bluuebunny/crossref_metadata_2025_split huggingface dataset:
X‐ray diffraction behaviour of W/Ti superlattices
Authors: Pan F. M. , Feng J. W. , Jin G. J. , Hu A. , Jiang S. S. 
Published: July 2007

AbstractThe structural properties of periodic and quasiperiodic W/Ti superlattices have been investigated by means of X‐ray diffraction. Intensity attenuation of even ordered peaks occurs in the spectra of W/Ti periodic superlattices with near‐equal‐layer thicknesses. This phenomenon is theoretically explained. Two series of quasiperiodic (Fibonacci) samples are prepared, one with thickness ratio dA/dB=τ, and the other dA/dB = 1/τ. X‐ray diffraction results of these quasiperiodic superlattices are discussed and compared. The possible application of Fibonacci films as optical elements in the soft X‐ray region is discussed. Furthermore some X‐ray diffraction spectra are simulated by computer calculation in order to understand the detailed structures. The calculated results are in good agreement with measured ones.
Analysis of the pressure dependence of the thermal expansivity of NaCl crystal
Authors: Thomas L. M. , Shanker J. 
Published: July 2007

AbstractThe pressure dependence of the thermal expansivity of NaCl crystal has been studied using various relations between α and the Anderson parameter δ The variation of α with pressure has been estimated and taken into account for determining the pressure dependence of α. A comparison of the results derived from various models has been presented with available experimental data. It is found that, the Anderson power law for the pressure dependence of δ is more consistent with the experimental data.
Tunnel electron current induction in n+‐I‐M structures
Authors: Volkov R. A. , Dyakov I. V. 
Published: July 2007

AbstractA novel effect of tunnel electron current induction (TECI) is theoretically considered in n+‐I‐M structures with a penetrable potential barrier (I‐layer) resulting from heating the n+‐layer electrons by an external electric field and tunnelling them into the n+‐layer through the I‐insulator. A tunnel electron current which is thus induced leads to charging the structure and to a potential difference ‐ the tunnel electromotive force (TEMF)‐between the n+‐ and M‐layers. TEMF is a practically significant consequence of the TECI effect. An equation for TEMF has been deduced using numerical calculations. Approximate analytical solutions of this equation and their application limits are cited in electron temperature approximation as functions of the external field, lattice temperature, and structure parameters. Calculations of the TEMF build‐up time are presented as functions of the external field. All expressions are calculated for lattice temperatures of 300 and 77 K. Experimental observation possibilities of TECI are also briefly viewed.
Grain boundary scattering in DC transport in thin metallic films
Authors: Gerlach E. 
Published: July 2007

AbstractThe energy‐loss transport theory is applied to calculate the resistivity due to grain boundary scattering in a thin metallic film adjacent to two dielectric media, e.g. vacuum/Ag/Si. The common “bulk” result by Mayadas and Shatzkes for small film thicknesses is found to be reduced by about 20% due to image effects.
Effect of high hydrostatic pressure on the magnetoresistance quantum oscillations of the quasi‐two‐dimensional organic superconductor x‐(BEDT‐TTF)2i3
Authors: Helm P. , Kraak W. , Schweitzer D. 
Published: July 2007

AbstractHigh‐field magnetotransport investigations of single crystals of the quasi‐two‐dimensional organic compound x‐(BEDT‐TTF)2I3 under hydrostatic pressure up to 9 × 108 Pa are presented. Pronounced Shubnikov‐de Haas oscillations are observed in magnetic fields up to 12 T over the whole pressure range. These quantum oscillations are affected remarkably by hydrostatic pressure. All of the four fundamental fields detected rise with increasing pressure corresponding to an enhancement of the extremal areas of the Fermi surface in x‐(BEDT‐TTF)2I3. The experimentally determined cyclotron effective masses of the charge carriers decrease with increasing pressure. The FFT amplitudes of the Shubnikov‐de Haas oscillations show a very complex pressure dependence reflecting a more complicated structure of the electron system than the relatively simple topology of the calculated Fermi surface involves. The pressure‐induced changes of the Fermi surface are discussed in the framework of an effective dimer model and compared with equivalent investigations on the isostructural compound x‐(ET)2Cu(NCS)2.
Finite cluster approximation study of spin‐1 ising model in transverse and crystal fields
Authors: Song Wei‐Ji , Yang Chuan‐Zhang 
Published: July 2007

AbstractA spin‐1 Ising model with the presence of transverse and crystal fields (CTIM) is studied within the scheme of the finite cluster approximation (FCA). The phase diagrams and the other critical behaviour are numerically investigated for the honeycomb lattice. FCA yields results which are superior to those of the standard mean‐field approximation (MFA).
Effect of the topological transition on the optical absorption edge of sulphur‐based glasses
Authors: Tsiulyanu D. I. , Marian S. I. 
Published: July 2007

AbstractExponential absorption edge of chalcogenide glassy alloys with sulphur in the region of topological transition is studied. It is shown that the slope of the tail depends on mean coordination number and stoichiometry of the materials, showing a common behaviour with position of the edge.
Optical properties of Er3+ ions in zinc borosulphate glasses
Authors: Kumar V. V. Ravi Kanth , Jayasankar C. K. , Jagannathan R. 
Published: July 2007

AbstractThe optical properties of Er3+ ions in zinc borosulphate (ZnSO4 · 7 H2O + B2O3) and alkali zinc borosulphate (R2SO4 + ZnSO4 · 7H2O + B2O3, R2SO4 = Li2SO4 · H2O, Na2SO4, or K2SO4 and Gd2(SO4)3 · 8H2O) glasses are reported. The assigned energy level data of Er3+(4f11) in borosulphate glasses are analyzed in terms of a parametrized model Hamiltonian and in turn satisfactory eigenvalues and eigenvectors for intensity analyses are obtained. The Judd‐Ofelt theory has been applied to predict various spectroscopic parameters for the fluorescent levels of Er3+ : borosulphate glasses and these results are compared and discussed with similar results.
Temperature dependence of elastic constants and thermal expansion coefficient for NaCl crystals
Authors: Thomas L. M. , Shanker J. 
Published: July 2007

AbstractThe second‐order elastic constants C11, C12, and C44, isothermal bulk modulus BT, and volume thermal expansion coefficient α are calculated for NaCl crystals in the temperature range (294 to 766 K) using Tallon's model based on the concept of modified Anderson‐Grüneisen parameters. The results obtained in the present study are compared with the experimental values reported in the literature. There is good agreement between calculated and experimental values for V/V0, C11, C44, BT, and α. It is found that C11, C44, and BT decrease whereas C12 and α increase with increase in temperature.
Luminescent associates of indium ions with interstitials and vacancies in an x‐irradiated KCl: In crystal
Authors: Aceves R. , Flores M. Barboza , Nagirnyi V. , Salas R. Perez , Usarov A. , Zazubovich S. 
Published: July 2007

AbstractThe spectral, polarization, and kinetic characteristics of luminescence are studied for In+ and In2+ ions associated with interstitials and vacancies in an X‐irradiated KCl: In crystal. It is shown that the 2.08 eV emission is caused by the electronic transitions from the tetragonal minima of the triplet relaxed excited state of an In+ ion perturbed by an interstitial halide atom (H centre) and a cation vacancy v. The emission bands peaking in the region from 1.9 to 1.7 eV are ascribed to various types of associates of an In2+ ion with v or with v and one or two H centres. It is concluded that the anisotropic impurity colour centres studied are produced by X‐irradiation mainly on the basis of the In3+v dipoles existing in the nonirradiated KCl:In crystal due to the changeable valence of indium. The processes of the production, destruction, and mutual transformation of the impurity colour centres of various types are studied in the temperature range from 4.2 to 400 K.
Non‐markovian behavior of quantum confined electronic systems
Authors: Bertoncini R. , Mauser N. 
Published: July 2007

AbstractThe holomorphic memory function method is modified to include geometrical confinement. A ‘ballistic memory function’ is identified, showing that energy quantization due to lateral confinement is associated with a retardation in the system. Consequently, the ballistic conductance quantization of waveguides is shown to be caused by long‐lived correlations between values of the applied field at different points in the device. A renormalized force correlation function shows the mutual influence of geometrical confinement and scattering mechanisms: confinement‐induced memory effects modify the elastic scattering white‐relaxation spectrum and transform it into a scattering mechanism with enhanced retardation properties. Evidence of these phenomena is given through the numerical evaluation of the ac conductance and time‐dependent current for a rectangular crosssection wire of finite length.
Extended chain approximation in quasi‐one‐dimensional ising model
Authors: Muraoka Y. , Idogaki T. 
Published: July 2007

AbstractThe extended chain approximation (ECA) in the quasi‐one‐dimensional Ising model is proposed and is found to give the same results as the Bethe‐Peierls approximation for the ferromagnetic Ising model. It is discussed that the ECA can be applied to complicated systems such as the axial next‐nearest‐neighbour Ising (ANNNI) model, etc.
Visible photoluminescence in porous silicon prepared in different conditions ‐ temperature dependence and decay
Authors: Ciurea M. L. , Pentia E. , Manea A. , Belu‐Marian A. , Baltog I. 
Published: July 2007

AbstractMeasurements of the visible photoluminescence and the decay of the photoluminescence, performed at different temperatures on porous silicon films, prepared by the anodization process under different conditions on (100) p‐type silicon wafers are reported. A separation of the broad visible band of the photoluminescence in two subbands with maxima situated at 1.54 and 1.72eV at room temperature related to the preparation conditions is obtained. This separation is still present at low temperatures but is very weak. The PL decay process is well described by a bimolecular recombination. The decay time α−1 is in the order of microseconds at room temperature and nanoseconds at liquid nitrogen temperature.
Charge transfer in the bonding of gaas
Authors: Chandrasekaran K. S. , Mohanlal S. K. , Saravanan R. 
Published: July 2007

AbstractCharge transfer in GaAs is analysed utilising our earlier precise and extensive X‐ray diffraction data. The h + k + l = 4n+ 2 structure factors are weak, “quasi‐forbidden” with the constituent atoms of nearly equal but opposite scattering. The measured structure factors are all systematically larger than their calculated values over the entire range of sin θ/λ up to about 10 nm−1. Moreover, they exhibit non‐equivalence of inversereflections with non‐zero indices which can arise only from bonding distortion or anharmonicity. A model calculation for the charge transfer inbonding from the III to the V atom, described by a single parameter x, valid over the entire reciprocal space, is proposed and found to yield a precise estimate for x, namely 0.52(0.12) for GaAs (in electron units). This result is in good agreement with the earlier models, and indicates an appreciable core contribution to the charge transfer.
Boundary least squares method for the solution of schrödinger's equation in quantum wires
Authors: Sirenko Yu. M. , Mitin V. 
Published: July 2007

AbstractWe present a method for the approximate semianalytical calculation of wave functions and eigenenergies in systems consisting of domains with knownbulk solutions of the corresponding Schrödinger equation (e.g. with piecewise constant potential). The trial wave function is written as a normalized linear combination of several bulk solutions for the given energy. The coefficients of the linear combination are found by minimization of the integral of square mismatch along the boundaries. Mathematically the problem is equivalent to the minimization of the Rayleigh quotient or solution of the generalized eigenproblem for the vector of coefficients. The value of the residual provides an estimation of the accuracy of the results and gives thepossibility to choose an optimal set of trial functions. We illustrate the use of the method by calculation of eigenfunctions of infinitely long triangular and quadrilateral wires.
Two‐LO‐phonon resonant Raman scattering in ii‐vi semiconductors
Authors: Garcí‐cristóbal A. , Cantarero A. , Trallero‐giner C. , Limmer W. 
Published: July 2007

AbstractRecently, absolute values of second‐order Raman scattering efficiency have been measured around the E0 and E0 + Δ0 critical points of several II‐VI semiconductor compounds. The measurements were performed in the z(x, x)z̄ backscattering configuration on (001) (ZnSe and ZnTe) and (110) (CdTe) surfaces. They show strong incoming and outgoing resonances around the band gap and larger scattering efficiencies as compared to III‐V compounds. A theoretical model which includes excitons as intermediate states in the Raman process is shown to give a very good quantitative agreement between theory and experiment. Only a small discrepancy exists, while in III‐V compounds the discrepancies were close to one order of magnitude. A discussion of the differences in the scattering efficiencies between II‐VI and III‐V compounds is also reported.
Correlations between the cohesive energy and a crystallographic ratio in group‐II chalcogenides
Authors: Koh A. K. 
Published: July 2007

AbstractCorrelations between the cohesive energy per mole and a crystallographic ratio in group‐II chalcodes are presented. It is shown that the linear combination of the anion radius and the nearest‐hbour distance is a constant in these materials. Results obtained agree with works reported earlier. This work highlights the significance of the anion radius in determining the cohesive energy in group‐II chalcogenides.
Phonon‐assisted two‐photon magnetoabsorption in an indirect band gap semiconductor quantum well
Authors: Kapatkar S. B. , Kubakaddi S. S. , Mulimani B. G. 
Published: July 2007

AbstractWe present a theory of phonon‐assisted two‐photon absorption in an indirect band gap semiconductor quantum well (QW) in a quantizing magnetic field for polarizations in the plane and perpendicular to the layer within a three‐band model. It is found that for both polarizations all transitions are possible between Landau levels due to phonon involvement unlike the case in direct band gap semiconductor QWs. Numerical calculations of the absorption coefficient are given for the SixGe1−x/Si QW.
Electron transport in GaAs at low lattice temperatures
Authors: Ghorai A. K. , Bhattacharya D. P. 
Published: July 2007

AbstractThrough numerical methods, investigations have been carried out to see how the finite energy of the deformation potential and piezoelectric acoustic phonons affects the ohmic and non‐ohmic mobility characteristics of n‐type GaAs taking the non‐parabolicity of the conduction band into account and under the conditions that, unlike the traditional approximations, the energy of the acoustic phonons can neither be neglected in comparison with the carrier energy nor the phonon population be represented by the equipartition law. The results show interesting features in that they are significantly different from those that follow from the traditional approximation of negligible phonon energy and also provide better agreement with the available experimental data. The inadequacies of the present theory and the scope for further refinements are discussed.
Ladder Ising spin configurations II. magnetic properties
Authors: Mejdani R. , Gashi A. , Ciftja O. , Lambros A. 
Published: July 2007

AbstractIn this paper we consider ladders with two, three, and four coupled Ising spin chains, characterized by interchain and intrachain couplings, to study in detail their magnetic behaviour for different ratios of the interaction constants and different values of magnetic field, by using a transfer matrix method and a complex algorithm, realizing the diagonalization and the differentiation. We have proposed a combined algorithm to realize also the generation of the elements of the transfer matrix for more complicated ladder configurations. The problem of Ising ladders is straightforward with a crossover between a 2D high‐temperature region and a 1D low‐temperature region when the 2D correlation length equals the width. To emphasize the fact that there is no finite magnetization in absence of the magnetic field, we study also analytically this case for the ladder with two coupled Ising chains. In presence of the magnetic field, for very weak magnetic fields (of the order 10−8, in reduced units) the magnetization goes from the value one to the value zero in a narrow interval of nonzero temperatures, where also the susceptibility exhibits a very high peak. This narrow interval, increasing the number of chains, is displaced towards higher temperatures. Also, in the case of interchain antiferromagnetic couplings, the formation of interchain spin pairs becomes clear.
The study of 57Fe Mössbauer spectra for La0.7Sr0.3FeO3−δ with different structure
Authors: Li Guangshe , Li Liping , Zhao Muyu 
Published: July 2007

AbstractSamples of La0.7Sr0.3FeO3−δ were obtained by sintering the precursor prepared by the Polyethylene Glycol (PEG) method. The measurements of XRD and 57Fe Mössbauer spectra showed that the heat treatment of the precursor at different temperatures leads to phase transformations from the orthorhombic to the cubic and finally to the rhombohedral phase, to an increase of average grain size, and to changes of the electronic states of the Fe ions. It was thought that in the perovskite oxides the conditions of synthesis or treatment may have an important influence on structure and properties by adjusting the valence state or/and introducing oxygen vacancies.
Ground‐state zero‐field splitting of Fe3+ ion in ZnO and CdSe crystals
Authors: Kuang Xiao‐Yu 
Published: July 2007

AbstractThe ZnO and CdSe crystals have similar hexagonal wurtzite structures with a contraction along the c‐axis of the crystal, however, different electronic fine structures for ZnO:Fe3+ (D « 0) and CdSe: Fe3+ (D » 0) have been displayed in EPR experiments. This interesting phenomenon has not yet been interpreted at present. In this paper, a reasonable calculation is given by considering the covalent spin‐orbit coupling interaction. Our results show that the ground‐state splitting in ZnO:Fe3+ is due to the trigonal distortion, whereas the main physical mechanism of the splitting in CdSe:Fe3+ can be attributed to the divergent contributions of |t2〉 and |e〉 sub‐orbitals to the spinorbit coupling interaction.
Temperature dependence of the spontaneous polarization in Rochelle salt and thiourea
Authors: Piekara† A. H. , Wiȩckowski A. B. 
Published: July 2007

AbstractThe occurrence of ferroelectric properties characterized by two (and three) Curie temperatures is explained phenomenologically by a model of structural antiferroelectrics with two sublattices, involving hydrogen‐like bonds with asymmetric potential wells. On the assumption of a slight discrepancy between the differences in energy levels ΔU1 and ΔU2 of the two sublattices, a non‐zero spontaneous polarization is obtained for certain well‐defined ranges of temperature. The model permits an explanation of the temperature dependence of polarization in Rochelle salt and thiourea.
The peculiarities of colour centre production in doped alkali halides
Authors: Vale G. 
Published: July 2007

AbstractThe peculiarities of colour centre production and recombination in KBr, KI crystals doped with Tl, In are examined. The photostimulated dopant ion luminescence (PSL response) follows that of the F‐centre production in the subnanosecond time range. It is concluded that the radiation defects in a doped crystal are spatially distributed in the near vicinity of the dopants. To a limited extent the photo‐ and thermostimulated defect recombination also takes place near the dopant.
Diffusion in the intermetallic phase Fe3Si under hydrostatic pressure
Authors: Gude A. , Freitag K. , Sepiol B. , Vogl G. , Mehrer H. 
Published: July 2007

AbstractDiffusion of iron in DO3 ordered Fe76Si24 has been studied under hydrostatic pressure at 934 K. The diffusion coefficients were determined using the radiotracer technique with the implanted radioisotope 59Fe and a precision grinding device for serial sectioning. The resulting activation volume of diffusion is ΔV = 1.48 × 10−29 m3 = 1.27Ω (Ω atomic volume). The large value of ΔV can be attributed to vacancy‐mediated Fe diffusion, in which divacancies or even larger vacancy clusters might be involved. This assumption is corroborated by positron annihilation experiments, which show a strong increase of the lifetime of trapped positrons in Fe75Si25 at higher temperatures.
A note on solute enhanced diffusion
Authors: Pelleg J. , Rabinovitch A. 
Published: July 2007

AbstractA reformulation of the solute/solvent diffusion enhancement problem is discussed by introducing a new set of two empirical parameters. A comparison with experimental data, both for solvent and solute enhancements, shows good agreement. A constant u is introduced relating the preexponential factor and the activation energy in the Arrhenius equation for the diffusion coefficient. This constant is attributed to the solute/solvent enhancement‐reduction transition temperature.
Lattice distortion effects within the generalized transverse Ising model
Authors: Kokshenev V. B. , Pires A. S. T. 
Published: July 2007

AbstractA qualitative analysis of lattice vibration effects including lattice distortions, spin‐phonon interaction, and phonon anharmonicity is given within the extended transverse Ising spin model (TIM). It is argued that the rigid‐lattice TIM is a credible model for real crystal in the sense that no new anisotropic‐type interactions emerge due to higher‐order lattice distortions. Instead of the known first‐order Kobayashi model a new effective second‐order nonrigid‐lattice TIM is proposed. Recent developments in the TIM spin dynamics are briefly discussed.
Investigation of electronic structure of the H.C.P. Ni75Nb25 MX phase
Authors: Pan J. S. , Huang X. Y. , Fan Y. D. 
Published: July 2007

AbstractThe total energy and electronic structure of the Ni75Nb25 MX phase with a h.c.p. structure have been calculated by means of discrete variational Xα (DV‐Xα) method. The total energy of this metastable crystalline phase was calculated as a function of lattice constant α. The predicted lattice constants agree well with the experimental result. The calculation gives an interpretation of the nature of bonds of this MX phase.
Disordered spin‐one Ising model with biquadratic exchange interaction within functional integration method
Authors: Rudavskii Yu. , Vatamaniuk O. , Savenko V. 
Published: July 2007

AbstractA disordered spin‐one Ising model with biquadratic exchange interaction is investigated within a functional integration approach. The free energy is presented in the form of a functional expansion in a series over the Fourier‐transformed density fluctuations. In random phase approximation expressions for phase transition temperatures are obtained. The structural disorder is simulated by means of hard core system structure factors.