bluuebunny/crossref_metadata_2025_split huggingface dataset:
Measurement of Forbidden Energy Gap of Semiconductors by Diffuse Reflectance Technique
Authors: Tandon S. P. , Gupta J. P. 
Published: July 2007

AbstractDiffuse reflectance technique for the measurement of forbidden energy gap, Eg, is discussed. The energy coordinate of the point at which the linear increase in the Kubelka‐Munk function starts gives the Eg‐value. The Eg‐values of fifteen semiconductors are reported. These Eg‐values are found to be in good agreement with those measured by other methods.
Cottrell‐Stokes Ratios and Dislocation Distributions in Copper
Authors: Bullen F. P. , McK. Cousland S. 
Published: July 2007

AbstractThe Cottrell‐Stokes ratio in polycrystals remains sensibly constant at low and intermediate flow stresses [1]; in single crystals deformed in simple tension it increases with flow stress, beyond stage I [2]. The present paper describes the C‐S ratio/flow‐stress relationship in single crystals in which “alien” dislocation distributions were produced by twisting, by constrained tensile strain, or by change of glide plane after prestrain. The C‐S ratios of such crystals were independent of their initial flow stress (beyond the range of normal stage I values) and remained constant during further tensile strain; at intermediate flow stresses, the C‐S ratios were always greater than those for single crystals deformed in simple tension and approximately equal to those for deformed polycrystals. It is proposed that the common value for our alien distributions and polycrystals corresponds to an isotropic dislocation distribution, and that “forest‐rich” anisotropic distributions approach isotropy more rapidly with increasing strain than those with excess primary dislocations. The difference in rate of approach is compatible with the different roles of primary and secondary dislocations in “single‐slip” deformation and with the single‐valued nature of the C‐S ratio/flow‐stress relationship for unconstrained tensile deformation of single crystals [2].
Description of Elastic and Dielastic Interactions in Superconductors by Quasidislocations
Authors: Kronmüller H. , Riedel H. 
Published: July 2007

AbstractThe interaction between dislocations and the superconducting state is usually attributed to the ΔV‐effect, the ΔE‐effect, and to non‐linear elasticity effects. It is shown that all three types of interactions may be described in a unified manner in terms of quasidislocations. For the interaction forces between crystal dislocations and quasidislocations which are generated by the superconducting state a generalized Peach‐Koehler‐type formula is derived.
Contribution à la théorie de la résistivité électrique des joints de grains métalliques
Authors: Guyot P. 
Published: July 2007

AbstractOn présente une méthode de calcul de la résistivité électrique des joints de grains de forte désorientation, pour les métaux à surface de Fermi anisotrope. Elle consiste à évaluer la fraction d'électrons de conduction complètement réfléchis sur les joints, dont on déduit une valeur limite inférieure de la résistivité. Une moyenne, effectuée sur des joints d'orientation simple dans le cuivre, donne un ordre de grandeur raisonnable comparé aux résultats expérimentaux trouvés dans la littérature.
Theory of F‐Centres in Alkaline Earth Fluorides
Authors: den Hartog H. W. 
Published: July 2007

AbstractF‐centres in alkaline earth fluorides have been investigated by means of optical and ESR experiments. From these results we can obtain information about the charge distribution, which appears to deviate from that observed in the alkali halides. We have found some evidence that LCAO‐type wave functions give a better description of the physical properties of F‐centres in alkaline earth fluorides than the conventional central wave functions, which were quite successful in describing the F‐electron in the alkali halides. Some new relations between the optical transition energy and the hfs constants and the radius of the monovalent cations surrounding the vacancy are given.
Effect of Impurity Precipitations on the Anomalous X‐Ray Transmission in Heavily Arsenic‐Doped Germanium
Authors: Efimov O. N. , Sheikhet E. G. , Datsenko L. I. 
Published: July 2007

AbstractExperimental data of quantitative studies of the integral characteristics of anomalous X‐ray transmission are given for germanium with different dislocation densities, doped with arsenic up to a concentration of ≈4 × 1019 at/cm−3 at various stages of existence and decomposition of the solid solution. The state of solid solution was controlled by electrophysical measurements and X‐ray topographs (Borrmann's method). On the basis of the results obtained some conclusions are drawn about the character of the disturbances generated by the above mentioned decomposition of the solid solution. Particularities of the solution behaviour are considered when the concentration of arsenic is near the limit.
Émission thermo‐électronique, conduction électrique et thermogravimétrie dans l'étude des défauts ponctuels de la zircone
Authors: Loup J. P. , Anthony A. M. 
Published: July 2007

AbstractL'émission thermo‐électronique de la zircone non activée est étudiée en présence d'oxygène de 10−6 à 10−11 atm dans le domaine de température 1650 à 1900 °K. Le réseau d'isothermes fait apparaitre deux domaines de pression; sous basse pression le courant émis varie en Po−1/62 et sous pression plus élevée en Po−1/32. L'énergie „d'activation apparente”︁ de l'émission à pression fixe, est trés proche dans les deux domaines. On montre que l'émission de l'oxyde ne dépend pas de son état de surface mais est liée à la nature et à la concentration des défauts atomiques ponctuels présents dans le volume du solide. Le désordre anti‐Frenkel, avec des ions oxygène simplement chargés, est proposé; il permet d'effectuer la synthèse des résultats expérimentaux d'émission, de conductivité, de nombre de transport et de thermogravimétrie.
Effect of Tensile Stress on the Magnetic Domain Structure of Iron Foils
Authors: Finbow D. C. , Havard D. A. 
Published: July 2007

AbstractThin electropolished foils of iron have been strained in an electron microscope. Their magnetic domain structures have been observed with the technique of Lorentz electron microscopy. The observed changes are consistent with theoretical predictions and macroscopic experimental studies. A simple geometrical construction is shown to explain some of the qualitative features of stress magnetization curves in small constant magnetic fields.
Low Temperature Motion of Néel and Bloch Walls
Authors: Bostanjoglo O. , Kreisel P. , Oelmann A. 
Published: July 2007

AbstractThe motion of Néel and Bloch walls in a quasistatic magnetic field was investigated by Lorentz microscopy in the range 4 to 300°K. Below a critical temperature (28 °K for polycrystalline Permalloy and 40°K for poly‐ and monocrystalline iron and cobalt films) the usual Barkhausen jumps of the wall motion with jump size 1 to 50 μm were abruptly quenched. The wall then moved by tiny jumps (size ≈ 0.1 or < 0.03 μm) and in a constant field. These effects – associated with the motion of Néel, Bloch, cross‐tie walls and circle Bloch lines along the walls of locked domains – were ascribed to the suppression of the diffusion and orientation after‐effect of crystal defects.
Energy Transfer from Donor–Acceptor Pairs to Deep‐Lying Impurity States in Semiconductors
Authors: Shaffer J. , Williams F. 
Published: July 2007

AbstractAfter briefly reviewing the formulation of resonance energy transfer, we consider resonance transfer from effective mass electronic states of donor‐acceptor pairs to tightly‐bound electronic states of impurities in semiconductors. Two general cases requiring different theoretical analyses are considered: 1. transfer from the donor‐acceptor pair to a distant point fluorescer and 2. transfer from the pair to intra‐core fluorescer states of the donor or acceptor. The energy transfer matrices for both cases are shown to depend on the radiative transition matrix for the fluorescer. For case 1, the transfer matrix depends on the overlap of the effective mass function of donor and acceptor; for case 2 the main contribution arises from effective mass functions in the unit cell within which is the fluorescer core. The analyses are applied qualitatively to ZnS:Cu, Ga, Mn and to ZnS:Cu, Tb, and comparisons made with other transfer mechanisms. Finally, transfer involving intra‐donor transitions is predicted.
Lattice‐Scattering Ohmic Mobility of Electrons in Silicon
Authors: Costato M. , Reggiani L. 
Published: July 2007

AbstractThe ohmic mobility of electrons affected only by lattice scattering has been investigated theoretically in Si. Using a displaced Maxwell‐Boltzmann distribution function and considering the permitted electron‐phonon interactions experimental data have been fitted to the results obtained. The results support the importance of intervalley scattering by low‐energy LA phonons in agreement with Dumke, with Onton, and with previous results of the authors on non‐ohmic mobility, and in disagreement with Long.
About the Crystal Field Theory of Tetrahedral Sites in Spinel Lattices
Authors: Jäger E. , Perthel R. 
Published: July 2007

AbstractIn a foregoing paper [1] the crystal field potential of an octahedral site in a spinel lattice was calculated using the point charge model and considering the ten nearest environments. Analogous to these calculations the crystal field potential of a tetrahedral site in the lattice of a normal spinel is calculated. As an example for application the spectrum of Co2+ions in a diamagnetic spinel is considered, taking into account also the influence of a magnetic field, and compared with experimental data.
Ionic Displacement in Currents in Irradiated Alkali Halides
Authors: Fuchs W. , Taylor A. 
Published: July 2007

AbstractA brief theoretical discussion is given of possible ionic and electronic displacement currents associated with the random walk annealing of Br− interstitials in KBr. Experimentally we have observed displacement current peaks during isochronal annealing at 22.0, 24, and 27°K subsequent to cobalt gamma irradiation at 10°K. Only the lowest temperature peak appears to be ascribable to an ionic current due to interstitial‐vacancy recombination. It is concluded that less than 1% of the Br− interstitials in the irradiated crystals were free to participate in a random walk annihilation process.
The Validity of the Tenth‐Power Law of the Magnetic Crystal Energy
Authors: Hausmann K. 
Published: July 2007

AbstractA general derivation of the M10‐law for the anisotropy constant K1 of cubic ferro‐ and ferrimagnets is presented in the frame of spin wave theory. No assumptions on the degree of localization of the magnetic electrons are needed. The M10‐law is valid if the vacuum state of magnons is temperature independent. The anomalous temperature dependence of K1 in the case of nickel is explained by the hypothesis of indirect anisotropic exchange.
Temperature Effects on Zircon Structure Lattice Parameters and Zero‐Field Resonance for Substituted Gd3+
Authors: Kahle H. G. , Schopper H. C. , Urban W. , Wüchner W. 
Published: July 2007

AbstractThe linear expansion coefficients of the unit cell of several zircon structure crystals were determined from high‐temperature X‐ray data and compared with the temperature dependence of the rotational parameters in the corresponding spin Hamiltonian for Gd3−, taken from zero‐field resonance work.
Faraday Rotation due to Excitons in Evaporated CuCl Films
Authors: Koda T. , Segawa Y. , Mitani T. 
Published: July 2007

AbstractFaraday rotation spectra which may be ascribed to excitons were measured on evaporated films of CuCl. The observed rotation anomaly due to the Z3 exciton was successfully analyzed in terms of a classical dispersion theory, thereby yielding data of the temperature‐dependent damping constant, the oscillator strength, and the effective g‐value for the Z3 exciton. On the basis of the effective mass approximation, estimates were made for the effective mass and g‐values of the relevant conduction and valence bands.
Effect of Three‐Body Interactions on the Shell Model of Alkali Halides: Application to KF and KCl
Authors: Singh R. K. , Verma M. P. 
Published: July 2007

AbstractA modified shell model of ionic solids described in two earlier communications [1, 2] has been applied to study the lattice dynamics of KF and KCl. The theoretical results obtained are found to agree excellently well with available experimental data.
Ultrasonic Attenuation in Nickel in the Vicinity of Curie Temperature
Authors: Basu B. K. 
Published: July 2007

AbstractAn investigation is made of the critical attenuation of longitudinal ultrasonic waves in nickel single crystals of different purity and the influence of small magnetic fields is examined. The attenuation is less in crystals of lower purity. In a magnetic field the attenuation shows considerable anisotropy. The data show that the critical temperature Tc lies above the temperature corresponding to the peak attenuation. Tc has been evaluated using the observations in transverse magnetic fields. The results support the dynamical scaling hypothesis.
Some Features of ESR and Spin–Lattice Relaxation of Electrons in Ge and InSb with Different Donor Concentrations
Authors: Gershenzon E. M. , Pevin N. M. , Fogelson M. S. 
Published: July 2007

AbstractThe concentration and temperature dependence of the ESR linewidth in n‐Ge and n‐InSb and spin–lattice relaxation times in Ge: As have been investigated in the X‐band. ESR line narrowing and the increase of the spin‐lattice relaxation rate with concentration in the low concentration range are explained by overlap of the donor electron wave functions. In the high concentration range the ESR data are compared with the theories of the spin relaxation of conduction electrons.
Optical and Photoelectrical Properties of β‐Rhombohedral Boron II. Photoeffects
Authors: Werheit H. 
Published: July 2007

Abstractβ‐rhombohedral boron is characterized as infrared phosphor. Below 100 °C the optical absorption in the region between absorption edge and lattice vibrations as well as the electrical conductivity show a considerable rise during illumination with white light caused by two trapping levels of great density of states. At low temperatures both levels cannot be occupied simultaneously. Optical ionization spectra of charged traps (“photoabsorption”) give high activation energies confirmed by glow curves derived from the temperature dependence of photoabsorption. The recombination of trapped electrons and free holes does not take place directly but via the conduction band. Therefore it is considerably delayed especially at low temperatures because of the high ionization energies of the traps.
ESR Study of Cadmium Boracites Doped with Nickel
Authors: Baberschke K. , Reich S. , Dormann E. 
Published: July 2007

AbstractThe ESR spectra of nickel in Cd boracites can be described by S = 1/2 and an axially symmetric g‐tensor. The spectra of nickel in Cd‐Cl boracites show a resolved superhyperfine structure. To describe it, we suggest Ni+ with a halogen vacancy. The results are compared with spectra of Mn‐doped Cd boracites.
Theory of Anharmonic Crystals. III. Three‐Dimensional Lattice
Authors: Plakida N. M. , Siklós T. 
Published: July 2007

AbstractThe properties of the f.c.c. lattice with central nearest neighbour interaction are investigated on the basis of the dynamical theory of the anharmonic crystal developed in [1]. It is shown that in the case of constant external pressure the lattice becomes unstable at sufficiently high zero point energy or temperature. The behaviour of the physical quantities in the vicinity of the unstability point is investigated.
Generation of a Longitudinal Electric Field in CdS by Intense Laser Irradiation
Authors: Vladimirov V. I. , Pyshkin S. L. , Ferdman N. A. 
Published: July 2007

AbstractThe paper is concerned with the investigation of longitudinal electric fields (≈ 1 V/cm) arising in a homogeneous piezoelectric crystal at high level of optical excitation. The sign of the effect corresponds to the drag of free carriers (electrons in the case of CdS) in the direction of light propagation. The magnitude of the effect and its kinetics have been related to light intensity, temperature, crystal orientation, and the distance between the probe points. The effect is assumed to be a result of the generation of a phonon packet, referred to by the authors as acousto‐optical domain, and carrier drag by this domain. Calculations based on the Boltzmann equation for the electron distribution function give a reasonable phonon density inside the domain which is necessary for generating the electric field observed. The estimations based on the calculated phonon density show that considerable mechanical stresses exist in the domain area which can result in the destruction of the crystal when increasing the light intensity; so far the effect examined can be directly related to the problem of optical strength.
Wave‐Number Integration for F.C.C. Lattices — An Extension of Houston's Method
Authors: Ra Ø. 
Published: July 2007

AbstractA simple wave‐number integration scheme applicable to functions of fully cubic symmetry is presented. The procedure, which is an extension of the Houston method, accounts for the non‐spherical shape of the Brillouin zone in a systematic fashion and remains useful in cases of non‐negligible contributions from the zone boundary regions. The method is applied, by way of illustration, to an investigation of local modes due to mass substitutions in BaF2. Local mode frequencies within gaps in the frequency spectrum as well as above the optical branches are computed for impurity ions of both signs, and of masses both greater and less than those of the host ions. When applied to the calculation of diagonal Green's function matrix elements, the integration procedure offers a substantial reduction of the numerical effort otherwise required in a direct summation over a discrete grid of points in k‐space.
Optical Emission from Surface Plasmons
Authors: Ritchie R. H. 
Published: July 2007

AbstractA theory of light emission by surface plasmons created on a semi‐infinite plane‐bounded electron gas by grazing incidence fast electrons is presented. Photon‐surface plasmon coupling is assumed to occur through surface roughness and is taken to be weak enough so that it may be treated in low‐order perturbation theory. Formulae are given for the distribution in angle and energy of emitted photons of both polarizations, assuming that the surface roughness may be described by a stochastic model.
On the Semi‐Classical Theory of Piezoreflection and Magneto‐Piezoreflection
Authors: Pistoulet B. , Mathieu H. , Camassel J. , Auvergne D. 
Published: July 2007

AbstractThe influence of the relaxation time on the position of the minimum of ΔR/R in the absence of an applied field, or on the position of its successive extrema in the presence of a magnetic field is shown. In this first article we neglect the role of excitons. and consider that in the neighbourhood of a critical point the variation of the matrix element due to the stress is negligible in comparison with the energy band displacements, so that
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The curves were calculated for germanium and compared with some of the results found experimentally.
Field‐Enhanced Ionization
Authors: Dussel G. A. , Böer K. W. 
Published: July 2007

AbstractAt field strengths which can lie markedly below the critical values for impact ionization and Zener extraction, field induced changes in the capture cross section, barrier height, and frequency factor of Coulomb‐attractive centers due to a deformation of the potential around the center and induced by the external field can cause a marked redistribution of carriers over these centers (field‐enhanced ionization). These changes in the kinetic parameters of the centers are estimated, using a classical model, and are given as a function of the external field. For a typical semiconductor at T = 200 °K, a possible decrease of trap‐occupation up to a factor of two, already, at fields of the order of 102 V/cm is calculated.
Field Quenching as Mechanism of Negative Differential Conductivity in Photoconducting CdS
Authors: Dussel G. A. , Böer K. W. 
Published: July 2007

AbstractIt is shown that the observed steep decrease of the electron density in photoconducting CdS(Al, Ag) with field in the range between 20 and 70 kV/cm is caused by a redistribution of holes from slow to fast recombination centres (field quenching). This redistribution is produced by field‐enhanced ionization of holes from Coulomb‐attractive slow recombination centers. The abrupt onset of the field quenching occurs because of the slow recombination traffic masking the fast center traffic until it becomes predominant. Competing infrared quenching reduces the masking effect and uncovers the earlier phases of field quenching already near 1 kV/cm (at 200 °K). Impact ionization and Zener extraction of holes from slow centers cannot explain the observed behavior. However, quantitative agreement between experiment and field quenching via field‐enhanced ionization can be reached.
Landau's Theory of Second‐Order Phase Transitions and the Magnetic Phase Transitions in Some Antiferromagnetic Oxides
Authors: Cracknell A. P. , Cracknell M. F. , Davies B. L. 
Published: July 2007

AbstractIt is argued that many magnetic phase transitions are not, according to Landau's theory, strictly second‐order phase transitions. A detailed discussion of the application of Landau's theory of second‐order phase transitions to antiferromagnetic UO2, MnO, FeO, CoO, and NiO is given in terms of Jahn‐Teller distortions and of soft phonon modes.
Influence of Pressure on the Shape of γ‐Lines Emitted by Sm‐Nuclei Recoiling with 3 eV in Eu‐Metal
Authors: Kalus J. 
Published: July 2007

AbstractThe deceleration of the Sm152 nuclei recoiling with an energy of 3 eV after the electron capture decay of Eu152, and thus the shapes of γ‐lines emitted after the neutrino emission, depends on the condition of the source material. The change of the γ‐line shape of a Eu‐metal source as a function of pressure was ascertained by measuring the yield of resonantly scattered 963 keV γ‐rays for pressures of 3.54 and 16.6 kbar. Features of the forces acting between the Sm‐atom and the Eu‐atoms are presented. In view of the low recoil‐energies involved and of the short lifetime of the nuclear state, the line shapes could be calculated to a good approximation by assuming that the recoiling nuclei were moving in a spherical potential [1, 2].
Die theoretische Deutung der magnetischen Anisotropie plastisch verformter Nickel‐Einkristalle
Authors: Gessinger H. 
Published: July 2007

AbstractDie Anisotropie der Einmündungssuszeptibilität wurde für einige bei der plastischen Verformung kubisch‐flächenzentrierter Metalle wichtige Versetzungstypen berechnet. Durch lineare Überlagerung der theoretisch bestimmten Effekte von Einzelversetzungen verschiedenen Typs konnten pauschale Versetzungsverteilungen angegeben werden, welche die in einer vorhergehenden Arbeit dargestellten Ergebnisse der Anisotropiemessungen befriedigend erklären. Danach ist die Versetzungsstruktur bei niederen Verformungsgraden über‐wiegend durch primäre Versetzungen bestimmt, die mit zunehmender Verformung mehr und mehr 60°‐Orientierung aufweisen. Bei stärkerer Verformung machen sich zunehmend isotrop angeordnete Sekundärversetzungen bemerkbar. Jedoch bleibt die Hauptgleitebene bis zu den höchsten Verformungsgraden ausgezeichnet.