bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Validity of the Column Approximation in Image Contrast Calculations of Crystals Containing Stacking Faults
Authors: Jap B. K. , Sheinin S. S. 
Published: July 2007

AbstractThe validity of the column approximation is assessed for image contrast calculations of stacking faults in plate shaped crystals. The basic approach is based on application of the appropriate boundary conditions at the fault to determine the exact wave functions describing the electrons both above and below the fault and does not involve the differential equation approach used in non‐column approximation calculations in the past. In order to assess the validity of the column approximation, a validity assessment parameter, based on the two‐beam theory, is defined. The results obtained show that the validity domain of the column approximation, for a particular stacking fault inclination, decreases with increasing deviation from the Bragg condition, and increases with increasing electron energy. Direct comparison of many‐beam profiles in the noncolumn and column cases show that significant differences in profile shape can be obtained for weak beam diffraction conditions even when the stacking fault inclination is less than 45°.
The Configuration ƒN in Cubic Symmetry: A Symmetry Adapted Weak‐Field Approach
Authors: Kibler M. , Grenet G. 
Published: July 2007

AbstractThe symmetry adapted weak‐field model recently introduced by the authors is applied to the case of the configuration ƒN in cubic symmetry. This leads to a 29‐parameter model which parallels the 32‐parameter strong‐field model.
Correlation Factors for Diffusion in Binary Alloys with Short‐Range Order
Authors: Stolwijk N. A. 
Published: July 2007

AbstractA method is presented for the calculation of the diffusion kinetics in binary alloys with only short‐range order. The method may be considered as an extension of Manning's theory on random alloys. Effects from atom‐vacancy exchanges on local order are taken into account in detail. The model is tested by comparing its results for alloys with nearest‐neighbour interactions with correlation factors obtained by computer simulation. For all sets of interatomic energies very good agreement is obtained over the entire temperature range. The present treatment of correlation effects may also be applied to more extended alloy models or to multicomponent systems.
Electrical Conduction of GeSe at Low Temperatures
Authors: Ishihara Y. , Nakada I. 
Published: July 2007

AbstractThe Hall coefficient and resistivity of germanium monoselenide were measured between 320 and 1.5 K. The ionization energy of the acceptor is estimated from the temperature dependence of the Hall coefficient. It changes from 3.9 to 5.3 meV according to the heat treatment. The impurity conduction is found to occur at low temperatures. There appear two activation energies corresponding to impurity conduction, the first of about 1.5 meV and the other of about 0.5 meV. The former value can be associated with the thermal excitation of holes from the Fermi level to a mobility edge in the upper Hubbard band.
Evaluation of Third‐Order and Fourth‐Order Elastic Constants of Cesium Halides and Thallium Halides
Authors: Shanker J. , Singh J. P. , Jain G. D. 
Published: July 2007

AbstractThe third‐order and fourth‐order elastic constants for CsCl, CsBr, CsI, TlCl, and TlBr crystals are calculated taking into account the effect of Lundqvist's three body potential. The nearest neighbour and next‐nearest neighbour repulsive interactions and the Van der Waals interactions are also included according to a recent scheme developed for NaCl‐structure alkali halides. The three body charge transfer parameter and its derivatives are evaluated using an exponential form suggested by Cochran. The pressure derivatives of second‐order and third‐order elastic constants are also calculated for the crystals under study. The results obtained are found to be in reasonable agreement with available experimental data.
Non‐Markovian Evolution of Crystal Electrons in a Strong Electromagnetic Wave Field
Authors: Kruglov V. I. 
Published: July 2007

AbstractThe non‐Markovian kinetic equations describing the interaction of two multi‐particle subsystems are defined and an approximate calculation procedure of the electron—phonon crystal system wave functions in an external electromagnetic field is suggested. A kinetic non‐Markovian equation for the electron density matrix is derived on the basis of results obtained without using perturbation theory. The general solution of the non‐Markovian kinetic equation describing multiphoton processes and the high‐frequency oscillations of the electron distribution function is obtained for the case of weak binding.
Free Carrier Compression and Galvanomagnetic Luminescence of Germanium at High Lorentz Fields
Authors: Kessler F. R. , Mangelsdorf J. W. 
Published: July 2007

AbstractA local variation in carrier concentration occurs in intrinsic semiconductors in the presence of crossed electric and magnetic fields which leads partly to an enhancement (“compression”) and partly to a depletion. In connection with these displacements from thermal equilibrium luminescent radiation can be observed which, when related to the thermal radiation under equilibrium conditions, is positive in enhanced and negative in depleted regions. The luminescent radiation spectrum in the region of the fundamental absorption edge is directly related to the free carrier concentration profile in the sample. The report deals with theoretical and experimental results obtained with germanium exposed to Lorentz field strengths of up to 20000 TV/m (or B ≦ 10 T) at 400 K. Non‐linear surface recombination must thereby be allowed for. The corresponding semiconductor parameters are given. The modulated galvanomagnetic luminescence exhibits the expected antiphase component at longer wavelengths, corresponding to an increase in the separation of the quasi fermi level from the band edges for constant lattice and electron temperatures.
On the Experimental Determination of Many‐Particle Effects at Interband Transitions
Authors: Jungk G. 
Published: July 2007

AbstractThe energy‐derivative spectra of the real and imaginary part of the dielectric function ε(ω) = ε1 + iε2 in the range of critical interband transitions can be used to determine a parameter which describes the influence of many‐particle effects. Afterwards the computation of the one‐electron spectra becomes possible from experimental spectra, which are modified by many‐particle interactions. The application of this procedure to ellipsometrically determined spectra of GaP and GaAs for the E1 transition results in the predominant influence of the continuum—exciton effect in accordance with theoretical predictions of Hanke and Sham.
Calculation of the Compton Profile of Beryllium
Authors: Rennert P. 
Published: July 2007

AbstractStarting from a pseudopotential calculation for h.c.p. beryllium the Compton profiles are calculated for the directions 〈101〉, 〈102〉, 〈111〉, and 〈112〉. The profiles for 〈001〉, 〈100〉, and 〈110〉 are improved by detailed considerations on the orthogonalization corrections. A strong anisotropy is found for I〈001〉 — I〈102〉 and I〈001〉 — I〈112〉, respectively. The contribution from the correlation tail in the momentum distribution is estimated. It must be included, if the calculated profiles are compared with high resolution measurements.
Influence of Dielectric Screening and Band Nonparabolicity on Ionized Impurity Scattering in Doped Semiconductors
Authors: Neumann H. , Tsipivka Yu. I. , Unger K. 
Published: July 2007

AbstractDielectric screening beyond the Thomas‐Fermi approximation and band nonparabolicity are included in the theory of ionized impurity scattering in semiconductors. The resulting mobilities are always smaller than the Brooks‐Herring mobility. The corrections to the Brooks‐Herring mobility increase with increasing nonparabolicity. Numerical results are given for the electron mobility due to ionized impurity scattering in n‐type GaAs, InAs, and InSb.
Host Spin—Lattice Relaxation Narrowing in Sm2Co3(NO3)12 · 24 H2O:Mn2+, Gd3+ Single Crystals
Authors: Jain V. K. 
Published: July 2007

AbstractThe electron paramagnetic resonance of Mn2+ and Gd3+ in single crystals of Sm2Co3(NO3)12 · 24 H2O is studied in the X‐band at 300 and 90 K. The spin‐Hamiltonian parameters are evaluated. The observation of resolved Mn2+ and Gd3+ spectra at 300 K and their broadening on lowering the temperature is discussed in terms of host spin—lattice relaxation narrowing.
Defects Induced in RbMgF3 Crystals by X‐ and UV‐ Irradiation
Authors: Trieman B. , Kristianpoller N. 
Published: July 2007

AbstractThe effects of X‐ and UV‐irradiation on pure and Pb‐doped RbMgF3 single crystals are studied. The temperature dependence and spectral composition of X‐luminescence (XL) as well as TSL, TSC, and optical absorption are measured. The XL shows main emission bands at 270, 305, 410, 430, 495, and 560 nm. Prolonged X‐irradiation at 80 K causes the appearance of absorption bands at 245, 315, 330, and 378 nm which are attributed to interstitial aggregates, F centers, VK centers, and F2 centers, respectively. Some of the TSL peaks which appear after X‐irradiation, appear also after monochromatic VUV irradiation. VUV excitation spectra of the TSL show maxima at 127 and 160 nm. The results indicate that a radiolysis process may be responsible for defect formation in both, the × and VUV irradiated samples, it appears, however, that this process is suppressed in the Pb‐doped samples.
Self‐Trapped Particles in Complex Oxide Crystals
Authors: Vakhidov Sh. A. , Ibragimova E. M. , Nuritdinov I. , Rakov A. F. , Ikramov G. I. 
Published: July 2007

AbstractSelf‐trapped hole (STH) and self‐trapped exciton (STE) states which are formed in Y3Al5O12, Y2SiO5, and TR2Si2O7 crystals under γ‐irradiation in the temperature interval of 77 to 200 K are investigated. The STH is shown to be molecular O, absorbing at 1.6 eV (for Y3Al5O12) and at 1.65 eV (for Y2SiO5) and causing the eleven‐component EPR signal; the corresponding STE emits at 3.9 and 3.6 eV. In metal‐doped crystals the exciton and hole delocalization lead to a decreasing of the emission energy, to a short‐wave shift of the absorption band, and to the growth of the anneal temperature. At the self‐localization temperature excitons are proved to migrate by jump diffusion and to transfer energy to the impurity ions exciting their emission.
Properties of the Rn and IR‐1 Luminescence Bands in Cadmium Sulfide Irradiated with Thermal Neutrons
Authors: Ermolovich I. B. , Gorbunov V. V. , Matvievskaya G. I. 
Published: July 2007

AbstractSpecific features of Rn (λmax equals; 728 nm) and IR‐1 (1040 nm) luminescence bands in CdS single crystals irradiated by thermal neutrons with doses 1013 to 1019 n/cm2 were studied. The joint investigations of luminescence and photoconductivity dependences on temperature and on both the intensity and the wavelength of excitation confirm the Rn and IR‐1 centre models proposed earlier, (VCd · VS) and (VCd · InCd), respectively. The electron‐phonon interaction at radiative carrier capture on Rn‐centres are investigated, its parameters are obtained. At the first time it is found that at sufficiently low temperatures (≧ 160 K) the photosensitivity centres in monopolar, photosensitive semiconductor with wide band gap are the centres of effective nonradiative recombination due to high electron‐phonon interaction.
Dielectric Relaxation of Chalcogen—Vacancy Centres in Potassium Halide Crystals
Authors: Kokott Ch. , Fischer F. 
Published: July 2007

AbstractO−−, S−−, Se−−, and Te− ions dissolved in potassium halides form electric dipoles by association with an anionic vacancy. Reorientation stops below characteristic temperatures. They are measured by TSD (ITC) techniques. Crystals, not optimally quenched, can have additional TSD bands which are regarded as belonging to dipole‐impurity associates. Measured activation energies favour the chalcogen‐vacancy jump as the dominating relaxation mechanism at lower temperatures. Additional dielectric loss results above room temperature are compared with TSD data.
Free Exciton Energy Transfer in KrAu Sandwiches
Authors: Schwentner N. , Martens G. , Rudolf H. W. 
Published: July 2007

AbstractThe photoelectron yield of KrAu sandwiches caused by energy transfer of Kr excitions to the Au substrate is measured. The range for energy transfer of Kr excitons is determined from the dependence of the yield on the thickness of the Kr overlayer for several excitation energies within the n equals; 1, n′ equals; 1, and n equals; 2 exciton bands. The derived diffusion lenghts of free excitons depend strongly on the individual exciton state and increase monotonically with the exciton energy within one exciton band as well as to higher exciton states from 30 Å for the n equals; 1 up to 300 Å for the n equals; 2 excitons. The efficiency for electron emission due to exciton decay exceeds the usual photoelectron yield of Au by a factor of ten.
Temperature Dependence of the Isothermal Elastic Constants of Alkali Metals
Authors: Soma T. , Kagaya S. , Matsuo H. 
Published: July 2007

AbstractThe temperature dependence of the isothermal elastic constants of alkali metals are calculated using second order perturbation theory and the local Heine‐Abarenkov model potential. The theoretical results are in quantitatively good agreement with available experimental data. The, the qualitative temperature dependence of elastic constants in the dynamical treatment using the expression for the temperature dependent two‐body interactions is obtained.
On the Pseudopotential Calculation from First Principles
Authors: Altshuler A. , Bezryadin S. N. , Kh. Vekilov Yu. , Verner V. D. 
Published: July 2007

AbstractThe dependence of the pseudopotential of free ions on the ion core electron structure approximation and on the description of the exchange and correlation scattering and pseudopotential nonlocality are discussed. An analysis is made of the Phillips‐Kleinman method. The formfactors for 17 elements are calculated. The problem of the pseudopotential ambiguity is discussed on the basis of the Hartree‐Fock Hamiltonian with nonorthogonal one‐particle wave functions. It is shown that in the weak bond approximation the effective potential is unambiguous.
Specific Heat of Ar‐Xe Solid Solutions at Low Temperatures
Authors: Tiwari M. D. 
Published: July 2007

AbstractThe measured specific heat of argon with solid solutions of xenon containing 5.01 and 10.88 at% Xe are analyzed on the basis of low concentration Green's function theory. Maxima are observed at about 4 K in the relative variation ΔC(T)/C(T) of the solid mixture. The maxima are related to the appearance, in the solid mixture phonon spectrum, of quasilocal oscillations due to introduction of heavy Xe impurity atoms into the Ar lattice. The changes in mass at the impurity site as well as changes in the closest‐neighbour force constants are taken into account in performing the computations. The force constants for the interaction between the impurity atom and its nearest neighbours are larger than the atomic interaction constants in the initial lattice. For the Ar‐10.88 at% Xe system the low‐concentration theory is modified. Reasonably good agreement with the experimental data is obtained.
Model of the Excitonic Surface Layer in Normal Incidence Reflection
Authors: Stahl A. 
Published: July 2007

AbstractA pair of semiclassical wave equations describing exciton polaritons of Wannier type is set up and solved for half‐space geometry under certain simplifying assumptions. The main results are: (i) the polarization as a function of the distance from the boundary; (ii) an energy dependence of the depth of the transition region; (iii) evidence for a possibly non‐monotonous behaviour of the polarization near the boundary if the frequency is above resonance; (iv) reflection curves that for certain parameter sets give spikes for ω > ωL.
Paraelastic Alignment and Electric Dipole Relaxation Behavior of Off‐Center Ag+ Defects in RbI
Authors: Jimenez R. V. , Lüty F. , Siu Li M. , De Souza M. 
Published: July 2007

AbstractSubstitutional Ag+ defects are investigated for the first time in RbI host material. The absorption spectrum of isolated defects – obtainable only after quenching and rapid cooling of the crystals – consists of three UV absorption bands at 4.81, 4.94, and 5.13 eV. Uniaxial stress application produces characteristic increases or decreases of these absorptions for 〈111〉 and 〈110〉 stress, due to elastic dipole alignment following a Curie (1/T) law, while dichroism is absent under 〈100〉 stress. This stress alignment is possible only above 27 K demonstrating freezing‐in of dipole reorientation below this temperature. In agreement with this, ITC measurements show a peak of the depolarization current at 23.4 K, yielding an activation energy for reorientation of 53 meV and an electric dipole moment of 0.64 eÅ. For interpretation of the elasto‐optical data, two models involving pure T2g elastic dipole reorientation are dipole reorientation are discussed: the normal 〈111〉 dipole model, and a restricted 〈110〉 dipole model, in which strong and immobile Eg distortions allow dipole reorientation only among four orientational states in a (100) plane. It is shown that both models cannot be distinguished in the linear range of the elasto‐optical effect and that both can be fitted well to the observed data. Several arguments, however, favor the 〈111〉 model with deep off‐center wells of Ag+ in RbI.
Stimulated resonant Raman scattering of light in anthracene crystals
Authors: Maksimov A. A. , Tartakovskii I. I. 
Published: July 2007

AbstractThe investigation of stimulated resonant Raman scattering of light (SRRS) is carried out on thin plane‐parallel anthracene crystals (d = 2 to 45 μm) at low temperatures (T = 1.5 to 40 K). The resonance excitation at the bottom of the lowest exciton band is produced by a pulsed tunable dye laser. It is shown that under resonance excitation at optical pumping levels P ≈︁ 3 MW/cm2 up to nine SRRS Stokes components of intramolecular vibrations 395, 1167, and 1402 cm−1, are observed, the three Stokes components of 1402 cm−1 vibrations being the most intensive ones. Characteristic dependences of the intensity of SRRS Stokes components on pumping level and crystal tempe ature for different exciting frequencies are obtained. An anomalous intensity increase of the 49 cm−1 RS Stokes component is found attributed to RS on nonequilibrium phonons of the lowest optical branch. The results of the measurements are compared with the data on spontaneous resonant RS of light in anthracene crystals.
The influence of a magnetic field on the ground and excited states of bound exciton complexes in ZnO
Authors: Blattner G. , Klingshirn C. , Helbig R. , Meinl R. 
Published: July 2007

AbstractThe Zeeman splittings of those luminescence and absorption lines of ZnO are investigated which are due to excitons bound to impurities. Additionally the thermalization of the Zeeman components is studied. The results are discussed in terms of excitons bound to neutral donors and acceptors. The g‐values for the different lines are determined and discussed. Excited states of the complexes, which are investigated by means of excitation spectroscopy, are identified by their magnetic field behaviour, as being due to a hole from a deeper valence band and excited states of the envelope function.
Optical properties of the surface plasmon of n+ silicon
Authors: Robusto P. F. , Braunstein R. 
Published: July 2007

AbstractThe optical properties of the surface plasmon of n+ silicon are determined by a least‐squares curve fit of the Drude intraband model to the ATR reflection spectra. The surface plasmon resonance of n+ silicon is highly damped ( ωpτ = 2.69), and causes the ATR dispersion curve calculated on the real frequency axis to exhibit back‐bending for its complex frequency‐like solutions; whereas the theoretical dispersion curve exhibits the standard wave vector divergence at the surface plasmon frequency. This discrepancy is rectified by converting the optical properties of n+ silicon into functions of complex frequency, and using them to calculate the ATR dispersion curve in the complex frequency plane. A comparison of the Drude dielectric function as a function of real and complex frequencies is analyzed. The comparison shows that the difference between their values is small at high frequencies and deviate the largest in the region near the surface plasmon resonance.
Investigations on a two‐valence band model for Sb2Te3
Authors: Simon G. , Eichler W. 
Published: July 2007

AbstractA two‐valence band model with a single‐and six‐valley structure is developed for the interpretation of galvanomagnetic effects in p‐type mixed crystals of the system (BixSb1−x)2Te3(0 ≦ x ≦ 1), especially for x = 0 under the assumption of a purely anisotropic scattering in each band, neglecting interband and intervalley scattering. This model, refering to results from Shubnikov‐de Haas investigations on Sb2Te3 at 4 K, is tested with galvanomagnetic data of undoped Sb2Te3 in the temperature region 100 K ≦ T ≦ 360 K. It is, however, not possible to fit such a two‐valence band model to these data sufficiently well due, possibly, of a more complicated scattering process of charge carriers.
Nuclear magnetic resonance in liquid InGa alloys
Authors: Ploumbidis D. , Böss E. 
Published: July 2007

AbstractMeasurements of the Knight shift of 115In and 71Ga in liquid InGa bulk samples are carried out as a function of temperature from 263 to 523 K and concentration from 0 to 100 at% Ga. It is shown that bulk and particle samples give, within the experimental error, the same Knight shift values. The results are compared with contradictory experimental data in the literature, and it is found that they agree with those of one of the earlier authors. A further important result based on these measurements extended over a broad temperature range is the determination of the temperature coefficient of the Knight shift of both isotopes 115In and 71Ga as a function of concentration. The 115In temperature coefficient decreases with increasing Ga concentration whereas the 71Ga one remains almost constant over the entire concentration range. Comparisons between the experimental and the theoretical results show satisfactory agreement in some cases but strong discrepancies in others.
Boltzmann equation and force–force correlation function for electrical resistivity
Authors: Sorbello R. S. 
Published: July 2007

AbstractThe frequency‐dependent electrical resistivity is investigated through the Boltzmann equation and the Kubo formalism in the low‐frequency weak‐scattering regime where the Boltzmann equation is known to be valid. A commonly used force‐force correlation‐function formula for dc resistivity is shown to be derivable from the Boltzmann equation as well as from the Kubo formalism. The derivation assumes that expansions used in the ωτ ≫ I regime for the “memory function” or for the inverse of the relaxation time τ are valid in the limit as the frequency ω goes to zero. This procedure and the correlation‐function formula are shown to give incorrect results even for the zero‐temperature case if the scattering is anisotropic, i.e., if τ varies over the Fermi surface. Thus the previous criticism of the force‐force correlation function is extended to the anisotropic scattering regime, and the direct connection between this function and the Boltzmann equation is shown.
Self‐trapping and hot luminescence of excitons in rare gas solids
Authors: Kink R. , Lôhmus A. , Selg M. 
Published: July 2007

AbstractThe mechanism of intrinsic luminescence of excitons in crystalline Xe and Ar is treated. The band at 9.7 eV in Ar is shown to be non‐elementary. The height of the exciton self‐trapping barrier in Ar is determined experimentally (ϵ = 3.5 meV). An experimental and theoretical study of hot luminescence of self‐trapping excitons in rare gas crystals is carried out. The contribution of hot luminescence to the total light sum increases in the series XeArNe.