bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intensity Distributions of the K Emission Spectra of Iron
Authors: Sørum H. 
Published: July 2007

AbstractA curved crystal spectrometry is applied for the study of the electron excited (30 kV) FeK emission spectra. No fine structure is directly seen in the α1,2 and β1,3 lines, but the lines are strongly asymmetric. The asymmetry is due to relatively strong low energy satellites, probably caused by the radiative Auger effects K → LV, K Deutsche Forschungsgemeinschaft MV, in addition to interactions between the final state hole and the unfilled 3d level for β1,3; and to unresolved splittings of the LIII and LII levels for α1 and α2. Weak high energy satellites are also present for the same lines and most likely due to a spectator vacancy in the M level and/or in the valence band V. The Kβ5 band is corrected for background, continuous radiation, self‐absorption, and overlap with β1,3. The intensity maximum of Kβ5 is (2.56 ± 0.1) eV below the Fermi energy. The FWHM value for α1 is (2.60 ± 0.05), for α2 (3.02 ± 0.05), for β1,3 (4.04 ± 0.05), and for β2,5 (5.56 ± 0.05) eV. The index of asymmetry for α1 is (1.57 ± 0.05), for α2 (1.26 ± 0.05), and for β1,3 (1.77 ± 0.05). The spin—Orbit splitting between the 3p3/2 and the 3p1/2 levels obtained from the Lorentzian fit for β1,3 is (1.22 ± 0.05) eV, whereas Hartree‐Fock calculations give 1.58 eV.
Excition Transfer Between the Manganese Ions in the Semiconductor Alloy Cd1−xMnxTe With x = 0.51
Authors: Müller E. , Gebhardt W. , Gerhardt V. 
Published: July 2007

AbstractThe 2eV luminescence in Cd0.49Mn0.51Te is studied by use of time resolved spectroscopy. A decay time of 24 μs is derived. Slow radiationless energy transfer between Mn2+ ions is observed. The change of the luminescence bandshape during decay suggests a random distribution of excited 4T1‐states with a width of 760 cm−1. These results are confirmed by experiments with varying excitation frequency. A weak residual 2 eV‐luminescence is observed under subresonant conditions. Its intensity is found to be proportional to the square of the laser power.
The Diffusion in the Exciton System and the Nonconservation of Excitons
Authors: Davidović‐ristovski G. S. , Ristovski Lj. M. , Tošić B. S. 
Published: July 2007

AbstractThe diffusion of excitions is considered in systems in which the number of excitons is not conserved. It is shown that in such a system stationary and nonstationary diffusion processes appear, and the corresponding diffusion cofficients are defined and calculated for a simple cubic crystal in the two level approximation. The results obtained show that in this system a nonstationary diffusion process is dominant, and that both diffusion processes are caused by nonconservation effects.
Luminescence Properties of an MA‐Type Center in KCl:SrCl2 and KCl:CaCl2
Authors: Bosi L. , Nimis M. 
Published: July 2007

AbstractLifetime measurements are performed on KCl:SrCl2 and KCl: CaCl2 by light excitation in the spectral region of the Z4‐center absorption band. The main results are as follows: i) confirmation of Briginets' discovery, in KCl:SrCl2, of an MA‐type center (i.e. an M‐center perturbed by a foreign positive ion), whose absorption band strongly overlaps the Z4‐center one; ii) evidence of an analogous MA‐type center also in KCl:CaCl2; iii) explanation of the puzzling results on the Z4‐center luminescence, obtained by Nishimaki, who found two emission bands for this center, in KCl doped with Ca, Sr, Ba; iv) assignment of the highest energy Nishimaki emission band to the MA‐type center and not to the Z4‐center. An analysis of the lifetime values for the unperturbed and for the perturbed M‐center in KCl, taking into account the data previously obtained by the authors for the MA‐center in KCl:NaCl and KCl:LiCl, shows their dependence on a relaxation parameter. A critical examination of the matter is also given: in particular, no contradiction is found with Briginets' hypothesis of a similarity between the Z4‐center and the N1‐center in undoped KCl crystals, although this analogy cannot be proved by measurements presented here.
Dielectric Relaxation in Smoky Quartz at Very Low Temperatures
Authors: Saint‐Paul M. , Frossati G. 
Published: July 2007

AbstractAudiofrequency dielectric measurements down to 4 mK on γ‐irradiated quartz are reported. At the lowest temperatures, the mean relaxation rate increases with dipole concentration and shows a field dependence in small ac measuring fields. Similar properties are observed in other dielectric systems containing randomly distributed electric dipoles.
On Charge Carrier Photogeneration Mechanisms in Organic Molecular Crystals
Authors: Silinsh E. A. , Kolesnikov V. A. , Muzikante I. J. , Balode D. R. 
Published: July 2007

AbstractAn extended phenomenological model of photogeneration mechanisms in organic molecular crystals is proposed which describes intermediate and final stages of multi‐step photogeneration processes in terms of a modified Onsager approach. It is shown that the intermediate geminate charge pair (CP) states can be populated through two independent competitive pathways: viz. via autoionization and subsequent hot electron thermalization in terms of a ballistic model and via optical charge transfer (CT) transitions. The thermalization processes and their dependence on photon energy, temperature, and electric field are studied in some detail. It is demonstrated that the threshold spectral dependence of intrinsic photoconductivity quantum efficiency β(hv) in anthracene‐type crystals is mainly determined by the spectral dependence of dissociation efficiency Ω(hv) of the intermediate CP‐states and can be approximated by Onsager's formula.
The Isotopic Shift of the Excitonic Absorption Lines in Cu2O Crystals
Authors: Bobrysheva A. I. , Jeru I. I. , Moskalenko S. A. 
Published: July 2007

AbstractIt is shown, that the isotopic shifts of the excitonic series in Cu2O crystals are caused by changes of the intra‐ and interband electron (hole)—phonon scattering, related to the change of phonon amplitude with isotopic mass. Estimates of the energy shifts of the excitonic series are obtained on the base of the Fröhlich electron—phonon interaction.
On the Problem of a Power‐Law Localization of Charge Carriers in a Two‐Dimensional Disordered Semiconductor
Authors: Bonch‐Bruevich V. L. 
Published: July 2007

AbstractConditions are studied under which the wave functions of localised charge carriers possess a power‐law asymptotics. It is shown that in a disordered semiconductor conditions may be realised under which such an asymptotics has no place to develop: there are no asymptotic regions. The states, however, remain localised in the sense that the static conductivity tends to zero at T → 0.
Absolute Hydrostatic Deformation Potentials of Tetrahedral Semiconductors
Authors: Vergés J. A. , Glötzel D. , Cardona M. , Andersen O. K. 
Published: July 2007

AbstractThe “absolute” hydrostatic deformation potentials of several band states of germanium and silicon are calculated with the LMTO‐ASA method. It is found that for the top valence band state dE/ d In V ≈︁ −8 eV. The results are compared with experimental data available. They agree with calculations based on empirical pseudopotentials provided one assumes dV0/d In V ≈︁ 0, where V0 is the spatially averaged pseudopotential. In order to obtain agreement with empirical tight binding results one must introduce a volume dependence of the term energies. Using the calculated deformation potentials, the dependence of the lattice constant on doping measured for n‐ and p‐type germanium, silicon, and GaAs is discussed.
Theoretical Treatment of the Diffusion Coupled with Reaction, Applied to the Example of a Binary Solid Compound MX
Authors: Maier J. , Schwitzgebel G. 
Published: July 2007

AbstractIt is shown, that the coupling of diffusion processes with reactions can be treated as a formal ambipolar diffusion of ensembles of particles, which are conserved in the reaction scheme. In this way an extension of the flow equations to a complex defect chemistry becomes possible, as exemplified by the ionization processes of the ionic point defects in a binary solid MX. In a first approximation Fick's laws with generalized diffusion coefficients are obtained. The boundary conditions are formulated for several important cases by considering the equations of balance of the conservative ensembles. It is further shown, how the new evaluation of the usual electrochemical measurements of transport quantities (e.m.f., polarization and permeation) has to be performed. Additional terms, caused by the ionization processes, appear in all evaluation formula.
Polariton Theory in Electron—Hole Configuration Space. Bulk Solution for a Wannier‐Type Model
Authors: Stahl A. , Balslev I. 
Published: July 2007

AbstractA pair of coupled wave equations for electromagnetic radiation and electron‐hole pairs in the Wannier limit is solved for the case of an unbounded crystal. The solution is discussed with respect to the following phenomena: (i) excitonic resonances, (ii) Coulomb enhancement of continuum, (iii) local current structure, (iv) spatial dispersion.
Band Effects on Charge Ordering in Fe3O4
Authors: Lorenz B. , Ihle D. 
Published: July 2007

AbstractThe stability of the electronic long‐range order in Fe3O4 with respect to the band term is investigated using a spinless fermion model with Coulomb interactions between nearest (U1) and next nearest neighbours (U2), where U1 > t > U2 (t overlap integral) is assumed. This model is treated by perturbation theory up to third order in t and an effective spin Hamiltonian is constructed. From an approximate solution the long‐range order condition at T = 0 is found to be \documentclass{article}\pagestyle{empty}\begin{document}$ t< 0,85\sqrt[3]{{U_1^2 U_2 }} $\end{document} and thedependence of the Verwey transition temperature TV on t is calculated. The experimentally observed pressure dependence of TV is explained.
Formation of Lattice Defects by Two‐Photon Excitation in Alkali Halides
Authors: Provoost J. , Debergh P. , Hoebeeck G. 
Published: July 2007

AbstractMeasurements by two‐photon excitation of the second harmonic of a ruby laser are made of the formation of lattice defects in four alkali halides; RbBr, KBr, RbI, and KI. The spectra and measured curves reveal the crucial role of the experimental conditions in the defect formation. In the measured alkali halides the F and H bands at LHeT are thermally stable, but can be bleached by a very small amount of probe light. Time resolved measurements in RbBr show that the ratio of the STE and F centre absorption depends on the intensity of the laser beam. In KBr the possibility is shown of excitation at LHeT with the second harmonic of the ruby laser. In RbI the F band is formed even at LHeT, and in KI the F′ band at LHeT is larger than the F band after two‐photon excitation.
New Theoretical Method for Studying Elementary Excitations in Crystalline Disordered Alloys. Application to Phonons in NixPt1−x
Authors: Gómez‐santos G. , Yndurain F. 
Published: July 2007

AbstractA new method for studying elementary excitations in disordered crystalline binary alloys is presented. The complex self‐energy due to positional disorder is calculated in a Bethe lattice and taking proper account of the short‐range order. The crystalline alloy is then described by a non‐hermitean Hamiltonian which includes the calculated self‐energy. Densities of states, as well as dispersion relations, can be calculated. The method is applied to the study of lattice vibrations in crystalline NixPt1–x random alloys. The results are in good agreement with neutron diffraction experiments. The experimentally observed phonon densities of states, lineshapes, and dispersion relations are well described in the model.
Influence of surface stress on the surface elastic waves in anisotropic cubic crystals
Authors: Velasco V. R. 
Published: July 2007

AbstractThe effects of surface stress on the surface dynamical properties of cubic crystals are discussed. Analytic expressions for the dispersion relations of surface waves propagating along [100] and [110] directions in the (001) surface are obtained. It is found that these surface waves are dispersive and that the dispersion relation exhibits a cut‐off. The same is true for an arbitrary direction of propagation. An application is made for W. It is found that the shifts in the velocities of Rayleigh waves due to the surface stress can not be detected by using the experimental techniques available now. The possible effects of surface stress on the thermodynamical properties of cubic crystals are also discussed briefly.
Electronic excited state and the phenomena of photo‐induced polarization and depolarization
Authors: Prakash J. 
Published: July 2007

AbstractThat the activation energy for the orientation of impurity—vacancy dipoles in the electronic excited state (ees) should be less than that required in the electronic ground state (egs) is not the sufficient condition for the occurrence of PIP and PID. It is observed that the activation energy is not the only parameter which controls the occurrence of PIP and PID. The fundamental relaxation time also participates in deciding the situations in which PIP and PID take place. The necessary condition found, is that the product of the activation energy and the fundamental relaxation time in ees should be less than the corresponding value in egs.
The dielectric response of a charge density wave (CDW) distorted electron—phonon system in the precritical region II. Macroscopic dielectric function and conductivity
Authors: Heiner E. 
Published: July 2007

AbstractStarting with a selfconsistent approximation (I) for the calculation of the selfenergies of the electron and phonon system, the dielectric function is calculated in the small momentum limit for a quasi‐one‐dimensional system in the precritical region above the Peierls temperature.
Symmetrical grain boundaries with special angles and their coincidence site lattices
Authors: An Nguyen , Worm G. , Herrmann R. 
Published: July 2007

AbstractA simple method for an explicite calculation of the coincidence site lattices is presented. This method based on clear geometrical conditions is convenient for the interpretation of experimental results. The indices of the grain boundary planes for symmetrical rotation axes are estimated. The type and the orientation of the Bravais lattice of the coincidence site lattices in cubic crystals are obtained.
Diamagnetic excitons and the indium antimonide energy band parameters
Authors: Efros Al. L. , Kanskaya L. M. , Kokhanovskii S. I. , Seisyan R. P. 
Published: July 2007

AbstractThe oscillatory absorption edge spectrum of InSb crystals exhibiting the discrete structure of the Wannier‐Mott exciton at H  0 is studied at 1.8 K in magnetic fields of up to 80 kOe. The experimental data obtained are analyzed with a computer taking into account the excitonic nature of the phenomenon and the effect on the Landau levels of the nonlocality of potential resulting from the electron—electron exchange interaction. A set of band parameters is presented which provides a minimum discrepancy between the theoretical and experimental spectra of not more than 0.65 meV per datum point: Ep  23.42 eV, F  − 1.18, N1  − 0.33, γ2  36.41, γ2   15.95, γ3  16.99, k  15.22, q  0.31, χ0  17.9. The possible contribution of the higher bands and the reasons for disagreement with other avialable parameters are discussed.
Electronic structure of intermetallic compounds by interpolation schemes
Authors: Rennert P. , Gläser U. H. , Hergert W. , Timoshevskii A. N. 
Published: July 2007

AbstractThe applicability is studied of a d‐band LCAO interpolation scheme and of the recursion method to intermetallic compounds with CsCl structure of two transition metals. Input data are APW energy eigenvalues, needed for this purpose at only a few points of high symmetry in the Brillouin zone. The interpolation scheme works with an accuracy that is sufficient for calculating densities of states, but works much faster than the APW calculation. From the LCAO hopping parameters local densities of states are obtained with the recursion method.
Coherent‐potential approximation for vibrations in Ga1—xInxSb and Ga1—xInxAs mixed crystals
Authors: Kleinert P. 
Published: July 2007

AbstractThe vibrational properties of the mixed crystals Ga1—xInxAs and Ga1—xInxSb are investigated using the coherent‐potential approximation (CPA). These III—V systems switch from one‐mode to two‐mode behaviour as the composition is changed. Results are obtained for a one‐dimensional model including self‐consistently mass defects and force constant changes. The calculated density of states and the dielectric susceptibility are compared with results of the mass CPA. In addition, a three‐dimensional CPA Bethe lattice treatment is carried out to calculate the optical properties of these disordered systems showing mixed‐mode behaviour. The force‐constant change is included by a virtual‐crystal interpolation. The theory explains the mode switching behaviour and agrees fairly well with experimental peak positions and line shapes of the response function.
Elastic‐wave surfaces in solids
Authors: Ledbetter H. M. , Kriz R. D. 
Published: July 2007

AbstractBased on Christoffel‐equation solutions, some interesting wave‐surface topological features are described for anisotropic media. These features include crossovers of transverse—longitudinal surfaces and continuous transverse—longitudinal mode conversion over a single surface. For orthorhombic symmetry (mmm), crossovers of transverse—transverse surfaces occur for all crystals: the transverse surfaces interconnect and form a single surface. Beyond this, some orthorhombic crystals exhibit a longitudinal—transverse crossover that causes all three surfaces to interconnect into a single surface. Crossover of longitudinal and transverse surfaces means that a transverse wave velocity will exceed a longitudinal wave velocity. A longitudinal—transverse mode conversion means that both longitudinal and transverse modes exist on the same wave surface.
Cellular density functional theory of the heat of formation of disordered simple alloys
Authors: González D. J. , Alonso J. A. , Iñiguez M. P. 
Published: July 2007

AbstractA cellular model is used to calculate the heat of formation in disordered solid MgxCa1—x alloys. The computations of the electron density and the energy are performed by the density functional formalism. The influence of the cell‐partitioning is analyzed. Neutral atomic spheres are the most convenient type of atomic cells for completely disordered alloys because an optimum number of physically satisfactory matching conditions can be imposed at the surface of the neutral atomic cells.
Integral representation of the incoherent field in disordered materials. V. Wave Diffusion in a Correlated Medium
Authors: Lenk R. 
Published: July 2007

AbstractBased on a generalized representation obtained in IV, the diffusion current in a macroscopically homogeneous disordered medium with varying wave intensity or quantum particle density, respectively, is determined. The conductivity can be calculated from the averaged diffusion coefficient. In the limit of long mean free path the theory essentially confirms the result of a semi‐classical treatment where each scatterer together with its correlation cloud acts as an effective scattering element whose scattering properties are influenced by interference effects.
Conduction spin density and knight shift of copper
Authors: Bross H. 
Published: July 2007

AbstractUsing Chodorow's potential the energy eigenvalues and wave functions of metallic Cu are obtained by the MAPW formalism. In accordance with other investigations the Fermi surface is in close agreement with de Haas‐van Alphen experiments. The Fermi‐surface average of the probability 〈Ψnk(0)|2〉FS yields the spin density at the nuclear sites. Due to many‐body corrections of the Pauli spin susceptibility a reliable value of the Knight shift cannot be derived from first principles. By comparing with the experimental value of the Knight shift it is found that many‐body effects enhance the Pauli susceptibility by a factor of 1.25.
Dynamics of two‐spin cluster in spin glass III. Magnetization process at finite, but low temperature
Authors: Heber G. , Zymierska D. , Beyer H. 
Published: July 2007

AbstractBased on the two‐spin cluster model of spin glass, the magnetization process at low T is investigated. The short‐range inter‐cluster interaction is taken into account by excitation waves, treated as free Bosons. They feel, however, additionally a Weiß‐type molecular field of long range. For certain parameter sets in the range T < TF magnetic instabilities are found, as well as metastable branches of m(H, T)‐curves, leading to magnetization jumps, induced by external magnetic field. The phase diagram shows a line of first‐order transitions and a point of a higher‐order transition. Hysteresis and domain patterns are the usual behaviour in this region.
Electron state associated with the unreconstructed (111) surface in diamond
Authors: Persson Astrid 
Published: July 2007

AbstractA calculation of the electron states associated with the unreconstructed (111) diamond surface is performed using Slater‐Koster parameters evaluated from first principles. The calculation gives a surface band in the lower half of the band gap. Close agreement with a self‐consistent pseudopotential calculation is found when the matrix elements of the surface atom is modified to contain non‐spherical parts of the potential.
Repulsive energy and the grüneisen parameter of alkali halides calculated on the basis of a quantum‐statistical ab initio theory
Authors: Kucharczyk M. , Olszewski S. 
Published: July 2007

AbstractThe Grüneisen parameter of alkali halides is calculated by an ab initio quantum‐statistical method and then compared with the experimental data. The crystal model applied assumes the crystal ions to be compressible but impenetrable spheres. The ions are described with the aid of a modified Thomas‐Fermi theory with exchange. At the next step it is possible to calculate the energy needed to transform the system of the non‐interacting ions into the ionic system represented by the crystal lattice. This calculation allows for an ab initio estimate of the parameters entering the Born, or the Born‐Mayer, repulsive part of the crystal energy. The parameters are then used in the calculation of the Grüneisen parameter and its dependence on the crystal compression.
Debye‐ waller factors for alkaline earth oxides
Authors: Singh R. K. , Sanyal S. P. 
Published: July 2007

AbstractA theoretical calculation of the Debye‐Waller factors and the mean square displacements is carried out for the alkaline earth oxides. The eigenfrequencies and eigenvectors required for this purpose are obtained from the recently proposed eight parameter generalised three body force shell model. A discussion in the light of available experimental data and earlier theoretical results revealed that the values are in excellent agreement in the cases of MgO and CaO and follow a systematic trend in the case of other members of the alkaline earth oxide family.
Dielectric and anharmonic behaviour of alkali halide crystals
Authors: Shanker J. , Sundaraj R. 
Published: July 2007

AbstractThe dielectric and anharmonic behaviour of alkali halide crystals is studied by determining the volume derivatives of low frequency dielectric constant and polarizability. An interionic force model which takes into account the contributions arising from the short range overlap repulsion and the van der Waals interactions is used in calculations. The implicit and explicit temperature derivatives of low frequency and high frequency dielectric constants are obtained separately for all the alkali halide crystals with NaCl and CsCl structures. The anharmonic contribution to the dielectric constant is calculated using theoretical models due to Szigeti and Havinga. The recent analysis of pressure dependence of effective charge parameter and dielectric constant of ionic crystals performed by Varotsos is shown to be invalid.