bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electronic Properties of Gallium Chalcogenides (Gas, GaSe, and GaTe)
Authors: Gupta V. P. , Gupta A. , Srivastava V. K. 
Published: July 2007

AbstractPhillips' and Van Vechten's theory (PVV) is applied to gallium chalcogenides (GaS, GaSe, and GaTe), which are layered semiconductors. The derived values of Eh and Ep are found inagreement with the values obtained from Phillips' model, Penn's model, and also with the reflectivity data. Polarizability is investigated using Chemla's relation and the investigated values are shown to be in accordance with the values from the Clausius‐Mossotti relation. Phillips' ionicity (fi) is evaluated and is used to determine the heat of formation (ΔH) for these materials. The values of ΔH are found in good agreement with the experimental data.
EPR Observation of an Au‐Fe Complex in Silicon: I. Experimental Data
Authors: Kleinhenz R. L. , Lee Y. H. , Corbett J. W. , Sieverts E. G. , Muller S. H. , Ammerlaan C. A. J. 
Published: July 2007

AbstractAfter quenching of Au‐doped FZ silicon an anisotropic axially symmetric EPR spectrum is observed. The spectrum exhibits a hyperfine interaction with 197Au nuclei (I = ½). In samples which were intentionally doped with isotopically enriched 57Fe (I = ½) an additional hyperfine interaction with this nucleus is observed. Due to the large nuclear electric quadrupole moment of 107Au the nuclear quadrupole interaction strongly influences the EPR spectrum. From this effect a lower limit for the quadrupole interaction can be derived by a computer diagonalization of the spin Hamiltonian. From the observed hyperfine interactions and the known properties of Fe and Au in silicon it is concluded that this spectrum originates from a [AusFei] complex.
Auger Recombination with Deep Impurities in Indirect Band Gap Semiconductors
Authors: Haug A. 
Published: July 2007

AbstractThe theory of Auger recombination involving traps is extended to indirect band gap semiconductors, indeed with special emphasis on deep impurities. Effects of the strong localization and of the lattice relaxation combined with these impurities are taken into account. The results give an explanation of the influence of goldimpurities on the recombination in silicon.
Electronic Structure of the Cd85Hg35 Alloy and Its Temperature Dependence near the Phase Transition
Authors: Surma M. , Maciejewski S. , Kubiak R. , Wolcyrz M. 
Published: July 2007

AbstractThe Cd65Hg35 alloy changes its crystal structure from the ordered phase, at temperatures below 238 K, into the disordered phase at temperatures above 238 K. The temperature involved change in the electronic structure of the alloy within the temperature range 202 to 290 K is analyzed. The band structure of the alloy at 202, 243, and 290 K is calculated using a pseudopotential method and taking into account the temperature lattice parameter changes only. The Debye‐Waller effect is neglected in the calculation because of its inessential influence on the dispersion relation that is discussed. The theoretical analysis of the electronic structure change of the Cd65Hg35 alloy is confirmed by X‐ray data.
From Band to Hopping Diffusion of Excitons and Charge Carriers in Molecular Crystals: I. Principles
Authors: Ĉápek V. , Munn R. W. 
Published: July 2007

AbstractThe diffusion coefficient is deduced for an exciton or charge carrier interacting with phonons in a perfect molecular crystal. The method derived is based on the generalized master equation description of the exciton or carrier kinetics. Correct results are obtained in both the band and the hopping limits, namely a Boltzmann‐like expression with a transport relaxation time where appropriate, and a polaron hopping formula, respectively. An interpolation between these two limits is also obtained.
Hot Luminescence of Self‐Trapped Excitons in Alkali Halide Crystals
Authors: Hizhnyakov V. V. , Plekhanov V. G. , Shepelev V. V. , Zavt G. S. 
Published: July 2007

AbstractThe hot luminescence of self‐trapping excitons is discovered in NaI and KI single crystals. The temperature behaviour of hot emission spectra in the range of 4.2 to 170 K and the corresponding excitation spectra are studied. Basing on the theory of resonant secondary emission developed recently a description of the observed luminescence in terms of the relaxation of a configurational coordinate is given. The calculations of local lattice dynamics of a self‐trapped exciton determining its relaxation law and the shape of the hot emission spectra are presented. A comparison of the theory with the experiment provides a detailed picture of the exciton relaxation into the self‐trapped state.
Effet du champ magnétique sur la luminescence de l'ion Pb2+ dans les luminophores CaO, CaS, CaSe et MgS
Authors: Asano S. , Yamashita N. 
Published: July 2007

AbstractEmission and excitation spectra of CaO, CaS, CaSe, and MgS phosphors activated with Pb2+ ions are measured at 300, 80, and 4.2 K. For these phosphors two emission bands appear corresponding to the transitions 3T1U, 3A1u → 1A1g. The zero‐phonon line on the 3A1u → 1A1g emission band is markedly enhanced by the external magnetic field. The magnetic field dependence of the intensity of the zero‐phonon line is well explained by the model containing the magnetic electronphonon interaction with the τ1g vibrational mode.
EPR and Magnetic Studies on γ:bis(N‐Methyl Salicylaldimine) Copper(II)
Authors: De D. K. , Ghoshal A. K. , Pal D. , Pal A. K. 
Published: July 2007

AbstractEPR and magnetic studies on single crystals of the dimeric copper (II) compound γ:bis (N‐methyl salicylaldimine) Cu(II) down to 1.5 K reveal that each Cu(II) dimer is ferromagnetically exchange coupled having negligible interdimer exchange interaction. The magnetic properties are best described with C4v ligand field symmetry around each Cu(II) ion. The principal axes of the susceptibility and the g‐tensor are not strictly coincident at low temperature.
Electronic Structure of Transition Metal Impurities in Zinc Sulphide
Authors: Majewski J. A. 
Published: July 2007

AbstractThe Green's function method is used to calculate the electronic states associated with the following neutral substitutional transition‐metal impurities in zinc sulphide:scandium, titanium, vanadium, manganese, iron, cobalt, nickel. Clusters of 17 atoms in a tetrahedral configuration are used to simulate the bulk and the locally perturbed crystal. The results indicate that the impurities studied yield acceptor energy levels deep in the crystal fundamental band gap. The role played by the metal d states in the formation of the impurity centres is disscussed and compared with available experimental data.
EPR Linewidth Studies of Gd3+‐Doped YbxY1–xCl3 · 6 H2O Single Crystals Yb3+ Spin‐Lattice Relaxation Times
Authors: Misra S. K. , Mikolajczak P. 
Published: July 2007

AbstractThe EPR linewidths of Gd3+ ion doping single crystals of YbxY1–xCl3 · 6 H2O for x = 0.75, 0.50, 0.25 are measured from room temperature down to liquid helium temperature in order to study the spin‐lattice relaxation times of the Yb3+ ion. It is found that for all samples there are three distinct regions in which the plots are linear: T > 180 K, 180 K > T > 30 K, and T < 30 K; the Debye temperatures of these samples are about 180 K and the Yb3+ ions solely populate the lowest lying Kramer's doublet below about 30 K. It is concluded that Gd3+ cannot be used as a probe to measure the spin‐lattice relaxation times of host Yb3+ ions at temperatures below 180 K.
Higher‐Order Test of the Kenkre‐Knox Relation for Excitonic Optical and Transport Properties of Molecular Crystals
Authors: Nedbal L. 
Published: July 2007

AbstractThe relation between optical and transport properties of the Frenkel excitons was derived by Kenkre and Knox by the second‐order theory in the regime of intramolecular vibrations. In this paper, the validity of this relation in case of a perfect molecular crystal with arbitrary phonon dispersion is tested. Higher orders of the dipole‐dipole interaction are taken into account. For these purposes, new formulas for the optical spectra of molecular crystals are derived, too.
Some Properties of Stochastic Diffusion in Constant Potential Fields
Authors: Das A. K. 
Published: July 2007

AbstractSome unusual features of Brownian motion in a class of one dimensional constant potential fields are discussed. The Smoluchowski diffusion equation for the problem is derived and solved. An anomalous (t + t2)‐behaviour of 〈x2(t)〉 obtains for a repulsive ‘unphysical’ potential. A similar result for a nonlinear repulsive potential is commented on.
Model of a Single Charged Dislocation in Tetravalent Semiconductors
Authors: Milshtein S. , Senderichin A. 
Published: July 2007

AbstractThe electric field around a single edge dislocation in a semiconductor is analyzed taking into account the screening effect of free electrons. Theoretical calculations are made on the temperature dependent single dislocation electrical barrier (SDEB). SDEB dependence on concentration of impurities is computed. The existence of a very narrow inversion layer around a single dislocation is strongly limited by the temperature and donor concentration. The validity of Read's dislocation model is discussed and the new model is considered.
Exciton Spectra of Orthorhombic Indium Bromide
Authors: Yoshida M. , Ohno N. , Nakamura K. , Nakai Y. 
Published: July 2007

AbstractAbsorption and reflection spectra of InBr single crystal are measured at 2 K with polarized light. Dichroic exciton peaks are observed in the reflection spectrum around 2.33 eV. Binding energy of the direct excition for E ‖ c is estimated as (12 ± 1) meV. Indirect absorption edge is confirmed for E ‖ c by using a wavelength modulation technique. The indirect exciton gap is determined to be 2.129 eV. Absorption components associated with five different phonon energies are resolved, one of which is presumably due to a two‐phonon process. The binding energy of the indirect exciton is estimated to be (6.9 ± 0.4) meV. The indirect gap increases rapidly with increasing temperature.
Spontaneous Radiation of Relativistic Electrons under Planar Channeling and Band Structure of Transverse Energy
Authors: Lasukov V. V. , Pivovarov Yu. L. , Kostareva O. G. 
Published: July 2007

AbstractThe concrete calculation of the band structure and spectral characteristics of the spontaneous electron radiation at channeling in the periodic potential of a system of crystal planes is carried out. The spectrum broadening due to multiple scattering is studied in detail.
EPR Study of the Relaxed Excited State of F‐Centres in Alkali Halides
Authors: Romanov N. G. , Veshchunov Yu. P. , Vetrov V. A. , Baranov P. G. 
Published: July 2007

AbstractEPR spectra in the relaxed excited state (RES) of F‐centres in isotope‐enriched crystals 41KCl, 39KCl, 85RbCl, and 87RbCl are studied by means of an optical detection technique. The EPR linewidth is established to be due to the hyperfine interactions of the F‐centre electron with the ligand nuclei. It is shown that the EPR data for the RES of F‐centres in alkali halides can be accounted for with a rather localised RES wavefunction. A hydrogenlike 2s wavefunction with the extremum in the region of the first coordination sphere is used as an envelope function. Additional lines in the optically detected spectra of F‐centres are studied.
Acceptor Point Defects in n‐Type α‐Sn
Authors: Myhra S. 
Published: July 2007

AbstractElectrically active point defects are formed in n‐type α‐Sn as a result of electron irradiation at 5 K. These defects give rise to acceptor resonance states near the conduction band edge. Anomalies in the carrier transport phenomena are examined and are interpreted within the framework of a model which proposes that high‐mobility carriers are transferred to low‐mobility resonance states as a result of defect injection. Therefore, in order of increasing defect concentration, the thermoelectric power will reverse polarity, the electrical resistivity will pass through a maximum and, finally, the Hall coefficient will reverse its polarity.
ESR Study of the Monoclinic—Orthorhombic Phase Transition in Neodymium Pentaphosphates
Authors: Parrot R. , Canny B. 
Published: July 2007

AbstractVery accurate electron spin resonance measurements are performed on Gd3+ impurities in single‐domain crystals of neodymium pentaphosphates. It is shown that the transition from Cs symmetry above the critical temperature (Tc = 421 K) to C1 symmetry below Tc can be interpreted in terms of a temperature‐dependent three‐dimensional rotation R(α, β, γ) of the principal axes of the tensor D. The Euler's angle β(T) and (α + γ) (T) are given by β(degrees) = 0.415 (Tc − T)1/2 − 0.007 (Tc − T) and (α + γ) (degrees) = 0.11 (Tc − T)1/2. Finally, the temperature‐dependent rotation of the tensor D is compared to the rotation of the quadrupolar tensor (tensor Q) appearing in the multipolar expansion of the internal crystal field.
Field Effect in a‐Si:H Films. Influence of Annealing and Light Exposure
Authors: Weber K. , Grünewald M. , Fuhs W. , Thomas P. 
Published: July 2007

AbstractThe field effect is studied in undoped glow discharge deposited a‐Si:H films. The reproducibility and reliability of the method is examined. The density of states is calculated using a new scheme which computes the charge density without explicit solution of Poisson's equation from the experimental field effect characteristics. The density of states near the gap center is raised by annealing and light exposure from below 1017 to about 1018 cm−3 eV−1.
Generalized Internal Strains
Authors: Anastassakis E. M. 
Published: July 2007

AbstractA generalized force (e.g. strain, electric or magnetic field, gradients of forces) applied to a crystal can introduce new atomic position parameters known as internal strains. Each internal strain may be looked as a “frozen” q ≈ 0 optical phonon of appropriate symmetry. Explicit matrix forms can be worked out for each internal strain produced by any type of external force and crystal class. This enables one to determine “selection rules” for deciding the type of force and choice of its components which are necessary to produce an internal strain of given symmetry. Related crystal parameters can be determined in any case with X‐ray diffraction techniques.
Size Effect on the Infrared Absorption Spectrum of Clustered Ionic Spheres
Authors: Clippe P. , Ausloos M. 
Published: July 2007

AbstractThe theory of Clippe, Evrard, and Lucas is extended for the infrared absorption spectrum of small aggregates in order to take into account the variation in size (radius) of ionic spheres. The lowenergy part of the spectrum cannot be explained due to size effects only in this crude dipolar coupling approximation, but a more recent theory taking into account retardation effects may explain the origin of the lower‐frequency absorption.
Anisotropy of the Relaxation Time T1 of NH3 Groups in Triglycine Sulphate Crystals
Authors: Ślósarek G. , Idziak S. , Piślewski N. , Stankowski J. 
Published: July 2007

AbstractThe anisotropy of the spin‐lattice relaxation time of NH3 groups in triglycine sulphate crystals is studicd. Measurements on powdered TGS crystalled to the determination of the spin‐lattice relaxation time minimum at 217 and 315 K at v0 = 90 MHz. T1 measurements performed on single crystal samples, at 217 and 302 K, close to the minimum temperatures, permit a selective study of the spin‐lattice relaxation rate, anisotropy of NH3 groups of individual glycine ions. This measurements confirm the conclusion of papers already published, that the low‐temperature minimum is associated with hindered rotation of NH3 group of glycine GI (activation energy Ea = 22.2 kJ/mol) and the high‐temperature minimum is due to hindered rotation of NH3 groups of glycines GII and GIII (Ea = 27.6 kJ/mol). Non‐exponential spin‐lattice relaxation due to the cross correlation of the intramolecular dipole‐dipole interaction is observed. A calculation of angular dependence of T1 is also performed and compared with experimental results.
The CNDO/BW Study of Lithium Clusters III. Different Crystallographic Structures
Authors: Skála L. 
Published: July 2007

AbstractThe CNDO/BW method is used to investigate the electronic properties of Li clusters in dependence on their crystallographic structure. Clusters with the b.c.c., f.c.c., and s.c. structure and linear equidistant chains are considered. The equilibrium distances between atoms, binding energies, and one‐electron energies of investigated clusters are given and discussed in detail.
L3‐Absorption Edge Studies of Rare Earths in Rare Earth–Aluminum Intermetallics
Authors: Prabhawalkar V. , Padalia B. D. 
Published: July 2007

AbstractThe L3 absorption edge region of rare earths in rare earth—aluminum intermetallics, RAl2 is recorded using an X‐ray focussing spectrograph. Chemical shifts are measured and valence states of rare earth ions are determined. The effective charge on the rare earth ion is estimated using Siegbahn's method. The present results are examined in the light of available reports on the RAl2 system nsing other techniques.
On the Density of States of a Broad‐Band Ferromagnetic Semiconductor at T ≧ TC
Authors: Auslender M. I. , Bebenin N. G. , Zolotovitskii A. B. , Kalashnikov V. P. 
Published: July 2007

AbstractThe density of states ϱ(E) of a broad band ferromagnetic semiconductor in the vicinity of the Curie point is calculated by means of a computer solution of Dyson equation without vertex renormalization. Non‐quasipartical behavior of ϱ(E) at E < 0 (convexivity of ϱ(E), dϱ(E)/dE ≠ 0 at the edge) is found.
Strong‐Field Hopping in Disordered Semiconductors A Problem of Directed Percolation
Authors: van der Meer M. , Schuchardt R. , Keiper R. 
Published: July 2007

AbstractStarting from a density matrix formulation the hopping current induced by phonons and a strong electric field in disordered semiconductors is discussed in dependence on the temperature and the electric field strength. The treatment of the corresponding rate equation makes use of the directed percolation method. Essential informations about the non‐ohmic behaviour can be obtained from the analysis of the vertex star.
Energy Band Calculation and Zero Energy Gap Conditions for Semiconductor Superlattices
Authors: Milanović V. , Tjapkin D. 
Published: July 2007

AbstractThe energy spectrum of the superlattice structure is analysed in detail, assuming that the spatial distributions of the potential energy and the effective mass are rectangular. It is shown that both wells and barriers may appear in the first and second materials, depending on the transverse component value of the wave vector. Two ZEG (zero energy gap) conditions are also derived; the second one being a direct consequence of the spatial dependence of the effective mass. The numerical analysis of results is performed on AlXGa1−xAs‐GaAs superlattice structure. This numerical results confirm theoretical results exposed in the first part of the paper.
Non‐Linear Optical Properties of the Degenerate Band Charge Carrier Gas in the Magnetic Field
Authors: Pokatilov E. P. , Klymin S. N. 
Published: July 2007

AbstractA theory of non‐linear optical properties of a band charge carrier gas of arbitrary concentration and temperature due to the influence of electromagnetic radiation on the probability of the carrier scattering by lattice vibrations is developed. A general expression for the polarization created by the carrier response in a laser field in the presence of other electromagnetic fields and a constant magnetic field is obtained. The generalized dielectric susceptibility tensor is calculated for various scattering mechanisms and arbitrary laser field intensities. The non‐linearity of the laser radiation absorption coefficient and the dependence of the probe wave absorption coefficient on the laser field intensity are studied.
Second‐ and Third‐Order Processes in the Theory of Spin‐Lattice Relaxation
Authors: Shrivastava K. N. 
Published: July 2007

AbstractA theory of spin‐lattice relaxation of isolated single paramagnetic ions present as impurities in insulating materials is discussed. A new case of the two‐phonon Raman process with a new temperature dependence of relaxation rate is found, T1−1 ∼ T4 exp (‐Δ/kBT). A new third‐order process is also pointed out, which for closely spaced levels leads to a T3 behavior.
Impact Ionisation and Quantum Efficiency in InSb
Authors: Beattie A. R. 
Published: July 2007

AbstractTransition rates for impact ionisation initiated by a) a conduction electron, b) a light hole, and c) double impact ionisation by a conduction electron are calculated using time‐dependent perturbation theory. The relative yields of secondary carriers produced by these processes, taking into account the relative numbers of primary carriers created and the loss of light holes by various transitions from the heavy hole band, are evaluated. It is shown that while process b) is a major contributor to the quantum yield along with a), it is unlikely that c) has an appreciable effect. It is also suggested that b) may provide a small contribution to electric field induced impact ionisation, particularly in p‐type material.
Cohesive Energy of Ionic Crystals within the Framework of Compressible Ion Theory
Authors: Gupta V. P. , Sipani S. K. 
Published: July 2007

AbstractCohesive energy for 24 alkali, silver, and thallous halides and 15 alkaline earth chalcogenides crystallizing in NaCl and CsCl structures are calculated within the framework of compressible ion theory proposed by Narayan and Ramaseshan, splitting the short‐range repulsive interaction into its ionic components. The nearest and next‐nearest neighbour interactions as well as van der Waals interactions are taken into account to evaluate the cohesive energy for these diatomic ionic solids. The results obtained are found to be in close agreement with recent experimental data.
The Paramagnetic Resonance of Nd3+ and Yb3+ in Zircon Structure Silicates
Authors: Ball D. 
Published: July 2007

AbstractThe electron paramagnetic resonance of the rare‐earth ions Nd3+ (4f3) and Yb3+ (4f13) in synthetic single crystals of zircon and hafnon is reported. The spectra, taken to be axial, have highly anisotropic g‐values making it possible to observe the spectra fully only along one axis. For Nd3+ g‖ < 0.5 and for Yb3+ g ⊥ < 0.5 Fully resolved hyperfine structure is observed for Nd3+ in ⊥ direction and for Yb3+ in ⊥‐direction. The spin Hamiltonian parameters are established by fitting the spectra observed for various angles θ between ‖‐ and ⊥ ‐directions. The parameters indicate the resonance takes place between the Zeeman split levels of an isolated doublet, though fitting the g‐values fully would require consideration of level mixing.
Random Walk of a Di‐Vacancy in an F.C.C. Lattice
Authors: Sakagami Y. 
Published: July 2007

AbstractThe diffusion‐process of a di‐vacancy on an f.c.c. lattice is investigated with the aid of the Markovian master equation which describes an evolution of a probability distribution on a diffusion lattice of a di‐vacancy in f.c.c. lattice. The problem is formulated in the Green function formalism. The dispersion relation, the relaxation spectrum, and the spectral function are calculated. An effective master equation is also obtained for an aged system. The usefulness of the Green function is discussed.
Crystal Field in the Laves Phase Compound PrNi2
Authors: Andreeff A. , Frauenheim Th. , Goremychkin E. A. , Griessmann H. , Lippold B. , Matz W. , Chistyakov O. D. , Savitskii E. M. 
Published: July 2007

AbstractThe crystal field splitting of the 3H4 ground state multiplet of Pr3+ in PrNi2 is studied by inelastic neutron scattering (TOF). The crystal field parameters are found to be B = (24.5 ± 1.8) × 10−4 meV and B = – (65.7 ± 6.9) × 10−6 meV. The ground state is the nonmagnetic Γ3 doublet. The derived crystal field level scheme is proved by measuring the specific heat. From magnetic measurements the molecular field constant λ = 67 kOe/μB and from the temperature dependence of the thermoelectric power the direct scattering potential of the conduction electrons V = –0.057 eV and the exchange coupling parameter J11 = –0.029 eV are derived.