bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theoretical Investigation of Auger Recombination in PbSnTe Structures
Authors: Lemke F. , Mocker M. 
Published: July 2007

AbstractAn approximate analytical formula of the Auger rate is developed, describing the rate in dependence on the dimension parameter v with v = 3, 2, 1 for bulk, quasi‐two‐dimensional, and quasi‐one‐dimensional structures, respectively. The main influence to the Auger coefficient is due to the increased effective gap in low‐dimensional structures, leading to an increased activation energy and therefore in lead chalcogenides to a reduced Auger rate compared to the bulk. The effects of anisotropy and of the changed matrix elements modify this main effect in such a way, that Auger recombination in some special planes and directions is more effective than in others.
Local Electric Field Gradients in Anionic and Cationic Positions of Cesium Perchlorate
Authors: Tarasov V. P. , Meladze M. A. , Kirakosyan G. A. , Shvelashvili A. E. , Buslaev Yu. A. 
Published: July 2007

AbstractPolycrystalline CsClO4 is studied over the range from 95 to 440 K by 35Cl and 133Cs NMR in the field B0 = 7.04 T. From the analysis of the lineshape the quadrupole coupling constant CQ and the asymmetry parameter η at the nuclei 35Cl and 133Cs are determined. The temperature dependence of CQ is linear for both the nuclei with a negative temperature coefficient. A sharp break of η(133Cs) at 342K is due to the change in the relative values of the tensor components qij of the electric field gradient on 133Cs. The temperature dependence of qij is considered in relation to the anisotropy of the thermal expansion and a numerical evaluation of the thermal expansion coefficient is made.
Anharmonic Effects in the Thermal Diffuse Scattering of X‐Rays
Authors: Tsarkov A. G. , Tsirelson V. G. 
Published: July 2007

AbstractThe thermal diffuse scattering (TDS) of X‐rays in the anharmonic one‐phonon and harmonic two‐phonon approximations is considered. The complete expression for the one‐phonon intensity of X‐rays is derived by perturbation theory and presented for a polyatomic crystal in the high‐temperature limit. The method of evaluating the corrections of the X‐rays intensities for the thermal diffuse scattering is given and the importance taking into account the anharmonic effects in the one‐phonon scattering for KZnF3, CsCl, and YBa2Cu3O7−δ crystals at room temperature is discussed. Anharmonic TDS‐effects achieve considerable magnitudes for soft (acoustic) anharmonic crystals as CsCl.
Evidence of Tetrahedral and Octahedral Aluminum Coordination in Rare‐Earth Aluminates
Authors: Landron C. , Badets M. C. , Douy A. , Coutures J. , Coutures J. P. , Daniel P. , Flank A. M. 
Published: July 2007

AbstractThe local order around the aluminum atoms in a series of rare‐earth aluminates with perovskite and garnet structure is characterized by X‐ray diffractometry and by near K‐edge X‐ray absorption. The aluminate samples are elaborated by an original sol‐gel technique. The Al XANES spectra contain features which appear to be similar to those recorded on other aluminum fluorites with similar structure. In both systems, K edge clearly demonstrat a structure showing the octahedral metal–oxygen coordination for the perovskite stoichiometry and a mixture of tetrahedral and octahedral coordination for the garnet stoichiometry.
Void Sink Strength in H.C.P. Materials
Authors: Grande N. Smetniansky‐De , Tomé C. N. , Savino E. J. 
Published: July 2007

AbstractThe strength of a void in h.c.p. lattices for the trapping of vacancies and interstitials is calculated. An analytic solution for the diffusion equation of point defects is used. The resulting expressions can be introduced in rate theory models, for simulating the performance of nuclear reactor components. The effect of a stress field on the anisotropic diffusion of vacancies and interstitials is studied. A discrete lattice approximation is used for calculating the elastodiffusion tensors. The dependence of the void sink strength on the anisotropy diffusivity ratio, Dc/Da, is studied. It is concluded that the anisotropy in the diffusion plays a fundamental role in the behaviour of spherical sinks.
Quadratic Force Constant of a Cleaved Jellium and Its Relation to Quadratic Response Functions of the Homogeneous Jellium
Authors: Streitenberger P. , Ziesche P. , Kaschner R. 
Published: July 2007

AbstractRigorous expressions are derived yielding the quadratic force constant B of a jellium interface in terms of the quadratic density‐potential response function and the quadratic dielectric function, respectively, of the homogeneous jellium. For the quadratic dielectric function an exact formula including quadratic exchange and correlation corrections is obtained. B is calculated analytically within the local density approximation and numerically within the gradient expansion method using different values of the bulk density. The connection of the linear and quadratic force constants with the jellium cleavage fracture strength and the fracture strength separation is discussed.
Band Structure and Charge Density Distribution of Cubic Face‐Centred TlI Single Crystals
Authors: Dovgii Ya. O. , Kityk I. V. , Kolinko M. I. , Krochuk A. S. , Franiv A. V. , Zamorskii M. K. 
Published: July 2007

AbstractFor the first time self‐consistent band‐structure calculations of TlI single crystals (space group O) are performed using nonlocal pseudopotentials. The method is described briefly. The contributions of the different band states to the charge density distributions are estimated. Correlations between the band dispersion, valence electron mobility, and charge density distribution are outlined. The origin of the different bands is defined and the total density of states is calculated.
Quantum Mechanical Properties of a Thin Cylinder. I. The Density of Electronic States
Authors: Makar M. N. , Ahmed M. A. , Awad M. S. 
Published: July 2007

AbstractThe electronic density of states is calculated in the case of a hollow metallic cylinder placed in a uniform magnetic field. The oscillatory features are estimated when the magnetic field intensity is weak. This shows rapid changes in the density of states on the contrary of the case of fields of intermediate densities where the effect is quite small.
Fine Structure of Quasi‐Bound Acceptor States in Germanium Induced by Magnetic Field
Authors: Palkin A. M. , Shegai O. A. 
Published: July 2007

AbstractThe energy spectrum of quasi‐bound states of shallow acceptors in pure p‐Ge is investigated experimentally by the method of far‐infrared (FIR) laser magnetospectroscopy. A fine structure of quasi‐bound states is observed which is connected with the removal of degeneracy of the total angular momentum parallel to the magnetic field. Additional peaks found in the photoconductivity spectrum are refered to the impurity combined resonance.
pf‐Hybridization and the Crystal Fields in RBa2Cu3O7—δ
Authors: Kuz'min M. D. , Popov A. I. , Zvezdin A. K. 
Published: July 2007

AbstractMechanisms are considered, which form the crystal field (CF) acting on rare earth ions (REI) in the high‐Tc superconductors RBa2Cu3O7—δ. The electrostatic component of the CF is calculated using the point‐charge model. A significant contribution to the CF is brought in by pf‐hybridization and is taken into account on the basis of a two‐centre approximation using Slater‐Koster parameters. A new parameterization of the hybridization contribution to CF is proposed, which is based on utilizing two parameters — the energies Eσ and Eπ of the σ‐ and π‐bonds in the pair R3+−O2−. Proceeding from the analysis of the experimental data, it is shown that for all compounds studied thus far (R = Nd, Dy, Ho, Er, Tm) a universal relation holds between these two parameters, Eσ ≈ 2.9Eπ, which enables to reduce the number of disposable parameters of the theory.
Intrinsic Broadening of F‐Electron Energy Levels Due to Phonon Mediated Hybridization of the Electronic States
Authors: Lagos M. , Monreal Mc. R. , Rogan J. 
Published: July 2007

AbstractIn a first step the temperature dependent lineshapes of F‐center optical features are obtained analytically from the usual small‐polaron theory and Condon approximation. Though the calculation may be considered already standard, it is improved in putting emphasis in retaining the full spectrum of lattice modes and in keeping control of the accuracy of the approximations. Although the latter is shown to be better than 0.1% for F‐centers the theory fails in giving the temperature dependent shifts of the spectral features and the difference between the emission and absorption linewidths. A parameter‐free test of the so obtained results with experiment shows good agreement, but significant deviations are also observed. Refining the theory it is shown that, in order to fully account for the optical properties of F‐centers, one has to go beyond the current treatments, drop the Condon approximation, and consider the splitting of the F‐electron energy levels due to phonons induced hybridization of the electronic states. The temperature dependence of the band shifts is calculated in this way, obtained excellent agreement with experiment. It is concluded that F‐centers have appreciable intrinsic structure which may be of interest for further experimental investigation.
Optical Properties of Anionic Gold Centers in CsBr and CsI Crystals
Authors: Shimanuki S. , Kawai T. 
Published: July 2007

AbstractOptical studies are for the first time performed on Au− centers in Cs‐halides. Absorption spectra above 90 K and emission and excitation spectra down to 13.9 K are investigated for CsBr:Au− and CsI:Au− crystals. In both the crystals four absorption bands exist called D1, C, B, and A and two emission bands called B′ and A′ in the order of decreasing energy. In CsBr, a luminescence resembling α emission known in other alkali systems is also observed, but it seems not to be peculiar to Au− centers because of its dependence on the thermal treatment of the specimens. The King‐Van Vleck factors, λ, which are obtained by analyzing the optical data are 2.5 (CsBr) and 2.2 (CsI), which are larger than unity as in the case of all other alkali halides: Au− so far investigated.
Short‐Range Order and Solid Solution Hardening
Authors: Blanter M. S. , Ya. Fradkov M. 
Published: July 2007

AbstractA Monte‐Carlo simulation is made of the short‐range order in TaO with oxygen—oxygen long‐range strain‐induced potential with the exception of the first coordination shell. In a wide temperature range short‐range order of cluster type is discovered. On the basis of dislocation‐obstacle interaction models the start stress of (1/2)〈111〉{110} screw dislocations in the solid solution with clusters is calculated. Cluster nucleation leads to solution hardening.
Some Conditions of Ferromagnetic Liquid Crystal Existence
Authors: Buivydas M. 
Published: July 2007

AbstractThe possibility of the existence of the ferromagnetic liquid crystal based on analogy between electric and magnetic phenomena is considered. Nematic and smectic liquid crystalline states and symmetry conditions are discussed. The most common case — hypothetical ferromagnetic‐ferroelectric liquid crystal (FFLC) and some of the field effects on it are described based on Landau free energy expression.
The Magnetic Phase Diagram of the Emery Model within the Hartree‐Fock Approximation
Authors: Saalmann U. , Hayn R. 
Published: July 2007

AbstractThe Hartree‐Fock approximation is applied to investigate the ferromagnetic, antiferromagnetic, and paramagnetic phases of the Emery model. The phase diagram in dependence on copper correlation and hole doping is calculated by comparing the total energy in the one‐dimensional case. The transition from the antiferromagnetic to the paramagnetic phase with increasing doping is only found for relatively small values of the correlation. In the other cases a transition to ferromagnetism is obtained.
The Ion Charge Fluctuation Effect on Impurity Depth Distributions for High‐Energy Ion Implantation. The Backward Transport Equation‐Based Simulation
Authors: Burenkov A. F. , Komarov F. F. , Fedotov S. A. 
Published: July 2007

AbstractA model of high‐energy ion implantation is formulated with allowance for fluctuations of the charge state of ions and the corresponding backward transport equation for post‐implantation spatial distributions of an impurity. Simulation results of experiments concerned with boron ion implantation into silicon by numerical solving the backward transport equation are reported. It is shown that the account of ion charge fluctuations in the high‐energy range leads to an increase of the range straggling of the implanted impurity and provides a better agreement with the experiment than the traditional methods of modelling based on the use of the Monte‐Carlo method or the backward transport equations.
Positron Annihilation Angular Correlation Studies in GaSb
Authors: Panda B. K. , Mahapatra D. P. , Padhi H. C. 
Published: July 2007

AbstractTwo‐photon angular correlation lineshapes along [100] and [111] crystallographic directions of GaSb are reported. The theoretical calculations of the lineshapes are carried out employing the pseudopotential band model for the calculation of the electron wavefunction. The positron wavefunction is evaluated under the point core approximation. The calculated lineshapes and their anisotropies are in good agreement with the experimental data.
Optical Determination of Carrier Concentration and Mobility in p and n Bulk GaSb by Infrared Reflectivity Spectral Analysis
Authors: Mezerreg A. , Llinares C. , Montaner A. 
Published: July 2007

AbstractInfrared reflectivity measurements are made on both, n and p bulk GaSb at 300 K to determine carrier concentration and mobility of the material by using a least‐square fit on a non‐linear model to experimental data after their transfer from spectrometer to a compatible computer in ASCII code. For n‐type GaSb a method is proposed for calculating density and mobility of carriers from plasma frequency and carrier scattering time given by the fit, taking into account contributions of both, Γ and L band electrons to conductivity. Good agreement is obtained between density and mobility given by reflectivity and those given by Hall measurements for density range 1.2 × 1017 to 3 × 1018 cm−3.
On the FMR Theory of Metallic Amorphous Ferromagnets
Authors: Fraitová D. 
Published: July 2007

AbstractThe formulae for dispersion relations, together with formulae for the surface impedance, skin depth, wavelength, and inflection linewidth are discussed, for the ferromagnetic resonance (FMR) in parallel configuration in amorphous alloys. The importance of the FMR cross‐over effect is pointed out.
A New Type of Domain Wall Excitation in Magnetic Systems
Authors: Talim S. 
Published: July 2007

AbstractA 2π domain wall excitation is studied in a magnetic system. The domain walls studied before by other authors are different because in theses works the spin rotates by an angle of π in the domain wall. In 2π domain walls the spins rotate by an angle of 2π and the problem is described by a double sine‐Gordon equation, which has a richer dynamics than the conventional sine‐Gordon equation.
The 4T1(F) → 4A2(F) Luminescence of the Co2+ (d7) Impurity Centre in Zinc Selenide Crystals
Authors: Goetz G. , Schulz H.‐J. 
Published: July 2007

AbstractThe 4T1(F) → 4A2(F) transition of Co2+ (d7) ions in ZnSe is detected by its emission at T ≈︁ 4 K. The no‐phonon line at v̄ = 5558 cm−1 is demonstrated to coincide with the inverse absorption transition. The luminescence shows medium coupling to ZnSe lattice vibrations. An exponential decay with a time constant τ = 100 μs is recorded. A rich fine‐structure is displayed by the 4T1(P) ← 4A2(F) absorption studied for comparison. Qualitatively, it can be described by spin–orbit and Jahn‐Teller interaction. Finally, the properties of two additional emission bands present in the 4200 to 5600 cm−1 region are illustrated, one of them dominated by a no‐phonon line at 5471 cm−1. Capture of a hole by a neutral donor is discussed as a possible interpretation of a broad luminescence band peaking near 4600 cm−1.
Reflectivity Spectra of YBa2Cu3O7−x in the 0.6 to 6.1 eV Range Evidence for Excitonic Absorption
Authors: Nag A. , Neogy C. , Ghosh B. , Joarder R. , Deb S. K. 
Published: July 2007

AbstractReflectance measurements at room temperature (298 K) on ceramic YBa2Cu3O7−x in the spectral range 0.6 to 6.1 eV and subsequent Kramers‐Kronig analyses of the spectra indicate the presence of excitations at 1.0, 2.1, 3.6, and 5.7 eV. It is argued that there is enough evidence to consider the 1.0 and 2.1 eV excitations as excitons.
Induced Radiation from a Relativistic Electron Beam in Periodic Structures
Authors: Baryshevskii V. G. , Batrakov K. G. , Dubovskaya I. Ya. 
Published: July 2007

AbstractThe spectral‐angular distribution of an induced X‐ray parametric quasi‐Cerenkov radiation (PXR), generated by a relativistic particle in periodic structures, is derived for different diffraction geometries. The possibility of experimental observation of such radiation is discussed.
Direct Observation of the Discommensuration in the Nearly Commensurate Charge‐Density Wave Phase in 1T‐TaS2 by Scanning Tunneling Microscopy
Authors: Ohta H. , Takase T. , Komiya Y. , Miyamoto H. , Mishima S. , Okada T. , Nomura K. 
Published: July 2007

AbstractThe charge‐density wave (CDW) structure of the nearly commensurate phase of 1T‐TaS2 is studied with scanning tunneling microscopy (STM). The hexagonal domain structure is observed in the CDW superlattice at room temperature. It is assigned to the discommensuration (DC) network. The domain size is about 8 nm and the width of domain walls is of the order of 3 nm. The observed structure agrees well with the DC model proposed by Nakanishi and Shiba. The DC structure is easily destroyed by disorder of the CDW lattice in the neighboring region.
Interaction between Excitons and Electrons in ZnSe1−xSx Epilayers under High Excitation
Authors: Guan Z. P. , Zheng Z. H. , Zhang J. H. , Lu Y. M. , Fan G. H. , Fan X. W. 
Published: July 2007

AbstractExcitonic properties are investigated of ZnSe1−xSx epilayer fabricated on GaAs substrate by a Ap‐MOCVD. Luminescence, excitation, and time‐resolved spectroscopy are employed to study the interaction between excitons and electrons at 77 and 300 K. Under pulsed N2 laser excitation it is found that the peak shift of the near band edge emission are more large, especially at room temperature. This is due to the fact that the bottoms of the conduction bands are filled at the higher temperature, so the carriers from the exciton‐exciton scattering must occupy higher energy levels. Therefore a shift of the peak towards lower energy is expected.
Coulomb Interaction and Polaronic Exciton States in Compositional Superlattices
Authors: Beril S. I. , Pokatilov E. P. , Kalinovski V. V. 
Published: July 2007

AbstractThe general theory of Wannier‐Mott polaron excitonic states is developed using the Pekar‐Fröhlich Hamiltonian of electron‐phonon interaction in a periodic structure consisting of alternating pairs of two different polar semiconductor layers, such as compositional superlattices (SL). The effects of dynamical screening of electron‐phonon interaction by inertial polarization are examined in two limiting cases, namely in the Haken limit with Rex > Ri and in the Meyer limit with Rex < Ri,; Rex, Ri, are the exciton and polaron radii of electron (i = e) or hole (i = h). For the first time the renormalization of the optical vibration spectrum is taken into account, and the exact potential of electron‐hole interaction is used to calculate the size dependent exciton binding energy. The theory is employed to calculate the binding energy of exciton states in GaAs/AlxGa1−xAs superlattices.
Role of Bulk d‐Electrons in the Formation of Ultraviolet Photoelectron Spectra for a Number of 4d‐Metals
Authors: Kormilets V. I. , Belash V. P. , Klimova I. N. , Sorokina M. F. , Shirokovskii V. P. 
Published: July 2007

AbstractThe contribution of bulk electron crystal states to the ultraviolet photoelectron spectra (UPS) is studied for the following 4d‐metals: molybdenum, rhodium, palladium, and silver. The discrepancy between the calculated curves of bulk contribution to the UPS and the experimental UPS curves is found to increase, when going from the elements at the end of 4d‐period to the elements closer to its beginning. This regularity appears to be connected with the decrease in the d‐electron localization in the above‐mentioned sequence of elements, which is demonstrated by the calculations. Comparison of the calculated bulk contribution to the UPS with the experimental UPS allows to distinguish those peaks in the UPS of molybdenum and rhodium, which are most likely due to the surface electronic structure.
The Diagram Technique for Calculation of Transport Constants of Random Inhomogeneous Materials. I. The AC Effective Conductivity
Authors: German A. I. , Chaikovskii I. A. 
Published: July 2007

AbstractDiagram methods are applied for evaluating the ac effective conductivity σ*(ω) of a disordered semiconductor (e.g., a highly doped compensated semiconductor, a composite, etc.). Expressions for σ*(ω) are obtained in a number of approximations — the cumulant approximation, the self‐consistent moment approximation, and the effective medium approximation. For a random binary mixture which consists of two materials with conductivities σ1 and σ2, the dependences of real and imaginary parts of σ*(ω) on the frequency ω of the external electric field, volume fraction x of the most conducting material and the ratio of the conductivities σ2/σ1 are presented for all approximations mentioned. For a metal‐insulator mixture (σ2 = 0) on the onset of percolation the cumulant and effective medium approximations predict the following behaviour of σ(ω): σ(0) ∼ (x — xc)t, σ(ω) ∼ ωs, here t = 1, s = 1/2. The results, obtained for σ(ω) are compared with those of computer simulation in the model of fully penetrating spheres (Balberg and Binenbaum). The cumulant approximation is in good agreement with the computer results.
Optical and Electrical Investigations of n‐Type Bi2Se3 Single Crystals
Authors: Stordeur M. , Ketavong K. K. , Priemuth A. , Sobotta H. , Riede V. 
Published: July 2007

AbstractBi2Se3 single crystals were prepared in the electron concentration range from 1.8 × 1019 to 5.6 × 1019 cm–3. At room temperature experimental values are given for the specific electrical resistivity, for the Hall and Seebeck coefficients, and the ir‐plasma reflectivity spectra were measured in the wave number range from 300 to 4000 cm–1. For the first time it was found that not only the resistivity and the plasma reflectivity but also the thermopower show a distinct anisotropy perpendicular and parallel to the trigonal c‐axis, whereas the Hall effect is isotropic. In terms of a one‐carrier, one‐valley conduction band model with elliptical isoenergy surfaces and a nonparabolic dispersion the anisotropy of the thermopower can be explained in the extrinsic range by an anisotropic mixed scattering mechanism on acoustic phonons and ionized impurities in the relaxation time approximation. In this frame a quantitative, consistent interpretation is reached for all experimental data. The calculated values for the high‐frequency dielectric constant, the carrier density, the Fermi level, the parameter of nonparabolicity, the mean optical relaxation times, the effective masses and the drift mobilities are given.