bluuebunny/crossref_metadata_2025_split huggingface dataset:
Improved Calculations of Phase Shifts for EXAFS Spectroscopy
Authors: Ghatikar M. N. , Mahesh K. V. S. , Bhatia S. N. 
Published: July 2007

AbstractThe full curved wave formalism is used to calculate the phase shifts for the pairs FeCo, CoZr, and FeZr in the Fe54Co36Zr10 amorphous system. The estimated phase shifts are compared with those obtained from the plane wave approximation and the important differences in the region of low k‐values are discussed. The comparison with the experimental phase shift functions obtained from the measured EXAFS spectra establish the improvement in the accuray of the calculated phase shifts using the curved wave formalism.
Grain Boundary Sink Strength in Anisotropic Materials
Authors: Sarce A. , Savino E. J. 
Published: July 2007

AbstractThe grain boundary sink strengths for intrinsic point defects in an anisotropic lattice are calculated. It is shown that the sink strength depends on the grain size, its shape, its metallurgical state, and for hexagonal symmetry, on the anisotropy factor for the diffusivity (Dc/Da). It appears to be independent of the volume averaged diffusivity constant. For the grain shape dependence, the Holt and Ibrahim anisotropy factor is obtained only as a limit case.
Channeling of Antiprotons and Electrons
Authors: Khokonov M. Kh. , Nitta H. 
Published: July 2007

AbstractBased on the diffusion model, the channeling fraction of antiprotons and electrons as a function of penetration depth is studied numerically. According to the calculations, the dechanneling length of antiprotons is of the same order of magnitude as that of electrons. It is found that, though the dechanneling length of antiprotons is much smaller than that of protons, a definite portion (≈ few %) of axially channeled antiprotons has anomalously large dechanneling length.
Analytical Representation of the Thermodynamic Functions of Simple Metals in the Model of Self‐Consistent Einstein Oscillators
Authors: Lemberg V. F. , Psakhie S. G. 
Published: July 2007

AbstractGeneral regularities of the model of self‐consistent Einstein oscillators are investigated. The analytical expressions for the Einstein temperature, for thermodynamic functions, and for state equations are obtained. The range of considered values is estimated.
On the Thermodynamics of Surface Transitions Close to the Bulk Critical Point
Authors: Mishin Yu. M. , Kats D. Ya. 
Published: July 2007

AbstractIn the Ginzburg‐Landau functional approximation, thermodynamics of phase transitions occuring at the surface of binary alloys, ferromagnets, and similar systems are analysed in detail, including finite bulk and surface thermodynamic fields. Equations describing the lines of the Nakanishi and Fisher surface transition diagram are derived. For all the lines and (multi‐)critical points of the diagram, complete sets of thermodynamic critical exponents are obtained and scaling properties of the free energy surface excess, δfs, are examined in detail. The classical scaling of the bulk only holds at the critical prewetting lines. At the rest of the transitions, δfs is either a sum of two scaling functions with different exponents or includes a logarithmic singularity in addition to the leading one. This kind of scaling apparently represents some general properties of systems with surface‐broken symmetry or in contact with a short‐range substrate.
High Pressure Raman Study of the “Chain” Chalcogenide TlInTe2
Authors: Ves S. 
Published: July 2007

AbstractThe effect of pressure on the Raman spectra of the “chain” compound TlInTe2 is investigated up to 17 GPa and at room temperature using a diamond anvil cell. Three Raman peaks are observed in the low pressure tetragonal phase. The pressure coefficients and the corresponding mode Grüneisen parameters γ of their frequencies are obtained. The modes are tentatively assigned by comparison to Raman spectra of related TISe‐type compounds. The frequency dependence of γ indicates that a hierarchy of bonding forces is present. The appearance and disappearance of a new Raman peak at about 1.75 GPa is probably due to a gradual, pressure induced mutual replacement of In atoms by Tl atoms and does not indicate the occurence of a structural phase transition. Near 7.0 GPa a phase transition occurs, while at even higher pressures indications for a second phase transition are found.
Polariton–Biexciton Nonlinear Nutation and Stationary Spectrum Renormalization
Authors: Shmiglyuk M. I. , Bardetskii P. I. , Tiron S. D. 
Published: July 2007

AbstractTwo macrofilled coherent modes ‐ a polariton and a biexciton one ‐ are assumed to exist simultaneously in a direct‐gap semiconductor. These modes are characterized by the sets of parameters kO ωo and qo = 2ko, Ω0 = 2ω0, where k0 is the wave vector of the polariton mode and ω0 is the external pumping frequency. In the stationary case the renormalized dispersion and the particle concentrations of the strong modes k0 and q0 are obtained. A selfconsisted equation for the quasi‐momentum k0 as a function of the frequency ω0 and the external pumping intensity is deduced. in the nonstationary limit the polariton and biexciton concentrations are found to vary periodically in time within certain ranges passing through their steady equilibrium values which are the same as the stationary ones.
The Relative Energies of Ionic Structures for the High‐Tc Superconductor YBa2Cu3O7 and Implications for the Superconducting Mechanism
Authors: Floros N. , Dunne L. J. , Murrell J. N. 
Published: July 2007

AbstractMadelung potentials are calculated for several choices of formal oxidation states of the ions in the high temperature superconductor YBa2Cu3O7. For p‐type CuO2 planes a slightly lower energy is found for a lattice with holes localised on copper (Cu3+) than for one with holes on oxygen (O−). Moreover, for the lattice with oxygen holes there is a negative energy for electron transfer between neighbouring Cu2+ O− sites. The near degeneracy of the ‘copper hole’ and ‘oxygen‐hole’ lattices suggests that they should be strongly mixed and this may play some role in the superconductivity behaviour.
Effect of Oxygen Concentration on the Resistive Superconducting Transition of YBa2Cu3O7−x in High Magnetic Field
Authors: Fuchs G. , Gladun A. , Drechsler S. ‐L. , Mueller R. , Ritschel M. , Krabbes G. , Koppetzki N. , Gilewski A. 
Published: July 2007

AbstractThe resistivity, Tc and Hc2 are studied in YBa2Cu3O7−x as a function of oxygen deficiency for 0 < x < 0.46. For small x the resistive transition is dominated by thermally activated flux creep. The temperature dependence of the activation energy is discussed. For x = 0.46, the influence of thermal activation could be neglected and a pronounced positive curvature of Hc2(T) and Hc2(0) > 45 T is found.
Hot Electron Transport in Submicron Semiconductor Devices
Authors: Kuivalainen P. , Lindberg K. 
Published: July 2007

AbstractHot electron transport is studied in small semiconductor structures by solving the coupled Boltzmann and Poisson equations using a simple relaxation time model and the integral formulation of the transport equation. Especially ballistic transport is investigated by calculating the electron distribution function f(x, v) in a submicron n+−n−−n+ diode. In the n−‐region f(x, v) is non‐Maxwellian and the ballistic electrons cause a dominant peak in f(x, v). The validity of the relaxation time approximation (RTA) is studied in the case of a large homogeneous electric field by calculating f(x, v) both, in RTA and using the full scattering rates for polar optical phonon scattering.
Analysis of Magnetostatic Modes Modified by Exchange and Anisotropy Energies
Authors: Li Shaoping , Cross L. E. 
Published: July 2007

AbstractAn investigation is made of magnetostatic modes modified by exchange interaction in anisotropic ferromagnets; and it gives a macroscopic description of influence of exchange interaction on Damon‐Eshbach surface modes. The classic Damon‐Eshbach (DE) and De Wames and Wolfram (DWW) theories of magnetic excitations in thin films is extended. A remarkable qualitative difference from previous theory is that all the spin wave vectors normal to the film are related to the exchange parameter. In case of weak exchange interaction, the critical angle between surface wave and bulk wave is modified according to the new circumstance and the spin wave dispersion relation is analysed.
Optical Absorption in Heavy Transition B. C. C. Metals
Authors: Ostanin S. A. , Shilkova N. A. , Shirokovskii V. P. 
Published: July 2007

AbstractThe complete relativistic calculation of electron states in heavy b. c. c. d‐metals is performed by the Green's function method to interpret the experimental optical absorption data. The interband optical conductivity is computed in the framework of the single‐particle density matrix formalism taking into account the dipole transition matrix elements. It is shown that consequent relativistic approach permits to interpret reliably the experimental results for the main band of the optical absorption. The effect of the spin‐orbit interaction on the absorption in the infrared region is investigated.
IR‐Spectroscopic Data of Thin Insulating Films on Semiconductors. New Methods of Interpretation and Analysis
Authors: Teschner U. , Hübner K. 
Published: July 2007

AbstractOn the basis of the Fresnel theory special IR optical equations for the description of the transmission (T), reflection (R), and attenuated total reflection (ATR) of thin films on semiconductors are derived. It is shown that these relations (quadratic approximations of film thickness) lead to a theoretical explanation for the detection and identification of transverse and longitudinal phonon‐polaritons by means of oblique incidence of polarized light realized in different experimental modes (T, R, ATR). A comparison of calculated model spectra of SiO2 with corresponding experimental spectra shows good quantitative agreement. Furthermore, in this framework a very effective method of determination of the dielectric functions of thin films from their IR spectra is developed and applied to an Al2O3‐film on silicon.
Optical Spectrum Model for a Substitutional Isoelectronic Impurity in Binary Semiconductors
Authors: Hugel J. , Parlebas J. C. 
Published: July 2007

AbstractThe effect of a substitutional isoelectronic impurity on the optical absorption spectra in binary semiconductors is investigated using a one‐electron NaCl crystal model containing two independent bands. It appears that wave‐vector conserving and wave‐vector non‐conserving transitions are responsible for the structures observed in the differential imaginary part of the dielectric function. However, the direct impurity induced transitions are dominant.
A Theoretical Study of Diffuse Scattering by Clusters in Alkali Halides
Authors: Augst G. R. , Vladislavskii Yu. I. 
Published: July 2007

AbstractIt is shown that in the case of dipoles located in one sublattice (divalent impurity with compensating vacancy), or its complexes, diffuse scattering very near to the Bragg reflections is determined only by short range non‐Coulomb forces affecting the lattice by the defect; in the case of dipoles in different sublattices (divacancies) or their complexes, the electrostatic forces also make a contribution to the amplitude of scattering, Strong compensation of contributions of this forces in the range near the Bragg reflection causes low cross‐section of scattering by divacancies and their complexes, in comparison with the cross‐sections by vacancies and divalent impurities with vacancies. In the case of the diffuse scattering far away from the Bragg reflection the cross‐sections of the same defects have a comparable value. The amplitude of near‐to‐Bragg‐reflection scattering on clusters is proportional to the number of dipoles in the cluster.
The Electronic Structure of the Alkaline‐Earth Oxides. II. Crystalline Cluster Approach Formalism
Authors: Lobatch V. A. , Sobolev A. B. , Rubin I. R. 
Published: July 2007

AbstractCrystalline cluster approach based on the multliple scattering technique is discussed within the context of its precision to reproduce the valence band top in oxides insulators. Possible types of boundary conditions are analysed. Detailed calculations are presented for the magnesium oxide.
Specific Features of Kinetic Effects Measured in (Cd, Hg) Te in Quantizing Magnetic Fields
Authors: Baranskii P. I. , Belyaev A. E. , Gorodnichii O. P. 
Published: July 2007

AbstractMagnetic‐field (0 ≦ B ≦ 5 T) and temperature (1.6 ≦ T ≦ 4.2 K) dependences are investigated of resistivity, ϱ, and Hall coefficient, R, in perfect enough and weakly compensated narrow‐gap (NG) and zero‐gap (ZG) n‐(Cd, Hg)Te crystals. A monotonic decline of R(B), observed in both the cases, is ascribed to an uncontrollable contribution of size‐quantized surface enrichment layers to the conductivity. The temperature dependence of ϱ⊥(B) in NG samples is related to the freeze‐out of electrons into an impurity donor band. An absence of such a dependence in the ZG samples studied evidences an absence of donor states even at the appearance of a gap. An anomalously strong dependence ϱ⊥(B) ∼ B5, measured in this case, is a consequence of a change of dielectric constant, ε, in magnetic field.
Amorphization of the Transverse Ising Model with Spin‐1
Authors: Zhong Jia‐Lin , Li Jia‐Liang , Yang Chuan‐Zhang 
Published: July 2007

AbstractThe amorphization of the transverse Ising model on square lattice with S = 1 is discussed by using the effective‐field approximation. The longitudinal and transverse magnetization, the fluctuation of spin operator Sz, Δ = (y – m)1/2, associated with the order parameter y  ≪(S)2≫r and the initial parallel susceptibility χ‖ are calculated in detail. Some interesting properties in their behavior are investigated.
The C3h Symmetry EPR Spectral Parameters for (0.005Gd, 0.995La) (C2H5SO4)3. 9 H2O and 9 D2O
Authors: Buckmaster H. A. , Kumar K. 
Published: July 2007

AbstractAn analysis is given of precision data sets describing the zx‐ and zy‐plane angular variation of the 9.396 GHz, 292.2 K EPR spectra for 0.5% Gd3+ impurity ions in both, the nonahydrated and nonadeuterated lanthanum ethyl sulfate host lattices. This analysis parameterized the spectral data to both a phenomenological spin Hamiltonian and a restricted symmetry‐adapted generalized spin Hamiltonian with C3h symmetry zero field splitting terms. It reports more precise values for the g‐factors and zero field splitting parameters for Gd3+ ions in the nonahydrated lattice than available previously and, for the first time, the values of these factors and parameters for the nonadeuterated lattice.
Particuliarities of Diffusion in Two‐Dimensional Systems with Random Forces
Authors: Dugaev V. K. , Tovstyuk K. D. 
Published: July 2007

AbstractThe diffusion is investigated of a classical particle in a two‐dimensional system with anisotropic random forces. It is shown that at largest time scales the renormalized diffusion coefficient is isotropic, and the diffusion laws at various time scales are obtained. The renormalization of the mobility in an external field is examined as well. Also the generalization of the results to dimensionalitics d = 2 – ε is presented.
Weak Localization and Interaction Effects in Thin Disordered Zinc Films
Authors: Meikap A. K. , Jana A. R. , De S. K. , Chatterjee S. 
Published: July 2007

AbstractThe low temperature resistance ΔR(T)/R and magnetoconductance Δσ(H, T) is measured of thin and quasi two‐dimensional disordered zinc films. At low temperatures, the thinnest films show a logarithmic temperature dependence of resistance. This is well explained by the localization and electron–electron interaction theory. The electron–phonon and electron–electron contributions to the resistance are described in detail. From the magnetoconductance data, the inelastic and spin–orbit scattering times are calculated and compared with theoretical values.
Interactions on Silicon Surfaces and Theory of Moments
Authors: Pick Š. , Tomášek M. , Gadiyak G. V. , Morokov Yu. N. 
Published: July 2007

AbstractExtensive recursive method calculations for high‐symmetry silicon surfaces both, ideal and non‐ideal, with matrix elements up to 2nd nearest neighbours included are analyzed using low order moments of the Hamiltonian. The relevance of the results for chare transfer and bond‐bending forces are mentioned. Some results obtained previously by the present authors are revised.
The Electronic Structure of the Alkaline‐Earth Oxides. III. Resonant Behaviour of the MgO Valence Band Top
Authors: Lobatch V. A. , Rubin I. R. 
Published: July 2007

AbstractCrystalline cluster approach (CCA) calculations show that in MgO, as contrasted to NaF, the valence band is situated above the “muffin‐tin” zero (MTZ). Self‐interaction correction results solely in lowering the MgO valence band bottom below the MTZ level. In this case valence band top states are assumed to be bonded by a barrier, appearing in the effective one‐particle potential due to the centrifugal potential contribution. It follows that such states are resonant ones and provide a substantial contribution to the electron scattering, which by Friedel's sum rule results in the appearance of additional electron density in the anion vicinity. Such an electron charge is localized in the interstitial region. Thus, MgO charge configuration can be defined as Mg2+ O− plus one electron, distributed in the inter‐ion region, which implies that a hole is to be found on the anion in the ground state. Such an interpretation may turn to be applicable to other oxides.
The Electronic Structure and Cohesive Energy of HfO2, ZrO2, TiO2, and SnO2 Crystals
Authors: Medvedeva N. I. , Zhukov V. P. , Khodos M. Ya. , Gubanov V. A. 
Published: July 2007

AbstractEnergy band structure calculations for tin, titanium, zirconium, and hafnium dioxides are made according to the LMTO method. The values of cohesive energies as well as of the total and partial densities of states are calculated. The results are used for the analysis of the change of the forbidden gap width in the series of dioxides. Relative values of the cohesive energy for TiO2 and SnO2 are explained as a result of repulsion between the oxygen atoms forming pairs, and – in the case of SnO2 – of the absence of hybridization between O2p‐ and d‐states as well.
Strain‐Induced Superconductivity in Lead Salt Superlattices
Authors: Agassi D. , Chu T. K. 
Published: July 2007

AbstractRecent data on lead salt superconducting superlattices are interpreted in terms of an electronic pairing mechanism. The strain in these structures is estimated within the uncertainties in the deformation potential parameters and boundary conditions. The results indicate that the PbS/PbTe superlattice on KCl [100] substrate is particularly susceptible to band inversion in the PbTe layers. Consequently, electrons (or holes) are trapped in the ensuing localized states associated with the PbS/PbTe interface. By virtue of an exciton‐exchange mechanism these electrons condense into a superconducting state. The estimated Tc is in reasonable agreement with the data. Finally the observed superconductivity in another IV–VI superlattice is discussed in light of the present model.
Charge Density Wave and Contact Effects in NbSe3 Observed with Microwave Harmonic Mixing
Authors: Mayr W. , Philipp A. 
Published: July 2007

AbstractIt is shown that the method of phase resolved harmonic mixing (PREHM) at microwave frequencies provides a powerful tool in the investigation of the non‐ohmic behaviour of NbSe3. The latter is due to the formation of two distinct charge density waves (CDW), one below T1 = 144 K and the other below T2 = 59 K. The observed PREHM signal is investigated in view of the contacts necessary for the detection of the PREHM signal possibly being a source of nonlinear behavior, too, and hence contributing to the signal. Several positions of the NbSe3 crystal in the waveguide are chosen to expose either the contact region or the undisturbed part of the sample to the microwave radiation and in this way separating corresponding contributions to the PREHM signal. For comparison, harmonic mixing by a rectifying microwave diode is observed for the first time in order to investigate the principal physical behavior of a rectifying contact. The measurements show that in NbSe3 there is a clear dominance of the CDW contribution over a negligible contact contribution at temperatures below T1 = 144 K.
On the Theory of the Faraday Effect in Dielectric Ionic Crystals and Crystals with Structural Phase Transitions of Jahn‐Teller Type
Authors: Stasyuk I. V. , Kotsur S. S. , Tupychak V. P. 
Published: July 2007

AbstractThe expressions for the components of the tensor of linear magnetooptical effect in ionic dielectric crystals and crystals with structural phase transitions of Jahn‐Teller type are obtained in general form. The Faraday effect in KH2PO4‐type crystals is considered. Calculations are made of the components of the tensor of linear magneto‐optical effect for TmAsO4 crystals and their temperature dependences are investigated.
Structural Stability and Energetics of F.C.C. Metal Microclusters. Empirical Many‐Body Potential Energy Function Calculation
Authors: Erkoç Ş. 
Published: July 2007

AbstractThe structural stability and energetics of microclusters containing 3 to 7 atoms of f.c.c. metal elements are investigated. A recently developed empirical many‐body potential function (PEF) is used in the calculations, which comprises two‐ and threebody atomic interactions. The PEF satisfies both, bulk cohesive energy and stability condition. It is found that the energetically most stable structures of microclusters are in compact form.
Optical Properties of GaSe Crystals Containing Mn Impurity Atoms. I. Exciton‐Phonon Interaction
Authors: Gnatenko Yu. P. , Zhirko Yu. I. , Kovalyuk Z. D. 
Published: July 2007

AbstractThe experimentally observed growth of the integrated intensity of the n = 1 exciton absorption band in GaSe crystals is due to its energy degeneracy with the indirect conduction band. Participation of a phonon in such a process is needed to meet the conservation laws. Introduction of a light impurity atom into the interlayer space gives rise to a local interlayer mode capable of controlling the exciton‐phonon processes.
Optical Properties of GaSe Crystals Containing Mn Impurity Atoms. II. Excitonic and Impurity Emission
Authors: Gnatenko Yu. P. , Zhirko Yu. I. , Kovalyuk Z. D. 
Published: July 2007

AbstractThe impurity band (Emax = 1.842 eV) observed in photoluminescence (PL) spectra of GaSe: Mn crystals is demonstrated to be due to intracentre transitions of the Mn2+ ion. The energy of a zero‐phonon transition (EZPL = 1.928 eV) and of optical phonons participating in the formation of the PL of the electronic‐vibrational band is determined. Emission of excitonic polarons — ferronic states, resulting from a spin polarization of the electron and hole, included in the exciton, and of local antiferromagnetic‐ordered magnetic moments of Mn2+ ions is observed at T < 20 K.
Calculation of Diffraction Effects Due to Double Positioning in (111) Gold Bicrystals
Authors: Wang D. , Bristowe P. D. 
Published: July 2007

AbstractThe diffraction effects from doubly positioned [111] twist boundaries are calculated using an embedded atom model for gold. It is found that the kinematical scattering from any two boundaries related by double positioning is always superimposed. However, in a limited misorientation range near 30°, the superimposed intensities in the boundary plane are equal and can therefore be separated. Consequently, the projected atomic structure of each doubly positioned boundary can be determined by X‐ray diffraction. It is found that the displacement field of [111] twist boundaries is generally characterized by rotational‐like displacements centered around ‘O’ lattice elements. Since these displacements are largest for near‐Σ1 and near‐Σ3 orientations, these boundaries have the largest scattering power per unit area.