bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics of Defect Accumulation and Recombination. I. General Formalism
Authors: Kuzovkov V. , Kotomin E. 
Published: July 2007

AbstractA general theory of the kinetics of radiation‐induced defect accumulation and recombination in solids and liquids limited by spatial correlations of Frenkel defects is presented and developed. Kinetic equations are solved making use of the superposition approximation. For the first time a correlation of the similar defects is taken into account, which arises indirectly due to dissimilar defect recombination. A radiation‐induced accumulation of immobile defects proves clearly a formation of loose aggregates of the similar defects. It is shown that a defect concentration grows with time t proportionally to 1 — exp (‐2μ0vat), μμ0 is the rate of defect production per unit volume and time, va being an annihilation volume. The less the initial defect correlation is in genetic (Frenkel) pairs, the greater is the defect concentration under saturation at high doses.
Sound Interactions with Nuclear Subsystem in Antiferromagnets
Authors: Chepurnykh G. K. , Tarasenko S. V. 
Published: July 2007

AbstractA dispersion relation is obtained and studied. It follows from the relation that at low temperatures in the flop‐field region the studies of effects due to a coupling between electron and nuclear spin vibrations as well as effects due to a strong coupling between electrons and lattice vibrations substantially depend on the fact whether one takes or does not take into account sound interactions with the nuclear spin subsystem. The influence is shown of anisotropy of the relativistic part of magnetostriction on the character of the orientational phase transformations and the value of the NMR amplification coefficient.
Intrinsic Urbach Rule and Electron—Phonon Interaction in GaAs and Related III‐V Compounds
Authors: Antonioli G. , Bianchi D. , Franzosi P. 
Published: July 2007

AbstractThe optical absorption at the edge of the fundamental absorption band is investigated in highpurity and high‐perfection GaAs crystals. The experimental curves show an exponential decay of the absorption coefficient as a function of the photon energy (Urbach's rule) with temperature dependent slope. Since the impurity contribution can be neglected, the data are analyzed within the framework of the polaron model of phonon‐assisted transitions. The good agreement obtained between experimental and calculated curves makes it possible to conclude that the interaction of electrons with LO phonons plays a dominant role in shaping the intrinsic Urbach tail in GaAs. The same theoretical model is also applied successfully to InP and InAs using previously published experimental data.
Calculation of Structural Parmeters of Spinels
Authors: Talanov V. M. 
Published: July 2007

AbstractA simple thermodynamical theory of crystal structure parameter calculation is suggested. Within the approximation of elastic atomic interaction formulae are obtained of the lattice parameter for different variants of cation distributions among non‐equivalent crystallographic positions in chemical compounds with spinel structure. The lattice parameter proved to be a function of two fundamental atomic characteristics: charge and bond length with an anion. The experimental and theoretical values are in good agreement. Calculation are made with sulfospinels.
The Local Density of States of Embedded Cu and Cu(Ni) Clusters
Authors: Van Dijkum C. E. , Lodder A. 
Published: July 2007

AbstractThe electronic structure of Cu and Cu(Ni) clusters is investigated being representative of the pure Cu and dilute Cu(Ni) alloy systems in a liquid or amorphous state. The clusters contain up to 43 atoms. The copper environment of the clusters is simulated by two kinds of embedding media, the John‐Keller medium and the Lenk‐Blaudeck medium. The local density of states (LDOS) for each atom in the cluster is evaluated using the formalism of Lloyd as well as of Anderson and McMillan. Calculations show that the Anderson‐McMillan LDOS, which follow from a local integration of the Green function, is preferable.
Self‐Diffusion of Iron in the Amorphous Alloys Fe40Ni40P14B6 and Fe80B20
Authors: Valenta P. , Maier K. , Kronmüller H. , Freitag K. 
Published: July 2007

AbstractIn amorphous and cystallized Fe40Ni40P14B6 and amorphous Fe80B20 alloys the diffusion coefficient of iron is investigated using radiotracers and a microsectioning technique. The diffusion coefficient in Fe40Ni40P14B6 can be described by an Arrhenius relation according to D equals; D0 exp (−Q/kT) with D0 equals; 10 cm2/s, and Q equals; 2.0 eV. In Fe80B20 no diffusion could be observed.
Raman Spectra of CaAs3, ús3, SrAs3, BaAs3, and α‐EuP3 and the Mixed Phases, Eu1−xSrxAs3, and Eu(P1−x Asx)3
Authors: Oleś B. , Stolz H. J. , Von Schnering H. G. 
Published: July 2007

AbstractThe Raman spectra of the triarsenides MAs3 (M equals; Ca, Eu, Sr, Ba), α‐EuP3 and of solid solutions, Eu1−xSrxAs3, and Eu(P1−x Asx)3, are measured. A great similarity between the phonon spectra and simple scaling relations between the corresponding lattice vibrations of the triarsenides reflect the strong structural relationships between the monoclinic MAs3 and slightly distorted triclinic CaAs3 and suggest very similar vibrational eigenvectors. The Raman spectra of the solid solutions, Eu1−xSrxAs3, and Eu(P1−x Asx)3, display a mixed one‐ and two‐mode behaviour. It is shown that the strong coupling between atoms in the puckered As(P) layers reflects itself in the appearance of high‐frequency modes associated mainly with vibrations of atoms within the puckered layer, whereas the low‐frequency modes are dominated by metal vibrations.
Infrared Absorption by Ag, Cu, and Au Acceptors in ZnTe
Authors: Samindayar K. , Magnea N. , Pautrat J. L. , Pajot B. 
Published: July 2007

AbstractInfrared measurements are made on ZnTe doped with Ag, Cu, and Au acceptor impurities. Observed transitions are discussed in the framework of the theory of Baldereschi. The binding energies Ea are (123.8 ± 0.5), (150.3 ± 0.5), and (271.6 ± 0.5) meV for Ag, Cu, and Au impurity, respectively, These results are in good agreement with that deduced from luminescence experiments. The average number of emitted phonons N̄ is deduced for all known acceptors in ZnTe (Li, P, As, Ag, Cu, and Au) using luminescence and IR measurements. An empirical relation N̄ equals; 62E2a is found. The cross‐section for Au in ZnTe is found to be (3.5 ± 0.7) × 10−16 cm2 with an effective field ratio which ranges between 2.3 and 4.
Very Large Phonon‐Drag Thermoelectric Power of HgTe in Strong Magnetic Fields
Authors: Takita K. , Landwehr G. 
Published: July 2007

AbstractThe magneto‐Seebeck effect of almost intrinsic HgTe is investigated up to 96 kOe in the temperature range 20 to 120 K. The thermoelectric power in strong transverse magnetic fields. α⟂, is positive because the contribution of high mobility electrons is suppressed. Below about 50 K, α⟂ at 96 kOe increases rapidly with decreasing temperature and shows a prominent peak. The peak value of α⟂ of a typical sample reaches about 2 mV/K around 25 K. The dominant part of the observed value comes from the phonon‐drag effect of holes with large effective mass. The observed phonon‐drag contribution is one order of magnitude larger than that of heavily doped p‐type samples which were investigated previously. Such a large value is attributed to a substantially reduced hole—phonon scattering in the phonon relaxation mechanism of the almost intrinsic sample. According to an analysis using a model of phonon relaxation through three‐phonon processes discussed by Whitsett and Nelson, the dilation deformation potential constant of the Γ8‐band is determined as a equals; +3.8 eV using a shear deformation potential constant of b equals; −1.5 eV.
Assignment of (Tl+)2 Absorption Bands in Alkali Halides by Magnetic Circular Dichroism Spectra
Authors: Tsuboi T. 
Published: July 2007

AbstractMagnetic circular dichroism spectra of absorption bands due to a Tl+ dimer center, i.e. (Tl+)2, in KI single crystals are investigated at temperatures from 25 to 300 K, which are compared with the spectra of (Tl+)2 bands in KBr and of (In+)2 bands in KCl. The absorption bands at 4.915 and 4.968 eV in KI:Tl+, which appear near the B‐band of Tl+ center, are attributed to the (Tl+)2 bands related to the B‐ and C‐bands, respectively.
Theory of Multiphonon Resonance Raman Scattering as a Function of Temperature in Polar Semiconductors
Authors: Trallero Giner C. , Lang I. G. , Pavlov S. T. 
Published: July 2007

AbstractA theory is developed which describes multiphonon resonance Raman scattering processes in polar semiconductors when the temperature is not very high and the primary radiation frequency is in the fundamental absorption region. A general formula for the scattering cross‐section for any Stokes or anti‐Stokes process is presented as a function of impinging radiation frequency and temperature in the event of excitonic state interaction with longitudinal polarization lattice vibrations (LO‐phonons) considered as intermediate states. It is shown that the multiphonon resonance Raman scattering cross‐section in any process is proportional, in the first order, to the exciton‐LO‐phonon interaction constant.
Role of Noble Metal d‐States in the Formation of the Electron Structure of Ternary Sulphides
Authors: Domashevskaya E. P. , Marshakova L. N. , Terekhov V. A. , Lukin A. N. , Ugai Ya. A. , Nefedov V. I. , Salyn Ya. V. 
Published: July 2007

AbstractCombined X‐ray spectroscopic and X‐ray photoelectron investigations are made of the valence electron energy spectra in the semiconducting ternary sulphides CuGaS2, AgGaS2, AgSbS2, Ag3AsS3, and CuFeS2. The main features of such spectra in the complex compounds of noble metals are shown to be governed by the resonance character of the interaction between the d‐states of noble metal and p(s)‐states of non‐metal as already observed earlier especially in binary compounds of noble metals. Its pecularities are manifesting themselves first of all by the splitting of sulphur p‐band into two components and by pushing the latter apart from the noble metal d‐band. The magnitude of this p‐band splitting increases almost linearly with the amount of copper or silver in the compound. With the use of these data for the first time the broadeningof band gap in AIBIIICVI2 ternary sulphides is explained, which occurs under substitution of copper by silver, contrary to the usual narrowing of it with the increase of the mean atomic number of a compound.
Problems of the OPW Method III. Rare Earths
Authors: Kurganskii S. I. , Farberovich O. V. 
Published: July 2007

AbstractThe application of the modified OPW method for calculating the band structure of rare earths is considered. The effect of the parameters of the MOPW method on the energy bands obtained is systematically studied for Eu and general rules on the choice of these parameters are found. The spin‐polarized band structure of the ferromagnetic semiconductor EuO is determined taking into account these rules. The effect of f‐states of the metal and the (m‐t) approximation of the crystal potential on the compound energy bands is studied.
Localized Positronium‐Like States in Ionic Crystals
Authors: Boev O. V. , Arefiev K. P. 
Published: July 2007

AbstractThe localized positronium‐like states in ionic crystals are considered as positron‐electron pair bound states in the Coulomb field of the charge Z. The system characteristics are evaluated as a function of the magnitude Z. The calculated data are in agreement with the experimental ones in alkali halides for charges Z < 0.7. The properties and the formation possibility of the positronium‐like states in ionic crystals are discussed.
Diamagnetic Band Structure Comparison of Second‐Order Perturbation with a First‐Principles Calculation
Authors: Rauh A. , Schellnhuber H. J. 
Published: July 2007

AbstractThe comparison is restricted to the Landau region where the periodic potential can be treated as a perturbation. The first‐principles calculation is done within a recently developed variational formalism. A two‐dimensional model potential is supposed and rational magnetic fields. For all Landau levels considered a striking agreement is found between the two energy spectra which are obtained by the perturbative and the variational method, respectively. The second‐order perturbation yields also the magnetic breakdown condition with high accuracy.
Electron‐Spin Polarization in Hexagonal Crystals Induced by Circularly Polarized Light
Authors: Wöhlecke M. , Borstel G. 
Published: July 2007

AbstractFrom symmetry arguments general wave functions generating the irreducible representations of the double group of C6v are derived. From these wave functions selection rules for the production of spin polarized electrons along Δ in unpolarized hexagonal crystals by circularly polarized light are derived. Equal strength for spin‐up and spin‐down electrons produced by a particular transition is predicted, if right circular polarization is changed to left circular polarization. The absolute strength depends on a parameter proportional to the spatial parts of the wave functions. Very general conclusions on the effect of hybridization can be drawn.
On the Luminescence of Cs3Bi2Br9 Single Crystals
Authors: Timmermans C. W. M. , Blasse G. 
Published: July 2007

AbstractThe luminescence properties of Cs3Bi2Br9 single crystals are reported. Cs3Bi2Br9 is an ordered perovskite, structurally and electronically related to the cesium lead halides. Emission and excitation spectra are measured at 4.2 K. The luminescence originates from the recombination of excitons bound to defects, except for a sharp line at 459.2 nm, which is ascribed to free exciton recombination. The band‐gap transition takes place at about 2.7 eV and is found to be direct and allowed. The intensity of the emission bands and the decay times are measured as a function of temperature. The results are interpreted assuming detrapping and exciton migration.
Infrared Spectra of Single‐Crystal NiO at High Temperatures
Authors: Mochizuki S. , Satoh M. 
Published: July 2007

AbstractThe reststrahlen spectra of single‐crystal NiO are measured at various temperatures from 300 to 1273 K in the spectral region from 250 to 700 cm−1 by the thermal‐emission and reflection method for the first time. Remarkable changes are observed in the reststrahlen band with increasing temperatures. The spectra are analysed by means of the two‐oscillator dispersion model, and the temperature dependence of the dispersion parameters is determined. These results are discussed in the light of the theory on anharmonic crystals. The anharmonic phonon‐frequency shift is seen to become prominent with increasing temperatures. Appearance of the high‐frequency sideband is ascribed to a process involving multi‐phonons through the intermediate virtual excitation of the TO‐phonon near the center of the Brillouin zone.
Zeeman Effect in Low‐Temperature Luminescence Spectra of Molecular Ions O−2 and S−2 in Alkali Halide Crystals
Authors: Sild O. , Sildos I. 
Published: July 2007

AbstractThe effect of the magnetic field up to 3.5 T is investigated on the zero‐phonon luminescence lines of the molecular ions O−2 and S−2 in alkali halide crystals at 4.2 K. For the molecules oriented along the twofold axis of the cubic crystal a triplet splitting of the luminescence lines is observed. A model for the selection rules and the polarization characteristic of the Zeeman triplets is developed. The parameters of the excited electronic state can be obtained from the Zeeman triplets.
The Role of Defects on Inelastic Scattering of Mössbauer Radiation near Structural Phase Transitions
Authors: Zolotoyabko E. V. , Kashcheev V. N. 
Published: July 2007

AbstractAn expression for the spectrum of critical inelastic scattering of Mössbauer radiation is derived at the structural phase transition. It is assumed that the central peak (which determines such characteristics of scattered radiation as the intensity and the width) is due to slow motions of point defects. The temperature dependence of the effective line width is found to arise from vacancy diffusion in BaTiO3 to the right of the transition temperature. Qualitative agreement with corresponding experimental data is obtained.
Excitation of the hybrid mode due to modulation of an intense laser beam in a transversely magnetised semiconductor plasma
Authors: Ghosh S. , Apte N. , Agarwal V. K. 
Published: July 2007

AbstractUsing the hydrodynamic model of a homogeneous plasma, the modulational decay of a laser beam into an acoustic wave and another electromagnetic wave is studied in heavily doped n‐type semiconductors in the presence of a transverse magnetic field. The decay process results in the excitation of the hybrid mode. The growth rate and the threshold electric field necessary for the onset of instability is obtained in presence as well as in absence of the magnetic field. The magnetic field couples the acoustic wave and the electromagnetic waves. The growth rate of the unstable hybrid mode increases with the square of the amplitude of the magnetic field.
Photolumineseenee of ZnO single crystals: Influence of k‐linear interaction and non‐analytic long‐range exchange on the emission spectrum of the free A‐exciton
Authors: Kuhnert R. , Helbig R. , Hümmer K. 
Published: July 2007

AbstractThe effect of the non‐analytic long‐range exchange interaction as well as the k‐linear interaction on the photoluminescence spectrum of the free A‐exciton in ZnO is investigated. By varying the angle between wave vector and crystallographic c‐axis in uniaxial crystals one is able to “switch on and off” and to vary the coupling strength of these interactions. In order to avoid refraction complications connected with non‐perpendicular incidence the measurements are carried out at crystal planes inclined under different angles to the crystallographic c‐axis. This method enables to observe and to study systematically the influence of k‐linear terms and non‐analytic long‐range exchange on the emission spectrum for the first time without an external field.
Absorption spectra of MgF2 and AlF3, in the region of the Mg and Al L2,3 excitations
Authors: Bartlett R. J. , Olson C. G. , Lynch D. W. 
Published: July 2007

AbstractThe absorption spectra of thin films of MgF2 and AlF2 were measured in the region of the Mg and Al L2,3 excitations using synchrotron radiation. The spectrum for MgF2 is similar to that previously reported, but with two differences. The lowest energy (exciton) structure is resolved into two peaks leading to new values of the spin‐orbit and exchange splitting, 0.33 and 0.21 eV, respectively, and there are a number of peaks in the original spectrum that were not obtained. The AlF3 spectrum shows that these arose from AlF3, contamination of the original films. The AlF3 spectrum bears a striking resemblance to that of MgF2, indicating that critical point structures probably play no role. Structure in the first exciton peak is not resolved in the absorption spectrum but thermotransmission spectra reveal a splitting of 0.44 eV.
Determination of static bond charge properties in Ga1−xInxAs and GaAs1−yPy, solid solutions
Authors: Pietsch U. 
Published: July 2007

AbstractThe integrated X‐ray intensity is determined for some monocrystalline reflections of (GaIn)As and Ga(AsP) layers, grown on GaAs substrates, nearly of those compositions where the scattering amplitude of the spherical atoms vanishes. These reflections are particularly apt to inform about the charge heaping up between next neighbours. By means of a bond charge model the experimental values are interpreted. Besides, data are obtained for the mean square displacement of the matrix atoms in the mixed crystal. The mean square displacements of the atoms in the mixed crystals cannot be extrapolated from those of the end components. The atoms of the substitutional sublattice oscillate less intensively than in its binary compounds. The bond charge, however, changes nearly linearly between the end components.
Local field effects and a model dielectric response matrix ϵG,G′(q) for a covalent semiconductor
Authors: Oliveira L. E. 
Published: July 2007

AbstractA model for the microscopic dielectric response ϵG,G′(q) of a covalent semiconductor is proposed in which the effects of the localized and plane wave features of the band structure on the polarizability are separated. Within this model for diamond a calculation is performed of the static longitudinal wave vector dependent macroscopic dielectric function ϵM(q), including local field corrections, together with an analysis in real space of the microscopic local field E(r) and polarization charge density ϱindr) induced by a uniform externally applied electric field. The results indicate that although the macroscopic dielectric function is essentially insensitive with respect to small changes in the effective charge model parameter Z, microscopic quantities such as the induced charge density and microscopic local field can be fairly sensitive to variations in Z. This suggests that careful tests on model based dielectric responses ϵG,G′(q) are probably necessary before one calculates, for instance, phonon frequencies.
Temperature dependence of ESR spectra of doped a‐Si:H
Authors: Dersch H. , Stuke J. , Beichler J. 
Published: July 2007

AbstractThe temperature dependence of the ESR lines with g = 2.01 for boron‐doped and with g = 2.0043 for phosphorus‐doped a–Si:H, associated with singly occupied tail states of the valence and conduction band, respectively, is investigated. Both resonances broaden considerably with increasing temperature, and the broadening δHpp(T) is related with the electrical conductivity σ(T) as δHpp(T) = c[σ(T]n with 0.64 < n < 1. The g‐values of both lines decrease with rising temperature. The spin density N8 is for weakly boron‐doped samples constant at low temperatures, for phosphorus‐doped a‐Si: H, however, an increase of N8 with rising temperature is observed. These results are explained in a model with a small correlation energy ( U < kT) for the conduction band tail and a large one (U ≫ kT ) for the valence band tail. The temperature variation of the g‐value is ascribed to its energy dependence. Electrons in localized states near the mobility edges are assumed to have smaller g‐values than those in states with a larger energy distance from the edges. The relation between the line broadening δHpp(T) and the conductivity can be understood by spin relaxation of the localized electrons due to exchange coupling with rapidly relaxing carriers in extended states.
Substitutional and interstitial hydrogen impurities in alkali halide crystals
Authors: Augst G. R. , Bakhshetsyan L. G. 
Published: July 2007

AbstractAn expression for the energy of an alkali halide crystal with a charged point defect is obtained using the Ewald method. The lattice relaxation is taken into account by the lattice static method. The repulsive overlap interaction between ions is approximated by the Hnggins‐Mayer potential. The Van der Waals interaction plays a very important part. Numerical calculations are done for KCI and KBr crystals containing interstitial and substitutional hydrogen ions with a view of obtaining the energy of formation of an impurity Frenkel pair. The activation energy of atomic hydrogen diffusion is calculated in the same crystals.