bluuebunny/crossref_metadata_2025_split huggingface dataset:
Absorption and Magnetic Circular Dichroism Spectra of CsI:Tl+3
Authors: Stillman M. J. , Jacobs P. W. M. , Gannon K. Oyama , Simkin D. J. 
Published: July 2007

AbstractThe temperature dependence of the optical absorption and magnetic circular dichroism (MCD) of CsI crystals doped with Tl+ is measured between liquid helium temperature and room temperature. The absorption spectra are more complicated than usual for impurity ions with the s2 ground‐state configuration and show five strong bands on the long‐wavelength side of the absorption edge. Three of these bands are assigned to internal transitions of the Tl+ ion and the other two to charge‐transfer transitions. The first and second moments of the first two absorption bands, as well as the first and third moments of thecorresponding MCD bands, are determined from spectra measured below 140 K. For these bands at higher temperatures and for the remaining bands strong overlapping precludes a meaningfull determination of the higher moments. Coupling constants and g‐values are obtained from the moments, and the origin of the spectral bands is discussed.
Correlation of Zero Field Splittings and Site Distortions Interstitial Incorporation of Mn2+ in Urea‐Ammoniumchloride (H2N)2CO · NH4Cl
Authors: Heming M. , Lehmann G. 
Published: July 2007

AbstractIn (H2N)2CO · NH4Cl single crystals doped with Mn2+ three crystallographically inequivalent sets of EPR spectra with relative intensities of 8:3:2 are observed and analyzed. The second order zero field splitting parameters b02 = ‐744.7; ‐712.2; ‐736.5 and b22 = ‐127.1; ‐160.8; ‐111.2 (all in 10−4 cm−1) and the directions of their principal axes can only be explained by incorporation of Mn2+ into interstitial sites midway between two NH4 sites with two water molecules replacing these ammonium ions in close analogy to NH4Cl:Mn.
Investigation of the Weak‐Field Charge Transport in Semiconducting V2—VI3 Compounds with Trigonal Symmetry I. Expanded Model for the Transport Coefficients
Authors: Stordeur M. 
Published: July 2007

AbstractIn the series of trigonal V2—VI3 semiconductorsBi2Te3, Bi2Se3, and Sb2Te3 up to now it has not been succeeded to interpret the temperature dependence of the weak—field charge transport for Sb2Te3 single crystals in terms of a physical relevant model with reasonable semiconductor data. Therefore, an expanded transport model is presented takinginto account nonparabolic manyvalley band structure as well as the simultaneous action of anisotropic mixed charge carrier scattering by acoustical phonons and ionized impurities in the relaxation time approximation. Under these conditions the expressions for the thermoelectric, galvano‐ and thermomagnetic coefficients and the Lorenz numbers are given. These formulas are also valid for Bi2Te3 at pure acoustical mode scattering and for Bi2Se3 at single‐valley band structure.
Neutron Scattering Studies on Phase Transition and Phonon Dispersion in Cs2NaBiCl6
Authors: Prokert F. , Aleksandrov K. S. 
Published: July 2007

AbstractThe structural phase transition (PT) of elpasolite‐type crystal Cs2NaBiCl6 is investigated by neutron scattering. At first the acoustic phonon dispersion is measured at room temperature for the highsymmetric directions Δ, ∑, and Λ of the Brillouin zone. The transverse rotary mode is studied for phonon wave vectors q parallel as well as perpendicular to Δ and the dispersion shows a quasitwo‐dimensional behaviour of the Cl‐octahedra rotation. At cooling down to the PT, this branch shows a softening along Δ, reaching the lowest energies at the zone centre. The PT, which is found to be of weakly first order, seems to be driven and triggered by the ferrorotative octahedra mode.
Cluster‐Bethe‐Lattice Treatment of the Interstitial Boron Centre in Irradiated Gallium Arsenide
Authors: Kleinert P. 
Published: July 2007

AbstractThe radiation‐induced interstitial defect B(1) in GaAs is theoretically analysed by a cluster‐Bethe lattice treatment. Theoretical results obtained for a B—Ga dumbbell in gallium arsenide agree quite well with experimental data. The dumbbell coupling is about three times stiffer than the bonds between host‐lattice atoms. The separation of thedumbbell atoms amounts to one lattice constant. Due to the isotopy of gallium atoms all B(1) bands should exhibit a double‐peak structure with a small frequency split of about 1, 0.1, and 0.4 cm−1 for the A1, B1, and B2 modes, respectively. A resolution of these splittings would supply additional evidence for the B(1) defectmodel discussed here.
The Energy Band Structure of the Corundum (0001) Surface with Different Extent of Hydroxylation
Authors: Pushkarchuk A. L. , Mardilovich P. P. , Trokhimets A. I. , Zhidomirov G. M. , Gagarin S. G. 
Published: July 2007

AbstractA theoretical study of the energy band structure is made for corundum (α‐Al2O3) (0001) surface within the frameworkof the crystalline orbital method. From the results, the dispersion dependences of the electronic energy in chosen directions of the surface Brillouinzone are obtained. For the Al atoms sp‐ and spd‐orbitals are considered to evaluate the effect of an appropriate basis on the results. The dependence of the energy band structure parameters on the extent of the surface hydroxylation is established. A comparison of the theoretical data with experimental ones is made.
A Theoretical Study of Simple Complexes of Point Defects in Alkali Halides by the Lattice Static Method
Authors: Augst G. R. , Vladislavskii Yu. I. 
Published: July 2007

AbstractExpressions are obtained for the energy of alkali halide crystals with two kinds of simple complexes of point defects – divalent impurity with vacancy and bivacancy – using the lattice static method. The heat of solution of Mg2+, Ca2+, Sr2+, and Ba2+ in NaCl, KCl, and KBr is calculated. Numerical calculations show that in some cases the nearest‐neighbour complex is less stable than the next‐nearest‐neighbour complex. The formation energy of a bivacancy is calculated in the same crystals. The results are consistent with those obtained experimentally. It is shown that in the latter case the configuration of the nearest‐neighbour complex is the most stable one.
Intraconduction Band Magneto‐Optical Study of InSb under Hydrostatic Pressure
Authors: Huant S. , Dmowski L. , Baj M. , Brunel L. C. 
Published: July 2007

AbstractThe cyclotron resonance and electron spin resonance of n‐InSb under hydrostatic pressure up to 1 GPa are investigated using photoconductivity techniques. All the transitions observed are fitted using a modified Pidgeon‐Brown model with a set of band parameters recently proposed by Goodwin and Seiler and a change of the band gap of dEg/dP = (0.140 ± 0.004) meV/MPa, a value in good agreement with experimental results.
The Electronic Spectrum of the CrO Ion in the Ca2SiO4 · CaCl2 Host Lattice
Authors: Borromei R. 
Published: July 2007

AbstractThe polarised absorption spectrum of single crystals of Ca2SiO4 · CaCl2 containing chromium as CrO or CrO is measured at 4.2 K in the range 8000 to 46000 cm−1. By a careful analysis based on a Td → D2d site symmetry perturbation and on the band polarisation behaviour, it is concluded that the observed spectrum is due to CrO, the ground state is 2E and the system of bands in the region 10000 to 20000 cm−1 corresponds to the ligand field transition. Moreover all the observed bands except that at 37730 cm−1 correspond to a 2T2 excited state.
Charge Ordering in the Anti‐Th3P4 Structure
Authors: Lorenz B. 
Published: July 2007

AbstractThe existence of charge ordering in rare‐earth compounds crystallizing in the anti‐Th3P4 structure is investigated. On the basis of Madelung energy calculations it is shown that for instance in Eu4As3 the electrostatic interactions stabilize a charge ordered low temperature phase. The thermodynamics and the transition to the disordered phase are described by a lattice gas model. The transition is found to be of first order. The transition temperature estimated for Eu4As3 lies well above room temperature. The theoretical results are compatible with recent experiments, although the transition itself has to be confirmed by high temperature measurements.
Low‐Temperature Photoluminescence of the Aggregate Centres in Eu2+‐Doped KCl Crystals
Authors: Mugeński E. , Cywiński R. 
Published: July 2007

AbstractThe emission spectra and fluorescence lifetimes of different aggregation products of Eu2+ dipoles in KCl matrix are examined in the range 15 to 300 K. Two aggregation types are formed in dependence on the annealing temperature. The optical properties of the aggregates (i) and (ii) formed at RT and 125 °C are very similar to those characteristic of isolated dipoles. Above 125 °C both aggregates undergo decomposition. A third aggregation product is formed between 200 and 250 °C. Differently from (i) and (ii) the pertinent absorption and emission spectra do not show any vibronic structure. The effect of the above aggregation products on the fluorescence lifetime of isolated dipoles present in crystals is ascertained.
Absorption of Circularly Polarized Light by Solids
Authors: Jalbert Ginette , Brandi H. S. 
Published: July 2007

AbstractThe multiphoton absorption rate of circularly polarized light, by direct‐gap crystals, is investigated following a non‐perturbative scheme proposed by Jones and Reiss. It is possible to derive closed analytical solutions, for the N‐photon transition rate, valid for all field strengths of practical interest. The accuracy of the approximations introduced in deriving these results is determined comparing the numerical computations of the multiphoton transition rate (“exact”) with the analytical solutions. Specific calculations are done for ZnS and GaAs in the presence of a Nd laser. It is shown that this formalism leads to a total transition rate which has not the tunneling behavior previously discussed by several authors within similar contexts.
Excitonic Surface Polaritons in Luminescence from ZnTe Crystals
Authors: Brodin M. S. , Bandura V. M. , Matsko M. G. 
Published: July 2007

AbstractThe form and structure of reflection and exciton–polariton luminescence spectra of ZnTe crystals are studied in the region of the ground (n = 1) exciton state. The longitudinal–transverse splitting magnitude ΔELT is determined from the shape of the reflection spectra. A detected doublet structure of an emission band from the lower polariton branch is associated with the k‐linear term. The evolution of bulk and surface polariton luminescence spectra versus temperature and wave length of the exciting light is investigated.
Dynamical Behavior of the High Density Electron–Hole System in CdSe
Authors: Unuma Y. , Abe Y. , Masumoto Y. , Shionoya S. 
Published: July 2007

AbstractTime changes of exciton reflection spectra in CdSe under high intensity excitation by picosecond pulses corresponding to band‐to‐band excitation are observed at 2 and 77 K, in order to obtain further information on the dynamical behavior of high density electron–hole plasma. It is found that just after picosecond excitation the exciton reflection structure disappears, but it recovers gradually with the lapse of time, and that the stronger the excitation intensity is, the longer the recovery time becomes. Comparing these results with time‐resolved luminescence spectra observed under the same excitation conditions, it is concluded that as time proceeds, the electron–hole plasma state is transformed to the high density exciton state, and that the luminescence in the late stage is due to the inelastic collision of excitons. It is sure that the formation of electron–hole liquid does not take place.
Pressure Dependence of the Melting Point of Al
Authors: Soma T. , Itoh T. , Kagaya H.‐Matsuo 
Published: July 2007

AbstractThe temperature dependence of the mean‐square displacement for Al is quantitatively calculated from first principles. The Debye temperature at higher and lower temperatures is also estimated using Debye's model. Then, using the volume dependence of the mean‐square displacement, the pressure effect on the melting temperature of Al is studied by Lindeman's melting law, and the melting curve obtained increases as function of the compressed volume.
Group Representation of the Formation Probabilities of Athermal Vacancy Clusters in Atomic Collision Cascades
Authors: Melker A. I. , Romanov S. N. 
Published: July 2007

AbstractAthermal formation of vacancy clusters in displacement cascades is considered in the binary collision approximation. A diagram technique describing the process is suggested. On this basis the group representation of the formation process of vacancy cluster is constructed. The vacancy distribution in the clusters is found in good agreement with the computer simulation results for both f.c.c. and b.c.c. metals.
Comparison of an Extended Interstitial with a Split Interstitial in Silicon
Authors: Wesser K. , Sahu S. N. , Karins J. P. , Corbett J. W. 
Published: July 2007

AbstractMolecular mechanics (MM) is a computer program used in organic chemistry to model the interactions of atoms in a molecule and thereby determine its configuration. The program models the interactions between atoms using two‐body potentials, bond‐bending and bond‐twisting force constants, and van der Waals interactions. In this paper MM is applied to silicon for the first time and used to study defect structures in crystalline silicon. In particular, the Jackson model and the <100> split interstitial are treated and configurations obtained. The resultant structures are then used for molecular orbital calculations using extended Hückel theory (EHT), to give oneelectron energy levels in the band gap. It is found that the Jackson interstitial has a high formation energy which does not favor this defect as a high temperature defect in silicon.
Divacancy in H.C.P. Metals
Authors: Monti A. M. 
Published: July 2007

AbstractStatic properties of divacancies at first, second, third, and fourth neighbours are investigated in a h.c.p. lattice by using computer simulation techniques. The calculations are performed with short range pair interatomic potentials fitted to some Mg properties. The formation, relaxation, and binding energies as well as the strength dipole tensor of the above defects are computed and the results compared with those of earlier authors. The corresponding formation and binding entropies are also calculated and the defect stability analysed. From the results, the instability of the third neighbour divacancy can be predicted.
Dispersion Relations for Magnon‐Polaritons in Uniaxial Ferrimagnetic Crystals
Authors: Merten L. , Kotzott R. , Lehmeyer A. 
Published: July 2007

AbstractGeneral dispersion relations are derived for the components of the permeability tensor and the refractive indices of uniaxial ferrimagnetic crystals making use of symmetry properties. The zeros of the polynomials in the dispersion relations can be interpreted as frequencies of special magnons and magnon‐polaritons. Some of these frequencies correspond to longitudinal magnons in the limit of large wave vectors.
On Phase Transitions in LiNH4SO4
Authors: Torgashev V. I. , Dvořák V. , Smutný F. 
Published: July 2007

AbstractA Landau‐type thermodynamie theory describing the sequence of phase transitions in lithium ammonium sulphate at atmospheric pressure is developed. The form of the phase diagram is derived and compared with that constructed on the basis of published experimental data. The existence of a new monoclinic high pressure phase is proposed. Formulae for permittivity are presented and compared with available experimental data. Soft mode features of Raman and infra‐red spectra are briefly discussed.
Time‐Resolved Reflectivity Measurements on RF Sputtered a‐Si:H Alloy
Authors: Lue Juh Tzeng 
Published: July 2007

AbstractPhotoinduced carrier lifetimes of RF sputtered a‐Si:H alloy are measured by time‐resolved reflectivity and photoconductivity decay methods. Both experiments indicate a lifetime of about 5 μs. A calculation of the relaxation time of photogenerated carriers from extended mobility edge to midgap localized states satisfactorily agrees with this value.
Crystal‐Independent Interionic Potentials and the Lattice Dynamics of the Perovskite‐Type Layer Material K2ZnF4
Authors: Rauh H. , Geick R. 
Published: July 2007

AbstractThe phonon dispersion relations of K2ZnF4 are analyzed by lattice dynamical rigid ion and shell model calculations. It is shown that the concept of crystal‐independent interionic potentials is applicable for this non‐cubic substance. There is a structural unit in the tetragonal perovskitetype layer material K2ZnF4 in common with the cubic perovskite KZnF3, namely the ZnF6 octahedra. The influence of the crystalline environment on the lattice dynamical behaviour of this structural unit is studied by comparison of the phonon dispersion relations of both materials.
Self‐Consistent Dynamical Theory for Heisenberg Spin Glasses
Authors: Schreiber J. , Schulz D. 
Published: July 2007

AbstractA sel‐consistent RPA theory is constructed to describe a spin glass (SG) state in the Heisenberg model (S = 1/2). The investigations are based on the assumption of a collinear spin structure and of strong quantum fluctuations: 〈S〉 ≪ 1/2 (quantum spin glass QSG). In the lowest order the structural fluctuations are expressed by the fluctuations of the molecular fields Hi, for which the probability distribution is self‐consistently determined by a Lorentzian one with a temperature dependent width Γ(T). This quantity plays the role of an order parameter. The temperature dependence of the specific heat and the susceptibility qualitatively agree with experiments.
Spin Green Functions for Ferromagnetic Films with Asymmetric Boundary Conditions
Authors: Kontos D. 
Published: July 2007

AbstractA microscopic theory is employed to calculate the spin Green functions for thin films of Heisenberg ferromagnets. The effect of general asymmetric boundary conditions is considered including surface anisotropy (“pinning”) and variation of the exchange parameters. Results are also obtained for the spin wave spectrum and the layer magnetization.
Influence of Perpendicular Field on Magnetic Fluctuations in Thin Films
Authors: Duszewski J. 
Published: July 2007

AbstractThe dynamic behaviour of fluctuations in magnetization is considered in inhomogeneous systems represented by thin films in the presence of an external magnetic field perpendicular to the easy magnetization axis. The damping and the diffusion coefficients are evaluated as a function of the intensity of the applied field. The spin correlation time observed at the Curie temperature should depend on the perpendicular field because of the Curie point shift due to the perpendicular field influence.
Analysis of Shubnikov‐De Haas Oscillations in HgSe
Authors: Hein G. 
Published: July 2007

AbstractFor the description of beating effects and of the angular dependence of Shubnikov‐De Haas oscillations (SDH) of the narrow‐gap semiconductor HgSe, a method is developed which can be used to estimate parameters from measurements of the transverse SDH effect. Also the influence of quadratic terms in the energy versus magnetic induction relation of the Landau levels can be studied.
Mössbauer Relaxation Spectra Due to Electric Field Gradient Reorientation and Nuclear Hopping for an I = 5/2 to 7/2 Nuclear Transition
Authors: Gorobchenko V. D. , Litterst F. J. 
Published: July 2007

AbstractThe shape of Mössbauer relaxation patterns is derived for a Mössbauer atom jumping in a tetrahedral cage with a correlated electric field gradient reorientation for an I = 5/2 → 7/2 nuclear spin transition. A stochastic relaxation model is applied.
Small‐Signal AC Response of Two‐Dimensional Hot Electrons in Quantum‐Well Structures of Polar Semiconductors
Authors: Bhattacharya A. , Ghosal A. , Chattopadhyay D. 
Published: July 2007

AbstractSmall‐signal ac mobility of hot electrons moving two‐dimensionally in the lowest sub‐band of a quantum‐well structure is studied on a drifted Maxwellian model incorporating polar optic and acoustic scattering. Numerical results are obtained for GaAs considering a dc bias field of 1 kV/cm. The small‐signal ac mobility is found to be constant up to 350 GHz at 77 K and up to 120 GHz at 120 K. The drift velocity, however, begins to lag behind the field from 50 GHz at 77 K and from 10 GHz at 120 K.
On Quasistationary States in the Multipulse Spin‐Locking
Authors: Feldman E. B. , Summanen K. T. 
Published: July 2007

AbstractA new approach to the problem of quasistationary state analysis in the multipulse spin‐locking experiment is developed. The readjustments of the quasistationary states under the influence of multispin resonance processes are discussed. The quasistationary magnetization values obtained within the scope of the approach are compared with experimental data.
LCAO‐Xα Calculations of Transition Metal Clusters
Authors: Seifert G. , Eschrig H. 
Published: July 2007

AbstractThe electronic structure of some transition metal clusters (V6, Cr6, Cu6, Ag6) is studied by an approximate LCAO‐Xα scheme. Energy level spectra are discussed with respect to other theoretical investigations. The density‐of‐states curves are represented and compared with those from band‐structure calculations. The correlation between binding energies of clusters and the corresponding cohesive energies of the bulk material is shown. Furthermore, the binding energies in copper clusters versus cluster size are discussed. Finally, some experimental results according beams of copper clusters and ESR studies of matrix isolated copper clusters are explained briefly.
Multiple Scattering of Axially Channeled Particles by Thermal Vibrations and Electrons
Authors: Ivanov M. A. , Kvashnina L. B. 
Published: July 2007

AbstractWithin the framework of the classical small‐angle scattering theory a microscopic description of positively charged particle behaviour during axial channeling in a crystal is given. Assuming that statistical equilibrium in a transverse plane is established, the differential Fokker‐Planck‐type equation is obtained from the detailed‐balance relation. The coefficients of this equation are determined by the atomic scattering potential and distribution function of scatterers and are studied at various relations between the amplitude of the thermal atom vibrations and their screening radius. It is shown that for relatively small depths (high transverse energies) the processes of direct particle knocking‐out of a channel are predominant. At low transverse energies the scattering particle behaviour is determined by nuclear and electron diffusion processes. In this case, if the distance of closest approach of the particle to a chain exceeds considerably the amplitudes of atomic displacements, the corresponding coefficients are analogous to those obtained earlier.
Optical and Energy‐Dispersive X‐Ray Investigations of the Mixed Halide SmFCl
Authors: Bolduan F. , Hochheimer H. D. , Beck H. P. 
Published: July 2007

AbstractThe mixed halide compound SmFCl is studied at room temperature by X‐ray and optical investigations in order to look for a pressure induced structural or valence change. The results show that in the pressure range up to 22 GPa there is no structural change. Though also an abrupt pressure induced valence change (Sm2+ → Sm3+) is excluded the results are not in contradiction with the occurance of a gradual valence change.
Overshoot in Low‐Conduction Semiconductors
Authors: Gerlach E. 
Published: July 2007

AbstractIt is shown that semiconductors, for particular scattering mechanisms, may have a strong peak in the conductivity s̀′(ω), if the ratio of the dc‐scattering frequency and the plasma resonance frequency is larger than one. This peak immediately leads to a velocity overshoot for cold electrons, when applying an electric field pulse.