bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nonlinear Optical Properties of CdS at Room Temperature. A Comprehensive Study
Authors: Spiegelberg Ch. , Puls J. , Henneberger F. 
Published: July 2007

AbstractA systematic study is given of the linear and nonlinear optical response at the fundamental absorption edge of CdS at room temperature. It is shown, that at low optical power the strong nonlinearity is due to the screening of excitons in the free carrier system. From single‐beam transmission experiments and degenerate four‐wave‐mixing the change of absorption and refraction, respectively, is deduced induced by one electron‐hole pair. Even 50 meV below the exciton resonances application of the strong dispersive nonlinearity at mW‐power is demonstrated.
Progress on Bose‐Einstein Condensation of Excitons
Authors: Mysyrowicz A. , Snoke D. W. , Wolfe J. P. 
Published: July 2007

AbstractNew results are presented which show evidence for Bose‐Einstein condensation of paraexcitons in Cu2O following creation of a high density of free carriers. Evidence relies on time and space‐resolved analysis of exciton luminescence. Extracted densities of paraexcitons exceed the critical value for Bose‐Einstein condensation by one order of magnitude. Luminescence spectra show anomalies which are discussed in the framework of the non‐ideal Bose gas. Anomalous transport properties are observed at high densities suggesting a superfluid flow of excitons.
High‐Density Spectroscopy of ZnSe/GaAs Epilayers in the Near‐Band‐Edge Region
Authors: Presser N. , Kudlek G. , Gutowski J. , Durbin S. M. , Menke D. R. , Kobayashi M. , Gunshor R. L. 
Published: July 2007

AbstractZnSe epilayers grown by MBE on (100) GaAs substrates are optically investigated in comparison with bulk ZnSe crystals using photoluminescence and excitation spectroscopy under high excitation densities. High‐density luminescence bands appear in both materials for relatively low excitation densities (about 30 kW/cm2), but their energetic positions do not correspond. The intensity‐dependent shape, and the behaviour of the dominant band in bulk ZnSe in excitation spectroscopy are similar to that of the M band in other II VI semiconductors. The main bands growing up in the ZnSe/GaAs films are much more corresponding to typical P‐band emission of exciton‐exciton collision. Further, the transmission of ZnSe epilayers released from the GaAs substrate is studied in dependence on the laser intensity.
Theoretical Investigation of Ferroelastic Phase Transition of Pure and Mixed Alkali Cyanide Systems by the Elastic Dipole Model. III. The Dipole‐Diluted and Mixed Alkali Cyanide Systems
Authors: Yang Zhengju , Ortiz‐Lopez J. , Luty F. 
Published: July 2007

AbstractThe elastic dipole model and results presented in two previous papers are applied to study the phase transitions of mixed and diluted alkali cyanide systems. The effect of impurities in the crystal on the phase transition temperature is analyzed at first. It is supposed that part of the CN− ions may be preferentially aligned in some directions and can not rotate freely due to the elastic interaction between CN− ions and impurites. When the concentration of CN− ions, taking part in the ordering process, is less than that corresponding to the suddenly changed amount of order parameter at the phase transition point, the maximum ordering energy in the lattice will not be large enough to permit the ordering process to take place, and the crystal will remain in a disordered state at all temperatures. With this model the experimental results obtained in these systems can be explained reasonably well. The effects of hydrostatic pressure on the phase transition temperature are attempted to be analysed too.
Optical Properties of Multi‐Layer Structures. III. Raman Scattering in Multi‐Layer Structures and Superlattices
Authors: Fomin V. M. , Pokatilov E. P. 
Published: July 2007

AbstractThe theory of Raman scattering is extended over multi‐layer structures with any number of semiconductor and dielectric layers; the explanation is based on the modulation transfer matrices. The location and configuration of Raman peaks are calculated as functions of the polarization of incident and scattered radiation caused by different types of oscillatory excitations in superlattices by spatially extended interface phonons, spatially decreasing phonons and “confined” bulk phonons.
Optical Properties of the Mixed‐Valent TmSe
Authors: Kikoin K. A. , Nizhnikova G. P. , Farberovich O. V. 
Published: July 2007

AbstractThe optical density of states (ODOS) of the mixed‐valent semiconductor TmSe is considered as the superposition of the interband ODOS for the selfconsistent band spectrum of TmSe calculated by the linear augmented plane wave method in the scalar relativistic approximation, and the interconfigurational DOS arising due to the excitation of the Tm f‐shell. This approach is based on the general description of the mixed‐valence semiconductor as an excitonic dielectric. The results of the calculations are compared with the experimental reflectivity spectrum of TmSe.
Plasma‐Electric Effect in Anisotropic Semiconductors in Heating Electric Field
Authors: Gorlei P. N. , Zagorodnyaya T. A. , Shenderovskii V. A. 
Published: July 2007

AbstractThe effect of appearance of a constant current (at a closed circuit) in anisotropic semiconductors at propagation of longitudinal oscillations with an external carrier‐heating electric field applied to the sample is investigated. The departure of the energy dispersion law from the isotropic parabolic one (as, e. g., in tellurium) is ascertained to result in an additional term in the expression for the current, which is absent for an equilibrium plasma; its contribution can be determined under certain conditions. Consideration of the energy dependence of the relaxation time as well brings about additions to the constant current, which may also be in an equilibrium plasma. Dependences of the current on the oscillation frequency and wave vector as well as on orientation of the external electric field relative to crystallographic axes are derived.
Optical Constants of Tin Sulphide Single Crystals Measured by the Interference Method
Authors: Elkorashy A. M. 
Published: July 2007

AbstractThe refractive index, n, of SnS single crystals is measured from reflectance after being normalized to account for the pronounced rise below the energy gap n is also measured by the interference method in the transparency region. An effective thickness smaller than the true one is introduced to account for the photon scattering by the layer structure of the material in this region. The effective thickness hypothesis gives a satisfactory explanation of the pronounced rise in reflectance for E < Eg. The extinetion coefficient, k, is calculated from the measured absorption coefficient. Measurements are performed at room temperature using plane polarized light with the plane of polarization parallel to the a‐ and b‐crystallographic axes which lie in the plane of cleavage. The real and imaginary parts of the complex dielectric constant (εr, εi) are calculated from the values of n and k. It is shown that SnS single crystals exhibit birefringence. Assuming that the SnS binding is partly ionic and partly covalent, the results of the optical constants are satisfactorly fitted to the model of a single effective oscillator.
Confined‐LO‐Phonon‐Limited Mobility in a Semiconductor Quantum Well
Authors: Leon H. , Comas F. 
Published: July 2007

AbstractLow‐field drift mobility for transport parallel to the interfaces in a semiconductor quantum well is calculated by means of an iterative procedure. Electron–confined‐LO‐phonon‐interaction Hamiltonian is taken from a previous work. Calculations are accomplished in the size‐quantum‐limit approximation (when just the first subband is considered) for a degenerate electron gas. Screening effect is neglected. Comparison with earlier works on the subject is made, and the conclusion is drawn that the effect of LO‐phonon confinement comes out in a increasing of mobility values when only this scattering mechanism is taken into account.
Electronic Structure of (001) Semiconducting MTe Surfaces (M = Zn, Cd, Hg)
Authors: Rodríguez F. , Camacho A. , Quiroga L. , Baquero R. 
Published: July 2007

AbstractBy using the tight‐binding scheme with ten orbitals per atom (SP3S* and two spin orientations) the electronic projected bulk band structure, surface band structure (both anion‐and cation‐terminated surfaces), and the wave‐vector‐resolved density of states for these II‐VI semiconductors are calculated. A quickly convergent iterative technique is employed for calculating the Green function of the actual semi‐infinite crystal. This calculational method allows to precise very accurately, the energy of localized surface states. All the materials considered in this work present surface states with energies lying in the fundamental gap as well as surface states in the lenses opened in the projected bulk valence‐band continum. The atomic weight of each surface state is determined. The states in the fundamental gap turn out to be ‘bridge‐bond’‐type states for anion‐terminated surfaces and ‘dangling‐bond’‐type states for cation‐terminated surfaces.
The New Mechanism of Physical Adsorption on Solid Surface. II. Adsorption of Polar Molecules
Authors: Lozovskii V. Z. , Khudik B. I. 
Published: July 2007

AbstractThe polar molecule adsorption is considered in the framework of an approach developed in a previous work (Part I) for the case of nonpolar molecule adsorption. An expression for the adsorption potential is obtained. Nonpolar molecule adsorption is considered for the case of surface‐induced molecule dipole moment bound at a certain distance from the surface.
Chemical Shifts of Auger Electron and Photoelectron Binding Energies of Phosphorus in Solid Compounds
Authors: Franke R. , Chassé T. , Al‐Araj B. , Streubel P. , Meisel A. 
Published: July 2007

AbstractA set of experimental 1s, 2s, and 2p photoelectron binding energy and KL2,3L2,3; 1D2 Auger energy shifts of phosphorus in 11 solid compounds referenced to elemental red phosphorus is presented. Correlations between the shifts are discussed. The Auger parameters, ξ, are used to estimate the changes in the extraatomic static relaxation energy ΔR. Line shifts and ΔR values are compared with differences in Pauling's electronegativity between phosphorus and the neighbouring atoms and averaged atomic electronic polarizabilities of the neighbours. Absolute R values are calculated and compared with data of gaseous P compounds which provides a systematic difference.
Band Structure of Sodium and Lithium Azides
Authors: Zhuravlev Yu. N. , Poplavnoi A. S. 
Published: July 2007

AbstractLiN3, α‐, β‐NaN3 band structure is determined by means of pseudopotential technique on the basis of localized Slater orbitals decomposed along plane waves. The nature of the complex bands and the effect of phase transition on the electron energy spectrum in NaN3 are discussed. Density of states data calculated by means of energy band interpolation by Fourier symmetrized series are compared with those on photoelectron spectra of azide salts. The peculiarities of both optical and photoemission NaN3 spectra are interpreted in terms of band–band electron transitions.
Parametric Interaction of Two‐Dimensional Electron Systems in a Strong Electromagnetic Field
Authors: Epshtein E. M. , Shmelev G. M. 
Published: July 2007

AbstractParametric interaction is considered of plasma oscillations in two‐dimensional electron gases (2DEG) placed in two parallel planes in the presence of an intense electromagnetic field (EMF). The spectrum of coupled plasmons is calculated for the case when the EMF frequency is high compared with the frequencies of 2D plasmons in isolated 2DEG's. The frequency of the coupled plasmons is found to be an oscillating function of the EMF amplitude. The case of parametric resonance is considered, and the parametric excitation gain is calculated.
Positron Distribution in Semiconductors
Authors: Aourag H. , Khelifa B. , Belaidi A. , Belarbi Z. 
Published: July 2007

AbstractThe positron distribution of charge along the (111) direction is calculated for elemental and compound semiconductors. The results show that the positron has a strong affinity for one sort of atom in binary semiconductors. This relative positron affinity may lead to the positron preferentially annihilating with the electrons of that sort of atom in compound semiconductors. The trends in going from Ge to CdTe through GaAs show an increase in positron affinity for the anion over the cation.
Surface Magnetic Properties of a Transverse Ising Model with a Diluted Surface
Authors: Sarmento E. F. , Kaneyoshi T. 
Published: July 2007

AbstractSurface magnetic properties of semi‐infinite spin‐1/2 Ising ferromagnet with a diluted surface in an applied transverse field are investigated by the use of an effective‐field theory with correlations. A number of characteristic behaviors arise in the temperature and transverse field dependences of the surface magnetization. A similarity exists between the temperature plots and the transverse field plots for the surface magnetization, which proposes that the research of surface magnetization in an applied transverse field fixing temperature at a very low one may open a new method for clarifying a variety of problems in surface magnetism experimentally.
Interface States in Subband Structure of Semiconductor Quantum Wells
Authors: Gerchikov L. G. , Subashiev A. V. 
Published: July 2007

AbstractAn analytical investigation is made of semiconductor quantum‐well subband structures using the three‐band Kane model. The analysis is based on the assumption, that electron and light hole masses are much smaller than heavy hole mass in the heterostructure. It is demonstrated, that some anomalies in the subband spectrum are due to the interaction with interface states, others are generated by the repulsion between the subbands near the points of their quasiintersections. For the heterostructure, composed of the gapless layer in a finite‐gap bulk material, the interface state is found to cause a nonmonotonous dependence of the gap on the layer thickness.
Quantum‐Chemical Calculations of Hydrogen Adsorption on the Polar Surface of Titanium Carbide
Authors: Sabiryanov R. F. , Novikov D. L. , Ivanovskii A. L. , Gubanov V. A. 
Published: July 2007

AbstractUsing the discrete variation method (DVM) the modelling of electronic and energy states of the (111) face of TiC, containing adsorbed hydrogen, is carried out. The peculiarities of the electron distributions, the parameters of the interatomic interactions, and the equilibrium distances of H adsorbed on the (111) face of TiC are calculated. The theoretical electron C K VV and TiL23M23V Auger‐spectra are presented for the ideal and containing adsorbed hydrogen polar (111) face of TiC.
On the Bond Orientational Order in Icosahedral Phases
Authors: Radulescu O. , Manaila R. 
Published: July 2007

AbstractIcosahedral phases in Al—transition metal alloys are characterized by long range bond orientational order (BOO). The composition of the TM sublattice can influence the degree of BOO, presumably by altering the rigidity of the bonds. This fact can be evidenced by measuring the widths of the X‐ray diffraction peaks, which are shown to be very sensitive to this particular kind of disorder. Quantitative comparison of experimental data with Hendricks‐Teller‐type calculations provides estimates for the degree of orientational disorder in AlCrxFe1−x samples.
A Study of the Structure and Thermodynamics of Liquid Metals Based on Some Reference Systems
Authors: Akinlade O. 
Published: July 2007

AbstractThe bulk modulus of liquid alkali metals is calculated using the one‐component plasma model and a perturbative correction to the structure factor. The use of a highly accurate non‐local pseudopotential yields a considerable improvement on previous results. A study of the charged hard‐sphere reference system as applied to metals with strong electron—ion pseudopotentials (Li, Mg, Cd, In, Tl, and Pb) indicates that it is a preferred system since it yields lower free energies. Results for the other thermodynamic quantities investigated are also reasonable.
The Analysis of Rydberg Potential and van der Waals Interactions in Alkali Halides
Authors: Gupta V. P. , Sipani S. K. 
Published: July 2007

AbstractThe short range Rydberg potential which assumes an attractive term along with the frequently used repulsive term for short range interaction is employed to calculate the transverse optic mode Grüneisen parameter (γTO), longitudinal optic mode Grüneisen parameter (γLO), Grüneisen parameter (γ), mode Grüneisen parameter (q), first and second order pressure derivatives of isothermal bulk modulus \documentclass{article}\pagestyle{empty}\begin{document}$\left({\frac{{{\rm dB}_T }}{{{\rm d}T}}{\rm and}\,\frac{{{\rm d}^{\rm 2} B_T }}{{{\rm d}P^2 }}} \right)$\end{document}, and volume expansion coefficient (β) for NaCl‐ and CsCl‐structure alkali halides taking into account the three different sets of van der Waals coefficients and three different theories namely, the Slater theory, Dugdale and McDonald (DM) theory, and free volume (FV) theory. It is observed that the results obtained from DM theory using the values of van der Waals coefficients from Shanker and Rajoria are in good agreement with experiment. The potential has further been extended to take into account the second neighbour and three body contributions. The inclusion of second neighbour and three body interactions improves the results satisfactorily.
Phonon—Phonon Interaction in a One‐Dimensional Anharmonic Lattice
Authors: Chatterjee R. 
Published: July 2007

AbstractA higher order partial nonlinear differential equation is obtained when phonon—phonon interaction in a one‐dimensional anharmonic lattice is treated quantum mechanically. Few assumptions are made to derive this equation of motion, such as long‐wavelength approximation, omission of normally ordered terms, continuum limit, and no umklapp scattering. The validity of these assumptions is discussed. The limitation to up to sixth higher order phonon—phonon interaction terms agrees with the earlier conclusion, reached from the stability consideration of the solitonic solution of this equation of motion.
Dynamical Correlations in Liquid Metals K and Cs
Authors: Jain K. C. , Gupta Neelam , Saxena N. S. 
Published: July 2007

AbstractThe theory of single particle motion in static harmonic well approximation is employed to study the dynamical correlations in potassium and cesium at their respective melting temperatures. Computation of dynamical variables like velocity autocorrelation function, power spectrum, and mean square displacement in both, potassium and cesium are made using the effective pair potential as obtained from the Ashcroft empty core model pseudopotential. The cooperative modes of motion of atoms is described in terms of the spectral functions of longitudinal current—current correlation which are obtained through the mean square displacement. Frequency corresponding to the peak positions in longitudinal current—current correlation functions are then plotted against the wave vector transfer. The above results of dynamical variables are compared with MD results of Miranda and the results of phonon dispersion with the results of Jacucci and McDonald. Good agreement is observed in the case of potassium.
Magnetoresistivity of a Crystal Field Split Kondo System
Authors: Prabhu R. B. , Barbosa A. F. 
Published: July 2007

AbstractAn expression for the magnetoresistivity of a crystal field split Kondo system is obtained. Numerical calculations are performed for the system Ce0.76La0.14Th0.1 for which all the parameters are available from the experimental data. Results are presented on the partial occupation numbers of the Zeeman split CEF levels as well as on the magnetoresistivity both as functions of temperature and magnetic field. It is found that the Kondo state persists for a field as high as 15 T. The system shows negative magnetoresistance. The magnetoresistivity decreases with increasing magnetic field. The results are in agreement with the experimental data on cerium based Kondo systems.
Discussion of the Ferromagnetic Simple Cubic Ising Lattice with Fluctuating Exchange Integral (s = 1/2)
Authors: Mielnicki J. , Balcerzak T. , Wiatrowski G. 
Published: July 2007

AbstractSome magnetic properties of simple‐cubic disordered ferromagnets with fluctuating exchange integral are investigated with the use of the 1‐st, 2‐nd, and 3‐rd Matsudaira approximations. The results of various approximations are similar only for small fluctuations. For large fluctuations significant differences appear. This indicates that for a proper description of disordered material besides the simple decoupling of correlation functions, also another commonly used approximations should be significantly improved.
Magnetic and Mössbauer Studies of the System LaCo1−xZrxO3 (x = 0.1, 0.3, 0.5)
Authors: Johri U. C. , Singru R. M. , Bahadur D. 
Published: July 2007

AbstractMössbauer studies on well‐characterized LaCo1−xZrxO3 (x = 0.1, 0.3, 0.5) are carried out in the 80 to 700 K temperature range and they show that cobalt ions exist predominantly in the low spin CoIII(te) and CoII(te) states at 80 K which transform partially to high‐spin Co3+ (te) ions upto ≈ 500 K. In the 80 to 700 K region the system LaCo0.9Zr0.1O3 behaves almost similar to LaCoO3. However, above 500 K, in the system LaCo1−xZrxO3 (x = 0.3, 0.5) Co3+ ions capture an electron from CoII and transform into Co2+ (te) and CoIII ions pairs. The magnetic susceptibility data recorded are consistent with the present Mössbauer resülts. The inverse magnetic susceptibility versus temperature curves for the systems LaCo1−xZrxO3 (x = 0.3, 0.5) show different slopes in the 300 to 800 K temperature range. The higher slopes above ≈ 500 and ≈ 550 K for the system LaCo0.7Zr0.3O3 and LaCo0.5Zr0.5O3, respectively, indicate lower μeff which, in turn, suggests the generation of Co2+ ions at the cost of Co3+ ions. The generation of low spin CoII and CoIII at low temperatures is attributed to larger crystal field splitting Δcf compared to exchange energy Δex in the system as a result of tetravalent Zr ion substitution.
Ising Ferromagnet with Three‐Site Four‐Spin Interaction
Authors: Iwashita T. , Uryû N. 
Published: July 2007

AbstractFor Ising ferromagnets, the effects of the three‐site four‐spin interaction J′(Si · Sj) (Sj · Sk) on the magnetization 〈Sz〉 and the Curie temperature Tc are studied in the cases of large spin S = 2 and S = 5/2. Using the three‐spin model approximation, the temperature dependence of 〈Sz〉 is calculated numerically. The results show a first order phase transition for positive J′ larger than a certain critical value and show also an abnormal behavior for negative J′ smaller than another critical value.
Phase Transitions of Heisenberg Ferromagnetic Superlattices
Authors: Endo Y. 
Published: July 2007

AbstractStatic properties of a ferromagnetic superlattice made from alternating layers of strong and weak Heisenberg exchange interactions are theoretically studied at finite temperatures. Using the Green's function, magnetizations in each layer and transition temperatures are calculated, and their dependence on the thicknesses and strengths of interactions in both the materials is discussed.
Low‐Frequency SERS from Ag Colloids in Alkali Halide Crystals
Authors: Abel H.‐B. 
Published: July 2007

AbstractThermally and photochemically prepared Ag colloids in various alkali halides show a low‐frequency mode (LFM) between 3 and 8 cm−1. By stepwise annealing the crystal the LFM band maximum is shifted to lower wave numbers. The average size of the Ag colloids is determined from the LFM spectrum. The independence of the LFM on the polarization of the exciting laser light indicates predominantly spherically shaped Ag colloids. The influence of temperature on the LFM is investigated both, on Stokes and anti‐Stokes side. After dividing the LFM intensities by the Bose function the reduced SERS signal is found to be temperature independent and mirror symmetric concerning the Stokes shift.