bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electric Current Effect on Metal Surface Layers
Authors: Roshchupkin A. M. , Bataronov I. L. , Troitskii O. A. , Moiseenko M. M. 
Published: July 2007

AbstractThe electric current hydrodynamic effect on the metal surface layers due to the electronic liquid braking by the metal surface is considered in terms of the diffusivity parameter 𝒫 approximation. The relation between the coefficient of the electronic liquid kinematik friction against the surface and the 𝒫 parameter is obtained. It is shown that when current flows, in the near‐surface layer of the order of about the mean electron free path length the mechanical stresses ≈ 𝓅pFj/e arise, where pF stands for the Fermi momentum, j for the current density in the metal, e for the electron charge. It is noted that under the conditions of electroplastic deformation these stresses amount to a fairly significant value and can stimulate the dislocational processes in the nearsurface layer of metal.
Landau Levels and Cyclotron Masses in GaAsAlGaAs Quantum Wells
Authors: Del Valle J. Sab Ín , Gondar J. López , De Dios Leyva M. 
Published: July 2007

AbstractIncluding the nonparabolicity and anisotropy effects the two‐dimensional cyclotron mass of electrons in GaAs is studied in the presence of a magnetic field parallel to the growth direction of the system. Numerical calculations for different quantum wells are reported and a comparison is made with recently reported experimental results.
Galvanomagnetic Properties of Graphite Fibers
Authors: Kulbachinskii V. A. 
Published: July 2007

AbstractUsing physical parameters extracted from the experimental studies of the negative magneto‐resistance the phenomena of resistivity rise with decreasing temperature and the subsequent onset of superconductivity at low temperature found in graphite fibers with NbC are explained by the electron‐electron interaction effect within the weak‐localization regime. It is shown that the galvanomagnetic properties of PAN‐, pitch‐, rayon‐based fibers before and after intercalation at low temperature can be explained completely by quantum corrections to the conductivity for the two‐dimensional case.
Two Valence Subbands in Single Crystals of Bismuth Telluride Doped with Lead and Its Electrical Properties
Authors: Biswas S. , Bhattacharya R. 
Published: July 2007

AbstractPresence of two valence subbands in bismuth telluride has been suggested before from the study of transport properties under high magnetic fields. Results of experimental investigation of electrical conductivity and Hall effect with lead‐doped Bi2Te3 are reported. It is suggested that excitation from one valence subband to another is taking place such that the total number of carriers remains unchanged but the conductivity changes exponentially due to the difference of mobilities in the two subbands. This can account for the change in the electrical conductivity in the low temperature region which cannot be satisfactorily explained so far. Hall effect in the low temperature region can also be accounted for. The mobilities of holes in the two valence subbands and electrons in the conduction band are determined.
Effect of a Finite Voltage on Statistical Properties of Resistance in One‐Dimensional Disordered Systems
Authors: Heinrichs J. 
Published: July 2007

AbstractResistance fluctuations in the presence of an applied voltage are studied, using the Riccati equation for the reflection coefficient of a random conductor obtained by an invariant imbedding approach. As in the previously studied zero‐field case the conductor of length L is described by a Gaussian barrier, V(L), with a systematic part V, and the analysis is restricted to incident kinetic energies of the order of typical values of V(L)/2. The reflection coefficient is related to a resistance variable ϱ via the Landauer formula. Expressions for the distribution of the Landauer resistance and for its low order moments are obtained for arbitrary voltages and lengths L. The distribution of ϱ is exponential for L → 0 and log‐normal for L → ∞, with exponentially increasing mean‐ and rms‐values. The variable ln ϱ is self‐averaging at sufficiently low voltage. The properties of the reflection coefficient are discussed exactly in a different energy range, namely for low incident kinetic energies.
Electric Field Induced Splitting of the Stretching Vibration Lines of SH−, SeH−, and TeH− Centres in Alkali Halides
Authors: Otto J. 
Published: July 2007

AbstractThe stretching vibration lines of SH−, SeH−, and TeH− centres in various alkali halides are split into several components by an external electric field. No similar effects are observed yet for other centres. The splitting patterns are measured with high instrumental resolution for various directions of field and light polarization. From the number of componental lines the orientations turn out to be 〈111〉 for all investigated centres. Possible reasons for the splitting are discussed. Paraelectric alignment, however, well known for the homologeous OH− centres, is not observed.
Electron Transport in Amorphous (Ti, Nb)O2 Solid Solutions
Authors: Lagnel F. , Poumellec B. , Picard C. 
Published: July 2007

AbstractAmorphous 1 μm thick (Ti, Nb)O2 films are prepared by r.f. sputtering in an argon atmosphere. Resistivity and thermopower measurements are carried out from room temperature up to 700 K in order to study the influence of the structural disorder on the electron transport properties. Experimental data are interpreted in the framework of Hurd's model, i.e. a hopping model including the temperature dependence of the tunnelling probability. Moreover, the analysis of the thermopower versus the Nb content indicates a partial electron transfer from Nb to Ti. On the other hand, these results suggest that, for the corresponding crystalline solid solutions at T > > 800K, the conduction is also caused by hopping and not delocalized.
On the Nature of the Self‐Trapping of Different Types of Polarons
Authors: Nagy P. , Markoš P. 
Published: July 2007

AbstractA generalized Huybrechts approximation is developed and used for the calculation of the ground state energy, E, of the polaron as the function of the coupling constant α. A simple criterion for the continuity of ∂E/∂α is given, which enables to discuss the nature of the transition of the polaron from the free state to the localised state in the framework of different approximations.
Transformation of Excitonic Spectra of PbI2 Layer Crystals under Order‐Disorder‐Order Structural Transistions
Authors: Bibik V. A. , Davydova N. A. 
Published: July 2007

AbstractThe influence of ruby laser irradiation on the exciton spectra of PbI2 crystals of 2H and 4H poly‐types is studied. It is shown that the first pulses of laser irradiation lead to the creation of one‐dimensional disorder due to generation of stacking faults. The presence of stacking disorder leads to a localization of the excitonic wave functions in the direction perpendicular to the layer packets, causing a “fine” structure of the exciton band. The repeated irradiation leads to stacking faults ordering into the high‐symmetry 2H polytype, which has a shorter translational period in comparison with other polytypes and, thus requires less time for its ordering.
Investigation of (AlGa)As/GaAs quantum wells by optical and phototransport measurements
Authors: Ghezzi C. , Martin D. , Parisini A. , Staehli J. L. , Tarricone L. 
Published: July 2007

AbstractAn optical and phototransport characterization of (AlGa)As/GaAs multi‐quantum‐well (MQW) structures grown by molecular beam epitaxy (MBE) is reported. Photovoltage, photoluminescence, and optical transmission spectra are studied on p‐i‐n photodiodes in which the intrinsic (nominally undoped) region contains the wells. The thickness of GaAs and (AlGa)As layers is in the range 8 to 11 and 12 to 17 nm, respectively. The Al x‐molar fraction is in the interval 0.25 to 0.30. In the photovoltage spectra transitions between the fundamental and also the first excited state of electron and hole subbands in the quantum wells are observed. Agreement is found between these spectra and the results of luminescence and transmission measurements. Theoretical calculation fits the temperature dependence of the peaks in the spectra; it is possible to estimate the well width with an accuracy of about 10%.
The donor‐acceptor electron transfer with participation of short polymer chains
Authors: Ostapenko M. G. , Petrov E. G. 
Published: July 2007

AbstractThe rate dependence is investigated of activation and tunnel electron transfer between donor and acceptor separated by a chain of finite length on the energy and the relaxation characteristics of donor, chain, and acceptor. The chain length effect is shown to be especially pronounced at chain lengths not exceeding 5 to 7 links.
Photoconductivity in germanium selenide single crystals
Authors: Elkorashy A. M. 
Published: July 2007

AbstractThe photoconductivity spectral response is measured for GeSe single crystals at different temperatures from room temperature to near liquid nitrogen temperature. Measurements are carried out with plane polarized light with the plane of polarization parallel to the a‐ and c‐crystallographic axes which lie in the plane of cleavage. The photon energy range of measurements extends from 0.5 to 3.0 eV. The photoconductivity energy gap is determined from the spectral response by the Moss rule. The room temperature photoconductivity energy gap is found to be (1.144 ± 0.011) and (1.167 ± 0.025) eV for the a‐ and c‐axes, respectively. The temperature dependence of the photoconductivity energy gap is also deduced. It is found that it is linear between 93 and 250 K with a negative temperature coefficient equal to −(0.35 ± 0.01) meV/K for the a‐axis. The results for the c‐axis show a large discrepancy which is attributed to crystal lattice bending introduced during the cleavage process. The minority carrier lifetime is determined from the photoconductivity frequency response using square modulated illumination. The photoconductivity frequency response is found to be characterized by two different lifetimes.
Effective second‐order elastic constants and the second pressure derivatives of a hexagonal crystal
Authors: Rao R. Ramji , Padmaja A. 
Published: July 2007

AbstractExpressions for the effective second‐order elastic constants of a hexagonal crystal and its second pressure derivatives are derived in terms of its natural second, third, and fourth order elastic constants using the finite strain theory. These formulae are employed to obtain the values for the combinations of the fourth order elastic constants of magnesium and zinc for which the experimental data are available. The combinations are positive in both of these metals. However, in zinc which is an example of extreme anisotropy among the h.c.p. metals, the combinations of the fourth order elastic constants are found to be larger compared to those in magnesium which has nearly the ideal c/a value.
Effective mass approximation for tunneling states with dissipation
Authors: Chen Hong , Wu Xiang 
Published: July 2007

AbstractThe dissipative tunneling in a symmetric double‐well potential is studied at low temperatures. Using effective mass approximation, the dissipation can be replaced by a temperature‐dependent effective mass. The effective mass increases with decreasing temperature and becomes infinite at T = 0. The partition function of the system is derived, which has the same form as that of a non‐dissipative tunneling system. Some possible applications in glasses and heavy Fermion systems are also discussed.
Hubbard systems with two channels for the localization
Authors: López‐Aguilar F. , Costa‐Quintana J. , Balle S. 
Published: July 2007

AbstractA method is given for obtaining the electronic structure of the systems which present strong correlated bands arising from different orbitals, for instance f and d. This is performed by means of a non‐local potential deduced from the Green function of the interacting system. In addition, this method is applied to γ‐CeAl2 and the results agree reasonably with available experimental results.
Amplification of acoustic waves in magnetised piezoelectric semiconductors. Effect of nonlinearity in electron effective mass and collision frequency
Authors: Dey (Bose) M. , Ghosh S. 
Published: July 2007

AbstractAn attempt is made to provide a theoretical approach to experimental studies of the acoustoelectric amplification in magnetised piezoelectric semiconductors showing that the attenuation of an acoustic wave crosses over to its amplification when the electron drift velocity exceeds the acoustic wave velocity. First a phenomenological theory is developed to study the relative change in electron effective mass and collision frequency when an acoustic wave passes through piezoelectric semiconductors. Then, analytically, it is shown that this nonlinearity due to the electric vector of the field associated with the wave can also explain this behaviour. Numerical computations are made for n‐InSb at 78 K. It is found that the magnetic field does not have any remarkable effect on amplification.
Magnetic and Mössbauer studies of magnesium‐chromium ferrites
Authors: Balaev A. D. , Bayukov O. A. , Savitskii A. F. 
Published: July 2007

AbstractThe magnetization, Curie temperature, cation distribution, sublattice magnetization, and parameters of Mössbauer spectra are measured in MgFe2‐xCrxO4. The ligand‐cation 3d‐electron transfer parameters and the cation‐cation exchange interaction integrals are found using the superexchange bond model.
A Kinetic Theory for the Motion of Accelerated Particles in Solids. II. Dechanneling in Complex Crystals
Authors: Urmanov A. R. , Grigoriev V. G. , Puzanov A. A. 
Published: July 2007

AbstractModels for the energy and angular distributions of the yield produced by Rutherford backscattering of fast ions and nuclear reaction products in the case of multiatomic crystals are suggested based on calculation of a generalized kinetic equation. Expressions for coefficients of this equation are obtained. The possibilities of the approach suggested are illustrated by interpreting experimental data on proton dechanneling in tungsten bronzes.
Temperature Effects of the Several Intense IR Absorption Peaks in NTD Si:H
Authors: Chen J. M. , Xei L. M. , Bai G. R. , Zhao Y. G. 
Published: July 2007

AbstractTemperature effects of 2210, 1946, and 1831 cm−1 IR absorption peaks in NTD Si:H are measured and analysed. The phonon scattering process is the dominant factor of the temperature effects, while the phonon decomposition process can be neglected. The symmetry, Td, of defect‐complex corresponding to the 2210 cm−1 peak can be transformed into D2d symmetry as temperature rises above 200 K. The transition causes anomalous temperature effects which broaden the linewidth of the peak and destroy its symmetric peak shapes, i.e. shoulders appear on the low frequency sides of the peaks. The symmetric breaking mechanism strongly supports that the V + 4 H model is responsible for the 2210 cm−1 IR absorption peak. The correlation between the temperature‐dependent linewidth and the degeneracy of its vibration mode is discussed.
Semiempirical Construction of LCAO Parameters for II–VI Compound Semiconductors
Authors: Li Yuan , Lin‐Chung P. J. 
Published: July 2007

AbstractA set of semiempirical expressions for the two‐center integrals which show the explicit dependence of these quantities on the atomic characteristics, on the dielectric constant, on the ionicity of the solid, and also on the interatomic separations is constructed for the II–VI compound semiconductors. The Slater‐Koster parameters are then constructed from these expressions for the two‐center integrals. The band structures of various zinc and cadmium compounds are obtained and are compared with other theoretical calculations and with experimental photoemission results.
Gyromagnetic Factor and Spin–Orbit Coupling of Ligands in CsVX3 (X = Cl, Br, I)
Authors: Du Mao‐Lu , Zhao Min‐Guang 
Published: July 2007

AbstractA perturbation expression of the gyromagnetic factor of d3 ions is derived considering the spinorbit coupling of the ligand ions and taking into account all the excited states besides 4T2 state. The molecular orbital coefficients are determined by means of a semiempirical method in estimating the g‐shift. The results show that the contribution of the spin–orbit coupling of the ligand ions to the g‐shift must be considered for ligand ions possessing large spin–orbit coupling constants. The g‐shifts of CsVX3 are calculated and the results agree well with experimental data.
Electron Spin Resonance and Optical Absorption Spectra of Mn2+ Ions in K2SO4ZnSO4 Glasses
Authors: Rao J. L. , Narendra G. L. , Sreedhar B. , Lakshman S. V. J. 
Published: July 2007

AbstractElectron spin resonance and optical absorption measurements are performed on K2SO4ZnSO4 glasses containing 1 to 5 mol% of MnSO4 · H2O. The ESR spectra of Mn2+ doped samples exhibit a sextet centered at g = 2.02. The optical absorption spectrum at room temperature shows six bands characteristic of Mn2+ ions in octahedral symmetry. The crystal field (Dq) and Racah interelectronic repulsion parameters (B and C) are evaluated. ESR and optical absorption studies reveal that the Mn2+ ions go substitutionally to zinc ion sites and the site symmetry around the transition metal ion is octahedral.
Mössbauer Spectroscopy of Cobalt in Germanium
Authors: Utzig J. 
Published: July 2007

AbstractMössbauer emission spectra of Co in Ge, introduced by high temperature diffusion, were recorded as a function of quenching rate and Fermi level. Two unbroadened single lines with different Debye‐Waller factors are found. One of the lines shows increasing intensity with decreasing quenchiing rates, and no shift with Fermi level. The other one exhibits a decreasing intensity with decreasing quenching rates and shows a small shift with Fermi level. Considering the Debye‐Waller factors a tentative attribution to Co on substitutional and on interstitial lattice is made.
Approximate Solution of the Peierls Equation for Screw Dislocations with Threefold Symmetry
Authors: Zhang H. T. , Mann E. , Seeger A. 
Published: July 2007

AbstractWithin the framework of the Peierls model an integral equation for the dislocation density distribution of 〈111〉 screw dislocations with threefold symmetry in b.c.c. crystals is derived. The dislocation core, described by a density of infinitesimal Burgers vectors, is extended along three {110} half‐planes intersecting at angles of 120° and acting as slip planes. The integral equation is approximately solved by an inversion procedure and by assuming appropriate functions with adjustable parameters representing the stresses along the slip planes. The results are in qualitative agreement with atomistic calculations reported in the literature. The total energy proves to be lower than in a planar Peierls model.
Comment on the Determination of the Midgap Density of States in Amorphous Semiconductors Using the Space‐Charge‐Limited‐Current Method
Authors: Chen Yang‐Fang 
Published: July 2007

AbstractIt is pointed out that the determination of the midgap density of states in amorphous semiconductors using the space‐charge‐limited‐current method is reliable only when the density of states is less than 1017 cm−3 eV−1 and the electrode spacing is in the order of μm. Beyond these restrictions the current will be affected by the Poole‐Frenkel effect which will distort the determination of density of states from current–voltage characteristics.
A Symmetry Adapted RPA: Dynamics of the Electronic Density Matrix in a Semiconductor
Authors: Schlösser J. , Stahl A. 
Published: July 2007

AbstractThe density matrix theory of electronic processes at the semiconductor band edge is developed in a symmetry adapted multi‐band version. A closed set of equations of motion describing coupled interband and intraband processes is derived on the basis of a Hartree‐Fock type RPA. From the general set of equations representing nonlinear crystal electrodynamics of the electronic edge a linearized subset is derived. The linearized set then forms the basis of linear crystal optics. As an example the polariton modes of the wurtzite type crystal CdS are discussed.
Study of Temperature Variation of EPR Linewidth of Gd3+‐Doped LiYbxY1−xF4 Single Crystals. Estimation of Yb3+ Spin–Lattice Relaxation Times
Authors: Misiak L. E. , Misra S. K. , Orhun U. 
Published: July 2007

AbstractX‐band EPR linewidths of Gd3+‐doped LiYbxY1−xF4 crystals (0.0 ≤ x ≤ 1.0) are measured in the temperature range 4.2 to 290 K. It is found that the peak‐to‐peak linewidth of the first derivative lineshape (ΔHpp) can be fitted to T−n (T = tempeature), where generally n < 2, in the various temperature regions, for all the crystals. ΔHpp is, in general, found to be quite sensitive to the mole fraction (x) of Yb3+ ions. The Yb3+ spin–lattice relaxation times (τ′1) are estimated in these crystals, using the theories of Anderson‐Weiss and Mitsuma, taking into account the fact that there are present two different kinds of paramagnetic ions, Gd3+ and Yb3+. It is concluded that the dipole–dipole interactions play an important role in the spin–lattice relaxation of Yb3+ ions.
Photoionisation and Inter (Conduction) Band Absorption in S and Te Doped Gallium Phosphide
Authors: Goldys E. 
Published: July 2007

AbstractThe absorption coefficient of S and Te doped GaP i the region 0.25 to 1.4 eV is measured at 300 K. The experimental data are interpeted quantitatively. The spectrum is dominated by transitions from excited donor states. In the theoretical description the “mean” state concept is successfuly employed.
ESR Study of Silver Clusters in AgCl and AgBr. An Attempt to Detect Photographic Latent Images
Authors: Stevens A. D. , Symons M. C. R. , Eachus R. S. 
Published: July 2007

AbstractESR signals observed after the bandgap irradiation of AgCl and AgBr sols and primitive emulsions are reported. Their parameters are similar to those of small, pseudo‐metallic silver particles. An assignment to latent images is proposed on the basis of the results of empirical ESR/photographic crossover experiments. The size(s) of the latent image agglomerates seems to vary according to the halide, but there appears to be discrete size or small size distribution for a given system. Although it would appear that the clusters are larger than Ag7, precise particle size deductions from the ESR data are shown to await the development of a suitable electronic theory. Smaller, neutral or charged molecular silver aggregates have not, so far, been detected in pure silver halide systems. However, it is possible that signals are present but are too dispersed through a large field range for detection. The existing ESR data for silver clusters are reviewed and reviewed and the possible electronic structures and associated magnetic properties of latent images are discussed.
Long‐Wavelength Optical Phonons in GaAsAlAs Superlattices
Authors: Bechstedt F. , Gerecke H. 
Published: July 2007

AbstractOptical phonons in polar semiconductor superlattices near the zone center are studied. The microscopic theory based on a rigid‐ion model is simplified by restriction to one elastic force constant per material and spatial average of the long‐range electric field. The theory allows much insight into the mode structure, particularly anisotropy and layer thickness dependence of frequencies. atomic displacements, and accompanying electric fields. Explicit results are given for short‐period GaAsAlAs superlattices. The relationship of confined and interface modes is discussed.