bluuebunny/crossref_metadata_2025 huggingface dataset:
Entropy Optimization in Texture Goniometry. I. Methodology
Authors: Schaeben H.
Published: July 2007

Pursuing the approach of finite series expansion to the texture problem of reproducing the orientation distribution function (ODF) from its pole distribution functions (PDF) measured in X‐ray or neutron diffraction experiments, the mathematical model of entropy maximization is introduced and elaborated in a discrete setting. The entropy maximizing solution yields the ODF with the smallest information content consistent with the experimental data, thus avoiding artificial textural components for which there is no evidence in the measured PDF's, especially “ghosts” caused by the specific properties of the diffraction experiment. This solution seems favorable particularly when the data are incomplete or afflicted with experimental errors.
Perturbative Approach to Dilute Off‐Diagonal Defects
Authors: Wiecko C.
Published: July 2007

A diagrammatic approach is developed to the problem of dilute concentration of off‐diagonal defects for short range interactions. The method is illustrated with the calculation of phonons when impurities that change the central force constant of the harmonic interaction with the nearest neighbors are present in three different structures: on the linear chain, on the square planar lattice, and the simple cubic structure. Systematic rules are obtained for the summation of the series. The procedure can inspire a more general algorithm for matrix inversion based on an eventually summable series.
Relations between Third Order Isothermal and Adiabatic Elastic Constants for an Isotropic Material
Authors: Sachs A.
Published: July 2007

Relations between the adiabatic and isothermal third order elastic constants are derived from a general expression for the free energy of an isotropic material. The relations include the linear terms in the temperature variations of the coefficient of thermal expansion and of the second order elastic constants. Numerical calculations are made for aluminium.
Magneto‐Optical Investigations on p‐InSb Bicrystals in the Submillimeter Wavelength Range
Authors: Ludwig F. , Müller H.‐U. , Herrmann R.
Published: July 2007

The magneto‐optical properties of p‐type InSb bicrystals are investigated in the submillimeter wavelength range from λ = 57 to 251 μm at temperatures T ≦ 4.2 K and magnetic fields up to B = 6.5 T. At wavelengths λ = 118.8 and 251 μm the cyclotron resonance of the conduction electrons in the n‐inversion layer adjacent to the grain boundary can be detected. At all other wavelengths strong magnetic field dependent absorption effects in the p‐type bulk mask the relatively small absorption effects in the inversion layer. The acceptor excitation spectrum of the bulk is discussed. From the periodicity of quantum oscillations three occupied electric subbands are identified. The experimental cyclotron resonance spectra are modeled as the superposition of three cyclotron resonance lines belonging to the three occupied electric subbands. Cyclotron masses are obtained with a three‐level model in the triangular‐well approximation and compared to the experimental data.
Size Dependence of Surface Thermodynamic Parameters of Microclusters and the Location of the Gibbs' “Surface of Tension”
Authors: Vogelsberger W. , Fritsche H.‐G. , Müller E.
Published: July 2007

The thermodynamic surface parameters surface stress and surface tension are calculated for icosahedral and cuboctahedral microclusters in dependence on cluster size. Analytical expressions can be obtained. The size dependent behaviour of these expressions is strongly influenced by the position of the surface to which the surface parameters are referred. If the “equimolecular dividing surface” is used the expected decrease of the values of the surface parameters with decreasing cluster size is observed. The location of the Gibbs' “surface of tension” for these clusters is determined. The thermodynamic equilibrium conditions, the equations of Young‐Laplace and of Kelvin, are formulated with emphasize to the importance of the location of the dividing surface.
Effect of Lattice Disorder on the Excitonic States in Superionic Crystals
Authors: Akopyan I. Ch. , Gromov D. N. , Klochikhin A. A. , Novikov B. V. , Ogloblin S. G.
Published: July 2007

The effect of the lattice disorder on excitonic states in superionic crystals is studied experimentally and theoretically. The spectral density of the excitonic states is measured in AgI‐type superionic crystals within a wide temperature region. The theory based on multiple scattering approach is developed. The Lipatov‐Brezin‐Parisi method is applied for the calculation of the averaged scattering matrix in the region of localized excitonic states. The experimental behaviour of the scattering matrix is recovered from the excitonic spectral density after removal of the exciton–phonon interaction effects. A comparison of the experimental and theoretical scattering matrices is made.
The Influence of Compensation on the Hall Effect and Magnetoresistance of n‐Hg0.8Cd0.2Te
Authors: Tsidilkovskii I. M. , Arapov Yu. G. , Zvereva M. L. , Brandt N. B. , Kulbachinskii V. A. , Gorbatyuk I. N. , Elizarov A. I.
Published: July 2007

Magnetic field dependences of the transverse (ϱxx) and the Hall (ϱxy) resistances in the temperature range 0.32 ≦ T ≦ 4.2 K on compensated n‐Hg0.8Cd0.2Te samples with 0.4 ≦ K ≦ 0.8 and K ⪆ 0.9 are studied. It is shown that the metal–insulator transition in fields H ⪆ H0xy (H0xy is the field in which ϱxy begins to grow sharply) is a result of the separation of the impurity states from the conduction band and is not connected with the Wigner crystallization. The weakening of ϱxy(H) and ϱxx(H) growth in strong magnetic fields with the increase of K may be satisfactorily explained in the framework of inhomogeneous medium theory.
Electronic Structure of Niobium Nitrocarbides
Authors: Nikiforov I. Ya. , Kolpachev A. B.
Published: July 2007

In terms of multiple scattering theory using the crystalline muffin‐tin potential and taking into account the scattering on a finite number of atoms the electronic structure of pseudobinary solid solutions NbCxN1−x is calculated for x = 1.0, 0.75, 0.5, 0.25, 0.12, and 0. A comparison with APW results is made for x = 0 and 1. It is shown, that the local partial densities of electronic states (DOS) of constituents differ from those in stoichiometric substances. The dependence of DOS at the Fermi level on carbon concentration x correlates with the dependence of superconducting transition temperature on x.
Anderson Localization in Ferromagnetic Semiconductors Due to Spin Disorder. II. Wide Conduction Band
Authors: Auslender M. I. , Kogan E. M. , Tretyakov S. V.
Published: July 2007

Theoretical investigation are made of the temperature induced metal–insulator transition in doped ferromagnetic semiconductors described by the s–d(f) exchange model. The transition is the result of the mobility edge movement, the disorder being due to interaction of electrons with the magnetic‐ion spin density fluctuations. The electrons are described in effective mass approximation. The mobility edge is obtained from the simple criterion due to Ioffe‐Regel.
The Influence of Disorder on Superconductivity
Authors: Kleinert P.
Published: July 2007

Using many‐particle Green's function techniques the influence of disorder on the transition temperature is investigated theoretically. Depending on the character of the pair‐correlation function of the random potential Tc, can both, decrease and increase with increasing disorder. The theory is applied to a recently proposed BCS mechanism for high‐Tc, superconductivity. For a constant pair‐correlation function an additional increase of Tc up to 3 K is obtained.
Calculations of Magnetotransport Properties of InSb Bicrystals with Several Populated Q2D Subbands
Authors: Nachtwei G. , Schulze D. , Gobsch G. , Paasch G. , Kraak W. , Krüger H. , Herrmann R.
Published: July 2007

The magnetic subband structure of the quasi two‐dimensional electron gas in an inversion layer with several populated electric subbands in InSb bicrystals is calculated using a straightforward and accurate method developed recently. The oscillating part of the magnetoresistance and the magnetic field dependence of the Hall resistance are evaluated by using the Ando model. Two different assumptions concerning the Fermi level position in dependence on the magnetic field are presented and discussed. A good description of the magnetotransport data determined in previous experiments is achieved. It is shown that the simple model of δ‐like Landau energy levels and the resulting discontinous magnetic field dependence of the Fermi energy for a fixed inversion electron density is not able to describe the magnetotransport behaviour determined in the experiments. Estimates of the electron mobilities in the electric subbands from the Landau level broadening lead us to the conclusion that the mobilities obtained from the onset of the Shubnikovde Haas‐oscillations are lower limits.
Surface Phase Diagrams of the Site‐Bond Diluted Surface Ordering Ising Ferromagnet with a Transverse Field
Authors: Song Wei‐Ji , Li Zhen‐Ya
Published: July 2007

Within the framework of an effective‐field theory with correlation phase diagrams for surface ordering in a semi‐infinite Ising ferromagnet with a site‐bond diluted free surface and a transverse field are discussed. A certain characteristic behaviour for the surface ordering is obtained.
Phase Diagram for the Simple Antiferromagnetic Ising Model Using Constant Coupling and Cluster Variation Approximations
Authors: Polat H. , Ekmekçi S.
Published: July 2007

An explicit formula is derived for the critical curve in the H vs. T plane of the two‐dimensional antiferromagnetic Ising square, three‐dimensional antiferromagnetic simple cubic and body‐centered (b.c.c.) lattices and the critical data are evaluated by using constant coupling (CC) and cluster variation (CV) approximations. In the case of H = 0, Onsager's exact solution is obtained for the square lattice. In the case of H ≠ 0, the critical curve dividing antiferromagnetic and paramagnetic regions for each lattice is obtained and compared with other approximations in the literature.
The Optical Properties of AuAl2 and PtAl2
Authors: Chen Liang‐Yao , Lynch D. W.
Published: July 2007

The dielectric functions of AuAl2 and PtAl2 are measured in the 1.5 to 5.5 eV range. The spectra of reflectivity, absorption, energy loss function, and joint density of states are obtained and discussed in detail. The onsets of interband transitions at 2.125 and 2.834 eV for AuAl2 and PtAl2 respectively, are determined by least squares fitting to the absorption edges in the spectra of the joint density of states, which could be attributed to transitions between only the s–p bands for both materials. The remaining stronger absorption in the 2 to 5 eV region can be attributed to transitions between the s–p bands for AuAl2 but between both the s–p bands and the d and s–p bands for PtAl2.
Transverse Spatial Resolution of Thermo–Optical Hysteresis in CdS
Authors: Nguyen H. X. , Egorov V. D. , Harendt A. , Nazvanova E. V.
Published: July 2007

Transmission beam‐profile variation thermally induced in CdS crystals is investigated at room temperature using a cw‐Ar+‐laser and an electro‐optical modulator to produce pulses in the ms range. The formation and development of a plateau (or a ring) of the brightness in the transmitted beam are observed which strongly depends on the actual temperature of the sample. Calculations for a thin sample based on the two‐dimensional heat transport equation yield a good agreement with the experimental results.
Self‐Trapped Exciton Emission of SnSO4
Authors: Donker H. , Smit W. M. A. , Blasse G.
Published: July 2007

The luminescence properties of SnSO4 and BaSO4–Sn2+ are reported and discussed. At low temperatures both compounds show Sn2+ luminescence. In SnSO4 energy transfer to defect centres occurs at higher temperatures. A comparison is made with the luminescence of related systems.
Electrons in MIS Inversion and Accumulation Layers. Exchange and Correlation Effects within a Modified Thomas‐Fermi Theory
Authors: Übensee H. , Paasch G. , Bundfuss D. , Zöllner J.‐P.
Published: July 2007

For the calculation of the electronic structure of inversion and accumulation layers in MIS‐structures self‐consistent methods based on the density functional formalism are well developed. The numerical effort for such calculations is drastically reduced by a modified Thomas‐Fermi method developed in the last years. The method is a unique one for both, inversion and accumulation layers and well suited for modeling of MIS‐devices. It is proved that this method is very accurate. Several problems are solved first by using it, but till now always neglecting exchange and correlation effects. It is shown how one can include them as a part of the effective potential into the modified Thomas‐Fermi method by using a simple calculation scheme. A systematic investigation of the influence of exchange and correlation effects on the complete electronic sub‐band structure is presented for several III–V‐semiconductors at low temperature and for Si at both room and low temperature.
Thermal Parameters and Probability Density Functions of the Narrow Gap Semiconductor Bi2Te3 under Hydrostatic Pressure
Authors: Kullmann W. , Rauh H. , Geick R. , Steigenberger U. , Kuhs W. F.
Published: July 2007

The thermal parameters and the probability density functions of the atoms in the narrow gap semiconductor Bi2Te3 are investigated by neutron diffraction experiments under hydrostatic pressure. The results show rather complex intrasandwich bonding properties of the atoms in this sandwich structure. Especially Bi shows relatively large vibration amplitudes parallel to the trigonal axis in contradiction to former X‐ray studies. The experiments show evidence for healing effects of crystal distortions under hydrostatic pressure.
Short‐Range Order and Atomic Displacements in Ni–20 at% Cr Single Crystals
Authors: Schönfeld B. , Reinhard L. , Kostorz G. , Bührer W.
Published: July 2007

Ni–20 at% Cr single crystals aged at 741, 828, and 973 K for up to 480 h are investigated by elastic diffuse neutron scattering. The contributions due to short‐range order and atomic size effect are separated by a least‐squares fitting procedure. The short‐range order with diffuse intensity maxima at l 1/2 0 positions increases with decreasing ageing temperature. In comparison, the intensity due to atomic displacements is weak. For the three ageing temperatures investigated the effective pair potentials, determined from the Clapp‐Moss high temperature approximation as well as with an inverse Monte‐Carlo method, are very similar.
Stress‐Induced Dichroism of the Vibrational Lines and Phonon Sidebands of SH− Centres in CsBr
Authors: Otto J.
Published: July 2007

Paraelastic alignment of SH− centres in CsBr leads to a stress‐induced dichroism of the infrared absorption lines and their phonon sidebands. The principal values of the elastic dipole tensor are determined from quantitative infrared measurements under uniaxial stress. The centres turn out to be 〈100〉 oriented and have a disk‐shaped elastic dipole tensor. The stress‐alignment is used to determine the polarization of the phonon sidebands with respect to the molecular axis. Those irreducible representations, by which phonons and localized modes mainly couple to the intramolecular vibration, are derived with the help of group‐theoretical considerations. Selection rules for the appearance of particular phonons in the sidebands are discussed.
Thermoelectric Coefficients of a Limited 2D Gas in Quantizing Magnetic Field
Authors: Karyagin V. V. , Lyapilin I. I. , Dyakin V. V.
Published: July 2007

The dependence of Hall conductivity and diagonal component thermopower of a limited 2D gas in high magnetic field is calculated using Kubo's formula. The main attention is paid to the effect of sample edges which are responsible for the universal properties of two‐dimensional systems (represented by inversion layers) as e.g. unusual properties of the thermopower at low temperatures.
Study of the Polarized Light Absorption on Electrically Charged Thin Films of Copper Monocrystals by ECPA
Authors: Romanowski S.
Published: July 2007

The relative absorbed power of polarized light is calculated for copper thin films by means of Green's functions technique and ECPA approach. A mechanism of polarized light absorption on the electrically neutral as well as electrically charged films is analysed. It is concluded that the crystallographic structure and a volume charge parameter \documentclass{article}\pagestyle{empty}\begin{document}$ \bar n_s $\end{document} play the most important role in light absorption.
Impurity Binding Energies in Heterostructures. Two‐Band Model
Authors: Albuquerque E. L. , Costa W. B.
Published: July 2007

A transfer‐matrix treatment is presented for a one‐dimensional semiconductor heterostructure to discuss its electronic density of states. A two band formalism is considered with direct gap between the valence and conduction bands. The system is described by a tight‐binding Hamiltonian, with interactions between first neighbours. Using numerical data of AlxGa1−xAs–GaAs some interesting features in its electronic structure frequencies around 2 eV are shown.
Quantized Photoemission from Quantum Wells in Ultrathin Films of Wide‐Gap Semiconductors in a Tilted Magnetic Field
Authors: Majumdar C. , Maity A. B. , Chakravarti A. N.
Published: July 2007

An attempt is made to investigate the effects of a tilted quantizing magnetic field on the photoemission from quantum wells in ultrathin films of wide‐gap semiconductors, taking n‐type GaAs as an example. The photoemission exhibits an increasing step‐like variation with increasing photon energy and is also found to have oscillatory dependence on the magnetic field, its orientation, and the film thickness. Strikingly, the dependence of the emission on film thickness, for photon energies considerably lower than the electron affinity, shows that it gets quantized.
A Self‐Consistent Method for Evaluating the Effective Mass of Electrons in Metals
Authors: Mishra L. K. , Tripathy D. N.
Published: July 2007

A self‐consistent method for determining the effective mass, m*, of electrons in metals is presented. This is done through the evaluation of the electronic specific heat of metallic solids. The calculated values for m* agree remarkably well with the experimental data for sodium and potassium.
The Influence of Phonons on Dielectric Properties of Molecular Crystals
Authors: Tošić B. S. , Šetrajčić J. P. , Mirjanić D. Lj.
Published: July 2007

In molecular crystals whose inversion centrum does not coincide with that of the molecule, the Hamiltonian of exciton–phonon interaction is a bilinear form in exciton as well as in phonon operators. This leads to the hybridization of excitons and phonons into new excitations. The dielectric constant is analysed in the system of hybrid excitations. The frequency dependence of dielectric constant is analysed numerically for different values of wave vector. A comparison of dielectric constants of molecular crystals with and without phonons is made. It is shown that the presence of phonons changes the trend and shifts the singularity towards higher frequencies.
Exciton Propagation in the Field of a Driven Vibration
Authors: Marlow F. , Esser B.
Published: July 2007

The propagation of excitons in the presence of a strongly excited vibration is considered using the generalized master equation (GME) approach. A model is developed in which the amplitude of the vibration is subjected to stochastic variations modelling the fluctuations of the energy supply into the driven mode. The corresponding GME kernel is calculated and the parameters separating the regions of coherent and incoherent exciton propagation are discussed. It is shown that the presence of a non‐equilibrium vibration substantially modifies the transport as compared to the interaction with equilibrium phonons.
Energy Distribution of Trapping Centers in Vitreous GeSc3 as Obtained from Transit Time Measurements in the Temperature Range 60 to 300 K
Authors: Calas J. , Maksoud S. M. Abdel , Averous M.
Published: July 2007

The decreasing parts of transient currents associated with photocarriers created by convenient light on one side of the samples are investigated as a function of the temperature in the range 60 to 300 K. From the slope of the two corresponding parts, two parameters, α1 and α2 are deduced. From their behavior several trapping center energy distribution models are discussed. The trapping center density is found to obey the law Nt(E) = CE exp [−E/kT]2. The width of the trapping center energy distribution is about 10 meV and their density reaches 1021 cm−3.
Localization in a System of N Coupled Chains – Recursion Method. II. Explicit Calculation for Two Coupled Chains
Authors: Kasner M. , Weller W.
Published: July 2007

On the basis of a previously derived general expression the localization length of an electron moving along two weakly coupled chains is analytically calculated. In the weak scattering limit an explicit equation is derived for the asymptotic probability density of the five parameters characterizing two matrices ϱ and ϰ which determine the localization length. This equation is solved in the limit of “strong” coupling (∣t⟂∣ · l/(∣t∥∣ · sin k) ≫ 1, although ∣t⟂∣/∣t∥∣ ≪ 1). The localization length is lloc(2) = 1.7756l. It is shown that also for arbitrary number of chains and arbitrary dimension of the cross‐section the ratio of the strength of disorder and the chain coupling is the essential parameter.
Transport Properties of Quasi‐Two‐Dimensional Mo4O11 Crystals
Authors: Inoue M. , Ōhara S. , Horisaka S. , Koyano M. , Negishi H.
Published: July 2007

The electrical resistivity under hydrostatic pressure up to 1.0 GPa, Hall effect, magnetoresistance, and thermoelectric power are measured over the temperature range from 1.5 to 300 K for both, orthorhombic γ‐Mo4O11 and monoclinic η‐Mo4O11 crystals with quasi‐two‐dimensional structures. All these properties show anomalies associated with the charge density wave (CDW) transition; particularly the hydrostatic pressure enhances the CDW instabilities through the increased electron–phonon interaction and partial nesting of the Fermi surfaces. It is also found that both, electrons and holes contribute to the conduction processes, for which a qualitative discussion is made.
Piezoresistance in CdIn2S4
Authors: Nakanishi H. , Isomae M. , Endo S. , Irie T.
Published: July 2007

Piezoresistance of n‐type CdIn2S4 single crystals is measured for various directions of the crystal axis. The values at room temperature are isotropic but large, in particular for degenerate samples, compared with those for materials which have spherical energy surfaces. The large values of the piezoresistance of CdIn2S4 is found to be due to its long time relaxation. The values measured immediately after the application of the stress are small and also isotropic, consistent with the spherical band model and are π11 = −17.2 × 10−7, π12 = 3.24 × 10−7, and π44 = −17.2 × 10−7 cm2/N. The same results are obtained by measurements at low temperatures. The time relaxation of the piezoresistance may be due to trapping centers in the crystals the depth of which depends on the stress and this is confirmed experimentally by measurements of the thermally stimulated currents under various strengths of the stress.
The Luminescence of Palladium‐Doped Silicon
Authors: Thomas V. , Barrau J. , Brousseau M. , Kirouni K. , Couloumiers G.
Published: July 2007

It is observed for the first time, the photoluminescence of palladium in silicon; the zero‐phonon line, located at 1.0084 eV, is analysed under magnetic field. It shows similitude with the 0,811 eV line of a platinum defect, preceedingly reported. It is concluded that the palladium atom is in the substitutional lattice site with neutral charge state.
Multiphoton Excitation of the 520 nm Luminescence Band in MgO:Al
Authors: Dunphy K. , Duley W. W.
Published: July 2007

MgO:Al crystals illuminated with pulses from a XeCl laser luminescence strongly in broad bands centered at 520 and 736 nm. The 520 nm band appears to be due to luminescence from F centers and exhibits a strong non‐linear dependence on XeCl laser intensity. On log–log plots of luminescent intensity vs. pump intensity, straight line segments with I4 and I6 dependence are observed, suggesting that the 520 nm emission is pumped by energy transfer from bi and tri‐excitons. Saturation of this emission at high laser flux appears to be due to electron or hole trapping at vacancy defects.
Background Spectrum Enhancement in Channeling Radiation
Authors: Ohzawa S. , Nitta H. , Ohtsuki Y. H.
Published: July 2007

The background enhancement is calculated of channeling radiation of electrons in the quantum energy region, making use of the “local” incoherent bremsstrahlung probability. By simple treatment of the transverse state population, the numerical calculations agree well with experimental results.
Interatomic Potentials with Multi‐Body Interactions
Authors: Haliciogli T. , Pamuk H. O. , Erkoc S.
Published: July 2007

Various model potentials comprising two‐ and three‐body interactions are analyzed comparatively. In this study Tersoff (T), Tersoff‐Dodson (TD), Stillinger‐Weber (SW), and Pearson‐Takai‐Halicioglu‐Tiller (PTHT) potentials are included and their capabilities in reproducing various bulk, surface, and small cluster properties of silicon are investigated. For a proper comparison properties of small Si clusters are also calculated in this work using the PTHT function. Applicability and limitations of each potential are delineated and discussed. In general, structural properties calculated by these functions are found to be in better agreement with experiments than corresponding energy‐related properties.
On Lorentz Symmetries in Solids
Authors: Günther H.
Published: July 2007

Soliton properties of kinks on dislocations allow a definition of natural standards for the measurement of length and time which are inherently related to the lattice structure. If dynamical processes such as wave propagation and the motion of screw dislocations are expressed in terms of standards of such a kind, Lorentz symmetries associated with sound propagation become evident.
Center Manifold and Phase‐Ordering Dynamics for the Onset of Nonequilibrium Organizations
Authors: Fernández Ariel
Published: July 2007

A general derivation is provided for transients or induction periods for the onset of organized temporal dissipative structures. The treatment applies in the case where the phase‐space contraction occuring beyond criticality can be accounted for by the existence of a locally‐attractive and locally‐invariant center manifold. Especially the case is considered of a reactive open system which operates far from equilibrium and sustains a hard‐mode instability. This class of systems is studied in the context of fluctuation amplifications leading to phase‐ordering dynamics, as in the case of spinodal decompositions and nucleation phenomena in ferromagnets and superconductors.
A Simple Scheme for Studies of Surface Phonons of Covalent Semiconductors. II. Surface Phonons at Ideal and Relaxed Si(110) Surface
Authors: Lin Zijing , Wang Kelin
Published: July 2007

On the basis of some formulae for force constants calculation and using ten‐atomic‐layer slab, surface phonon dispersion curves along symmetry lines \documentclass{article}\pagestyle{empty}\begin{document}$ \overline \Gamma $\end{document}X, XS, SY and Y\documentclass{article}\pagestyle{empty}\begin{document}$ \overline \Gamma $\end{document} in two dimensional Brillouin zone are displayed. For relaxed surface an interesting surface mode is found, which cannot be understood in the elastic‐continuum approximation even for long wavelength limit.
A SIMS Analysis of Hydrogen Involved Reactions on InSb Surfaces
Authors: Wolf B. , Zehe A.
Published: July 2007

An analogy is established on physical grounds between an ion‐beam damaged cleavage plane and a ‘transient’ imperfection rich growing MBE‐layer. Chemical reactions between the former and hydrogen are analyzed using SIMS as an analytical tool. A high chemical reactivity of the ion‐beam damaged InSb (110) cleavage plane with hydrogen is found and explained by the assumption that the generated imperfections induce molecular dissociation into atomic hydrogen that easily reacts with the surface. Transient imperfections in growing MBE‐layers are suggested to play a similar role with respect to an increased reactivity found during MBE growth.
Dynamical Image Potential of a Point Charge Approaching a Metal Sphere
Authors: Thoai D. B. Tran , Zeitler E.
Published: July 2007

The dynamical image potential for a point charge approaching a metal sphere is calculated; it shows a pronounced dependence on the velocity and on the impact parameter of the moving charge. The moving of the point charge causes a change in the value of the image potential and renders it finite at the metal surface. For higher velocities the dynamical image potential tends to zero. However, for large distances between point charge and center of the sphere, the dynamical image potential hardly deviates from the classical image potential.
The Study of Energy Band Structure and Chemical Bonding in Yttrium Carbide, Yttrium and Strontium Dicarbides by the LMTO and Xα DV Method
Authors: Zhukov V. P. , Medvedeva N. I. , Novikov D. L. , Gubanov V. A.
Published: July 2007

The energy band structures of yttrium carbide, yttrium and strontium dicarbides are studied by the LMTO‐method. The cohesive energies and the total and partial pressures are calculated. The local electronic structure of yttrium dicarbide is studied by the Xα discrete variational method; the cluster Y6C2 which includes the group C and all the nearest neighbours of this group is used in this study. The results of this calculations are used to analyse the chemical bonding and some properties of the compounds. It is shown that the main contribution to the chemical bonding between C group and yttrium atoms is provided by the orbital of the eg‐local symmetry which belongs to the zone of metallic state. In the SrC2 this orbital is empty which explains the instability of its crystal lattice.
Energy Band Structure of Phenazine N Oxide and Phenazine N Dioxide. Candidate Materials for Organic Photovoltaic Devices
Authors: Kumar B. , Agarwal H.
Published: July 2007

A tight binding method with SCF AO's is employed to investigate the energy band structure of phenazine N oxide and phenazine N dioxide. The mode of charge transport along various crystallographic directions is examined in the light of existing theories of charge transport in organic semiconductors. The effect of heteroatoms on the mode of charge transport is discussed. Phenazine N Oxide and phenazine N dioxide are found to be candidate materials for organic photovoltaic devices.
Theory of the Superconductivity in Two Energy Band Systems
Authors: Ciobanu G. , Corcotoi I. , Fazakas A. B.
Published: July 2007

Functional integral techniques are utilized in the study of the superconductivity in a system of electrons containing both, a large band and a narrow‐one with large effective mass and an attractive coupling. After deducing the free energy functional, the equations for the order parameter and transition temperature are obtained and discussed. Finally the electronic specific heat and its jump at Tc are calculated.
Electronic Properties of Liquid TlGeTl2Se4 and TlSnTl2Se4 Systems
Authors: Ishikawa H. , Kameda Y. , Uemura O. , Satow T.
Published: July 2007

Measurements of the electrical conductivity, magnetic susceptibility, and thermoelectric power for the liquid TlGeTl2Se4 and TlSnTl2Se4 systems are made in wide temperature and composition ranges. It is observed that the conductivity for both the systems has a minimum near the composition of 66.7 mol% Tl. However, the results of magnetic susceptibility reveal that the metalnonmetal transition of the present two systems occurs not at 66.7 mol% Tl but at 80 mol% Tl. The temperature dependence of thermoelectric power in both the systems is complex particularly in the composition range between 60 and 80 mol% Tl. The experimental results of the present work are compared with the previous data of liquid telluride systems and are discussed in the light of current transport theories employed in liquid semiconductors.
Monte‐Carlo Study of Two‐Dimensional Antiferromagnets with Competing Anisotropies
Authors: Aplesnin S. S.
Published: July 2007

Phase diagrams of the ground state of the “easy plane” (EP) and “easy axis” (EA) antiferromagnet, the “oblique” phase, and the spin glass are calculated by the Monte‐Carlo method for an antiferromagnet with random distribution of competing anisotropies. The radial distribution function of spins in the plane and along “easy axes” and the correlation radius of EA and EP phases near the critical concentration of the transition are obtained. The phase diagram of the antiferromagnet, the “oblique” AF, and the paramagnet is estimated for the constant of anisotropy (EA) D∥ = J, (EP) D⟂ = −5J in the variables concentration and temperature.
Magnon Spectrum of Two‐Component Amorphous Ferromagnets
Authors: Vakarchuk I. A. , Margolych I. F.
Published: July 2007

The equations for the energy spectrum and damping of magnetic excitations caused by their scattering on structural fluctuations are obtained for a topologically disordered many‐component system of magnetic atoms. The acoustic and optic branches of the spectrum of the two‐component amorphous ferromagnet are calculated explicitely in the quasi‐crystalline approximation. Numerical calculations of the “energy‐momentum” dependence are made for an amorphous ferromagnet with liquid‐like structure.
The Microscopic Approach to the Description of the Optical Activity in Dielectric Crystals
Authors: Kotsur S. S. , Stasyuk I. V.
Published: July 2007

Various aspects of the microscopic description of the natural optical activity of ionic dielectric crystals are discussed. In the presented approach the electron and phonon excitations as well as their interactions are taken into account. The crystalline contributions to the effect and contributions from single ions or ionic groups are separated; they are studied in detail. Formalism of the Hubbard operators and two‐time Green functions method give the possibility to develop the theory of gyrotropy for a wide family of crystals having a complicated structure of the spectrum of active electron levels. Using the mechanical exciton conception the possibility to apply the crystal point symmetry is demonstrated.
Simple Numerical Method for the Estimation of Multiple Scattering in the Compton Effect
Authors: Das G. , Panda B. K. , Mahapatra D. P. , Padhi H. C.
Published: July 2007

A simple numerical estimation of multiple scattering in the Compton effect is made for six different samples at 60 keV γ‐ray energy by taking the experimental collimation into account and restricting the scattering in a plane. Photon paths are generated through geometrical methods and the scattered intensities up to triple scattering are estimated. Present results are in good agreement with earlier Monte Carlo results. The double scattered spectral distributions for different sample thicknesses show shape dependence on sample thickness.
Mechanism of Concentration Quenching of Gd3+ and Eu3+ Emission in Perovskite‐Like Aluminates
Authors: de Vries A. J. , van Vliet J. P. M. , Blasse G.
Published: July 2007

The mechanism of concentration quenching of the Gd3+ emission in (La, Gd)AlO3 and the Eu3+ emission in (Eu, Gd)AlO3 is reported and discussed. Nearest and next‐nearest neighbors are involved in the concentration quenching process. Nearest neighbor transfer occurs by exchange interaction. Even for next‐nearest neighbors this type of interaction seems to dominate. In GdAlO3 energy migration via the 6I level is reported. After excitation of the 6I level, the excitation energy migrates at 300 K about 1350 steps over the 6I level before nonradiative decay to the 6P level occurs. The energy migration in EuAlO3 at low temperatures can be described with a phonon‐assisted process.
Diffusion Mechanisms in B.C.C. Metals. Calculation of the Correlation Factor for Mixed Nearest and Next‐Nearest Neighbour Vacancy Jumps
Authors: Neumann G. , Tuijn C. , de Vries G. , Bakker H.
Published: July 2007

The correlation factor for mixed nearest and next‐nearest neighbour monovacancy jumps is calculated as a function of the jump frequency ratio. The diffusion is discussed in terms of a onedefect and several two‐defect models. A pronounced temperature dependence of the diffusion energy as well as a marked divacancy contribution at high temperatures can be excluded for the refractory metals. While the measured temperature functions of the isotope effect are compatible with mixed nearest and next‐nearest neighbour jumps, there is no proof for the existence of selfinterstitial contributions to the diffusion.
Vibrational Energy as a Function of Interatomic Distance in Rare‐Gas Solids. A Universal Relationship
Authors: Mohazzabi P. , Behroozi F.
Published: July 2007

A universal relationship between the reduced vibrational energies and average interatomic distances is derived for rare gas solids within the Lennard‐Jones (6‐12) interatomic potential model. This relationship is employed to obtain the zero‐point energies as well as the zero‐pressure heat capacities of the rare gas solids. The overall agreement with the existing data is very good.
Electronic Structure of CuCl, CuCl, and CuCl Clusters
Authors: Takeuchi T.
Published: July 2007

Electronic properties are obtained of CuCl, CuCl, and CuCl Clusters using the SCF Xα multiple‐scattered wave method. The calculation shows that the “cluster band gap energy” in the CuCl clusters is 3.6 eV, fortuitously close to the experimental direct band gap of 3.4 eV of CuCl. Cu0 in CuCl introduces a “donor” level at Vc − 0.3 eV. In CuCl the energy levels corresponding to the upper valence bands of CuCl almost overlap and the energy gap widens substantially. The energy level 3t2 with a hole is almost at the same level as that of 1t1 of other clusters. A significant Cu 3d–Cl p hybridization is introduced in CuCl.
Dynamic Potentials for Unstable Narrow Band Systems. Application to Intermediate Valence and Heavy Fermion Compounds
Authors: López‐Aguilar F. , Balle S. , Costa‐Quintana J.
Published: July 2007

The one‐body propagator for interacting systems with strongly correlated electrons is determined. The self‐energy functional is constructed from a GW approximation and a self‐consistent procedure is given for determining the electronic structure of the f systems (4f and 5f). The method is applied to the intermediate valence phase of SmS and to UAl2 which is a heavy fermion compound. The resulting electronic structure is compared with available experimental results. The obtained density of states presents reasonable agreement with these results.
Dynamical Effects on the Binding Energies of Core Excitons in Covalent and Polar Semiconductors
Authors: Fliyou M. , Khan M. A. , Ringeissen J.
Published: July 2007

The binding energies of core excitons in covalent and polar semiconductors are obtained by the polaron model taking into account the dynamical screening by the valence electrons. The binding energies of core excitons thus obtained are comparable to the available experimental values.
The Quantum Corrections to the Conductivity in Strong Spin–Orbit Coupling Semiconductors
Authors: Bilgildeeva T. Yu. , Polyanskaya T. A.
Published: July 2007

An anomalous positive magnetoresistance is observed in layers of GaAs and GaAs0.94Sb0.06 doped with Ge (p‐type conductivity) which is found to be governed by quantum effects. In the analysis the degeneracy of the valence band is considered and the contribution extracted corresponding to the total moment, I = 0, of the pair of particles. The wave function phase relaxation time is found. The origin of the magnetoresistance which cannot be described by the theoretical expression for I = 0 is discussed.
Condition for Superconductivity
Authors: Krüger E.
Published: July 2007

Commutation properties of the electronic Hamiltonian operator indicate that superconductivity is caused by a spin–phonon interaction rather than by the usually considered spin‐independent electron–phonon interaction. The proposed spin–phonon interaction is a new exchange effect which goes beyond the Born‐Oppenheimer approximation and in which the electron spins couple to phonons as a consequence of the Pauli principle, the crystal symmetry, and the conservation of spin angular momentum.
Nuclear Polarization of Atomic Hydrogen
Authors: Mertig M. , Luppov V. G. , Pilipenko Yu. K.
Published: July 2007

The spontaneous nuclear polarization of atomic hydrogen is calculated from the decay equations under different experimental conditions. In particular at high densities the influence of the three‐body processes described by the theory of Kagan, Vartanyants, and Shlyapnikov is investigated. To achieve a high nuclear polarization, optimum conditions are found in dependence on temperature and density.
A Recursion Method for Calculating Many‐Particle Green's Functions. Resonant Secondary Radiation and Excitation Spectra in the Exciton Region
Authors: Sherman A. V.
Published: July 2007

A procedure for calculating many‐particle Green's functions is suggested, which is based on the information supplied by the recursion method. The advantages of the procedure are the possibility of introducing a renormalized energy spectrum of the considered system, exactly definable within the recursion method, into calculations and their relative simplicity. As an illustration of the general method a calculation of a two‐particle Green's function, describing a resonant secondary radiation in the region of a three‐dimensional isolated band of excitons interacting mainly with optical phonons, is carried out. The range of parameters covers the cases of a weak exciton‐phonon coupling and a vibronic exciton. The main attention is paid to the relation of luminescence and scattering components. The obtained spectra are compared with experimental results.
Intrinsic Luminescence of CsCdBr3
Authors: Andraud C. , Pelle F. , Pilla O. , Blanzat B.
Published: July 2007

Electron–hole recombination luminescence is investigated in CsCdBr3 crystals. This luminescence consists mainly of a single band at 1.9 eV, assigned to a transition 3Σ → 1Σ. The comparison between this emission and emission observed under the 4 eV excitation confirms that the latter is due to Br centers.
Angle‐Resolved X‐Ray Emission Spectra (ARXES) of Carbon in Potassium Graphite C8K
Authors: Šimůnek A. , Wiech G.
Published: July 2007

Measurements are presented of angle‐resolved carbon K X‐ray emission (ARXES) bands for first‐stage intercalated potassium graphite C8K and pure graphite. The corresponding p‐like carbon partial densities of states are calculated by the ab‐initio pseudopotential method. It is found that in the electronic structure of graphite potassium creates new carbon pz‐like valence states near the Fermi edge. The good agreement between the measurements and the calculations makes possible a detailed analysis and interpretation of the experimental results. It appears that the terms ionicity, charge transfer, degree of hybridization, and electron occupancy are non‐adequate for the description of the potassium–carbon bond. As compared to available UPS and XPS results for C8K new features in the ARXES spectra provide complementary data for the understanding of the nature of the potassium–carbon bond.
Positron Annihilation in BaF2 and SrF2
Authors: Shishkin A. V. , Linderoth S. , Svirida S. V.
Published: July 2007

Positron life‐time measurements are performed on the ionic crystals BaF2 and SrF2 in the temperature range 80 to 550 K. The results are discussed in terms of positron interactions with defects created by decay of excitons produced in the path of the positron.
Third‐Order Elastic Constants for Alkaline Earth Oxides and Fluorides
Authors: Hans D.
Published: July 2007

The interionic potential model recently developed by taking account of the composite effect of short range repulsive and dispersion forces along with three body interactions is applied to investigate the elastic behaviour of alkaline earth oxides and fluorides. Values of third‐order elastic constants and pressure derivatives of second‐order elastic constants are obtained for MgO, CaO, SrO, BaO, CaF2, SrF2, and BaF2 crystals. The calculated values are found to present close agreement with experimental data.
On the Evaluation of Entropy and Thermodynamic Properties of 1:1 Type of Molten Salts through the Generalized Debye Inverse Screening Length
Authors: Rao R. V. Gopala , Satpathy A.
Published: July 2007

Blum's generalized inverse screening length parameter Γ is solved numerically for 1:1 type of fused salts. Using these Γ parameters for the salts, a method is evolved for the evaluation of the entropies of fused salts by treating the different components of the salts as seperate mass entities along with the concept that the total entropy is a sum of the contributions from neutral hardspheres and that due to charging process. The entropies so calculated are found to be in good agreement with experiment. Further from the parameters Γ, the excess thermodynamic properties and the contact values of the partial radial distribution functions are calculated. A simple method is given in the evaluation of the parameter Γ which is found to yield almost similar values as that given by Blum.
Acoustic Mode Vibrational Anharmonicity in the Intermediate Valent Compound Samarium Sulfide
Authors: Gupta B. R. K.
Published: July 2007

Anharmonic elastic properties of SmS in its semiconducting form are analysed in terms of third order elastic constants and pressure derivatives of second order elastic constants calculated using an interionic force model. This potential model consists of long‐range Coulomb and three‐body interactions and short‐range overlap repulsion, effective up to second neighbour ions. Repulsive parameters (b, ϱij) are determined using the equation of equilibrium condition and overlap integrals. The results reported are compared with experimental values and fairly good agreement is obtained.
Phonon Localization in Disordered Systems. Application of the Potential‐Well Analogy Method
Authors: Böttger H. , Theuerkauf M.
Published: July 2007

Using a self‐consistent equation for the diffusion coefficient of vibrational excitations, the potentialwell analogy (PWA) method for studying localization of vibrational excitations in disordered systems is formulated in analogy to the electron problem. Results obtained by the PWA‐method for vibrational systems with mass disorder are in good agreement with numerical data.
High‐Energy Tails in the Total Energy Distribution of Field Emitted Electrons from Tungsten
Authors: Bakhtizin R. Z. , Yumaguzin Yu. M.
Published: July 2007

Methods of evaluation are considered and results presented of the study of the total energy distribution of electrons field‐emitted from tungsten at emission current densities of up to 105 A/cm2. The high‐energy tails in the energy distribution are examined and their dependence on electric field strength, emission current density, work function, and residual gas pressures in the vacuum chamber.
Statistical Operator for Thin Solid Films
Authors: Onyszkiewicz Z.
Published: July 2007

Using the Schrödinger variational principle for average energy in the case of a system interacting weakly with environment and for a given entropy, the equilibrium statistical operator is obtained. In the case when the interaction with the environment can be neglected this statistical operator is identical with that of the canonical Gibbs distribution. This statistical operator may be useful in describing thermodynamical properties of thin solid films and similar systems.