bluuebunny/crossref_metadata_2025_split huggingface dataset:
Non‐Linear Temperature—Band Gap Variation in Small‐Gap Semiconductors and Semimetals
Authors: Fau C. , Charar S. , Averous M. 
Published: July 2007

AbstractA model is proposed to determine the high‐temperature band gap for small‐gap or semimetal II–VI compounds as Hg1‐xCdxTe or Hgi1‐xCdxSe, from an analysis of Hall data. It is shown that there exists a non‐linear band gap‐temperature dependence for a given Cd concentration. A variation law valid for 0 < x < 1 is proposed. This law is checked for a lot of samples, and it is demonstrated that there exists a very good agreement with experimental results even near the semimetal‐semiconductor transition.
A Study of a Stable AlCuFe Quasicrystal in Solid and Liquid State
Authors: Chen Lifan , Chen Xishen 
Published: July 2007

AbstractA stable Al65Cu20Fe15 quasicrystal with an icosahedral structure is studied in solid and liquid state. It is found that the icosahedral phase in Al65Cu20Fe15 alloy does not grow directly from the pure liquid state, but rather forms between monoclinic Al13Fe4 and residual liquid state at 865 °C. The melting point of the Al65Cu20Fe15 icosahedral quasicrystal occurs at 865 °C and that of the Al65Cu20Fe15 alloy occurs at 1008 °C. Moreover, the monoclinic Al13Fe4 is transformed into the icosahedral phase easily at the temperature of 845 °C. The icosahedral quasicrystal in Al65Cu20Fe15 alloy has a high thermal stability even at 950 °C. Above 950 °C, the icosahedral structure tends to an amorphous structure.
Energy Gap Structure in Semiconducting Bi1−xSbx Alloys
Authors: Kirakozova L. A. , Krapf A. , Kraak W. , Lavrenyuk M. Yu. , Minina N. Ya. 
Published: July 2007

AbstractThe Fermi surface, Dingle temperature, and galvanomagnetic characteristics in semiconducting Bi1−xSbx (0.1 < x < 0.16) alloys under strong uniaxial compression along binary and bisectric axes are investigated. Uniaxial deformations up to 0.3% give a possibility for the Fermi level to pass through the energy gap in particular energy extrema. The totality of experimental data does not confirm the presence of the deep donor level with high density of impurity states in the energy gap of these alloys assumed in some recent papers. It is observed that a specific microscopic inhomogeneity of “cluster type” about 10 to 20 μm in size does not reveal itself in oscillation properties, but determines the anomalous behavior of resistivity in the strain interval when the Fermi level passes through the energy gap.
Polaron Pairing in Multi‐Layer Structures I. Bipolaron States in Multi‐Layer Structures with Quantum Wells
Authors: Pokatilov E. P. , Beril S. I. , Fomin V. M. , Ryabukhin G. Yu. 
Published: July 2007

AbstractInteraction of two electrons with each other and with polar vibrations in a system consisting of a non‐polar layer bordered from two sides by polar media is examined. The electrons are considered to be in the layer. It is shown that under suitable selection of system parameters (dielectrical constants, effective masses, layer thickness, etc.), the conditions can be given under which the bipolaron is formed in the layer. The bipolaron coupling energy in that case is calculated and cited. It is shown that in favourable cases it can reach hundreds of Kelvins. Maximum coupling takes place in the case when l → 0 and with l‐growth it quickly decreases, in the case when l/Rs ≧ 1 (where l — nonpolar layer thickness, Rs is radius of the three‐dimensional polaron) it comes to zero. Thus, for the existence of strongly coupled bipolarons it is necessary to have the following condition: l ≦ Rs.
Molecular‐Dynamics Computer Simulation of Aluminum Clusters (Aln; n = 3 to 55). Empirical Many‐Body Potential Energy Function Calculation
Authors: El‐Bayyari Z. , Erkoç Ş. 
Published: July 2007

AbstractThe structural stability and energetics of Aln (n = 3 to 55) clusters are investigated by using a recently developed empirical many‐body potential energy function which contains two‐ and three‐body atomic interactions. Molecular‐dynamics technique is employed in the simulation. It is found that the energetically most stable structures of aluminum clusters are in compact distorted buckled form.
The Effect of the Electronic Density of States on the Stability of Dilute Cu‐Based Alloys with 3d‐Metals
Authors: Stepanyuk V. S. , Szasz A. , Katsnelson A. A. , Kozlov A. V. , Hendry A. 
Published: July 2007

AbstractThe electronic properties of dilute Cu‐based alloys are calculated by the method of linear augmented plane waves. The results are correlating with the stability of these alloys, and giving possibility to approximate the solubility of the alloying elements in Cu. A successful comparison with the experiments is given.
Phase Diagrams of a Spin‐One Ising Model with a Random Crystal Field in the Correlated Effective‐Field Treatment
Authors: Kaneyoshi T. 
Published: July 2007

AbstractThe phase diagram of the spin‐one Ising model with a random crystal field Di on a square lattice is investigated by the use of the correlated effective‐field theory, when the random crystal field is distributed according to the law P(Di) = pδ (Di − D) + (1 − p) δ (Di). A number of characteristic phenomena are obtained, such as the p‐dependence of the tricritical point and the reentrant phenomenon due to the disorder of the crystal field.
Magnetic Properties of Monolayers with Modified Gaussian Distribution of Exchange Integrals
Authors: Balcerzak T. , Mielnicki J. , Wojtczak L. , Wiatrowski G. , Reinhold J. 
Published: July 2007

AbstractMagnetic properties of a monolayer with a Gaussian‐type distribution of exchange integrals are investigated within the Ising model. The Gaussian distribution is modified in order to omit the range of negative exchange interactions as well as extreme positive values. The obtained results concern phase diagrams, magnetization, and correlation functions. A comparison with analogous results obtained for an ordinary Gaussian distribution is also made.
87Rb NMR Study of the Low Temperature Phase of Rb2ZnCl4
Authors: Apih T. , Blinc R. , Dolinŝek J. , Milia F. , Ailion D. C. 
Published: July 2007

AbstractThe 87Rb 1/2 → − 1/2 NMR spectra and spin‐lattice relaxation rates T−11 are studied in the high temperature paraelectric phase, the incommensurate phase, the ferroelectric commensurate phase, and the low temperature commensurate phase of Rb2ZnCl4 between 325 and 6 K. The changes in the 87Rb NMR spectra on going into the low temperature commensurate phase are compatible with the proposed crystal structure of this phase, whereas the observed T1 anomaly reflects the condensation of the soft mode inducing this transition.
Studies on Some Ground State Properties and Specific Heat of Mixed‐Valence Systems
Authors: Ghosh N. K. , Ghosh S. C. , Sarkar R. L. 
Published: July 2007

AbstractA simple two‐site model with spin is considered for which the exact solution is admissible. The phenomenon of valence transition is investigated. Finite temperature specific heat and magnetic intersite spin correlations are also studied. It is shown that strong f‐d Coulomb interaction makes the first‐order transition possible. It is also shown that the magnetic intersite spin correlations are sensitive to f‐d Coulomb interaction and hopping interaction. The results are compared with previous works.
Magnetic Susceptibilities of Low‐Dimensional Organic Donor–Acceptor Salts
Authors: Schulte J. , Böhm M. C. 
Published: July 2007

AbstractThe magnetic susceptibility χ of the low‐dimensional organic charge‐transfer salts TTF‐TCNQ, (TMTSF)2PF6 and (2,5‐CH3DCNQI)2Ag is studied by a theoretical model which takes into account the χ‐enhancement due to electronic correlations as well as volume effects of the lattice as a function of temperature. Experimental data are reproduced both under constant pressure and constant volume conditions. The suggested approach reproduces the absolute values of χ and the corresponding temperature gradient. The theoretical expressions are valid for any band filling and correlation strength.
EPR of Mn2+‐Doped Tutton Salts. Role of Hydrogen Bonding
Authors: Pandey R. C. , Chaudhry A. K. , Shukla S. R. , Pandey S. D. 
Published: July 2007

AbstractThe work deals with electron paramagnetic resonance of Mn2+‐doped zinc potassium selenate hexahydrate and zinc cobalt selenate hexahydrate Tutton salt single crystals. The different field parameters for the two hosts are evaluated from the observed z‐ and x‐axes spectra. The D parameters for the two hosts are compared with the corresponding reported values for hexahydrate. This parameter shows a systematic variation with the change in radii of the M′ ion in the series of salts ZnM′2(SeO4)2. 6H2O with M′ as K, Rb, and Cs. The case of M′ as NH4, however, does not show such a systematics. Similar behaviour is found for two other such series of Tutton salts, as well. Further it is found that D is, in general, negative for K, Rb, and Cs Tutton salts but is positive for NH4 Tutton salts. This unusual behavior of NH4 Tutton salts is attributed to two types of hydrogen bondings existing in such Tutton salts, in contrast to the only one type linking the H2O groups to the sulphate groups in all other Tutton salts. An attempt is also made to explain the unusual reported negative value of D in ammonium‐iron, ammonium‐cadmium, and ammonium‐nickel Tutton salts.
Surface Spin Waves in Semi‐Infinite Antiferromagnetic and Ferrimagnetic Semiconductors in the Narrow‐Band Limit
Authors: Shen Wen‐Zhong , Li Zhen‐Ya 
Published: July 2007

AbstractSurface spin waves are investigated in semi‐infinite s‐d (or s‐f) interaction antiferromagntic and ferrimagnetic semiconductors in the narrow‐band limit by use of combined Green's function theory with the transfer‐matrix method. The influence of s‐d (or s‐f) interaction on surface spin‐wave spectra is discussed.
No Longer Transcendental Equations in the Homogeneous Mean‐Field Theory of Ferromagnets
Authors: Millev Y. , Fähnle M. 
Published: July 2007

AbstractThe transcendental equation for the determination of the magnetization within the mean‐field approximation is reduced to the problem of solving an explicit polynomial equation of degree 2S where S is the spin of the localized magnetic moments. Various possibilities to achieve this reduction are pointed out and the physically most tractable variant is singled out. It is demonstrated that the solution of the obtained polynomial equation is equivalent to finding the inverse of the Brillouin function explicitly.
Stochastic Processes and Asymmetry of Raman Scattering at the Surface of Opaque Crystals
Authors: Semjonow A. Je. , Holz L. , Lau A. , Richter W. 
Published: July 2007

AbstractFirst experimental results are presented about a new type of asymmetry of the spontaneous Raman scattering (ASRS) in crystals (Si after UV irradiation), where not only the probabilities of light scattering are different for the scattering to the right and to the left directions, but also the phonon frequencies and halfwidths are different. The experimentally observed features of ASRS in crystals are explained theoretically by a chaos model of nonlinear optics (a chaotic Raman attractor). The interactions between Stokes, anti‐Stokes, and pump laser waves cause the new type of ASRS in crystals. It is shown that Stokes and anti‐Stokes modes may exhibit the redistribution of phonon intensities, different phonon frequencies, and linewidths.
Temperature Dependent Energy Shifts in the Resonance Absorption and Resonance Fluorescence Scattering of Mössbauer γ‐Quanta in FeS2
Authors: Jex H. , Hillmann H. , Müllner M. 
Published: July 2007

AbstractThe relativistic Doppler effect of Mössbauer γ‐quanta from a 57Co source is investigated in the resonance absorption of FeS2 powder and in the resonance scattering from the (200) reflection of FeS2 single crystals in the temperature range 298 K ≦ T ≦ 598 K. The shift of resonances is d ln ω/dT = −(2.58 ± 0.07) × 10−15 K−1, while the quadrupole splitting dEQ = (633 ± 9) μm/s is temperature independent. Single crystal data exhibit an unexpected additional broadening of one quadrupole resonance, which originates in an interference of nuclear resonance and electronic Rayleigh scattering.
Effect of Isotope Substitution on Thermal Expansion of LiH Crystal
Authors: Tyutyunnik V. I. 
Published: July 2007

AbstractThe isotope effect on the lattice parameter and the coefficient of thermal expansion of the LiH crystal is investigated by means of rigid‐ion model. It is demonstrated that the differences in lattice parameters between LiH isotopes can be related directly to changes in the thermal‐expansion coefficient which varies inversely as the cation‐anion reduced mass. These differences should disappear at a temperature of 0 K. For the first time, the thermal‐expansion data are calculated for the six isotopic components 6LiH, 7LiH, 6LiD, 7LiD, 6LiT, and 7LiT. The lattice parameters of LiH isotopes are also calculated and agree with those observed earlier within the experimental error.
Differential Photoluminescence Excitation Spectroscopy A Novel and Sensitive Tool to Probe Gain and Absorption in Semiconductor Nanostructures
Authors: Bongiovanni G. , Mura A. , Staehli J. L. 
Published: July 2007

AbstractDifferential photoluminescence excitation (DPLE) spectroscopy is shown to be an efficient way to measure gain and absorption spectra of excited semiconductors. Very small excited volumes can be probed, and thus DPLE spectroscopy is ideal to probe nanostructures. This technique is applied to investigate the width of the gap between the second electron and hole subbands of a quantum well versus carrier density, in a sample which contains only a few wells. It is found that the reduction of this gap is a smooth function of the electron–hole pair density, and no drastic change occurs when the second subbands start to be populated.
Surface‐Emitting Laser Logic
Authors: Olbright G. R. , Jewell J. L. , Bryan R. P. , Brennan T. M. 
Published: July 2007

AbstractIn the future optoelectronic integrated circuits (OEICs) are destined to evolve into sophisticated functional circuitry upon which a multiplicity of applications will be based such as: optical communications, optical interconnects, optical computing, optical memory, laser printing and scanning, visual displays, pattern recognition, and neural networks. This evolution of OEICs involves the integration of phototransmitters (semiconductor lasers and light‐emitting diodes), photoreceivers (photodetectors and phototransistors), spatial‐light modulators transistors (bipolar and field‐effect), diodes, resistors and capacitors, and micro‐optic components (e.g. micro lenses). Our efforts to date and future directions are described which are concentrated on the integration of vertical‐cavity surface‐emitting laser diodes (VCSELs) with transistors, photoreceivers and micro‐optic components. VCSELs, which may be patterned in high densities (over a million in a cm2) and emit light perpendicular to the plane of the substrate, have an ideal light‐emitting geometry for the above‐mentioned applications and for integration with micro‐optic components. Our effects to develop monolithic surface‐Emitting Laser Logic devices are described which are referred to as CELLs consisting of phototransistors, current controlled bipolar transistors, and voltage‐controlled field‐effect transistors integrated with a VCSEL to form optically and electrically addressable photonic switching devices having high contrast. Included are reports of recent progress in decreasing VCSEL series resistance and therefore operating voltage, and an optically‐pumped visible‐emitting (657 nm) VCSEL. Also discussed are the integration of micro‐optics with VCSELs. Finally combinations of OEIC components and subassemblies and their applications to several of the above‐mentioned photonic switching applications are described.
Synthesis and Characterization of the Layered Compounds in the ZnIn2S4–ZnIn2Se4 System
Authors: Razzetti C. , Attolini G. , Bini S. , Lottici P. P. 
Published: July 2007

AbstractBy the chemical vapour transport technique some compositions in the ZnIn2S4–ZnIn2Se4 system are synthesized. The layered reaction products obtained are characterized by X‐ray diffraction, atomic absorption spectroscopy, and Raman scattering. According to the crossed characterization the reaction products have a composition strongly different from the loaded charge, and their structure is related to that of Zn2In2S5 rather than to that of ZnIn2S4. According to the characterization, the structure shows a large degree of disorder both in the anion and the cation sublattices which is mirrored by the Raman spectra apart from very narrow Raman lines which are observed at very low frequencies.
Influence of Sample Temperature on the Process of Hot Spot Formation and Degradation after Powerful Laser Pumping
Authors: Pronin D. A. 
Published: July 2007

AbstractThe degradation of a hot spot obtained near one of the surface of a thin crystal plate of anthracene at helium temperatures is investigated. The experimental results are discussed in terms of the local thermal conductivity with both specific heat and thermal conductivity as well‐known function of temperature. A good agreement between experimental results and model calculations is achieved. Analyzing the results of calculations a conclusion is drawn on the strong influence of sample temperature on the process of hot spot formation immediately after laser pumping. The role of the sample defectiveness is also discussed. The solution of the non‐linear thermal conductivity equation used to describe experimental results is analyzed. It was found that initial conditions strongly affect the time evolution of the hot spot width.
Lattice Dynamics of Acetylene
Authors: Binbrek O. S. , Anderson A. 
Published: July 2007

AbstractA simple force constant model is described and applied to the vibrations of crystalline acetylene, C2H2 and C2D2, in its low temperature orthorhombic phase. The model uses ten (six intermolecular and four intramolecular) adjustable parameters to calculate the frequencies of seven lattice modes and fourteen internal mode components, and good agreement with spectroscopic data is obtained. Intermolecular force constants decrease sharply with increasing sepration and are well represented by exponential functions. Intramolecular force constants show only minor changes from their gas phase values.
Non‐Coherent Light Reflection from Photoelastic Media
Authors: Grechko L. G. , Motrich V. V. , Ogenko V. N. , Semchuk A. Yu. 
Published: July 2007

AbstractThe present study is concerned with non‐coherent light scattering due to interaction of an incident electromagnetic wave with fluctuations of Rayleigh surface waves at the isotropic photoelastic medium boundary. Two mechanisms of the interaction of an electromagnetic wave with Rayleigh surface waves are considered: interaction of electromagnetic wave and surface wave a) by means of the inhomogeneity of the dielectric constant and b) by means of the photoelastic mechanism. A general expression for the coefficient of non‐coherent reflection is obtained.
Modelling of Thulium Ion Luminescence in Zinc Sulphide
Authors: Rodionov V. E. , Rakhlin M. Ya. , Zolotovskii A. A. 
Published: July 2007

AbstractThe modelling of luminescence of the Tm3+ ion in zinc sulphide for TmS4, TmS3Vs, TmS3Cl, TmS3F, TmS3Br, TmS2F2, TmSF3, TmVsF3 clusters is considered by the quantum‐chemical MO AOLC (molecular orbitals of atomic orbital linear combinations) method within the limits of the Routan approximation. The intensities of luminescent transitions are calculated. The dependence of intensities and the ratio of intensities of blue and red emissions of a cluster on its composition, symmetry, and geometry are analysed.
On the density of electron states and magnetization of the crystalline narrow band sd model
Authors: Ponedilok G. V. , Shabat I. E. 
Published: July 2007

AbstractThe model which describes exchange interaction of localized magnetic moments with itinerant conduction electrons and Hubbard correlations is considered. The set of equations necessary to calculate self‐consistently the density of electron states (DOS) for the narrow band sd model is obtained. The numerical analysis of the zone electron magnetization for the rectangular model zone is given.
Finite lifetime effects in the coherent exciton transfer
Authors: Barvík I. , Heřman P. 
Published: July 2007

AbstractMemory functions entering the generalized master equations are calculated for trimer, with the sink in the center. The whole dynamics of the system – coherent transfer, capture of the excitation by the sink, and finite lifetime effects in the host – are taken into account. The simple example of the trimer is chosen (method and results being simply extendable to more complex systems) to present the analytical solution, which is obtainable also by the use of the program package Mathematica for symbolic computing.
General dispersion equations for diluted magnetic semiconductor superlattices
Authors: Shen Wen‐Zhong , Li Zhen‐Ya 
Published: July 2007

AbstractOn the basis of the magnetostatic theory, we derive the general dispersion equations for diluted magnetic semiconductor (DMS) superlattices. Both bulk and surface dispersion relations are obtained in the superlattices with the elementary unit consisting of l different DMS layers.
Phenomenological description of magnetic relaxation in magnetic crystals with induced anisotropy
Authors: Lyakhimets S. N. 
Published: July 2007

AbstractA phenomenologic description of a magnetic dissipation in crystalline magnets with induced magnetic anisotropy is suggested. The components of the second‐order tensor describing the induced anisotropy are taken as thermodynamic variables and the nonequilibrium linear Onsager thermodynamics is formulated for them. Such an approach comprehends all symmetry aspects of the relaxation problem. With the help of the dissipation function the relaxation parameters and their angular dependences are calculated for spin waves and moving domain walls.
An electron paramagnetic resonance study of Fe3+ ions doped in langbeinites
Authors: Böttjer T. , Stockhausen M. 
Published: July 2007

AbstractPowder and single crystal X‐band EPR spectra are measured of the cubic (high temperature) phase of eleven langbeinites, A2+B (SO4)3, doped with Fe3+. One center of axial symmetry is observed, the ZFS parameter B of which is discussed in comparison with corresponding results on manganese‐doped langbeinites. Very probably Fe3+ forms a substitutional center in the more spacious of the two non‐equivalent B sites, which leads to local relaxation depending on ionic radii. Charge compensation by an A site vacancy is likely.
Confinement effects on the LO‐phonons in CdSexS1–x doped glasses
Authors: Bersani D. , Lottici P. P. 
Published: July 2007

AbstractRaman scattering on commercial filters containing CdSexS1–x microcrystals is reported. The composition x is determined by the difference between CdS‐ and CdSe‐like LO phonon frequencies. A simple phonon confinement model in the microcrystals is suggested to explain the observed red‐shift of the Raman frequencies and the lineshapes.
On Electron Emission from Quantum Wells in Ultrathin Films of Wide‐Gap Semiconductors in Crossed Fields
Authors: Das N. R. , Chakravarti A. N. 
Published: July 2007

AbstractAn attempt is made to investigate the effects of an oriented magnetic field on the field emission from quantum wells in ultrathin films of wide‐gap semiconductors taking n‐type GaAs as an example. The field emission current density is found to increase both with increasing electric field and with increasing film thickness. Furthermore, the emission shows an oscillatory nature with a quantizing magnetic field, its orientation, and the film thickness. At a given value of the magnetic field, the oscillatory nature is most significantly influenced by the effects of size quantization at relatively small values of the film thickness.