bluuebunny/crossref_metadata_2025 huggingface dataset:
Diffuse X‐Ray Scattering from the Displacement Field of Point Defects in KBr Single Crystals
Authors: Spalt H. , Lohstöter H. , Peisl H.
Published: July 2007

Diffuse X‐ray scattering from the displacement field of point defects in low temperature X‐irradiated KBr single crystals was measured. The distribution of diffuse scattered intensity in reciprocal space confirms the theoretical predictions of scattering from isolated point, defects. From absolute scattered intensities the double force tensors describing the long range displacement field of an interstitial anion and anion vacancy are derived. The volume changes per interstitial anion and anion vacancy are determined to be (2.5 0.2) atomic volumes and (0.7 ± 0.2) atomic volumes, respectively. The displacement field of the interstitial ion has tetragonal symmetry. Models for the interstitial ion configuration which are in accordance with this symmetry are proposed.
Excitonic Effects on the Valence Absorption Edge of Solid Rare Gases
Authors: Rössler U. , Schütz O.
Published: July 2007

Bound exciton states and excitonic resonances have been computed at the valence absorption edge of the solid rare gases Xe, Kr, and Ar. A two‐band model was used to calculate the Green's function of the uncoupled electron–hole pairs and the Coulomb interaction was treated in the resolvent formalism. The matrix elements of the electron–hole interaction were calculated in the pseudopotential approximation. The computed binding energies, oscillator strengths, relative hydrogenic defects, and spectral functions are compared with experimental data.
Electron Magnetic Susceptibility and the Band Structure of Silicon‐Rich n‐Type Silicon–Germanium Alloys
Authors: Geist D. , Balck F.
Published: July 2007

Earlier measurements have been extended to a larger number of samples of high crystalline perfection, high purity, and well‐defined homogeneous doping. Furtheron the measuring equipment has been improved. The before made statement could be confirmed, that the transverse electron mass as derived from the magnetic susceptibility in silicon–germanium alloys with a silicon content between 65 and 100 at% Si is constant with a value m⟂ = 0.27 m (m free electron mass).
On the Influence of Electronic Exchange and Correlation on Pseudopotential Calculations I. Form Factors, Energy‐Wave Number Characteristics, and Effective Interionie Pair Potentials
Authors: Hafner J.
Published: July 2007

The influence of electronic exchange and correlation on pseudopotential calculations is discussed within the framework of Harrison's first principles pseudopotential formalism. The Xα local exchange and correlation approximation is used for the calculation of the core states and for the conduction band–core exchange interaction. Exchange and correlation between the conduction electrons are taken into account using different modified forms of the dielectric function. The influence of these approximations on the form factors, normalized energy‐wave number characteristics, and effective interionie pair potentials of 14 simple metals is discussed.
Exchange‐Quadrupole Forces and Phonon Dispersion for the Simplest Cubic Crystals
Authors: Tolpygo K. B.
Published: July 2007

Systematic discrepancies between the experimentally observed phonon dispersion law and that predicted by the theory of the lattice with polarizable ions in the short wavelength region are discussed. The discrepancies appear to be due to the quadrupole deformation of ions, primarily of anions. The adiabatic lattice potential which depends on the displacements, uls, on the dipole moments, P1s, and on the quadrupole moments, Qlsαβ, of all the atoms is determined and equations for the lattice vibrations are derived. Besides the Coulomb forccs the adiabatic potential includes the short‐range forces which are due to the alteration of the exchangc interaction of neighboaring atoms with the quadrupole deformation of one of them. Equations for the Fourier components of dynamic variables using the Ewald transformation for sums of the Coulomb potential of dipole and quadrupole interactions are given.
Investigation of the Electronic Structure of Molybdenum Single Crystal Surfaces by Means of the Positron Annihilation Method
Authors: Adonkin V. T. , Dekhtyail I. Ya. , Silantev V. I.
Published: July 2007

A model is proposed explaining the “fine structure” of angular distribution curves of annihilation photons (ACAP) obtained by the interaction of positrons with the electron density on the crystal surface. Data were presented which prove the influence of a deformation on the (110) plane of Mo and of weak magnetic fields (1.2 Oe) on the shape of ACAP curves obtained from the surface of this crystal face. The deformation effect is discussed in conjunction with the interaction between positrons and crystal structure defects on the crystal surface. The influence of a weak magnetic field is discussed with the excitement of the surface magnetic levels.
Perturbation Theory in Transmission Electron Diffraction II. The Perturbing Matrix is Constant but not Hermitian
Authors: Serneels R. , Gevers R.
Published: July 2007

Instead of using the usual Schrödinger equation, perturbation theory is directly applied to the system of Howie and Whelan. According to the nature of the perturbing dynamical matrix generally three different types of perturbation are distinguished. The perturbing matrix may be a) constant and Hermitian b) constant but not Hermitian c) not constant but depth dependent. The first case has been discussed previously, now case b) is considered. In full matrix notation both generate and degenerate perturbation theory is presented. Special attention is given to the usual treatment of absorption effects. General recurrence relations are presented for the calculation of the corrections on eigenvalues and eigenvectors. The influence of these corrections on the amplitudes and the intensities of the constituent beams is discussed.
Colour Centres near Ionic Crystal Surfaces I. The Surface VK Centres
Authors: Bartczak W. , Sugier H.
Published: July 2007

A simple theoretical model of the Vk‐centre situated on the (001) external surface of the f.c.c. alkali halide crystal has been derived. The energy of the VK‐centre calculated for the case of KCI using this model appeared to be about 0.49 eV less then that inside the crystal.
One‐dimensional anion vacancy diffusion in the calcium apatites
Authors: Welch D. O. , Royce B. S. H.
Published: July 2007

Correlated random walk statistics are used to derive an expression for the diffusion coefficient for vacancies in a linear chain containing impurities. The results are applied to the problem of anion mobility in the calcium apatites. For fluorapatite the analysis indicates energies of motion for fluorine and oxygen ions to be 0.77 and 2.0 eV, respectively.
Semi‐Empirical LCAO Band Structures for Different Crystalline Phases of Tellurium
Authors: Weigel C. , Messmer R. P. , Corbett J. W.
Published: July 2007

The electronic band structure of trigonal tellurium is calculated by the extended Hückel theory using parameters adjusted to match known features of the band structure as determined by experiment. These same parameters then are employed to predict the band structures of arsenic‐type, rhombohedral, and hypothetical simple cubic tellurium. All predicted band structures turn out to be metallic.
Some Properties of Type‐II Superconductors Derived from a Non‐Local Theory
Authors: Brandt E. H.
Published: July 2007

Some properties of flux lines and of the flux‐line lattice are derived from the non‐local theory for type‐II superconductors given in a previous article. The curvature of the magnetic field increases with decreasing temperature (even in reduced units), resulting in a sharp cusp at zero temperature and B = Hc2 (clean limit). At large distances from the vortex core the magnetic field reverses its sign for small x and T < 0.78 Tc′, whereas the gap parameter increases monotonically to the BCS‐value. Both effects can separately explain the attraction of flux lines observed in experiment for small x and T.
Microscopic Magnetic Field Distribution in Superconducting Niobium Single Crystals in the “Dirty Limit”
Authors: Weber H. W. , Schelten J. , Lippmann G.
Published: July 2007

Neutron diffraction experiments on the flux lines in superconducting niobium single crys‐ tals varying in their Ginzburg‐Landau parameter x1 between 1.8 and 3.0 are reported. In all cases the flux line lattice was found to be single crystalline. Using the analysis of the integral reflectivities described previously [ l ] the local magnetic field distribution is obtained as a function of the flux densitny. Comparing the results for different x a systematic variation of the magnetic microstructure is observed: with increasing x the attractive inter‐action between individual flux lines disappears, the maximum field decreases, and the mni‐mum and saddle point fields increase; the linear superposition of the fields of single flux lines observed with x ≈ 4 changes systematically into a nonlinear one a t x ≈ 1. Finally, the results on the “isolated” flux line are compared with theory.
Electrical and Optical Properties of Amorphous and Monoclinic Selenium under Very High Pressure
Authors: Fuhs W. , Schlotter P. , Stuke J.
Published: July 2007

The conductivity of amorphous, monoclinic, and trigonal selenium has been measured at 300°K as a function of quasihydrostatic pressure up to 150 kbar. Amorphous and monoclinic samples after exposure to pressure above 120 kbar are transformed irreversibly to the trigonal modification. This result is confirmed by the direct observation of the corresponding shift of the absorption edge. Besides conductivity, for amorphous selenium the shift of absorption edge with pressure is investigated. The resulting pressure coefficient of the band gap is in good accordance with the value obtained from the pressure dependence of the conductivity with the assumption that intrinsic conduction predominates in amorphous selenium.
Metal–Insulator Transition and Lifshits Instability in the Hubbard Model. II. Stationary Point Approximation for the Functional Integral
Authors: Gobsch G. , Weller W.
Published: July 2007

The self‐consistent approximation scheme developed in an earlier paper [1] was evaluated numerically in the stationary point approximation (SPA) and in Hubbard's alloy analogy (AA). The results confirm the occurrence of a Lifshits instability leading to a discontinuous metal‐insulator transition.
Role of Singlet and Triplet Excitons in Extrinsic Photocurrent Production in the Anthracene–Gold System
Authors: Chance R. R. , Prock A.
Published: July 2007

Extrinsic hole photocurrents in a gold coated anthracene crystal are measured as a function of the absorption depth of the exciting light. Charge pairs are formed at the gold‐anthracene interface as a result of exciton–gold interactions. It is found that both singlet and triplet excitons are involved as precursors to charge formation. The contributions of singlets and triplets to the observed photocurrent quantum yields are determined for 394 nm excitation light (a and b polarized) and 340 nm excitation light (a and b polarized). Since reabsorption is known to have a significant effect on the distribution of excitons and on the effective singlet lifetime, a steady state numerical solution for the reabsorption problem is offered for this system. The inclusion of the reabsorption effect allows the calculation of a “reabsorption free” singlet diffusion length (316 Å) and an evaluation of the electron transfer efficiency ratio (ηT/ηS ≈ 3.5) where ηS is the probability of electron injection per singlet exciton quenched by the surface and ηT is the corresponding probability for a triplet exciton. The magnitude of the ratio ηT/ηS is interpreted in terms of singlet energy transfer to the gold layer.
EPR Spectra of Transition Element Impurities with 3d2 Configuration in Hexagonal CdS and CdSe Single Crystals
Authors: Böttcher R. , Dziesiaty J.
Published: July 2007

Electron paramagnetic resonance has been studied for divalent titanium with 3d2 configuration substituting for Cd in hexagonal single crystals of cadmium sulphide and cadmium selenide. The parameters of the spin‐Hamiltonian have been determined at T = 27 and 77 K. It is found that the symmetry of the centre is axial, corresponding to the C3V symmetry of an isolated impurity on normal lattice sites in wurtzite.
The Paraelastic Interaction between Lattice Defects and Flux Lines
Authors: Kronmülleb H. , Schmucker R.
Published: July 2007

Within the framework of the micromagnetic theory of superconductivity explicit expressions for the elastic stresses of flux lines are derived. The dependence of the stress tensor on the superconducting parameters λ, ξ, and χ is discussed. It is shown that the magnetic pressure associated with the magnetic field gives rise to elastic stresses of the same order of magnitude as the contribution from the Δ V/V effect of the order parameter. Explicit expressions are derived for the pinning forces exerted by dislocations on flux, lines. They are found to be approximately proportional to the condensation energy H/8π.
Model Pseudopotential and Lattice Vibrations of Alkaline Earth Metals
Authors: Prasad B. , Srivastava R. S.
Published: July 2007

The phonon frequencies and the binding energies of alkaline earth metals Ba, Sr, and Ca have been computed using the two parameter model pseudopotential proposed by Krasko and Gurskii. The exchange and correlation effects in the Hartree dielectric function have been adequately considered in the manner of Singwi et al. The calculated results are compared with experimental data. Reasonable agreement is found between experiment and theory.
Electric Field Gradients in Charge‐Perturbed Lattices
Authors: Pustówka A. J. , Sawicka B. D. , Sawicki J. A.
Published: July 2007

Computer experiments were performed to find the electric field gradients at nuclei in randomly charge perturbed cubic and hexagonal lattices up to 50% defect concentration. Possible modifications of Mössbauer spectra and TDPAC attenuation factors are discussed.
The Optical Properties of Silicon Ditelluride
Authors: Lambros A. P. , Economou N. A.
Published: July 2007

The optical properties of SiTe2 have been studied in the region 2.5 to 0.5 μm and in the temperature range 300 to 100°K. In the absorption spectrum three distinct regions have been observed which have been attributed to Te vacancies, indirect, and direct transitions, respectively. The fine structure in the vicinity of the indirect transitions indicates the participation of four phonons and a two‐dimensional exciton. The absorption in the vicinity of the direct transitions follows Urbach's rule. The main parameters characterising the indirect and direct transitions are determined.
Elastic Energy and Shape of New Phase Coherent Inclusions
Authors: Khachatubyan A. G. , Hairapetyan V. N.
Published: July 2007

An analysis is made of the shape of coherent inclusions of a new phase in an elastic an‐isotropic medium in dependence on the surface tension energy, the elastic medium anisetropy, and the crystal lattice rearrangement. It is shown that the internal stress energy consists of two terms if the inclusions are of plate‐like shape. The first term is proportional to the inclusion volume and the second to the length of the closed contour, which encircles the inclusion along its periphery in the habit plane. Formally the second term gives the dislocation loop energy, where the Burgers vector is the product of the plate thickness and the characteristic deformation produced by the phase transition. The minimum of this term defines the shape of the inclusion in the habit plane. A detailed analysis of the shapes in the extreme case of a small plate thickness with respect to the length is made.
Screw Instability in a Three‐Component Electron‐Hole Plasma
Authors: Meilikhov E. Z.
Published: July 2007

A theory of the screw instability in a three‐component electron‐hole plasma of semiconductors in a weak magnetic field is formulated. At these conditions the screw instability has two modifications (monopolar and bipolar modes). The role of intervalley (interband) scattering in developing of the monopolar screw instability is estimated. It is supposed that the observation of the latter is possible in GaSb. The results of numerical calculations of threshold electric fields and oscillation frequencies are given for both modes of the screw instability in p‐ and n‐GaSb.
Optical Absorption of Tellurium in the Region between 39 and 250 eV
Authors: Sonntag B. , Tuomi T. , Zimmerer G.
Published: July 2007

The absorption spectrum of evaporated thin films of crystalline and amorphous tellurium was measured in the region between 39 and 250 eV. The electron synchrotron DESY was used as a light source. A sharp doublet around 42 eV and a weak structure on its high energy side associated with transitions from the spin—orbit split 4d core levels to the conduction band were observed and compared with the density of conduction states of crystalline tellurium and with the calculated multiplet splitting of the 4d95p5 configuration of atomic Te. The doublet was also observed in the amorphous phase. At higher energies the absorption spectrum is dominated by a broad, large maximum at 87 eV. After a minimum at 165 eV the absorption increases again with increasing photon energy. This behavior is very similar to the absorption spectrum of solid and gaseous xenon. It can be explained by quasi‐atomic d–f transitions.
Raman Scattering by α‐HgS (Cinnabar)
Authors: Nusimovici M. A. , Meskaoui A.
Published: July 2007

Raman scattering is observed in first and second order by optically active phonons in mercury sulphide HgS having the cinnabar structure (α‐HgS). For the first time these spectra could be obtained in polarised light and interpreted using selection rules derived by group theoretical considerations. The experiments have been performed both at room temperature and at low temperatures (90 °K).
Phonon‐Assisted Interband Absorption and Electroabsorption in Disordered Semiconductors
Authors: Esser B.
Published: July 2007

The phonon assisted interband absorption coefficient is calculated for a disordered semiconductor having a random field of impurities with high concentration (compensation). The frequency dependence of the contributions to the absorption coefficient due to the emission and absorption of phonons is obtained. The corresponding optical tail may be described approximately by an exponential dependence with the same characteristic energy as that obtained in case of direct transitions. Several cases are considered where the total optical tail coincides with that given by the contributions in question. The phonon‐assisted interband electroabsorption coefficients are calculated for the random field of impurities and for a smooth random field. In case of the impurity field the graphs are plotted. In case of the smooth field the asymptotic tail of the electroabsorption coefficient is calculated explicitly. The shifted band edge representation is discussed.
Cyclotron Resonance of n‐Type Semiconducting Bi1‐XSbx Alloys
Authors: Oelgart G. , Herrmann R.
Published: July 2007

Measurements are presented of cyclotron resonance on n‐type semiconducting Bi1‐xSbx alloys within the wavelength range of 4 mm and a temperature of 4.2 K. The anisotropy of cyclotron masses can be explained by means of an ellipsoid as a model of the iso‐energy surface. This model resembles that of electrons in pure Bi except of the stretching of the ellipsoids. It is found that the mass values strongly depend on the antimony concentration.
Photoelectric Properties of Mg2Si, Mg2Ge, and Mg2Sn I. X‐Ray Excitation
Authors: Tejeda J. , Cardona M. , Shevchik N. J. , Langer D. W. , Schönherr E.
Published: July 2007

The energy distribution spectra of photoelectrons (XPS) and Auger electrons (AES) excited with AlKα radiation in Mg2Si, Mg2Ge, and Mg2Sn are reported. For the purpose of determining core shifts, measurements were also performed on the elemental constituents. These measurements yield information about the density of valence states, the position and the chemical shifts of the core levels. The energy of the valence plasmons is also obtained. This paper (I) is followed by a second one (II) in which similar results obtained with far UV excitation are reported and discussed in the context of the present work.
Magnetoresistance Anisotropy in Bismuth and Bismuth—Antimony Crystals
Authors: Jacobson D. M.
Published: July 2007

The transverse magnetoresistance anisotropy along the bisectrix axes of Bi and Bi (98)Sb(2) single crystals at 4.2 and 89 K is compared with the theory for magnetic fields applied in two symmetry directions. It is found that the changes in shape of the magnetoresistivity anisotropy curves are consistent with expressions derived from Aubrey's magnetoconductivity tensor for bismuth.
Thermodynamics of the Hot Electron System I. Gradient of the Phonon Temperature
Authors: Alvarez‐Torres J. , Negrete P.
Published: July 2007

The effects of electron‐phonon interaction in a system of hot electrons are discussed. Particular consideration is given to the effect associated with the generation of a temperature gradient in the phonon system. An expression for this gradient as a function of the electric field is obtained and some experimental implications are discussed.
Reversible Photochemical Reactions in Additively Coloured CaF2 Crystals
Authors: Görlich P. , Ullmann P.
Published: July 2007

The influence of selective light irradiation on the absorption behaviour of additively coloured CaF2 crystals at 84, 300, and 500 °K is investigated. It was found that reversible photochromic reactions occur especially at 500 °K. Irradiation into the F band gives rise to an absorption increase of the long‐wavelength absorption peaks. A complete reconversion is possible, so that the formation of colloids can be ruled out.
Interaction of Exciton‐Polaritons with Charged Impurities in Semiconductors
Authors: Skaistys E. , Sugakov V. I. , Zinets O. S.
Published: July 2007

The retarded exciton Green's function G(ω) is calculated for semiconductors with randomly distributed impurities. The expression of the exciton absorption band shape due to polariton scattering by charged impurities is obtained using a relation between the complex conductivity tensor σα β (ω) and G(ω). The band shape is of Lorentz type with Γ depending on the frequency, Γ(ω) = (h/2) v nc (σ + σ), where v is the velocity of the light generated exciton, σ and σ are the cross sections of elastic and inelastic S‐scattering by an isolated charged impurity, nc the charged impurity concentration. Numerical calculations concerning CdS and GaAs have been made. This band broadening mechanism may be dominant at high impurity concentrations.
Photoelectric Properties of Mg2Si, Mg2Ge, and Mg2Sn II. UV Excitation
Authors: Cardona M. , Tejeda J. , Shevchik N. J. , Langer D. W.
Published: July 2007

In the previous paper (I) the energy distribution spectra of photoelectrons (XPS) and Auger electrons (AES) excited with AlKα radiation in Mg2Si, Mg2Ge, and Mg2Sn were presented. Here similar measurements are reported performed with He resonant radiation (48.4, 40.8, and 21.2 eV). The effect of surface contamination by O2 or H2O is shown to be very important in these UPS spectra and results meaningful of the material under study can only be obtained if such contamination is kept to less than 0.2 monolayers. The strong structure which appears in less clean samples has been identified as related to the compounds MgO and Mg(OH)2. The UPS spectra of the clean materials yield information about the densities of valence states and about the outermost d electrons of the Ge and Sn core. Very accurate values for the corresponding spin‐orbit splittings and chemical shifts are obtained.
A Scanning Electron Diffraction Study of Vapor‐Deposited and Ion Implanted Thin Films of Ge (II)
Authors: Graczyk J. F. , Chaudhari P.
Published: July 2007

The reduced intensity function and the structure factor for several models of amorphous Ge have been calculated. These include the diamond cubic, the amorphon, and a random network model. It is found that the data on amorphous Ge is best described by the random network models. Also the effect of interparticle interference function in evaluating the models is taken into account.
A Low‐Temperature Phase Transition in the One‐Dimensional Conductor K2Pt(CN)4Br0.30 ·x H2O
Authors: Comes R. , Lambert M. , Zeller H. R.
Published: July 2007

It is shown that the linear superlattice distorsion of periodicity 6 × 2.88 Å, which was recently observed by X‐ray diffuse scattering in the one dimensional conductors of the type K2Pt(CN)4Br0.30 · x H2O, looses progressively its one‐dimensional character for temperatures lower than 120 °K. This seems to announce a phase transition at a temperature lower than 77 °K leading to a unit cell 3 c × 2 a × 2 a, referring to the room temperature parameters. It is suggested that this phase transition arises from the condensation of the lowest frequency longitudinal soft modes due to a giant “Kohn anomaly”.
Quenching of Benzophenone Phosphorescence in the Vitreous Phase by Long‐Lived Guest Triplet States
Authors: Peter L. M. , Vaubel G.
Published: July 2007

Triplet (host)‐triplet (guest) annihilation has been observed and characterised in vitreous benzophenone. The quenching of the benzophenone phosphorescence by long‐lived guest triplet states was measured and the bimolecular annihilation rate constant γhg determined using naphthalene, pyrene, and coronene as guest materials. γhg is found to be independent of the nature of the guest, being of the order of 10−16 cm3s−1. This low value is related to the slow rates of exciton migration in the vitreous phase.
Elastic Field of a Shear Dislocation Loop in an Anisotropic Hexagonal Crystal by the Green's Function Method
Authors: Ohr S. M.
Published: July 2007

Analytical expressions for the components of displacement and stress around a circular shear dislocation loop in the basal plane of an anisotropic hexagonal crystal are derived by the Green's function method. The components of displacement are obtained in terms of surface integrals over the area of the loop of the partial derivatives of the Green's function. It is shown that the surface integrals can be expressed in terms of Lipschitz‐Hankel integrals for a shear, as well as for a prismatic, dislocation loop. Calculations have been carried out in the case of graphite and the results are presented graphically by means of contour plots. In agreement with previous results on the prismatic dislocation loop, the most noticeable effect of crystal anisotropy is to reduce the magnitude of stresses and the displacement components parallel to the basal plane around a shear dislocation loop. The method can be extended to problems of anisotropic elasticity of non‐basal dislocation loops.
Calculation of the Surface Energy of Solid Metals from Work Function Values and Electron Configuration Data
Authors: Missol W.
Published: July 2007

A formula for surface energy, ω, in terms of electron work function, φ, and the effective number of free electrons per atom, z, is given. The basis for its derivation were the known equations of the free electron theory of metals and the known advanced Frenkel's relation between electron work function and heat of sublimation. Furthermore in the formula (M atomic mass, γ density) \documentclass{article}\pagestyle{empty}\begin{document}$ \omega = \frac{{1530}}{q}\,\frac{\varphi }{{(M/\gamma)^{2/3} }}z^{2/3} $\end{document} details of the crystal structure of metals were taken into account by introducing the structural coefficient q. The calculated values of surface energy were compared with experimental data.
Hot Electron Faraday Rotation and Birefringence in Semiconductors with Non‐Parabolic Energy Bands
Authors: Almazov L. A.
Published: July 2007

The phenomenon of Faraday rotation arising in semiconductors with isotropic dispersion law of carrier energy in the presence of dc electric and magnetic fields has been considered on the basis of expressions for the dielectric tensor obtained in a previous work [1]. It is shown that in the case of non‐parabolic energy bands the free‐carrier Faraday rotation is accompanied by birefringence. n‐type InSb is taken as an example for numerical calculations.
A Study of the Effect of Deformation on Optical Absorption of MgO Single Crystals
Authors: Turner T. J. , Murphy C. , Schultheiss T.
Published: July 2007

The concentration of V centers, produced by a hole trapped at a magnesium vacancy, has been found to increase linearly with deformation in single crystals of magnesium oxide, When one slip system is operative in the deformation process an anisotropic defect is produced whose axis is 〈100〉 perpendicular to both the {110} slip plane and 〈110〉 slip direction. This defect produces optical absorption bands at 4.07 and 5.17 eV when the deformed crystal is X‐irradiated. These bands are attributed to vacancy complexes which have trapped one or more electrons. Bleaching experiments are reported in which these bands are annihilated by electron release or the capture of holes released from the V band.
Temperature dependence of the hyperfine interaction of trivalent gadolinium in single crystal thorium oxide
Authors: Marshall S. A. , Nistor S. V. , Huang Chao‐Yuan , Marshall T.
Published: July 2007

Hyperfine structure splittings for the M = − ½ → ½ transition of trivalent gadolinium in single crystal thorium oxide have been measured from 1.25 to 350 K. The temperature dependence of these splittings is interpreted in terms of a modified Šimánek‐Orbach theory.
Mössbauer studies of low‐temperature radiation damage in α‐iron
Authors: Vogl G. , Schaefer A. , Mansel W. , Prechtel J. , Vogl W.
Published: July 2007

The Mössbauer effect has been used to study radiation damage in α‐iron, doped with 0.6 at% Os and 4 at% Pt. The samples were irradiated in a nuclear reactor at 4.6 K. The Mössbauer nuclei of Ir193 and Au197 were produced by capture of thermal neutrons in Os192 or Pt196, a process which simultaneously could lead to radiation damage. Compared with annealed samples, the average magnetic field was reduced after the irradiation by about 2% and the line width was increased by approximately 30%. Isochronal annealing processes were studied. The annealing of the irradiation effects took place primarily between 90 and 140 K with activation energies in the range between 0.30 and 0.40 eV. These effects are interpreted as mainly due to a vacancy as nearest or next nearest neighbour of the displaced Mössbauer atom combined with an interstitial several lattice sites away from the vacancy. The Mössbauer atom does not come to rest as an interstitial atom. These results are in good agreement with results from computer experiments of Vineyard's group.
X‐ray spectroscopic investigation of the electronic structure of diamond
Authors: Umeno M. , Wiech G.
Published: July 2007

The X‐ray K‐emission band and the so‐called self‐absorption spectrum of diamond have been measured with a concave grating spectrometer using primary excitation. The results are compared quantitatively with recent calculations of the energy band structure, and with the density of states of the valence and conduction bands of diamond. From the experiment the width of the valence band is determined to about 21 eV, while the calculated width varies from 19 up to 31 eV. It is found that structural features in the density‐of‐states curve to a high degree are reflected in the K‐band. X‐ray emission bands together with X‐ray photoelectron spectra seem to yield valuable information about the electronic structure of the valence band of second period elements.
The Jahn‐Teller effect in the 3000 Å Emission of KCl:Tl+: An investigation by time‐resolved emission spectroscopy
Authors: Gerhardt V. , Gebhardt W.
Published: July 2007

The 3000 Å emission of KCl:Tl+ which contains a fast and a slow decay process was investigated by time‐resolved emission spectroscopy. This technique permits sampling of photons which are emitted at a chosen delay time after excitation. Emission and excitation spectra and the polarization of emission were measured separately for both components with and without applied stress. The results give information about the Jahn‐Teller effect of the 3T1u, and 3A1u excited states. It is concluded that the 3A1u‐APES follows the 3A1u‐APES near the potential minima.
Far‐infrared absorption in amorphous III‐V compound semiconductors
Authors: Prettl W. , Shevchik N. J. , Cardona M.
Published: July 2007

The infrared spectra of amorphous films of GaP, GaAs, GaSb, InAs, and Ge prepared by sputtering have been measured from 10 to 4000 cm−1. The absorption spectra in the region of the “optical” phonon frequencies show similarities to the phonon density of states as deduced from Raman scattering but the absorption becomes much smaller at low frequencies. It is shown that while the coupling constant for Raman scattering by an amorphous material varies as the square of the wave vector, it varies in the case of infrared absorption as its fourth power. The results are compared with those of Raman scattering and with the predictions of a simple model.
Atomic structure of Cu3Au and Ni3Fe at temperatures above Tc
Authors: Golosov N. S. , Dudka B. V.
Published: July 2007

Atomic configurations of Cu3Au and Ni3Fe which are in agreement with the experimental values of a short‐range order in the first and second coordination shells have been constructed by a Monte Carlo method on a model of 4000 atoms. By studying the atomic arrangement on the sites of the lattice it was established that in the model the short‐range order is not homogeneous. Three‐dimensional complexes of atoms are formed having short‐range order considerably exceeding the average value. The size of the complexes increases with decreasing temperature.
The influence of a free surface on nuclear spin waves
Authors: Sarges K. H.
Published: July 2007

The existence of nuclear surface spin waves in ferromagnetic and antiferromagnetic substances is shown. The dispersion laws for the coupled electronic and nuclear surface spin wave branches are obtained by solving numerically a system of linearized equations for the spin wave operators. The influence of changed surface parameters and of an applied magnetic field is investigated.
Two‐step excitation of photoluminescence in GaP
Authors: Schindler A. , Bindemann R. , Kreher K.
Published: July 2007

Donor‐acceptor pair luminescence and radiation of bound excitons have been excited in GaP using radiation with photon energies lower than the band gap. This anti‐Stokes luminescence is explained by a two‐step excitation process via the deep donor oxygen. Excitation with radiation lower than the band gap results in a very low homogeneous excitation density throughout the bulk of the sample and enables the investigation of the phonon structure of the donor‐acceptor pair bands.
Determination of the domain wall energy from hysteresis loops in YIG
Authors: Guyot M. , Globus A.
Published: July 2007

The energy lost by the continuous pinning and depinning of the domain wall as it moves and the energy lost by the formation and destruction of a fraction of the wall surface may be the origin of the losses which find their expression in the hysteresis loop. This new hypothesis, based on Globus' model, allows to calculate the wall energy γ and the pinning force/Experimentally, only a simple measurement of the loop areas is needful to calculate the γ value, which is in very good agreement with theoretical values deduced from the theory of Landau and Lifshits. In addition, the γ values measured are proportional to the global anisotropy of polycrystals K (K = K1 + σn λs), that results in a very small wall thickness (0.07 μm) which is almost constant as a function of T. The connection between the natural stresses σn and the intrinsic properties is confirmed by revealing a relationship between K, K1, and A.
Solitary excitons in one‐dimensional molecular chains
Authors: Davydov A. S. , Kislukha N. I.
Published: July 2007

The change in time of the state of intramolecular excitation in an one‐dimensional molecular chain is investigated, where its deformability is taken into account. It is shown that the excitation which is accompanied by a local deformation of the chain, can move uniformly along the chain, the size of the region under excitation remaining constant. These excitations in one‐dimensional molecular chains can be called particle‐like excitons or solitary excitons.
Propriétés des alliages InSb1‐xBix. III. Estimation théorique de la bande interdite
Authors: Jean‐Louis A. M. , Duraffourg G.
Published: July 2007

La bande interdite d'un composé hypothétique InBi cristallisant dans la structure de la blende est estimée en utilisant trois méthodes indépendantes basées respectivement sur la règle d'évaluation des effets relativistes de Herman, sur une extension de la méthode des pseudootentiels empiriques de Cohen et Bergstresser et sur le modèle “ssemiconduteur” de Van Vechten. La variation de la bande interdite des alliages InSb1−xBix avec la concentration x est ensuit déduite: dans le domaine des faibles concentrations le calcul conduit à und diminution de al bande interdite de 2,4 eV par mole InBi à comparer avec la valeur expérimentale (3,6V/mole).
Effect of internal excitations of polarons on magneto‐optical absorption and cyclotron resonance in polar crystals
Authors: Devreese J. T. , Kartheuser E. P. , Ward R. , Baldereschi A.
Published: July 2007

The energy spectrum of Fröhlich polarons in a magnetic field is investigated theoretically. The constants of the motion of the system are studied and a “Feynman model” serves as B guide in this study. A crucial difference between the energy spectra of polarons and rigid particles is predicted at rather strong coupling strengthsor large magnetic fields. It is due to the internal structure of the polaron system. When the electron‐LO‐phonon coupling constant becomes large enough to allow internal excitations, a resonance may appear in the one‐phonon continuum. This resonance is split by Zeeman effect at small field values and the components of the multiplet tend asymptotically to the Landau levels with increasing field strengths. The stability of one component at least is enhanced by the magnetic field, so that magnetic fields could be used to reveal internal excitations of polarons, in cyclotron resonance or magneto‐optical absorption experiments. Recent experimental results on magneto‐absorption by excitons are discussed in the light of the present work.
The density of states of the anderson model of cellular disorder with random diagonal and random off‐diagonal elements in CPA
Authors: Braeter H. , Eifrig Th. , Kirsten E.
Published: July 2007

Using a generalized version of the single‐site coherent potential approximation (CPA) the electronic density of states is calculated for the Anderson model of cellular disorder with random diagonal and random off‐diagonal elements. An elliptical probability distribution for the site energies is assumed. The off‐diagonal matrix elements are assumed to be linearly dependent on the site energy. In dependence on the fluctuation widths the electronic density of states in this model can have an appreciably different shape compared to models with non‐fluctuating off‐diagonal elements.
High‐field conduction mechanism in amorphous germanium
Authors: Telnic M. , Vescan L. , Croitoru N. , Popescu C.
Published: July 2007

Current‐voltage measurements on a‐Ge in the temperature range 77 to 143 °K and the field range 10 to 5 × 104 V/cm are analysed in the frame of the conduction model used to explain low‐field conduction in the T−1/4 region. In this model the conduction is due to non‐degenerate carriers tunnelling without thermal activation between localized states in two linear tails. Assuming that the high field effects concentrate essentially upon the distribution function quantitative expressions are obtained for the current which ensured a good fit to the normalized experimental data for unannealed and annealed a‐Ge.
Hyperfine quadrupole splitting and mössbauer spectra for an orbital doublet
Authors: Bersuker I. B. , Borshch S. A. , Ogurtsov I. Ya.
Published: July 2007

A theoretical investigation is made of the effect of vibronic coupling on the line shapes of Mössbauer spectra in an orbital degenerated E‐term system including relaxation transitions among the vibronic states and magnetic hyperfine interaction. The vibronic interaction is taken into account in the limiting case of strong linear coupling and arbitrary second‐order contribution. The quadrupole splitting of the energy levels for a nuclear spin I = 3/2 and the transition probabilities for I = 1/2 → I = 3/2 transitions were obtained. The effect of relaxation transitions on the line shape is studied on the basis of a generalized Kubo‐Andersen model. For a set of actual relaxation and vibronic parameter values the Mössbauer spectra are calculated numerically with a computer. The possibilities of comparison with experiment are discussed.
Fine structure of shallow wannier‐mott exciton levels in a polarizable field
Authors: Fedoseev V. G.
Published: July 2007

A theory of the fine structure of Wannier‐Mott excitons, due to the interaction of the electron and hole with the polarizable vibrations of the lattice, is developed. The “non‐hydrogen‐like” corrections to the exciton energy, and also the corrections to the effective mass of the exciton, depending on the internal state of the exciton, are calculated.
Interband faraday rotation in silicon
Authors: Kessler F. R. , Metzdorf J.
Published: July 2007

The nonresonant interband Faraday rotation in silicon single crystals was measured in the spectral region 0.55 to 3.1 eV. A new modulation method is developed for measuring rotations of the plane of polarization of linearly polarized radiation to an accuracy of better than 0.001° in normal cases. The range of measurements was extended up to 2 eV above the indirect energy gap with sample thicknesses between 1 mm and 1 μm, at temperatures between 100 and 350 K, and in a magnetic field of 2 T. The Faraday rotation increases monotonously in the whole range up to a photon energy of 3.1 eV. As the analysis by means of theoretical dispersion functions, of the dispersion relation known as Becquerel equation, and the temperature dependence shows, the interband Faraday rotation in silicon is only associated with direct transitions, the band gap of which should be between 3.2 and 3.4 eV and is not below 3.1 eV.
On the mobility of holes in deformed semiconductors
Authors: Düster F. , Labusch R.
Published: July 2007

The scattering of free holes at dislocations is calculated by a Born approximation. The scattering potential is composed of a coulomb interaction with the charged dislocation core and an interaction with the strain field via the deformation potential. Combination of these two mechanisms with phonon scattering in the transport equation leads to a modification of Matthiessen's rule for the total mobility. Comparison with mobility data on deformed p‐Ge shows that the modifications are essential for a quantitative agreement between theory and experiment. A sharp peak in the second derivative of the mobility with respect to temperature is predicted, when the charge in the dislocation core goes through zero. This may turn out to be an accurate means to determine the “neutrality temperature” independent of other methods.
High‐field transport and low‐field mobility in tellurium single crystals
Authors: Hoerstel W. , Kusnick D. , Spitzer M.
Published: July 2007

The Hall effect and the conductivity in a low electric field and the conductivity in a pulsed high electric de‐field were investigated on carefully prepared and long‐time annealed samples. The reproducible experimental findings obtained at largely undistorted crystals were compared with calculated values. The calculations were carried out for a simple isotropic but non‐parabolic energy band model and for different scattering mechanisms. The result, which states that the temperature dependence of the mobility within the range extending from 65 to 180 K as well as the field dependence of drift velocity up to approximately 1.5 kV/cm, can be explained only by means of polar optical scattering for a parabolic energy band structure, can serve as a starting point for more detailed analyses.
Comments on the evidence for sharp and gradual optical absorption edges in amorphous germanium
Authors: Connell G. A. N. , Lewis A.
Published: July 2007

Several investigators have analyzed optical data on amorphous Ge films prepared by evaporation on room‐temperature substrates to derive a sharp absorption edge near 0.5 eV. A re‐examination of their work shows that the sharp edges, found hitherto, may be artifacts resulting from either experimental or calculational errors and that the preponderance of the current evidence favors a gradual absorption edge.
Investigation of k = 0 phonons in Bi, Cd, Mg, and Zn by Raman scattering
Authors: Grant W. B. , Schulz H. , HÜfner S. , Pelzl J.
Published: July 2007

Measurements are reported for optical phonons (k = 0) by Raman scattering at 300, 80, and 2 K for Bi, Cd, Mg, and Zn. The linewidths are found to increase, and the frequencies to decrease, as the temperature is raised. The temperature dependent portion of the linewidth is attributed to a two‐phonon decay process. In addition, the contributions to the line‐width from the isotope effect, the electron‐phonon interaction, and strains are discussed.
Magnetoresistivity of n‐Si at High Magnetic and Strong Electric Fields
Authors: Asche M. , Bondar V. M. , Kurtenok L. F. , Martynchenko V. I.
Published: July 2007

The magnetoconductivity of n‐Si at a strong but not quantizing magnetic field is presented for 77 °K. In contrast to weak magnetic fields a superlinearity of the current‐voltage characteristics is obtained. This agrees with theoretical predictions of the inversion of the ratio of the mean carrier energies and repopulation of electrons between the valleys.
Contribution of Excitons to the Optical Properties of GaSe
Authors: Bianchi D. , Emiliani U. , Podini P. , Paorici C.
Published: July 2007

Faraday effect measurements were performed on excitons in GaSe using a pulsed magnetic field up to 80 kG in synchronous operation. The interpretation of the experimental data showed the necessity of Zeeman splitting, magnetoabsorption and dichroism measurements. The analysis of the results suggested an analytical model taking into account the contribution of excitons to the optical constants of GaSe. Using this model the experimental data were successfully fitted. Such an approach is quite general and can be used every time one has well isolated resonances for which Nƒ ≪ (ϵ0 μ γ ω0)/(2 π e2). It is shown that this condition is satisfied for GaSe, for Nƒ = 1.06 × 1017 cm−3, g+ = −3.5 is obtained while the damping factor γ changes from sample to sample between 3.6 × 1012 and 4.5 × 1012 s−1.