bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diffusion of 113Sn in the Intermetallic B82 Compounds of the System Ni/Sn
Authors: Schmidt H. , Frohberg G. , Miekeley W. , Wever H. 
Published: July 2007

AbstractThe direction dependence of the diffusion coefficient of 113Sn has been measured in single crystals of Ni61Sn39 by the layer grinding technique. The activation energies for diffusion parallel and perpendicular to the hexagonal c‐axis are 2.93 and 3.07 eV, respectively, the D0‐values 4.6 and 9.9 cm2/s. The experimental values of ϕ = D⊥/D| are between 0.56 and 0.75 depending on the temperature. The experimental values are compared with theoretical values calculated for the different possible diffusion mechanisms. The main mechanism should be a normal vacancy mechanism superimposed by minority mechanisms the increase of which with rising temperature explains the temperature dependence of ϕ.
Growth and Optical Characterization of CrSi2 Thin Films
Authors: Lange H. , Giehler M. , Henrion W. , Fenske F. , Sieber I. , Oertel G. 
Published: July 2007

AbstractCrSi2 thin films are grown by dc magnetron sputtering of Cr single layers on Si and Cr/Si multi‐layer configurations on SiO2 and subsequent external annealing. In the optical spectra around the band edge the phonon emission and the absorption branches of the indirect transition at 0.5 eV and the direct transition around 1 eV can be discerned. Spectral features in the reflectivity spectrum at higher energies are discussed on the basis of published density of states calculations. The reflectivity spectrum in the IR region exhibits pronounced structures which can be fitted by a six‐oscillator model yielding the TO frequencies, oscillator strengths, and damping constants of the lattice modes. The Raman spectrum shows bands in the 310 to 410 cm−1 wave number region.
AC Conduction of Charge Density Waves in η‐Mo4O11 with Quasi‐Two‐Dimensional Structure
Authors: Koyano M. , Inoue M. , Hughes H. P. , Yoffe A. D. 
Published: July 2007

AbstractThe real and imaginary components of the resistive voltage (ZR) and Hall voltage (ZH) impedances of a quasi‐two‐dimensional η‐Mo4O11 crystal are measured over the temperature range 4.2 to 300 K and frequency range 100 Hz to 100 kHz under magnetic fields up to 4.6 T. The resistive impedance shows an appreciable ac response of electrical conduction due to an oscillating charge density wave (CDW) condensate below the first CDW transition temperature Tc1 (= 105 K), and below the second CDW transition temperature Tc2 (= 35 K) Shubnikov‐de Haas oscillations due to free conduction carriers that locate on the remaining Fermi surfaces produced by the CDW transitions. A qualitative discussion is given for these dynamic properties.
Low‐Field Magnetoresistance in Ferromagnetic Amorphous Alloys
Authors: Ziman J. , Zagyi B. , Novák L. 
Published: July 2007

AbstractThe low‐field longitudinal magnetoresistance in amorphous ribbons is measured. The contribution of “excess resistance” associated with the presence of the transverse domain walls is determined by transverse magnetoresistance measurements. The influence of the tensile and torsion stresses is discussed, taking into account the presence of the transverse domain walls and anomalous ferromagnetic anisotropy of the resistance.
Hopping Hall Conductivity in Disordered Systems from the Generalized Stochastic Liouville Equation Model
Authors: Čápek V. 
Published: July 2007

AbstractAs recently proved, equilibrium field‐independent hopping (transfer) rates disappear in the linearized (in the electric field) kinetic equations owing to cancellation on both sides as far as the theory is sufficiently rigorously formulated beyond the lowest‐order treatment of scattering. Thus, standard kinetic (rate) equation formulations have to be scrutinized, possibly avoiding the approximate kinetic equation stage. The present work shows how to perform the task treating the hopping Hall conduction in the site representation via the generalized stochastic Liouville equation model which has previously been used mostly for exciton transfer in condensates. Corrections to standard hopping Hall conductivity results are revealed.
The Perpendicular Magnetization Component in Single Crystals of Permanent Magnetic Materials
Authors: Hermann R. , Elk K. , Scholl R. 
Published: July 2007

AbstractA systematical study of the perpendicular component of the magnetization in single crystals is carried out. Using the model of Stoner and Wohlfarth and restricting to the first‐order anisotropy constant K1, the perpendicular component m⊥ as a function of h for different angles 9 is calculated. A practicable alternative method to determine the anisotropy field Ha from the point of intersection of the second derivatives of different m⊥(h) curves is presented.
Intraband Luminescence in Ionic Crystals
Authors: Deich R. G. , Abdrakhmanov M. S. 
Published: July 2007

AbstractTime‐resolved luminescence spectra of CsI, NaI, α‐Al2O3, and AgBr are investigated under sub‐ nanosecond electron pulse excitation. New intrinsic emission bands with a decay time less than 20 ps are revealed. It is proposed that the fast emission components originate from hot carrier intraband radiative transitions. The intraband luminescence spectra and light output are temperature independent and are not affected by crystal impurities. The correlation between the intraband luminescence spectra and crystal band structure is discussed.
Raman Scattering in ZnAs2 Monoclinic Crystals
Authors: Weszka J. , Balkanski M. , Jouanne M. , Pishchikov D. I. , Marenkin S. F. 
Published: July 2007

AbstractRaman scattering in ZnAs2 monoclinic crystals is studied at room temperature in backward geometry. Features within the 190 to 270 cm−1 frequency interval are due to As‐chain modes. Low frequency features within the 10 to 100 cm−1 area are attributed to modes with considerable contribution from Zn atoms involved.
Why a Complete Solution Has not Been Found of a Mode I Crack in an Elastic Plastic Solid
Authors: Weertman J. 
Published: July 2007

AbstractNo demonstrated satisfactory solution, complete or partial, has ever been found for the plastic zone of a mode I crack in an elastic plastic solid. (By complete is meant a stress‐strain field solution of both the crack tip plastic zone and the elastic region which surrounds it.) In this paper it is shown, as well as a negative can be shown, that it is unlikely that a solution exists for this problem if a condition on the solution is that an active plastic zone touches the crack tip and/or the crack faces behind the crack tip. The specific mode I crack problem considered is the stationary mode I crack in plane strain in an elastic perfectly plastic and incompressible solid with a plastic zone size which is small compared with the crack length (small scale yielding).
Diffusion in Nanostructured Metals
Authors: Gleiter H. 
Published: July 2007

AbstractNanostructured materials are polycrystals with a crystal size of a few (typically 20 or less) nm and hence consist of about equal volume fractions of grain (interphase) boundary cores and crystals. Due to the large volume fractions of incherent interfaces, the diffusional processes in these materials seem to differ from the ones in single or coarse grained polycrystals with the same chemical composition. The diffusion data available today for nanostructured metals suggest that self and solute diffusion is enhanced relative to lattice as well as grain boundary diffusion, provided the solute atoms are substitutionally dissolved in the host lattice. This enhancement seems to originate from the free volume in the boundary cores. The diffusivities of atoms that are interstitially dissolved in the lattice of the host metals (e.g. B in Fe, H in Pd) are comparable to the corresponding lattice diffusivities.
Temperature and Volume Dependence of Positron Lifetime in Y1Ba2Cu3O6+x
Authors: Hentrich D. , Kluin J.‐E. , Hehenkamp Th. 
Published: July 2007

AbstractPositron lifetimes in sintered Y1Ba2Cu3O6+x are determined between 80 and 1200 K using 22Na from 80 to 450 K and 58Co from 450 to 1200 K as a positron source. Below 450 K two lifetimes are detectable. A constant τ2 at 192 ps is attributable to a shallow trap supposed to be due to twin boundaries and growth steps, the binding energy of which can be estimated to be 0.16 eV. A second lifetime is increasing with temperature and understood as bulk lifetime. At higher temperatures only one mean lifetime is detectable. Taking the volume changes (T, p) properly into account it becomes apparent that the bulk lifetime is the only significant lifetime besides the shallow trap lifetime at low temperatures and that it increases uniformly with volume, whatever is the reason for its change, temperature, transformation, or oxygen partial pressure.
Monte Carlo Study of the Phase Stability of Ordered F.C.C. Phases under Irradiation
Authors: Haider F. 
Published: July 2007

AbstractThe phase stability of different ordered phases on the f.c.c. lattice in a binary Ising crystal with competing thermal and forced jumps is studied to model the behaviour of high energy particle irradiation. A special Monte Carlo technique is used to compute a so‐called stochastic potential, the equivalent of a thermodynamic potential under nonequilibrium conditions. Furthermore the case of irradiation‐induced phase separation is studied in a simple one‐dimensional model with a similar technique.
On Sequences of Alternate Stable and Unstable Regions along Tensile Deformation Curves
Authors: Kalk A. , Schwink Ch. 
Published: July 2007

AbstractThe occurrence and boundaries of (in‐)stabilities along stress–strain curves are investigated for f.c.c. solid solutions of CuMn. There are up to four temperature intervals where the σ(ϵ)‐curves over their whole extension are either smooth (stable deformation) or serrated (unstable deformation). In between, three transitional intervals, named α, β, and γ, are constituted. Here two or more regions of stable and unstable deformation alternate along σ(ϵ). In particular, inside interval β a region of stability is embedded between two regions of instability. For two Mn concentrations the variatin of the boundaries with temperature and strain rate is investigated for the intervals α and β. The results allow a comparison with theoretical “scenarios” developed by Kubin and Estrin. Possibilities for an improvement and/or extension of this model are discussed.
Reversibility and Hysteresis of Martensitic Transformations
Authors: Hornbogen E. 
Published: July 2007

AbstractThe term martensitic is used for a diffusionless structural phase transformation β → αM which is associated with a considerable amount of lattice variant shear: γβα ≈ 0.2. This reaction is defined as reversible if the reverse reaction αM → β faultlessly restores the original parent crystal β. Sets of factors are established which favour the reversible (or irreversible) mode. Hysteresis is due to lattice friction acting on the moving β/αM‐transformation interfaces during a transformation cycle. It can vary by several orders of magnitude. Analogies are indicated between ferromagnetic and martensitic hysteresis.
TEM and HREM Investigation of Secondary Dislocations in a Near‐Coincidence Σ19‐[011]‐Tilt Grain Boundary in Germanium
Authors: Möller H. J. , Griess M. 
Published: July 2007

AbstractGermanium bicrystals with [011]‐tilt grain boundaries are grown by the two‐seed Czochralski method. Dissociated near‐coincidence grain boundaries with an orientation between Σ19 and Σ27 and asymmetric boundary planes contain networks of secondary dislocation which account for the deviation from the ideal coincidence orientation. Both conventional TEM and HREM are applied to determine the Burgers vectors and arrangements of the secondary dislocations. The complex dislocation structure can be analyzed and related to the Σ19 DSC lattice. The main result that uncommon and nonprimitive Burgers vectors are observed is discussed from the perspective of the total energy of the grain boundary.
The Dissociation of a Screw Superdislocation in the B2 Structure
Authors: Saada G. , Veyssière P. 
Published: July 2007

AbstractCross‐slip of a dissociated 〈111〉 screw superdislocation in the absence of an applied stress is studied within the frame of anisotropic elasticity in model B2 crystals. Lattice friction is ignored. The superdislocation can either be coplanar, and then confined to either of the {110} and {112} habit planes, or dihedral. The stability of these configurations is governed by the values of one elasticity parameter named N, by the ratio z between the antiphase boundary (APB) energies on these planes, and by the cross‐slip angle α. The different situations of interest are studied. By contrast to what occurs in L12 alloys, it is shown that besides two alternative planar configurations, one may encounter dihedral stable or metastable configurations which add to the variety of possible locking configurations in B2 alloys. The relative stability of these possible locking modes is discussed in details with respect to N and z, for the different cases of cross‐slip.
Model for Anomalous Power Dependence of Microwave Heating in Ceramic Materials
Authors: Kenkre V. M. , Kus M. , Katz J. D. 
Published: July 2007

AbstractA model is presented to explain the anomalous power dependence of microwave heating in ceramic materials. The anomaly considered consists of a saturation effect wherein the dependence of the heating rate on microwave power becomes sublinear. Our proposed explanation is based on the idea of spatial confinement of the absorbing charges in grain boundary regions. The mechanism of saturation, more generally, of a decrease in absorption efficiency, arises from a mismatch of two lengths, one of which measures the maximum distance an absorbing charge travels under the combined action of damping and of the oscillating microwave field, and the other measures the spatial extent of the confining region. Explicit calculations for a simple model are presented and the results are examined in the light of observations on ferric oxide.
On the Instability Leading to the Martensitic Transformation of Cu–Zn–Al Single Crystals
Authors: Amazit Y. , Zarembowitch A. 
Published: July 2007

AbstractCu–Zn–Al alloys are known to exhibit shape memory properties when the temperature is varied. This behaviour is directly connected to the martensitic transformation that such materials undergo. If the general characteristics of this transformation are well understood, the nucleation mechanism of the transformation is not completely clear. However, it seems that the residual stresses play a major role in the process of nucleation. As a consequence, the measurement of the nonllnear elastic parameters as a function of temperture for shape memory single crystals may clarify the process of nucleation. Such data are reported in this paper; a model is proposed for the interpretation of the experimental results.
Structure Sensitive Electronic Properties of Quasi‐Two‐Dimensional η‐Mo4O11 Crystals
Authors: Ôhara S. , Negishi H. , Inoue M. 
Published: July 2007

AbstractThe electrical resistivity, Hall effect, and magnetoresistance are measured over the temperature range from 1.5 to 300 K for a number of η‐Mo4O11 crystals, that undergo two charge density wave transitions at Tc1 = 105 K and Tc2 = 35 K, prepared by a chemical vapor transport method using TeCl4 (10 and 2 mg/cm3) as a carrier gas. Good samples grown with 10 mg/cm3 TeCl4 have high carrier mobilities, showing quantum oscillations in the magnetoresistance and Hall coefficient at low temperatures. Poor samples grown with 2 mg/cm3 TeCl4 have rather low mobilities and anomalous temperature dependence of resistivity with a negative coefficient, together with a log T‐dependence. These behaviors may be due to microscopic structural imperfections, such as excess oxygen or vacancies. Based on these experimental results, a tentative band model for conduction electrons and holes, as well as some localized states lying near the Fermi energy, is proposed.
Evaluation of the Potential Function of Liquid Germanium from Experimental Structure Factors and Computation of Elastic Constants and Phonon Frequencies
Authors: Rao R. V. Gopala , Debnath D. 
Published: July 2007

AbstractRao‐Joarder's equation for the determination of potential function is used to derive the latter. The computed potential function of liquid Ge shows an inflection in the positive region and a negative minimum. The inflection is attributed to the first nearest‐neighbour distance and the negative minimum to the second nearest‐neighbour distance. The present computed potential function is found to be similar to that obtained by different methods. The derived potential function along with the measured values of g(r) is used in the evaluation of longitudinal and transverse phonon frequencies through Takeno and Goda's equations. The low‐k values of phonon frequencies are found to be nearly linear with k. From the slope of these frequencies the elastic constants are calculated. Schofield's equations are also used in the calculation of elastic constants. The values obtained by different methods are found to be interconsistent. The potential function is utilised in the evaluation of the characteristic frequency of the atoms in the liquid. The computed value is compared with that obtained from low temperature heat capacities and average frequencies obtained by different methods. They are found to be fairly interconsistent.
Vacancy‐Type Defects in Cd, Al, Si, and GaAs Studied Using Variable‐Energy Positron Beam
Authors: Takamura S. , Ito Y. 
Published: July 2007

AbstractThe S‐parameter versus incident positron energy is measured using variable‐energy positron beam method in Cd, Al, Si, and GaAs after irradiation with Ar or He ions at liquid nitrogen temperature. The fraction of positrons trapped in defects and in the bulk is calculated from the defect distribution based on the computer code TRIM and the fitting procedure is performed. It is suggested that the migration of vacancy‐type defects occurs below the irradiation temperature in Cd and n‐type Si.
Tunneling in Periodic and Quasi‐Periodic Superlattices
Authors: Singh M. , Tao Z. C. , Tong B. Y. 
Published: July 2007

AbstractA comparative study of electron tunneling in periodic and quasi‐periodic systems is made. The quasi‐periodic systems considered are Fibonacci and Thue‐Morse superlattices. The transfer matrix method and Landauer formula are used to calculate the electron transmission coefficient and tunneling conductance, respectively. For the numerical calculation the superlattices are considered to be made from GaAs and GaAlAs semiconductors. Numerical calculations are performed for the tunneling conductance for different values of potential barrier height and width. The present calculations show that the peak positions of the tunneling conductance are at different energies for periodic, Fibonacci, and Thue‐Morse superlattices with equal number of layers. The height of peaks changes from one system to another. We also investigated the effect of temperature, damping, and magnetic field on the tunneling conductance in simple approximations. It is found that the peak height of the tunneling conductance decreases as the temperature increases and peak width increases at the same time. As magnetic field increases, the position of peaks of the tunneling conductance shifts to higher energy. The tunneling conductance decreases as the damping increases. Theses calculations can be extended to hole tunneling in these systems.
Compton Profile Anisotropy Studies in Hexagonal CdS
Authors: Panda B. K. 
Published: July 2007

AbstractThe Compton profile anisotropies are calculated by empirical pseudopotential method for [0001], [1010], and [1120] directions of CdS with wurtzite structure. The earlier theoretical anisotropy between [0001] and [1010] directions obtained by LCAO method could not explain the corresponding measured anisotropy. But the present calculation yields a better result.
Ab Initio Calculation of Electron Effective Mass in Crystals
Authors: Shilkova N. A. , Shirokovskii V. P. , Trubitsin V. Yu. 
Published: July 2007

AbstractUsing the Hellmann‐Feynman theorem an expression for the electron effective mass in crystal is derived. Calculations are carried out at some points of Fermi‐surface cross‐section of vanadium by the plane z = 0. The comparison with the data of numerical differentiation demonstrates the reliability of the results as well as the high accuracy of the technique presented. The method proposed for obtaining the effective mass is suitable for any calculation technique of electron spectra.
Interplay between Diagonal and Off‐Diagonal Disorders on the Density of States
Authors: Hamdache F. , Brezini A. 
Published: July 2007

AbstractCalculations of the density of states of the Anderson model Hamiltonian are reported in presence of both, diagonal and off‐diagonal disorders for a Bethe lattice. In particular an analytical mean field treatement is developed in the dilute limit. Extensive results are presented displaying their characteristic features and discussed in the light of other theories.
Oxygen in InxGa1−xAsyP1–y Grown on GaAs
Authors: Zhu Q. S. , Hiramatsu K. , Sawaki N. , Akasaki I. 
Published: July 2007

AbstractThe measurement of DLTS on the alloy In xGa1–xAsyP1–y (0 ≦ y ≦ 0.3; 0.5 ≧ x ≧ 0.35) shows a new signal, labeled as E2, with an activation energy of Ec–0.61 eV and the SIMS signals show a large number of oxygen. To clarify is further, the energy of the deep level E2 is quantitatively calculated by using Vogl's tight‐binding theory and Hjalmarson's deep level theory. As a result, the deep A1‐symmetric level associated with an oxygen on the anion site of InxGa1–xAsyP1–y located deeply in the band gap. Thus, the level E2 is considered to be induced by the oxygen impurity.
Acoustoelectric Amplification in the Presence of Non‐Uniform Electric Field and Carrier Concentration in Solids
Authors: Misra K. D. , Pandey M. K. 
Published: July 2007

AbstractAcoustoelectric amplification in a strain‐dependent, transversely magnetised semiconductor is studied in the presence of non‐uniform electric field and carrier concentration along the sample length. A generalised expression for the amplification coefficient in strain‐dependent and piezoelectric materials is also discussed for a single carrier semiconductor. Application to a multilayered system of different single carrier semiconductors coupled to one elastic wave is also suggested. The non‐uniformity in carrier concentration is found to have significant effect on the amplification coefficient in a multilayer system.
Coherent and Incoherent Exciton Dynamics in II–VI Semiconductors
Authors: Pantke K.‐H. , Lyssenko V. G. , Razbirin B. S. , Schwab H. , Erland J. , Hvam J. M. 
Published: July 2007

AbstractDynamics of free and bound excitons in CdSe and localized excitons in CdSexS1−x are studied by degenerate four‐wave mixing and light‐induced grating experiments. In the coherent range, the dephasing of excitons is determined as a function of temperature, density and energy. For incoherent excitons, recombination lifetimes and diffusion coefficients are determined. In particular, the mobility of excitons in CdSexS1−x near the mobility edge is studied.
Polarization Dependence in the Intraband Optical Stark Effect of Quantum Wells
Authors: Fröhlich D. , Spitzer S. , Uebbing B. , Zimmermann R. 
Published: July 2007

AbstractExperiments and a theoretical description of the optical intraband Stark effect in multiple quantum wells for an in‐plane polarization of pump and test fields are presented. The nonlinear absorption spectra show a pronounced dependence on the angle between pump and test field polarization. For a quantitative agreement between theory and experimental results it is necessary to take the inhomogeneous distribution of the pump field into account, which is due to multiple reflections of the CO2 laser beam in the sample.