bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Model of the Temperature Dependent Part of Stage I Work‐Hardening due to Jog‐Dragging (I)
Authors: Messerschmidt U. 
Published: July 2007

AbstractA 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

AbstractMeasurements 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

AbstractStatic 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

AbstractMeasurements 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

AbstractThe 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

AbstractThe 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

AbstractMacroscopic 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

AbstractThe 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

AbstractBasing 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

AbstractFor 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.
Ultrasonic Attenuation due to Charge Carriers in Semiconductors and Semimetals
Authors: Sarges K. H. 
Published: July 2007

AbstractThe 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

AbstractIn 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

AbstractAfin 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

AbstractEnergy 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

AbstractThe 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

AbstractThis 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

AbstractThe 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

AbstractAn 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

AbstractA 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

AbstractMittels 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

AbstractThe 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

AbstractThe 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

AbstractEmission 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

AbstractAbsorption 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

AbstractParamagnetic 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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.