bluuebunny/crossref_metadata_2025 huggingface dataset:
Frequency Dependence of Warm Carrier Conductivity in Germanium
Authors: Dienys V. , Kancleris Ž. , Martūnas Z.
Published: July 2007

The frequency dependence of the warm carrier conductivity in n‐ and p‐Ge is measured in the frequency range 0.4 to 150 GHz. The experiments are carried out at 80 and 273 K. A phenomenological theory of the warm carrier conductivity for the semiconductor having two degenerate bands at k = 0 is developed. By applying this theory to the experimental data it is shown that in p‐Ge at 80 K the warm carrier conductivity relaxation process at microwave frequencies is strongly influenced by the hole interband repopulation effect. The values of the energy relaxation time τϵ are evaluated for both materials at both temperatures. It is established that τϵ in p‐Ge is isotropic and the anisotropy of the conductivity relaxation time observed is caused by the warping of the constant‐energy surfaces of heavy holes.
OD Stretching Vibrations in Deuterated Potassium Ferrocyanide Trihydrate
Authors: Savatinova I. , Chisler E. V. , Rohleder J. , Jakubovski B.
Published: July 2007

Deuterated and isotopically dilute single crystals of K4Fe(CN)6. 3 D2O are investigated using low temperature Raman spectra. The work involves an attempt to asses the origin of the numerious OD modes using the isotope dilution technique. An estimate of the magnitude of the intra‐ and intermolecular interactions in formation of OD stretchings is made from available experimental data. Three crystallographically nonequivalent water molecules with different extent of vibrational distortion are established in the ferroelectric phase of the crystal.
On the Theory of Plasmon Satellite Structures in the Photoelectron Spectra of Non‐Metallic Solids I. Soluble Model
Authors: Becrstedt F.
Published: July 2007

Intrinsic and extrinsic plasmon effects on the photoelectron spectra of non‐metals are studied simultaneously. The spectral behaviour of the photoionization cross‐section is represented by a convolution integral of the spectral functions of the outgoing electron and the excited core hole. Considering the relaxation of the valence electron gas the spectral functions are calculated in the frame of a linear dielectric formalism. It is shown, that the relaxation of the valence electrons in the presence of the electron depends strongly on the kinetic energy. For large kinetic energies (XPS) the electron effects are small and the photoelectron spectrum is nearly represented by the hole spectral function. For small kinetic energies (UPS) neither the hole mechanism nor the electron one dominates and the plasmon satellites are due to both, intrinsic and extrinsic effects.
Charge Order in the Spinless Fermion Model
Authors: Lorenz B.
Published: July 2007

The spinless fermion model which takes into account the transfer and the nearest neighbour Coulomb interaction of fermions is treated in a two site cluster approximation. For the linear chain the results are compared with the exact solution for the ground state and with other approximations. In two‐and three‐dimensional lattices the order–disorder transition is considered in dependence on the transfer energy and the phase diagram is calculated. The validity of the theory for the description of the order–disorder transition in superionic conductors is discussed.
Optical Spectra of EuP5O14 between 77 and 583 K
Authors: Sekita M. , Minami F. , Okamoto E. , Masui H.
Published: July 2007

The polarized absorption and fluorescence spectra of Eu3+ in a single crystal of EuP5O14 are studied from 77 to 583 K. The energy levels and eigenvectors are presented for septet and quintet states of Eu3+ in an intermediate coupling scheme. Values of E1 = 6420.08, E2 = 26.12, E3 = 765.93, and ζ = 1290.13 cm−1 are found to give the best overall agreement between the observed and calculated energy levels. The change in spectral structure is observed in the 7F0 to 5D2 absorption spectra at temperatures between 297 and 583 K. This change is attributed to the structural phase transition of the crystal by observing the temperature dependence of degree of polarization and of the oscillator strength of the lines.
The Effective Density of States in the Conduction and Valence Bands for Arbitrary Band Structures
Authors: Van Vliet K. M. , Marshak A. H.
Published: July 2007

A formula is proposed for the effective density of states for materials with an arbitrary band structure. This effective density is chosen such that for nondegenerate statistics the conventional form n = Nee−z where z = (Ec ndash; Ef)/kT remains valid. The result is applied for some simple cases, including the Kane band for InSb. For parabolic bands, Nc → Nc. Results for holes are analogous.
Dielectric Function of Free Carriers with a Nonparabolic Dispersion Relation
Authors: Tsipivka Yu. I. , Neumann H. , Unger K.
Published: July 2007

General expressions for the Bloch density matrix, the Dirac density matrix, and the generalized density matrix for free carriers with a spherical but nonparabolic dispersion relation are derived in arbitrary order of perturbation theory. The linear response function of a free carrier gas with Kane's dispersion law is considered in detail. The deviations from the case of parabolic bands are discussed.
Theory of Intensity Dependence of Refractive Index
Authors: Moss T. S.
Published: July 2007

The variation of refractive index with intensity of irradiation is explained on the basis of a three stage process, viz. (i) photogeneration of free carriers, (ii) shift of the absorption edge by a dynamic Burstein‐Moss effect, and (iii) reduction in total absorption and hence of refractive index as a result of the inter‐relation of the optical constants. The theory gives the correct sign, magnitude, and wavelength dependence of the effect.
Decimation and Anderson Localization
Authors: Lambert C. J. , Weaire D.
Published: July 2007

A numerical decimation procedure is applied to a Hamiltonian with diagonal disorder for a square lattice in two dimensions. The renormalized interactions are found to scale towards weak coupling (indicative of localized states) for large disorder and towards strong coupling for low disorder, consistent with previous estimates of an Anderson transition at W ≈︁ 6.
Environment Effects on Electronic Density of States in Narrow‐Band Alloys Using the Cluster‐Bethe‐Lattice Method
Authors: Maiti P. B. , Moitra R. K.
Published: July 2007

The cluster‐Bethe‐lattice method is used to study the environment effects on the electronic density of states in narrow‐band alloys. The intra‐atomic Coulomb interaction, U, is treated in the statistical (0, 1) approximation and the coherent potential approximation is used for the alloy disorder. These approximations lead us to consider the alloy system as a quaternary alloy. A general approach for an n‐component alloy in the Bethe lattice is presented using Yonezawa's approach. It is shown that the result obtained gives the result of Yonezawa in the limit z → ∞, z being the coordination number of the alloy system. The quaternary alloy is then treated as a special case of an n‐component alloy. A cluster consisting of (Z + 1) atoms is chosen to study environment effects. A comparison is made between the electronic density of states for the Bethe lattice and that for the cluster‐Bethe lattice. Interesting features in the electronic density of states are observed due to clustering effects.
Hydrostatic Pressure and Kinetic Phenomena in NaNbO3 Single Crystals
Authors: Pisarski M.
Published: July 2007

Electrical conductivity σ, electric permeability Σ, and the Seebeck coefficient α in the 20°C < T < < 500 °C temperature range and in the 0 < p < 1 GPa pressure range are investigated. A strong linear dependence of these quantities on pressure for T < 360 °C and a shifting of the P ⇌ R phase transition temperature at a rate of dTa/dp = (120 ± 12) K/GPa are determined. From the linear dependences In σ(l/T) and In μd(l/T) for various p = const, the activation energy is determined. The experimental relationship Ea = E0 — Bp is derived on the basis of the small‐polaron theory. Results related to transport phenomena are interpreted through the small‐polaron non‐adiabatic hopping theory. On the basis of the experimental and theoretical relations σ(T, p) = = σ0(T) (1 + Cp), and In μb(T) the LO phonon energy ħωo, = 0.12 eV is determined, as well as the band half‐width J = 0.14 eV at normal pressure, and also the remaining small‐polaron parameters.
Electronic Structure of Thin Alloy Films
Authors: Wysokiński K. I. , Sobczuk H. , Pilat M.
Published: July 2007

The coherent potential approximation is adopted to the problem of an electron moving in a sub‐stitutionally disordered alloy with thin film geometry (i.e. thin alloy film). The theory is formulated for a one‐band tight‐binding Hamiltonian of the alloy film consisting of N atomic planes. The numerical calculations illustrate the dependence of the local density of states for various layers on the parameters describing the alloy film.
Determination of the Cyclotron Masses of the Conduction Band of Bi1−xSbx near the Semimetal‐Semiconductor Transition
Authors: Fellmuth B. , Krüger H. , Rudolph R. , Herrmann R.
Published: July 2007

In a number of n‐doped Bi1−xSbx samples approaching the semimetal‐semiconduct or transition (0.070 ≦ x ≦ 0.083), the propagation of magnetoplasma waves is investigated in the B ⊥ C2, ∥ k orientation at 4.2 K. The plane‐parallel samples are prepared from a single crystal exhibiting a slight gradient in the antimony concentration. By means of an ellipsoidal model of the conductivity tensor, the low cyclotron mass mc2 and the anisotropy mc3/ mc2 are determined from the experimental dependence of the wave vector on the frequency and the magnetic field. In the samples with x < 0.073, the dispersion and the attenuation of the waves show peculiarities which can be explained by the presence of holes at the point T. The results obtained indicate a continuous dependence of the band characteristics on the antimony concentration in the neighbourhood of the point x0, where the overlapping of the bands at L and T is removed.
Equation d'état et structure de bandes d'énergie de l'argent métallique
Authors: Perrot F.
Published: July 2007

La méthode linéarisée des “orbitales muffin‐tin” (LMTO) est appliquée au calcul auto‐cohérent de la structure électronique de l'Argent métallique. La pression est calculée en fonction de la densité, dans une gamme allant de la densité normale ϱ0 à 5ϱ0. L'accord avec les résultats de mesures statiques, jusqa' à 170 kbar, est bon; il en est de měme avec l'isotherme 0 K déduite de mesures dynamiques, jusqu' à 1,3 Mbar environ. Les modifications de la structure de bandes d'énergie sous pression sont ensuite discutées.
The Metal‐Insulator Transition in Electron‐Hole Systems
Authors: Balslev I.
Published: July 2007

Theoretical studies of the metal‐insulator transition in electron‐hole systems in indirect semiconductors are presented. The model is based on various screening theories and on thermodynamical continuity requirements. In case of Debye‐Hückel‐like screening the phase diagrams of Si and Ge contain two separate transitions, the gas‐liquid and the metal‐insulator transition. Stronger and weaker dependence of the band energies on the free pair density favors the metal‐insulator and the gas‐liquid transition, respectively.
X‐Ray Compton Scattering Study of Electronic Distribution in Beryllium
Authors: Loupias G. , Petiau J. , Issolah A. , Schneider M.
Published: July 2007

Compton scattering of 10 keV X‐rays by single crystals of beryllium is performed using the synchrotron radiation beam provided by the LURE‐DCI storage ring of Orsay. By means of a three‐axes spectrometer the scattering of the monochromatized beam, the spectral analysis by a focusing curved crystal, and the detection by a position sensitive counter are performed. A resolution of 0.15 momentum at. units is obtained. Seven directional profiles are measured with 106 counts in each of them. Anisotropies of the Compton profiles and of their Fourier transforms are compared to those predicted by the available theories. None of the models gives a good description of the profiles especially in the region of the Fermi momentum. The pseudopotential calculation is in a qualitative agreement with the momentum distribution anisotropy.
Absolute Cross‐Section for Raman Scattering by Phonons in Silicon
Authors: Grimsditch M. , Cardona M.
Published: July 2007

The absolute cross‐sections for Raman scattering in silicon measured at various frequencies in the visible spectrum by two different experimental techniques are reanalysed in the light of recent developments. Agreement between the results obtained by both the methods clears the discrepancies previously observed at high frequencies. Experimental results are compared with theoretical calculations.
Optical Determination of Mean Free Path of Hot Electrons in Metals
Authors: Kroó N. , Szentirmay Zs. , Félszerfalvi J.
Published: July 2007

Light emission via surface plasmon excitation can be used as a sensitive detector for hot electrons in metal‐insulator‐metal structures. Ballistic and electron‐electron scattering mean free pathvalues obtained for silver with this method in the 2.19 to 2.44 eV energy range are in good agreement with theoretical predictions.
A Theory of the Motion of an Extra Electron in Quasi‐One‐Dimensional Structures
Authors: Davydov A. S.
Published: July 2007

A theory of the motion of an extra electron, strongly interacting with acoustic phonons, along a molecular chain is developed. It is shown that as the binding energy increases a discontinuous autolocalization of an electron can occur when the electron goes into a “superconducting” state.
Effect of High Excitation on Carrier Density in Direct Gap Semiconductors
Authors: Egorov V. D.
Published: July 2007

A rate equation for quasiparticles (electron‐hole pairs, excitons) including stimulated optical transitions is solved at simplifying assumptions. The density of quasiparticles at high excitations in direct gap semiconductors with insignificant Auger recombination and without any resonator is shown to be limited by a root function of generation rate with the exponent depending on the dimension of the excited region.
Calculation of the Spin Wave Energy Gap at k = o for a Simple Cubic Ferromagnet with Anisotropic Exchange Interactions
Authors: Belorizky E. , Casalegno R. , Niez J. J.
Published: July 2007

Spin waves in a system of pseudo‐spins forming a simple cubic ferromagnetic lattice are analysed by considering the most general bilinear interaction between nearest neighbors allowed by a four‐fold order symmetry of the bond ℋ︁ij = J∥SizSjz+J⟂(SixSjx+SiySjy) for a pair (i,j) oriented along the z axis. For that extended Heisenberg system, the excitation energy a t the center of the Brillouin zone is found to be zero with the usual theory, a result which violates the Goldstone theorem predicting a gap a t this point. This gap is calculated through two different but consistent methods and its variation with the anisotropy of the exchange parameters is determined numerically. It is seen that even for a small gap, strongly anisotropic exchange is possible.
Family of O Centres in SrO Crystals
Authors: Seeman V. , Reifman S. , Lehto T. , Haldre Ü.
Published: July 2007

Several types of O centres are found and investigated by the electron spin resonance method in X‐irradiated SrO single crystals. All the centres consist of an O molecule stabilized near various defects. The presence of superhyperfine structure in the spectra of two of the centres allows to perform an identification of these centres.
Analysis of the Repulsive Hardness Parameters in Alkali Hydrides, Silver Halides, and Alkaline‐Earth Fluorides
Authors: Shanker J. , Agrawal D. P.
Published: July 2007

The validity of an additivity rule is demonstrated for the repulsive hardness parameters in three crystal families viz. alkali hydrides, silver halides, and alkaline earth fluorides. The additivity rule provides a direct method of determining the repulsive hardness parameters for individual ions and thereby reduces the number of parameters considerably. Using the repulsive hardness parameters for individual ions derived from the overlap integrals an investigation is made on the crystal binding of LiH, NaH, KH, RbH, CsH, AgCl, AgBr, CaF2, SrF2, and BaF2. The interionic force model used here takes into account the long‐range electrostatic interactions, three‐body forces, shortrange repulsive, and van der Waals interactions. The cohesive energy and the pressure derivative of bulk modulus are calculated. The results are found to compare well with experimental data.
Stability of Relaxed States of Excitons in Cesium Halides
Authors: Nakaoka Y. , Iida T.
Published: July 2007

Stability of relaxed excitons in CsCl‐type cesium halides, which are described by a cluster model already developed in a previous paper, is studied. The particle (electron or hole)–phonon interaction is used, in which the discreteness of crystal is emphasized. By a semi‐empirical method based on the Landau‐Pekar theory, the relaxation energies are calculated for one‐particle states as well as exciton states. The results are consistent with those obtained experimentally.
Electron Density Distribution at Point Defects. Application of the Quadratic Response Theory
Authors: Heinrich A. , Paasch G.
Published: July 2007

The static quadratic response theory of the electron gas including exchange and correlation corrections is applied to point defects. Induced electron densities, potentials, and screening lengths are calculated for a point charge and for a vacancy in the jellium. The results are compared with existing self‐consistent calculations for these systems as a test for the reliability of the quadratic screening. In general a large part of the deficiency of the linear screening is removed already by the quadratic terms. The calculations presented here are a first step towards an ab initio inclusion of the host ion potentials in a non‐linear screening of defects in simple metals.
Relaxations Due to Vacancies in Copper
Authors: Sen S. K. , Dutt M. B.
Published: July 2007

The relaxations due to vacancies in copper have been calculated using lattice statics method. Using the measured phonon dispersion relation of copper by Sinha and the elastic constants as constraints, the dynamical matrix is derived including interactions up to five neighbours. Unlike most of the previous calculations all the neighbours are found to relax towards the vacancy. Distortions are found to be large in close‐packed directions as compared to the directions along the cube axes in the crystal.
Thermoluminescence of NaF X‐Irradiated at 80 K
Authors: Ortega A. , Aguilar M. , Meseguer F. , Jaque F.
Published: July 2007

A study of the thermoluminescence and the X‐ray induced luminescence in NaF X‐irradiated at 80 K is realized. Activation energy and pre‐exponential factor of the three prominent glow peaks are carefully calculated. These parameters for peak V have a clear dose dependence. The emission spectrum of the various glow peaks is the same as that during X‐irradiation. Finally the thermoluminescence origin is discussed in function of the thermal stability of different defects created by irradiation like hole‐type centres.
Properties of the n‐th Response of a Fermi Gas
Authors: Pickenhain R. , Unger K.
Published: July 2007

The diagonal elements of the Dirac density matrix of a free electron gas perturbed by a potential are considered in the momentum space representation in an expansion of the potential. Conditions for the n‐th order filter functions which are contained in corresponding terms of the Dirac density matrix expansion are derived from general considerations on the symmetry of the problem.
DC Conductivity of a Random Barrier Network
Authors: Sinkkonen J.
Published: July 2007

The current–voltage characteristics of a single potential barrier is highly nonlinear. The conductivity of a random barrier network is analyzed by extending the effective medium theory to the nonlinear case. Below the percolation threshold the conductivity shows nonlinear behaviour similar to the regular barrier network. Above the percolation threshold the conductivity is constant up to voltages comparable to the barrier height. In the ohmic region the activation energy of conductivity decreases when the fraction of barriers decreases. In the case of distributed barriers the activation energy decreases with decreasing temperature.
Optical Phonons and Crystalline Symmetry of InSe
Authors: Carlone C. , Jandl S. , Shanks H. R.
Published: July 2007

A survey of the Raman and infra red data for the layered structure InSe shows that there is no agreement upon its crystallographic structure. The polytypes, β, ε, and γ are equally invoked by the various groups. Some experiments on samples from different laboratories are repeated. Infrared transmission at different temperatures and Raman spectra away from resonance are obtained. It is concluded on the basis of the optical data that InSe crystallizes only in the β‐polytype. All previous optical measurements can be explained with the β‐polytype if one takes into account the resonance Raman effect. It is inferred from the Raman and infra red data that the interlayer interaction cannot be exclusively of the van der Waals type and that long range Coulomb forces contribute to the lattice dynamics of InSe.
The Anderson Parameter and Temperature Dependence of Bulk Modulus for Alkali Halide Crystals
Authors: Shanker J. , Singh K.
Published: July 2007

The relation is studied between the Anderson parameter δ and the temperature dependence of the bulk modulus for 16 alkali halides with NaCl structure. Two Anderson parameters δS and δT are considered, corresponding to the adiabatic and isothermal bulk moduli, BS and BT, respectively. It is found that the assumption δS ≈ δT taken by several previous workers is not correct. The difference between δS and δT arises largely due to difference between the temperature derivatives of BS and BT at fixed volume. An analysis of the volume dependence of the bulk modulus is performed in terms of interionic potentials. Values of δS and δT are calculated using seven different potential forms for the short‐range repulsive energy.
X‐Ray Absorption Spectroscopic Study of Rare Earth–manganese Intermetallic Compounds
Authors: Hatwar T. K. , Ghatikar M. N. , Padalia B. D. , Malik S. K. , Vijayaraghavan R.
Published: July 2007

Chemical shifts of the K‐absorption edge of Mn and the L3‐absorption edges of rare earths (R = Gd, Tb, Dy, Ho, Er, Tm, and Lu) in RMn2 intermetallic compounds are measured and the effective charges on the Mn and R ions are estimated. Extended X‐ray absorption edge fine structures (EXAFS) associated with the absorption edges are investigated and R‐Mn and Mn‐Mn bond lengths in R–Mn2 compounds are determined. The results are interpreted in the light of the available data on these intermetallic compounds.
Thermoluminescence, Fluorescence, and Optical Absorption Studies on Europium‐Doped Rubidium chloride
Authors: Sastry S. B. S. , Sapru S.
Published: July 2007

Thermoluminescence, fluorescence, and optical absorption studies on Rbcl:Eu2+ indicate that Eu2+ ions convert to Eu3+ on irradiation and gain the electron back on thermal or optical treatment. FZ1 centres are formed on bleaching and a glow peak attributable to these centres is identified. Fluorescence measurements give an emission around 3.0 eV and this emission is affected by irradiation and quenching of the sample. The integrated light intensity of these samples is quite high compared to undoped samples which indicates that this material may be a useful TLD phosphor. Spectral distribution of emission under various glow peaks shows emission bands around 1.5, 1.7, 1.9, 2.1, 2.8, and 3.0 eV. The high‐temperature glow peak shows an additional (weak) emission around 4.8 eV. A tentative energy band diagram is suggested showing the various emission processes.
Mobility and Recombination Coefficient of Charge Carriers in Disordered Pentacene
Authors: Maruyama Y. , Bässler H.
Published: July 2007

Both transient and stationary photoconduction of pentacene layers prepared by vapor deposition at 180 K and annealing at 295 K is studied in a surface electrode arrangement. Except at low light intensities photocurrents are recombination controlled. A ratio γ/μ = 1.8 × 10−7 V cm is obtained. The sum of electron and hole mobility monitored in a time interval 5 × 10−5 to 5 × 10−4 s after carrier generation is 10−2 cm2/Vs. It agrees with a value determined previously employing the initial photocurrent pulse method thus proving the reliability of that method to monitor transport properties of disordered solids on a short time scale.
Picosecond Spectroscopy of CdSe at High Excitation
Authors: Collet J. , Pugnet M. , Cornet A. , Brousseau M. , Razbirin B. S. , Mikhailov G. V.
Published: July 2007

At 4.2 K, the time resolved luminescence is studied of CdSe platelets, using two‐photon excitation at 1.064 μm and monopulsed excitation. At first the importance is shown of lattice heating and quasiparticle heating in high excitation experiments in CdSe. Then, the simultaneous kinetics of the A–LO excitonic line and the so‐called P line is studied. In the experiments, the P line cannot at all be interpreted as resulting of radiative exciton–exciton collisions. It is shown that the previously proposed radiative transition from the Γ1 biexciton ground state to the 2p exciton state provides the best understanding of the dynamical behaviour of the P line. A binding energy of 1.4 meV for the biexciton in CdSe is deduced.
Formation of a Complex Charge Carrier Due to the Interaction between a Free Frenkel Exciton and Excess Electron in Molecular Crystals
Authors: Singh J.
Published: July 2007

Microscopic theory of a complex charge carrier formed by the binding of a free exciton and an excess electron is briefly described. The potential of interaction between the exciton and excess electron is shown to be attractive as a function of the dipole moments induced by the excess electron on the molecule that carries the exciton. The complex charge carrier, like exciton, is shown to move throughout the molecular crystal.
Dipole–Dipole Interaction and Short‐Range Order in Amorphous NiP, NiCuP, and NiPB Alloys
Authors: Bakonyi I. , Takács L. , Tompa K.
Published: July 2007

The field‐independent 31P NMR linewidth, δHo, is measured in nonmagnetic amorphous Ni‐based alloys. In addition, the second moment contribution M originating from direct nuclear dipole–dipole interaction is calculated using Van Vleck's theory based on a computer generated DRPHS amorphous model cluster. The calculated second moment M and the experimental second moment M obtained from δHo by Gaussian line shape approximation (i.e., M = (δHo)2/4) agree fairly well for a (Ni0.27Cu0.73)82P18 metallic glass. In the case of amorphous NiP and NiPB alloys M exceeds M by a factor of two or three. This excess second moment seems to indicate the presence of some indirect indirect interactions between nuclear spins.
Phonon‐Polaritons by Two‐Photon Absorption in Solids
Authors: Hassan A. R.
Published: July 2007

A semiclassical theory of the two‐photon absorption of phonon polaritons in solids is developed. A four‐band model is introduced for the phonon assisted two‐photon electronic transitions to polariton states. A numerical calculation is performed for Gap. The results show three different absorption peaks. The first peak, at low energy, corresponds to the phonon polariton band due to transitions through the indirect gap. The other two peaks are associated with transitions across the two lowest gaps of Gap.
Electronic States and Fermi Surface Properties of NiH
Authors: Tewari S. , Singru R. M.
Published: July 2007

The band structure of Nih is calculated using the APW method for two atomic configurations of Ni, A: 3d84s2and B: 3d94s1. The curves for the density of states show that for the configuration B new low‐lying states are formed in Nih which are attributed to the bonding states. The density of states at the Fermi energy,N(EF), is compared with the value determined from the measurements of electronic specific heat. Cross‐sections of Fermi surface and de Haas‐van Alphen frequencies are calculated for two values (11.0 and 10.76) of the number of electrons in the unit cell. The results show that the band structure and Fermi surface of Nih cannot be understood in terms of the protonic (or rigid‐band) model.
Lattice‐Gas Model for a Simple Fluid: Condensation, Orientation; and Solidification
Authors: Sivardière J.
Published: July 2007

The thermodynamical behaviour of a simple fluid made of elongated molecules is described by a generalized lattice‐gas model. Phase diagrams showing gas, liquid, nematic, and solid phases are reproduced.
Evaluation of Third‐Order Elastic Constants and Pressure Derivatives of Second‐Order Elastic Constants for AgCl–AgBr Mixed Crystals
Authors: Shanker J. , Jain G. D. , Sharma S. K.
Published: July 2007

Six third‐order elastic constants and the first pressure derivatives of second‐order elastic constants for AgCl–AgBr mixed crystals with varying compositions are evaluated. Suitable interionic potentials are developed for mixed crystals starting from an analysis of potentials in pure crystals. Long‐range electrostatic forces, the overlap repulsive forces extended up to second neighbours, the van der Waals dipole–dipole and dipole–quadrupole interactions, and three‐body forces are considered. Calculated values of the pressure derivatives of second‐order elastic constants are found to present reasonable agreement with experimental data.
Picosecond Relaxation Processes of High Density Electron–Hole Plasma in CdSe
Authors: Yoshida H. , Saito H. , Shionoya S.
Published: July 2007

Picosecond time‐resolved spectra of the spontaneous luminescence from high density electron‐hole plasma in CdSe are measured at 4.2 K with changing excitation photon energy in the vicinity of the bandgap energy by using tunable picosecond pulses. Spectra observed are analyzed, and the electron‐hole concentration and effective carrier temperature of the plasma are obtained as a function of excitation photon energy as well as of the delay time. It is found that both the electron‐hole concentration and effective carrier temperature decrease remarkably for the first 150 ps after pulse excitation, and that thereafter the concentration and temperature remain almost unchanged at ≈3 × 1017 cm−3 and ≈20 K, respectively, until to the very late stage down to the 800 ps delay time. It is concluded that the effective carrier temperature does not fall below ≈20 K in spite of decreasing the excess energy given to the carriers at the instance of pulse excitation by means of changing the excitation photon energy. It is sure that there exists a process which makes the plasma hot. The phonon‐assisted Auger process is suggested as such a process.
On the Theory of Electroreflectance of Metals
Authors: Brodskii A. M. , Daikhin L. I.
Published: July 2007

A theory is developed to explain the electroreflectance (ER) of metals in a light energy interval near the photoemission threshold under the assumption that the microscopic mechanism of electromodulation is caused by the dependence of the external photoemission threshold on the field applied. Expressions for electroreflectance are derived containing parameters which depend on the electron structure of surface. The theory is compared with the experiment.
Optical Absorption Study of Nickel Fluoride Thin Films
Authors: Gevers G. , Pichon J. , Barrière A. S.
Published: July 2007

An optical absorption study is made of crystallized thin films of nickel fluoride obtained by sublimation under vacuum. The influence of the structure disorder and of the composition of the samples are investigated by varying the substrate temperature Ts and the residual pressure P during the condensation of the vapors. For well crystallized and quasi stoichiometric thin films, the optical gap is about 9 eV. The spin transitions between the 3d states of Ni2+ ions already reported for single crystals are observed. When P > 10−6 Torr and after an air exposure of the layers, two absorption edges characterizing the presence of NiO appear. For low values of Ts the structural disorder involves a broadening of the fundamental absorption edge. Conversely for high‐temperature values (Ts ≫ 650 K) a lack of fluorine due to a partial dissociation of the compound gives an extra absorption at an energy about 1.75 eV.
The Parity‐Forbidden 4f5 → 4f5 Transition of the Sm3+ Ion in CaF2
Authors: Tsuboi T.
Published: July 2007

The infrared absorption spectra of Sm3+ ions in CaF2 crystals are measured between 15 and 300 K. The temperature independence or dependence of the absorption bands, which are due to electric‐dipole forbidden 4f5 → 4f5 transitions, is interpreted in terms of static or dynamic electron–lattice interaction, respectively.
Polarization Dependence of Three‐Photon Absorption in Solids
Authors: Hassan A. R. , Raouf R.
Published: July 2007

The polarization dependence of three‐photon absorption in solids is developed using the Wigner‐Eckart theorem for finite symmetry groups. The expression for the absorption coefficient is separated into two parts: (i) The geometrical part, which depends on the polarization vectors of the three photons, (ii) the dynamical part, which contains the product of three electron‐photon matrix elements. New information can be gained by studying these two parts. An application to TlCl crystal is given and an experimental method is suggested.
Multiple‐Phonon Resonant Raman Scattering in Zn1–x CdxSe Crystals
Authors: Valakh M. Ya. , Litvinchuk A. P. , Pekar G. S. , Polysskii G. N.
Published: July 2007

Resonant Raman scattering in bulk Zn1–x CdxSe crystals obtained from the vapour phase by the “free‐growing” method is studied experimentally. The existence of seventh‐order LO‐phonon lines under condition of excitation above the band gap and fourth‐order LO‐phonon lines under condition of excitation below the band gap is observed for mixed semiconductor crystals for the first time. The obtained ratios of intensities of different lines in multiple‐phonon spectra are compared with the results of the theory involving the continuous exciton spectrum as an intermediate state.
Pinning by a Macroscopic Spherical Cavity in a Type II Superconductor
Authors: Shehata L. N.
Published: July 2007

The magnetic field created by a vortex line located near a macroscopic spherical cavity as well as the magnetic field within the superconductor are calculated by solving London equations using the generalized spherical function technique. The interaction energy between the flux line and the cavity and consequently the pinning force are also calculated. It is shown that one possible cause of the pinning is that an attractive image force exists at the superconductor sphere boundary.
Lattice Vibrations Around a Vacancy in B.C.C. Transition Metals
Authors: Masuda K.
Published: July 2007

A tight‐binding‐type electronic theory is used to calculate the atomic relaxation and force constants between atoms around a vacancy in b.c.c. transition metals (α‐Fe, Mo, and W). This calculation takes into account the d‐function anisotropy as well as the short‐range repulsive energies. The calculated atomic relaxation and force constants are used to obtain the local vibrational spectra around a vacancy. Finally, the so‐called stage III temperature (at which single vacancies migrate) is estimated from the local vibrational spectra and compared with recent experimental results (both positron annihilation experiments and investigations using a high‐voltage electron microscope).
The Role of Symmetry in Mössbauer Relaxation Spectra
Authors: Cianchi L. , Moretti P. , Mancini M. , Spina G.
Published: July 2007

A perturbation procedure for dealing with the relaxation operator for a Mössbauer atom undergoing electronic transitions is presented. When the restrictions imposed by the symmetry are also taken into account, it is found that one can greatly reduce the complexity of the computations. For example in the case of Yb3+ in YES using the present theory the problem of deriving the line shape of the Mössbauer spectrum is reduced to that of inverting a 40 × 40 matrix and not a 80 × 80 matrix as in previous theories.
Charge Order‐Disorder Transition in the Extended Hubbard Model. Finite Bandwidth Effects
Authors: Lorenz B.
Published: July 2007

The charge order‐disorder transition in the extended Hubbard model which takes into account the intra‐ and intersite Coulomb interactions is investigated with respect to finite bandwidth effects. It is shown that above a critical bandwidth the charge order is destroyed even in the ground state in contradiction to the results of the mean field approximation. For finite temperatures the phase diagram is calculated. Depending on the model parameters the transition may be of either first or second order. Especially, a parameter region is found where the transition changes from first to second order with increasing bandwidth.
Theory of Planar Channelling of Relativistic Positrons
Authors: Zimin N. I. , Wedell R. , Greschner O.
Published: July 2007

A theory of planar channelling of relativistic positrons taking into account multiple scattering, bremsstrahlung on valence electrons, and spontaneous radiation at channelling is developed. The dependence of the energy losses on the impact parameter leads to a stronger broadening of the angular distribution of channelled particles.
Phase Diagrams of the SiSn and GeSn Systems
Authors: Soma T. , Matsuo H. , Kagaya S.
Published: July 2007

The phase diagrams of the SiSn and GeSn systems are investigated using the previous electronic theory based on pseudopotentials. The calculated results negate the presence of the Si1−xSnx and Ge1−xSnx solid solutions. The obtained curves near the melting point show reasonable agreement with experimental data.
Absorption Coefficients in the Dynamical Theory of Electron Diffraction for Non‐Column Calculations of Stacking Fault Contrast
Authors: Sheinin S. S.
Published: July 2007

A method is described which permits absorption coefficients in the dynamical theory of electron diffraction to be obtained for non‐column approximation calculations of stacking fault contrast. The method is based on the use of the exact form of the dynamical equations which include the wave vector change due to the imaginary part of the lattice potential. The results obtained show that absorption coefficients of the Bloch waves excited at the fault are quite different from the absorption coefficients of the Bloch waves excited at the entrance surface.
Theoretical Study of Single Vacancies in GaSb
Authors: Brescansin L. M. , Fazzio A.
Published: July 2007

Using clusters with 17 atoms the electronic structure of Ga and Sb single vacancies is studied in GaSb, using the MS‐Xα method. For the Ga vacancy an impurity level of t2 symmetry is obtained, occupied with three electrons, and in the case of the Sb vacancy two impurity levels are obtained, one a fully occupied a1 level and a t2 level occupied with one electron.
Magnetic Field Dependent Carrier Mobility in Ferromagnetic Semiconductors
Authors: Patil C. G. , Krishnamurthy B. S.
Published: July 2007

The electron mobility in ferromagnetic semiconductors in an external magnetic field due to the electron—two magnon scattering is calculated below the Curie temperature. The calculated two‐magnon mobility is found to be linearly dependent on the external magnetic field in EuO. This is in agreement with experimental observation. Incorporating ionized and neutral impurity scattering besides the two‐magnon process, the Hall mobility data are analysed and the exchange coupling constant I = 0.17 eV and electron effective mass m* = 0.42m are obtained.
Calculations of Phonon Dynamics in Solid Biphenyl. Mixing Between Interphenyl and Lattice Vibrations
Authors: Natkaniec I. , Bielushkin A. V. , Wasiutyński T.
Published: July 2007

The calculation of the lattice dynamics in the high‐temperature phase of solid biphenyl is performed with the inclusion of low‐lying interphenyl motions. The quasi‐harmonic approximation is applied and use is made of the semiempirical atom—atom potential of the form „6‐exp”︁. On the basis of calculated phonon curves the effect of mixing between external and internal modes is studied. The frequencies of the phonons in the Brillouin zone centre are compared with optical spectroscopic results. The phonon density of states weighted on the hydrogen motions is compared with low‐temperature inelastic incoherent neutron scattering spectra. Comparison of the calculated and measured values shows good agreement.
Infrared Band Assignments in Oxidised Hydrogenated a‐Si Films
Authors: John P. , Odeh I. M. , Thomas M. J. K. , Tricker M. J. , Wilson J. I. B.
Published: July 2007

The infrared transmission spectra of two ‘polysilanes’ of approximate composition (SiH2)x and (SiH)x, prepared by chemical means, have been measured in the range 4000 to 650 cm−1. The appearance of new bands in the infrared spectra during the oxidation of films of these materials by exposure to air is interpreted in terms of changes in the local environment around the silicon‐hydrogen moieties. It is demonstrated that the wave number of the silicon—hydrogen stretching modes of SiH and SiH2, groups vary systematically with the number and electronegativity of the next neighbouring atom. The influence of the inductive effect on the stretching frequencies can be empirically related, following the methodology of Lucovsky, to the Pauling electronegativity sum of the adjacently bound oxygen atoms. The infrared band frequencies exhibited in the oxygenated ‘polysilane’ samples correspond exactly with bands that arise during the exposure of certain undoped and P‐doped hydrogenated a‐Si films to air. Ageing phenomena produced in r.f. discharge a‐Si films are associated with the porosity and oxidation of a hydrogen rich phase in the amorphous material.
Self‐Diffusion of Phosphorus in the Amorphous Alloy Fe40Ni40P14B6
Authors: Valenta P. , Maier K. , Kronmüller H. , Freitag K.
Published: July 2007

In amorphous and crystallized Fe40Ni40P14B6 alloys the self‐diffusion coefficient of phosphorus is investigated using radiotracer and a microsectioning technique. Diffusion coefficients of 4 × 10−19 to 5 × 10−17 cm2 s−1 are determined in the temperature range between 553 and 823 K. They do not obey an Arrhenius law.
On the Defect Structure of Zinc‐Doped Zinc Oxide
Authors: Neumann G.
Published: July 2007

The reinterpretation of the EPR investigations of electron irradiated and doped zinc oxide reveal that the EPR signal with the g‐factor near 1.96 has to be attributed to the conduction electron. Oxygen vacancies with the EPR signal near 1.99 solely can be created by electron irradiation or strong mechanical damaging. These results are exclusively compatible with the assumption that zinc oxide contains excess zinc in the form of zinc interstitials.
On the Theory of Radiation of Non‐Relativistic Electrons Grazing into Metal Targets
Authors: Gevorgian L. A. , Korkhmazian N. A.
Published: July 2007

It is shown, that the experimentally observed abnormally high radiation intensity caused by electrons grazing into the metal is a mixture of the undulator radiation resulting from the roughness of metal surface and the transition radiation. Close to the radiation spectrum peak the undulator radiation predominates over the transition radiation contrary to the far‐from‐the peak region.
Etude du gradient de champ électrique dans la muscovite par spectrométrie Mössbauer du fer
Authors: Bonnin D. , Muller S.
Published: July 2007

La spectrométrie Mössbauer est utilisée pour l'étude du Fe2+ dans la couche octaédrique des micas. Dans le cas qui nous occupe, il s'agit d'un monocristal de muscovite. l'analyse des spectres en fonction des angles entre la direction des γ incidents et les axes cristallographiques permet de trouver les directions principales du gradient de champ électrique. Les axes du feuillet ne sont pas équivalents, les spectres sont symétriques par rapport au plan a, c* et non symétriques par rapport au plan b, c*. Nous montrons que la direction principale du gradient de champ électrique est proche du plan a, b du cristal et fait un angle de 45° avec l'axe b. Les directions du gradient de champ électrique trouvées sont comparées à la symétrie locale du site M2 et aux valeurs trouvées par le calcul dans un modèle à charges ponctuelles.
Size‐Dependent Electric Conductivity in Semiconducting thin Wires
Authors: Arora V. K.
Published: July 2007

A quantum theory for electric conductivity in a thin rectangular‐shaped wire is developed taking into account the wave character of an electron. It is shown that the quasi‐one‐dimensional (QOD) gas behaves somewhat like the strictly‐one‐dimensional (SOD) gas when the wire is ultra‐thin, so that the spacing between the quantized levels is quite large, and all the electrons are assumed to be in the lowest quantized level. In the ultra‐thin limit (UTL), the ratio of longitudinal resistivity to bulk resistivity is shown to be proportional to λD2/A, where λD = h/(2m*kBT)1/2 is the de‐Broglie wavelength of an electron of effective mass m* at temperature T, and A is the area of the cross‐section of the wire. The transverse resistivity ratio depends strongly on the scattering parameters and is inversely proportional to the area for wires of square cross‐section.
Electron Momentum Distribution and Compton Profiles of Ag
Authors: Kanherem D. G. , Singru R. M. , Harthoorn R.
Published: July 2007

A band structure calculation of the electron momentum distribution for Compton scattering in Ag is made employing Hubbard's approximate scheme. Plots are shown of the contributions of the individual bands to the total momentum distribution along the 〈100〉, 〈110〉, and 〈111〉 directions. The graphs of the total momentum density in the form of isodenses in the (100) and (110) planes are also presented. The results are used to calculate the anisotropy in the Compton profiles viz. J110 — J100, J100 — J111, and J110 — J111 in Ag.
Variational Hartree‐Fock Calculations of the Ground State Energy of Metallic Hydrogen
Authors: Tua P. F. , Mahan G. D.
Published: July 2007

The ground state energy of metallic hydrogen is calculated by a variational method in the Hartree‐Fock approximation. The periodic wave functions are taken to be a linear combination of Slatertype orbitals and k‐dependent and the exchange energy is treated exactly. Then it is shown that the inclusion of correlation effects, in the same approximation of the Kohn‐Sham equation, does not modify the result appreciably. The introduction of additional parameters confirms the previous results except those obtained by density functional method.
Charge Instabilities in Lateral Super‐Lattices under Conditions of Population Inversion
Authors: Ferry D. K.
Published: July 2007

Lateral super‐lattices along the surface of a semiconductor can generate mini‐band structure for distances of the order of 1000 Å or less. The detailed gap structure depends noticeably on the charge in the structure. Under conditions of strong population inversion, synergetic switching behavior and space‐charge waves can be expected to occur.
Structure de bande électronique de CdAl2Te4 dans les modifications avec les groupes spatiaux D, D, D et S
Authors: Chizhikov V. I. , Panyutin V. L. , Ponedelnikov B. E. , Rozenson A. E.
Published: July 2007

Les structures de bande d'énergie sont calculées pour CdAl2Te4 dans quatre modifications par la méthode du pseudopotentiel empirique. Le pseudopotentiel du cristal ternaire utilisé dans ce calcul a été approximé par une superposition des pseudopotentiels atomiques des semi‐conducteurs binaires. La relation entre les structures de bande électroniques dans les modifications de CdAl2Te4 est discutée.