bluuebunny/crossref_metadata_2025_split huggingface dataset:
Positron Annihilation in Si and Ge
Authors: Aourag H. , Belaidi A. , Kobayasi T. , West R. N. , Khelifa B. 
Published: July 2007

AbstractA computational technique is developed to evaluate electron and electron—positron momentum densities in silicon and germanium and the use of these to provide means of interpreting the k‐space densities obtained by experimentalis's using the two‐dimensional angular correlation of positron annihilation radiation technique (2D ACAR). As a consequence of the good agreement observed in the momentum densities and the LCW folded data obtained for silicon and germanium the independent particle approximation (IPM) coupled with the use of electron pseudo‐wavefunctions represent an excellent starting point for a systematic many‐particle description of the process, since significant deviations from the experimental angular correlation distribution can be ascribed to the electron—positron and electron—electron interactions.
The Temperature Dependence of Dielectric Response in Relation to Distribution Functions
Authors: Kliem H. , Arlt G. 
Published: July 2007

AbstractThe transformation of temperature dependent dielectric relaxation spectra χ″(ω, T) into temperature independent distribution functions of activation energies is derived and demonstrated at the example of polyethylmethacrylat. Linear superposition of thermally activated dielectric relaxation processes is anticipated. The calculated distribution function describes the observed variation of the relaxational curves with temperature and yields for χ″(χ′) in the complex plain Cole‐Davidson plots.
Temperature Dependence of the Elastic Constants for Biaxial Nematic Liquid Crystals
Authors: Monselesan D. , Trebin H.‐R. 
Published: July 2007

AbstractThe elastic constants Kij of the Frank‐Oseen energy density for uniaxial nematic liquid crystals depend on the Maier‐Saupe order parameter S and hence on temperature. Longa et al. recently used an extended Landau‐Ginzburg‐de Gennes theory to expand the functions Kij(S) up to fourth order in S. Here, a similar procedure is applied for the elastic energy density of biaxial nematic liquid crystals. The three chiral and 15 achiral constants are expressed as fourth‐order polynomials in the order parameter S and the degree of biaxiality T. Via the temperature dependence of the quantities S and T also the temperature dependence of the elastic constants is fixed.
H‐Centre in LiF‐H−
Authors: Egranov A. V. , Nepomnyachikh A. I. , Otroshok V. V. , Chernyago B. P. 
Published: July 2007

AbstractThe H‐centre in LiF is studied by optical and ESR techniques. The centre is produced by reaction between H and H‐centres. The H‐centre ESR spectrum shows three broad lines which are due to the hyperfine interaction of an unpaired electron with the two protons. The resolved superhyperfine structure (as in case of F‐centre) arises from the interaction with the lithium nuclei in a first shell and the fluoride nuclei in a second shell. Optical absorption band of the H‐centre at 5.05 eV is similar to that of the F‐band, only slightly shifted to higher energies. The centre has the character of molecule‐ion as well as of F‐centre.
Lattice Dynamics of Nitrogen and Carbon Dioxide
Authors: Binbrek O. S. , Higgs J. F. , Anderson A. 
Published: July 2007

AbstractA simple force constant model is used to calculate the normal mode frequencies and eigenvectors of the cubic crystals α‐N2 and CO2. Good agreement with spectroscopic data is obtained for the lattice frequencies, and crystal field splittings of the molecular modes are found to be small in all cases. For α‐N2, the calculations suggest that the non‐centrosymmetric structure is more likely, but the possibility that this result is merely a consequence of the larger number of parameters involved cannot be ruled out. For CO2, the intermolecular CO interactions appear to play a relatively minor role.
Partial and Total Electronic Stoppings of Solids and Atoms for Energetic Ions
Authors: Kaneko T. 
Published: July 2007

AbstractPartial and total electronic stopping cross sections of solids and atoms for protons are estimated by the recently developed wave packet theory and the Lindhard theory. The wavepacket theory presents the one‐shell dielectric function for the bound electrons (BE's) in the framework of RPA by adopting the momentum space representation, where the BE's are treated as an interacting electron gas. Numerical estimation of the stoppings are performed over a wide specific energy range, i.e., 1 to 104 keV/amu, on the basis of the independent shell model. The oscillatory behavior of the stopping cross sections are also shown with respect to target atomic number. The calculated results are in good agreement with the data.
Analysis of Crystal Binding and Structural Phase Transition in Alkaline‐Earth and Alkali Chalcogenides
Authors: Chaturvedi S. D. , Sharma S. B. , Paliwal P. , Kumar M. 
Published: July 2007

AbstractAn analysis of crystal binding and structural phase transition is presented using an analytical potential form for the overlap repulsive energy derived by Harrison from quantum mechanical considerations. The potential model is applied to calculate the cohesive energies, bulk modulus, and its pressure derivative for fifteen alkaline‐earth chalcogenides and fourteen alkali chalcogenides. Calculated values of bulk modulus are found to exhibit empirical correlationship with unit cell volume. The problem of relative stability and structural phase transition is also investigated for alkaline‐earth chalcogenides. Values of transition pressure are obtained and found to present good agreement with experimental data.
The Influence of Hybridization of the Impurity and the Conduction Bands on the Density of States of Doped Semiconductors
Authors: Radjenovic B. , Tjapkin D. 
Published: July 2007

AbstractA two‐band model of a doped semiconductor is presented. The model includes both, impurity and conduction bands as well as their hybridization. Hybridization of impurity band with the unperturbed conduction band is discussed in more detail. The density of states of the impurity band of Si:P is calculated using the modified Matsubara‐Toyozawa method on the basis of the suggested two‐zone model. Physical aspects of the results obtained are analyzed as well as possible connections with experimental facts.
Luminescence Decay Times of the Sb3+, Pb2+, and Bi3+ Ions in Alkaline‐Earth Sulfides
Authors: Donker H. , Yamashita N. , Smit W. M. A. , Blasse G. 
Published: July 2007

AbstractThe luminescence decay times of Tl+‐type ions in MgS, CaS, SrS, and BaS are measured as a function of temperature from 4.2 to 150 K. By applying a three‐level model, the energy difference ΔE between the lower excited states 3T1u(3P1) and 3A1u(3P0) and the transition probabilities from the two excited states to the ground state 3A1g(1S0) are derived. The values of the parameters are compared with each other and with those for alkaline‐earth oxides.
Propagation of Gamma‐Radiation through a Resonance Medium with RF Modulated Magnetic Hyperfine Interaction
Authors: Sadykov E. K. , Skvortsov A. I. 
Published: July 2007

AbstractThe influence of the rf perturbation (magnetization reversal) in the magnetically ordered system on its Mössbauer spectrum (MS) is discussed theoretically. Similarly to the traditional MS the behaviour of the time gated MS in this condition is analysed as an extension of the time‐dependent Mössbauer spectroscopy methodology to the magnetization dynamics problem. This problem is discussed on the basis of Blume's theory generalized for time dependent hyperfine interactions. The calculations in the framework of a rotating field model reveal a remarkable distortion in MS at nonresonant radio frequencies. The phenomenon of supression of the nuclear Zeeman structure under rotating rf field is revealed. The time‐dependent effects in MS can be used to understand the high frequency magnetization reversal processes in magnetic materials.
The Intra‐ and Intersublattice Exchange Interactions in RFe12xTx Intermetallics
Authors: Stefański P. , Szlaferek A. , Wrzeciono A. 
Published: July 2007

AbstractThe experimental values of Curie temperatures of RFe12−xTx (R = rare earth, T = V, Ti, Si, Cr) are used to calculate the effective exchange coupling constants in iron sublattice and between rare earth and iron sublattices. A mean field approximation is used. Values of molecular field, Bmol, acting on the rare earth ion are also established. The coupling constant in Fe sublattice is found to be the largest for T = V; JFeFe = 10.14 × 10−22 J. The molecular field has its maximum value for R = Sm in each series of RFe12−xTx compounds.
About the SERS Phenomenon I. The Cross‐Section in Adiabatic Perturbation Theory
Authors: Polubotko A. M. 
Published: July 2007

AbstractThe theory of SERS (surface enhanced Raman scattering) is developed. First the light interaction with molecules is considered. The wave functions of the molecule are received in the first order of the adiabatic perturbation theory. Then the cross‐section of Raman scattering with the dipole and quadrupole light interaction with a molecule taken into account is obtained.
The Parametric X‐Ray Radiation in Case of Three‐Wave Asymmetric Diffraction
Authors: Dubovskaya I. Ya , Savchuk G. K. 
Published: July 2007

AbstractThe spectral and angular distributions of parametric X‐ray radiation from relativistic electrons in the case of three‐wave asymmetric coplanar diffraction are obtained. A detailed numerical calculation of angular and spectral distributions in Si is derived for the case of arbitrary angle of particle incidence on the crystal target surface.
Two‐Photon Spectroscopy of PbMoO4 Single Crystals Indirect Interband Transitions
Authors: Efendiev Sh. , Darvishov N. , Shakhdgan S. , Gavryushin V. , Raciukaitis G. , Puzonas G. , Kazlauskas A. 
Published: July 2007

AbstractTwo‐photon interband absorption spectra are obtained first in PbMoO4 crystals. They are shown to be attributed to indirect two‐photon absorption (TPA) with the assistance of phonons to exciton state formed band transitions with the extrema in different points of the Brillouin zone. The energy parameters of excitons Eexi = 3.56 (80 K) and 3.53 eV (300 K), Ebi = 50 meV, of phonons (65, 180, and 270 meV), and of the interband absorption edge Egi = 3.61 (80 K) and 3.58 eV (300 K) are obtained. Anomalously high efficiency of electron–phonon interaction is found in crystals studied. The phonon energy observed in TPA at indirect transitions is shown to be determined probably by joint participation of several active phonon modes of MoO4−2 tetrahedral group in PbMoO4 crystal.
Free‐Carrier Optical Absorption Induced by Dislocation Scattering Mechanisms in Semiconductors Application to GaAs
Authors: Vignaud D. , Farvacque J. L. 
Published: July 2007

AbstractThe intraband absorption induced by the dislocation scattering mechanisms (charged line potential, piezoelectric potential, and deformation potential) is calculated. These expressions are then used to discuss the possibility to observe the dislocation scattering effect in GaAs: one finds that dislocations are rather weak scattering centres, which is confirmed by measurements.
Simple Model for the Ferroelectric Phase Transition in KTa1−fNbfO3
Authors: Vugmeister B. E. , Antimirova T. V. 
Published: July 2007

AbstractThe concentration dependence of niobium‐induced ferroelectric phase transition temperature Tc(f) in KTa1−fNbfO3 is explained assuming an eight‐well niobium off‐center potential. Single‐ion model and mean‐field theory is used. The best agreement between the theory and experiment is reached with the following values of parameters: barrier height U = 60 K, off‐center displacement x0 = 0.008 nm which are in good agreement with previous experimental results.
Dependence of the Line Strength of f–f Transitions on the Manifold Energy. II. Analysis of Pr3+ in KPrP4O12
Authors: Kornienko A. A. , Kaminskii A. A. , Dunina E. B. 
Published: July 2007

AbstractTo describe the experimental data of the line strength and the oscillator strength of electric dipole transition between manifolds a formula is suggested that takes into account the dependence on the energy of manifolds and the effect of electron correlation. It contains four phenomenological parameters and is applied to describe the experimental data of Pr3+ in KPrP4O12. It is shown that the dependence of the line strength on the energy of manifolds improves essentially the description of 3H4 → 3P2 transition.
Excited Acceptor States in II–VI and III–V Semiconductors
Authors: Said M. , Kanehisa M. A. 
Published: July 2007

AbstractHigher excited states of acceptors in CdTe, ZnTe, and GaAs are obtained by using the Baldereschi and Lipari spherical model including the cubic correction and the central‐cell effect. This is done by solving the coupled radial equations by the finite‐element method with Arnoldi's algorithm, which gives several (≈ 20) low‐lying states simultaneously. The procedure permits to determine very accurately the host band‐structure parameters. In the case of II–VI compounds, the Luttinger parameters γ1 = 5.30, γ2 = 1.62, γ3 = 2.10 and the dielectric constant ϵ0 = 9.3 for CdTe and, γ1 = 3.80, γ2 = 0.86, γ3 = 1.32 and ϵ0 = 9.4 for ZnTe are obtained. For GaAs, γ1 = 7.20, γ2 = 2.15, γ3 = 3.05, and ϵ0 = 12.49 are obtained.
On the Representation of Orientation Distributions in Texture Analysis by σ‐Sections. II. Consideration of Crystal and Sample Symmetry, Examples
Authors: Matthies S. , Helming K. , Kunze K. 
Published: July 2007

AbstractIn this second paper on σ‐sections for representation of orientation distributions in texture analysis the results of the first one are generalized by the consequences of all crystal and sample symmetries of practical interest. The connections of σ‐sections with pole figures and inverse pole figures are given. the analytical results of both the papers are demonstrated by examples.
The Electronic Structure of Copper Oxide Crystalline Compounds. II. Chemical Bonding in Copper–Oxygen Crystals
Authors: Evarestov R. A. , Veryazov V. A. 
Published: July 2007

AbstractThe crystalline structure of copper‐oxygen compounds with copper atom in the oxidation states I, II, and III is reviewed. A calculation is made of the electronic structure of the row of crystals with copper‐oxygen bonding. It is shown that the covalence effects are essential for copper oxide compounds containing copper atoms in oxydation states CuII and CuIII LUC‐CNDO calculations of La2CuO4 and YBa2Cu3Ox (x = 6,7) crystals are made. It is concluded that the higher copper valency is favourable for superconductivity.
Thermal Conductivity and Thermoelectric Figure of Merit of Thin Antimony Films
Authors: Völklein F. , Kessler E. 
Published: July 2007

AbstractThe thermal conductivity λ and thermoelectric figure of merit z of Sb films with thicknesses from 27 to 230 nm are measured in the temperature range 80 to 400 K. The lattice thermal conductivity λφ is determined from the measured total thermal conductivity λ and the calculated charge carrier contribution λe. The results are discussed in the framework of a two‐band model for the charge carriers and of a grain boundary and surface scattering model for phonons. The transport properties of isotropic and texturized films are compared.
Pulse Propagation and Carrier Kinetics in Laser Excited Semiconductors
Authors: Schäfer W. , Henneberger K. 
Published: July 2007

AbstractPropagation of an intense ultrafast pulse (100 fs) of Gaussian shape with its central frequency above band gap in a GaAs halfspace is investigated theoretically. Nonequilibrium occupation of one particle states, memory effects in the polarization, Coulomb interaction, LO‐phonon Scattering, and spatial inhomogeneities, i. e. the deformation of the pulse shape are taken into account in a strict microscopic approach. The numerical analysis allows to follow the various mechanisms involved on a fs‐time scale, e. g. (1) saturation, spectral hole burning, and relaxation of the one particle distribution, (2) memory effects, dephasing processes, and Coulomb‐enhancement of the polarization and (3) the interplay between that during pulse propagation. The resulting behaviour cannot be simulated by phenomenologically introduced dampings and/or relaxations, thus underlining the importance of accounting for the above mentioned effects in a microscopic way.
Time‐Resolved Four‐Wave Mixing Experiments in CuCl
Authors: Gomes M. J. M. , Kippelen B. , Levy R. , Grun J. B. , Hönerlage B. 
Published: July 2007

AbstractBy a light‐induced grating technique with three degenerate laser beams, the diffusion constants and the decay times of optical nonlinearities in CuCl are determined. By comparison with results from induced absorption, the nonlinearities may be identified as being due to different excitonic populations as well as to thermal effects.
Excitons and Phonons in CdTe/MnTc and ZnTe/MnTc Single Quantum Wells. Aspects of Confinement and Optical Phonon Coupling
Authors: Nurmikko A. V. , Gunshor R. L. 
Published: July 2007

AbstractWith the incorporation of wide gap cubic zineblende MnTe, a range of optical studies are carried out on single quantum wells of ZnTe/MnTe and CdTe/MnTe. By using thin MnTe barrier layers the highly strained structures appear to be nearly pseudomorphic and show evidence for good electron hole confinement. This has provided a means to examine the exciton‐LO‐phonon coupling through different indicators.
Carrier‐Induced Pulse Narrowing in Indium‐Doped CdS
Authors: Hönig T. , Gutowski J. , Broser I. 
Published: July 2007

AbstractStrong optical nonlinearities and bistability in the band‐gap region are known to occur in CdS doped with indium by 1016 to 1018 cm−3, which are due to the neutralization of ionized acceptors. In time‐resolved single‐beam measurements an absorptive effect becomes dominant for excitation densities higher than 1 MW/cm2 in addition to the known induced transmission. The combination of both processes yields a narrowing of the shape of the transmitted pulse. This phenomenon is studied in dependence of the laser wavelength, intensity, and polarization, as well as on the temperature and the dopant concentration. The experimental results can be understood in a model of interaction of free carriers with photonic polaritons.
Electron–Hole Plasma in Cross‐Over‐Near Ga(As, P)
Authors: Fieseler H. , Schwabe R. , Staehli J. L. 
Published: July 2007

AbstractThe spontaneous emission spectrum of an electron–hole plasma (EHP) in direct‐gap Ga(As, P) near the Γ‐X cross‐over is investigated as a function of the excited electron–hole pair density. Special attention is paid to a multicomponent EHP, i. e. to the case of an additional occupation of the conduction band X valleys. The EHP luminescence bands and the excitation induced band gap shrinkage are calculated in random phase approximation (RPA). The theoretical results for the reduction of the band gaps are compared with data obtained from luminescence experiments. The EHP luminescence is investigated at T = 2 K on high‐purity direct‐gap GaAs0.55P0.45 islands using an intense band‐edge resonant dye‐laser excitation.
Dissipation of Excitonic Polaritons in CdS
Authors: Pantke K.‐H. , Over H. , Broser I. 
Published: July 2007

AbstractExperiments are discussed wherein scattering of excitonic polaritons with acoustic phonons between different polariton modes can be observed. Information about this dissipation process is given by the luminescence of deep impurities acting as microscopic detectors within the crystal which are sensitive to the distribution of energy to the different polariton branches. The calculated intensity for an ensemble of ideal micro‐detectors containing constant quantum yield and absorption probability agrees excellently with measurements.
Instrinsic and Impurity‐Related Point Defects in Amorphous Silica. A Spectroscopic Study
Authors: Pio F. , Guzzi M. , Spinolo G. , Martini M. 
Published: July 2007

AbstractAbsorption, photoluminescence emission, and excitation measurements of “as grown” and neutron irradiated amorphous silica characterized by different impurity and OH content, confirm the composite nature of the ≈ 5.1 eV (B2) absorption band and make it possible to distinguish between structural defects and impurity‐related centers. A detailed analysis of the published results on the subject shows that none of the up to date existing models fully accounts for the complex of the experimental observations. A new scheme is proposed in which all the available data find a consistent collocation. It is suggested that two structurally different centers, with optical absorptions in the B2 region, can be simultaneously present in amorphous SiO2; they exist in two variants: bare defect (also produced by neutron irradiation) or impurity‐perturbed center. Some proposals for a deeper understanding of absorption and photoluminescence in glassy SiO2 are finally advanced.
Chemical Trends in the Formation and Binding Energy of Native Defects in III‐V Semiconductors
Authors: Gu Y. M. , Fritsche L. , Christensen N. E. 
Published: July 2007

AbstractChemical trends are reported in the formation and binding energy of mono‐ and divacancies in nine III‐V semiconductors. In addition, results are given on self‐interstitial energies. The calculations are carried out within the density functional theory. In self‐consistently solving the scalar‐relativistically extended Kohn‐Sham equations for defect‐specified supercells, Andersen's LMTO‐method is used and the atomic sphere approximation (ASA). The exchange‐correlation energy per particle and the associated one‐particle potential is assumed to have the local spin density form suggested by von Barth and Hedin.
The High‐Frequency Quantum Size Effect in the Impedance of Metal Films
Authors: Zakharov S. P. , Ustinov V. V. 
Published: July 2007

AbstractA novel high frequency quantum size effect in the surface impedance of metal films under quantum anomalous skin effect conditions is predicted. The suppression of the Landau damping by the size quantization leads to reconstruction of the skin layer and to specific magnetic field dependence of the impedance near the cyclotron resonance conditions.
On Conditions of Spectroscopic Manifestation of the Dynamical Jahn‐Teller Effect
Authors: Fugol I. Ya. , Ratner A. M. , Yurtaeva E. M. 
Published: July 2007

AbstractImpurity level splitting in a crystal due to the lowering of the lattice symmetry under its vibrations is considered. Since the interaction of low‐symmetry vibrations with the optical center is generally weaker than that of the full‐symmetry one which makes the optical lines broader, the dynamic level splitting is masked by the broadening. The dynamic splitting manifests itself by a mechanism which promotes weakening in the interaction of the optical center with the full‐symmetry vibration rather than with the low‐symmetry ones. In the case of rare‐gas crystals with atomic impurities such a mechanism is associated with the compensation of contributions of repulsive forces and the Van der Waals attraction to the line brodening. The degree of compensation correlates with that of spectral separation of the splitting components in experimental absorption spectra.
A Generalized Ballistic Aggregation Model for the Simulation of Thin Film Growth with Special Consideration of Nodular Growth
Authors: Müller‐Pfeiffer S. , Anklam H.‐J. , Haubenreisser W. 
Published: July 2007

AbstractStarting from the well‐known idea of atomic shadowing during growth (i. e. ballistic aggregation) a computer model is developed which includes surface relaxation by thermally induced surface diffusion, desorption, angular distribution of the oncoming atoms, and atomic attraction as well for one‐and two‐ (or more‐) component systems. This enables to consider such deposition parameters as substrate temperature, energy of oncoming particles, deposition geometry, and inert gas pressure. The model is applied to investigate the influence of various deposition parameters on the morphology of thin films, especially on the structure of nodular defects.