bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Activation Energy of Phosphorus Donors in Silicon‐Rich Silicon–Germanium Alloys
Authors: Krüssmann R. , Vollmer H. , Labusch R. 
Published: July 2007

AbstractThe activation energy of phosphorus substituted into Si1−xGex alloys (0 ≦ x ≦ 0.27) is investigated by IR absorption. A weak shift of the activation energy with germanium content is found: E(A1) = (45.5 − 26x) meV. This can be explained by multivalley effective mass theory with a phenomenological central cell potential which does not depend on alloy composition within the investigated range. The experiments show that P atoms are distributed at random in the alloy and that their positions are uncorrelated to those of the Ge atoms.
Vibrational Behaviour of Mixed Diatomic Crystals AB1−c Cc within the Bethe Lattice
Authors: Kleinert P. 
Published: July 2007

AbstractThe lattice dynamics of a simple Bethe lattice is treated exactly for the single‐defect problem and within the framework of the coherent potential approximation (CPA). There is a critical mass ratio of an impurity for the emergence of localized modes, if the coordination number is greater than two. This simple approach successfully predicts the one‐ and two‐mode behaviour as well as the mixed‐mode behaviour of many III–V and II–VI mixed crystals. The CPA calculation reproduces essential results already obtained by more elaborated theories.
Theory of Electron–Hole Liquid in Doped Semiconductors. Application to GaP
Authors: Rösler M. , Thuselt F. , Zimmermann R. 
Published: July 2007

AbstractFunctional equations for the self‐energy of an electron‐hole plasma in doped semiconductors are derived and specialized to RPA expressions. Numerical calculations are performed for doped GaP. From thermodynamical considerations a theoretical phase diagram is deduced indicating a critical point and immediately below a coexistence region of two plasma phases with finite densities. The RPA results are compared with simple analytical formulas.
Phonon Spectrum of Boron Nitride with Wurtzite Structure
Authors: Sokolovskii T. D. 
Published: July 2007

AbstractUsing the quantum mechanics methods the interatomic force constants for the rigid‐ion model of boron nitride with wurtzite structure are calculated. An analysis of the symmetry of the fundamental vibrations of the lattice is performed by construction of the projection operators. The calculations of the phonon dispersion relations along seven directions of high symmetry of this lattice are carried out in the harmonic approximation. In terms of this model the phonon state density and the specific heat temperature dependence are determined for boron nitride with wurtzite structure, the results being in good agreement with the experimental data on the specific heat.
Radiation at Planar Channeling of Relativistic Electrons in Thick Crystals
Authors: Baier V. N. , Katkov V. M. , Strakhovenko V. M. 
Published: July 2007

AbstractThe distribution kinetics with respect to the transverse energy at electron channeling is discussed. The asymptotic expressions for the radiation intensity into a given collimator at electron channeling in thick crystals are derived. An optimal thickness at which the radiation output is maximal is found. The spectral distribution of the radiation intensity is analysed for the case of a single diamond crystal.
Valence Fluctuations and Magnetic‐Nonmagnetic Transitions in a Model for Intermediate‐Valence Systems
Authors: Sharma H. V. , Singh I. 
Published: July 2007

AbstractThe magnetic properties of the mixed‐valence systems are studied using the Anderson lattice model, including an intersite exchange interaction. It is found that (i) the ferromagnetic ordering is favoured in the nearly integral‐valent case and (ii) in the intermediate‐valence case the ratio of exchange to hybridisation dictates the absence or presence of magnetic ordering. The magnetic phase diagram and the variation of magnetic moment with exchange and temperature is investigated and also the static magnetic susceptibility and specific heat in the paramagnetic phase. Fairly good qualitative agreement with the experimental findings is obtained.
Magneto‐Resistance of a Semiconductor with the Dislocation Wall in the Quantum Limit
Authors: Kechechyan K. O. , Kirakosyan A. A. 
Published: July 2007

AbstractBy the use of the “energy loss” method the longitudinal and the transverse magneto‐resistances of a semiconductor at magnetic field orientations, normal to and along the wall of edge dislocations are calculated. The dependences of the magneto‐resistance on temperature, the charge carrier concentration, the magnetic field, and the interdislocation distance in the wall are obtained. In particular it is shown that there is a maximum in magneto‐resistance versus interdislocation distance dependence, the location of which depends on the values of the rest of parameters.
Cobalt Centres in Ammonium Chloride: Optical Absorption Studies
Authors: Rambabu B. , Ramasastry C. , Chowdari B. V. R. 
Published: July 2007

AbstractThe optical absorption data for Co2+ ions in NH4Cl single crystals grown under different conditions and measured in the temperature range of 300 to 10 K are presented. The observed absorption spectrum is interpreted by considering the absorption within the crystal field levels determined mainly by the ligands of octahedral coordination. The spectrum at low temperatures is considered to be due to two different centres in which Co2+ ion occupies an interstitial position, i.e. the centre of a square of four Cl− ions with either two NH3 ions or H2O ions on either side of the square. In addition to these, the stabilization of a centre in which a Co2+ ion occupies an edge centre position at room temperature is also suggested. The crystal field parameters for the cobalt centres stable at low temperature are evaluated.
On the Chemical Shifts of the K‐Absorption Discontinuity of Copper in Some of Its Systems
Authors: Rao B. Jagannatha , Chetal A. R. 
Published: July 2007

AbstractThe K‐absorption edge of copper in different copper systems is studied using a 40 cm Cauchoistype bent crystal spectrograph. It is observed that the K‐edge shifts towards the high‐energy side in all the copper systems under study (except in Cu2O). This indicates that the copper ion behaves as a cation (except in Cu2O). The shift is correlated with the partial charge on an absorbing ion in the system and the correlation is found to be linear. The partial charge on the copper ion in the systems chalcopyrite, copper perchlorate, and copper fluoborate is determined from the plot of the chemical shift versus the partial charge.
Application of Special‐Directions Method to the Optical Properties of Copper and Silver
Authors: Ahuja A. K. , Auluck S. , Joshi S. K. 
Published: July 2007

AbstractUsing the interpolation scheme (with four OPW's) the density of states N (E), joint density of states JDOS (E), and the frequency dependent dielectric function ϵ2(ω) for copper (non‐relativistic) and silver (relativistic) are calculated. The summation over the k‐vectors lying in the first Brillouin zone are performed using the special directions (SD) method. The effect of increasing the number of SD's is investigated. The optical matrix elements are evaluated by a method given by Smith. The effect of including a relaxation time τ on ϵ2(ω) is studied. Also a calculation of ϵ2(ω) for copper including 16 OPW's in the interpolation scheme is given and found that the agreement with experimental results is improved at the higher energies by increasing the number of OPW's in the interpolation scheme.
The Influence of the Variation of the Chemical Composition and of the Nitrogen Doping Level on the Energy Spectra of the Bound Excitons in GaAs1−xPx:N
Authors: Nurtdinov N. R. , Stegmann R. , Griepentrog M. 
Published: July 2007

AbstractThe spectras of photoluminescence (PL), photoexcitation (PE) and cathodoluminescence (CL) in GaAs1−xPx:N (x ≧ 0.67) are investigated. The spectral position of the Nx‐line can be described by a logarithmic dependence on the excitation level and on the nitrogen concentration. Different methods are worked out to determine the nitrogen concentration by measurements of PL, PE, and CL. The results allow assertions about the influence of the disorder in the As–P sublattice and of the interaction of the nitrogen atoms on the energy spectra of the bound excitons.
Heterodyne Correlation of Scattered Light from a Sr++‐Doped NaCl Crystal. A Feasibility Study
Authors: Sahoo Debendranath 
Published: July 2007

AbstractA theoretical calculation of the heterodyne correlation function of scattered light is presented for a (suitably heat‐treated) NaCl crystal doped with 250 ppm divalent Sr++ impurities. It is assumed that the impurity‐vacancy complexes (A1) diffuse and aggregate to form dimers (A2) and trimers (A3) by the reactions A1 + A1 ⇌ A2 and A2 + A1 ⇌ A3. Light scattering arises due to fluctuations in concentrations of A1, A2, and A3. The correlation function, calculated under equilibrium condition, is a sum of three decaying exponentials. It reduces to 85% (of its initial value) in 10 ms at 800 K, to 30% in 10 s at 600 K, and to 6% in 10 s at 500 K, thus indicating the feasibility of the experiment at relatively high temperatures.
Free‐Carrier Absorption in n‐PbSe at Low Temperatures Due to Electron–Electron Scattering
Authors: van Huong Nguyen 
Published: July 2007

AbstractFree‐carrier absorption due to electron‐electron interaction in strongly degenerate n‐PbSe is calculated using the theory developed in a previous paper. This theory is specified for the case of weakly anisotropic conduction band. Numerical results for the free‐carrier absorption are compared with those corresponding to other electron scattering processes, and with experimental data on this material at 30 K.
Modified Phase Modulation‐Only Approximation of Incommensurate Phases in K2SeO4‐Type Crystals
Authors: Mashiyama H. 
Published: July 2007

AbstractThe incommensurate‐commensurate transition in K2SeO4‐type crystals is studied on the base of a Landau free energy. The phase modulation‐only approximation is modified to take account of the effect of the amplitude modulation partially but in a consistent way. The soliton density decreases continuously with a logarithmic law near the lock‐in temperature. It is also shown that the specific heat and the dielectric susceptibility diverge at the transition point.
Role of Phonon‐Induced Hybridization in the Spinless Anderson Model
Authors: Zieliński J. , Kowalska J. 
Published: July 2007

AbstractThe spinless Anderson model accomplished by phonon‐induced hybridization is considered. It is found that in the periodic case an insulator‐metal transition appears depending on the values of parameters and temperature. In the case of an isolated impurity a pronounced temperature dependence takes place leading to an increase of the virtual state width.
Photoemission Studies of Pd80−xSi20Cox Amorphous Alloys
Authors: Hricovíni K. , Mikušík P. , Krempaský J. 
Published: July 2007

AbstractX‐ray and UV photoemission measurements of the core levels and valence bands of Pd80−xSi20Cox amorphous alloys are reported. XPS spectra show a broadening of the cobalt 2p‐levels in the alloys while the binding energies are the same as in the polycrystalline Co. The behaviour of Co atoms during the alloying process is discussed. UPS spectra of the valence bands show a shift of Pd 4d‐band to higher binding energies and a cobalt contribution to the density of states above the Fermi level of PdSi alloy.
Monte carlo determination of long‐range pair interaction energies from diffuse scattering of X‐rays by alloys
Authors: Stark Yu. S. , Steinberg A. S. , Vasilev V. M. , Dimitrov V. I. 
Published: July 2007

AbstractA method for the determination of the long‐range interparticle interaction energies in alloys from the experimentally measured short‐range order parameters is presented. This way of determining which is based on the Monte Carlo method is applied to the problem of calculating of the first five pair interaction energies in Cu3Au. The results are compared with those obtained through the analytical theories of ordering.
Optical absorption by an exciton bound to an ionized donor impurity in anisotropic semiconductors
Authors: Stauffer L. , Stébé B. , Munschy G. 
Published: July 2007

AbstractThe oscillator strength is determined for the dipole absorption of the anisotropic exciton—ionized donor complex, taking into account the electronic structure and using our previously obtained anisotropic envelope wave function. It is shown that the anisotropy of the electron lowers markedly the oscillator strength, whereas the hole anisotropy does not give any significant effect. In the case of CdS, the results improve previous variational calculations made in the isotropic case.
Isotope effect of manganese and simultaneous impurity diffusion of chromium and zinc in copper
Authors: Rockosch H.‐J. , Herzig Ch. 
Published: July 2007

AbstractThe isotope effect E = 0.310 as a mean value is measured at T = 1200 K for impurity diffusion of 52Mn/54Mn in copper. The corresponding correlation factor f2 = 0.36 is relatively small in comparison with the published results of Fe, Co, and Ni in Cu. The small value of f2 and the faster diffusivity of Mn with regard to self‐diffusion of Cu can be explained by the strong lattice distortions of Mn in Cu. Valence effects are accordingly less important. The frequency ratios for vacancy jumps and the vacancy flow effect are calculated. The free binding enthalpy of the vacancy—impurity complex is estimated. Simultaneously to Mn, the tracer diffusion of 51Cr and 65Zn is determined. The different evaporation effects of the tracer are taken into account in the evaluation of the diffusion coefficients.
Impurity pinning, interface roughening, and the incommensurate—commensurate transition
Authors: Nattermann T. 
Published: July 2007

AbstractA model of incommensurate—commensurate transition with frozen impurities which pin the domain wall is discussed. The domain wall density vanishes at the transition with an exponent β′ = = (dR — d)/2(d — d1), with dR = 5 and d1 = 1, as a function of the reduced temperature or chemical potential, in agreement with experiments in d = 3 dimensions. There is an analogy with an Ising model with a weakly fluctuating exchange coupling, which exhibits wall roughening for dimensions d ≦ 5.
On thermopower and thermal conductivity of the periodic anderson model
Authors: Schumann R. , Elk K. 
Published: July 2007

AbstractThe periodic Anderson model is used as a simple model describing intermediate‐valence compounds. In that model a strong electron—electron correlation is taken into account. The correlation term is decoupled using the alloy‐analogy approximation. Then the energy‐dependent conductivity σ(ω) is obtained from the Kubo‐Greenwood formula. Using σ(ω) the thermopower and the thermal conductivity can be calculated. For the absolute value of the thermopower a rapid increase with increasing temperature is found in the low‐temperature regime with a broad maximum at mean temperatures, whereas a weak decrease occurs in the high‐temperature regime. The thermal conductivity increases very rapidly with the temperature.
Electronic properties of dilute copper alloys III. Influence on the de haas‐van alphen effect
Authors: Mertig I. , Mrosan E. , Zeller R. , Dederichs P. H. 
Published: July 2007

AbstractA calculation of the Dingle temperatures and changes of the Fermi surface areas of Cu resulting from alloying with 4d transition metal impurities and with sp impurities of the third, fourth, and fifth rows of the Periodic System is presented. The theoretical results are compared with experimental information obtained from de Haas‐van Alphen investigations.
Dimer center luminescence in low‐doped KI:Tl+ crystals
Authors: Benci S. , Fermi F. , Lenzi G. 
Published: July 2007

AbstractThe emission spectra and the polarization characteristics of the luminescence versus the temperature and the excitation wavelength in low‐doped KI:Tl+ crystals allow to determine the nature of the center observed for excitation at λ > 290 nm. From the results it can be concluded that this center is a dimer center (Tl+)2 with D2h symmetry.
Van der waals' forces in face centred cubic cobalt
Authors: Singh S. P. , Rathore R. P. S. 
Published: July 2007

AbstractFor analysing the role played by the Van der‐Waals' forces in the phonon dispersion of metals, four different models are developed for the face‐centered configuration. It is found that these forces enhance the efficacy of the models. The model parameters, calculated by the knowledge of the measured frequency, are free from the errors originating from the variation of elastic constants with temperature and the nature of the forces dominant in elastic behaviour. The least attended metal, face centered cubic cobalt, is chosen for the present analysis.
Parametric conversion of an electron plasma wave into an electromagnetic wave in longitudinally magnetized n‐type piezoelectric semiconductor plasmas
Authors: Ghosh S. , Khan S. 
Published: July 2007

AbstractThe interesting nonlinear process of parametric conversion of a high frequency electrostatic wave into an electromagnetic wave is investigated analytically in an n‐type piezoelectric semiconductor plasma to which an uniform and static magnetic field is applied along the direction of wave propagation. A general dispersion relation is obtained and solved for both the cases of excited electromagnetic waves (i.e., in the cases of left‐hand and right‐hand circularly polarized waves) to study the threshold condition and the growth rate of the unstable mode at a pump amplitude well above the threshold. Numerical estimates are made for n‐InSb at 77 K irradiated with a large amplitude electron plasma wave of frequency 1013 s−1 and wave number 5 × 107 m−1. The threshold electric field is independent of applied magnetic field and the growth rates of the excited modes have linear dependence on the magnetic field.
On the physical tensor field criterion in birman's theory of symmetry changes
Authors: Osuch K. 
Published: July 2007

AbstractBirman's theory of symmetry changes at continuous phase transitions is applied to transitions induced by representations which are connected with a non‐null star, when the high‐temperature group is I4/m(C54h). It is shown that the generalized physical tensor field criterion of Birman rules out some of the low‐temperature groups which appear in Landau's theory as well as in the theory of Birman restricted to its first two criterions (the subduction criterion and the chain criterion).
Density functional theory of metal surface properties
Authors: Raykov B. 
Published: July 2007

AbstractA new functional is proposed for the surface kinetic energy of an electron gas. It is a sum of the kinetic energies of two parts of the space — close to and far from the jellium surface. The decrease of the electron density is approximated by an exponential function. The values of the surface energies and surface dipole barriers thus obtained are close to those of Lang and Kohn. The errors of the method lie between those of the functional of Smith and of the functional of Ma and Sahni. The electron work function of five alkali metals is calculated and very good agreement with the experiment is found.
Nonlinear kinetics and optical properties of band charge carriers
Authors: Fomin V. M. , Pokatilov E. P. 
Published: July 2007

AbstractA theory of the nonlinear response of band charge carriers in semiconductors is developed for arbitrary degeneracy conditions taking into consideration the influence of a strong electromagnetic radiation field on the scattering probability and carrier heating. A comparison of the contributions made by said sources of nonlinearity to the absorption coefficient is carried out for the main mechanisms of interaction of charge carriers with optical and acoustical phonons to first order in the intensity of the electromagnetic radiation. The temperature dependence of the absorbtion coefficient for the non‐degenerate carriers is studied.
Phonon relaxation due to anharmonism and central peak in structural phase transitions. II. Soft optic modes in uniaxial ferroelectrics and soft acoustic modes in cubic crystals
Authors: Kashcheev V. N. 
Published: July 2007

AbstractIn the mode—mode coupling approximation the critical exponents (CE) are calculated for the dampings and frequency shifts of soft optic modes and acoustic phonons (in uniaxial ferroelectrics) and for the dampings of soft acoustic phonons (in cubic crystals) in the structural transition point. The CE are traced back to the anharmonic interaction (of all orders) of soft phonons with the intrinsic dynamic central peak of any nature.
One‐phonon and multiphonon absorption in EuSe and Eu1—xSrxS (0 < x < 1)
Authors: Mützenich G. , Faymonville R. , Grosse P. 
Published: July 2007

AbstractTransmission and reflection measurements on single crystalline samples of stoichiometric EuSe show a number of intrinsic absorption structures in the far infrared. They are explained by one‐, two‐, and three‐phonon processes. The results are consistent with measurements of second‐order Raman scattering and agree with theoretical calculations of the density of states and phonon dispersion published earlier. The reststrahl bands of the alloys Eu1—xSrx S show a typical onemode character with additional weak structures. The shift of the phonon frequencies with composition and temperature is reported.
Density functional pseudopotential calculation of the cohesive properties of disordered solid alloys of nontransition metals application to Zn—Cd
Authors: González D. J. , Zorita M. L. , Alonso J. A. , I≁iguez M. P. 
Published: July 2007

AbstractA density functional pseudopotential method is used to calculate the heat of formation and the equilibrium volume of ZnxCd1—x as a function of the concentration x. Then an estimation of the free energy of formation is given and the results are used to explain the main features of the solid part of the phase diagram of this alloy. The influence of the form of the pseudopotential is studied by performing the calculations both with Ashcroft's and with Shaw's pseudopotentials.
Quantization procedure for phonons in an isotropic elastic half‐space
Authors: Oliveros M. C. , Tilley D. R. 
Published: July 2007

AbstractIn classical elasticity theory, a stress‐free surface leads to mixing of longitudinal and transverse waves with displacement in the plane of incidence, to the existence of a “pseudo‐surface” wave, and to the existence of the localised Rayleigh wave. Expressions for the quantized displacement, the quantized harmonic Hamiltonian, and the density of allowed states are presented taking proper account of these effects. The form of the cubic anharmonic Hamiltonian is outlined, and possible applications are briefly discussed.
Negative magnetoresistance in heavily doped and compensated n‐type InSb
Authors: Sethi B. R. , Goyal P. K. , Sharma O. P. , Mathur P. C. 
Published: July 2007

AbstractTransverse magnetoresistance measurements are made on heavily doped n‐type InSb single crystals in the temperature range 77 to 300 K. The magnetoresistance at low temperatures is found to be negative indicating a contribution of impurity band conduction to the electrical transport phenomenon. The conductivity and Hall mobility measurements also provide evidence of impurity band conduction near liquid nitrogen temperature. The mobility of the charge carriers in the impurity band is estimated from the experimentally observed mobility.