dependence of the reorientation rates is determined. The rates are described in terms of phenomenological rate equations, considering thermal reorientation processes in the electronic ground and excited state. The reorientation parameters for thermally stimulated reorientations are determined for the ground and the excited 3B1 state. The low‐temperature photostimulated reorientation, which results from a strong linear electron‐phonon coupling, mainly takes place during the relaxation from the 3B1 triplet to the 1A1 ground state and is supposed to occur via the A2(τx) sublevel from which a radiative decay is symmetry‐forbidden.
Computing Method of Elastic Moduli and Young's Modulus for Texturized Materials with Hexagonal Crystal Symmetry
Authors: Kalvoda L. 
Published: July 2007

AbstractA calculation method of the generalized Reuss, Voigt, and Hill approximation of the elastic moduli and the Young modulus for rolled polycrystalline materials with hexagonal crystal symmetry is presented. The method proposed is based on the knowledge of the coefficients of the generalized spherical harmonic expansion for the crystallite orientation distribution function. The method is demonstrated by computing a cold rolled Zr sheet.
Fast‐Ion Conduction in the Presence of a Lattice Phase Transition
Authors: Bingham D. , Burton C. H. 
Published: July 2007

AbstractA mixed pseudo‐spin 1/2 model of ionic conduction in the presence of a displacive phase transition of the lattice is derived from a consideration of the microscopic forces acting on the migrating ions. A phonon‐mediated interaction between the ions entering into the lattice transition and the mobile ions results in a number of phase transitions in the mobile ion order parameter 〈Sz〉. These are correlated with the ionic conductivity. A search is suggested for a material displaying the required properties and some possible advantages of such a material are discussed.
A Theoretical Study of the Vibrational Properties of InxGa1‐xAs1‐ySby Quaternary Alloys
Authors: Kleinert P. 
Published: July 2007

AbstractFirst theoretical investigations of the lattice dynamics of InxGa1‐xAs1‐ySby quaternary semiconducting alloys are presented. All corresponding pseudobinary end member components are known to exhibit mixed‐mode behaviour. Within a mean‐field approximation a Bethe lattice is self‐consistently constructed in such a way that for all mixed ternary end member compounds the results of the coherent‐potential approximation (CPA) are reproduced. Special results are obtained for the dielectric susceptibility spectra, which display only one dominant band for mixed quaternaries mainly containing GaAs but two bands for systems which contain mainly InSb. With respect to an interchange between x and y the lineshape of the spectra is nearly unchanged.
Phonon Scattering by Inhomogeneously Distributed Paramagnetic Ions
Authors: Toombs G. A. , Sheard F. W. 
Published: July 2007

AbstractThe Green function for phonons scattered by an inhomogeneous distribution of resonant centres is evaluated. A diagrammatic expansion in two parameters is used: the coupling strength and α, the ratio of the resonant phonon wavelengths to the characteristic wavelength for the distribution of scatterers. For small values of α, a spatially dependent local dispersion and damping of the phonons is obtained. The effect on the linewidth for inelastic neutron scattering is discussed.
Specific Heat and Magnetic Susceptibility Studies on Bromobis (1,4‐Diazacycloheptane) Copper(II) Perchlorate, [Cu(dach)2Br](C104), at Low Temperatures
Authors: Khattak G. D. , Hussain M. S. , Hunter G. W. , Wenger L. E. 
Published: July 2007

AbstractSpecific heat and magnetization investigations are made on polycrystalline [Cu(dach)2Br](Cl04) at low temperatures. For temperatures above 25 K, the dc magnetization shows a Curie‐Weiss behaviour with a Curie constant of 7.92 × 103 e.m.u. K/g and a paramagnetic Curie temperature of −60.8 K. The downturn of 1/X vs. T below 25 K is indicative of ferrimagnetic system. The specific heat between 4 and 8 K can be described by the relation: C = 11.9T3 mJ/mol K with the cubic term leading to a Debye temperature of θD = 194 K. Below 4 K the specific heat rises very rapidly suggesting magnetic ordering. This is substantiated by the presence of a sharp peak at 0.95 K in the ac susceptibility results which can be interpreted as being due to a ferrimagnetic phase transition. Both the magnetization and specific heat investigations indicate the behavior of the system to be ferromagnetic at low temperatures which is interpreted as the result of the canted antiferromagnetism of sublattice moments.
Wavelength‐Modulated Spectra of the Optical Properties of β′‐CuxZn1−x from 1.5 to 5.1 eV at the β′ ⇄ α + β′ Phase Transition
Authors: Stearns R. , Braunstein R. , Muldawer L. 
Published: July 2007

AbstractWavelength‐modulated derivative spectra of the reflectivity of β'‐CuxZn1‐x are determined between 1.5 and 5.1 eV for compositions near the β' ⇄ α + β' phase transition. The alloys are annealed and quenched in the β' phase on both sides of the phase transition. Both the intraband and interband properties show marked changes at the transition. The Drude effective mass increases dramatically for the β' phase in the region where α + β' composition is thermodynamically preferred, indicating flattening of the bands. Shifts in interband properties also show a marked change at the phase transition, with the conduction bands showing a much greater sensitivity than the d‐bands.
Simple Model Calculations for Optical Constants of Copper
Authors: Ahuja A. K. , Auluck S. , Joshi S. K. 
Published: July 2007

AbstractA simple s‐d band model is used for the interpretation of ϵ2(ω) for copper. Fitting simple polynomials for transition matrix elments, analytical expressions are obtained for ϵ2(ω) in terms of band parameters of the s‐d model. This expression is used to study the effect of matrix elements and variation of relaxation energy on ϵ2(ω) of copper. It is shown that such a simple model is sufficient to study such a variation and, therefore, to study the qualitative variation of ϵ2(ω). The model is also used to explain the peaks in dϵ2(ω)/dω curve successfully. The effect of hybridization amongst s and d bands is also taken into account for the calculation of transition matrix elements and the resulting effects in ϵ2(ω) are calculated.
Relativistic Theory of Photoemission from Solids II. Fully Dynamical One‐Step Formulation
Authors: Braun J. , Thörner G. , Borstel G. 
Published: July 2007

AbstractA fully dynamical one‐step theory of photoemission is presented. The present model is a relativistic generalization of the original non‐relativistic work due to Pendry and allows for calculating theoretical ultraviolet photoemission and bremsstrahlung isochromat spectra from non‐magnetic and ferromagnetic solids.
Many‐Body Theory for the Dense Exciton Gas of Direct Semiconductors II. Calculation of Exciton Level Shift and Damping in Dependence on Exciton Density
Authors: Boldt F. , Henneberger K. , May V. 
Published: July 2007

AbstractThe spectral properties of a dense exciton gas are discussed using an exciton self‐energy in second collisional Born approximation with respect to exciton‐exciton interaction. The shift of the continuum edge and the ls exciton as well as the increase of the damping of the ls exciton are calculated linearly in the exciton density. The distribution of ls excitons is assumed to be either a macro‐occupation of the k = 0 state or a Boltzmann distribution with effective temperature varying between 10 and 60 K. A weakening of the level shift is obtained with increasing temperature. In the case of macro‐occupation damping is calculated self‐consistently resulting in a sublinear dependence on density.
X‐Ray Photoelectron and Auger Electron Spectra of Cadmium Thin Films
Authors: Jewell B. E. , Halder N. C. , Swartz W. E. 
Published: July 2007

AbstractThe X‐ray photoelectron spectra (XPS) and Auger electron spectra (AES) are measured for Cd thin films deposited on microscopic glass slides by thermal evaporation at a pressure of 10−8 Torr. The deconvolution procedure is utilized with appropriate error control and response function for resolution and enhancement of the spectral lines. The binding energies of the valence and core orbitals are determined and the MNN transitions for the AES analyzed. The results of the present study indicate a reasonable agreement with the results for Cd metal.
Mössbauer Study of Two‐Electron Exchange between Neutral and Ionized Tin Donor Centers in Solid Solutions on the Basis of PbS and PbSe
Authors: Nasredinov F. S. , Prokofieva L. V. , Seregin P. P. , Zarubo S. V. , Ermolaev A. V. , Kurmantaev A. N. 
Published: July 2007

AbstractThe Mössbauer spectroscopy with 119Sn isotope shows that tin atoms in Pb1‐xSnxS and Pb1‐xSnxSe solid solutions are electrically active donor centers with charge states determined by acceptor impurities occuring in the solid solutions. The neutral state and the ionized one of the tin donor centers are identified as Sn2+ and Sn4+, respectively. A two‐electron exchange between the neutral and ionized tin centers is observed for the Pb1‐xSnxSe solid solutions doped with sodium and thallium acceptor impurities.
EPR of Mn2+ in Strontium Tartrate Trihydrate Single Crystals
Authors: Korkmaz M. , Aktaş B. 
Published: July 2007

AbstractElectron paramagnetic resonance spectra of Mn2+ doped in single crystals of strontium tartrate trihydrate grown by a diffusion technique are investigated at room temperature. Mn2+ enters the lattice substitutionally and is trapped at two magnetically equivalent but crystallographically inequivalent sites. The EPR measurements give the following values for the spin‐Hamiltonian parameters: gx(= gy) = 1.9781, gz = 2.0012, Ax(= Ay) = −94.9 × 10−4 T, Az = −96.2 × × 10−4 T, BB(= D/3) = +160.9 × 10−4 T, B(= E) = +101.2 × 10−4 T, B = +0.013 × 10−4 T, and B = +0.088 × 10−4 T.
Dielectric Screening, Polar Phonons, and Longitudinal Electronic Excitations of Quantum Well Double Heterostructures Application to Light Scattering from Charge Density Fluctuations
Authors: Bechstedt F. , Enderlein R. 
Published: July 2007

AbstractThe screened Coulomb potential and the inverse dielectric function of a quantum‐well double heterostructure (DHS) are expressed in terms of bulk dielectric functions. The spatial dispersion is fully taken into account. The polar LO‐phonon modes, longitudinal electronic modes, and coupled electron‐phonon modes of a DHS are derived from the poles of the inverse dielectric function. Emphasis is paid to phonon slab modes. The close relation between the screened Coulomb potential and the density‐density correlation function is used to calculate the Raman cross section for scattering from charge density fluctuations. In typical cases slab modes are essential for Raman spectra of DHSs and superlattices.
On the Relation between Stopping Power and Proton‐Induced Electron Emission for Intermediate Energies: Aluminum
Authors: Brauer W. , Rösler M. 
Published: July 2007

AbstractA theory is given of proton stopping power −dEo/dx in polycrystalline aluminum for energies between Eo = 40 and 800 keV corresponding to the calculation of proton‐induced electron emission. In good agreement with the experimental data a maximum of the stopping power (− dEo/dx)max = 13.9 eV/10−10m is obtained at E = 55 keV. The main contribution to the stopping power in the whole energy range is found to be the individual interaction between protons and valence electrons. Calculated and measured values of the 2p ionization cross section are proved to be in accordance. The averaged energy loss per collision ΔE0 turns out to be weakly dependent on the proton energy Eo. The validity of the empirical relationship between electron yield γ and stopping power is investigated.
Piezo‐Optical Activity of Cubic Crystals
Authors: Tsitsishvili E. G. 
Published: July 2007

AbstractEffects of the piezo‐optical activity in the cubic crystals are studied. It is shown that if the stress and the wave vector are directed along different fourfold axes polarisation plane rotation takes place, but only a “weak” gyrotropy may be observed at P ‖ [001] and q ‖ [110] (as well as at P ‖ {111} ⟂ q). It is shown that in the case of the crystals with a sufficiently high exchange splitting Δst the stress‐induced k‐linear term plays a dominant role. In the case of interband effect the bilinear term leads to the splitting of the spin‐degenerate subbands. In the exciton case there is a mixing of exciton states and it is shown that the optical activity is better observable for the Z3‐exciton.
Critical Currents in Type‐II Superconductors
Authors: Przełoźny Z. 
Published: July 2007

AbstractThe flux‐line lattice stability in the longitudinal and transverse problems is investigated within the Ginzburg‐Landau theory. In the longitudinal problem the vortex lattice is unstable against growth of helical deformation, if the current along the flux‐lines exceeds a critical value. If the current is perpendicular to the vortex direction, the homogeneous flux‐line lattice is always unstable if there is no volume pinning. The long range of an effective interaction leads to increase of both, the pinning and critical current value. The peak effect in longitudinal current versus magnetic field dependence is interpreted by a collective behaviour of bent flux‐lines close to upper critical magnetic field.