bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transition Rates for Auger and Other Processes in Situations far Removed from Thermal Equilibrium
Authors: Pickin W. 
Published: July 2007

AbstractRecombination rates into traps in semiconductors are usually calculated from the corresponding ionization rates by application of the principle of detailed balance; but this procedure is only valid if the carrier distribution function is Maxwellian. Results are presented which allow the calculation of Auger and other recombination rates for an arbitrary heated carrier distribution. They are shown to reduce to the detailed‐balance results when the distribution is Maxwellian.
Gain and Reflection Spectroscopy and the Present Understanding of the Electron–Hole Plasma in II–VI Compounds
Authors: Bohnert K. , Schmieder G. , Klingshirn C. 
Published: July 2007

AbstractThe reflection and gain spectra of CdS and ZnO are investigated as a function of excitation intensity and temperature. For the gain spectroscopy the two beam method and the variation of the excitation strip length are used. The results indicate, that an electron–hole plasma is formed under high excitation, preferentially if small excitation spots are used. The electron–hole plasma comes close to its thermal equilibrium only in especially favourable cases. Excitonic recombination processes are predominant, if larger excitation spots are used.
Micromagnetic Theory of Phase Transitions in Inhomogeneous Ferromagnets. II. Applications
Authors: Fähnle M. , Kronmüller H. 
Published: July 2007

AbstractThe influence is calculated of spatially random fluctuations of the Landau parameters A(r) and B(r) as well as the influence of inhomogeneous stress fields on the magnetic behaviour near the phase transition of inhomogeneous ferromagnets. In general this behaviour is determined by fluctuations of the Landau parameter A(r), whereas there is only a negligibly small contibution of spatially random fluctuations of B(r) and of inhomogeneous stress fields. The shifts of the ferromagnetic Curie temperatures due to the fluctuations of A(r) are of the order of magnitude of 1 to 10%. However, for actual material parameters only small curvatures are derived of the Arrott plots and the inverse paramagnetic susceptibility when considering spatially random fluctuations of A(r).
Manganese Centers in Low Temperature X‐Irradiated CaF2:Mn
Authors: Alcalá R. , Alonso P. J. , Lalinde G. , Carretero A. 
Published: July 2007

AbstractThe changes in the optical absorption and emission properties of CaF2:Mn after 15 and 80 K X‐irradiation are measured. A new absorption band is created at 450 nm. The same band appears in the excitation spectrum corresponding to Mn2+ emission. Optical and thermal bleaching experiments combined with emission measurements indicate that the 450 nm band is due to Mn+ created by X‐irradiation. The new band is tentatively assigned to the 7S(3d54s) → 7P(3d54p) electronic transition of Mn+ in CaF2.
The Magnetic Susceptibilities of Some Liquid Chalcogenides
Authors: Uemura O. , Satow T. 
Published: July 2007

AbstractThe magnetic susceptibilities for seven binary alloy systems (SnTe, SnSe, InTe, InSe, AgTe, AgSe and AgS) are measured as a funtion of temperature and composition. The diamagnetic susceptibilities of these systems fall rapidly on melting except for the InSe system, and decrease gradually with increasing temperature in the liquid state. The change of magnetic susceptibility at the melting point is considerably large in SnTe and SnSe, while rather small in Ag2X (X: Te, Se, and S). Diamagnetic maxima appeared around the stoichiometric composition (SnTe, SnSe, In2Te3, In2Se3, and Ag2X) and correspond well to minima in the electrical conductivity reported previously. These data suggest that electrons tend to localize at these compositions. Relationships between the degree of electron localization and the chemical bonding are discussed using the bond orbital approximation for the diamagnetism of semiconductors. The result indicates that the electron localization is stongly influenced by the bonding nature of anions.
Hall Effect of Magnetically Ordered MnAs1−xPxMixed Crystals
Authors: Bödecker G. , Bärner K. , Funke K. 
Published: July 2007

AbstractThe Hall resistivity ϱHof MnAs1−xPxpolyerystals is measured for three compositions:x= 0.11,x= 0.08,x= 0.05, for magnetic inductions up to 0.28 T and for temperatures between 80 and 370 K. Forx= 0.11, ϱHcould be separated into a normal and an anomalous contribution to the Hall effect. The total free d‐carrier density may be inferred at high temperatures (ndf= 7 × 1021cm×3at 300 K); also, d‐electron localization effects are detected at the high spin–low spin transition atThland at the Néel temperatureTN. The anomalous Hall effect below the Curietype temperatureT1is assigned to anisotropic scattering of free d‐carriers on localized cation d‐spins.
Lattice Dynamics of ZnS, GaAs, and GaSb
Authors: Kushwaha M. S. 
Published: July 2007

AbstractLattice dynamics of ZnS(II–VI), GaAs(III–V), and GaSb(III–V) compounds is investigated using an eight‐parameter bond‐bending force model (BBFM) recently developed for II–VI and III‐V compounds having zincblende (ZB) structure. The total potential energy of the system embodies three types of interactions which give rise to central (radial), bond‐bending, and long‐range forces. The model involves in total eight disposable parameters which are calculated by making use of six critical‐point phonon frequencies, two elastic constants, and the lattice equilibrium condition. The model is physically correct as it satisfies all the symmetry requirements of a perfect crystal. The phonon dispersion relations, phonon density of states, and temperature variation of the Debye characteristic temperature of the above‐mentioned crystals are calculated. Theoretical results are compared with the available experimental data. A fairly good agreement is observed between theory and experiments and thus lends support to the success of the dynamical calculations.
Plasma Reflection and Magnetoreflection in Epitaxial Graded‐Gap CdxHg1−xTe Layers
Authors: Dudziak E. , Jędral L. , Brzezińki J. , Becla P. 
Published: July 2007

AbstractMeasurements of reflectivity and magnetoreflectivity in the region of the plasma edge are performed at 300 K on n‐type graded‐gap epitaxial CdxHg1–xTe layers. From these measurements the position‐dependent effective masses and concentrations of free carriers are determined in the semimetallic region (x < 0.1) and for small composition gradient (≦ 10−3 μm−1). It is found that the position‐dependent effective masses determined by combined reflectivity and magnetoreflectivity measurements in the examined graded‐gap CdxHg1–xTe, at least within experimental error limits, are the same as in homogeneous CdxHg1–xTe crystals with the respective composition x. This result is discussed in the light of the recent effective mass theory for carriers in graded mixed semiconductors.
The Role of the Normal Phonon–Phonon Scattering in the Lattice Thermal Conductivity and Phonon Drag in Metals at Low Temperatures
Authors: Borchi E. , De Gennaro S. , Pelosi G. , Rettori A. 
Published: July 2007

AbstractThe problem of computing the lattice thermal conductivity and the phonon‐drag contribution to the electrical resistivity in presence of normal phonon–phonon processes is examined in the framework of the Boltzmann‐Callaway equation. A previous treatment for the lattice thermal conductivity of insulating crystals by Callaway and Krumhansl is appropriately extended in order to treat the properties of interest. The so‐obtained expressions for the lattice thermal conductivity and the phonon‐drag contribution are presented. Some inconsistences of recent works on the same arguments are discussed in reference to the results obtained.
Extended de Launay Model Study of Debye‐Waller Factors of B.C.C. Metals
Authors: Cavalheiro R. , Shukla M. M. 
Published: July 2007

AbstractThe temperature variation of the Debye‐Waller factor exponents for three body centered cubic metals, namely sodium, α‐iron, and chromium, are studied theoretically on the extended de Launay model. The theoretical computations show reasonable agreement with experimental observations.
Calculations of the Multiple Scattering of Low‐Energy Heavy Ions in a Finite‐Range Potential
Authors: Scanlon P. J. , Macarthur J. D. 
Published: July 2007

AbstractThe calculation is considered of the multiple scattering of heavy ions by a finite‐range potential that gives zero scattering angle at the range of the potential and is compared with the truncated cross‐section method used by Meyer. For a suitable choice of the range of the potential and the number of collision centres encountered by a projectile traversing a thin foil, substantial agreement can be obtained with experimental data on polycrystalline foils in the energy range of a few tens of keV. For higher energies, of the order of 500 keV, some of the trends in the experimental data are reproduced. To obtain agreement with experimental data for amorphous materials a change in the model describing the number of collisions is found to be necessary.
Light Scattering on Residual Sb Layers Formed After Surface Oxidization of Ga1−xAlxSb
Authors: Charfi F. , Zouaghi M. , Joullie A. , Balkanski M. , Hirlimann Ch. 
Published: July 2007

AbstractThe Raman spectra of Ga1–xAlxSb alloys (x > 0.2) exhibit at low frequencies two peaks: 118 and 150 cm−1 which are attributed to the presence of Sb in the transition region between surface oxide and bulk material. The evolution of this peaks with concentration x and temperature is investigated. The analogy between the experimental results obtained on Ga1–xAlxSb and those obtained on binary oxidized III–V compounds lead to the demonstration that the peaks 118 and 150 cm−1 are the vibrational modes of the Sb‐enriched layer resulting from the preferential oxidization of the group III element.
Interface Model of Impurity Incorporation into Vicinal Faces
Authors: Pfeiffer H. 
Published: July 2007

AbstractThe capture of solvent as impurity during the growth of vicinal faces from dilute solutions is treated analytically. Rate equations for the incorporation of the host and impurity into the steps on the vicinal face are derived within the SOS‐lattice model. In this approach the influence of the “immuring effect” on the impurity capture is automatically taken into account. Especially, analytical expressions for the impurity concentration in the crystal in dependence on the growth rate are given and discussed with special emphasis on the growth of garnets.
Elementary Electronic Excitations in Pure Sodium Silicate Glasses
Authors: Trukhin A. N. , Tolstoi M. N. , Glebov L. B. , Savelev V. L. 
Published: July 2007

AbstractElectronic structure in high‐purity sodium silicate glasses is studied. The spectral dependence of the relative quantum yield of the external and internal photoemission, the luminescence excitation spectra, the luminescence decay, and the polarization degree of the luminescence are measured. The luminescence band at 3.4 eV is created by the intrinsic anisotropic luminescence centre labelled L, whose absorption causes the fundamental absorption tail of high‐purity silicate glasses, where the localized elementary excitations are created by photons. The phonon‐assistent or tunneling delocalization processes produce colour centres. An electron release from the L‐centre leads to the creation of the H‐centre. An electron capture of the L‐centre results in the E‐centre. A model of the structure Na+ ‐ O−‐ Si = is proposed for the L‐centre. Hence the structure for the E‐centre model will be Na0. O−  Si =, but for the H‐centre it will be Na+ O  Si =. The pair of E and H‐centres can probably recombine in a tunneling process.
Electroabsorption on the Indirect Gap of As2Se3
Authors: Althaus H. L. , Weiser G. 
Published: July 2007

AbstractThe electroabsorption spectra of As2Se3 single crystals are studied near 2 eV for polarization of light E o and E c. The low temperature spectra show fine structure related to indirect transitions with creation of phonons of an energy of 5, 11.5, 24.5, and 26.5 meV. This fine structure broadens rapidly above 50 K and disappears at 77 K. With rising temperature a low‐energy tail of the spectra develops which is attributed to indirect transitions with annihilation of phonons. The energy of the indirect gap is determined to 1.989 eV at 10 K. Above 100 K it decreases with a temperature coefficient of ‐6.25 ∧ 10−4 eV/K.
Superimposed Effects of Three Arrays of Scattering Planes on Electrical Conductivity
Authors: Pichard C. R. , Tellier C. R. , Tosser A. J. 
Published: July 2007

AbstractStarting from a three‐dimensional conduction model a comparison is made between the initial equations and those derived by assuming that the three arrays of scatterers act independently. A sufficient fit is obtained, in good agreement with experiments. A tool is thus available for calculating strain coefficients.
Theory of Photoelastic Constants of Alkali Halide Crystals
Authors: Shanker J. , Verma T. S. 
Published: July 2007

AbstractA theoretical model for evaluating the photoelastic constants of ionic crystals, is developed by considering the short range repulsive interactions between nearest and next nearest neighbours, the van der Waals potentials, and three body interactions as well as the electronic polarizabilities of cations and anions. The model is applied to calculate the photoelastic constants of alkali halide crystals with NaCI structure. The results obtained are in good agreement with experimental data. The importance of the short range polarizability effect is demonstrated in determining the photo‐elastic constants of the crystals under investigation.
Optical and Thermal Stimulation of Reactions in α‐A12O3 Containing V3+, V4+, Co3+, and Co2+
Authors: Delbecq C. J. , Marshall S. A. , Yuster P. H. 
Published: July 2007

AbstractOptically or thermally stimulated reactions among the species V,V,Co, and Coin single crystals of α‐A1,O, and the location of the ground state energy levels of these species with respect to the valence or conduction band are studied. A previously unidentified anisotropic absorption band, peaking near 310 nm, is identified as a charge transfer transition of V.Excitation in this band results, with appreciable probability, in the formation of free positive holes and the consequent conversion of Vto Vand of Co to Co;this probability is found to increase as the excitation wavelength decreases. At temperatures above 400 oC an equilibrium is readily established among these four ions and the temperature dependence of this equilibrium is studied. It is shown that this equilibrium is arrived at by a mechanism involving the thermal formation of holes at Co and V.
Study of Energy Band Structure and X‐Ray Emission Properties of Some 5d Metals
Authors: Nemoshkalenko V. V. , Antonov VL. N. , Antonov V. N. 
Published: July 2007

AbstractEnergy band structure and partial densities of states are calculated for 5d metals with the method of relativistic augmented plane waves. The theoretical intensity distribution is obtained for NVI, NVII‐spectra of iridium, platinum, and gold taking into account the transition probability, the inner level finite width, and instrumental distortions.
AC Conductivity Tensor of Disordered Systems in the Presence of a Magnetic Field
Authors: Fishchuk I. I. , Rudko V. N. 
Published: July 2007

AbstractIn the presence of magnetic field the anti‐symmetrical part (s̀xy) of the ac conductivity tensor in disordered systems with localized electronic states is calculated by the Kubo formula. The large range of not too low frequencies, where the phononεess contribution to the conductivity predominates the phonon‐assisted contribution, is investigated. In calculating s̀xy(ω) the exact diagonalization of the used three‐site Hamiltonian is performed. In the same frequency range the symmetrical part (s̀ xx) of the conductivity tensor is calculated in the two‐site approximation. The results obtained show that in the frequency region where Re s̀xx(ω) has a maximum (the absorption band) the curve Re s̀xy(ω) undergoes a twofold sign inversion.
Surface Dynamics of Molecular Crystals. A Calculation for Naphthalene
Authors: Pawley G. S. , Chaplot S. L. 
Published: July 2007

AbstractA model for calculating the statics and dynamics of a surface of a molecular crystal is presented. The (001) surface of naphthalene is chosen. The potential function used is the 6‐exp non‐bonded atom‐atom function, which has gained success in lattice dynamics. Surface layers of different thicknesses are investigated, all indicating that the third layer deep has a maximum binding energy. A slab of twelve layers thickness is used for the dynamics calculation, which shows clear evidence of surface modes. These are in general of lower frequencies than the bulk modes. The frequency distributions presented are divided into translational and librational parts, showing more clearly the nature of the surface modes.
Decay Model for AT and Ax Emissions in KBr:Tl
Authors: Benci S. , Manfredi M. 
Published: July 2007

AbstractThe decay signal of AT and Ax emissions in KBr: Tl is studied in the temperature range 80 to 300 K. A complex decay with three time constants is observed for both the emissions. The experimental results of the lifetimes and intensities versus temperature are explained with a single model for AT and Ax emissions.
Paramagnetic Properties of the Mott Isolator LaCoO3
Authors: Marx R. 
Published: July 2007

AbstractThe paramagnetic properties of LaCoO3 are investigated theoretically. LaCoO3 belongs to those perovskites which enjoy because of their catalytic qualities as exhaust catalyst increasing interest. The theoretical temperature dependence of the susceptibility is given and compared with experimental results. Good agreement between theory and experiment is achieved under the condition that only every second Co ion is excitable into the magnetic quintet state. The energy gap between low spin CoIII and high spin Co3+ is determined and compared with the gap resulting from the optical data.
A Structure Model and the Description of Structural Changes in Amorphous Metals
Authors: Hermann H. , Mattern N. , Kobe S. 
Published: July 2007

AbstractThe structure of an amorphous metal is assumed to consist of an arrangement of structural units which are generated from a basic unit by a coordination transformation. The parameters of the transformation matrix are distributed statistically. The basic unit is produced by energy relaxation of an assembly of dense random packed hard spheres and a dense arrangement of several icosahedral clusters of compressible spheres, respectively. The model provides realistic pair distribution functions. An interpretation of structural changes which occur during low‐temperature annealing and isothermal creep in amorphous substances is suggested.
Influence of 3d Ions on the Production Efficiency of Intrinsic Defects in CaF2
Authors: Alonso P. J. , Orera V. M. , Alcalá K. 
Published: July 2007

AbstractThe influence of 3d impurities on the production efficiency of VK and F centers is studied in low‐temperature X‐irradiated fluorite crystals. The optical absorption spectra of pure CaF2 and CaF2 doped with Mn, Fe, Co or Ni are compared before and after 15 K X‐irradiation. An increase in the efficiency for Vk‐centers production accompanied by the formation of M+ ions (M = Mn, Fe, Co, Ni) is observed at 15 K. A decrease of the F‐centers production efficiency is also detected.
Correlation of Zero‐Field Splittings and Site Distortions. II. Application of the Superposition Model to Mn2+ and Fe3+
Authors: Lehmann G. 
Published: July 2007

AbstractSign and size of b for Mn2+ and Fe3+ with O, F, or Cl as ligands are correlated with axial site distortions. Consistent values of b are obtained by application of the superposition model. These values are more than twice as large for Fe3+ than for Mn2+, but their sign may vary for different compounds and/or metal ion‐ligand pairs. Local charge compensation and effects of lattice relaxation are apparent in several cases. Unambiguous assignments of EPR spectra to specific lattice sites via these correlations are also demonstrated.
Electron Paramagnetic Resonance of Gold in Silicon. I. Single Atoms; Strong Nuclear Quadrupole Effect
Authors: Höhne M. 
Published: July 2007

AbstractIn Si: Au rapidly quenched two centres are observed by EPR, the first of which is investigated in this paper. The spectrum, is characterized by a dominating Zeeman interaction and by a nuclear quadrupole interaction large compared to the hyperfine interaction. Passage conditions depend on the direction of the magnetic field. The lattice site of the gold atom localized in a trigonal distortion is supposed to be an interstitial one.
Luminescence de l'ion Ce3+ dans le luminophore MgS
Authors: Asano S. , Yamashita N. , Ohnishi T. 
Published: July 2007

AbstractLes spectres d'émission et d'excitation des phosphores MgS: Ce3+ ont été mesurés à 300,80 et à 6 K. Les bandes d' émission 2T2g(5d) → 2F7/2, 2F5/2(4f) et les bandes d'excitation 2F5/2(4f) → 2Eg, 2T2g(5d), attributées à transitions intraioniques dans Ce3+, ont été observées. On a trouvé, également, une bande d'excitation, qui peut ětre attribuée à une transition de transfert de charge. La connaissance de la position des raies à zéro‐phonon de ces bandes a été utilisée pour déterminer les paramètres de champ de cristal 10Dq, V, V et les constantes du couplage spin‐orbite ζf et ζd pour les orbites 4f et 5d.
Interstitial Hydrogen Centres in LiF Crystals
Authors: Kamikawa T. 
Published: July 2007

AbstractIn LiF:OH crystals neutron‐irradiated at low temperatures a new ESR absorption is observed after thermally annealed and aged at room temperature for some time. From the analysis of the ESR spectra the absorption is identified to be due to interstitial hydrogen atoms (H01centers) grown in LiF crystals during aging. This hydrogen center is unusually stable and decays very slowly even at room temperature. The ESR absorption lines of this center broadens at low temperatures. The (g‐factor, proton hf constant and shf constants are determined from the spectra obtained at room temperature measurements.
Some Investigations on the Description of Optical Absorption of Hole Centres in Oxide Crystals
Authors: Bernhardt H. J. 
Published: July 2007

AbstractThe common properties of colour centres in YAG, LiNbO3, and PbMoO4 crystals are discussed basing on the good applicability of the polaron model to these centres. A simplified Coulomb model enables one to describe the influence of melting point, lattice constant, and other properties of the host lattice on the properties of colour centres. Regarding the optical data of other oxide crystals known from literature the generalizability of colour centre properties in oxides is tested.
Quantum Numbers for Bloch Electrons in a Magnetic Field
Authors: Wannier G. H. 
Published: July 2007

AbstractLandau functions characterize the motion of an electron in a plane perpendicular to a magnetic field. They have the degeneracy parameter ky. This parameter is resolved into four quantum numbers by a periodic crystalline potential. Two are phase angles; two are restricted to a finite set of values. Only one of the latter is a degeneracy parameter. A constructive proof is given for this proposition; it is valid under wide conditions, the only restriction being the famous ‚rationality condition’︁. The two discrete quantum numbers have as their range the numerator and denominator of the representative fraction. Group theory yields three of the numbers; the fourth labels the subbands, that is the equivalent representations within the spectrum. In the Peierls‐Onsager low field approach, the same four quantum numbers arise from one (two‐dimensional) Bloch band.