bluuebunny/crossref_metadata_2025_split huggingface dataset:
Exciton States of Lithium Hydride in LiH1−xFx Solid Solutions
Authors: Polienko A. N. , Tabachnik M. E. , Cholakh S. O. , O'Connel‐bronin A. A. 
Published: July 2007

AbstractExciton states of LiH1−xFx in the exciton band of lithium hydride are investigated by optical methods. It was found that spectra of the lowest‐energy exciton band of these crystals follow the persistent type of behaviour. The relation of exciton energy to solution composition points to the effect of symmetry changes of the conduction band bottom and average sizes of lithium hydride clusters. The structure of the luminescence spectra is determined by direct, phonon‐forbidden indirect, or disorder‐assisted quasidirect transitions with increasing fluorine content.
On the Efficiency of Different Schemes for the Evaluation of the Density of States and Related Properties in Solids
Authors: Bross H. 
Published: July 2007

AbstractIt is shown that similar to the tetrahedron method the method originally proposed by Gilat and Raubenheimer can be used for all kinds of Bravais lattices to evaluate the density of states and related properties. For a great variety of such properties analytical expressions well suited for numerical computations are given. Based on explicit calculations in the case of Cu it is shown that the improved Gilat‐Raubenheimer method needs by a factor of 2 less CPU time than the tetrahedron method in order to obtain the density of states functions with the same accuracy.
Energy Levels in Quantum Wires with Finite Barrier Potential
Authors: Nag B. R. , Gangopadhyay Samita 
Published: July 2007

AbstractFormulae are derived for the calculation of the energy eigenvalues in cylindrical and elliptic quantum wires with finite potential barriers. Calculated values are given for quantum wires of the Ga0.47 In0.53As/InP system and experimental results are explained.
On the Photoconductivity in Hydrogenated Amorphous Silicon
Authors: Licea I. , Tomozeiu N. 
Published: July 2007

AbstractSome experimental data about the photoconductivity of n‐type a‐Si: H samples obtained by glow discharge technics are presented. The photoconductivity and the shape of the lux ampere characteristics presenting two straight lines with variable slopes are explained in terms of electron trapping and recombination kinetics. A comparison between the experimental data and the corresponding expressions which result from the considered model is made.
Magnetic Properties and Structure of (VxAl1−x)2O3 Solid Solutions
Authors: Viktorov V. V. 
Published: July 2007

AbstractOn the basis of the magnetic properties the statistical homogeneity of the solid solutions in the Al2O3‐V2O3 system is investigated. It is shown that the V3+‐ion distribution in the ( VxAll−x)2O3 lattice in the range of vanadium content 0.0096 ≦ x ≦ 0.195 does not obey statistical regularities. Clusters of two and three exchange‐interacting V3 + ions are observed in the structure of the (VxAl1−x)2O3 solid solutions.
Optical Study of Valence Band Splitting in Weakly Strained In1−xGaxAsyP1−y/InP Heterostructures
Authors: Weihofen R. , Weiser G. 
Published: July 2007

AbstractValence band splitting resulting from strain ε ≈ 10−3 or less is observed in electroabsorption spectra of quaternary LPE material grown on (001) InP. Although exciton lines are not resolved their contribution leads to narrow, near‐gap features in electroabsorption which provides the necessary spectral resolution. The variation of lineshape with dc bias, temperature, and strain is studied in detail. Small fields and low temperature are required to resolve splitting by a few meV. Even if linewidth broadening prevents resolution of valence band splitting, strain is evident by characteristic distortion of the spectral lineshape, different for compressive and tensile strain. Small splitting is resolved in case of tensile strain but not for compressive strain. This difference is attributed to stronger coupling of the valence bands for compressive strain where calculations show anti‐crossing for dispersion in the layer plane.
Investigation of True Ni2+–Halogen Distances in Alkali Halide Lattices
Authors: Ma Xuanrong , Du Maolu 
Published: July 2007

AbstractUsing the μkα model of Ni2+−6X− clusters the true distances between impurity Ni2+ cation and halogen anion in alkali halide lattices are estimated from the optical spectral data. The results suggest that the true impurity cation‐ligand anion distances are close to the sum of ionic radii of the impurity cation and anion but not the cation‐anion distance of the perfect lattices in the case that the ionic radius of host cation is larger than that of impurity cation.
Reflectivity of GaAs Thin Films
Authors: Bassani F. , Chen Y. , Czajkowski G. , Tredicucci A. 
Published: July 2007

AbstractAn accurate study of the optical properties of GaAs thin layers in the excitonic absorption region, obtained with a real‐space density‐matrix approach adapted to the case of thin films with degenerate valence bands is reported. The computed polarization decreases gradually to zero near the surfaces in a transition layer whose thickness decreases with increasing photon energy. The oscillatory behaviour of the reflectivity is well reproduced and can be interpreted in terms of polaritonic effects by relating the dispersion of the propagating modes to the calculated spectra. The effect of the confining material on the lineshapes and on the intensity of the peaks is also explained.
A Theoretical Study of Si Chemisorption on Ru(001) Surface
Authors: Wei Pan , Gong X. G. , Qi Zheng Qing 
Published: July 2007

AbstractThe embedded cluster model is used to study the electronic structure of Si chemisorption on Ru(001) surface, within the framework of local‐density theory regime. The Kohn‐Sham equation is solved self‐consistently using the discrete variational method. The most possible adsorbed site of Si is obtained by calculating the adhesive energy for two positions. The distributions of Si 3s, Si 3p, and Ru 4d orbitals are clearly identified by our calculations. The interaction between Si adatom and Ru(001) surface and its influence on the d‐d interatomic interaction of Ru atoms are also discussed.
Impurity Effects on the Local Density of States of an Hexagonal Husumi Cactus
Authors: Glass B. , Lazo E. 
Published: July 2007

AbstractThe electronic structure of a hexagonal Husumi cactus with a finite number of substitutional impurities in essentially two different cases is studied: (i) one impure hexagon in a pure Husumi cactus system and (ii) a Husumi cactus formed by infinite repetition of a contaminated hexagon (heterocactus). The tight‐binding Hamiltonian is used considering interaction to nearest neighbors and one orbital per site, with diagonal and off‐diagonal disorder. The Dyson equation describing the electron dynamics is solved using two types of effective transfer matrices. Localized states appear in the electronic gap for the heterocactus formed by infinite repetition of a hexagon with two impurities on sites 1. All genuine heterocactuses generate a gap, but only one has a localized state in between as a function of the normalized self‐energy ϵ.
Power Losses of a Type‐II Superconducting Slab of Arbitrary Thickness
Authors: Saif A. G. 
Published: July 2007

AbstractThe distribution of the internal and external magnetic vector potentials of systems of a type‐II superconducting infinite slab of arbitrary thickness subjected to (i) a vibrating wire (between two vibrating wires) carrying dc currents, (ii) a normal conducting wire (between two wires) carrying ac currents, are obtained. A modified London equation is developed to study these systems in case the slab is moving. The power losses on the surface of the slab and its two constituent terms due to dissipated and reactive energies are calculated. The rcactive term is found to be either capacitivel or inductively reactive. It is found that the power losses are dependent on frequency, London penetration depth, permeability, conductivity, velocity, and the distance between the normal conductors and the surfaces of the superconducting slab. Moreover, the power losses decrease as the distance between the normal conductors and the surfaces of the superconducting slab decreases, and increase as frequency, London penetration depth, permeability, conductivity, velocity increase. These analytical solutions can be used for testing the superconducting slabs in motion and the related problem of the losses of moving superconductors. In the limiting case, a satisfactory agreement with previous results is achieved.
Multiple‐Quantum EPR Transitions of MnII in CaS: MnII Phosphor
Authors: Gourier D. , Simons D. , Vivien D. , Ruelle N. , Thi M. Pham 
Published: July 2007

AbstractMultiple‐quantum transitions in the electron paramagnetic resonance spectrum of naturally doped (≈ 10 ppm) CaS: MnII powder are reported. Considerable resolution enhancement is achieved because of the lack of strain broadening of the EPR lines, due to the very good crystallinity of the powder. Multiple‐quantum transitions are identified by their linewidth, their saturation behavior, and their magnetic field position. Two‐, three‐, and five‐quantum transitions were identified, but not the four‐quantum transitions. A line at g = 1.983 is assigned to CrIII impurities at low concentration, which also exhibits a two‐quantum transition at high microwave power.
Si‐Related Point Defects in CdTe
Authors: Zielinska‐Purgal R. , Nazarewicz W. 
Published: July 2007

AbstractInfrared absorption associated with localized vibrational modes is studied in CdTe highly doped with silicon. On the basis of the experimental data obtained it is established that Si can form two kinds of point defects in CdTe: SiCd defects acting as donors and SiTe defects acting as acceptors. No evidence is found of the presence of Sica‐SiTe pairs and other defect complexes which could be formed as a result of electrostatic interaction between electrically active defects.
Optical Measurements in MOVPE‐Grown ZnSe/InP Epilayers
Authors: Coquillat D. , Bouchara D. , Abounadi A. , Ribayrol A. , Lascaray J. P. , Calas J. , Haidoux A. , Tomasini P. , Tédenac J. C. , Maurin M. 
Published: July 2007

AbstractThe X‐ray diffraction pattern of MOVPE‐grown ZnSe/InP epilayers in the thickness range between 0.15 and 2.2 μm shows that the relaxation is obtained for a few monolayers. The splitting between light hole E1h and heavy hole Ehh excitonic transitions is observed at 4.2 K by reflectivity and is explained in terms of thermoelastic strain due to the difference in the thermal expansion coefficients of layer and substrate. In addition photoluminescence is studied and shows neutral‐donor‐bound‐exciton lines I2 and I'2 as well as the neutral‐acceptor‐bound‐exciton line I1.
Band and Localized States in Finite and Infinite Crystals
Authors: Evarestov R. A. , Smirnov V. P. 
Published: July 2007

AbstractThe connection of symmetry groups, their irreducible and band representations for the models of finite and infinite crystals is considered in detail. The relation between localized (electronic and vibrational) states of finite and infinite crystals is studied on models. It is found that the Wannier states of an infinite crystal are reproduced well by Wannier states of cyclic systems with size slightly exceeding the region of their localization.
On the Acoustic and Electroacoustic Properties of Incommensurate {N(CH3)4}2CuBr4 Crystals
Authors: Kityk A. V. , Soprunyuk V. P. 
Published: July 2007

AbstractThe influence of hydrostatic pressure on the temperature dependences of transverse USW velocities is studied in the region of phase transitions and of triple points of {N(CH3)4}2CuBr4 crystals. The pressure‐temperature phase diagram is obtained. The linear electroacoustic effect is detected only in the region of the ferroelectric phase. The anomalies of acoustic and electroacoustic properties are considered within the framework of a phenomenological theory.
Critical Exponents and Randomness in SrTiO3 : Ca
Authors: Maglione M. , Santos M. Lopes Dos , Chaves M. R. , Almeida A. 
Published: July 2007

AbstractSince its discovery, the SrTiO3: Ca system is known to exhibit a number of features which were thought to arise from an impurity induced disorder. Non‐linear dielectric measurements are used to obtain a more quantitative insight into this disorder. For 0.001 < xCa < 0.05, it is found that the non‐linear susceptibility diverges at low temperatures. This is similar to what was previously reported in the dielectric random system KTaO3: Na. A method is proposed to quantify the contribution of the disorder to the non‐linearities. It is found that the deviation from a true ferroelectric behaviour is not enough to call the low‐temperature phase of SrTiO3: Ca a glass one. The maximum non‐linearity observed for xCa = 0.003 and 0.004 decreases for higher xCa contents. It is shown that a simple model of temperature dependent dipole moment may account for both the linear and non‐linear dielectric behaviour of SrTiO3: Ca.
Effect of the Image Potential on Plasmons in Cylindrical Quantum‐Well Wires
Authors: Wendler L. , Grigoryan V. G. 
Published: July 2007

AbstractThe collective electronic excitations in quasi‐one‐dimensional cylindrical quantum‐well wires are studied theoretically. Using a two‐subband model the dispersion curves of the intra‐ and intersubband plasmons in the random‐phase approximation for the cases of one and two occupied subbands are calculated. The influence of the image forces on the intra‐ and intersubband plasmon is studied in detail. New explicit analytical expressions for the dispersion relations, valid in a wide range of the wave vector are derived. It is shown that the additional intrasubband plasmon, arising if two subbands are occupied, has for small wave vectors a linear dispersion and is independent of the dielectric screening of the quantum‐well wire. The intersubband plasmon is split in two branches, one with a positive and one with a negative dispersion. The electric dipole moment of the collective excitations is calculated and the selection rules for the coupling of light with the plasmons are derived.
Hydrostatic Pressure Effect on Point Defect Electronic States in Narrow‐Gap and Gapless Semiconductors
Authors: Strikha M. V. , Vasko F. T. 
Published: July 2007

AbstractA study is made of the influence of hydrostatic pressure on point defect states in narrow‐gap and gapless semiconductors, described by the three‐band Kane model. It is shown that shifts of energy levels of centres of different symmetry with pressure are different. The h‐centre level follows strictly the v‐band top. On the contrary, the l‐c level shift depends on pressure in a more complicated way, and is determined by system parameters. The transition from resonance to localized defect states due to the transition from gapless to narrow‐gap semiconductors caused by hydrostatic pressure is also studied.
On the Geometry of Dipolar Dislocation Structures Formed by Multislip
Authors: Saxlová M. 
Published: July 2007

AbstractA prediction of dipolar wall geometry is based on the theory of dislocation structure formation. The three‐dimensional model simulates in a simplified linearized form the dislocation cell structure development in a crystal where several slip systems operate. The theoretical framework is formed by the balance law for stored dislocations which are drifted or swept into the forming cell walls. The model explains the multislip wall arrangement observed in a copper single crystal deformed along the [001] tensile axis.
Acoustic Studies of LiKSO4 Crystals in the 290 to 930 K Region
Authors: Borisov B. F. , Charnaya E. V. , Radzhabov A. K. 
Published: July 2007

AbstractThe temperature dependence of velocity and absorption coefficient of longitudinal and transverse acoustic waves are studied for LiKSO4 crystals within the temperature range 290 to 930 K. Anomalies in the velocity and absorption values are detected near 708 and 743 K. The observed considerable hysteresis of velocity for the longitudinal wave propagating along the y‐axis of the hexagonal structure at room temperature, suggests the presence of an intermediate incommensurate phase. A similar hysteresis was also observed for the transverse wave, propagating along the x‐axis and polarized along the y‐axis.
Optical and Acoustic Properties of (NH4)2ZnCl4 Crystals near the Phase Transitions
Authors: Kityk A. V. 
Published: July 2007

AbstractOptical activity, electrooptical effect, and ultrasound wave velocities are investigated in the vicinity of phase transitions in the incommensurate ferroelectric crystals (NH4)2ZnCl4. The influence of hydrostatic pressure on the acoustic properties and phase transitions are studied as well. The optical activity and electrooptical effects are found only in the ferroelectric phase. It is shown that the normal‐incommensurate phase transition shifts to high temperatures under the action of hydrostatic pressure. At the same time, the temperature region of modulated phase coexisting becomes narrower and disappears finally at the triple point (Pk = 196 MPa, Tk = 249.5 K). The obtained results are considered within the framework of the phenomenological theory.
Birch Equation of State for Alkali Halide Crystals
Authors: Thomas L. M. , Shanker J. 
Published: July 2007

AbstractThe Birch equation of state (BES) derived from the theory of finite strain is used to calculate the pressure versus volume compression data at room temperature for eleven alkali halide crystals, viz. LiF, LiCl, LiBr, LiI, NaF, NaCl, NaBr, NaI, CsCl, CsBr, and CsI. These crystals can be compressed to rather high pressures without appearance of any structural phase transformation. The parameters of BES are determined from the ultrasonically measured experimental values of the bulk modulus and its first pressure derivative and the calculated values of second pressure derivative of bulk modulus derived from interionic potential models. The resulting P‐V data for all the crystals compare well with the corresponding experimental values reported by Vaidya and Kennedy and by Yagi.
Dynamical Transport Theory of Two‐Dimensional Systems
Authors: Farvacque J.‐L. 
Published: July 2007

AbstractA formulation of a dynamical transport theory based on the dielectric properties of the electronic carriers has recently been proposed for bulk materials. The present paper shows how to apply this approach in the case of two‐dimensional electronic layers. An expression of the effective scattering potential is given, taking into account the actual band structure of the 2D layer, local field effects, and the layer surroundings. It is finally shown that the present approach is fully consistent with the semiclassical approach of the relaxation time solution of the Boltzmann kinetic equation, as soon as standard approximations are made.
Absolute Seebeck Coefficients of Ultrathin Cr Films
Authors: Schröuder K. , Zhang Le , Ger W.‐T. 
Published: July 2007

AbstractThe thermopower of very thin Cr overlayers deposited on Ge films or glass plates is measured near room temperature “in situ” in a high vacuum system. It is found that the absolute Seebeck coefficient Sab of Cr overlayers deposited on Ge films approaches zero for very thin films. Sab reaches a minimum near d = 3 nm, and is 16 μV/K for d = 21 nm, close to bulk data.
Planar Channeling Radiation from Relativistic Electrons and Positrons in Silicon
Authors: Kumar V. Hari , Pathak A. P. 
Published: July 2007

AbstractThe characteristics of the radiation emitted from relativistic positrons and electrons channeled along the (110) plane in silicon single crystals is calculated using a realistic potential which is based on the atomic shell structure of target atoms. The results are compared with experimental results and are found to agree reasonably well.
Pressure Dependence of the Band Gaps and Charge Densities in Si
Authors: Benkabou F. , Badi N. , Dufour J. P. , Kobayasi T. , Nara H. , Khelifa B. , Aourag H. 
Published: July 2007

AbstractThe empirical local and nonlocal pseudopotentials of Si which can describe the electronic energy structure over a wide energy range of more than 20 eV from the bottom of the valence band is determined for different pressures. The nonlocality of the potential is described by the Gaussian model. The predictions for the linear and quadratic pressure coefficients are consistent with the experiment. The valence charge densities of Si under high pressure are studied. The forbidden X‐ray factor F(222) is very stable under pressure and changes by less than 3% under volume changes of the order of 5%.
Anomalous Variation of the Recoil‐Free Fraction of 151Eu Nucleus in Euba2Cu3O7−x around the Superconducting Transition Temperature
Authors: Jia Y. Q. , Jin M. Z. , Liu X. W. 
Published: July 2007

AbstractMössbauer spectra of the superconductor EuBa2Cu3O7−x are measured at various temperatures (83 to 120 K) and the effective absorber thickness is calculated from the experimental spectra. The temperature variation of the recoil‐free fraction of the 151Eu nucleus in Euba2Cu3O7−x is obtained. An anomaly in the temperature dependence of the recoil‐free fraction of the 151Eu nucleus in the superconductor EuBa2Cu3O7−x is found around the superconducting transition temperature. This may provide evidence of softening of lattice vibrations about the Eu atom in the crystal in the normal state‐superconducting state transition process of the EuBaCuO system.
Analysis of the Debye Temperature for ANB8–N Type Ionic and Partially Covalent Crystals
Authors: Narain Sarvesh 
Published: July 2007

AbstractA simple method for calculating the Debye temperature for 64 binary crystals of ANB8−N type with NaCl, CsCl, and ZnS structures is developed. First the short‐range force constants are calculated by establishing an empirical relationship between isothermal bulk modulus and lattice parameter. These force constants are then used to estimate the values of Debye temperatures. The results are compared with the corresponding values reported in literature. The importance of the present calculations has been emphasized in view of recently discovered high‐temperature superconductors.
A Cluster Study of the Stabilities of Adsorption Sites and Charge Transfers at the Na/Si (100) Surface
Authors: Hira A. S. , Lin P.‐C. , Ray A. K. 
Published: July 2007

AbstractThe adsorption properties of sodium adatom on silicon (Si) surfaces are investigated using ab initio molecular orbital theory. Twenty‐three bare silicon clusters are studied at the unrestricted Hartree‐Fock (UHF) many‐body perturbation theory (MP4) levels. Twenty‐seven alkali atom‐silicon (AM‐Sin) adsorbate systems are studied with adsorption sites classified as on‐top, open, and bridge sites. Adsorption distances are found by optimizing the distance between the alkali atom and Sin clusters at the UHF level and then chemisorption energies are calculated at the Mp4 level. Electron correlation is found to have significant effects on cluster stability and chemisorption energy. The chemisorption energies are smaller at the Mp4 level than at the SCF level for most systems, and usually increase with increasing number of atoms in the cluster. Am‐Si bonds appear to be of mixed type.
Soliton Energy in the F.C.C. Antiferromagnet Ceas
Authors: Liu Wu‐Ming , Zhang Xin‐Ming , Zhang Dan , Li Shi‐Hong , Zhou Ben‐Lian 
Published: July 2007

AbstractEmploying the Dyson‐Maleev transformation and the coherent state ansatz, two partial differential equations of motion from the Hamiltonian of the f.c.c. antiferromagnet CeAs are obtained. By using the multiple scalar method and the long‐wavelength approximation, these equations are reduced to a nonlinear Schrödinger equation. The single soliton solution is obtained by using the inverse scattering transformation. For the single soliton bound state, the energy and the spatial configurations of the spin are given.