bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical Properties and Nature of Coordination of Cu+ Ions in Calcium Metaphosphate Glass
Authors: Debnath R. , Chaudhury J. , Bera S. Chandra
Published: July 2007

Absorption, emission, and excitation spectra of copper(I) ions in calcium metaphosphate glass are investigated. Analysis of the absorption spectrum in the light of ligand field theory reveals that the oxygen coordination surrounding the ion in glass is grossly a trigonally distorted octahedron. A chemical model for the copper(I) ion site in glass is proposed and the mode of distortions that brings about strong trigonal fields at the central ion is discussed. The lowest triplet (3Eg) in the system is identified from emission and lifetime measurements. The observed duality of the triplet emission and its excitation dependence are ascribed to the existence of two relatively predominant slightly different copper(I) sites under the same gross coordination field structure of the glass.
Rearrangement Features of the Vibrational Spectra of TlInS2xSe2(1−x) and TlGaxIn1−xSe2 Solid Solutions
Authors: Sardarly R. M. , Aliev R. A. , Kerimova E. M. , Bakhyshov N. A. , Sadykhov I. Sh.
Published: July 2007

TlInS2xSe2(1−x) (0 ≦ x ≦ 0.25) and TlGaxIn1−xSe2 (0 ≦ x ≦ 0.3) solid solutions are studied by the methods of long‐wave infrared (IR) spectroscopy. The domain of existence of an experimentally unobserved tetragonal modification of TlInS2xSe2(1−x) and TlGaxIn1−xSe2 solid solutions at (0.3)0.25 ≦ x ≦ 1 is described and the frequencies of the IR‐active phonons of a tetragonal modification of TlInS2 and TlGaSe2 of A2u and Eu symmetries are determined by a virtual‐crystal approximation in an isodisplacement model without adjustable parameters for intermediate compositions in the case of many oscillators.
The Behaviour of the Hydrogen‐Localized Vibrational Mode in Proton‐Implanted GaAs
Authors: Wang L. P. , Zhang L. Z. , Zhu W. X. , Lu X. T. , Qin G. G.
Published: July 2007

A hydrogen‐induced infrared absorption band located around 1835.4 cm−1 is observed in protonimplanted GaAs single crystal at 4.2 K and identified as a hydrogen localized vibrational mode (LVM). The dependence of absorption intensity, linewidth, and frequency of the hydrogen LVM on temperature is presented for the first time. Both, the linewidth and frequency shift due to temperature variation are much larger than those of the hydrogen‐vibration in GaAs observed by Cleriaud et al. A structure model for hydrogen LVM in proton‐implanted GaAs is suggested.
Gapless State in CuFeS2
Authors: Mikhailovskii A. P. , Polubotko A. M. , Prochukhan V. D. , Rud Yu. V.
Published: July 2007

A theoretical group analysis of the CuFeS2 structure is made in the presence of magnetic order. It is shown that in such a structure a gapless state may obtained at a point P of the Brillouin zone of chalcopyrite. The existence of ferron states is pointed out. A construction is made of a ferron state corresponding to the specified irreducible representation of the wave vector group of point P of the Brillouin zone. As a result of the analysis the conclusion is made that CuFeS2 refers to gapless magnetic semiconductors where the gapless state is materialized at the boundary of the Brillouin zone and corresponds to a special case of spatial symmetry. In addition, the gapless state appears to be implemented not in usual but in ferron bands. The existence of a ferron hole is predicted. It is pointed out that the gapless state in CuFeS2 corresponds to the first type gapless state according to the character of the temperature dependence of concentration.
Magnetic Susceptibility of an Ising Ferromagnet with Biquadratic Exchange and Uniaxial Anisotropy
Authors: Iwashita T. , Uryǔ N.
Published: July 2007

For the Ising ferromagnets with S = 1, S = 3/2, S = 5/2, the magnetic susceptibility λ is calculated with the use of the pair model approximation. Assuming the bilinear and biquadratic exchange interactions (J and J′) between nearest‐neighbouring pair of spins and the uniaxial single‐ionic anisotropy D‐term for each spin, the behaviours of χ as a function of these exchange parameters and the uniaxial anisotropy parameter are investigated for four cases of the Ising spin system with the above spin values.
Entropy Optimization in Texture Goniometry. II. Practical Applications
Authors: Schaeben H. , Siemes H. , Auerbach S.
Published: July 2007

Pursuing the approach of finite series expansion methods to the texture problem of recovering an orientation density function (ODF) from its pole density functions (PDF) measured in X‐ray or neutron diffraction experiments, the mathematical model of entropy maximization is applied to pole figure data and numerical results are presented. It is shown that this model as well as its results compare favorably with other methods of ODF restoration because it can yield a solution free of artifacts, also ghosts, if this is at all theoretically possible.
On the Charge Distribution of Ions after Auger Neutralisation at Surfaces
Authors: Taute E. , Blum K.
Published: July 2007

Auger neutralisation of Li3+‐nuclei moving parallel to a metal surface (Al) is considered. For the case of capture of one electron in the 2p‐orbital of the nuclei the charge distribution of the ions is calculated and interpreted.
A Study of Manganese Oxides by EXAFS Spectroscopy
Authors: Mande C. , Deshpande A. P.
Published: July 2007

The experimental data of the EXAFS associated with the K absorption discontinuity of manganese are analysed in four manganese oxides, viz. MnO, Mn3O4, Mn2O3 and MnO2 using the graphical method originally proposed by Lytle, Sayers and Stern and recently modified by Deshpande, Sapre and Mande. It is observed that the backscattering parameter β1 decreases nonlinearly with the increase in the O: Mn ratio. A relationship of this kind can be useful in obtaining information about the content of the ligand atoms attached to the metal atom in compounds.
Femtosecond Studies of Transient Nonlinearities in Wide‐Gap II‐VI Semiconductor Compounds
Authors: Rudolph W. , Puls J. , Henneberger F. , Lap D.
Published: July 2007

Femtosecond light pulses are a convenient tool to excite and measure various optical nonlinearities with temporal resolution, where today these pulses are available in a broad energy and spectral range. Systematic studies are made of femtosecond transients of wide‐gap II‐VI semiconductor compounds for below‐gap, near exciton‐resonant, and above gap excitation, with pump probe and transient grating techniques. By these means gap‐shrinkage, intraband relaxation and carrier diffusion could be observed with fs resolution. Possibilities are discussed to utilize the nonlinearities for fs pulse shaping and diagnostics.
Absorption and Optical Gain Spectra and Band Gap Renormalization of Highly Excited Quantum Well Systems
Authors: Ell C. , Haug H.
Published: July 2007

Optical spectra of highly excited quantum well systems are calculated. Many‐body effects are included within the random phase approximation (RPA). In order to describe a realistic semiconductor quantum well system, finite barrier heights, a thickness‐dependent Coulomb potential and several subbands are taken into account. Furthermore, for quantum well systems like InP/InGaAs or GaAlAs/GaAs, light and heavy hole subbands are included within an effective mass approximation. The renormalization of the band gaps of the allowed transitions are discussed and compared with experimental data of Lach et al. In the range of very high densities deviations between experiment and theory are found, which are probably due to increased intersubband scattering.
Quasi‐Two‐Dimensional Screening of the Electron‐Hole Interaction in Modulation‐Doped Quantum Wells
Authors: Wendler L. , Bechstedt F. , Fiedler M.
Published: July 2007

The screening of the electron‐hole interaction is studied for n‐type modulation‐doped double heterostructures including the effects of size quantization and spatial dispersion accompanying the presence of free carriers. Two different screening models are studied and compared. The resulting screcned potentials are applied to estimate the exciton binding energies by means of a variational procedure. The results are discussed in dependence on the sheet carrier concentration and the well width.
Optical Nonlinearities of GaAs‐Based Epitaxial Structures for All‐Optical Switching
Authors: Oudar J. L. , Sfez B. , Kuszelewicz R. , Michel J. C. , Azoulay R.
Published: July 2007

An experimental study is made of GaAs/AlGaAs monolithic bistable etalons fabricated by metalorganic vapor‐phase epitaxy. Optical bistability is observed in the reflective mode, with a minimum threshold power of less than 3 mW and a switching contrast as high as 30: 1, with a cavity resonator designed to achieve simultaneously a high finesse and a high reflectivity contrast. The dispersive optical nonlinearity of the multiple quantum well active medium is measured as a function of the intracavity intensity, and a strong saturation behavior is observed. The origin of this saturation and its implication on the design of future devices is discussed briefly.
Theoretical and Experimental Results on Coulomb Effects in Semiconductor Quantum Dots
Authors: Hu Y. Z. , Koch S. W. , Lindberg M. , Peyghambarian N.
Published: July 2007

Recent theoretical and experimental studies of semiconductor quantum dots are summarized. The one and two electron hole‐pair states are investigated and the effects of quantum confinement and Coulomb interaction are discussed. Besides intrinsic quantum dots, also the effects of trapped carriers and surface polarizations are analyzed. The nonlinear properties are studied by computing the pump‐induced absorption changes (differential transmission spectra). Good agreement with nanosecond and femtosecond hole‐burning experiments is found.
Nonlinearities of CuCl Microcrystals
Authors: Gilliot P. , Hönerlage B. , Levy R. , Grun J. B.
Published: July 2007

Using a “pump and probe” technique, a strong blue shift and a bleaching is measured of the Z3 excitonic absorption line of CuCl microcrystallites embedded in glass. These effects are attributed to exciton exciton‐interactions. They show a response time shorter than the nanosecond. This seems to be mainly due to a fast non‐radiative decay of the excitonic population, leading to a heating‐up of the microcrystals.
Optical Spectroscopy on One‐Dimensional Compound Semiconductor Structures
Authors: Forchel A. , Maile B. E. , Leier H. , Mayer G. , Germann R.
Published: July 2007

The emission of compound semiconductor wires is investigated. Two types of structures are studied. Open wires defined by electron beam lithography and dry etching show a strong reduction of the quantum efficiency due to sidewall recombination if the quantum size range is approached without any indication of lateral quantization. Overgrown etched structures in contrast show a reduced influence of the etched sidewalls on the quantum efficiency and for a lateral width of the order 50 nm indicate the onset of lateral quantization. Buried quantum wires are fabricated by implantation induced disorder. The evaluation of the wire spectra for different widths down to 40 nm indicates the formation of a significant lateral confinement potential in the structures. Using cw and ps spectroscopy carrier capture into the wires and band filling effects are investigated.
Computation of the Structure Factors of the Peculiar Metals Sb, Bi, Ga, and Sn Using Lebowitz's Solution of Hard‐Sphere Mixtures
Authors: Rao R. V. Gopala , Satpathy A.
Published: July 2007

The peculiar metals Bi, Sb, Ga, and Sn, which show a subsidary right‐hand shoulder in the structure factor at or near the melting point, are studied through Lebowitz's solution of hard‐sphere mixtures by assuming the liquids to be a mixture of two types of species of different diameters. The agreement between theoretical and experimental structure factors throughout the whole range of momentum space is excellent. It is found that metalloids like Bi and Sb can be treated as simple hard‐sphere mixtures of two different species while in the case of metals like Ga and Sn a square well attractive tail is used as a perturbation of the hard‐sphere mixture.
Crystal Field and Metamagnetic Behavior of Rare‐Earth Orthoaluminates: DyAlO3
Authors: Kolmakova N. P. , Krynetskii I. B. , Lukina M. M. , Mukhin A. A.
Published: July 2007

The 15 crystal field parameters of a Cs‐symmetry Hamiltonian are determined for the Dy3+ ion in DyAlO3 by fitting the temperature dependences of susceptibility along the three crystal axes, Stark splittings, and the g‐tensor to the values observed. Metamagnetic transitions are investigated for various directions of the field in the ab plane between T = 1.52 and TN = 3.52 K. The metamagnetic behavior of DyAlO3 is in accordance with the character of the Dy3+ ground state, determined by our crystal field data.
Magnetic Properties of Single Crystals of Bismuth Telluride Doped with 0.2 at% Lead and Its Thermoelectric Power
Authors: Biswas S. , Bhattacharya R.
Published: July 2007

At temperatures above 200 K the diamagnetic susceptibility of Bi2 Te3 doped with 0.2 at% Pb decreases with rising temperature which cannot be accounted for by the change in the diamagnetic contribution of the free carriers present in the substance. It is shown that this decrease can be accounted for if χL (diamagnetic contribution of core and valence electrons) decreases with temperature. The thermoelectric power is measured to determine the effective mass of carriers.
Magnetopolaron in a Quantum Well. LO‐Phonon Confinement Effects
Authors: Rücker H. , Mora‐Ramos M. , Comas F.
Published: July 2007

Magnetopolarons in a polar‐crystal slab are studied considering electron coupling with confined LO‐Phonons. The electron self‐energy is calculated by using the standard perturbation theory treatment. Screening effects are included within the static Thomas‐Fermi approximation. It is demonstrated that phonon confinement lowers the polaron effects. Special attention is paid to the magnetophonon resonance. Phonon dispersion is shown to be important for the interpretation of the interpretation of the pinning of the transition frequencies for high magnetic fields to values much lower than the Brillouin zone center longitudinal optical phonon frequency ω0.
Optical Properties of Gold in the Nonequilibrium Thermalized Stage
Authors: Wenschuh U. , Heiner E.
Published: July 2007

Basing on a recent paper and a linear response theory for highly excited systems far from equilibrium the macroscopic dielectric function (MDF) is evaluated for highly excited noble metal layers by means of the density–density Green's function in RPA with a crude consideration of the band structure of the metal. The evaluation of the time evolution of the directly measurable reflectivity and absorption is added. The results of a model calculation for gold are compared with the results of new time‐resolved pump‐probe‐experiments.
Electric Quadrupole Interaction of 181Ta in Hf2Fe Remeasured
Authors: Akselrod Z. Z. , Komissarova B. A. , Kryukova L. N. , Ryasnyi G. K. , Shpinkova L. G. , Sorokin A. A.
Published: July 2007

The time‐differential perturbed angular correlation (TDPAC) of the 133–482 keV γ‐ray cascade in 181Ta in the intermetallic compound Hf2Fe is measured in the temperature range 78 to 903 K. At 78 K the following parameters of the electric field gradient (EFG) at the two unequivalent Hf sites are obtained: V = (1.91 ± 0.14) × 1022 V/m2, η(1) = 0.505(7); V = (1.05 ± 0.2) × 1021 V/m2, η(2) = 0 (fixed parameter). Discontinuities in the temperature dependence of the EFG parameters at T ≈︁ 600 K are observed as well as an indication at the possible existence of the third Hf site above 600 K.
Theory of Silicon Vacancy in Vitreous Silica
Authors: Dianov E. M. , Sokolov V. O. , Sulimov V. B.
Published: July 2007

Electronic properties of a silicon vacancy in solid silicon dioxide are investigated by a semiempirical method, MINDO/3, in a cluster approach. Charge states of the vacancies V, V, V, V, V are considered with taking into account the relaxation of the oxygen atoms of the first co‐ordination sphere of the defects.
Super Hyperfine Structure in the EPR Spectrum of Divalent Manganese in Single Crystal Zinc Selenide
Authors: Marshall S. A. , Yoder‐Short D. R. , Yu C. , Zhang Y. N. , Furdyna J. K.
Published: July 2007

The EPR spectrum of divalent manganese in single crystals of zinc selenide having the zinc blende modification is reinvestigated. In addition to the fine structure and self‐hyperfine structure spectra, the super‐hyperfine structure spectrum due to interactions with host ion nuclei of the first three neighboring shells is observed. A list of spectral parameters deduced from data taken at 4.2 K is given.
Angular Distribution of Elastically Reflected Electrons from Au
Authors: Ding Z.‐J. , Yoshikawa H. , Shimizu R.
Published: July 2007

The angular distributions of elastically reflected electrons from an evaporated gold film surface are measured at primary energies 400, 600, and 800 eV for different angles of incidence between 0° and 75°, and the influence of 2 keV Ar+ ion bombardment is investigated. By means of Monte Carlo simulations the theoretical distributions incorporating multiple scattering are also derived and compared with the experiment. The results reveal that the angular dependency of elastically reflected electrons for polycrystalline Au is dominated by the atomic differential cross sections for elastic scattering.
Tin and Iron Impurity Atom States in Modified As2Se3 Films
Authors: Turaev E. Yu. , Seregin P. P. , Nasredinov F. S.
Published: July 2007

Electrical and optical properties of amorphous As2Se3 films modified by tin (a non‐transition metal) and iron (a transition metal) as well as the state of the modifying impurity atoms are investigated. Tin is found electrically inactive in the modified films like in vitreous As2Se3. Iron in the modified films is shown to form donor centers with the ionized and neutral states corresponding to the Fe3+ and Fe2+ ions, respectively. A conclusion is made that an electrical activity of impurities in the chalcogenide semiconductors modified films results from the chemical nature of modifiers whereas the rf co‐sputtering technique provides their high concentration only.
On the Anisotropy of Scattering in Doped n‐Ge at Low Temperatures
Authors: Matveev G. A. , Tsidilkovskii I. M. , Lonchakov A. T.
Published: July 2007

On Ge : Sb crystals with dopant concentrations, N, ranging between 8 × 1016 and 1.5 × 1018 cm−3, the temperature and concentration dependences are found of the mobility anisotropy coefficient, K, over the temperature interval 4.2 K ≦ T ≦ 180 K and at T ≦ 4.2 K. At temperatures Tc close to the Hall‐coefficient‐maximum temperature, the K versus T curve exhibits a minimum at T = Tmin. The temperature Tmin corresponds to the boundary that separates the regions of weak and strong electron scattering. At sufficiently low temperatures, where the scattering is strong (the impurity and band states of electrons are mixed), neither the formulae for classical conductivity nor the formulae of the theory of quantum corrections permit a reliable determination of the value of mobility anisotropy K.
Ashcroft‐Langreth Prescription for Effective Core Diameter in Liquids. A Variational Analysis
Authors: Das T. , Bhuiyan L. B. , Joarder R. N.
Published: July 2007

The Ashcroft‐Langreth (AL) ansatz for the effective hard‐sphere diameter in a simple liquid is analysed in the light of Gibbs‐Bogoliubov variational theory for the free energy of the system. It is seen that for a reasonable choice of the pair potential, for example, the Lennard‐Jones potential for liquid Ar and the effective pair potential based on the Ashcroft model for liquid alkalis, Na, K, Rb, and Cs, the prescription is in general valid at or near the normal melting temperatures. However, at the thermodynamic states away from the normal melting point, the ansatz becomes increasingly inaccurate.
First‐Principles Calculation of the Lattice Dynamics of the Co0.92Fe0.08 Alloy
Authors: Shyam R. , Upadhyaya S. C. , Upadhyaya J. C.
Published: July 2007

First principles calculation of the lattice dynamics of the f.c.c. Co0.92Fe0.08 alloy is done by applying the transition metal model potential of Animalu. The ab initio radial and tangential force constants are calculated upto 10th nearest neighbours for pure Co and Fe at the lattice constant of the f.c.c. alloy. Next concentration averages of the force constants and masses of Co and Fe are used to compute the phonon frequencies of the Co0.92Fe0.08 alloy. A reasonably good agreement is found between the computed and experimental dispersion results. Phonon density of states, specific heat, Debye temperature, and elastic constants are also computed and the results are compared with available calculations of others.
Electron–Hole Exchange Interaction of Excitons in Direct Band Gap Cubic Semiconductors with Degenerated Valence Band
Authors: Huong Nguyen Que , Thang Nguyen Toan , Viet Nguyen Ai
Published: July 2007

Fine structure of excitons in direct band gap cubic semiconductors is studied. The general formulae for exchange energy of any excitonic states are given. Splitting of energy levels and corresponding wave functions are written for nS and nP exciton states for example.
The Electronic Structure of the Alkaline‐Earth Oxides. V. Peculiarities of the Hole‐Trapping in NaF and MgO
Authors: Lobatch V. A. , Rubin I. R. , Lushnikov P. V.
Published: July 2007

Calculations are made for clusters simulating the Vk‐center in NaF and a hypothetic self‐trapped hole in MgO within the embedded cluster approach. The “non‐ionic” charge configuration of MgO, described earlier, is analysed as a possible cause of the absence of the hole self‐trapping manifestations in the oxide according to the mechanism known for NaF. Due to the delocalization of oxygen 2p‐states the hole orbital is oriented, in contrast to NaF, perpendicularly to the 2‐anion quasi‐molecule axis, while the hole state itself lies close to the top of the potential barrier bonding this state.
The Thermoelectric Figure of Merit in the Mixed Crystal System p‐(Bi1−xSbx)2Te3
Authors: Stordeur M.
Published: July 2007

The figure of merit Z is a measure for the effectiveness of the thermoelectric material p‐(Bi1−xSbx)2Te3and depends on the valence band structure, the charge carrier scattering, the lattice thermal conductivity, and the free carrier density. It is shown that crystals with the compositionx= 0.75 are favoured by the band structure to have the highest figure of merit in this mixed crystal series. In the frame of a consistent model for the electronic structure the theory—experiment comparison gives good quantitative agreement for theZ(S)‐plot in terms of effective masses and lattice thermal conductivity over a wide range of the Seebeck coefficientS.
Bloch Walls in Magnetostrictive Metallic Glasses
Authors: Kraus L.
Published: July 2007

One‐dimensional Bloch walls in weakly anisotropic magnetostrictive media are investigated theoretically. It is shown that there are two effects of magnetoelastic coupling on the walls: 1. magnetic anisotropy induced by external stress and 2. internal stress of the wall required by compatibility. The resulting magnetic anisotropy is generally of orthorhombic symmetry implying that the wall energy depends on the orientation of the wall. The internal stress of the wall can be a determining factor for the energy and the width of the walls in weakly anisotropic and highly magnetostrictive amorphous alloys.
Lattice Dynamics of Ammonia
Authors: Zeng W. Y. , Anderson A.
Published: July 2007

A simple force constant model is developed and applied to the vibrations of solid ammonia, NH3 and ND3. Four intramolecular (two stretching and two bending) and six intermolecular force constants are adjusted to obtain the best fit to the crystal field splittings and lattice mode frequencies observed by Raman and infrared spectroscopy. Isotopic shifts are also calculated. The principal intermolecular interactions are of the HH and NH type, but there is no evidence of hydrogen bonding in the crystal. The intramolecular N–H bond is weakened by about 8% from its gas phase value.
Mobilities and Concentrations of Charge Carriers in Polycrystalline Bi0.87Sb0.13 Films
Authors: Völklein F. , Dillner U.
Published: July 2007

The carrier mobilities and concentrations of polycrystalline films of Bi0.87Sb0.13 with thicknesses between 30 and 330 nm are presented and discussed in the temperature range between 80 and 360 K. They are calculated from the electrical conductivity as well as the low‐field Hall and magnetoresistance coefficients in a magnetic field directed orthogonally to the film plane. An anisotropic two‐carrier model is taken as a basis for the calculation.
Theory of Germanium‐Related Defects in Vitreous Silicon Dioxide. I. Germanium Atom in Silicon Site
Authors: Dianov E. M. , Sokolov V. O. , Sulimov V. B.
Published: July 2007

A germanium substitutional impurity (Ge atom in a silicon vacancy) in vitreous silicon dioxide is investigated by a quantum chemical MNDO method in a cluster approach taking into account the relaxation of the nearest atomic environment of the defect.
Temperature Dependent Field Ionization of Phosphorus Atoms in Silicon
Authors: Dargys A. , Žurauskienė N. , Žurauskas S.
Published: July 2007

Temperature dependent transient tunneling spectra of Si〈P〉 are considered on the basis of two models. The influence of sound vibrations on the field ionization of phosphorus atoms in silicon is analysed numerically and compared with available experimental data. It is found that eletron thermal transitions from ground to orbit‐valley split levels and their subsequent tunneling through the barrier with lower potential gives the main contribution to the ionization rate of phosphorus atoms at high electric fields.
Resistive Wires Instead of Ideal Leads. Breakdown of the Channel Equipartition Rule
Authors: Lenk R.
Published: July 2007

A quantum wire with constant cross‐section and ideally reflecting lateral boundaries, filled uniformly (on the average) with point‐like elastic scatterers in the dilute limit, is considered as an idealized model of a resistive lead. Due to the unavoidable energy and channel dependence of the mean free path, the conducting channels contribute differently to the current which is dominated by the fast channels. This result disagrees with the usual channel equipartition rule for ideal leads fed by reservoirs in statistical equilibrium. The nontrivial behaviour of the mean free path prevents also the employment of separate chemical potentials, in the strict sense of corresponding partial equilibrium states, for the carriers moving in both directions within a current‐carrying wire.
EPR of a Gd3+‐Doped NH4Pr(SO4)2 · 4 H2O Single Crystal. Study of Phase Transition and Superposition Model Calculation of Zero‐Field Splitting Parameters
Authors: Misra S. K. , Sun Jiansheng
Published: July 2007

X‐band EPR spectra of a single crystal of Gd++‐doped NH4Pr (SO4)2 · 4 H2O (APST) are recorded in the temperature range 4.2 to 410 K. The angular variation of the EPR line positions indicates the presence of two magnetically‐inequivalent Gd3+ ions. The orientations of their principal axes are determined. The Gd3+ spin‐Hamiltonian parameters are evaluated using a rigorous least‐squares‐fitting procedure. The superposition model is applied to calculate the values of the zero‐field splitting parameters b, b of Gd3+, and those of the intrinsic parameters b2 and b4. The temperature variation of the EPR spectra reveals the occurrences of two first‐order phase transitions in APST crystal at 266 and 155K.
Exciton Reflection Spectra of NaI Crystals. Effect of Surface Irradiation by Photons and Incidence Angle Dependence
Authors: O'Connel‐Bronin A. A. , Treshchalov A. B.
Published: July 2007

Reflection spectra of NaI crystals cleaved in liquid helium are investigated in detail. A fine structure is discovered in the spectral region adjacent to 2S exciton resonance at the high‐energy side. It is interpreted as the manifestation of the splitting of the n = 2 exciton state which was predicted by Balslev. The LO structure below the 2S line is observed, which is interpreted as the revealing of vibrational states of self‐trapped excitons. The influence of irradiation by photons on the crystal surface is studied. Considerable changes are detected in the 2S reflection line region, which are discussed involving the “dead” layer model. The character of the dispersion contour of the 2S exciton line is discussed. The dependence of the reflection spectrum on the incidence angle is investigated. A stronger angular dependence in the 2S region of the spectrum than in the 1S region is pointed out.
Dipole Polarizability of O2− Ions near the (011) and the (111) Surface of Alkaline Earth Oxides
Authors: Kassim H. A.
Published: July 2007

The effect of (011) and (111) surfaces on the dipole polarizability of O2− ions in alkaline earth oxides is estimated by employing a variational perturbation method in the manner of Kirkwood, Pople, and Schofield. Initially the study concentrates on O2− ions in the bulk and then moves gradually to surface sites. The reduced surface polarizability as compared with the bulk value is attributed to the variation in the crystalline medium when moving from the bulk to top layers. In all the cases, ideal surfaces are assumed. Modifications in these surface values due to surface reconstruction may be important but are not included in the present study due to the uncertainty in the actual surface geometry.
Nonequilibrium Thermoreflectance Evolution of Laser Irradiated Noble Metals
Authors: Wenschuh U. , Heiner E.
Published: July 2007

A theory for the evalution of the optical properties of laser irradiated noble metal layers in a thermalized nonequilibrium stage presented recently is applied to the calculation of transient thermoreflectance alterations in gold, silver, and copper. An improvement of the theory that simplifies direct comparisons with experiments is given after the introduction of the laser intensity into the interacting term of the model Hamiltonian which describes the coupling of the laser field to the electron system. Numerical results are discussed in view of new time‐resolved pump‐probe‐experiments.
Structural Modelling of Low‐Symmetry Phases of Spinels. II. Phases with 1:3 Octahedral Order
Authors: Talanov V. M.
Published: July 2007

On the basis of the phenomenological theory of phase transitions the structural mechanism of ordering of octahedral cations of the type 1:3 in spinels is studied. With the help of the basic functions of the active six‐dimensional irreducible representations of the group Fd3m the structure of the ordered phase is deduced theoretically from the non‐ordered phase. The qualitative pictures of possible displacements of atoms near the temperature of the phase transition are given. The existence of isostructural modifications of the ordered structure is predicted.
X‐Ray Analysis of Structural Defects in a Semiconductor Superlattice
Authors: Holý V. , Kuběna J. , Ploog K.
Published: July 2007

The structural defects in a (GaAs)m/(AlAs)n superlattice are studied experimentally and theoretically as well. Three models for the defects are proposed, which follow from the SL growth kinetics. Direct expressions for the reflectivities are derived from the semikinematical approximation of X‐ray diffraction, assuming that the statistical parameters characterizing the defect models are distributed normally. On the basis of a numerical fit of the theoretical and experimental double crystal X‐ray rocking curves the mean lattice parameter and the mean chemical composition as well as their statistical dispersions are found for a [(GaAs)m/(AlAs)n]120 superlattice. The X‐ray diffraction curves enable one to find the most probable model for the actual structural defects in the real superlattice.
Multifractal, Localized, and Extended Wave Functions in Generalized Fibonacci Chains
Authors: Böttger H. , Kasner G.
Published: July 2007

The ƒ(α) singularity spectrum of wave functions in a 1d generalized Fibonacci tight binding electron model are investigated. Localized, extended, and critical wave functions are found in contrast to the pure Fibonacci chain.
Transient Thermoelectric Effect in Quasi‐Two‐Dimensional η‐Mo4O11 Crystal
Authors: Sasaki M. , Tai G. X. , Inoue M.
Published: July 2007

Dynamic measurements of thermal diffusion of conduction carriers in quasi‐two‐dimensional η‐Mo4O11 crystals which undergo charge‐density‐wave transitions are made over the temperature range 12 to 300 K and time range 50 ns to 2 ms using a pulsed laser‐induced “transient thermoelectric effect (TTE)” technique. The light‐generated TTE voltage decays exponentially with multiple relaxation times τi (i = 1 to 5), from which the nature of the Fermi surfaces of both electrons and holes is discussed based on recent tight‐binding band calculations.
Positron Studies of the Chemical Composition of Guinier‐Preston Zones in AlZn Alloys
Authors: Dlubek G. , Gerber W.
Published: July 2007

Various decomposed AlZn alloys are investigated by positron lifetime and angular correlation technique in order to study the potential of positron method in estimating the composition of Guinier‐Preston zones. From experiments the curve shape parameters, S, the core annihilation rate, λc, and the number of free conduction electrons, z, derived from the zeros of the one‐dimensional Fourier‐transform of the angular correlation curve are estimated. The response of the various annihilation parameters to zone composition, positron affinity, and alloying effects (lattice change, charge transfer) is discussed. The number of free electrons per atom reflects most clearly the chemical composition of the GP zones.
Electron Mobility for a SiSi1−xGex Quantum Well: Acoustic Phonon Scattering Mechanism
Authors: Tutor J. , Bermudez J. A. , Comas F.
Published: July 2007

Drift mobility is calculated at the low temperature regime along the Si channel of a SiSi1−xGex quantum well (QW). Boltzmann transport theory is applied assuming electron interaction with acoustic phonons via the deformation potential mechanism. Infinite potential barriers are supposed at the interfaces and the electron states are obtained in the effective mass approximation. The acoustic phonon spectrum is treated in the standard 3D approach using an electron–phonon Hamiltonian adapted from the bulk case. Obtained results are compared with experiment.
Frequency Dependednt Losses in YBaCuO Superconductors
Authors: Nag A. , Joarder R. , Ghosh B. , Neogy C. , Deb S. K.
Published: July 2007

The real and imaginary parts of the frequency dependent response of YBaCuO samples doped with scandium are measured over a wide frequency range (5 Hz to 13 MHz) both, in the normal (at 298 K) and in the superconducting (at 77 K) states. An attempt is made to made to identify the relaxation mechanisms responsible for ac conduction in the samples. It is suggested that 2p hole‐polarons associated with the oxygen atoms play an important role in determining the frequency dependent behaviour in the normal state as well as at their superconductivity.
Properties of p‐Polarized Nonlinear Surface Polaritons
Authors: Groza A. D. , Strizhevskii V. L.
Published: July 2007

A solution is obtained of the stationary problem of p‐polarized nonlinear surface polaritons (NLSP) near the interface of two media, one of which is optically linear and the other one has an optical nonlinearity with saturation. On this base the properties of the NLSP propagating along the interface of the self‐focusing medium with positive dielectric fanction and the linear medium with positive dielectric function are investigated in detail.
Computer Simulations of ESR Spectra of Amorphous Thiomolybdates
Authors: Berger R. , Haddad M.
Published: July 2007

ESR spectra of amorphous chalcogenides MoS2+x (1 ≧ x ≧ 0) at 9.5 and 35 GHz reveal three different signals whose parameters are determined by computer simulation. The corresponding paramagnetic centers are: a) an electron hole center, with three principal values of the g‐tensor, localized on a sulfur atom, b) a Mo(V) center surrounded by sulfur atoms and characterized by an axial g‐tensor, c) a Mo(V) center surrounded by oxygen atoms, with also an axial g‐tensor, which results from a contamination by oxide traces. An anisotropic linewidth is taken into account to obtain an acceptable fitting for the different signals, it means distributions of g‐values originating from random local structural fluctuations in the amorphous compounds. Amorphous Li2MoS3 is also examined by ESR for comparison.
Shear Instability in a System of Point Defects
Authors: Gluzman S. L. , Psakhe S. G.
Published: July 2007

Impurity behaviour (both thermodynamic and mechanic properties) are investigated under pressure and shear application. The conditions are found of shear instability occurrence — the critical temperature θc and critical shear stress τc. θc decreases with shear stresses application and τc decreases with temperature growth. The used Green's functions method could be applied for the different cases of atomic Hamiltonians and for the different types of mechanical loading.
Orientationally Disordered Hydrogen. Freezing of Short‐Range Order
Authors: Kokshenev V. B.
Published: July 2007

The RMS (root mean square) polarization magnitude of an orientationally disordered ortho‐parahydrogen mixture is analyzed in terms of a microscopic model. Various models of the quadrupolar glass theory are considered; the calculated orientational polarization values are compared with the data of the NMR absorption signal in hydrogen. It is found that fluctuations of the ortho‐hydrogen molecule crystalline field produce an essential effect on freezing of the short‐range orientational order at temperatures above 1 K.
Luminescence of Lead Ions Associated with Interstitials and Vacancies in Alkali Halides
Authors: Egemberdiev Zh. , Usarov A. , Zazubovich S.
Published: July 2007

Several types of luminescent associates of lead ions (Pb2+, Pb+) with interstitial halide ions (X−i) as well as with cation (v−c) and anion (v+a) vacancies are observed in alkali halides X‐irradiated at 80 or 295 K. Optical properties and a detailed structure of these associates, the processes of their creation and destruction as well as their optically or thermally stimulated transformations are studied. The associates investigated form the three following groups each containing several types of centres: (1) centres on the basis of a PbX‐molecular ion; (2) centres on the basis of a Pb2+X dipole; and (3) centres of the laser‐active structure on the basis of a Pb+X−v+a associate. The optical characteristics of the various centres of each group are shown to be similar. It is concluded that they are determined by electronic transitions between the energy states of the basis associate (PbX, Pb2+X, or Pb+X−v+a), and that the influence of some other defects (v, X, X3, etc.) may be considered as a small perturbation.
A Study of Cobalt Centers in 3 CdSO4 · 8 H2O Single Crystals
Authors: Prasad P. S. S. , Radhakrishna S.
Published: July 2007

The optical absorption spectra of Co2+ in 3 CdSO4 · 8 H2O single crystals are studied at ambient (300 K) and liquid nitrogen temperatures (80 K). From the nature and position of the observed bands, a successful interpretation could be made assuming octahedral symmetry for the Co2+ ions in the crystals. The splittings observed for the 4T2g(F) band in Co2+ at 80 K is explained as due to the spin—orbit interaction. The band positions are fitted with the four parameters: B = 960 cm−1, C = 3840 cm−1, Dq = 940, and γ = 550 at 300 K and B = 990 cm−1, C = 3960 cm−1, Dq = 940, and γ = 600 at 80 K. The polarized crystal spectra of Co2+ doped 3 CdSO4 · 8 H2O are recorded at 80 K and the three anisotropic bands observed near 8097, 14422, and 18692 cm−1 are presumed to be due to the spin allowed 4T1g(F) → 4T2g(F), 4T1g(F) → 4A2g(F), and 4T1g(F) → 4Tlg(P) transitions of substitutional Co2+ in 3CdSO4 · 8H2O. The observed anisotropy indicates that the 4T2g(F) band is largely magnetic dipole while the other two are electric dipole in nature.
Crystal Field in Some Rare Earth Intermetallics Analysed in Terms of the Superposition Model
Authors: Diviš M.
Published: July 2007

The reliable experimental data of the crystal field parameters in the REPd3 (RE = Pr, Nd, Tb, Dy, Ho, Er, Tm), (RE, Y)Pd3, REB6 (RE = Pr, Nd), PrX2 (X = Ni, Rh, Ir, Pt, Ru, Mg), RENi2, (RE, T)Al2 (T = Sc, Y), and RENi5 intermetallic compounds are analysed in terms of the superposition model. The obtained systematic behaviour of intrinsic parameters supports the applicability of the model in RE intermetallics. The validity of the usual power‐law expression, connection with the results of ab‐initio calculations, and further possible tests of the model are discussed.
Some Magnetic Properties of Thin Ferromagnetic Film with Enhanced Surface Exchange Interactions
Authors: Wiatrowski G. , Mielnicki J. , Balcerzak T.
Published: July 2007

Thin S = 1/2 ferromagnetic film with exchange interaction enhanced near the film surface is considered in the Ising model. As a result the phase diagrams, the magnetization profiles, and magnetization curves for several particular cases are presented. A modified definition of the critical δc parameter for the thin film case is also proposed.
Laser modulation of photochromic effect in crystals with sillenite‐type structure
Authors: Efendiev Sh. , Gavryushin V. , Raciukaitis C. , Bagiev V. , Kazlauskas V. , Puzonas G. , Aliev R. , Mustafaev E.
Published: July 2007

In sillenite‐type crystals at low temperatures the phenomena of effective laser modulation of the photochromic effect (LM PCE) previously investigated in steady‐state conditions are found. The lack of effects of spatial excitation transfer during PCE is shown from the kinetics of PCE laser “switching”. Conclusions about intracentre behaviour of the above processes are made. The IR laser illumination is found to lead to anomalous LM PCE (optical obscurity of crystals) relative to the previously known steady‐state IR effect on PCE (crystal brightening). Based on the LM PCE data, a new model of intracentre optical processes and PCE centers with anomalously strong electron—phonon interaction (EPI) near the centers with a number of excited states is proposed. The idea of the above model is the assumption of non‐photoactivity of the ground states of PCE due to strong EPI from which the centers remove at IR illumination. The main regularities of PCE previously known are also explained by the microscopic model proposed with regard to Stokes losses of lattice relaxation.
A model for describing dielectric breakdown in vitreous solids based on the concept of low‐energy excitations
Authors: Danziger M. , Bernhardt A.
Published: July 2007

The anomalous behaviour of different physical characteristics in vitreous solids compared to the behaviour in the crystalline phase, in particular their dielectric behaviour, can be described by the concept of a system of low‐energy excitations in these solids. This concept is also applicable for amorphous SiO2 layers in MOS structures. Thus, a model of breakdown behaviour based on the assumption of the existence of fluctuations of correlated local internal electrical fields and low‐energy excitations within these layers is elaborated.
Phonons in Some H.C.P. Solids
Authors: Rathore R. P. S. , Singh A. , Agrawal R. M.
Published: July 2007

The phonon dispersion along the directions [0001] and [0110] in Hf, Ti, and Cd is determined by employing the combined form of a pairwise and non‐pairwise potential, which derive their forms from the generalised exponential nature of repulsive and attractive interactions.
Coherent Potential Method in the Electronic Theory of Disordered Alloys
Authors: Kulish N. P. , Petrenko P. V. , Repetskii S. P. , Shatnii T. D.
Published: July 2007

A general solution of the problem of multiple scattering on a localized random potential is achieved in a single‐band model of diagonal disorder for a binary substitutional alloy. A configurationally averaged 〈T〉‐matrix is presented as a cluster‐type expansion. The short‐range order effect on the electronic spectrum, specific heat capacity, and residual electrical conductivity is studied with regard to the multiple scattering on a two‐particle cluster (on pairs of atoms) for the coherent potential satisfying the condition of the single‐site approximation. Expressions for the electronic density of states and electrical conductivity (allowing for the scattering on pairs) are presented in an analytical form.
Low‐Temperature Heat Conductivity of a Crystal Lattice with Nondiagonal Disorder
Authors: Zhernov A. P. , Salamatov E. I. , Chulkin E. P.
Published: July 2007

A theory is developed which allows investigation of the phonon‐transfer processes in a harmonic crystal lattice with nondiagonal disorder taking into consideration the weak localization phenomenon. In the expressions obtained for the heat conductivity coefficients the phonon and impurity modes are taken into account.
The Electronic Structure of Crystalline Lead Oxides. I. Crystal Structure and LUC‐CNDO Calculations
Authors: Evarestov R. A. , Veryazov V. A.
Published: July 2007

The crystalline structure of lead oxides is rewieved. In the framework of LUC‐CNDO computational scheme the electronic structure of PbO, PbO2, Pb2O3, and Pb3O4 crystals is investigated. The results obtained are compared with experimental data.
The Electronic Structure of Crystalline Lead Oxides. II. Chemical Bonding in the Crystalline Lead Oxides
Authors: Evarestov R. A. , Veryazov V. A.
Published: July 2007

A quantum‐chemical definition is proposed of the full atomic valence taking into account both, covalent and ionic components of chemical bonds formed by an atom in molecules or crystals. Atomic charges, covalent bond orders, and full atomic valencies of lead and oxygen atoms in the crystalline lead oxides are calculated in the framework of the LUC‐CNDO approach.
Exciton Trapping at Au and Ag Atoms in Rare Gas Matrices
Authors: Schrimpf A. , Herkert B. , Manceron L. , Schriever U. , Stöckmann H.‐J.
Published: July 2007

The fluorescence of Au and Ag atoms in Ar and Kr matrices is investigated as a function of the excitation wavelength in the UV and VUV range. The occurrence of a fluorescence of the dopants during excitation into the exciton bands of the matrices demonstrates the existence of energy transfer from the solid host to the embedded metal atoms. The emission spectra after exciton and inner‐shell excitation, respectively, as well as the temperature dependence of the emission yield show striking similarities. From this it is concluded that the exciton trapping leads to an excitation of the same inner‐shell states that are also populated by direct inner‐shell excitation of the metal atoms.
A Functional‐Integral Study of the t̃pp‐Jpd‐Jdd Model for CuO2‐Based Superconductors
Authors: Bryja L. , Kolley E. , Kolley W.
Published: July 2007

A functional‐integral representation of the ˜pp‐Jpd‐Jdd model for a CuO2 layer in high‐Tc superconductors is exploited in the saddle‐point approximation. The self‐consistent mean‐field scheme resulting from the static and homogeneous approximation of the saddle‐point equations is solved numerically at T = 0. The O‐hole pairing connected with the superconductivity is investigated as a function of the doping concentration of O holes. The interplay between the Cu–O Kondo‐type and the Cu–Cu superexchange interactions is illustrated.
Transfer Matrix Formalism for Retarded Waves in Layered Magnetic Structures. Bulk and Surface Modes
Authors: Barnaś J.
Published: July 2007

The retarded modes of layered magnetic structures are considered theoretically for arbitrary direction of wave propagation. A 4 × 4 transfer matrix formalism is used to derive the dispersion equations for bulk and surface modes of semi‐infinite superlattices.