bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interpretation of the Ultraviolet Spectrum of Trigonal Selenium
Authors: Sandrock R. 
Published: July 2007

AbstractBased on an earlier pseudopotential calculation [1] the imaginary part of the dielectric function for Se is recalculated between 6 and 11 eV including lifetime broadening. Our results agree well with UV reflectivity measurements by Leiga [3], a detailed interpretation of which is given. In particular, the strong polarization dependence of several peaks is explained, and also the crossover of the ∥ and ⟂ spectra at 10 eV. The spectrum is shown to be largely determined by additional gaps between the subbands of both the valence band and the conduction band.
Magnetic Susceptibility for a Dilute Magnetic Alloy
Authors: Kjöllerström B. 
Published: July 2007

AbstractFor a dilute magnetic alloy the two‐body Coulomb interaction U is replaced by the interaction with two external fields, and the partition function is then transformed into a Gaussian average over these fields. In the case of static external fields the magnetic susceptibility is calculated. When A(0) U > 1 there are localized magnetic moments which have a Curie‐law susceptibility with the correct limiting value of the Curie constant for large U. When A(0) U < 1 there are no moments and the susceptibility is temperature independent approaching the correct Pauli‐enhanced susceptibility.
Optical Spectra of M, F‐Singlet, and F‐Triplet Centres in NaF
Authors: Elsässer K. , Seidel H. 
Published: July 2007

AbstractX irradiated NaF crystals contain after bleaching the F band mainly M and F centres. Complete orientation of the M centres and partial orientation of the F centres can be achieved. The F centres, identified by their 545.6 nm zero‐phonon line, have broad absorption bands at 512 and 303 nm. Upon strong excitation in the region of the 303 nm band a temporary bleaching of both the bands and the zero‐phonon line is found and ascribed to population of a metastable F‐centre triplet state with a lifetime of τ = 1.9 s at 77 °K.
Infrared Modulation and Energy Band Parameters in Multivalley Semiconductors through Uniaxial Stress Dependence of Free Carrier Contribution to Optical Constants
Authors: Walton A. K. 
Published: July 2007

AbstractThe influence of uniaxial stress in 〈111〉 direction on the free carrier contribution to the optical constants of multivalley semiconductors is considered according to the electron transfer model. Calculations are made of the resulting change in absorption and shift of the wavelength for minimum reflection. It is shown that these effects may be large and experimental observation of them provides a method of determining the effective mass and relaxation time parameters and their anisotropies. The possibility of constructing infrared modulators based on these phenomena is also examined.
Mössbauer Effect Study of Calcium Magnetites
Authors: Hrynkiewicz A. Z. , Kulgawczuk D. S. , Mazanek E. S. , Pustówka A. J. , Sawicki J. A. , Wyderko M. E. 
Published: July 2007

AbstractMössbauer effect measurements for a series of iron compounds of the type CaxFe3−xO4 (0 ≦ x ≦ 0.55), known as calcium‐magnetites, are performed at room temperature and liquid nitrogen temperature. A single calcium‐magnetite phase giving Mössbauer spectra with magnetite‐like Zeeman splitting was observed up to x ≈ 0.28. For higher Ca concentrations a second phase, represented by the additional quadrupole doublet, was detected. This new phase may be identified as CaFe2O4 ferrite.
Pinch Effect in Semiconductors in the Case of an Injected Plasma — The Field‐Controlled Current Regime
Authors: Boiko I. I. 
Published: July 2007

AbstractThe pinch effect in semiconductors is considered for the case when excess current carriers are injected from contacts into a semiconductor. A crystal with dimensions long compared to the bipolar diffusion length, permits to use the field‐driven current approximation [1, 2]; in most of the volume of the solid the longitudinal field flows of carriers dominate over the longitudinal diffusion flows and the volume of the solid absorbs most of the applied voltage and hence determines the current‐voltage characteristic. The treatment is limited to the high injection level situation, when a local density of non‐equilibrium carriers significantly exceeds that of equilibrium electrons and holes. The carriers are supposed to be non‐degenerate. For crystals of plate and cylinder geometry the current‐voltage characteristics, the electric field, and the carrier density distribution are calculated. The calculations are performed for two aspects of space recombination kinetics — the monomolecular and the bimolecular recombination. It is shown that the bimolecular recombination reduces the current at pinch conditions.
Role of Jahn‐Teller Effect in the Ligand Field Theory of Octahedrally Coordinated Trisacetylacetonato Manganese
Authors: Bhattacharyya B. D. 
Published: July 2007

AbstractA theoretical expression for the magnetic susceptibility and anisotropy of an Mn (111) ion having trigonal symmetry in octahedral trisacetylacetonato manganese have been derived on the basis of the more general molecular orbital method of Van Vleck, Stevens, and Bose et al., considering quantum mechanical tunnelling which links equivalent vibronic states of the Jahn‐Teller ion. Attempts have been made to fit the experimental data of optical absorption and magnetic susceptibility with a unique set of parameters in the theoretical expressions at all temperatures. From this an estimate of the parameters which describe the Jahn‐Teller potential is made.
Comments on the Theory of Anharmonic and Tunnel‐Phonon Interactions in KCl:Li+
Authors: Benedek Giorgio 
Published: July 2007

AbstractThe local third‐order anharmonicity, the tunnel splitting of phonon levels, and the interaction between phonons and tunnel excitations, occurring for an off‐centre defect ion in crystals, are considered in connection with the resonant mode isotope shift. The phonon self‐energy related to the above interactions is evaluated to the lowest order of perturbation theory. The first two mechanisms are found to be responsible for the anomalous isotope shift recently discovered by Kirby and Sievers in KCl:Li+.
Screening of a Fixed Charge in Metals
Authors: Pathak A. P. 
Published: July 2007

AbstractUsing a modified Hubbard formula for the dielectric function which has been previously shown to give results for the pair distribution function which are better than those given by the original Hubbard dielectric function, numerical calculations of the screening charge density around a fixed foreign charge in an electron liquid are presented for values of rs corresponding to the metallic density range. The results are compared with those calculated by Langer and Vosko based on the original Hubbard approximation and appreciable differences are found at distances corresponding to the first three shells of ions around the impurity.
Theory of Plasma Electroreflectance of Light from Semiconductors
Authors: Dmitruk N. L. , Tyagai V. A. 
Published: July 2007

AbstractA calculation of the influence of the surface field on the plasma reflection coefficient (plasma electroreflectance) is presented. It is shown that the field and spectral dependences of plasma electroreflectance are significant for the determination of a considerable number of semiconductor parameters (that of free carriers, surface parameters, etc.). An oscillatory behaviour of the plasma electroreflectance is predicted when the Debye screening length is small enough with respect to the spatial inhomogeneity length of the light wave.
Electronic Transitions in Some Alkali and Chromium (III) Chloride Double Salts
Authors: Musa M. , Lébl M. , Botez M. , Lulea C. 
Published: July 2007

AbstractInvestigations are made of the absorption spectra — d‐d transitions — of a series of A3CrCl6 double salts, where A = Li, Na, K, Rb, and Cs. Using Tanabe and Sugano's energy matrices for d3 configuration in Oh point group an assignment of the bands is made. An influence of the next alkali cation on the Racah parameter B is observed and qualitatively explained by introducing a new parameter μ depending on both the charge and the radius of cations.
Study of the Temperature Dependence of the Resistivity in the Kondo Side‐Band Model
Authors: Maranzana F. E. , Bianchessi P. 
Published: July 2007

AbstractThe influence of the crystal field on the Kondo effect in a magnetically non‐dilute inter metallic compound is analysed. An expression for the resistivity versus temperature is obtained. Some resistivity versus temperature curves are reported and discussed.
Dislocations at and near Planar Interfaces
Authors: Brækhus J. , Lothe J. 
Published: July 2007

AbstractDislocations at and near the planar interface between two anisotropic media are considered. It is shown that the energy factor for a dislocation at the interface can be expressed simply in terms of the K‐matrices for the two media. The K‐matrix is defined so that E=(1/2)biKijbj where E is energy factor and the bj are the components of Burgers vector. It is also shown that the force on a dislocation in one of the media and parallel with the interface is simply given in terms of the energy factor for the dislocation in that medium and the energy factor for the interface dislocation.
Properties of Sodium Halide Molecules from Shell Model Parameters
Authors: Pirie J. D. , Smith T. 
Published: July 2007

AbstractModel parameters which give a good description of measured phonon dispersion curves have been used in a shell model description of the corresponding molecules. The internuclear distance, the binding energy, the electric dipole moment, and the vibrational frequencies were then calculated. A comparison of these results with experiment provides a test for the model parameters over much larger displacements than are encountered in lattice vibrations at normal temperatures, and suggests which models may provide a useful description of the forces associated with the displacements near defects in crystals.
Electronic band structure of the layer‐type crystal MoS2 (atomic model)
Authors: Harper P. G. , Edmodson D. R. 
Published: July 2007

AbstractThe theory is presented for the electronic band structure of the dichalcogenide layer‐type crystal MoS2 in its 2H form. Group theory is used to treat an LCAO model based on s, p, d Mo atomic states, and s, p S atomic states. Hybridised spin‐orbit bands are examined along the Δ‐axis, and at the M‐ and K‐points in the Brillouin zone. A simple choice is proposed for the valence and conduction band Δ‐axis symmetry types.
Étude cristallographique et magnétique de MnGeO3
Authors: Herpin P. , Whuler A. , Boucher B. , Sougi M. 
Published: July 2007

AbstractLe composé MnGeO3 possède une structure orthopyroxène. Ses Paramètres réticulaires sont a = 5,44 Å b = 19,24 Å, c = 9,23 Å et son groupe d'espace Pbca. On affine les positions atomiques des divers atomes. Les mesures de diffraction de neutraons permenttent de déterminer la structure magnétique, la température de Néel (TN = 16 °K) et la valeur des moments magnétiques de chacun deux sites cristallographiques occupés par les ions Mn2+ pour 1,1 °K < T < TN. On étdie, à 1,1 °K la variation de la direction des moments magnétiques en fonction d'un champ magnétique (H ≦ 15 kOe) appliqué suivant le vecteur de diffusion. Le signe et l'ordre de grandeur des intégrales d'échange des trois premiers voisins sont discutés.
Determination of optical constants: Disordered germanium
Authors: Jungk G. 
Published: July 2007

AbstractThe transition from the amorphous to the crystalline state has been studied by ellipsometric determination of the room‐temperature optical constants on evaporated germanium films and single crystals in the spectral range from 2.0 to 4.0 eV. For evaporated samples the substrate temperature varied over the range 20 °C ≦ Ts ≦ 400 °C. For Ts ≦ 200 °C no any fine structure but an increase of ϵ2(ω) with decreasing disorder has been found. For Ts > 200 °C characteristic structures occurred at energies comparable with critical points of the crystalline state. The absolute value and the line shape of ϵ(ω) however are different for single crystals and films.
Formation of twist boundaries in germanium deformed in torsion
Authors: Wagner R. , Wöhler F. D. , Haasen P. 
Published: July 2007

AbstractGermanium single crystals of [111] orientation were deformed in torsion at several temperatures to various specific angles φ0 [deg/cm]. Slip lines showed the deformation to occur only on (111) planes. The plastic torsion was stable with annealing up to 900 °C. Electron transmission showed that (111) twist boundaries with hexagonal dislocation networks are formed already during deformation at 685 °C. The percentage of network dislocations increased with φ0 and with the temperature of annealing. The fraction of screw dislocations increased by 15% during an anneal up to a total of about 80%. The dislocation arrangement after annealing closely corresponds to theoretical expectations.
The atomic configuration of screw dislocations in the b.c.c. lattice
Authors: Diener G. , Heinrich R. , Schellenberger W. 
Published: July 2007

AbstractA new simplified model for the calculation of the atomic structure of screw dislocations in b.c.c. metals is suggested. The results for the two different equilibrium configurations are discussed. They are in good agreement with those obtained by lattice relaxation techniques. In contrast to the high energy metastable configuration, the low energy configuration was found to be asymmetric with respect to the {112} planes; therefore, two energetically degenerated equilibrium configurations are possible.
The asymptotic behaviour of wannier functions
Authors: Lix B. 
Published: July 2007

AbstractThe treatment of many problems in electron theory is considerably simplified if the Wannier representation is used, provided the Wannier functions are well localized and decrease exponentially for large distances from their centres. It is shown that in the case of band groups with point and line degeneracies it is possible to define pseudo‐Wannier functions with exponential tails, which everywhere in the crystal deviate as little from conventionally defined Wannier functions as one wants. The question how far the Wannier functions extend with appreciable magnitude from their centres into the crystal is not considered.
Anisotropie current decay in tellurium due to the acousto‐electric effect
Authors: Arnold J.‐U. , Nimtz G. , Roth E.‐P. 
Published: July 2007

AbstractThe time dependence of the current decay due to the acousto‐electric effect was measured in p‐type tellurium at 77 K. The dependence of the current decay on the crystallographie orientation, the carrier density, and the carrier mobility was investigated. The experimental results for drift fields parallel to the x‐ or y‐axis agree with the theory of acousto‐electric amplification. A current decay was also found for a drift field along the z‐axis. This coupling is about a third of that in the x‐direction, but according to the theory of piezoelectric effect in tellurium no coupling is expected.
Electromultipole interaction and paramagnetic relaxation in ruby. III. Distant wing shape of EPR lines
Authors: Peskovatskii S. A. 
Published: July 2007

AbstractIt is found that the wings of the EPR lines in ruby are an order of magnitude longer than they should be according to the theory of the magnetic dipole‐dipole broadening. The observed wings and calculated shape of the lines broadened by the electric quadrupole‐quadrupole interaction [I] are in good agreement.
X‐ray emission spectra of manganese borides
Authors: Shashkina T. B. 
Published: July 2007

AbstractX‐ray Kβ5‐emission spectra from manganese and five borides have been obtained under primary and secondary excitation. The investigation of the borides included also measurements of the B K‐emission band of each compound and of pure boron. The resolution for the Mn K‐band was 0.2 eV and for the B K‐band 0.1 eV. The structures of the spectra of both components are compared and discussed in view of their concentration dependence.
On the theory of optical interband transitions in the presence of resonance scattering
Authors: Keiper R. 
Published: July 2007

AbstractThe effect of resonance states on the behaviour of the density of states ϱ(E) and the absorption coefficient α(ω) is studied for a doped semiconductor having a special band structure. It is shown that if the photon energy is higher than the absorption edge (ħ ω > Eg) characteristic thresholds and peaks appear in the absorption spectrum, the magnitude and position of which depend on the impurity concentration n, the energy Er, and the width Γr of the resonance levels, the effective masses mv and mc of the valence and conduction bands.
Optical properties and electronic structure of white tin
Authors: Schwarz H. 
Published: July 2007

AbstractThe optical properties of a tin single crystal and of a tin film deposited by vacuum evaporation were measured in the energy range from 0.5 to 5.5 eV in dependence on temperature and crystal orientation. The absorption curves differ appreciably for the two polarizations and show many structures which become more pronounced at low temperatures. These structures in the optical absorption are related to regions of the band structure where the bands are nearly parallel. The results show that existing band structure calculations of tin are accurate near the Fermi energy, for energies above and below EF, however, the shape of some of the bands should be corrected.
Magnetic properties of DyAsO4 at low temperatures
Authors: Kahle H. G. , Klein L. , Müller‐Vogt G. , Schopper H. C. 
Published: July 2007

AbstractThe magnetic properties of DyAsO4 were investigated by specific heat and magnetic moment measurements. The specific heat shows two λ‐type anomalies, one at TN = 2.44 K caused by a magnetic phase transition, and the other at Tc = 11.2 K. Magnetic measurements show an antiferromagnetic ordering perpendicular to the optical axis with magnetically nonequivalent a‐ and a′‐axes. Exchange integral and critical parameters were determined in different ways and compared with theory. The splitting of the two lowest components (Kramers' doublets) which is constant above Tc becomes temperature dependent below Tc; it increases with decreasing temperature and originates from a cooperative phenomenon.
Microscopic theory of lattice dynamics for ionic crystals. I. Theoretical framework
Authors: Gliss B. , Zeyher R. , Bilz H. 
Published: July 2007

AbstractA microscopic theory of lattice dynamics of the ionic crystals is developed in the self‐consistent Hartree‐Fock approximation. The work is based on a splitting of the dynamical matrix into two parts, a rigid ion and a polarization part. For ionic crystals such a splitting is especially convenient, because here the rigid ion contribution represents the dominant contribution to the total dynamical matrix. In the theory presented, this part results from the classical Coulomb interaction of the cores and electrons among themselves and with each other within the Heitler‐London approximation. It is obtained without using perturbation theory, therefore no excited states are involved. For a special choice of the localized wave functions the energy expression of Löwdin [23] and Lundqvist [24] is obtained which describes the perturbation of the electron density during a lattice mode by a rigid displacement of localized electron densities including exchange effects. The polarization part takes into account virtual electronic transitions caused by a weak driving electron‐ion potential additively to the rigid ion part. This part is determined by a variational method.
The green function method in the theory of magnetic thin films. I. Calculation of a general expression for the magnetization of magnetic thin films
Authors: Brodkorb W. 
Published: July 2007

AbstractAn anisotropic magnetic thin film is considered with atomic spins, S, arranged in a lattice with inversion symmetry and arbitrary surface orientation. The Hamiltonian of the system contains the Zeeman term, the Heisenberg exchange term, and a term for the uniaxial volume anisotropy in the film plane. An implicit system of equations calculated on the basis of the Green function method is given in order to estimate all layer magnetizations in the film.
Interaction of singlet excitons in organic materials with an absorbing surface
Authors: Kallmann H. , Vaubel G. , Baessler H. 
Published: July 2007

AbstractIt is shown both experimentally and theoretically that the fluorescence of an anthracene crystal is strongly quenched if the crystal is excited close to a metal layer. The fluorescence is reduced by a factor of two if the penetration depth of the exciting radiation is equal to the diffusion length of singlet excitons. This is caused by energy transfer taking place across distances of 10 to 30 Å. The experimental values for the energy‐transfer parameters are in agreement with a theoretical estimate assuming a metal absorption index of about one. This energy‐transfer process also influences the fluorescence decay time. Its significance for the probability of exciton induced electron ejection from the crystal into a metallic or non‐metallic electrode is discussed.
Anomalous skin‐effect in inclined magnetic field
Authors: Naberezhnykh V. P. , Tsymbal L. T. , Purchinskii M. S. 
Published: July 2007

AbstractThe dependence of the effective depth of penetration of an electromagnetic field in a metal on the inclination angle of the magnetic field to the sample surface and the temperature is studied by the radio‐frequency size effect on Cd under conditions of anomalous skineffect and l ≫ D.
The magneto‐optic Kerr effect and Faraday rotation of CdCr2S4 for radiation between 0.1 and 4 eV
Authors: Wittekoek S. , Rinzema G. 
Published: July 2007

AbstractThe complex polar Kerr effect (rotation and ellipticity) of CdCr2S4 has been measured between 1.6 and 4 eV at temperatures between Tc = 84 and 6 °K. Four well separated magneto‐optical transitions have been identified. Two sharp peaks at 2.12 and 2.29 eV are attributed to the Cr3+ crystal field transitions 4A2 → 2T2 and 4A2 → 4T1, respectively. Crystal field parameters satisfying the optical data have been derived. Only one transition at 1.9 eV shows a magnetic red‐shift. It depends on sample‐stoichiometry and doping. The strongest resonance is found at 3.4 eV and is assigned to a charge transfer transition of an electron from a p‐orbital of sulphur to a chromium orbital. The Faraday rotation in the infrared region is also reported and shown to be caused by the charge transfer transition at 3.4 eV.
Dynamical theory of AIII BV‐type crystals with fractional and variable charges of ions
Authors: Korol E. N. , Tolpygo K. B. 
Published: July 2007

AbstractAn adiabatic theory of lattice vibrations is developed for sphalerite type crystals, based on the concept that each pair of nearest atoms is bound by two electrons which state is a superposition of three parts, both electrons “belong” to one or the other atom or form a σ‐bond between them. The distortion of the electron wave function by atomic vibrations is described by a system of dipole moments of the electron shells 𝒫n, the coefficients of mentioned linear combination change by changing the mean charges of ions en. The adiabatic potential, containing all 𝒫n, en, and the equations of motion are introduced. For long wavelength oscillations the electrodynamical forces due to currents which flow along n‐n′‐bonds and which appear by the change of the charges en, become of great importance. Concrete calculations and comparisons with an experiment are given for GaAs.