bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nonequilibrium Statistical Theory of Channeling. Energy–Momentum Balance Equation and Transverse Quasitemperature of a Channeled Particle Subsystem
Authors: Kashlev Yu. A. 
Published: July 2007

AbstractPlanar channeled particles (protons, helium ions, etc.) are considered as an individual thermodynamic subsystem. A statistical operator for the nonequilibrium system under conditions of multiple electron scattering and an energy‐momentum balance equation are obtained on the basis of the nonequilibrium statistical thermodynamics. The formalism presented is applied to analyze the transverse quasitemperature of the channeled particle subsystem in steady state, its quasiequilibrium energy distribution, and the diffusion coefficient of the particles.
Electronic and Cohesive Properties of NbC, NbN, and NbO
Authors: Onwuagba B. N. , Sundararajan V. 
Published: July 2007

AbstractThe electronic and cohesive properties of the refractory metal compounds NbC, NbN, and NbO are calculated using the tight‐binding linear muffin‐tin orbital (TB‐LMTO) method. The electronic structure agrees very well with the previous calculations obtained by other methods. The hybridisation increases as we go from the C to O compounds. The cohesive energies and the bulk moduli are increased compared to the pure Nb metal indicating the role of C, N, and O in the enhancement of binding.
Segregation Kinetic Simulation and Segregation Energy Determination on a CuAg(111) Alloy
Authors: Jouaiti A. , Mosser A. , Romeo M. 
Published: July 2007

AbstractUsing a method based on the kinetic tight binding Ising model (KTBIM), the segregation energy on the (111) face of a CuAg 0.45 at% alloy, is derived as a function of surface coverage, from segregation kinetics measured at 763 K. Nearly the same segregation energy value as from equilibrium experiments is obtained. Besides, it is shown that a surface size effect term, proportional to the square of the surface concentration, has to be introduced in the segregation energy, in order to take into account the surface strain energy which occurs in the first layer when the silver atoms segregate at the surface.
Density of States in Ordered and Disordered Pd2TiAl and Pd2TiSn Heusler Alloys
Authors: Jezierski A. 
Published: July 2007

AbstractThe band structure of the ordered and disordered Pd2TiAl and Pd2TiSn Heusler alloys is studied by using the LMTO and LMTO‐CPA methods. The self‐consistent spin‐polarized LMTO calculations show that these systems are not magnetic and the shape of the density of states is in good agreement with the ultraviolet photoemission spectra for the Pd2TiAl alloy. Our theoretical calculations indicate the existence of a small sub‐peak near E = −9 eV in the UPS spectra for Pd2TiSn.
Random Impurity Potential and Hopping Conduction in ZnSe
Authors: Kasiyan V. A. , Nedeoglo D. D. , Timchenko I. N. 
Published: July 2007

AbstractHall effect, electrical conductivity, carrier mobility, and magnetoresistance of Cu‐doped n‐ZnSe bulk crystals are studied in the temperature range 2 to 300 K. Compensating Cu impurity amplifies the random impurity potential, modulates the band edges, and leads to electron localization in the potential wells of the conduction band bottom in slightly doped, highly compensated crystals (K = 0.82 to 0.97). High‐temperature hopping conductivity through the localized states of such type observed in the range 100 to 200 K and accompanied by negative magnetoresistance is first investigated in n‐ZnSe.
Electron Transport in Vapor Deposited Molecular Glasses. The Role of Group Dipole Moments
Authors: Borsenberger P. M. , Gruenbaum W. T. , Magin E. H. 
Published: July 2007

AbstractElectron mobilities are measured in vapor deposited layers of N1N′‐bis(1,2‐dimethylpropyl)‐1, 4, 5, 8‐naphthalenetetracarboxylic diimide (NTDI). NTDI is a weakly polar compound with a molecular dipole moment of 0.3 D. The molecular moment is the vector sum of two group moments, each approximately 3.3 D. The results are described by a formalism based on disorder, due to Bässler and coworkers. The formalism is based on the assumption that charge transport occurs by hopping through a manifold of localized states with superimposed energetic and positional disorder. The key parameter of the formalism is the energy width of the hopping site manifold. For NTDI, the width is 0.093 eV. The width can be described by a model based on dipolar disorder. The model assumes that the width is comprised of a dipolar component and a van der Waals component. A comparison of the experimental results with predictions of the model leads to the conclusion that the dipolar component to the width is determined by group dipole moments of two carbonyl groups adjacent to the imide acceptor functionalities. The positional disorder parameter is 2.3 and attributed to packing constraints. The prefactor mobility is 1.0 × 10‐2 cm2/Vs.
Structural and Optical Properties of the System (Ca, Sr, Eu)5(PO4)3CI
Authors: Nötzold D. , Wulff H. , Herzog G. 
Published: July 2007

AbstractPolycrystalline materials of the composition Sr5−x−yCaxEuy(PO4)3Cl with 0 ≦ x ≦ 4.99 and 0 ≦ y ≦ 0.1 crystallize in the hexagonal crystal system. The space group is P63/m. The alkaline earth ions occupy two different crystallographical sites. In addition to X‐ray diffraction measurements, the optical properties are studied at room temperature. Moreover the emission spectra are measured at liquid nitrogen temperature. Refinement of the structure parameters is carried out using the Rietveld method. A varying calcium portion influences the lattice constants a0 and c0 and therefore the luminescence of the samples. The luminescence arises from transitions between 4f65d and 4f7 configurations of the Eu2+ ion.
Self‐Diffusion of Ni in Single and Polycrystals of Ni3Al. A Study of SIMS and Radiotracer Analysis
Authors: Frank St. , Södervall U. , Herzig Ch. 
Published: July 2007

AbstractDiffusion of nickel in the intermetallic compound Ni3Al is measured in the temperature range from 1004 to 1422 K by applying two different techniques for the determination of the concentration profiles. The diffusion of the radioactive 63Ni tracer in Ni3Al polycrystals (75.2 at% Ni) is analyzed in the temperature region from 1223 to 1422 K by the conventional serial sectioning technique using a precision parallel grinding device and an improved technique of detecting the low‐energy β‐decays of 63Ni with high efficiency by liquid scintillation counting. In the low‐temperature region (1004 to 1259 K) the concentration profiles are determined by secondary ion mass spectrometry (SIMS) using the highly enriched stable 64Ni tracer and Ni3Al single crystals (75.9 at% Ni). The SIMS technique is considered as particularly suitable for profile detection, owing to its potential of measuring also low diffusion coefficients with high accuracy. The temperature dependence of the diffusion coefficient DNiv follows a perfect linear Arrhenius relation in the investigated temperature range for Ni3Al. The frequency factor D0 = (3.59) × 10−4 m2s−1 and the activation enthalpy Q = (303.0 ± 5.3) kj mol−1 correspond to a vacancy mechanism. An enhanced diffusivity at lower temperatures, which was previously reported in the literature and ascribed to the presence of constitutional vacancies, is not observed. It is concluded that Ni self‐diffusion in Ni3Al only occurs via thermal vacancies. This result is in agreement with recent positron annihilation studies by Badura and Schaefer where, independent of the composition, no constitutional vacancies are detected in the Ni3Al compound.
The Dynamics of Dislocation (Kink) in the Frenkel‐Kontorova Model in the Case of a Nonzero Environment Temperature
Authors: Landau A. I. 
Published: July 2007

AbstractComputer simulation is used to study the dependence of the velocity of a dislocation (kink) on the applied motive force and temperature in the Frenkel‐Kontorova model (discrete sine‐Gordon system). The applied forces used exceed the Peierls‐Nabarro barrier. Heating of the atomic chain by the environment is simulated by introducing random thermal forces and frictional forces acting on individual atoms of the system into the Frenkel‐Kontorova equations. It is found that though in this model the velocity of a dislocation depends on temperature, this dependence is very weak. In the range of dislocation velocities studied, smaller velocities monotonically rise with growing temperature, while larger velocities depend on temperature nonmonotonically, first decreasing and then increasing with rising temperature.
Lattice Dynamics of Dichlorodifluoromethane
Authors: Zeng W. Y. , Anderson A. 
Published: July 2007

AbstractA simple force constant model is applied to the vibrations of crystalline CCl2F2 at low temperatures, and good agreement with recent spectroscopic results is obtained. The calculations suggest that two weak Raman peaks observed in the lattice region should be re‐assigned as fundamentals. Principal intermolecular interactions are identified, and it is shown that the intramolecular force constants change only slightly from their gas phase values.
Si/SiGe Quantum‐Well Electron Mobility. Main Scattering Mechanisms
Authors: Tutor J. , Comas F. 
Published: July 2007

AbstractMobility calculations for a symmetrically strained Si/SiGe quantum well are reported considering conduction along the Si channel. The Boltzmann transport theory is applied taking into account two scattering mechanisms:electron scattering by acoustic phonons (via deformation‐potential coupling) and electron scattering by ionized impurities (both remote and background). It is compared with experimental results reported by Schäffler et al., where the QW was grown avoiding threading dislocations in the Si channel, and an excellent agreement is achieved. As in our previous works only one adjustable parameter is introduced: the deformation‐potential energy.
About a Conjunction between Electrical and Optical Phenomena in p‐Type Heavily Doped Silicon at Room Temperature
Authors: Van Cong H. , Debiais G. 
Published: July 2007

AbstractThe conjunction between electrical and optical phenomena in p‐type heavily doped silicon at room temperature is investigated, based on our accurate empirical models for the band‐gap narrowing, apparent band‐gap narrowing, and unperturbed Fermi energy shift. The numerical results of optical band gap, reduced interacting Fermi energy, and reduced interacting density‐of‐valence band states effective mass are presented and compared with other theoretical results and experiments. It is concluded that, taking into account the unperturbed Fermi energy shift effect, the values of band‐gap narrowing, obtained from electrical and optical phenomena, are found to be the same, removing the disagreements or discrepancies in theoretical and experimental values of band‐gap narrowing existing so far in the literature.
Concentrations of Atomic Defects in B2FexAl1−x. An Ab‐Initio Study
Authors: Mayer J. , Elsässer C. , Fähnle M. 
Published: July 2007

AbstractThe concentrations of various atomic defects are calculated within the framework of a grand canonical formalism for the ordered compound FexAl1−x with B2 structure as functions of temperature and composition. The input parameters for the grand canonical formalism are determined by the ab‐initio mixed‐basis pseudopotential theory in local‐density approximation. It is shown that FexAl1−x is neither a compound with pure antisite disorder nor a compound with pure triple‐defect disorder but that it exhibits a hybrid behaviour in which vacancies on the Fe sublattice and antisite atoms on both sublattices appear. The concentration of vacancies on the Al sublattice is negligibly small. The implications of this result for the modelling of diffusion mechanisms in FexAl1−x are discussed.
Hole Transport in a Vapor Deposited Phenylenediamine Molecular Glass
Authors: Borsenberger P. M. , Shi J. 
Published: July 2007

AbstractHole mobilities have been measured in vapor deposited amorphous layers of N,N′‐bis(1‐naphthalenyl)‐N,N′‐diphenyl‐4,4′‐phenyldiamine (NPPDA) over a wide range of fields and temperature. The results are described within the framework of a formalism based on energetic disorder of the hopping sites. The variance of hopping site energies is 0.098 eV. The energy variance can be described by a model based on dipolar disorder. The model is based on the assumption that the total variance is comprised of a dipolar component and a van der Waals component. For NPPDA, the dipolar component is 0.080 eV and the van der Waals component is 0.067 eV.
Influence of Electrostatic Field on Excess Conductivity of Thin YBaCuO Films
Authors: Sorkin B. , Konsin P. 
Published: July 2007

AbstractThe influence of a strong electrostatic field perpendicular to the electric current on the excess conductivity of YBa2Cu3O7−y thin films near Tco (R = 0) and also in those with weak links is investigated by modelling with an Arrhenius‐type law. One film with weak links is treated by Aslamazov‐Larkin formulas, too. It is shown that the excess or paraconductivity depends on the polarity and strength of the electric field and this dependence may be explained as a change of the dimension of fluctuation conductivity with the increase of the hole concentration.
Anisotropic Magnetization of Some MnAs1−xSbx Single Crystals
Authors: Kohnke H. J. , Dankelmann V. , Kleeberg Ch. , Schünemann J. W. , Bärner K. , Vetcher A. , Govor G. A. 
Published: July 2007

AbstractThe anisotropy of the magnetization of MnAs1−xSbx single crystals is investigated in the temperature range 4.2 K < T < 600 K, for fields up to 0.6 T and concentrations x = 1, 0.5, and 0.1. The first spin reorientation temperature of MnSb, Ts1 = 270 K, is connected with the influence of the thermal expansion on the local anisotropy constants; the second spin reorientation at Ts2 = 520 K is also due to volume expansion, but after the displacement disorder transition at Td = 458 K has occurred. Anomalies of the angular dependence of the magnetization and nonlinear magnetization versus field curves along the hard axis are related to the occurrence of an easy cone.
To the Problem of the Description of Ordered Structures in Binary Cubic Solid Solutions
Authors: Bugaev V. N. , Chepulskii R. V. 
Published: July 2007

AbstractWithin the framework of the static concentration wave method by means of the geometrically complete procedure a number of new types of ordered substitutional structures with the stoichiometric structural formulae AB, AB3, and A3B5, as well as of corresponding isomorphic interstitial structures, A2X, A4X, and A8X3 (A, B, and X are the types of atoms situated at sites and interstices, respectively) are established that complete the list of all thermodynamically stable with respect to the violations of macroscopic homogeneity (Lifshitz) ordered structures arising from the disordered state of f.c.c. and b.c.c. binary solid solutions.
Determination of Quasi‐Plastic Strains in a Crystalline Plate Based on a Solution of the Inverse Problem of the Theory of Elasticity (One‐Dimensional Case)
Authors: Voloshin A. E. , Smolsky I. L. 
Published: July 2007

AbstractAn approximate solution of the inverse problem of the theory of elasticity is considered in terms of distortions for a crystalline plate with a one‐dimensional inhomogeneous distribution of point defects. It is shown that near the plate surface the distribution function of quasi‐plastic strains can be represented as a linear combination of distortion tensor components, up to second‐order infinitesimals. The errors of determining the distribution function using various approximations to a solution of the corresponding direct boundary‐value problem are evaluated. The stability of the solution is demonstrated by reconstruction of the distribution function using a set of simulated topographic images.
Electromagnetic Forces on Type‐II Superconducting Rotating Cylinders
Authors: Saif A. G. , Refai T. F. , El‐Sabagh M. A. 
Published: July 2007

AbstractAnalytical solutions of the electromagnetic fields are presented for a system composed of an infinitely long superconducting cylinder rotating about its axis and placed parallel to two infinitely long normal conducting wires. Both wires carry the same alternating current. From the obtained electromagnetic fields the electromagnetic power loss on the cylinder surface, electromagnetic forces due to induced currents, electromagnetic torque, and the work opposing the rotation of the cylinder are calculated.
Surface Magnetization of a Semi‐Infinite Spin‐1/2 Ising Model with a Diluted Spin‐1 Surface
Authors: Jaščur M. , Kaneyoshi T. 
Published: July 2007

AbstractThe temperature dependence of magnetization at or near the surface in a semi‐infinite spin‐1/2 Ising ferromagnet with a diluted spin‐1 surface is examined within the framework of an effective‐field theory with correlations. Magnetic behaviors associated with the surface dilution as well as the surface single‐ion anisotropy are discussed. A number of interesting phenomena are obtained, which may be observed experimentally.
A Non‐Dangling Bond Model of Paramagnetic Defects in Ge‐S Glasses
Authors: Černošek Z. , Černošková E. , Frumar M. , Swiatek K. 
Published: July 2007

AbstractThe ESR spectra of the intrinsic defects in GeS glasses are studied at liquid nitrogen temperature in the whole glass‐forming region. The Ge‐related signal is found in glasses of all compositions and this signal is assigned to a two‐atomic defect center (DCI) which is formed by the interaction of broken bonds of Ge with two‐coordinated sulphur atoms forming (Ge4…S3)0 centers, the subscript is for coordination, superscript for the charge, and the dots for a chemical bond of order 1/2. A multi‐line spectrum is found not only in GeS glasses with excess of sulphur but also in glassy sulphur after excitation by Ar+ laser light (454 nm). This signal can be assigned to two defect centers: DCII (S2 … trans‐S3)0 and DCIII (S2 … cis‐S3)0 formed by interaction of a dangling bond of sulphur with a two‐coordinated sulphur atom S in the Sn chains. Sulphur of these chains can be either in trans‐coordination (DCII) or in the cis one (DCIII). The experimentally found compositional dependence of the DC densities is qualitatively explained. The proposed model is the first one which is able to explain the compositional dependence of the intrinsic paramagnetic defects in the whole glass‐forming region. The model can also shed light on the absence of paramagnetic centers in other chalcogenide glasses.
Physical Aspects and Technological Realization of Amorphous Silicon Thin Film Solar Cells
Authors: Wagner H. 
Published: July 2007

AbstractThin film solar cells represent the major option for photovoltaic electricity production at economically acceptable costs. Especially cells and modules based on amorphous silicon can be produced on cheap large area substrates and are presently the choice to enter mass production. The understanding of the physical properties of amorphous silicon and amorphous silicon alloys forms the basis for an optimized cell design and the use of appropriate deposition processes. Stacked cell structures and improved interfaces in each single cell minimize the effect of light induced degradation. Multi junction cells of different band gap absorber materials are being developed and are already used which utilize the solar spectrum even better, and lead to higher stabilized efficiencies.
Optical Properties of Silicon Nanostructures
Authors: Stutzmann M. 
Published: July 2007

AbstractStrong visible luminescence of porous silicon has triggered renewed general interest in the optical properties of silicon nanostructures. In addition to porous Si itself, Si‐based molecules, nanometer‐size Si particles, one‐dimensional Si chains, two‐dimensional Si layers, and many Si alloys are known to exhibit optical properties (absorption and luminescence) which strongly deviate from those of bulk crystalline Si. Here, we review and compare the main properties of the above‐mentioned systems and present a brief discussion of the experimental observations in terms of existing theories. Current prospects for Si‐based optoelectronic applications are also discussed.
Two‐Photon Photoemission Spectroscopy of Electronic States at Metal Surfaces
Authors: Steinmann W. 
Published: July 2007

AbstractIn two‐photon photoemission a photon from a pulsed laser excites an electron from a state below the Fermi level to an unoccupied intermediate state below the vacuum level. A second photon of the same pulse ionizes the intermediate state. The energy distribution of the photoelectrons yields information on the position and the lifetime of both the initial and, in particular, the intermediate state. Most of the work in two‐photon photoemission spectroscopy has been devoted to the investigation of image potential states (image states). They are bound states of electrons in front of metal surfaces in the potential well built by the image potential and the surface. The situation is analogous to the hydrogen atom, with a binding energy of the lowest state of 850 meV in first approximation. Up to four members of the Rydberg series are detected. Experimental results on the binding energy of image states in (111) and (100) surfaces of Ag, Au, Cu, and Pd agree with calculations by a one‐dimensional scattering model. The results for Co, Ni, and Fe are not yet understood. The effective mass is close to unity except for Ag(111). Lifetimes between 5 and 170 fs are measured. They can be explained by decay via electron‐hole pair creation in the bulk. Image states on metal overlayers yield information on film growth and surface morphology. Dielectric overlayers are been investigated. Adsorbate states of atoms and molecules adsorbed on metal substrates can also be studied by two‐photon photoemission spectroscopy. Results for Na, O, CO, and NO on Cu(111) are reported.
Low Energy Electron Microscopy of Nanostructures
Authors: Bauer E. 
Published: July 2007

AbstractThe various imaging modes which are possible in non‐scanning surface microscopy with slow electrons are discussed, in particular the information which can be gained on surface potential, topography, crystal structure, magnetic microstructure, and chemical composition. Applications relevant to semiconductor microelectronics, magnetic storage technology, and heterogeneous catalysis are reported.
Nitrogen Incorporation into Hard Amorphous Carbon Films Obtained by RF Plasma Decomposition of CH4‐N2 Gas Mixtures
Authors: Freire F. L. , Lazaro J. R. , Franceschini D. F. , Achete C. A. 
Published: July 2007

AbstractRecent results on the incorporation of nitrogen into amorphous hydrogenated carbon films (a‐CNx: H) are reviewed. The films are deposited onto silicon substrates by rf plasma decomposition of methane‐nitrogen mixtures. The samples are characterized by a combination of analytical techniques: nuclear techniques (RBS, NRA, and ERDA), SIMS, infrared absorption, Raman scattering, and positron annihilation spectroscopy (Doppler broadening method). The Vickers hardness and the internal stress of the films are also determined. The results indicate that the incorporation of nitrogen increases the density of voids and induces a progressive graphitization of the films. The incorporation of nitrogen up to 11 at% reduces the internal stress of the films without significant modification of the film hardness. Results on the thermal stability of a‐CNx: H films are also presented: for annealing temperatures higher than 300 °C, hydrogen and nitrogen losses occur as well as the graphitization of the films.