bluuebunny/crossref_metadata_2025_split huggingface dataset:
Time Dependence Calculation of the Breakdown Rate for Electrical Breakdowns in Vitreous Solids
Authors: Danziger M. , Bernhardt A. 
Published: July 2007

AbstractThe anomalous behaviour of different physical quantities in vitreous solids contrary to the behaviour in crystalline solids, mainly the dielectric behaviour, can be described by the effect of a system of additional low‐energy excitations in these solids. This also applies to the amorphous SiO2‐layers in MOS structures. Therefore, a model of breakdown behaviour is developed basing on the assumption that there are fluctuations of the correlated local electrical fields and low‐energy excitations present in these layers. On this basis, the time dependence of breakdown rate is determined. By these calculations, a good correspondence of the experimentally and theoretically determined characteristics is obtained. In these calculations, it should be paid attention to the fact, that the properties of the vitreous solids and the character of the internal interaction change by breakdowns already occured.
Investigations of the Dynamic Properties of the Liquid Phase of Glassy CaAl Alloys
Authors: Rao R. V. Gopala , Venkatesh R. 
Published: July 2007

AbstractThe Ashcroft pseudopotential is used in the evaluation of the partial potentials in the case of Ca60Al40 glass melts. These potentials are found to give minima at the principal peaks of the partial radial distribution functions. The partial structure factors are evaluated and compared with literature values. From the partial potentials and partial structure factors the corresponding effective potential and total structure factor are evaluated. The effective radial distribution function is calculated from the total structure factor. These effective quantities are used in the evaluation of phonon frequencies through Takeno and Goda's equations. It is found as predicted by Bhatia and Singh that the structure factor maximum is around the first minimum of the longitudinal phonon frequency. From the slopes of the phonon frequencies the elastic constants are evaluated. The elastic constants are also evaluated from Schofield's I1 and I2 integrals. Further from Kirkwood‐Buff's equation using the partial direct correlation functions in the long‐wave limit the compressibility is evaluated and the elastic constant C11 is calculated. There is a good interconsistency in the computed values of the elastic constants.
Real Space Approach to the Linear Phason Strain
Authors: Cheng Y. F. , Pan G. Z. , Li F. H. 
Published: July 2007

AbstractIt is illustrated that the quasilattice distortion originated from a linear phason strain can be treated as the projection strip rotation. A fictitious strip is obtained by rotating the original strip with the phason matrix. The distorted reciprocal quasilattice can be obtained by projecting the undistorted high dimensional reciprocal lattice onto a newly defined physical space parallel to the fictitious strip with a new projection matrix. The transformation from icosahedral quasilattice to body center cubic lattice caused by strip rotation or linear phason strain is demonstrated with the change of tiling.
Ordering of Protons at the Phase Transition in Superionic Crystals of CsHSO4 Type
Authors: Dzhavadov N. A. , Rustamov K. A. 
Published: July 2007

AbstractThe phase transition (PT) D → C in CsH(D)SO4‐type crystals by one wave vector of the star {k13} (X‐point of the Brillouin zone (BZ)) and of the wave vector {k14 = 0} (Γ‐point of BZ) is considered. A symmetry analysis of proton ordering at the PT is performed with account of proton–phonon interaction. The method of concentration waves is applied. The expression for the average occupation number of proton positions is obtained. The experimentally observable ordering of protons and the dynamics of SO4 tetrahedra at the PT is described. The entropy jump at the PT is calculated. The obtained theoretical results are in good agreement with experiment.
Perturbation Method of Computation of Entropies of Vaporization of Fused Salts
Authors: Rao R. V. Gopala , Venkatesh R. 
Published: July 2007

AbstractBased on the assumption that thermodynamic and structural quantities of salts can be divided into contributions from neutral hard spheres and from Coulomb interactions an expression for the entropy of vaporization of fused salts is formulated. The theoretical results of the entropy of vaporization at the melting point are found to be in good agreement with experiment except in the case of lithium salts.
Acousto‐Helicon Interaction in Semiconducting Superlattices
Authors: Misra K. D. , Pandey M. K. 
Published: July 2007

AbstractAcousto‐helicon interaction in semiconductor superlattices is examined in the presence of an applied magnetostatic field. Assuming that the collective mode propagates along the growth axis of the superlattice, using the self‐consistent‐field and hydrodynamic equations, the dispersion relation of the acousto‐helicon mode for the finite as well as infinite periodic systems having piezoelectric and deformation potential coupling is obtained. The effect of changes in alternating layer thickness on the branch‐folding effect of the acousto‐helicon mode is examined. The modifications in frequency due to phonon–helicon interaction in the strong coupling limit are also obtained.
Optical and Structural Properties of Amorphous Silicon Obtained by Low Pressure Chemical Vapour Deposition
Authors: Amato G. , Fizzotti F. , Manfredotti C. , Menna P. , Nobile G. , Spagnolo R. 
Published: July 2007

AbstractOptoelectronic and structural properties of thin, hydrogenated amorphous silicon samples grown by thermal decomposition of disilane in different positions along a low pressure chemical vapour deposition reactor are investigated by means of infrared spectroscopy, Raman scattering, and photothermal deflection spectroscopy. Correlations between the character and the hydrogen content versus density of states and between the hydrogen bonding configuration versus transverse optical/acoustic phonon modes are found. The purely thermal excitation of gas molecules gives rise to an amorphous material with a rather low density of states. Samples grown at different positions inside the reactor show different hydrogen concentration and bonding configuration, bond angle deviation, Urbach tail slope, and density of states. The most important parameters governing the LPCVD of a‐Si: H are discussed.
Redistribution of Resonance Bonds and Dynamics of Two‐Center Self‐Trapping in Rare‐Gas Crystals
Authors: Fugol I. Ya. , Ratner A. M. , Tarasova E. I. 
Published: July 2007

AbstractIt is shown that in the process of the exciton two‐center self‐trapping the resonance bonds generating a free exciton state are redistributed so that the total resonance contribution to the energy increases. 50% of the electronic excitation is concentrated inside a two‐center quasimolecule close to the self‐trapping threshold. The rest is distributed in neighbouring atoms, resulting in a generation of weaker extrinsic bonds along with the intermolecular resonance one. The attendant deformation of the molecular term produces a decrease in the self‐trapping barrier and an appreciable increase in its transparency.
Compton Profile Anisotropy Studies in Hexagonal Semiconductors
Authors: Panda B. K. 
Published: July 2007

AbstractThe Compton profile anisotropies are calculated by empirical pseudopotential method for different semiconductors with wurtzite structure. The anisotropies are reduced with increasing ionicity in consistency with the observations in cubic semiconductors. The comparison of the autocorrelation functions of the cubic and hexagonal forms show that the differences in the valence wave functions are quite large for II–VI semiconductors.
The Warm‐Electron Distribution Function in the Energy Noncollision Plasma in Submicron Semiconductor Layers
Authors: Gurevich Yu. G. , Logvinov G. N. 
Published: July 2007

AbstractThe warm‐electron distribution function is obtained from the kinetic equation in semiconductor submicron layers under the assumption that the surface energy relaxation is considerably higher than the bulk energy relaxation rate and the frequency of the electron–electron interactions as well. A divergence in the point ϵ = 0 is shown (where ϵ is the electron energy) if the surface scatterers are acoustic phonons. The reason of this anomaly is that small energy electrons have infinitly high partial electric conductivity while their energy relaxation rate turns to zero. In order to obtain the correct results it is necessary to take into account the e–e interaction between small and high energy electrons. This interaction leads to energy pumping from one carrier group to another and then to the external thermostats.
Thermal Conductivity and Electrical Resistivity of Intermetallic RECu2 Compounds (RE  Lu, Ho, Er, Dy)
Authors: Bartkowski K. , Gratz E. , Rafałsowicz J. , Tyc T. 
Published: July 2007

AbstractThe temperature dependence of the thermal conductivity, λ (T), and the electrical resistivity, ϱ (T), is measured for the heavy rare‐earth RECu2 (RE  Lu, Er, Ho, Dy) compounds in the temperature region from 2 up to about 30 K. Anomalies observed in both λ (T) and ϱ (T) curves correspond to magnetic transitions as are known from susceptibility measurements. Assuming the validity of the Wiedemann‐Franz law the electronic (λe) and the lattice (λg) contributions of the total thermal conductivity are separated. The anomalies caused by spin‐dependent scattering processes, due to the change in the arrangement of magnetic moments, are much more pronounced in λe, but they are also visible in the temperature dependence of the Lorenz number L (T).
Interaction of the Superconducting Domains Induced by External Electric Field with Electromagnetic Waves
Authors: Shapiro B. Ya. 
Published: July 2007

AbstractThe behavior of a superconductor in time‐independent electric field perpendicular to the surface and in the external electromagnetic wave is theoretically investigated. A new type of the resonance interaction between superconducting domains localized along the magnetic field (if the superconducting phase transition takes place in the external magnetic field perpendicular to the surface) and electromagnetic waves is predicted. The surface impedance of the superconductor with domains is calculated. It is shown that the real part of the impedance has a saturation if the skin length equals the domain size.
The Role of Polar Additives on Charge Transport in Molecularly Doped Polymers
Authors: Borsenberger P. M. , Bässler H. 
Published: July 2007

AbstractThe role of polar additives, o, m, and p‐dinitrobenzene, on hole transport in 1,1‐bis(di‐4‐tolylamino‐phenyl)cyclohexane doped polycarbonate is investigated. The results are described by a model based on hopping through a manifold of states with superimposed energetic and positional disorder that remains static on the time scale of a hopping event. The results lead to the conclusion that the main effect of the polar additives is the enhancement of disorder, both energetic and positional, the dipolar reorientation being relatively unimportant.
Calculation of the Spin System Correlation Functions in the Frames of the Functional Integration Method. II. The Heisenberg Model
Authors: Vakarchuk I. A. , Matskevych P. A. 
Published: July 2007

AbstractNew equations for the correlation functions obtained in the frames of the functional integration method are applied to investigate the magnetic ordering in the Heisenberg isotropic quantum model. The Curie temperature of this model is calculated from the pole of the longitudinal Green function. Good agreement with known data is obtained in the crystalline case. It is shown that the magnetic order can be destroyed by the amorphization of the crystal.
Wave Vector Dependent Two‐Photon Interband Transitions between Landau Levels
Authors: de Salvo E. , Girlanda R. 
Published: July 2007

AbstractA perturbative calculation, out of the electric dipole approximation (EDA), of the absorption threshold of the two‐photon interband transitions between the Landau levels of direct gap semiconductors without inversion symmetry is presented. This approach allows to explain with good approximation the absorption peaks with selection rule Δμ = 0, also in a simple two‐band model. As an application, the case of cuprous chloride in a 5T external static magnetic field is considered.
Relaxation and Recombination of Photoexcited Carriers in a‐Si: H Calculated by Monte‐Carlo Simulations
Authors: Gutschker O. , Bindemann R. 
Published: July 2007

AbstractThe relaxation and recombination of photoexcited carriers in a‐Si: H is simulated by means of Monte‐Carlo calculations taking into account radiative and nonradiative recombination processes. The results are in good agreement with experimental data. The measured maximum in the luminescence quantum efficiency at a temperature of T ≈ 50 K can be quantitatively explained by nonradiative Auger recombination. The minimum in the negative decay exponent at T ≈ 30 K obtained in long‐time luminescence decay experiments is explained by a shift of the peak position of the lifetime spectrum of the nonradiatively recombining carriers to longer times.
Polarization Dependences of Two‐Photon Absorption in Narrow‐Gap InSb and HgCdTe Type Semiconductors
Authors: Ismailov T. G. , Bagirov M. A. 
Published: July 2007

AbstractTwo‐photon absorption of light in narrow‐gap semiconductors of InSb and HgCdTe type is considered in the framework of the two‐band Kane model. The analytical expressions for the TPA coefficient in dependence on the energies of pumped radiation and band gap of semiconductor is obtained. All the possible nonequivalent geometries of experiment are considered. In the calculations the excitonic effects are neglected. The polarization dependences are discussed and the comparison with experiment is carried out.
Dynamical Correlations and Phonon Dispersion in a Liquid Binary Alloy
Authors: Bhandari D. , Pratap A. , Saxena N. S. , Saksena M. P. 
Published: July 2007

AbstractTheory of Brownian motion of particles in static harmonic well approximation is applied to study the vibrational dynamics of liquid NaxCs1−x (x = 0.5; 0.85) alloys. Dynamical variables like velocity autocorrelation function, power spectrum, and the mean square displacement are computed. The effective interatomic potential of the alloy used is obtained through the pair‐potentials of individual components. The co‐operative motion of atoms is described in terms of spectral functions of longitudinal current–current correlation functions which are obtained through the mean square displacement. These spectral functions of longitudinal current–current correlations are then used to get phonon dispersion in the alloy. The results are compared with the recently reported quasi‐dispersion results of neutron inelastic scattering (NIS) experiments. Good qualitative agreement is observed.
Thermal and Transport Properties of Liquid Alkali Metals Using a Soft‐Sphere Reference System
Authors: Khanna K. N. , Quayoum A. 
Published: July 2007

AbstractThe density dependent structural properties of liquid alkali metals derived in earlier work are used to calculate thermal and transport properties. The results show improvement over those obtained with the hard‐sphere system. The effect of softness in the pair potential is discussed.
Exact Phonon Green's Functions of One‐Dimensional Quasiperiodic Lattices
Authors: Zhong J. X. , Yan J. R. , You J. Q. 
Published: July 2007

AbstractA real‐space renormalization‐group (RSRG) scheme is presented for calculating the local phonon Green's functions of one‐dimensional Fibonacci lattices. In this scheme, the phonon diagonal, off‐diagonal, and combined models can be treated in a unified way.
Phonons in F.C.C. Iron
Authors: Singh D. , Rathore R. P. S. 
Published: July 2007

AbstractA model is reported which accounts for the attractive and repulsive ionic forces in terms of a more realistic and less parametric generalized exponential potential, which incorporates the exchange and correlation effects due to electrons in a simple and effective manner. The electronic contribution is computed by using the Ashcroft model potential combined with the modified dielectric screening due to Shaw. The phonon dispersion in f.c.c. iron shows good agreement with experimental findings.
Mixed Crystal Electronic Structure of MS3−xSex
Authors: Lazo E. 
Published: July 2007

AbstractThe electronic structure of a quasi‐one‐dimensional disordered system represented by mixed‐crystal compounds MS3−xSex, with M  Zr, Hf is investigated. These compounds are made up of weakly coupled pairs of chains, coupled through van der Waals forces. A single chain is considered assumed to be completely independent of the neighboring chains. The problem is formulated in terms of the Green function formalism, using a tight‐binding Hamiltonian with interaction to nearest neighbors with diagonal and off‐diagonal disorder. The infinite set of equations is renormalized by means of the matrix inversion method, and then the average Green functions are evaluated using the transfer function method which is based on a work by Schmidt. Numerical results of the global density of states are provided for the strictly one‐dimensional model of a mixed crystal, and for the quasi‐one‐dimensional model as function of the concentration x.
On the Quantized States in a Cylindrical Quantum Box of a Narrow‐Gap Semiconductor in Crossed Electric and Magnetic Fields
Authors: Das N. R. , Chakravarti A. N. 
Published: July 2007

AbstractThe energy eigenvalues of the electrons in a quantum box of a simple Kane‐type narrow‐gap semiconductor having cylindrical symmetry are investigated through a perturbation technique in the presence of crossed electric and magnetic fields. The effects of changing the dimensions of the box as also of changing the fields on the lowest quantized state are discussed using the relations obtained, taking n‐InSb as a typical example of such a semiconductor.
Studies of the Autocorrelation Functions in Aluminium
Authors: Panda B. K. 
Published: July 2007

AbstractThe long‐slit angular correlation of positron annihilation radiations are measured in the polycrystalline Al sample. The theoretical autocorrelation function (AF) calculated with the band electron and positron wave functions agrees very well with the experimental AF. The AF derived with the positron–electron product wave function is not suitable to explain the oscillations in the experimental AF.
Semiempirical Crystal Field Calculations for fN‐Systems. III. Crystal Field Splitting and Jahn‐Teller Effect in Cubic (NEt4)4U(NCS)8 Crystal
Authors: Mironov V. S. , Rosov S. P. 
Published: July 2007

AbstractThe crystal field spectrum of 5f2‐configuration of cubic U(NCS) anion in (NEt4)4U(NCS)8 is calculated by using the new semiempirical many‐electron method, developed in previous papers. The Γ5‐triplet is found to be the ground state of U(NCS) anion. The T ⊗ (eg + t + t) Jahn‐Teller problem is studied quantitatively for U(NCS) anion. It is shown that tetragonal Jahn‐Teller minima in the adiabatic potential of U(NCS) are much deeper (EJT = 78 cm−1) than the trigonal ones. The temperature dependence of the effective magnetic moment of the U4+ ion in (NEt4)4U(NCS)8 is reproduced very well in the frame of modified Jahn‐Teller model suggesting simultaneous existence in (NEt4)4U(NCS)8 both, tetragonally compressed and elongated U(NCS) anions arising due to Jahn‐Teller distortions and influence of cation vacancies, respectively.
Magnetostatic Waves in a Thin Uniaxial Platelet with Stripe Domains Magnetized along the Easy Axis
Authors: Kostenko V. I. , Sigal M. A. 
Published: July 2007

AbstractThe theory of magnetostatic waves propagating along the domains is introduced. It is shown that only uniform‐surface and volume‐uniform waves may exist. In the case kx → 0 we obtain two FMR frequencies: the low‐frequency mode ωlf as a limiting case of volume‐uniform waves and the high‐frequency mode ωhf of uniform‐surface waves. Comparison with the theory of uniform resonance and experiment on barium ferrite platelets is carried out.
Curie Temperatures in Mixed Ferromagnetic Systems with Different Types of Interactions
Authors: Zheng Siming 
Published: July 2007

AbstractThe Curie temperature, TC, of a ferromagnetic system with different spins and different type interactions is considered – spin ½ with Ising‐like interaction JI, spin 1 with Heisenberg‐like interaction JH, and Ising‐like interaction JIH between unlike spin pair. The TC vs. p (concentration of Ising‐like spin) curves are drawn under different JH/JI and JIH/JI for square and s.c. lattices. The condition of the convex behaviour of the curves is discussed.
EPR of Triclinic Fe Centers in KCl and RbCl
Authors: Callens F. , Maes F. , Matthys P. , Moens P. , Boesman E. 
Published: July 2007

AbstractA new paramagnetic Fe center with triclinic g‐tensor symmetry is reported. This type of defect is detected in both KCl and RbCl single crystals doped with iron, after they were quenched, irradiated at 77 K, and annealed at 160 K. The g‐tensors exhibit a very large g‐tensor anisotropy with g∥ ≈ 10 and g⟂ ≈ 5 in an axial approximation. Several models for this type of paramagnetic defect are discussed.
Excitons in BeO
Authors: Feldbach E. , Laasch W. , Varding D. , Zimmerer G. 
Published: July 2007

AbstractBeO crystals in both orientations (⟂ c and ∥ c) are studied under polarized synchrotron radiation. The long‐wave shift (43 meV) and the splitting (29 meV) of the main excitonic reflection peak in the case of E ∥ c are detected at 10 K. The correspondence of the observed transitions to the selection rules is discussed. The excitation spectra of the luminescence band of self‐trapped excitons are measured in the excitonic region. It is found that in the case of E ∥ c the excitation spectrum is characteristic of localized excitations. Possible evidence of the coexistence of large‐ and small‐radius (self‐trapped) exciton states is discussed.
Comparative Study of the Polarized XANES at the Cu K Edge of Bi2Sr2Ca1Cu2O8, Bi2Sr2Ca2Cu3O10, and Y1Ba2Cu3O7 Thin Films
Authors: Poumellec B. , Cortes R. , Labdi S. , Raffy H. , Roas B. , Fretigny C. 
Published: July 2007

AbstractThe angular dependence of the Cu K edge in films of BiSrCaCuO (2212, 2223) and YBa2Cu3O7 are measured for both orientations (e ⟂ c, e ∥ c). A similar XANES is observed (but magnitudes and energy positions change slightly) although the compounds are quite different except the first shell. Specifically, anisotropy spectra are very close. After connecting the same XANES features to the local arrangement, it is found that the pyramidal site in 2223 is flattened compared to the one in 2212 by only (0.003 ± 0.001) nm. In addition, it is deduced that the electron density in the copper sphere is similar in all compounds whatever the site (CuII). Then, taken into consideration that pyramidal sites in 2212 and in YBaCuO are rather close to each other, an estimate is deduced of the absorption edge arising from the chain site following the two polarization directions. The major resonance on these spectra yields 0.009 nm of distance anisotropy, a result in very good agreement with the XRD data. In the course of the discussion, it is explained why the anisotropy spectrum is smaller in YBaCuO than in 2212. Lastly, the difference spectrum published by Tranquada et al. on oxygen reduction of YBa2Cu3Ox is revisited. It is deduced that the electron density increases in the copper sphere as soon as x = 7 when the copper atoms in the chains change from four to three oxygen coordination. Then, when the local structure evolves from three to two oxygen coordination, the local valence on the copper sphere does not change anymore but on the bridging oxygen.