bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Problem of Electron Capture Coefficients of the Group III Acceptors in Silicon
Authors: Pokrovskii Ya. E. , Svistunova K. J. 
Published: July 2007

AbstractThe data on the electron capture coefficients of the neutral group III acceptors in silicon published by various authors differ by many orders of magnitude. Principal features of the methods of determining these coefficients are discussed and possible sources of such a disagreement are pointed out.
Plasma Reflection Edge in Crystalline MB6 Compounds
Authors: Kierzek‐Pecold E. 
Published: July 2007

AbstractThe room temperature ultraviolet reflectivity and plasma reflection edge in crystalline samples of MB6 such as LaB6, PrB6, NdB6, and SmB6 have been investigated. The theoretical analysis of the experimental curves in the region of plasma edge allows to determine the dielectric constant ϵ, the relaxation time τ, and the N/m* ratio. The optical constants such as refractive index n, extinction coefficient k, and absorption coefficient α are evaluated in the region 1.2 to 6.0 eV using the Kramers‐Kronig relation.
The Investigation of Trapping Levels in CdWO4, ZnWO4, and CaWO4
Authors: Furtak S. P. , Pashkovskii M. V. 
Published: July 2007

AbstractLocal trapping levels in unactivated monocrystals of CdWO4, ZnWO4, and CaWO4, were investigated by the method of thermoluminescence (TL), thermally stimulated conductivity (TSC), and photoelectret state (PES). Thermal activation energies for various trapping levels were found, and the order of recombination kinetics in these materials was determined. From the obtained data on temperature dependence of the stationary X‐ray luminescence the thermal activation energies for non‐radiative transitions were found. On the basis of the obtained experimental data a model is suggested, which explains the relation between thermoluminescent and luminescent properties of the investigated tungstates.
Infrared Spectra of Cubic and Tetragonal Manganese Ferrites
Authors: Brabers V. A. M. 
Published: July 2007

AbstractThe infrared absorption spectra in the range from 200 to 700 cm−1 of cubic and tetragonal manganese ferrites, MnxFe3–xO4, are reported. An analysis of the spectra is made with a model by which the lattice vibrations are classified into species of the point group D2 d on the analogy of the results for gas molecules of equivalent symmetry. For cubic spinels with manganese concentrations x ≦ 1.0 the classification can be made according to the model of Waldron into the species of the point group Td. However, at 335 cm−1 an absorption has been observed which is out of the scope of the Td or D2 d classification, and which is caused by the substitution of a part of the octahedral Fe3+ ions by Mn2+ ions. The IR spectra of manganese ferrites with compositions 1 < x ≦ 3 can be analysed with the D2 d classification. The spectra of these materials do not change suddenly with the manganese concentration or with the crystal structure. From the splitting of the absorption bands in cubic ferrites with x > 1 it is concluded that there are local tetragonal distortions originating from the Jahn‐Teller effect of the octahedral Mn3+ ions.
Temperature Dependence of Mean Free Path in Secondary Electron Emission
Authors: Taub H. , Stern R. M. , Dvoryankin V. F. 
Published: July 2007

AbstractThe temperature dependence of the anisotropic secondary emission of electrons from a single crystal is determined by the relative effect of thermal scattering on the inelastic mean free path for the incident electrons, and the escape depth for the secondaries. A diffraction model for the anisotropic secondary emission based on the two‐beam dynamical theory of Bethe is discussed. This model predicts a temperature dependence for the anisotropy that is qualitatively observed for a (110) surface of a tungsten single crystal.
Optische und photoelektrische Eigenschaften von β‐rhomboedrischem Bor. I. Optische Konstanten, Bandkante und Absorption freier Landungsträger
Authors: Jaumann J. , Werheit H. 
Published: July 2007

AbstractDer Temperaturgang des Absorptionsspektrums zwischen Kante und Gitterschwingungen kann durch indirekte Bandübergänge und Anregungen aus einem thermisch besetzten Haftniveau großer Zustandsdichte beschrieben werden, welches bei tiefen Temperaturen durch Untersuchung der starken Beeinflussung optischer Absorption und Photoleitung durch Lichteinwirkung im Teil II dieser Arbeit nachgewiesen wird. – Die Absorption freier Träger ist bei hohen Temperaturen dem Gitterspektrum überlagert; ihr Anstieg ∼λ3 deutet auf Streuung an geladenen Zentren hin, deren Konzentration von etwa 5 × 1020 cm−3 der Zahl der Elementarzellen des Gitters entspricht und die Zahl der Fremadtome um zwei Größenordnungen übersteigt. Eine Abschätzung der effektiven Masse freier Löcher liefert 8 m0; dies entspricht einem hopping‐Modell der elektrischen Leitfähigkeit. Das komplizierte Gitterschwingungsspektrum ist zwischen 4 und 13 μm fast temperaturunabhängig; es liegen dort also keine Kombinationsbanden vor.
Crossed and Parallel‐Field Magneto‐Electro‐Reflectance of Germanium in Nonuniform Electric Fields
Authors: Evangelisti F. , Frova A. 
Published: July 2007

AbstractRoom‐temperature magneto‐electro‐reflectance experiments near the fundamental edge of germanium have been performed in both the crossed and parallel‐field configuration, using a “day” field‐effect system to achieve zero‐to‐peak modulation of the electric field. The results show that the E ‖ H spectra can be described in terms of photon‐assisted tunneling at each of the Landau levels, although the interpretation of the data is not straightforward due to the strong nonuniformity of the electric field. For E ⊥ H the period of the Landau levels is smaller than in the E ‖ H case and there is evidence that quantization effects are absent in the region of high electric field immediately below the surface. The results suggest that the technique described here may be a convenient tool to investigate magneto‐electro‐effects.
Radiation‐Induced Interstitial Centres in Alkali Halides
Authors: Itoh N. , Saidoh M. 
Published: July 2007

AbstractFormation of H‐, H′‐, and V1‐centres in pure KBr and KCl in Na+‐doped KBr is studied. It is shown that the growth of the H‐band is suppressed and the growth of the V1‐band is enhanced by Na+ impurity, and that the height of the V1‐band is proportional to the height of the H‐band. It is shown also that the height of the H′‐band is proportional to the square of the height of the H‐band below a certain H‐centre concentration, suggesting that the centres associated with the H′‐band are di‐H‐centres. The kinetics of the formation of these three centres is discussed in terms of the interaction volume of ejected halogen interstitials with H‐centres and impurities.
Transmission Electron Microscope Study of the Dislocations in Plastically Deformed Synthetic Quartz
Authors: McLaren A. C. , Retchford J. A. 
Published: July 2007

AbstractTransmission electron microscopy has been used to study the dislocations associated with the plastic deformation and recovery of single crystals of synthetic quartz. The crystals were deformed in compression at a constant strain rate under confining pressure over the temperature range 300 to 900°C. At 300°C rapid work‐hardening occurs due to the development of a high uniform density of tangled dislocations. The dislocation substructures which are produced during deformation at higher temperatures correspond closely to the substructures which develop on annealing a work‐hardened crystal. There is evidence that the rate of this recovery is strongly dependent upon the concentration of hydrogen present due to the influence of this impurity on dislocation climb. It is suggested, therefore, that the well‐established hydrolytic weakening of quartz occurs when the rate of recovery exceeds the rate of work‐hardening. This hypothesis predicts the observed variation of the hydrolytic weakening temperature with hydrogen concentration, strain rate, and crystal orientation.
Thermosensitive Discontinuities and Hystereses of the Photoemission of Alkali–Antimonide Cathodes at High Light Intensities
Authors: Hora H. , Kantlehner R. 
Published: July 2007

AbstractAnomalies of the dependence of the photoemission from multialkali and Cs3Sb cathodes on temperature between 12 and 300°K were analysed. The sublinearities, discontinuities, and hystereses of the emission current at varying intensities were measured in dependence on the spectral properties of the incident light, temperature of the cathode, time, geometry of illumination, preillumination and, partial pressure of helium. We find the optical absorption independent of the effects and conclude that the mechanism does not depend on the decreased dark conductivity of the non‐illuminated cooled cathode. An explanation is possible on the base of an increase of the surface potential due to trapped photoelectrons, creating consequently an electric field in the border zones of illumination where charge transport processes excite and emit additional electrons.
Systematic Reflections in Transmission Electron Diffraction
Authors: Serneels R. , Gevers R. 
Published: July 2007

AbstractThe transmission and diffraction of electrons by a perfect plate‐shaped foil is considered. It is assumed that the crystal orientation with respect to the incident beam is such that there is only a single family of lattice planes, defined by the reciprocal lattice vector g, at the exact Bragg orientation, i.e. sg = 0. The active reflection g is the reflection of lowest order on the reflecting planes. Reflections on other families of lattice planes are ignored. Furthermore one considers only the case of a crystal with a center of symmetry, or that of reflecting plane in a non centro‐symmetrical crystal, which is a mirror plane or belongs to the zone of a symmetry axis of even order. The systematic reflections 2 g, – g, 3 g, – 2 g, 4 g, – 3 g, etc. on the reflecting plane are taken into account. First it is shown that the four‐beam case (0, g, 2 g, – g) can be solved analytically, giving rise to very simple formulae, which can be easily discussed. In particular one obtains a simple expression for the corrected extinction distance. Next the influence of the further beams is discussed. It is shown that the four‐beam case is a good approximation, and a quick method is described for obtaining the further corrections on the extinction distance.
The Influence of Internal Stress Fields on the Velocity of Dislocations
Authors: Guiu F. 
Published: July 2007

AbstractThe influence of periodic internal stress fields of various types on the average dislocation velocity is investigated. An Arrhenius type equation is used to describe the dislocation velocity, and the calculations are carried out assuming that the activation volume is a) constant, and b) a function of the stress. It is shown that for almost any type of periodic field the average dislocation velocity can be expressed as a simple function of the ratio α = τ0/τa, where τ0 is the amplitude of the stress field and τa is the applied stress. The average value of the internal stress, or the hardening produced by the internal stress field, is not strictly athermal, although its temperature dependence is small. Both the temperature and stress dependence of the average dislocation velocity is influenced by the presence of internal stresses. However, this effect is small and can be neglected for most practical cases, especially at low temperatures.
The Influence of Local Potential Fluctuations on the Low‐Temperature Radiative Recombination of Compensated Germanium
Authors: Dobrego V. P. , Shlimak I. S. 
Published: July 2007

AbstractThe luminescence of p‐Ge doped both with Ga and As impurities in the region of “intermediate” concentrations (1016 to 1018 cm−3) has been investigated. Potential fluctuations due to random distribution of impurities in a crystal were shown to be the main factor in compensated semiconductors affecting the spectrum of radiative recombination in this region of concentrations. Under conditions of low temperatures and low excitation nonequilibrium carriers localize in close‐to‐generation‐site potential wells. The character of their recombination therewith is similar to inter‐impurity recombination with the difference that the carriers are captured not by separate impurity atoms but by their aggregates. The distances between recombination carriers in this case are shown to depend on optimal dimensions of fluctuations rather than on impurity concentration. It has also been shown that at low temperature the energy distribution of non‐equilibrium electrons does not correspond to the density‐of‐states function in the impurity band of donors.
Magnetic Field Influence on the Gunn Effect
Authors: Levinshtein M. E. , Nasledov D. N. , Shur M. S. 
Published: July 2007

AbstractThe magnetic field influence on the Gunn vibrations and the low‐frequency oscillations of the Gunn diode are investigated up to magnetic fields of 20 000 G. A considerable increase of the threshold field and a decrease of the threshold current are observed. The obtained results are explained in the limits of the two‐valley model.
Photostimulated Luminescence due to Hole Release in KCl and NaCl
Authors: Jaek I. , Kink M. 
Published: July 2007

AbstractIn the stimulation spectra of KCl–Ag and NaCl–Ag crystals, X‐rayed at 80°K, additional bands have been found for the visible emission, due to the tunneling between Vk‐ and Ag°‐ centres. The temperature dependence of these bands and the kinetics of the initial growth curves of the photostimulated luminescence allows one to connect these bands with the optical release of holes from Vk‐centres.
On Some Properties of TlInS2 (Se2, Te2) Single Crystals
Authors: Guseinov G. D. , Mooser E. , Kerimova E. M. , Gamidov R. S. , Alekseev I. V. , Ismailov M. Z. 
Published: July 2007

AbstractThe results of studies on the structure and physical properties of grown TlInS2 (Se2, Te2) single crystals are presented. Based on an X‐ray investigation the parameters of the tetragonal cells of these crystals have been determined. The electric conductivity and the Hall effect for the TlInS2(Se2, Te2) crystals have been measured over a wide temperature range. It has been revealed that in the purest crystals of the above compounds the mobility obeys the usual T−3/2 law. Some data on the photoelectric and optical properties of these materials are also reported. These crystals are shown to be photoconductors in the infrared and visible regions of the spectrum. The photoconductivity maxima for the TlInS2, TlInSe2, and TlInTe2 crystals correspond to the wavelengths of 0.525, 0.87, and 1.36 μm, respectively. In photoconductivity the respective values for the forbidden gap width are 2.3, 1.07, and 0.68 eV. From the experimental data obtained the main characteristic parameters of the crystals have been calculated.
Microscopic Theory of Band and Local States in Ionic Crystals
Authors: Evseev Z. Ya. , Tolpygo K. B. 
Published: July 2007

AbstractThe theory of band and local states of electrons in ionic crystals with due regard for interelectronic interaction and with some approximation to the interelectron correlation was proposed [1]. It is developed for NaCl crystals having one excess electron. The law of dispersion and the wave functions of a band electron are defined here. The minimum E(k) is at k = 0 and the effective mass is equal to 0.624 m, where m is the mass of the free electron. The energy and the radius of the polaron in strong‐bond approximation practically coincide with the results of the macrotheory [2]. This gives an opportunity to apply its methods and the approximation of intermediate and weak bonds, for at \documentclass{article}\pagestyle{empty}\begin{document}$ \mu /m = 0.624,\,\alpha = 3.95\sqrt{2\,.} \left[3 \right] $\end{document}
. The calculated potential of deformation and the acoustic mobility are in good agreement with the results of experiments [4] in a temperature range of 30 to 200°K.
Triboluminescence of Some Alkali Halide Crystals
Authors: Belyaev L. M. , Martyshev Yu. N. 
Published: July 2007

AbstractA photoelectric method for the registration of the triboluminescence spectra is described. Using this method the triboluminescence spectra of LiF crystals at destruction in air, vacuum, and in an argon atmosphere are obtained. The experimental study of triboluminescence of some alkali halide crystals have been carried out under the simultaneous control of the deformation and fracture processes, surface electrization, and electromagnetic radiation in the radio range. The correlation between the nature of these processes and the light emission is established.
X‐ray Topographic Study of Defects in Quartz I. Brazil Twin Boundaries
Authors: Phakey P. P. 
Published: July 2007

AbstractA systematic investigation has been made of the diffraction contrast effects observed by X‐ray traverse topography at Brazil twin boundaries in natural quartz. Evidence is presented to show that the crystal axes are not coincident across the Brazil twin boundaries but are displaced by a vector R which depends upon the composition plane of the boundaries. Consequently the displacement vectors for intersecting Brazil twin boundaries are not identical. These displacement vectors have been determined from the observed vanishing conditions for the diffraction contrast fringes at the boundaries. The expected stair‐rod type dislocations at the intersections of the twin boundaries have been found. Probable atomic models for the Brazil twin boundaries are proposed and discussed.
Field Effect and Surface Photoconductivity Studies on InSb Single Crystals
Authors: Pagnia H. 
Published: July 2007

AbstractSurface photoconductivity (SPC) under light, electron, and X‐ray irradiation, and the field effect were measured below 100°K on single crystalline samples of InSb (weakly p‐doped mainly). CP‐4A etched samples have bands bent upwards on the surface (about 0.1 eV). The main excitation processes are interband transitions in InSb. Electrons then surmount the 2 eV oxide barrier of the real surfaces (internal emission) and are captured and frozen‐in in surface states, or escape into the vacuum (external emission). Information is further obtained on surface state positions, state densities, SPC kinetics, and a slowly relaxing component of SPC at the low temperature.
Binding Energy and Compressibility of Body‐Centered Cubic and Close‐Packed Hexagonal Sodium
Authors: Saxena V. K. , Kapoor Q. S. , Bhattacharya D. L. 
Published: July 2007

AbstractThe binding energies of the b.c.c. and c.p.h. phases of sodium have been computed using Hellmann‐type and modified Coulomb pseudopotentials. The binding energy of the c.p.h. structure is found to be about 2% more at 5°K than that of the b.c.c. structure as calculated from these pseudopotentials. The compressibility of the b.c.c. phase has also been calculated. The computed values give a fair agreement with the experimental results wherever available.
On Tunnelling and Avalanche Processes at Electroluminescence of SiC p–n Junctions
Authors: Vereshchagin I. K. , Kirichuk A. S. , Kosyachenko L. A. 
Published: July 2007

AbstractThe processes of the influence of a strong electric field on p–n junctions biased in reverse direction have been investigated. At voltages sufficient for electroluminescence almost in all samples a multiplication of the charge carriers created by light in the region of the SiC fundamental absorption was observed. The dark current of the initial charge carriers entering the junction increases with the rise in voltage both at low voltages when there are no luminescence and multiplication and at high voltage when such phenomena are observed. In this case the dependence of the initial current on voltage and temperature agree with tunnel effect theory. In some samples the luminescence was not accompanied by a marked carrier multiplication; both impact and tunnel mechanisms of electroluminescence exitation occur in SiC.
Influence of Lattice Vibrations on the Hyperfine Structure Constants of VK‐ and VF‐Centres in Earth Alkaline Fluorides
Authors: Assmus W. , Dreybrodt W. 
Published: July 2007

AbstractThe ESR spectra of diatomic F molecules of the type VK and VF in CaF2, SrF2, and BaF2 show temperature‐dependent hyperfine structure constants. This temperature dependence results from a vibration with sharp frequency ω, coupling to the hfs. It can be described by A(T) = A0 + α coth (ħ ω/2 kT). The frequencies ω for the VK‐ and VF‐ centres are determined from the experimental data. Molecular vibrations of the centre or lattice vibrations may produce change of the hfs‐constants. The frequencies of such vibrations are calculated. From the comparison with the measured ones it is concluded that the change of the hfs‐constants results from a lattice vibration of the cation sublattice in [110] direction with k at the vicinity of the edge of the Brillouin zone.
Brillouin Scattering Studies of Acoustoelectric Domain Formation in Semiconducting CdS
Authors: Wettling W. , Bruun M. 
Published: July 2007

AbstractThe growth of the flux intensity in acoustoelectric domains in semiconducting CdS has been followed over five orders of magnitude for frequencies between 0.2 and 5 GHz using the Brillouin scattering technique. The form of the flux domains is exponential on both sides with a halfwidth of about 300 μm. By studying their formation in the very early stage before the current decay, it was found that the frequencies and amplification factors of the flux appearing first are close to those predicted by the linear theory. After the current has started to decay, higher and lower frequencies are observed, the lower with much higher amplification and intensities. It seems that the electric field inside the domain does not have an essential influence on the flux growth. The experimental results are compared with some acoustoelectric amplification models.
Injection and Field‐Induced Excitation of charge Carriers in CdS single Crystals
Authors: Rohde H. J. 
Published: July 2007

AbstractThe current‐voltage characteristics of CdS single crystals were investigated in the temperature range of liquid nitrogen up to fields of the order 105 V/cm. At low electrode separations double injection predominates. At larger distances, however, impact ionization of a shallow trapping state, positioned in the range of 0.1 to 0.2 eV below the conduction band is found. An investigation of the characteristics at different electrode separations and temperatures as well as different directions of the electric field intensity with respect to the c‐axis supports the statements.
Contribution to the Theory of the Electric Impedance of Crystals in the Presence of an Acoustic Instability
Authors: Ioffe I. V. , Shapiro B. I. 
Published: July 2007

AbstractIt is shown that the real part of the electric impedance of a semiconductor can oscillate with a definite frequency in the presence of an acoustic instability. Conditions of the change of the sign of the real part of the impedance are found.
The ESR of Cu2+ ions in Lithium Chloride
Authors: Pilbrow J. R. , Stevenson R. W. H. 
Published: July 2007

AbstractElectron spin resonance measurements on lithium chloride containing copper at 20°K show that Cu2+ ions with an |x2 – y2〉 ground state are produced in cation sites by X‐irradiation at low temperatures. The Cu2+ centres, which are thermally unstable at room temperature, possess [100] tetragonal symmetry which is believed to arise solely from the Jahn‐Teller effect. Analysis of the g‐values and the Cu2+ hyperfine structure indicates that the admixture of the |3 z2 – r2〉 level into the |x2 – y2〉 ground state is unimportant.
Raman Scattering by Manganese Impurities in Zinc Sulphide
Authors: Beserman R. , Nusimovici M. A. , Balkanski M. 
Published: July 2007

AbstractThe experimental study of Raman scattering of light in a cubic crystal of zinc sulphide by a substitutional manganese impurity has been achieved. A theoretical approach based on symmetry properties of the lattice gives a satisfactory interpretation of the resonant modes of vibration of the manganese impurity for various concentrations.