bluuebunny/crossref_metadata_2025 huggingface dataset:
Negative Magnetoresistance in p‐CdSb
Authors: Andronik I. K. , Arushanov E. K. , Emelyanenko O. V. , Nasledov D. N.
Published: July 2007

Negative magnetoresistance is observed at low temperatures in cadmium antimonide crystals with hole concentration ≦ 5 × 1016 cm−3. The results of the investigation of the field, angular and temperature dependences in the temperature range 2.2 to 77°K of the magneto‐resistance of copper, silver, germanium, and tin doped samples with carrier concentrations ranging from 1016 to 1018 cm−3 are described. It is shown that the negative magnetoresistance is related probably to impurity band conduction. It is noted that the regularities observed, namely the quadratic dependence of the negative magnetoresistance on magnetic field strenght at weak fields and saturation at strong fields, the linear change of the negative magnetoresistance with temperature and the isotropy of the effect have the same character as in AIV and AIIIBV crystals and conform qualitatively Toyozawa's theory.
Theory of Urbach's Rule
Authors: Davydov A. S.
Published: July 2007

A general theory of the long‐wavelength edge of the fundamental optical absorption in crystals is developed which explains the empirical Urbach rule.
Optical Properties of GeSi Alloys in the Energy Region from 1 to 13 eV
Authors: Schmidt E.
Published: July 2007

The reflection spectra of GeSi alloys are measured in the photon energy range 1 to 13 eV at room temperature and in the photon energy range 1 to 6 eV at liquid nitrogen temperature. For these energy ranges also the dielectric constant ϵ1 + iϵ2 is calculated. The curves giving the dependence of the ϵ2‐spectra on the composition of the alloy show changes in the energy band structure in some critical points.
Anisotropy of Electroconductivity in CdSb
Authors: Anatychuk L. I. , Iskra V. D. , Luste O. J. , Rarenko I. M. , Zarubin L. I.
Published: July 2007

The anisotropy of the electroconductivity of p‐ and n‐type CdSb single crystals is investigated by a modified four‐probe method in the temperature range 5 to 500°K. In the interpretation of the experimental data obtained the energetic model proposed by Tovstyuk with three nonequivalent valence band maxima in the Γ point of the Brillouin zone and nonequivalent minima of the conduction band on the axes Σ, Δ, and Λ is used.
Polarized Luminescence of X‐Irradiated CaF2:Y and SrF2:Y Crystals and the Structure their Luminescence Centres
Authors: Görlich P. , Karras H. , Kötitz G. , Rauch R.
Published: July 2007

Y‐doped CaF2 and SrF2 crystals coloured subtractively by X‐rays at room temperature exhibit a broad luminescence band at 86°K in the near infrared if they are irradiated with light of the three long‐wavelength bands of the four‐band absorption spectrum. The peak of luminescence lies at 1.32 μm for CaF2: Y and 1.46 μm for SrF2:Y. The luminescence is partially polarized, the luminescence centres are oriented along the threefold axes ([111]‐directions). The results are shown to be in contradiction to earlier conceptions of the origin of the atomic centres in Y‐doped alkaline earth fluoride crystals. They are however compatible with a new model consisting of an electron trapped in a fluorine vacancy which is disturbed by a nearest neighbour Y3+‐ion.
Nonlinear Thermodynamics of Thermoelectric Phenomena in Ionic Semiconductors
Authors: Georgescu L.
Published: July 2007

A theoretical study is made of nonlinear thermoelectric phenomena in semiconductors calculating the thermoelectric coefficients as a function of the phenomenological coefficients Lik for an ionic semiconductor. The interaction mechanism considered is the scattering of electrons and holes by acoustical and optical phonons. An expression for the entropy production is given assuming a nonlinear relationship between the coupled thermodynamic flows and forces.
Thickness Dependence of the Quantum Yield of Cesium‐Antimony Films
Authors: Deutscher K. , Hirschberg K.
Published: July 2007

The quantum yield of SbCs3 films is measured as a function of film thickness in the spectral range 440 to 546 nm. The quantum yield is calculated from the energy distribution within the layer as determined from optical constants and layer thickness, and from the attenuation length. The calculated curves agree well with the measured dependences for film thicknesses down to about 30 nm. Below 30 nm the measured curves bend off. Measurements of the conductivity show that the decrease of the quantum yield is not due to a change in the excitation or emission process, but to a steep rise of the electrical resistance of the film.
On the Behaviour of a Cylindrical Electron‐Hole Plasma in a Magnetic Field with Transverse Component
Authors: Brauer M.
Published: July 2007

The properties of a cylindrical semiconductor plasma generated by injection and placed in a longitudinal magnetic field with a small transverse component are investigated both for the stable and unstable state. The plasma is described by the macroscopic equations of motion and continuity for electrons and holes. For the stationary case formulae are derived and discussed concerning the density distribution of the plasma as well as the radial and azimuthal electric field. The investigation of the density instabilities follows a method developed by Johnson and Jerde for parallel fields. It is shown that the introduction of a transverse component of the magnetic field leads to a coupling of the modes. In the simplest case this causes the simultaneous appearance of the n = 0 and n = 1 mode with the same frequency above certain threshold values of the fields. On this basis an explanation of the oscillistor effect is possible.
Magnetic Domain Wall Dynamics
Authors: Feldtkeller E.
Published: July 2007

Some calculations exist for the mobility and the effective mass of ferromagnetic domain walls of special wall structures. More generally valid derivations and formulas are presented here, which are not restricted to a special wall structure. It is shown that the nonlinearity observed by several authors in the dependence of the wall velocity on the field can be predicted theoretically if the material inhomogeneities causing the coercivity are taken into account in an appropriate manner. For a special example the existence of the wall contraction and the velocity limit shown by Enz for a wall without damping and without field is shown for a wall with damping and with field. As is the approximation by Enz, the present approximation also is not able to indicate the value of this velocity limit.
Influence of Uniaxial Stress on the Optical Properties of CdSe
Authors: Grynberg M.
Published: July 2007

The absorption edge, luminescence, and birefringence of CdSe single crystals under uniaxial stress are measured at 300 and 77°K. The Thomas‐Hopfield model of the valence bands is verified. Some relations between the components of the deformation potential tensors are obtained. The electron–phonon interaction term in dEg/dT at 300 and 77°K, respectively. The stress depencence of the bound exciton luminescence line and absorption edge is found to be the same.
Thermal Conductivity of Solid Ammonia
Authors: Krupskii I. N. , Manzhely V. G. , Koloskova L. A.
Published: July 2007

The thermal conductivity of solid ammonia is measured by the linear stationary method with continuous visual control of the sample state. The measurements are carried out in the temperature range 28 to 114°K. The temperature dependence of the thermal conductivity is discussed. The experimental method described in this paper has previously been used when studying the thermal conductivity of solid argon and methane.
The Nature of Oxide Layers on Single Crystals of Cadmium and Magnesium
Authors: Michell D. , Smith A. P.
Published: July 2007

The oxide layers formed on cadmium and magnesium single crystals on exposure to air at room temperature have been studied by electron diffraction, optical and electron microscopy, and X‐ray topography. A single crystal oxide layer of CdO2 is formed on cadmium with (111) parallel to (0001) and [110] parallel to [1120]. For magnesium, the oxide is a textured polycrystalline layer of MgO with an orientation relationship to the metal similar to that for cadmium and its oxide. The oxide layers on both metals are initially adherent but with increasing time of exposure to air, blisters form and cracking of the oxide occurs. The formation of oxide on cadmium produces visible defects within the crystal but no similar defects are observed in magnesium.
Flat Ferromagnetic, Epitaxial 48Ni/52Fe(111) Films of few Atomic Layers
Authors: Gradmann U. , Müller J.
Published: July 2007

Flat epitaxial 48Ni/52Fe(111) films are prepared by evaporation onto atomically flat Cu(111) films. All films consisting of three or more layers (d ≧ 6 Å) show a far‐reaching fit to the model structure of a flat single crystal. The magnetic properties are determined for (70 ≦ T ≦ 400) °K with an oscillation type torsion magnetometer, which can detect a moment of 5 × 10−8 G cm3. All films of three or more layers are ferromagnetic without any indication of superparamagnetism; Curie‐temperature and magnetization decrease monotonously with film thickness; there is good qualitative agreement with spin‐wave theory and Green's function theory; the magnetization is independent of the field, however, within 1%, for (300 ≦ H ≦ 5000) Oe, while the theory predicts considerable dependence on the field. Strong anisotropies relating to the surface normal as easy axis may easily be interpreted as Néel‐type surface anisotropies.
Effect of Low Energy Electron and UV Irradiations on the Charge Condition of Etched Germanium Surfaces
Authors: Bose D. N.
Published: July 2007

Using field‐effect and contact potential difference (c.p.d.) measurements the effect of low energy (180 to 960 V) electron irradiation on etched germanium surfaces has been studied. On all n‐ and p‐type samples examined, a loss of negative charge was found to occur from the surface as shown by an increase in surface potential and decrease in c.p.d. with electron irradiation. Changes in c.p.d. were larger than changes in surface potential, the ratio being dependent on surface preparation. The difference between surface potential and c.p.d. changes can be explained by desorption of neutral atoms from the surface causing a change in surface dipole. UV irradiation above a threshold energy of approximately 5.0 eV was found to have a similar effect. If, however, dc fields were used for band‐bending, it was found that changes in surface potential and c.p.d. were equal and hence as expected no desorption occurred.
Untersuchung dreiwertiger Übergangsmetallionen in Silberhalogeniden. I. AgCl:V
Authors: Ulrici W.
Published: July 2007

Es wird durch Messung der optischen Absorption und der Ionenleitfähigkeit nachgewiesen, daß V2+ im AgCl auf Kationenplatz unter Bildung einer zusätzlichen Silberlücke eingebaut wird. Durch Anlagerung von Defektelektronen (Anlaufreaktion mit Chlor) können diese V2+‐Ionen in V3+‐Ionen umgeladen werden. Die Umwandlung in dreiwertiges Vanadium wird wieder durch Messung der optischen Absorption nachgewiesen. Durch Messung der Ionenleitfähigkeit wird gezeigt, daß das V3+ auf Kationenplatz unter Bildung von zwei zusätzlichen Silberlücken pro V3+‐Ion substituiert bleibt. Durch Elektronenanlagerung (Kontakt mit Ag‐Metall) ist die Rückumladung des V3+ in V2+ möglich. Der Einfluß der Wechselwirkung der Silberlücken mit den dreiwertigen Kationen auf die Ionenleitfähigkeit wird berechnet und diskutiert.
Green's Function Calculation of Electro‐Optical Effects in Semiconductors. I. General Formalism and Interband Transitions
Authors: Porsch M.
Published: July 2007

A general expression for the dielectric tensor induced by a light wave in the presence of a time‐dependent external electric field is given in terms of double‐time nonequilibrium Green's functions whose spectral representations are derived in the case of a static field. Neglecting field‐induced interband transitions, the poles of the one and two‐particle Green's functions for a Bloch electron in a static electric field are determined. The imaginary part of the dielectric function at the M0 edge is calculated for a lattice with no centres of inversion symmetry.
Radiation Hardening in Platinum
Authors: Galligan J. M. , Attardo M. J.
Published: July 2007

Some measurements of the hardening introduced by fast neutrons in pure platinum are reported. It is found that the change in yield stress of neutron irradiated platinum varies as (Φt)1/2, in agreement with a lattice hardening mechanism. The rate of increase in damage, as observed with field ion microscopy in irradiated platinum, is compared with the rate of increase of yield stress for fixed total damage. This also indicates that the hardening is solely associated with depleted zones. Annealing studies of irradiated platinum, show that when vacancies are mobile, dislocation loops are formed from the vacancy clusters; the yield stress then varies as (Φt)1/3. Finally the total damage in the specimens is removed in the same temperature range where clusters of vacancies are removed.
Elektronenmikroskopie eingefrorener Versetzungen. II. Ergebnisse in den Bereichen I und II der Verfestigungskurve
Authors: Alexander H.
Published: July 2007

Germaniumkristalle mittlerer Orientierung wurden bei 520°C dynamisch durch Zug verformt. Nach Verformung bis zu verschiedenen Punkten in den Bereichen I und II der Verfestigungskurve wurden die Kristalle unter Last abgekühlt. Dünne Folien parallel zur Hauptgleitebene und zu anderen {111}‐Ebenen wurden mit Transmissions‐Elektronen‐mikroskopie untersucht. Die Bilder zeigen eine ausgeprägte Ähnlichkeit der Versetzungsanordnung mit der in kubisch flächenzentrierten Metallen gefundenen. Das Peierlspotential hat keinen Einfluß auf den Verlauf der Versetzungen. Die Verteilung der Waldversetzungen wurde mit Ätzmethoden untersucht.
Optical Absorption by Polarons in Rutile (TiO2) Single Crystals
Authors: Bogomolov V. N. , Mirlin D. N.
Published: July 2007

The optical absorption in rutile single crystals doped with Nb and other impurities as well as partially reduced is investigated in the temperature range 10 to 900°K. It is shown that the spectrum and the magnitude of the optical absorption by current carriers can be satisfactorily explained in terms of the small polaron theory. The oscillator strength for the absorption band studied as well as the polaron binding energy, the mean electron‐phonon coupling constant, and the nearest neighbour overlap integral are estimated from the experimental data.
Effect of Phonon Drag on the Kinetic Properties of Alloys
Authors: Masharov S. I.
Published: July 2007

The kinetic coefficients, i. e. the electrical conductivity, thermal conductivity, and thermo e.m.f. of a binary ordered alloy are calculated on the basis of the many‐electron model of an alloy previously used in [1] taking into account the non‐equilibrium of the phonon system. It is shown that at low temperatures phonon drag becomes important and leads to qualitatively new temperature dependence of the kinetic coefficients as compared to pure metals. Under definite conditions in the electrical resistivity vs. temperature curves a minimum and maximum may occur.
Ultrasonic Attenuation in Unirradiated and Neutron Irradiated Quartz
Authors: Fitzgerald T. M. , Silverman B. D.
Published: July 2007

The ultrasonic attenuation of unirradiated and neutron irradiated quartz is discussed in terms of recent theoretical formulations of the three‐phonon scattering mechanism. It is shown that the temperature dependence of the attenuation in the unirradiated quartz crystal can be understood by invoking this scattering mechanism. It is also shown that upon neutron irradiation the observed changes in the attenuation can be qualitatively understood by assuming that neutron irradiation decreases the thermal phonon lifetimes in the crystal.
Untersuchung dreiwertiger Übergangsmetallionen in Silberhalogeniden. II. Chrom und Titan
Authors: Ulrici W.
Published: July 2007

Durch Messung der optischen Absorption und der Ionenleitfähigkeit wird gezeigt, daß Cr2+‐Ionen, die auf Kationenplätzen im AgCl und AgBr eingebaut sind, durch Anlagerung von Defektelektronen in Cr3+‐Ionen auf Kationenplätzen umgewandelt werden können. Die Anlagerung von Elektronen führt zur Rückumwandlung des Cr3+ in Cr2+. Die Untersuchung der optischen Absorption und der Ionenleitfähigkeit titandotierter AgCl‐ und AgBr‐Kristalle zeigt, daß Ti3+ auf Kationenplätzen eingebaut wird.
The Temperature Dependence of the Flow Stress of Copper Single Crystals
Authors: Bullen F. P. , McK. Cousland S.
Published: July 2007

It is shown that the Cottrell‐Stokes ratios of copper single crystals are not constant during tensile deformation in stages II and III at temperatures from 77 to 443°K. However, there appears to be a fixed relationship between the Cottrell‐Stokes ratio and the flow stress (as measured at a standard temperature). This relationship is independent of crystal orientation and the temperature or stage of deformation. The relationship is similar to that previously reported for polycrystalline copper [1], although not quantitatively identical. These relationships have been interpreted as evidence that the obstacles responsible for temperature‐dependent hardening are formed by the action of stresses from arrays of primary dislocations. The nature of the unloading yield point and its relevance to the reversible change in flow stress are also discussed.
Untersuchungen zur Deutung der kantenfernen Feinstruktur der Röntgen‐K‐Absorptionsspektren
Authors: Brümmer O. , Dräger G.
Published: July 2007

Die physikalischen Voraussetzungen der Fernordnungs‐ und Nahordnungstheorien zur kantenfernen Feinstruktur der Röntgen‐K‐Absorptionsspektren kristalliner Festkörper werden überprüft. Aus der Literatur bekannte Spektren von amorphem Ge und glasigem GeO2 sowie eigene Messungen an wassergelöstem K3 [Fe(CN)6] werden interpretiert. Im Spektrum dieser Substanzen, deren atomarer Aufbau nur Nahordnungen und keine Fernordnung besitzt, tritt trotzdem eine kantenferne Feinstruktur auf. Ihre Existenz sowie die weitgehende Übereinstimmung mit den entsprechenden Absorptionsstrukturen der kristallinen Zustandsformen dieser Stoffe weisen somit deren kantenferne Feinstrukturen als Nahordnungseffekt aus.
Electron Microscope Image Profiles of Paired and Triple Dislocations
Authors: Murphy R. J. , Crawford J. L.
Published: July 2007

Numerical solutions for the dark field images which arise when electrons pass through thin films containing paired or triple dislocations have been obtained for conditions under which the kinematical approximation holds. The results show that the diffraction contrast of any dislocation in a group is a sensitive function of the relative position of that dislocation in the group. There are arrangements where some dislocations can be out of contrast even though the individual dislocations which come together to form a pile‐up or group may be in strong contrast. The results point to the extreme care which should be used when evaluating electron micrographs of dislocation structures, particularly when there is a measure of strain field overlap amongst the dislocations.
The Self‐Energy of a Dislocation and the Elastic Energy of Piecewise Straight Dislocation Configurations
Authors: Jøssang T.
Published: July 2007

A comparison is made of the models of Bullough and Foreman [1], and of Kröner [2] and Jøssang et al. [3] for determining the self‐energy of a straight dislocation. The differences and their physical implications are pointed out. It is concluded that, from a physical point of view, the methods of Kröner and Jøssang et al. are the more correct ones. A discrepancy between the formula of Jøssang et al. [3] and that of de Wit [4] for the interaction energy between two straight dislocation segments is shown to disappear when an error in de Wit's formula is corrected.
Combined Infrared Photoemission From Cs3Sb
Authors: Hora H. , Kabiersch G. B.
Published: July 2007

The time dependence of the photoemission current of Cs3Sb cathodes shows at high light intensities a Boltzmann factor with an activation energy of 0.08 eV (according to an IR radiation of 15 μm wavelength). In order to study the influence of infrared radiation on the usual photoemission process Cs3Sb layers are irradiated with broad band radiation of 2 μm wavelength. This infrared radiation alone produces no emission current. The photoemission caused by light of a sufficient high intensity to which the cathode is sensitive, however, is changed by the infrared radiation up to quantum efficiencies of 10−3 additionally emitted eletcrons/IR photon. This combined photoemission can be a positive or negative effect.
Magnetisierung in der Umgebung unmagnetischer Einschlüsse in Ferromagnetika
Authors: Dietze H.‐D. , Schröder K.
Published: July 2007

Schneidet man aus einem Ferromagneten einen Hohlraum heraus, so wird die Verteilung der Magnetisierungsrichtung in der Umgebung des Hohlraums in komplizierter Weise verändert. Sind diese Änderungen gegenüber dem Ausgangszustand klein, so lassen sich die mikromagnetischen Gleichungen linearisieren. Als Ausgangszustand werden die Magnetisierungsverteilung einer Blochwand und der homogen magnetisierte Zustand mit einem homogenen äußeren Feld behandelt.
Magnetisierung in der Umgebung unmagnetischer Einschlüsse in Ferromagnetika. II. Kugelförmige Hohlräume in Ferromagnetika ohne Wände
Authors: Schröder K. , Dietze H.‐D.
Published: July 2007

Es wird die Magnetisierungsverteilung in der Umgebung eines kugelförmigen Lochs mit den in Teil I angegebenen Gleichungen berechnet. Hieraus wird dann die Energie und der Einfluß von Löchern auf das Einmündungsgesetz in die ferromagnetisch Sättigung abgeleitet.
Mössbauer Experiments with Coulomb‐Excited 73Ge after Coulomb Recoil Implantation
Authors: Zimmermann B. H. , Jena H. , Ischenko G. , Killan H. , Seyboth D.
Published: July 2007

The nuclear resonance absorption of the 67.03 keV de‐excitation radiation of 73Ge*, Coulomb‐excited by 20 to 30 MeV 16O ions, is studied. The recoiling 73Ge° nuclei are implanted into a chromium substrate. The electronic configurations Ge (4s1 p3) in Ge (cryst.), Ge (15% (4s2 p0), 85% (4s2 p2)) in Ge (II)Se, Ge (62% (4s0 p0), 38% (4s1 p3)) in GeO2 (hex.) and GeO2 (tetr.), and the ratio δ R/R=1.12 × 10−3 of the nuclear charge radius are compatible with the measured isomeric shifts. Line broadenings and recoil‐free fractions f of the implantation target and the absorbers are determined. At 78 °K f is greater than f by a factor of six.
On the Reverse‐Biased Capacitance of Step p+‐n Junctions with Traps
Authors: Auth J.
Published: July 2007

The steady‐state occupation of multiple chargeable deep trap levels of a depletion‐layer is calculated. Using this result, the capacitance of reverse‐biased p+‐n step junctions with traps is obtained by integration of the Poisson equation. It is shown that measurements of the ac and dc capacitance of the p‐n junction with traps and of the capacitance of an equivalent junction without traps give some information about the capture cross‐section ratios for electrons and holes of the trap levels.
On the Theory of Low‐Temperature Exciton Absorption Spectra
Authors: Fedoseev V. , Hizhnyakov V.
Published: July 2007

The absorption spectrum of Wannier‐Mott excitons at low temperature is studied in the case of weak exciton–phonon coulping. The one‐phonon approximation is used. Only the interaction of excitons with acoustic phonons is taken into account. It is shown that for low temperatures (k0T ≪ 2 m c2) the exciton spectrum consists of a resonant line with its halfwidth tending to zero if T → 0, and of a phonon wing of finite width with the maximum being shifted from the resonant line. In the case T = 0 the resonant line appears to be a zero‐phonon line and the wing represents the vibrational recurrences of the first.
On the Theory of Hydrogen‐Bonded Ferroelectrics
Authors: Konwent H.
Published: July 2007

The hydrogen system in hydrogen‐bonded ferroelectrics of type KH2PO4 is investigated. Using double‐time temperature‐dependent Green's functions the equations for the spectrum of elementary excitations and the average dipole moment are derived. The equations are valid for a large temperature interval.
Electronic Absorption Spectrum of K2CoF4
Authors: Tiwari J. S. , Mehra A. , Srivastava K. G.
Published: July 2007

The optical absorption of K2CoF4 has been measured and compared with that of KCoF3. The observed bands are assigned to transitions from the ground state to various excited levels of Co2+ in Oh symmetry and the band positions are fairly well fitted with B = 890 cm−1, Dq  840 cm−1, and C = 4.4B.
Consideration of Polarization and Covalency Corrections to the Quasi‐Coulomb Shift of Optical Lines of Ion Pairs in Crystals
Authors: Cherepanov V. I. , Nikiforov A. E.
Published: July 2007

The effect of polarization and covalency corrections on the Coulomb interaction of impurity ion pairs in ionic crystals is taken into account. A simple semi‐empirical theory is suggested for the explanation of the quasi‐Coulomb shifts of the optical lines belonging to the pairs of equivalent impurity ions (in relation to the corresponding lines of single impurity ions). In this theory we use effective charges and effective electric dipole moments of ions. The theory is applied to the explanation of the optical spectrum of Cr3+Cr3+ pairs in ruby. The problem of a microscopical calculation of effective parameters is discussed.
Spin‐Wave Distribution Function and Thermodynamics of the Heisenberg Ferromagnetic
Authors: Mitsek A. I. , Kolmakova N. P. , Feigin V. A. , Gaidanskii P. F.
Published: July 2007

The application of the elementary excitation theory to the spin system of a ferromagnetic is investigated on the basis of the Heisenberg model. It is found that the spectrum of elementary excitations considered as a gas of quasi‐particles, and their distribution function are completely determined by the Hamiltonian of the system. The spectrum of the transverse spin waves and the distribution function both of the transverse and the longitudinal spin waves are calculated by the double‐time anticommutator Green's function method. Since the distribution functions have no singularities, it is possible to obtain expressions for the thermodynamic quantities in the form of convergent power series in a small parameter τ T/Tc. Expressions for the specific heat and the spontaneous magnetization of a ferromagnetic are calculated.
Forbidden Transitions (ΔM  2) Induced by an Axial Crystal Field in Electronic Paramagnetic Resonance
Authors: Marti C. , Romestain R. , Visocekas R.
Published: July 2007

For certain angles between an applied magnetic field and the optical axis of a crystal, magnetic dipolar transitions ΔM = 2; Δm = 0, ± 1 (M and m: electronic and nuclear azimuthal quantum numbers) can be induced by an axial crystal field, including hyperfine interaction. We calculate the corresponding oscillator strengths for a level with effective spin S (2 S + 1 odd). These results can be applied to paramagnetic resonance near g = 4 of Mn++ in wurtzite.
Directional Dispersion of Extraordinary Optical Phonons of α‐Quartz
Authors: Merten L.
Published: July 2007

It is shown that eight ordinary and twelve extraordinary branches of long optical phonons exist in α‐quartz. The ordinary phonons are always transversal and characterized by orientation independent frequencies; the extraordinary phonons are mixed transversal‐longitudinal for general orientations and characterized by orientation dependent frequencies. The extraordinary branches are divided in: two (t → t)‐branches, two (1 → 1)‐branches, six (t → 1)‐branches, and two (1 → t)‐branches (t: transversal, l: longitudinal). The orientation dispersion of these extraordinary branches is quantitatively calculated. The results are compared with hitherto presented data of the orientation dispersion in the Raman spectrum. The agreement is partly excellent.
Lattice Disorder in Alkali Halides X‐Irradiated at Room Temperature
Authors: Balzer R. , Peisl H. , Waidelich W.
Published: July 2007

Combined measurements of lattice parameter and length change give evidence that in the alkali halides KBr, LiF, KCl, NaF, and NaCl Frenkel disorder is present after X‐irradiation at room temperature.
Some Effects of Material Inhomogeneities on the Near‐Field Pattern of GaAs Diode Lasers
Authors: Hatz J.
Published: July 2007

Studies are made of the near‐field patterns of diode lasers fabricated from slices of Czochralski‐grown GaAs crystals with dislocation densities between 105 cm−2 and zero per slice. Four of the crystals were Te‐doped, the fifth Si‐doped, to 2 × 1018 atoms cm−3. Comparison of the crystal qualities with the near‐fields shows that filamentary emission is not an intrinsic property of diode lasers. With decreasing dislocation density the near‐fields become more homogenous. Diodes made from dislocation‐free material, having in addition almost perfect mirrors, emit uniformly over nearly the whole width of the diode at 1.5 times threshold current. The emission from diodes having a high dislocation density (higher than 104 cm−2) in the active region was strongly filamentary and in some cases the intensity difference between both ends of a filament was as high as 25%. This difference has been accounted for by a simple model of the cavity, which allows for variations of absorption and gain along the optical path.
Effect of Applied Electric Field on EPR Spectra of Crystal Impurity Centres
Authors: Sherstkov Yu. A. , Nepsha V. I. , Vagenin V. A. , Nikiforov A. E. , Krotkii A. I.
Published: July 2007

The spin‐Hamiltonian term which describes the linear effect of an applied electric field on EPR spectra of impurity ions is suggested to be expressed by irreducible tensor operators of the spin and electric field. The method of determining the number of the linear independent coefficients which describe the shift of EPR signals in electric fields is given for 3 dn and 4 fn ions in sites lacking inversion symmetry. The experimental results of the “pseudo‐Stark splitting” for Fe3+ ions in α‐Al2O3 with the electric and magnetic fields parallel and perpendicular to the C3−crystal axis are considered. It is established that the transverse pseudo‐Stark‐effect for Fe3+ ions in α‐Al2O3 is more pronounced than the longitudinal one and exceeds the corresponding effect for Cr3+ in α‐Al2O3.
Dynamical Treatment of the Thermal Diffuse Scattering of X‐Rays
Authors: Afanasev A. M. , Kagan Yu. , Chukhovskii F. N.
Published: July 2007

A dynamical theory of the thermal diffuse scattering of X‐rays from thick crystals is developed which consistently takes into account the Bragg scattering of both the incident and diffusely scattered X‐rays. Special attention is paid to the analysis of the intensity distribution of the diffusely scattered waves near the Bragg peak. The known singularity of the one‐phonon scattering of type 1/q2, where q is the phonon wave vector, is shown to be transformed at small q to the more weak singularity of type1/q| for the case of the Bragg diffraction (here,q| is the projection of the vector q ona plane parallel to the crystal surface).
Electron Diffraction and Electron Microscopic Study of Long‐ and Short‐Range Order in Ni4Mo and of the Substructure Resulting from Ordering
Authors: Ruedl E. , Delavignette P. , Amelinckx S.
Published: July 2007

The ordering process in Ni4Mo gives rise to three different classes of interfaces within a single crystal of the basic structure. The geometry of these interfaces and the diffraction effects to be expected from them are discussed. Evidence for the different classes of interfaces is given. The interfaces resulting from slip are discussed and compared with the observations. Quenched specimens exhibit short range order. A model for short range order in this alloy is presented. Preliminary experiments indicate that quenched Ni3Mo also shows short range order of a similar type as Ni4Mo.
360° Walls and Strong Stripe Domains in Permalloy Films
Authors: Ferrier R. P. , Puchalska I. B.
Published: July 2007

In permalloy films evaporated at oblique incidence weak stripe domains [1, 11, 12, 13] and a new type of stripe domains designated “strong stripe domains” can coexist in the same film when the angle of incidence is in range40 to 50°. The creation of the strong stripe domains proceeds either by the formation of 360° walls and their multiplication and subsequent realignment or they may be nucleated directly in the Bloch walls and grow from these nuclei. These two mechanisms are discussed in detail and models for the spin configurations in the films are proposed.
Theory of Orientation Contrast from Inclusions
Authors: Guyot P.
Published: July 2007

The diffraction contrast in transmission electron microscopy for non‐diffracting inclusions in a diffracting matrix not distorted around the inclusion is calculated on the basis of the two‐beam dynamical theory. The normal and anomalous absorption in the matrix and the normal absorption in the inclusion are taken into account. The computed intensity profiles are given for several values of the parameters, i.e. foil thickness, deviation from the Bragg condition, inclusion thickness, inclusion position, absorption coefficients of matrix and inclusion.
On the Double Injection Current Noise in Solids
Authors: Fazakas A. B. , Friedman A.
Published: July 2007

Current noise in dielectrics and semiconductors is investigated under the following conditions: double injection, negligible traps and recombination centre effects, space‐charge‐limited region, negligible diffusion and direct electron‐hole recombination. A method of calculating the spectral noise density based on the Lax approach and the Debye‐Hückel position correlations between carrier densities is used. Expressions for low and high frequencies are given in closed form; an enhancement effect is found at low frequencies. In the limit of the quasineutral (ambipolar) region, a small correction to the Hill‐van Vliet formula is obtained.
The Normal Spectral Emissivity of Tungsten‐Molybdenum Alloys
Authors: Thomas L. K.
Published: July 2007

Results of investigations of the normal spectral emissivity of W‐Mo alloys are reported. The measurements were made at 2000, 2200, and 2400 °K with the wavelength range being 0.4 to 4 μm. Emissivity values of the alloys lie in between those of the pure constituents. The temperature coefficient of the emissivity and the x‐point position change with composition. The results are discussed in terms of the rigid band model.
Characteristics of Plastic Electrets
Authors: Jain V. K. , Pillai P. K. C.
Published: July 2007

Surface charge characterics of PVC and SR10 vinyl electrets prepared in 15 min time by the application of low polarizing voltages are presented in this paper. It is also shown that the forming field is an important requirement for the formation of stable electrets.
Storage Effects in Photoconducting GaPCu
Authors: Grimmeiss H. G. , Olofsson G.
Published: July 2007

Experimental evidence is given that charge storage exists in photoconducting GaPCu after excitation with both intrinsic and extrinsic light. Appreciable storage is still observed one hour after excitation even at roomtemperature. Measurements of stored charge as a function of ir photon energy, external voltage, and excitation density confirm that such effects as supralinear photoconductivity, etc., are governed by optical charge exchange in agreement with previous investigations.
Multiphononabsorption von Kristallen mit Punktdefekten im starken Strahlungsfeld
Authors: Böttger H.
Published: July 2007

Es wird die Gitterabsorption durch Summenprozesse in Kristallen mit einer lokalisierten Schwingung im starken Strahlungsfeld unter Verwendung einer Diagrammtechnik untersucht. Für die hochfrequenten Seitenbanden der lokalisierten Schwingung von H−‐Defekten in Alkalihalogeniden wird die kritische Feldstärke, in deren Nähe die betrachtete Absorption rapide anwächst, zu ca. 106 V/cm abgeschätzt.
Surface Photoconductivity of CdS Influenced by Chemisorption and Desorption of Oxygen
Authors: Weber E.‐h.
Published: July 2007

Using investigations of the spectral dependence of photoconductivity and of the influence of oxygen on photoconductivity a method is developed to test the properties of space‐charge layers at the surface of CdS, at least in some extreme cases. The surface space‐charge layer of thick CdS platelets with a photoconductivity greatly sensitive to an oxygen atmosphere is found to be of accumulation type. This makes a re‐interpretation necessary of the models so far accepted for the chemisorption and desorption processes. As their rate‐ limiting steps the direct capture of electrons and holes by neutral and negatively charged oxygen, respectively, is assumed. Theoretical calculations on the basis of this model show qualitative agreement with the experimental results, but desorption seems to be a process more complex than pure photodesorption.
Long‐Wavelength Longitudinal Phonons of Multi‐Mode Crystals
Authors: Chang I. F. , Mitra S. S. , Plendl J. N. , Mansur L. C.
Published: July 2007

It is shown that the application of the so‐called Drude's rule in obtaining the k ≈︁ 0 longitudinal optic mode frequencies (LO's) of multi‐resonance damped oscillators is not correct, although it may be used as an approximate method only when a few oscillators, all of appreciable strength, are present. A rigorous procedure suitable for all cases, single or multi‐resonance, is shown to be to identify the frequencies at which the minima of the modulus of the complex dielectric constant (|ϵ|) occur with the LO modes. The frequencies of the maxima of |ϵ|, on the other hand, approximately represent the k ≈︁ 0 transverse optic modes. It is also shown that for a general n‐mode crystal it is possible to obtain the LO frequencies individually provided that all the parameters of the Lorentz oscillators needed to represent an observed optical property are known. In the case of a single resonance oscillator the equations reduce to the well‐known Lyddane‐Sachs‐Teller relation. Examples are given where LO's are obtained by the above methods using reflectivity data and compared with whatever available directly measured experimental LO values, e.g., from Raman or neutron scattering measurements.
Phase‐Dependent Superconductive Current Density in a Superconductor _ Normal Metal _ Superconductor Junction at T = TCN
Authors: Yeh R. H. T. , Mechetti H.
Published: July 2007

A general equation for the phase‐dependent supercurrent density across the weak‐link is obtained, from which we find that Jmax at T = TCN decreases very slowly with dN when compared with Jmax at T near TCS.
On the Problem of Recombination Autooscillations
Authors: Bonch‐bruevich V. L.
Published: July 2007

The conditions are studied under which autooscillations of the concentration of free carriers may take place. A unipolar semiconductor sample is considered containing besides the standard doping impurity some traps of one or of two types. The criteria of the soft self‐excitation of the oscillations in question are stated explicitly, together with the conditions of the fluctuational stability of the system. The decisive role of extrinsic illumination is pointed out.
Stability of Surface‐Barriers in Semiconductors
Authors: Fazakas A. B. , Handel P. H.
Published: July 2007

In order to test a recently proposed recurrence method for studying the stability of the semiconductor surface‐barrier, we apply it to the currentless state up to second order. We obtain the expected stability at arbitrary values of the surface potential. Furthermore, we investigate the stability in the presence of an applied electrical field at sufficiently small values of the surface potential and restrict ourselves to the first order calculation. The obtained critical field exceeds the breakdown value. Thus, at least for small values of the surface potential (|V8| ≤ 0.75 kT) stability prevails.
Conductivity of Intrinsic InSb in High Electric Fields
Authors: Weissglas P. , Blötekjaer K.
Published: July 2007

A theory is developed for the carrier transport properties and impact ionization rate in an intrinsic polar semiconductor with high carrier density. Polar scattering prevails in weak fields but it is shown that intercarrier interactions become important at higher field strengths. The carrier concentration is found to vary approximately exponentially with applied field. Numerical results for data representative of InSb are presented.
Role of Gradual Capture in the Photoelectromagnetic and Photoconductive Effects
Authors: Dolocan V.
Published: July 2007

A theoretical study is made of the role of the gradual capture in the photoelectromagnetic and photoconductive effects. The results obtained show that the photoelectromagnetic lifetime is not affected, while the photoconductive lifetime is affected by gradual trapping. The gradual recombination affects both the photoelectromagnetic and photoconductive lifetime.
On the Origin of High Photovoltages in Semiconductors
Authors: Zhadko I. P. , Romanov V. A.
Published: July 2007

A new possible mechanism is proposed for explaining the high photovoltage arising in semiconductor films assuming an anisotropic conductivity of the photosensitive crystallites of which the films consist. In this case the high photovoltage is the sum of the elementary transverse Dember photo‐e.m.f.'s. This model may explain practically all peculiarities of the high‐photovoltage effects.
The Theory of Cohesion of Noble Metals (II)
Authors: Nikulin V. K. , Trzhaskovskaya M. B.
Published: July 2007

On the basis of the results obtained in previous papers a calculation is made of the cohesive energy, Wigner‐Seitz sphere radius, and compressibility of Cu and Ag using the nonlocal model potential. An isotropic band effective mass is also estimated for these elements.
Exciton Theory in Crystals with Complicated Band Structure with Electron‐Phonon Interaction
Authors: Kudykina T. A. , Tolpygo K. B. , Zubkova S. M.
Published: July 2007

The theory of the exciton is developed on the basis of the many‐electron model. It is supposed that the excited electron can pass from any occupied state of one atom to a free state of this atom or of another one. Two limiting cases are considered: the large‐radius exciton in many‐valley semiconductors with the value of the many‐valley splitting of its level being estimated, and the small‐radius exciton in alkali halide crystals. In the last case the energy of the exciton, composed of Känzig's autolocalized hole and an electron, moving over ten nearest neighbours, is calculated.
Effect of Lattice Distortions on the Magnetic Behaviour of Perovskite‐Type Manganites
Authors: Bokov V. A. , Grigoryan N. A. , Bryzhina M. F. , Tikhonov V. V.
Published: July 2007

Some series of solid solutions with perovskite‐type structure are synthesized and investigated, viz. the binary systems Nd1−x, MexMnO3 where MeCa2+, Sr2+, Ba2+, and the ternary systems (Bi1−xLax)0.5Ca0.5MnO3 and Bi0.5(Ca1−xMex)0.5MnO3 where MeSr2+, Pb2+, Ba2+. Distortions from the cubic perovskite structure are detected at room and liquid nitrogen temperature. Magnetic measurements are made in the temperature interval 77 to 800 °K. For all the compounds, a correlation between lattice distortions and magnetic behaviour is observed; 1. cubic and slightly distorted compounds exhibits a pure ferromagnetism; 2. distortions from the cubic structure give reduced spontaneous moments and in some cases antiferromagnetism developes. The ferromagnetic nature of the Mn3+ O2−Mn3+ and Mn3+O2−Mn4+ interactions which are found in the non‐distorted compounds is interpreted according to the Goodenough‐Kanamori rules assuming that the quasi‐static hypothesis is satisfied. The lattice distortions observed are thought to give rise to a static distortion in the Mn3+ ion environment and an ordering of covalent bonds. As a result, some part of exchange couplings becomes antiferromagnetic. The influence of the decreased subtended angle in the MnO2−Mn linkage is discussed. This angle decreases from 180° when the lattice becomes distorted and this fact disturbs the orbital orthogonality. This results in an increase of the antiferromagnetic t2g−t2g interaction via σ‐bonding and in the occurence of the other superexchange antiferromagnetic interactions which couple both the eg and t2g orbitals and the t2g and t2g orbitals via π‐bonding. The contribution of double exchange to the ferromagnetism of mixed manganites is believed to be not important.
Investigation of the Mössbauer Effect in Some Fe–Al Alloys
Authors: Nemoshkalenko V. V. , Rasumov O. N. , Gorskii V. V.
Published: July 2007

From a general consideration of the isomeric shift and the parameters of the X‐ray emission K‐spectra of Al and Fe in FeAl2 alloy it is concluded that the transition from Fe3Al to FeAl is accompanied by an electronic transition from the Al atom to the Fe atom with the filling of the 3d states; this process seems to be complete in the equi‐atomic alloy. Further increasing of the Al content in the alloy (transition from FeAl to FeAl2) leads to an increase in the p‐shell population in the Fe atoms.
Mössbauer Effect in Antimony–Organic Compounds
Authors: Gukasyan S. E. , Shpinel V. S.
Published: July 2007

The isomeric chemical shifts (IS) of the Mössbauer 37.2 keV γ‐line of the Sb121 nucleus in organic compounds of antimony (type Ar3SbX2, Ar4SbX, and Ar3Sb) have been measured. The spectra of the resonance absorption are mainly found to be broadened single lines with appreciable asymmetry. The results obtained are interpreted on the basis of the semi‐empirical method of hybrid orbitals.
Analysis of Point Defect States in Copper I. The Influence of the Point Defect State on the Irradiation Damage Rate at 80 °K
Authors: Dworschak F. , Schuster H. , Wollenberger H. , Wurm J.
Published: July 2007

The present measurements of the irradiation damage rate at 80 °K and those from the literature demonstrate the validity of the unsaturable trap model of Walker for copper over a wide range of trap concentrations and radiation induced defects. These results imply the free migration of interstitials below 80 °K. By damage rate measurements at 80 °K effective concentrations of vacancies and interstitial traps introduced by any pretreatment can be determined.
Temperature Dependence of the Magnetocrystalline Energy Constants K1, K2, and K3 of Iron
Authors: Gengnagel H. , Hofmann U.
Published: July 2007

The magnetocrystalline energy constants K1, K2, and K3 of spherical iron single crystals are determined by the torque method in the temperature range 20 to 800 °K. The temperature dependence of K1 is in good agreement with recent measurements of other authors. The constants K2 and K3 are very small as compared to the constant K1. K2 is always negative and K3 is positive within the whole temperature range.
Pressure Dependence of the Elastic Constants of Single Crystalline Aluminum Oxide
Authors: Gieske J. H. , Barsch G. R.
Published: July 2007

The six single crystal elastic constants of aluminum oxide have been measured by the ultrasonic pulse superposition method at 25 °C as a function of hydrostatic pressure up to 10 kbar. A linear pressure dependence has been found in all cases. The results are compared and found to agree approximately with theoretical data for the hexagonal close‐packed structure with nearest neighbor central forces. They are also used to calculate the pressure dependence of the lattice parameters from Thurston's equation of state. The agreement with directly measured experimental data of Hart and Drickamer is excellent for one, and poor for the other lattice parameter.
Optical Energy Gap in TlSe
Authors: Pickar P. B. , Tiller H. D.
Published: July 2007

The results of a study to characterize samples of single crystals of TlSe grown by the Bridgman‐Stockbarger and zone recrystallization techniques are given. The X‐ray diffraction patterns were indexed as a tetragonal lattice whose parameters were a = 8.02 Å and c = 7.00 Å. The absorption and transmission measurements in the region from 0.64 to 1.20 eV yield an estimate for the band gap for the indirect transition as 0.73 eV, which agrees with that obtained from photoconductivity experiments.