bluuebunny/crossref_metadata_2025 huggingface dataset:
The Separability of the Diffusion Equation with Drift Term
Authors: Seeger A.
Published: July 2007

The paper investigates the diffusion equation with drift term, ∂C/∂t = div (D grad C + + μ C grad U), in particular the question of its separability in three dimensions. (D is the diffusion coefficient, μ the mobility, both assumed to be constant scalar quantities; U denotes the potential giving rise to the drift.) The transformation to a new dependent variable f = C exp (μ U/2 D) transforms the equation into a Schrödinger equation. Using this it is shown that, for appropriate choices of the potentials U, the diffusion‐drift equation is separable with modulation factor in the ellipsoidal coordinates (and its degenerate special cases) but in no other coordinate systems. The conditions to which U has to be subjected in order to lead to separability are stated and shown to have a close relationship to the factorization of the solutions of the original equation.
Magnetic Properties of As2Sx Glasses
Authors: Cimpl Z. , Kosek F. , Matyáš M.
Published: July 2007

The diamagnetic component of the magnetic susceptibility of As2Sx glasses is interpreted under the assumption that this material consists of As2Sx molecules having no magnetic moment in the ground state. The van Vleck formula [6] is applied and the Langevin diamagnetic and van Vleck paramagnetic terms are discussed in details.
A Model of the Temperature Dependent Part of Stage I Work‐Hardening due to Jog‐Dragging (I)
Authors: Messerschmidt U.
Published: July 2007

A model is presented explaining the temperature dependent part of stage I work‐hardening of ionic crystals. The model is based on the assumption that the flow stress in the early stages of deformation is composed of two parts, one due to pinning effects of impurities and the other to the nonconservative motion of jogs. The mono‐jogs produce point defects by thermal activation, whereas the higher ones trail dislocation dipoles. In order to get the kinetics of jogs, the possibilities of jog motion and of jog production are considered. Since jogs can be nucleated by the absorption of point defects on dislocations, the point defects produced during deformation must be included into the kinetics of deformation. Thus, two differential equations are derived, one of the jog density and the other of the point defect supersaturation. In Part II of the paper the equations will be analyzed.
Diffusion of Sulfur in Selenium
Authors: Brätter P. , Gobrecht H.
Published: July 2007

Measurements of sulfur diffusion have been carried out on single crystals and polycrystalline samples of the semiconductor element selenium using the residual activity method and a continuous surface method by means of the tracer S‐35 in the temperature range 40 to 95 °C. In the direction of the trigonal axis (‖ c) the volume diffusion in single crystals can be represented by D‖ = 1.1 × 10−5 exp (−0.6 eV/kT) cm2 s−1 and in the plane perpendicular to the trigonal axis (⟂ c) by D⟂ = 1.7 × 103 exp (− 1.15 eV/kT) cm2 s−1. Using the surface method the diffusion in polycrystalline material can be described by DP = 2.35 × 104 exp (− 1.20 eV/kT) cm2 s−1. The coefficient for the diffusion along short circuit paths is estimated to be in the region of 10−9 cm2 s−1. It can be presumed that S‐diffusion in both crystallographic directions of Se is governed by different mechanisms. The absorption of β‐radiation in Se can be expressed by the equation μ/ϱ = 26 E cm2 g−1.
Critical Magnetic Behavior of Nickel near the Curie Point
Authors: Arajs S. , Tehan B. L. , Anderson E. E. , Stelmach A. A.
Published: July 2007

Static magnetization of polycrystalline nickel spheres (diameter about 0.3 cm) has been studied in detail as a function of the magnetic field above and below the Curie point, Tc, using a vibrating sample magnetometer. Above Tc the initial magnetic susceptibility is proportional to ϵ−γ, where ϵ = ∣1 − (T/Tc)∣ and γ = 1.33 ± 0.01, T being the absolute temperature. The spontaneous magnetization, determined by the kink method, is proportional to ϵβ, where β = 0.50 ± 0.02 for ϵ < 5 × 10−3 and β = 0.34 ± 0.02 for ϵ > 5 × 10−3. The magnetization at Tc is proportional to H, where Hi is the internal magnetic field and δ = 4.17 ± 0.05. These results are compared with the power values obtained by other investigators and are discussed from the viewpoint of various theoretical models.
Pinning of Flux Lines in Superconducting Niobium due to Point Defects
Authors: Ullmaier H. , Papastaikoudis K. , Takács S. , Schilling W.
Published: July 2007

Measurements of pinning forces due to statistically distributed vacancies and interstitials (Frenkel pairs) in niobium are reported. The defects were produced by low temperature 3 MeV electron irradiation. The results indicate that fluctuations in the defect density and not the interaction between a single point defect and a flux line are responsible for the observed pinning effects.
Thermal Radiation and Electronic Density of States of WTa Alloys
Authors: Thomas L. K.
Published: July 2007

The normal spectral emissivity of W, Ta—50 W, and Ta is calculated in the wavelength range 0.35 to 2.3 μm for the temperature 2400 °K using literature values of the electronic density of states for W. At the wavelength 0.57 μm calculations are made for the temperatures 2800 and 2000 °K. The calculations follow the theory of radiative energy transfer in gases and the theory of Einstein's transition probabilities. The matrix element of the electron—phonon interaction is used for the comparison of the theoretical and experimental results. The calculated temperature coefficient of the emissivity has the correct sign.
Fermi Surface of the Laves Phase MgZn2
Authors: Rennert P. , Taut M.
Published: July 2007

The Fermi surface of the intermetallic compound MgZn2 is calculated. The potential is obtained from the local model potential of the pure metals Mg and Zn recalculated to the changed electron density in the compound. Fermi surfaces exist in the 10th to the 14th band and show a strong deviation from those of free electrons. The calculated extremal cross sections depend strongly on the Fermi energy. It is possible to assign values of the cross sections from de Haas‐van Alphen‐measurements of MgZn2 to the calculated ones.
Spin Waves in Coupled Ferromagnetic Films
Authors: Goedsche F.
Published: July 2007

Macroscopic spin‐wave theory is used to discuss the spin‐wave spectrum of two exchange‐coupled ferromagnetic films. The coupling between the films is assumed as ferromagnetic or antiferromagnetic. Further, the effect of surface anisotropies on the spectrum is taken into account. Three types of coupled spin‐wave modes can exist in such a sandwich: bulk spin‐waves in both films, a bulk mode in the one film and a surface mode in the other film and finally surface modes in both of the films.
Dynamics of a weakly bound impurity spin and Mössbauer effect in the Heisenberg paramagnet
Authors: Krivoglaz M. A. , Los V. F.
Published: July 2007

The time‐dependent correlation function (CF) of a weakly bound impurity spin in a paramagnet and its spectral representation are defined. It is found that the dynamics of such a spin correspond to the Brownian precession under the action of random forces from the spins of crystal atoms. The spectral representation for the correlation function of the impurity spin in a wide frequency range has a Lorentzian shape while its width is much smaller than in a perfect crystal. The spin broadening of the Mössbauer line in the Heisenberg paramagnet is defined. The spin broadening in ideal crystals at high temperatures does not depend on temperature and is much larger than in the ferromagnetic region. In case of the Mössbauer effect on impurity atom nuclei with weakly bound spins such a broadening may be some orders greater than in perfect crystals. Peculiarities of the energy distribution of inelastically scattered neutrons on weakly bound spins are discussed.
Conduction band of IVa and Va subgroup transition metal monocarbides (I)
Authors: Geld P. V. , Tskhai V. A. , Borukhovich A. S. , Dubrovskaya L. B. , Matveenko I. I.
Published: July 2007

Basing on the general conceptions of the band structure of stoichiometric IVa subgroup transition metal monocarbides and assuming two types of atomic interactions a conduction band model for nonstoichiometric carbides has been elaborated which takes into account the vacancies in the carbon sublattice. It is assumed that the formation of vacancies is accompanied by the appearance of local electronic levels in the vicinity of the Fermi level of stoichiometric carbide which, in the case of high concentrations of C‐vacancies, form a subband of unscreened MeMe bonds. This results in a filling of the MeC band, a shift of the Fermi level into the MeMe band, followed by an increase of the electron density of states and an increase of the Fermi level. The increasing density of states leads to an increase in the magnetic susceptibility [17]. On the basis of the above band model, the results of measurements of the Hall effect (in the range 20 to 300° K), thermopower (77 to 300° K), and electric resistivity (77 to 1200° K) of zirconium monocarbide of different composition are discussed. The observed temperature dependence of the Hall coefficient of ZrCx samples indicates that two types of carriers take part in the conduction process, their mutual contribution to this phenomenon changing with the composition of the sample.
Coherence of matter waves in the effect of electron waves modulated by laser beams in solids
Authors: Hora H.
Published: July 2007

For the interpretation of the experiment, where electron beams are modulated at transmission of a laser‐illuminated solid, transferring and generating photons at nonluminescent targets, a simple interaction of electron waves with energies changed by discrete numbers of photons can be assumed. It is concluded that this interaction involves coherence effects of electrons. The coherence length at the conditions of the experiment is of the order of 10−4 cm. The consequences of measuring these coherence effects are discussed with respect to analyse the interaction effect in the crystal, to study free electron beams at electronoptical modifications, and to examine possible coherence effects of electrons at or before emission from solids.
Band structure of HgSe and HgTe
Authors: Bloom S. , Bergstresser T. K.
Published: July 2007

The band structures of HgSe and HgTe are calculated, including spin. The empirical pseudopotential form factors agree with estimated values and the energy differences confirm some previous experimental spectral line assignments.
Ultrasonic Attenuation due to Charge Carriers in Semiconductors and Semimetals
Authors: Sarges K. H.
Published: July 2007

The electronic contribution to the ultrasonic attenuation in single‐valley semiconductors and in two‐valley semimetals at low temperatures is calculated for the case of Fermi statistics, using a semiclassical approach due to Mikoshiba. Analytical expressions for the attenuation coefficient are obtained and computed numerically for frequencies in the range 103 to 1012 Hz. It is found that minority carriers govern the attenuation in noncompensated semimetals and that the attenuation may rise in doped specimens.
The role of p‐phase shifts in covalent solids
Authors: Gilbert R. , Morgan G. J.
Published: July 2007

In this paper we examine the behaviour of the phase shifts of the potentials in a covalent solid when the crystal potential is approximated by a “muffin tin” form. The purpose of this investigation is to try and reconcile the tight binding method with “precision” methods for calculating band structures. We suggest that the role of bound atomic p‐states could be taken over by p‐resonances in the scattering cross sections of the potential wells in a solid.
Déformation plastique du tellure monocristallin. II. Théorie
Authors: di Persio J. , Doukhan J. C. , Saada G.
Published: July 2007

Afin d'expliquer les propriétés mécaniques du tellure décrites en I, nous avons calculé l'énergie élastique des dislocations, compte tenu de l'anisotropie élastique, et montré que la tendance des dislocations à s'aligner parallèlement à l'axe c n'est pas un effet élastique. Nous l'expliquons par un effet de coeur qui peut être décrit comme une dissociation sur trois plans prismatiques de première espèce pour une dislocation c. Pour les dislocations a un tel effet implique sans doute une très forte anisotropie des liaisons interatomiques. Divers modèles de dissociation sont discutés.
Electron and exciton states in solid rare gases
Authors: Rössler U.
Published: July 2007

Energy band calculations of the solid rare gases Ne, Ar, Kr, and Xe and calculations of the conduction band density of states of Kr and Xe are presented. Except for Ne the calculations are based on the relativistic formulation of the Green's function method. Exciton states of the valence Γ‐excitons in Ar, Kr, and Xe have been computed using the pseudopotential formalism of the exciton problem proposed by Hermanson and Phillips and on the basis of the calculated energy bands. The dependence of the exciton binding energies on certain band parameters has been studied. The results are discussed in connection with the optical spectra of the solid rare gases measured by Baldini and the DESY group.
On bonding and structure of epitaxial bicrystals. II. Thin films
Authors: Ball C. A. B.
Published: July 2007

The bonding in epitaxial films on semi‐infinite substrates and its influence on their structural properties are considered. More accurate relationships between the dislocation energy of the system and elastic constants, lattice parameters and thickness, than have been obtained previously, are deduced. Minimum energy configurations are discussed and the dependence between critical thickness and misfit is calculated.
Stress‐ and field‐induced dichroism of the vibrational absorption of OH− Molecules in alkali halides
Authors: Härtel H.
Published: July 2007

This paper presents experimental data about the absorption band of the stretching vibration of OH− in RbCl, KBr, and KCl, and about the field‐ and stress‐induced dichroism of this band at low temperatures. For small concentrations (NOH < 10−4) the spectrum was found to consist of a single band with a halfwidth ≦ 0.1 cm−1 (LHeT). The experiments about the dichroism clearly indicate that for RbCl and KBr the molecule axis of the OH− is pointing along 〈100〉. For OH− in KCl the results are more complicated and cannot be explained completely. However, the general model of a 〈100〉 dipole seems to hold also for this system.
The effect of phonon heating on photoelectric phenomena
Authors: Yassievich I. N. , Schleifstein M.
Published: July 2007

The influence of phonon nonequilibrium on photoelectric and photomagnetic phenomena at low temperatures (T ⪅ 20° K) has been studied. It is shown that the effects essentially depend on the sample dimensions and that in thick samples they are determined by phonon‐phonon collisions. Non‐stationary photoconductivity under the conditions of electron heating has been investigated. The time dependence of photoconductivity is then characterized by two different decay times: the time necessary for the transition to a stationary electron temperature and the usual electron lifetime.
Zero point oscillation energy effect on plastic deformation in solidified gases
Authors: Leonteva A. V. , Stroilov Yu. S. , Lakin E. E. , Bolshutkin D. N.
Published: July 2007

An investigation is made of the deformation of molecular crystals of methane and argon under the conditions of tension and stress relaxation. The Peierls barriers are shown to be the main obstacles for dislocation movement in these crystals in a wide low‐temperature range. The result obtained is in good agreement with data determined for hydrogen, deuterium, and ammonium and is discussed in terms of the peculiarities of intermolecular interactions in molecular crystals. In particular, it is shown, that the contribution of zeropoint oscillation energy to the bonding energy increases with decreasing temperature at which the transition from the Peierls mechanism to higher energy mechanism occurs.
Helicon method for investigation of many‐valley semiconductors
Authors: Tolutis R. B. , Riauka V. L. , Pozhela Yu. K.
Published: July 2007

A theoretical and experimental analysis of dispersion, polarization, and size resonance frequency of helicon waves in many‐valley semiconductors is made under various assumptions with respect to the structure of the valleys. A new technique to measure carrier concentration, mobility, and coefficient of mobility anisotropy, K, is proposed. The dependence of the dispersion of the helicon waves upon carrier intervalley repopulation in n‐Ge subjected to uniaxial compression P at 78 °K is discussed theoretically along with experimental results. The possibility to measure transverse mobility is shown. The dependence of K on P is observed.
Der Zwischenzustand bei Supraleitern zweiter Art
Authors: Krägeloh U.
Published: July 2007

Mittels der Dekorationstechnik von Träuble und Essmann wurde an Blei‐Thallium‐Legierungen mit Werten des Ginzburg‐Landau‐Parameters χ etwas größer als 2−1/2 bei T = 1,2 °K ein Zwischenzustand beobachtet, bei dem Meissner‐Bereiche und Shubnikov‐Bereiche mit konstanten Gitterparametern nebeneinander vorkommen, was auf eine positive Grenzflächenenergie S ihrer Phasengrenzen schließen läßt. Die Grenzflächenenergie S der Phasengrenzen zwischen Meissner‐ und Shubnikov‐Bereichen bzw. normalleitenden Bereichen wurde in Abhängigkeit vom GL‐Parameter χ im Bereich 0,43 ≦ χ ≦ 0,82 aus den magnetischen Strukturen des Zwischenzustandes unter Anwendung der Modelle von Landau, Lifshits und Sharvin bestimmt; S verschwindet bei χ = 2−1/2 nicht. Das Auftreten isolierter Shubnikov‐Bereiche in dem sie umgebenden feldfreien Meissner‐Gebiet wird mit einer noch unbekannten Wechselwirkung zwischen den Flußlinien erklärt, die zusammen mit deren besser bekannten abstoßenden Wechselwirkung zu einem Gitter mit bestimmtem Gitterparameter führen kann. Die Bindungsenergie EB zwischen Flußlinien wird aus der Grenzflächenenergie S abgeschätzt.
Excitonic electroabsorption of CdTe
Authors: Babonas G. , Šileika A.
Published: July 2007

The absorption (4 to 77 °K) and electroabsorption (77 °K) spectra of the recrystallized CdTe thin films were investigated in the vicinity of the fundamental absorption edge. Structures due to optical transitions to states of free and bound excitons and exciton transitions with LO phonon emission were observed. The dependences of the magnitude and position of the electroabsorption peaks on the electric field strength were investigated in the field range 1.5×103 to 7×104 V/cm. The electroabsorption spectra can be interpreted in terms of a field induced excitonic line broadening and interband oscillations.
Electron drift velocity and related phenomena in Si
Authors: Costato M. , Reggiani L.
Published: July 2007

The theoretical evaluation of the electron drift velocity in Si has been performed taking into account the lattice scattering mechanisms and the effect of an energy increasing effective mass. A large range of electric fields (1 to 105 V/cm) running from the ohmic region up to the saturation region has been explained for different lattice temperatures between 77 and 300 °K. The longitudinal anisotropy of the drift velocity for the crystallographic directions 〈111〉, 〈110〉, and 〈100〉 has been successfully evaluated through the valley repopulation mechanism. The fit with experimental data of various authors ranges from fair to good. The results support the correctness of the present interpretation. Lattice scattering mechanisms and their coupling constants have proven to be self‐consistent in the framework of the theory where the predominance of g type over f‐type scattering is confirmed.
Phonon‐assisted exciton annihilation in CdSe crystals
Authors: Abramov V. A. , Permogorov S. A. , Razbirin B. S. , Ekimov A. I.
Published: July 2007

Emission spectra of exciton annihilation are measured in CdSe crystals from 2 to 77 °K. Especially the line‐shape, due to exciton annihilation with simultaneous creation of one or two phonons is considered. This shape can adequately be described on the basis of energy and momentum conservation laws only if the momentum dependence of the exciton‐phonon interaction probability is properly taken into account. As a result analytical expressions E3/2 exp (–E/kT) for the one‐phonon line and E1/2 exp (–E/kT) for the two‐phonon line, where E is the exciton kinetic energy, are obtained. An additional broadening of exciton emission lines, clearly observed at lower temperatures, is assigned to the inherent width of exciton levels.
Intrinsic optical absorption in single crystal β‐rhombohedral boron from 1.8 to 3.5 eV
Authors: Werheit H. , Hausen A. , Binnenbruck H.
Published: July 2007

Absorption coefficients between 2.5 × 103 and 8.5 × 104 cm−1 have been obtained by measurements on wedge‐shaped sample sections of some 10−4 mm thickness at room temperature. The variation of the absorption depending on the photon energy can be adapted to indirect allowed transitions on a rather great energy scale. The threshold energy of (1.605 ±0.01) eV supplies a gap of (1.531 ±0.01) eV, when the energy of the emitted phonons is taken into account.
Paramagnetic resonance of FeLi associates in CdS
Authors: Kemp R. C.
Published: July 2007

Paramagnetic resonance spectra attributed to three Fe3+:Li+ associated centres FL(I), FL(II), and FL(III) have been studied at 77 °K in CdS single crystals. FL(I) may be described with an orthorhombic spin Hamiltonian magnified image with S = 5/2, g0 = 2.018, D = 0.304 cm−, and E/D = 0.265. The x‐ and y‐axes for centre FL(I) lie in the (11±20) plane and the y‐axis makes an angle of (15±2)° with the c‐axis. The centres FL(II) and FL(III) cannot be fitted satisfactorily, probably due to anisotropy in g0.
F‐Centre saturation phenomena in KCl during low‐energy electron irradiation
Authors: Soul P. B.
Published: July 2007

The absorption levels in the F‐ and M‐bands in KCl have been monitored during controlled high‐intensity irradiation with 5 keV electrons at room temperature, and novel saturation effects have been observed. The F‐centre concentration rises to a maximum of between 4 and 7 × 1019 cm−3 (depending on the dose rate) and then decays slowly to an equilibrium level. The M‐band absorption rises steadily except for a “plateau” coinciding with the F‐centre maximum. After irradiation F‐to‐M‐centre conversion takes place, but this is reversed on re‐irradiation. These effects can be explained using a model in which F‐centres produced less than about 25 Å apart aggregate spontaneously; in addition, M‐centres appear to be split up into F‐centres by the radiation itself. The relatively large amount of energy (45 keV) apparently expended in forming each vacancy suggests that there is also a high rate of recombination with interstitial defects during irradiation.
The isotope dependence of the self‐trapping energy of a light interstitial in a metal, and its effect on activation energies in diffusion
Authors: Matthew J. A. D.
Published: July 2007

The isotope dependence of the strain energy or “self trapping energy” of a light interstitial in a metal is considered for a model in which the interstitial interacts with the lattice through a two body potential. Estimates indicate that the difference in the volume of solution of hydrogen and deuterium in various metals will be at maximum only a few percent. These results suggest that the “self trapping energy” barrier in the quantum mechanical diffusion theory of Flynn and Stoneham will not lead to large isotope effects in the activation energy.
The relaxation of mobile space charge in solids
Authors: Lemke H.
Published: July 2007

The system of differential equations governing the relaxation of free space charge in semiconductors and in insulators with trapped space charge is discussed neglecting diffusion. In both cases general solutions can be given if symmetrical initial distributions are considered. They are of the form magnified image respectively, where δp is the free space charge, ξ the space coordinate, t the time, t the dielectric relaxation time, t the relaxation time of electrons in p‐type semiconductors under complete hole extraction. In the case of small disturbance δp≪p0 at any place an exponential decay with t occurs (dielectric relaxation). In the case of large disturbance δp≫p0 within t the space charge is steeply reduced tot he regime of small disturbance, decaying further exponentially with t. The propagation velocity of steep space charge gradients is initially proportional to the central charge concentration and decays (dielectric relaxation) or grows exponentially with the constant t or t.
Energy Band Structure of the Tetragonal Crystals ZnP2 and CdP2
Authors: Sobolev V. V. , Syrbu N. N. , Sushkevich T. N.
Published: July 2007

The anisotropic spectra of edge absorption, photoconductivity, emission, and reflectivity of the tetragonal ZnP2 and CdP2 crystals have been experimentally investigated in the range 1 to 12.5 eV. The selection rules for interband transitions, the points of zero slope, and the dispersion relations at general points of the Brillouin zone have been derived by group‐theoretical methods. From an analysis of the experimental and theoretical data conceivable energy band models of the tetragonal ZnP2 and CdP2 crystals are proposed.
The Mobility of Grown‐in Dislocations in the Intermetallic Compound MgZn2 II. Stress Dependence of Basal Slip at 390 °C
Authors: Paufler P. , Marschner J. , Schulze G. E. R.
Published: July 2007

The velocity ẋ of grown‐in (0001) 〈1210〉 dislocations in the intermetallic compound MgZn2 has been determined as a function of the shear stress τ at 390 °C. The results show that ẋ fits an exp (—const/τ) dependence as in the case of prism slip. Comparison of basal and prism slip gives evidence for a low anisotropy of the Peierls stress. Microscopic measurements are in good agreement with stationary creep data when experimental results of the mobile dislocation density are used.
Linear Stark Effect of the R' Center in LiF
Authors: Davis J. A. , Fitchen D. B.
Published: July 2007

A resolved linear Stark splitting is observed for the R' zero‐phenon line in absorption in good agreement with the predictions for an A → E transition at a center of C3v symmetry.
Heat Transport in Impure Insulators at Low Temperatures
Authors: Joshi Y. P. , Verma G. S.
Published: July 2007

The Boltzmann transport equation is solved for phonons in an impure insulator slab to obtain the simplest possible and physically plausible solution. The equation is not treated as a boundary value problem, but it is assumed that the occupation number for phonon states corresponding to a given frequency and polarization is a smooth function of the direction of phonon wave vector. Heat flux and energy density in the crystal are studied when such a solution is assumed to exist.
Extrinsic Stacking Faults in Iridium
Authors: Fortes M. A.
Published: July 2007

The stacking faults in Shockley type loops, observed in iridium field‐ion images, have been analyzed for the type of fault, using a method developed in a previous paper [1]. In all cases where the identification was possible, the faults were found to be extrinsic. This result is discussed in the light of the origin of the defects, and related to the large negative hydrostatic pressures that occur in field‐ion specimens.
Helmholtz Free Energy of an Anharmonic Crystal: A Green Function Approach
Authors: Shukla R. C. , Muller E. B.
Published: July 2007

The thermodynamic Green function of a weak anharmonic crystal, obtained through the equation of motion method, has been used to derive an explicit expression for the interaction energy. The Helmholtz free energy (F) has been obtained by integrating this interaction energy over a formal coupling parameter. Under certain conditions the expression for F has been shown to be identical with that obtained from perturbation theory and diagrammatic methods.
Polarization Effect in the Soft X‐Ray Absorption of CdS
Authors: Watanabe M. , Yamashita H. , Nakai Y. , Sato S. , Onari S.
Published: July 2007

A strong polarization dependence of the optical transition from the inner core level is observed in the S LII,III absorption spectra of hexagonal CdS (160 to 170 eV), using the synchrotron orbital radiation. The present results are discussed in comparison with the interpretation made on reflection spectra obtained in the ultraviolet region (3 to 12 eV).
Electron Energy Losses and Optical Constants of Ne and CH4
Authors: Daniels J. , Krüger P.
Published: July 2007

From energy loss measurements of fast electrons on solid neon and methane the energy loss functions Im (−1/ε) and the dielectric constants ε = ε1 + iε2 are calculated. The ε2‐spectra of the solids are compared with the energy loss spectra of gaseous Ne and CH4.
Optical Properties of Cadmium Single Crystals
Authors: Schwarz H.
Published: July 2007

The optical properties of cadmium single crystals and of a cadmium film deposited by vacuum evaporation were measured in the energy range from 0.5 to 5.5 eV in dependence on temperature, crystal orientation, and the pressure in the vacuum chamber. The results prove that oxide layers become effective only at higher energies. The influence of adsorbed impurity films, which arise on the sample surfaces at low temperatures, is negligible at a pressure of p = 10−9 Torr, while the results obtained at higher pressures are falsified in the whole energy region investigated. The results obtained at a pressure of p = 10−9 Torr agree with theoretical calculations of the optical absorption.
Covalent bonding effect on Van Vleck paramagnetism in AIIBIII2CVI4 semiconductor compounds
Authors: Manca P. , Muntoni C. , Raga F. , Spiga A.
Published: July 2007

The magnetic susceptibility of some AIIBIII2CVI4 defect tetrahedral compounds was measured at room temperature. The experimental data are analyzed along the line of previous theoretical considerations in which the Langevin and the Van Vleck magnetic susceptibility components are described, respectively, in terms of atomic and bonding parameters of the compounds considered. A comparison of the experimental results with those of ANB8–N normal tetrahedral compounds can be made by introducing the number of bonds per formula as a normalization factor.
Theory of the current‐voltage (I‐U) characteristics of monopolar and quasi‐monopolar semiconductors with different intensities of contact and volume injection
Authors: Zyuganov A. N. , Pismennyi Yu. G. , Svechnikov S. V.
Published: July 2007

An undiffused theory of the static current‐voltage characteristics of photosensitive semiconductors is proposed within the limits of the two‐level band scheme which is usual for such materials. The analysis of I‐U characteristics permits the determination of some parameters of the band scheme, injecting properties of the contact and to fix the switching of recombination channel under the conditions of excitation of the semiconductor in the intrinsic absorption region. The finite value of contact injection leads to definite values of the greatest slope of the I‐U characteristic in the region of trap filled limited voltage (VTFL).
Étude spectroscopique du grenat d'europium gallium (EuGaG)
Authors: Boccara A. C. , Briffaut J. P. , Hodges J. A. , Moreau N.
Published: July 2007

A partir du spectre d'absorption du grenat d'europium gallium (EuGaG), nous avons déterminé les paramètres A02 et A22 de l'hamiltonien du champ cristallin agissant sur Eu3+. Le modèle de charges pontuelles se révèle, dans ce cas, très satisfaisant pour le calcul du rapport A22/A02. Des mesures de dichroïsme circulaire magnétique (DCM) nous ont permis de détecter des doublets non résolus en absorption, de confirmer le résultat obtenu par le modèle de charges ponctuelles et de déduire les facteurs de Landé des niveaux 7F1 et 5D1.
Die Dichte der beweglichen Versetzungen in Germanium
Authors: Springer E.
Published: July 2007

Mittels Doppelätzungen wird in Germanium‐Einkristallen der Anteil der bewegten unter den angeätzten Versetzungen bei Intervallverformungen bestimmt. Im Bereich I der Verformungskurve sind es ≈ 90%. Für den Bereich II ergeben sich Anhaltspunkte, daß der Prozentsatz der bewegten unter den angeätzten Versetzungen wesentlich kleiner ist (nahe 45%).
Surface electron‐phonon interaction
Authors: Ilkovič V.
Published: July 2007

The scattering of conduction electrons by surface waves is studied theoretically basing on energy considerations. The relaxation time for this scattering mechanism and the quantity \documentclass{article}\pagestyle{empty}\begin{document}$ (\overline {\partial \varepsilon /\partial t})_s $\end{document} characterizing the mean energy which is transferred by the conduction electrons to the surface lattice per unit time are calculated.
The optical anisotropy of cubic nickel‐iodine boracite due to quadrupole transitions
Authors: Pastrňák J. , Cross L. E.
Published: July 2007

Measurements of the optical absorption of NiI boracite crystals for [100], [110], and [111] directions of light propagation reveal an unexpected angular dependence of the value of absorption coefficient and for the [110] direction also a dependence on the orientation of the plane of polarization of the incident light. These results as well as the existence of pronounced birefringence for the [110] direction of light propagation can be explained by the presence of quadrupole transitions. The results obtained are compared with Hellwege's theory of quadrupole transitions [1]. The functions which describe the angular dependence of the radiation probability for a cubic crystal with quadrupole transitions are found to be in agreement with the experimental results, if the theoretically determined functions [1] are taken in linear combination so as to fulfill the requirement of cubic symmetry.
Superconductivity in interacting chains some exact results
Authors: Mubayi V. , Gupta K. K.
Published: July 2007

It is shown that for a system of interacting one‐dimensional chains superconductivity cannot exist.
Generalized exchange interaction and Kondo effect
Authors: Ganguly B. N.
Published: July 2007

The internal degree of freedom of the impurity atom is taken into account in calculating the anomalous part of the resistivity leading to the Kondo effect. This is achieved by adopting a generalization of the usual s—d exchange interaction, first proposed by Vonsovskii and Svirskii. We find that, if the intra‐atomic exchange interaction is neglected, the logarithmically divergent character of the anomalous part of the resistivity is retained with an effective coupling strength. It is argued that the inclusion of the intra‐atomic exchange term may affect the logarithmically divergent character of the conduction electron scattering amplitude near the Fermi surface.
On the acoustical asymptotics of the phonon spectrum of a finite crystal
Authors: Iosilevskii Ya. A.
Published: July 2007

The acoustical asymptotics of the spectral distribution of the vibrations of separate atoms in dependence on their positions in the crystal are considered for the cases of a semispace and a plane‐parallel plate of arbitrary thickness. The general solution of the problem is obtained in the case of an arbitrary orientation of the boundary surfaces with respect to the crystallographic axes. In the elastically isotropie continuum approximation this solution is analysed in detail. For the surface atoms the tensor of the Debye effective frequencies is constructed. The method is taken from the dynamics of a crystal with extended defects which in the case under consideration are the stress‐free plane boundaries and is based on an accurately solving of integral equations such as the Dyson ones. The results obtained are discussed in connection with the mean square fluctuations of the positions and momenta of the crystal atoms determining the intensity and the energy position of the Mössbauer no‐phonon line and the Debye‐Waller factor in the cross section of the low‐energy particles. They are also discussed with respect to the surface contribution to the low‐temperature heat capacity. In particular, the statistical weight of the Rayleigh waves in the scale of the squared frequencies is shown to be proportional to √ω2 as well as the density of the three‐dimensional phonon states. Thus the surface vibrations do not lead to deviations of order T2 from the T3‐behaviour of the lattice thermal capacity. Such deviations are due to the surface not in itself as a two‐dimensional manifold but to its closeness, leading to quantization of the volume vibrations and to appearance of new specific modes.
Thermal conductivity of indium antimonide at low temperatures
Authors: Kosarev V. V. , Tamarin P. V. , Shalyt S. S.
Published: July 2007

A detailed experimental investigation was made of the phonon thermal conductivity on n‐ and p‐type indium antimonide of single crystals (carrier concentrations 1014 to 1018cm−3) in the temperature range 2 to 100 °K. It is shown that the experimental results may be explained by a new mechanism of phonon scattering by charge carriers in the electrical field of impurity centres [2] and a more consistent consideration of the role of normal processes of phonon‐phonon interaction at low temperatures.
Electromultipole interaction and paramagnetic relaxation in ruby. IV. Spin‐lattice relaxation
Authors: Peskovatskii S. A.
Published: July 2007

The influence of the stretched line wings on the spin‐lattice (longitudinal) relaxation rate is considered. It is shown that in the spin‐system with long line wings even the direct process of the spin‐lattice energy exchange may involve mainly nonresonant phonons. The component of the relaxation rate owing to the wing (Wg) has a stronger temperature dependence than that of the conventional direct process. The shape of the line wings determines the power of this dependence, The wings of the quadrupole‐quadrupole broadened lines give n = 2.4. The relaxation owing to the wings explains anomalies in the temperature, concentration, and frequency dependences of the longitudinal relaxation rate observed. The relaxation model proposed fits well the experimental results of Cr3+ ions in corundum and rutile. It is quite possible that this model plays an important role in other paramagnetics, too.
Optical properties of silver iodide
Authors: Suri S. K. , Henisch H. K.
Published: July 2007

Measurements are reported of the fundamental optical absorption edge, its temperature dependence and anisotropy, for pure and copper‐doped β‐AgI single crystals grown by the gel method. The temperature range spans the β → α phase transition. Studies of photoluminescence and cathodoluminescence are also described, and interpreted in terms of band and defect structure.
Free excitons and optical spectra of semiconductors
Authors: Auvergne D. , Camassel J.
Published: July 2007

It is shown, that the excitonic wave functions exhibit a discontinuity at the transition between free and bound states. In the real case where carriers spend a finite time on excited levels, it is possible to neglect the Coulomb interaction when the two particles have a kinetic energy greater than a few Rydbergs. Using this hypothesis, an absorption curve in good agreement with the experimental results on GaAs is calculated.
Low lying resonant band modes in CsBr and CsI crystals doped with In+ and Tl+
Authors: Prettl W. , Siep E.
Published: July 2007

Measurements of the far infrared absorption due to In+ and Tl+ impurities in CsBr and CsI single crystals yielded low frequency resonances with narrow linewidths at 11.0 cm−1 in CsBr:In+, 12.0 cm−1 in CsI:In+, 14.1 cm−1 in CsI:Tl+, and 16.95 cm−1 in CsBr:Tl+. The frequencies of the resonant band modes in the Tl+ doped crystals shift to higher values with increasing temperature. Using a model of the perturbed crystal which involves the mass defect and the change of the central force constants between the defect and its eight nearest neighbours, the force constant change is fitted to the various resonance frequencies. The resulting linewidths are compared with the experimentally determined values.
The mössbauer study of Fe57 and Sn119 in FeSn at 5 °K
Authors: Ligenza S.
Published: July 2007

Mössbauer investigations have been performed for both Fe57 and Sn119 nuclei in FeSn at 5 °K. The numerical analysis of the absorption spectra and calculations of the hyperfine parameters have been made using the GIER computer. It was found that 1/6 of the total number of Fe spins is aligned at an angle of 60° relative to the main spin directions [100] or [210]. The values of the effective field for iron atoms is discussed in terms of the difference in isomer shifts.
Analysis of point defect states in copper. III. Interaction between copper interstitials and impurities
Authors: Kraut A. , Dworschak F. , Wollenberger H.
Published: July 2007

The influence of impurities on the production of stable defects by electron irradiation at 80 °K has been studied in dilute alloys of copper with Ni, Mn, Au, Mg, or Sb. Using damage rate measurements the capture radii of the different impurities for freely migrating copper interstitials are determined with respect to the capture radius of the vacancy (rt/rv). The interstitial impurity interaction can quantitatively be accounted for by the continuum theory of elasticity.
The critical magnetic field of thin superconducting films
Authors: Litovchenko V. A.
Published: July 2007

In recent papers [1 to 4] on critical magnetic field of superconducting films the one‐electron state is treated almost in a “semiclassical” way. Though the motion of electrons in the direction of the film thickness is described by a quantum number n [2], the special features of electron pairing in thin films were not taken into account. Thus the results are valid only for thick metal films (L ≧ 10−5 cm). In this paper the quantization of electron motion in the direction of the film thickness is taken into account. This motion is described by a wave function Ψ(z) and a quantum number n. Moreover Cooper pairs are built in a correct way [5]. He is calculated for thin metal films. In the limiting case of thick films the result agrees with that of [2]. Furthermore, the approach used permits to study semi‐metal and semiconducting films too, where Hc is calculated for the whole range of thicknesses (50 to 1000 Å). All results are valid near Tc.
Effect of uniaxial compression on the thermomagnetic effects in bismuth
Authors: Ertl M. E. , Rahman I. U.
Published: July 2007

Thermomagnetic transport parameters have been measured in bismuth at 80 °K and found to be strongly pressure‐dependent. Results indicate that in addition to a decrease in the energy overlap, E0, there is an increased participation of a light hole band increasing the mobility of holes. The Nernst effect and the magneto‐Seebeck effect are particularly sensitive to changes in hole mobility. In some orientations the Seebeck voltage in a field of 0.47 Wb/m2 can change sign under uniaxial compression.
Hyperfine fields in concentrated FeCr alloys
Authors: Schwartz L. H. , Chandra D.
Published: July 2007

Mössbauer spectra of alloys in the range Fe–24 at% Cr to Fe–60 at% Cr have been analyzed using an extension to high concentrations of the results for dilute alloys. The decrease in hyperfine field at an Fe nucleus due to the presence of one Cr near or next near neighbor was found to be 7.5%, concentration independent over the range studied, and in excellent accord with the value of 7.6% found for dilute alloys of Cr in Fe. The isomer shift per Cr neighbor was found to be −0.02 mm/s, also independent of concentration and in good agreement with the value of −0.03 mm/s found for dilute alloys. The same parameters gave equally satisfactory fits to the spectra for randomly polarized absorbers and for high field experiments with the absorber magnetization saturated parallel to the direction of γ‐ray propagation.
Influence of the Electric Field on the Exciton Absorption in Germanium
Authors: Aronov A. G. , Mochan I. V. , Zemskii V. I.
Published: July 2007

In germanium the electro‐absorption in the indirect absorption region was measured by two differential methods: the method of frequency modulation and the method of electro‐modulation. The experimental results are compared to calculations taking the electron–hole interaction into account. A quantitative description of the electro‐absorption spectra is obtained both for the allowed and for the forbidden transitions. It is shown that the first maximum of the electro‐absorption spectrum corresponds to the threshold energy in the case of allowed transitions (if no broadening effects are taken into account), whereas for the forbidden transitions the zero‐point corresponds to the threshold energy. The Franz‐Keldysh effect was also observed in the region of transitions to the continuous spectrum. This effect is found to be considerably smaller than the effects leading to the change of the absorption coefficient by the electric field in the region of transitions to the exciton band.
Interpretation of Far UV Spectra in Solid Rare Gases from Calculated Density of States
Authors: Rössler U.
Published: July 2007

The conduction band density of states has been calculated for solid Ar, Kr, and Xe on the basis of KKR energy bands. The joint density of states between conduction bands and core states is determined and an interpretation of core excitation spectra of solid Ar, Kr, and Xe is given. The results show that up to minor excitonic effects the far uv spectra are mainly determined by the conduction band density of states.
The Mössbauer Line Shape for Divalent Iron in Silver Chloride Crystals
Authors: Tumolillo T. A.
Published: July 2007

The Mössbauer line shape is calculated for 57Fe in a fluctuating electric field gradient. This gradient is produced by the random jumping of a charge compensating positive ion vacancy which is bound to divalent iron in silver chloride. In order to simplify the calculations the vacancy is only allowed to occupy the nearest and next nearest positive ion sites with respect to the iron ion. Examples of computed spectra are presented and discussed.
A Neutron Diffraction Study of Palladium Hydride
Authors: Nelin G.
Published: July 2007

Neutron diffraction measurements have been made on palladium hydride formed by soaking powdered palladium in gaseous hydrogen. The results obtained are best described in terms of a palladium lattice with hydrogen atoms in octahedral positions.
Calculation of the Mössbauer Parameters for a Disordered Cubic Crystal Lattice
Authors: Srivastava B. P. , Sharma H. N. K. , Bhattacharya D. L.
Published: July 2007

A theoretical expression is derived for a cubic crystal lattice disordered by the introduction of a vacancy‐interstitial pair. Considering only the nearest neighbour interaction for the interstitial atom, the double‐time Green's function has been formally calculated and the ratio of the Debye‐Waller factor for the disordered lattice to that of the perfect lattice has been obtained. It is found that in the presence of a point defect pair, the exponent ratio of the disordered lattice to that of the perfect lattice becomes [1 + 4 Γlk, × {u(−2)−(h/2 kT) u(−1)}] where γtk is a factor, for which the major contribution comes from the position vector of the interstitial atom and u(2p) is the 2 p‐th moment of the frequency spectrum of a cubic lattice.
Localized Non‐Magnetic Impurities in Metals
Authors: Dubey S. K.
Published: July 2007

The problem of non‐magnetic impurities in metals has been studied using the double‐time Green's function technique. An interaction term for impurity and metal interaction similar to that of Anderson has been defined. This gives rise to inelastic and incoherent scattering of the electrons. An expression has been developed for the transition probability and the temperature dependent part of the impurity resistivity.
27Al NMR Spectra in Al3d Transition Metal Alloys
Authors: Grüner G. , Kovács‐Csetényi E. , Tompa K. , Vassel C. R.
Published: July 2007

The electric and magnetic perturbations around Mn, Cr, and Fe impurities in aluminium were investigated by measuring the 27Al NMR spectra of these alloys. The first order quadrupole wipe‐out numbers measured at low impurity concentrations, and the magnetic field dependence of the signal amplitude in more concentrated alloys are discussed in the framework of the Friedel‐Anderson picture.