bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Simple Analysis of the Einstein Relation in Ultrathin Films of Nonparabolic Semiconductors in the Presence of an Arbitrarily Oriented Magnetic Field
Authors: Ghatak K. P. , Bhattacharya D. , Basu D. , Nag B. 
Published: July 2007

AbstractAn attempt is made to study the Einstein relation of the diffusivity—mobility ratio of carriers in ultrathin films of nonparabolic semiconductors in the presence of an arbitrarily oriented magnetic field. This is done on the basis of a new electron dispersion law. It is found, taking Hg1−xCdxTe and In1−xGaxAsyP1−y lattice‐matched to InP as examples, that the diffusivity‐mobility ratio increases with increasing surface electron concentration and decreasing alloy composition and film thickness in various oscillatory manners. The magnetic field enhances the numerical value of the diffusivity‐mobility ratio and an experimental method is suggested to determine it in degenerate materials with arbitrary dispersion laws. In addition, the well‐known corresponding results for relatively wide‐gap materials in the absence of a magnetic field are obtained as special cases of our generalized analysis.
Theoretical Investigations of the Sideband Effect in Mössbauer Spectra of FeBO3
Authors: Maier Ch. , Gonser U. 
Published: July 2007

AbstractA theoretical investigation of the sideband effect in Mössbauer spectra of FeBO3 induced by radio frequency (rf) magnetic fields is presented. Because the interpretation of the sideband effect of FeBO3 with existing theoretical models reveals no satisfactory results modifications are developed to improve the description. Especially nonlinear acoustic properties of the sample under investigation are taken into account. It can be shown that new resonances occur leading to additional sidebands at fractional integers of the applied rf frequency which have also been experimentally observed. Taking into account this feature an improved empirical description of the sideband effect of FeBO3 is developed. This implies that nonlinear acoustic properties must be considered to obtain an appropriate description of the sideband generation in FeBO3.
A Model B.C.C. Iron Including Angular Interactions. The Self‐Interstitial
Authors: Simonelli G. , Pasianot R. , Savino E. J. 
Published: July 2007

AbstractSelf‐interstitial configurations in Fe are simulated using an embedded‐atom‐method (EAM) interatomic potential and an embedded‐defect (ED) one recently developed by the authors. The latter potential includes angular‐dependent many‐body local terms. Formation energy and lattice distortion for the 〈110〉 and 〈111〉 oriented dumbbells are calculated. The relative contributions of the pair and many‐body interaction terms to these properties are discussed. Comparisons with other many‐body potentials from the literature are made.
Intersubband Transitions in Thin Bismuth Films
Authors: Peschke Ch. 
Published: July 2007

AbstractThe reflectivity and transmittivity of thin monocrystalline bismuth films on barium fluoride are measured in the spectral range of 80 to 4000 cm−1. The measurements are performed at room temperature and at 5 K. At 5 K, thickness dependent absorption maxima occur if the film thickness is less than 50 nm. These maxima are interpreted as transitions between subbands of valence and conduction band at the L‐points of the Brillouin zone. The spectral position of the maxima is explained assuming an elevated gap energy due to lattice mismatch between films and substrates. Conclusions on the boundary condition of the electron wave function are supported by an analysis of the plasma frequencies of the films.
On the Influence of Weak Spatial Disorder on the Stress Fields of Finite Dislocation Walls
Authors: Raabe D. 
Published: July 2007

AbstractNumerical simulations of the three‐dimensional elastic stress fields associated with finite ordered and weakly disordered dislocation walls are carried out. The walls consist of discrete dislocations which are regarded as piecewise linear defects embedded within an otherwise isotropic elastic medium. The dislocation line vectors and Burgers vectors involved constitute a simple cubic lattice. The dislocations are subdivided into small segments. Two basic types of dislocation walls are studied, namely, a finite small angle tilt boundary and a finite dislocation cell wall consisting of 45° edge dislocation dipoles. The tilt boundary consists of 100 straight parallel dislocations. The dipole wall contains 100 alternately antiparallel edge dislocations. For both wall types the influence of weak spatial disorder on their stress fields is investigated. For this purpose non‐straight dislocations with a fractal dimension of 1.05 are used instead of straight dislocations. The study substantiates that weak spatial disorder considerably affects the stress field in the vicinity of the dislocation walls. However, the course of the long‐range stress is not predominantly determined by spatial disorder of the dislocation lines but by the finite geometry of the walls. The maximum shearing stress which is associated with the finite tilt boundary reveals a strong (but not exponential) decay in the direct vicinity of the wall. A local minimum occurs within a distance which exceeds the dislocation spacing in the wall by less than one order of magnitude. A local stress maximum is generated within a distance which exceeds the dislocation spacing by about two orders of magnitude. Finally, a long‐range stress field is predicted which corresponds to the solution obtained for a corresponding super‐dislocation with bsuper = 100bsingle (bsuper the Burgers vector of the super‐dislocation, bsingle the Burgers vector of the dislocations in the wall). The stress field of the dipole wall is not negligible but reveals short‐ and intermediate‐range stress components which decay with 1/distance.
A Bound State of Positrons with Sulphate Ions
Authors: Serna J. , Troev T. 
Published: July 2007

AbstractPositron lifetime spectra are obtained in four different single crystals of sulphates: sodium, strontium, barium, and lead sulphate. The spectra can be resolved into four components, although only the intermediate ones are significant since the other components, with a very low intensity percentage, are associated to positronium formed at the interface of the source with the specimen. The intermediate short‐lived component is associated with the annihilation of the outer electrons of the oxygen ions. The annihilation of positrons in cation vacancies or in interstitial impurities may also contribute to this component. Annihilation in other defects, like clusters of vacancies, is associated with the intermediate long‐lived component, whose main contribution seems to be a bound state of positrons with electrons belonging to the covalent bonds between sulphur and oxygen.
Calculated Electronic Structure and Hyperfine Interactions on γ′Fe4Z (Z  N, C)
Authors: Kong Yong , Zhou Rongjie , Li Fashen 
Published: July 2007

AbstractThe spin‐polarized linear muffin‐tin orbital (LMTO) method is used to calculate the electronic energy bands of γ′‐Fe4Z (Z = N, C) and to study the hyperfine interactions in Fe4Z. In comparison with the effect of N atoms, the C atom enhances the itineracy of electrons and then in turn prevents the exchange splitting. The C atom brings about a larger charge transfer among the atoms in the unit cell. The results show that the interaction between the Z and the nearest Fe atoms (FeII) is stronger than that between the Z and the next‐nearest Fe atoms (FeII). According to the calculated Fermi contact hyperfine magnetic field (HFC), the proportionality constant between the core contribution of HFC and the local magnetic moment of the atom is evaluated as ≈︁  13 T/μB. The calculated values of HFC and the Mössbauer isomer shift (IS) indicate that the FeIFeII and FeZ interactions strongly depend on the Z atom. The results of Hhf and IS are qualitatively in agreement with the experimental results.
Study of Balance Equations for Hot‐Electron Transport in an Arbitrary Energy Band
Authors: Wu Hang‐Sheng , Wu M. W. 
Published: July 2007

AbstractIn view of the recent disputes of Huang and Wu and Lei about Lei's balance equation theory for an arbitrary energy band, the balance equations for hot‐eléctron transport in an arbitrary energy band are reformulated. In the new formulation the adoption of the effective Hamiltonian method is avoided and all calculations are carried out in laboratory coordinates. In the mean time the crystal momentum k is carefully distinguished from the physical momentum. By introducing a correct equilibrium density matrix of the drifting electron gas in place of that used by Lei, the balance equations together with the distribution function can be derived directly with no need to distinguish the degree of freedom of the center of mass from the relative degree of freedom of the electrons, which is in our opinion neither possible nor necessary at least for a nonparabolic energy band. Some problems associated with the foundation of the balance equation theory are also examined. The result shows that the comment to Lei's theory given by Huang and Wu is correct and to the point. Nevertheless, contrary to their assertion that this theory is inapplicable to the nonparabolic band transport, Lei's balance equations, after a few, however, important corrections, are still applicable to transport for nonparabolic energy bands.
The Perspectives of Hydrogenated Amorphous Germanium as an Electronic Material
Authors: Chambouleyron I. , Graeff C. F. , Zanatta A. R. , Fajardo F. , Mulato M. , Campomanes R. , Comedi D. , Marques F. C. 
Published: July 2007

AbstractThis paper refers to the perspectives of the use of hydrogenated amorphous germanium and its alloys (deposited by the rf sputtering method). It is shown that considerable progress has been made in the optimization of aGe: H films. The deposition conditions leading to a good quality material and the corresponding properties are discussed. The problem of material stability, as well as recent progress in the understanding of the n‐ and p‐type doping mechanisms in the aGe: H network are presented. The main issues and perspectives of hydrogenated GeSi, GeN, and GeSn alloys are analyzed. Finally, results in the aGe: H device area are presented.
Mössbauer effect in atomic ordered and disordered Fe0.75−xMnxAl0.25 alloys
Authors: Babu T. V. S. M. Mohan , Bansal C. 
Published: July 2007

AbstractA Mössbauer effect study of the effect of chemical order on hyperfine magnetic field distributions in the quasi‐binary alloy system Fe0.75−xMnxAl0.25 (based on substitution of Fe by Mn in Fe3Al) shows that a preferential substitution of Mn at one of the sites leads to a B2 order in the ternary system. The kinetics of the ordering process in Fe0.45Mn0.3Al0.25 shows distinctly different relaxation behaviours at the two possible inequivalent sites in the ordered structure.
Spin‐lattice relaxation in diluted magnetic semiconductors
Authors: Scalbert D. 
Published: July 2007

AbstractThe contribution of pairs and triads of nearest‐neighbor spins to the spin‐lattice relaxation of magnetization is evaluated in Mn‐based diluted magnetic semiconductors. Modulation of the exchange interaction by lattice vibrations allows transitions in the cluster which change the total magnetization when the Dzyaloshinski‐Moriya interaction is taken into account. Spin‐lattice relaxation rates are calculated for pairs and open triads due to a two‐phonon Orbach process. In Cd1−xMnxTe it is found that the main contribution to relaxation of magnetization comes from triads. For temperatures ranging from 10 to 35 K and for x between 0.002 and 0.02 relaxation of triads can account very well for the observed relaxation rates, if one assumes rapid spin diffusion. Fitting of the experimental data yields an approximate value of a = J/(dJ/dr) ∼ 0.35 A, where J is the nearest‐neighbors exchange constant and r the Mn‐anion bond length, in good agreement with the expected value for a superexchange interaction.
Decoupling approach for the Hubbard model
Authors: Gehlhoff L. 
Published: July 2007

AbstractThe U = ∞ one‐band Hubbard model with large spin degeneracy N formulated with X operators is considered. The single‐particle Green's function is determined by applying the equation‐of‐motion method and a decoupling approach which is exact in the large‐N limit.
Single crystal EPR studies of water bridged one‐dimensional paramagnet diacetato‐copper (II)‐bis‐(p‐toluidine) trihydrate
Authors: Datta S. , Pal A. K. 
Published: July 2007

AbstractX‐band EPR measurements of g‐factor, lineshape, and linewidth in three mutually orthogonal planes of diacetato‐copper(II)‐bis‐(p‐toluidine) trihydrate at 77 and 300 K are reported. The lineshape is found to be Lorentzian in all directions including the chain and the magic angle. Excellent fitting of the linewidth anisotropy is obtained on the basis of the anisotropic exchange (AE) theories of McGregor and Soos and Ritter et al. The z‐direction of the AE tensor is found to be coincident with the chain direction. Values of isotropic and anisotropic exchange parameters derived from the above fitting are found to be in good agreement with those obtained from magnetic susceptibility measurements and the well‐known Moriya relation, respectively.
Magnetization curves of disordered cellular domain patterns in thin magnetic films
Authors: Zablotskii V. A. , Mamalui Yu. A. , Soika E. N. 
Published: July 2007

AbstractObservations of the coarsening of two‐dimensional cellular domain patterns with increasing film temperature at a constant bias field in magnetic garnet films are reported. It is shown that during this coarsening the value of the relative film magnetization increases just as it occurs on a magnetizing film by an external magnetic field at a fixed temperature. The dependences of the film magnetization on temperature as well as the bias field strength are calculated.
Recent advances of the photovoltaic activities in Japan
Authors: Hamakawa Y. 
Published: July 2007

AbstractA review is given on recent progress in solar photovoltaic technology in Japan and its contributions as a clean energy resource for solving the worldwide environmental issue. First, a new concept to reform the energy strategy for future civilization is postulated taking account of the environmental issue. Organizations and objectives of the New Sunshine Project are introduced. Second, some unique advantages of solar photovoltaics are described and compared with conventional electric power generation technologies. Third, key issues to develop photovoltaic technology are revealed, and recent R & D efforts to solve them are demostrated with live technologies in progress. Finally, possible new roles to contribute to the global environment issues by the photovoltaic technology are proposed and discussed.
Heterojunctions in photovoltaic applications
Authors: Elstner L. , Conrad E. , Eschrich H. , Füssel W. , Flietner H. 
Published: July 2007

AbstractNumerical simulations on silicon solar cells with heteroemitter layers made from various wide‐gap semiconductors are described and the dependence of the I–V curves on the band offsets is explained. The main advantage utilizing heteroemitters on silicon is the chance for an improved response in the blue region of the solar spectrum which may achieve an increase of the total photocurrent up to 10%. Experimental results on test solar cells with μc‐Si, ZnO, and SIPOS heteroemitters are presented and compared with these predictions.
Loss minimization through recombination center identification in solar cells
Authors: Lu Fu‐Hsing 
Published: July 2007

AbstractCarrier recombination, one of the major loss mechanisms in solar cells, has been found to be quite sensitive to the charge character of the Shockley‐Read‐Hall recombination center. Varying either the capture cross sections of the carriers or the density of the recombination centers results in a substantial change of the open‐circuit voltage as well as the fill factor in a solar cell. Compared to a neutral center, the center which remains repulsive to the opposite carrier after capturing a first carrier is beneficial to the open‐circuit voltage, when maintaining a constant density of recombination centers, whereas the center which becomes attractive to the minority carrier is detrimental to the open‐circuit voltage.
Excitonic effects in the light‐harvesting Chl a/b–protein complex of higher plants
Authors: Voigt J. , Renger Th. , Schödel R. , Schrötter Th. , Pieper J. , Redlin H. 
Published: July 2007

AbstractExciton states and their coupling to long‐wavelength protein vibrations are investigated both, experimentally and theoretically, in Chl a/b pigment–protein complexes acting as light‐harvesting antennae in higher plants. It is shown that the 12 chlorophyll molecules located within the involved protein‐monomers form extended exciton states and act cooperatively in the light absorption process. Besides one‐exciton excitations also two‐exciton excitations are demonstrated at higher photon densities incident on the monomer clusters resulting in nonlinear transmission and emission effects. The distribution of excitons over the exciton energy levels follows a Boltzmann law as shown by emission and nonlinear transmission experiments. The exciton–vibration coupling is weak as indicated by a resonance‐like zero‐phonon emission line which shows a strong reabsorption. Conclusions are drawn about the structure–function relationship of this antenna type. Interesting similarities between the biological structure investigated and semiconductors or semiconductor structures are discussed.
Stochastic theory of cluster dynamics
Authors: Pal L. 
Published: July 2007

AbstractAn exactly soluble stochastic model of the clusterization process is developed and the time dependence of the probability of the cluster size is calculated. The condition of stationarity is derived and the correlation function of the stationary cluster size fluctuations is determined. The properties of the spectral density function and that of the distribution function of the cluster lifetime are analysed.
A non‐planar crack analysis using continuously distributed sinusoidal edge dislocations and linear elasticity
Authors: Anongba P. N. B. 
Published: July 2007

AbstractNon‐planar cracks, propagating along crystallographic directions in the cleavage fracture of brittle materials and fluctuating about a mean plane, are represented in a simple model by a distribution of sinusoidal edge dislocations in a linear elastic medium; the dislocations are perpendicular to the crack propagation direction. The opening mode I loading is assumed. It is shown that, at the front of the sinusoidal crack and out of the mean fracture plane, the stresses are bounded and the derivative G of the energy decrease of the system with respect to crack area is zero. Only the positions of the crack front located on the mean fracture plane are associated with a nonzero value of G always lower than the well‐known crack opening force G0 = K(1−v2)/E per unit edge length of the planar crack (K1 is the stress intensity factor of mode I loading and E is Young's modulus). It is concluded that the sinusoidal crack cannot start propagating from positions on the crack front that are out of the mean fracture plane; instead, crack propagation could begin very near to the intersections of the crack front with the mean fracture plane if certain assumptions about the anisotropy of the surface energy are made.
Electrical and thermal studies of NaNO2
Authors: Ahmed S. A. , Ali M. H. 
Published: July 2007

AbstractThe present paper reports on experimental results on polycrystalline NaNO2 employing the dc resistivity, DTA, and unit cell parameters (measured by X‐ray diffractometry) in the temperature range from 298 to 480K. All the presented results confirm, in addition to the well‐known phase transitions at 436.5 and 438 K, the existence of a second‐order phase transition occurring at 448 K. We found clear evidences that the ferroelectric phase transition of NaNO2 is of second order close to the first‐order one, and the rotation of the NO radical mostly takes place around the c‐axis. The high‐temperature phase transformation occurring at 448 K is thought to be due to the completely disordered arrangement of the NO radicals in the normal paraelectric phase.
Eight‐band k·p Hamilton matrix for strained tetrahedral semiconductors: 4 × 4 block diagonalization for symmetric k‐directions
Authors: Enders P. , Woerner M. 
Published: July 2007

AbstractIn its mostly used form, the eight‐band k·p Hamilton matrix for diamond and zincblende structure semiconductors exhibits a twofold (Kramers) degenerated spectrum throughout the Brillouin zone (BZ), though its general block diagonalization (being valid for all k‐vectors) into two 4 × 4 blocks is not known yet. As a step in this direction, the 4 × 4 block diagonalization is achieved for k being parallel to the cubic symmetry axis. Using this, the calculation of electronic properties can be largely simplified, as demonstrated explicitly for the optical transition matrix elements. These results apply both to unstrained and to uni‐or biaxially strained materials.
The hot electron distribution function under impurity breakdown conditions
Authors: Kundrotas J. , Dargys A. , Cesna A. 
Published: July 2007

AbstractThe Boltzmann transport equation is solved by sparse‐matrix method under conditions that are typical for experiments of neutral impurity breakdown at low lattice temperatures. A strong cooling effect due to impact‐ionizing collisions is found on the hot carrier distribution function in moderately doped semiconductors. Implications of the cooling effect on the impact ionization coefficient are discussed. The results of simulation are presented for parameter values that are typical for n‐type GaAs doped with shallow donors and compensating acceptors, and compared with experimental data.
Magnetic measurements and crystal field investigations on Yb(BrO3)3 · 9 H2O
Authors: Neogy D. , Chakrabarti P. K. , Chattopadhyay K. N. , Chatterji A. 
Published: July 2007

AbstractYtterbium bromate (Yb(BrO3)3 · 9H2O) single crystals were grown, and the magnetic susceptibility perpendicular to the symmetry axis (χ⟂) and the magnetic anisotropy (Δχ = χ∥ − χ⟂) were measured in the temperature range 300 to 14 K and 300 to 90 K, respectively. The magnetic anisotropy at 300 K is considerable (≈ 23%). The smooth variation of χ⟂ down to 14 K does not suggest any structural phase transition or symmetry breaking. An analysis of the observed results undertaken for the first time invoking crystal field theory based on rare‐earth site symmetry D3h provides a satisfactory explanation to the experimental results.
Extended novel slab model analysis of overlaid bent step‐index single‐mode fiber half‐couplers. II. Coupled‐mode approach and design of overlays
Authors: Haubenreisser W. , Ecke W. 
Published: July 2007

AbstractWe present for the modal analysis of overlaid bent step‐index single‐mode fiber half‐couplers (OL‐BSSF) a coupled‐mode approach where the overlay (OL) and the BSSF structure are analyzed in isolation and the design criterion of suited BSSF and OL parameters is based on the phase‐matching condition of the coupled‐mode theory. The BSSF is mapped modally by an equivalent slab waveguide (ESW) structure. For the OL structure a general three‐layered overlay is considered which takes into account lossless, lossy, leaky, and plasmon active properties. Analytical expressions for the propagation characteristics of bound, bound surface plasmon polariton (SPP), leaky, and leaky SPP overlay modes are derived on which OL parameters at given BSSF/ESW parameters can be designed.
A non‐quadratic irrationality associated to an enneagonal quasiperiodic tiling of the plane
Authors: Franco B. J. O. , da Silva F. W. O. , Inácio E. C. 
Published: July 2007

AbstractA enneagonal tiling of the plane is proposed. A self‐similar pattern is obtained by using eight basic shapes. This pattern presents rotational symmetry and no translational invariance.