bluuebunny/crossref_metadata_2025_split huggingface dataset:
Magnetic Properties of a Surface with an Amorphous Layer
Authors: Kaneyoshi T. 
Published: July 2007

AbstractA semi‐infinite simple cubic spin‐½ Ising ferromagnet with surface amorphization is investigated by extending the mean‐field theory of amorphous bulk ferromagnets. The magnetic properties of the surface are examined as a function of averaged surface exchange 〈J〉r = J(1 + Δ) and fluctuation of the surface exchange interaction. Some characteristic behaviours of the system are found.
Single and Multiple Electron Scattering Description in X‐Ray Absorption Spectrum Theory and the Problem of Solid Structure Investigation
Authors: Vedrinskii R. V. , Bugaev L. A. , Levin I. G. 
Published: July 2007

AbstractThe effect of photoelectron double and threefold scattering processes on XANES (in KCl K K‐spectrum, in BaTiO3 Ti K‐spectrum) and EXAFS (in Re L3‐spectra in ReO3 at various pressures) are investigated within the spherical wave formalism. The main contributions into the near edge absorption cross‐sections are shown to be due to the photoelectron scattering processes in the approximately linear atomic chains originating and terminating at the absorbing atom. The results obtained for EXAFS show good agreement with the experiment that enables one to solve the bondangle determination problem by EXAFS.
Laser Excited Semiconductors: Light‐Induced Gaps and Saturation Kinetics
Authors: Henneberger K. , Jahnke F. 
Published: July 2007

AbstractA theoretical description of the electron–hole plasma resonantly excited in the interband absorption region by a monochromatic laser is developed. A set of equations governing the spectrum and kinetics of electrons and holes as well as the nonlinear propagation of the laser wave is investigated for stationary excitation under the assumption of a local quasi‐equilibrium. Numerical results are represented concerning the spatial dependence of the electron–hole density and the laser intensity from which the saturation of absorption can be discussed.
Subpicosecond Dynamics of the Nonequilibrium Electron–Phonon System in GaAs
Authors: Mickevičius R. , Reklaitis A. 
Published: July 2007

AbstractThe relaxation of hot photoexcited electrons and the ultrashort laser pulse transmission under nonequilibrium LO phonon conditions in GaAs are studied by the Monte Carlo technique. It is shown that the electron relaxation from photoexcited levels consists of two stages. The first stage is controlled by the nonequilibrium phonons, and the second one – by intervalley processes. The laser pulse transmission is governed by the first stage.
Cavity‐Less Optical Bistability in Semiconductors
Authors: Borshch A. A. , Volkov V. I. 
Published: July 2007

AbstractThe way to obtain transverse cavityless OB based on the self‐defocusing of counterpropagating light waves in nonlinear medium is proposed. The theoretical analysis of the transverse OB made it possible to optimize parameters of the bistable cell involved. The experimental investigation are carried out with a semiconductor crystal of CdS. The results show a good agreement with the theory.
Effect of Optical Feedback on Self‐Induced Change of Light Polarization in Cubic Crystals with Directions Instable for Polarization
Authors: Brodin A. M. , Boiko S. A. , Valakh M. Ya. , Tarasov G. G. 
Published: July 2007

AbstractPolarization optical bistability (POB) in crystals with FA‐centers mounted into a Fabry‐Perrot cavity is analysed. This type of optical bistability is caused by amplification of fluctuations of light polarization in crystals under consideration and has no threshold on radiation intensity. The range of parameters is found for impure crystals and cavity under POB conditions.
Theory of Ultrashort Pulse Generation and Amplification by Gain‐Switched Semiconductor Lasers
Authors: Schöll E. , Schell M. 
Published: July 2007

AbstractA theory of the nonlinear ultrashort dynamic response of unbiased gain‐switched semiconductor laser amplifiers is presented. For suitable time delays between the incident laser pulse and the injection current pulse driving the laser amplifier, optical pulse compression due to self‐induced gain depletion is found. The finestructure of the emitted pulse resulting from multiple reflections is shown to depend crucially upon the detuning off cavity resonances and upon the ratio of input signal width to cavity round‐trip time.
Phenomenological Model for the Optical Properties of Semiconductor‐Doped Glasses
Authors: Peschel Th. 
Published: July 2007

AbstractThe optical properties of semiconductor‐doped glasses are determined by semiconductor crystals with diameters of 3 to 5 nm embedded in a glass matrix. The confinement of charge carriers leads to discrete energy states. The motion of the carriers is described by a Ritz ansatz for the wave function combining properties of free particles in a box with those of bulk excitons. In a first approximation the dynamical behaviour of the system can be described in analogy to a two‐level system. Since each energy level can contain only two pairs strong saturation of absorption occurs. Additionally the size distribution of the crystals is taken into account. It results in an inhomogeneous broadening of the spectral lines that can be described by convolution of the spectrum with the diameter distribution of the crystals.
Laser‐Induced Transient Grating in Semiconductor‐Doped Glasses
Authors: Feng Zhao , Li Han , Yun Zhang , Sheng Fei Hao 
Published: July 2007

AbstractThe characteristics are investigated of a transient grating induced by laser in glasses doped with CdSSe semiconductor and the nonlinear response time of the material is obtained. Also the properties of photoluminescence of the glasses are studied and a blue shift in luminescence spectra with increasing intensity of the input beam is observed. It is assumed that the nonlinearity of the material is due to band filling in semiconductor microcrystallites.
Dynamical Nonlinearity and Bistability of Narrow Gap Semiconductors
Authors: Allan G. R. , Chua P. L. , Hunter J. J. , Mackenzie H. A. , Pidgeon C. R. , Walker A. C. 
Published: July 2007

AbstractA brief review is presented of new photo‐Hall studies of linear and nonlinear optical properties of narrow gap semiconductors with specific relevance to optical bistability. InSb is chosen as the prototype crystal for this work. The nonlinear refractive cross‐section (σ = Δn/ΔN) is determined to be −1.1 × 10−18 cm3 near 5 μm at 77K and −(2.3 ± 1) × 10−18 cm3 near 10 μm at 300 K. The two‐photon absorption coefficient is found to be β = 7 cm MW−1. The results are in good agreement with theoretical prediction.
Excitonic Electroabsorption in GaAsGaAlAs Single Quantum Well Waveguide Structures
Authors: Seisyan R. P. , Toropov A. A. , Khvostikov V. P. , Shubina T. V. 
Published: July 2007

AbstractThe electroabsorption spectra of GaAsGaAlAs waveguide p–n heterostructures with single quantum well grown by LPE method are studied at room temperature. The modulation spectra correspond to the quasi‐2D excitonic electroabsorption spectra. An external adjustable laser is used as a source of light propagating parallel to the epitaxial layers. A photolithographically fabricated two‐section sample consisting of LED and modulator regions is investigated as well. An on/off ratio of about 10:1 with a bias voltage U = 6 V is obtained.
Nonlinear Polarization Spectroscopy of Impure Cubic Crystals
Authors: Lisitsa M. P. , Valakh M. Ya. , Tarasov G. G. , Boiko S. A. , Brodin A. M. , Shpak A. M. , Voska R. , Feldvari I. 
Published: July 2007

AbstractNonlinear polarization spectroscopy, a new type of laser spectroscopy of solids, is used for the investigation of cubic crystals with reorienting centers. This technique based on the self‐induced change of light polarization (SICLP) is applied for the determination of fine parameters of FA(Li)‐, FA(Na)‐, F2‐centers in KCl. It is shown that the mechanism of phonon‐induced mixing of wave‐functions belonging to nondegenerate and degenerate excited electronic states of FA‐centers is responsible for SICLP manifestation in KCl with FA‐centers.
Covariant Theory of the Multiwave Bragg‐Laue X‐Ray Diffraction in Crystals
Authors: Maksimenko S. A. 
Published: July 2007

AbstractDiffraction is considered of a plane monochromatic wave by a crystal lattice in the X‐ray fre quency region. A covariant solution of the boundary problem for the multiwave Bragg‐Laue diffraction in a plate‐like crystal is obtained on the basis of the Takagi diffraction equations written in the matrix form.
On the Integrated Intensity of X‐Ray Diffraction in Crystals with Randomly Distributed Defects
Authors: Holý V. , Kuběna J. 
Published: July 2007

AbstractThe dynamical theory of X‐ray diffraction in crystals with randomly distributed small defects based on an optical coherence formalism is used for calculations of integrated reflectivities (in the Laue case) of crystals with statistically placed small precipitates. It is shown that in the case of thinner crystals the integrated reflectivity is influenced mainly by the diffuse scattering, which increases the integrated reflectivity, for thicker crystals a decreasing effect of the diffuse absorption dominates. The calculated thickness dependences of integrated reflectivities are proved experimentally by projection topography of wedge‐shaped crystals with growth striations containing precipitates.
VK Centres in Alkali Halides. Direct Spin‐Lattice Relaxation and Electron‐Phonon Interaction
Authors: Stolovich A. , Liidja G. 
Published: July 2007

AbstractRecent experimental results on the anisotropy of the Kronig Van Vleck one‐phonon spin‐lattice relaxation rates of self‐trapped hole centres in KBr, RbBr, and KI are used to obtain electron‐vibration interaction constants for even non‐totally symetric vibrations of VK centres. A simple centre model, consisting of the X molecule and two nearest cations with normal vibrations of β1g, β2g, and β3g symmetry, is used. A qualitative agreement with the experimental data on various cations and anions can be obtained when ion size corrections are taken into account in evaluating electron‐vibration matrix elements.
Determination of Electron Momentum Density from Electron Number Density. New Version of Semiclassical Transformation
Authors: Kokko K. 
Published: July 2007

AbstractIt is possible to determine the approximate momentum density of an inhomogeneous electron gas from the corresponding electron density by a semiclassical transformation. For the present by this method it is possible to calculate only isotropic total momentum densities. A method is introduced which can be used to calculate directional momentum densities in some special cases as well as partial momentum densities.
Conditions for the Occurrence of the Electric Quantum Limit in Inversion Layers
Authors: Zöllner J.‐P. , Paasch G. 
Published: July 2007

AbstractIn the electric quantum limit (EQL) only the lowest two‐dimensional subband of an inversion layer is populated. Whereas in some materials EQL is observed in others many subband states are populated. An almost analytical description of the inversion layer is derived. It yields conditions for the occurrence of the EQL. An upper limit for the EQL is calculated in dependence on material parameters, interface orientation, and doping concentration. Results are presented and discussed for a series of MIS systems and semiconducting bicrystals. The few available previous theoretical and experimental values for the EQL are well reproduced by the general description.
Properties of the Si‐S1 Center in Si1−xGex Solid Solutions
Authors: Bugai A. A. , Kravtsova I. N. , Maksimenko V. M. , Shanina B. D. , Shakhovtsov V. I. 
Published: July 2007

AbstractChanges in the widths and integral intensities of the EPR lines of the Si‐S1 center depending on the content of germanium in a Si1−xGex solid solution are examined. The appearance of a line‐width anisotropy is accounted for by the effect of the Ge atoms in the immediate environment of the center on the spin‐spin interaction of the electron pair belonging to the center.
Optically‐Detected Magnetic Resonance of Excitons Bound at Te2 Isoelectronic Centres in CdS1−xTex
Authors: Hilton C. P. , Davies J. J. , Nicholls J. E. , Goede O. 
Published: July 2007

AbstractThe first ODMR experiments on excitons bound at isoelectronic traps in a II‐VI semiconductor are reported. In CdS1−xTex with x ≈ 0.02, recombination emission is obtained at 700 nm from excitons bound at Te2 pairs. The ODMR spectra obtained by monitoring polarization changes in this emission shows that the recombination occurs from a triplet state, thus confirming that the number of bound particles in the exciton is two. The symmetry of the ODMR spectra is related to the Te2 pair orientation and this, together with the spin‐Hamiltonian parameters, is consistent with the strong binding postulated for the hole in such an exciton. The additional observation of ODMR signals from shallow neutral donors is taken as evidence for efficient energy transfer between donor‐acceptor pairs and the excitons bound at the Te2 centres.
Role of Interlayer Interactions in High‐Tc Superconductors
Authors: Zieliński J. , Matlak M. 
Published: July 2007

AbstractAnisotropic superconductivity is investigated for layered structures. An increase of interlayer hopping drastically reduces the transition temperature. The coupling between Cooper pairs on adjacent layers seems to be of primary importance in such systems whereas the interlayer Cooper pairs play a rather marginal role. The uniaxial pressure experiments could help to elucidate the nature of this interlayer coupling.
Superconductivity in Disordered and Ordered Niobium Carbide
Authors: Gusev A. I. , Rempel A. A. 
Published: July 2007

AbstractThe magnetic susceptibility, low‐temperature heat capacity, and superconducting transition temperature of an ordered and disordered niobium carbide are investigated. Features peculiar to the electronic structure of a nonstoichiometric niobium carbide are discussed. To explain the superconductive properties of the niobium carbide, a quasi‐two‐dimensional model is proposed which takes into account the peculiarities in the crystal structure of this compound. It is suggested that an exciton mechanism of superconductivity is possible which may be due to the layered structure of the niobium carbide.
Critical Relaxation of Uniform Precession of Magnetization in Cubic Ferrimagnets
Authors: Berzhanskii V. N. , Ivanov V. I. 
Published: July 2007

AbstractThe static (magnetization M(T) and susceptibility X(T) and the dynamic (magnetic resonance line width Δ‐B(T) properties of cubic ferrimagnets Y3Fe5O12 and MnFe2O1 are studied experimentally in the vicinity of the phase transition (PT) into the magnetically‐ordered state. The critical “speeding‐up” of the spin relaxation rate Γ which is available in cubic ferrimagnets is found to be absent. Scattering of the uniform precession of magnetization on the spin waves, including the optical ones, is shown to be the process dominating the relaxation below the Curie temperature Tc but not the fluctuation mechanism.
Anisotropic Ferromagnet with Biquadratic Exchange
Authors: Chaddha G. S. , Kalsi G. S. 
Published: July 2007

AbstractEffect of biquadratic exchange on Curie temperature of a spin‐1 ferromagnet with anisotropic exchange interaction is studied using the Green function approach in the Anderson‐Callen decoupling approximation. The variation of Curie temperature with biquadratic exchange interaction is calculated for crystal lattices of different coordination numbers and for spin systems of various anisotropy parameters of the exchange interaction. Anisotropy parameters for which biquadratic exchange interaction has no effect on the Curie temperature are determined. The results of various approaches are compared.
Two‐Photon Absorption of Bismuth Germanate
Authors: Casalboni M. , Francini R. , Lohmeier F. J. , Grassano U. M. 
Published: July 2007

AbstractTwo‐photon absorption of BGO is observed between 4.8 and 5.7 eV. The results confirm and extend previous investigations on two‐photon excited luminescence. In particular the two‐photon spectra do not show the first three structures observed in the reflectivity measurements. Therefore these structures should be assigned to excitonic transitions and to Bi3+ ion transitions that are parity forbidden in two‐photon spectroscopy. In the region just above the onset, the two‐photon absorption coefficient increases with the photon energy in reasonably good agreement with the theory. Above 5 eV it increases more rapidly than predicted by the present theories for direct interband two‐photon transitions.
Optical Properties of High‐Refractory Disilicide Thin Films
Authors: Henrion W. , Lange H. 
Published: July 2007

AbstractOptical reflectivity spectra are measured for TiSi2, TaSi2, and WSi2 thin films in the spectral range from 0.05 to 6 eV. The optical constants are obtained by Kramers‐Kronig analysis. The spectra are characterized by two spectral regions: the low‐energy free‐carrier response and the interband part. The spectra are discussed on the basis of presently existing band structure information and bonding trend calculations.
A Double Bond Charge Model for Si
Authors: Klenner M. , Falter C. , Ludwig W. 
Published: July 2007

AbstractStarting from a picture of bonding dynamics of covalent crystals based on ab‐initio density response calculations, a phenomenological model is constructed which more clearly shows the principles governing the microscopic density redistribution than does the usual bond charge model. A tetrahedral configuration is introduced of four bond charges rigidly attached to each ion, but free to rotate. The resulting system is treated by means of methods used in the lattice dynamics of molecular crystals. The accuracy of the phonon dispersion curves obtained is comparable to that of the best other models. The analogies are worked out to the microscopic partial density model and the importance of the “chains” in the crystal structure to the lattice dynamics of zinc‐blende materials demonstrated by computing the effective force constants.
Multiple Scattering Approach to the Density of States and Electron Energy Loss Spectra of Amorphous Carbon
Authors: Mühling I. , Blaudeck P. 
Published: July 2007

AbstractFor a set of different carbon clusters the electronic density of states per atom is computed by multiple scattering. Electron energy loss experiments with thin films of sputtered amorphous carbon are carried out as well. By comparing the ε2E2 function with the joint density of states and the C Is near‐edge structure with the conduction band density of states some information about the film structure is obtained.
Potential Surfaces for Chemisorption on Semiconductor Surfaces from Pair Potential Considerations
Authors: Engler C. 
Published: July 2007

AbstractA pair potential method, recently proposed by Tersoff, is extended in order to treat chemisorption problems on semiconductor surfaces. The modified version is tested for chemisorption of atomic hydrogen and oxygen on Si(100)‐surface. The calculated data are compared with experiments and ab‐initio results.
Magnetic Resonance in Magnetically Diluted Solids at Low Temperatures
Authors: Dzheparov F. S. , Henner E. K. 
Published: July 2007

AbstractThe paramagnetic resonance in the disordered spin systems with dipole‐dipole interactions is considered. The theory is extended into the region where βĒ ≪ 1 (β is the inverse dipole temperature, Ē is the interaction energy at the average distance between the spins). The kinetic equations are formulated and the heat capacities for real systems and the resonance form function for the Anderson model are calculated. The correlation expansion is advanced to calculate the form function and the heat capacities are calculated using the concentration expansion.
Influence of the Magnetostatic Interaction on the Outer Hysteresis Loop
Authors: Elk K. , Christoph V. 
Published: July 2007

AbstractTo study the magnetostatic interaction, clusters of N magnetic particles in an infinite sample are considered. The magnetic hardness of a single particle is described by its coercivity field being distributed with different distribution functions. On the base of analytical solutions the shape of the hysteresis loop and information on the remagnetization process result.
Anisotropy of the Optical Band Edge Absorption in CuInTe2 Single Crystals
Authors: Medvedkin G. A. , Prochukhan V. D. , Rud Yu. V. , Tairov M. A. 
Published: July 2007

AbstractOptical absorption of p‐CuInTe2 (I42d) single crystals is studied near the band edge in linearly polarized light in the temperature range 370 to 77 K. Band edge absorption in E ∥︁ c and E ⟂ c polarizations follows Urbach's rule and is described by an electron‐phonon mechanism. The minimal optical transitions in CuInTe2 are allowed primarily in E ⟂ c polarization and correspond to a band gap of 0.983, 0.994, and 1.038 eV for T = 370, 300, and 77 K, respectively. The single crystals reveal optical linear dichroism near the band edge reaching an amplitude 𝒫T ≈ 70%. The optical anisotropy correlates with the deformation of the chalcopyrite lattice, the transmission in linearly polarized light obeying the generalized Malus law. The CuInVI2 (VI = S, Se, Te) crystals are found to have a temperature coefficient of band gap width substantially smaller than that typical of their binary analogs, the II‐VI compounds.
Dynamical theory of electron diffraction for quasicrystals
Authors: Cheng Yifan , Wang Renhui 
Published: July 2007

AbstractThe dynamical theory of electron diffraction for crystals in the wave‐optical and the wave‐mechanical formulations is extended to quasicrystals. In these formulations the basic equations satisfied by the electron wave amplitudes have the same forms for both crystals and quasicrystals.
The structure of the defect chalcopyrite ZnGa2Se4 studied by EXAFS
Authors: Antonioli G. , Lottici P. P. , Razzetti C. 
Published: July 2007

AbstractEXAFS (extended X‐ray absorption fine structure) measurements on the defect chalcopyrite ZnGa2Se4 are performed at the K‐absorption edges of all the atomic species. The bond lengths and the internal distortion parameters are determined by standard EXAFS data analysis techniques in the plane wave approximation, using CuGaSe2 and ZnSe as structural standards for the EXAFS phase shifts. It is shown that the EXAFS radial distribution function contains informations also on the second and third neighbours coordination shells.
Volume capture of 1.5 to 5.7 MeV electrons in quantum channeling states
Authors: Kaplin V. V. , Gridnev V. I. , Khlabutin V. G. , Rozum E. I. , Vorobiev S. A. 
Published: July 2007

AbstractVolume capture of (1.5 to 5.7) MeV electrons into the quantum states of planar and axial channeling along (100), (110), (111), and 〈110〉 directions of Si crystal is investigated. The measurements carried out on crystals with the thickness of 2 and 7 μm reveal two different mechanisms for the volume capture: a small‐angle multiple scattering and strong single scattering of electrons. In the former case the near‐barrier weakly bound states are populated basically, in the latter one they are strongly bound states.
The force constant of a bijellic interface
Authors: Streitenberger P. , Ziesche P. , Nafari N. 
Published: July 2007

AbstractThe equivalence of different expressions for the force constant of a bijellic interface is shown. Within the local density approximation of the universal functional, G[n], the force constant can be expressed solely in terms of bulk quantities. The Thomas‐Fermi‐Dirac approximation is applied and the results are compared with other ones obtained recently within the gradient expansion method.
Subsurface hydrogen exciton‐like states in solid catalysts
Authors: Szász A. , Fabian D. J. 
Published: July 2007

AbstractSubsurface hydrogen electronic levels are discussed in terms of exciton‐like states generated by vacancy‐hydrogen interaction in transition‐metal catalysts. Trapped hydrogen atoms have binding energies that depend exponentially on the density of electronic states at the Fermi level.