bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ohmic Mobility of Quasi‐One‐Dimensional Semiconducting Structures. Acoustic and Piezoelectric Phonon Scattering
Authors: Comas F. , Giner C. Trallero , Tutor J. 
Published: July 2007

AbstractMomentum relaxation times and ohmic mobilities are calculated for a quasi‐one‐dimensional (QID) semiconducting system assuming that carriers are scattered by acoustic and piezoelectric phonons. A detailed discussion of inter‐sub‐band transitions is done with special emphasis on the conditions where size‐quantum‐limit (SQL) is accomplished. A comparison of the acoustic and piezoelectric mechanisms is done for GaAs and CdS with detailed analysis of which mechanism dominates transport under given conditions. The temperature dependence of the mobilities is also discussed and asymptotic analytical expressions are obtained for the low temperature regime.
Donor‐Type Tm Centres in ZnS Crystals
Authors: Zimmermann H. , Boyn R. 
Published: July 2007

Abstract4f—4f excitation and emission spectra involving various intermanifold transitions are determined for two Tm3+ centres in ZnS crystals by dye‐laser site‐selective measurements at helium temperatures. A crystal‐field analysis together with polarization data indicates that in both cases Tm is located on lattice sites, probably Zn sites. One of the sites (D3) is thought to be in „unperturbed”︁ environment, whereas in the second case (D2) the four nearest‐neighbour atoms are probably replaced by impurity atoms. The excitation and deexcitation mechanisms of the blue 1G4 → 3H6 emission of these centres are studied by site‐selective broad‐band excitation spectra and kinetical measurements. These studies demonstrate that donor‐acceptor pairs involving the two Tm centres as the donors play an important role in the excitation process. Estimates are given of the relevant pair to 4f state transfer rates.
Magnetoresistivity of ZnSe in the Region of Hopping Conduction over Localized States in the Coulomb Gap
Authors: Kasiyan V. A. , Nedeoglo D. D. , Simashkevich A. V. , Timchenko I. N. 
Published: July 2007

AbstractIn the temperature range from 1.65 to 4.2 K and in magnetic fields with a strength up to 4.6 T conductance and magnetoresistivity of heavily doped (ND + NA ≈︁ 1×1018 cm−3) compensated (HDC) (0.84 ≦ K ≦ 0.98) n‐ZnSe crystals are investigated. In the temperature range investigated a conductivity with a smoothly changing activation energy is observed. It is established that the positive magnetoresistivity (PMR) is conditioned by a compression of electron wave functions at impurities. From an analysis of PMR within the framework of the recently derived theory of the magnetoresistivity for the variable range hopping conduction and σ(T), parameters as the localization radius of the electron wave function a and the dielectric constant χ are determined. The character of their behaviour while approaching the metal—insulator transition in HDC n‐ZnSe crystals is studied. The ratio of critical indices is found to be ξ/v = 2.5 ± 0.5.
Partial structures of compound‐forming liquid gold–caesium alloy. A model potential approach
Authors: Rao R. V. Gopala , Bhattacharyya M. 
Published: July 2007

AbstractThe compound‐forming AuCs alloy is studied with a square‐well potential as a perturbation over a hard‐sphere mixture. The partial structure factors S11(k), S12(k), S22(k) and also SNN(k), SCC(k), and SNC(k) are computed at various concentrations and temperatures. Here 1 refers to gold and 2 refers Cs. The total structure factors obtained by the present method agree very well with the measured values. The most important aspect of the computations is the accurate evaluation of the number density of each of the species. Density measurements indicate strong contraction at 50% concentration and it is found to give a subsidiary peak in S11(k) and a high principal peak for SNC(k) at this concentration. The present calculations show that if the correct density measurements and hence the number densities are available, the evaluation of partial structure factors with sufficient accuracy is possible. Also the present calculations show many similarities with the CuPb alloy which also forms a compound.
Exoemission theory: The exciton model
Authors: Merkin M. M. , Tsertsvadze A. A. 
Published: July 2007

AbstractA possibility of defect annealing of the alkali halide structure with free exciton formation is discussed and a two‐stage exciton model of exoelectron emission (EEE) is suggested. According to this model, within the scope of the mechanism previously proposed by the authors, the defect annihilation results at the first stage in formation of an exciton which can ionize an electron centre (the second stage of the process). The probability of an elementary act for the NaCl crystal is calculated. The dependence of the exoemission parameters and energy spectra of exoelectrons on the crystal orientation is studied.
Zero‐field splitting and the d–d transitions of Mn2+ on Ca(II) sites in Ca5(PO4)3F
Authors: Wan‐Lun Yu , Min‐Guang Zhao 
Published: July 2007

AbstractOn the basis of the crystal field theory the energy matrices of a d5 ion in Cs (or C2) symmetry are derived, which are applicable to all orthorhombic and tetragonal symmetries. Using the perturbation theory the analytical expressions connecting the zero‐field splitting parameters with the crystal field parameters are obtained for a 6S‐state ion in arbitrary symmetry. It is shown that the zero‐field splitting of Mn2+ on Ca(II) sites in Ca5(PO4)3F, possessing Cs point symmetry, can be reasonably understood by the spin–orbit coupling mechanism, and that the d–d transitions can be interpreted well by the crystal field model proposed by Zhao et al.
Photoluminescence in a‐Si1−xCx:H films
Authors: Siebert W. , Carius R. , Fuhs W. , Jahn K. 
Published: July 2007

AbstractA study of steady‐state and time‐resolved photoluminescence (PL) and optical properties of a‐Si1–xCx: H‐films prepared by glow‐discharge decomposition of gas mixtures of SiH4 and CH4 is presented. With increasing carbon content x the PL‐spectra shift to higher energies and broaden considerably. Simultaneously the quantum efficiency decreases at low x but increases again above x ≈ 0.6. The PL‐decay after pulse excitation (10 ns) is enhanced with increasing x, the lifetime spectra shift to shorter times by more than two orders of magnitude (x < 0.45). The data indicate a strong decrease of the average radiative lifetime with x. This behavior is explained by an enhancement of the Coulomb attraction between the recombining carriers and/or faster thermalization in the band tails.
Localized vibrations of hydrogen and deuterium in GaAs. A comparison with Ge and Si
Authors: Tatarkiewicz J. , Król A. , Breitschwerdt A. , Cardona M. 
Published: July 2007

AbstractA detailed study is made of the localized vibrational stretching modes of hydrogen in GaAs using high‐energy proton implantation and low‐temperature Fourier transform infrared spectroscopy. New mode frequencies are found and confirmed with the help of deuterium implantation. A comparison with proton‐ and deuteron‐implanted germanium shows a different shape of the vibrational bands in comparison to GaAs. The oscillator strengths and effective charges are determined for the vibrational bands observed.
Cohesion in d‐state metals at high pressures
Authors: Walzer U. 
Published: July 2007

AbstractA description of the d‐band structure in which the pseudopotential theory is combined with the muffin‐tin orbital theory serves for the calculation of the cohesive properties of d‐state metals. The coupling of free‐electron states and local, non‐overlapping d‐states is also taken into account. On this basis, two new models are developed. In both the models, it is assumed that the ratio of nearest‐neighbour separation to the atomic radius is independent of the pressure. In the first model (MB), the additional condition is that a redistribution of electrons between the two outer shells, which are not completely filled, is permissible. In the second model (MC), the requirement is that for elements with a filled d‐shell the theoretical bulk modulus at vanishing pressure is exactly equal to the experimental bulk modulus at vanishing pressure and that the pressure exactly vanishes for the zero‐pressure volume. In a comparison with various kinds of measured values, MC proves to be particular successful for all d‐state metals except Sc, Ti, and Nb. In both the models, the initial pressure derivative of the bulk modulus is not an input parameter, but can be predicted.
Screening of a proton moving through the electron gas. II. Kinetic Properties of the screening cloud
Authors: Stachowiak H. 
Published: July 2007

AbstractAn RPA type approximation developed in an earlier paper is used to study the kinetic properties of the screening electronic cloud forming around a proton moving through the electron gas. It is shown that the motion of the screening cloud in this approximation is compatible with no kinetic energy associated with this motion. The finite total electronic charge of the screening cloud is due to infinitesimal excitations of electrons with momentum in the immediate vicinity of the Fermi surface. If the proton is moving, the distribution of these excitations becomes anisotropic. Its angular dependence is a function of the proton velocity. A formula for this function is derived.
Ruthenium LII and rhodium LII,III X‐ray absorption‐edge structures
Authors: Sugiura C. , Kitamura M. , Muramatsu S. 
Published: July 2007

AbstractThe Ru LII absorption‐edge spectra of Ru(NH3)6Cl3, K3RuCl6, and RuCl3 · nH2O and the Rh LII absorption‐edge spectra of (NH4)3RhCl6 and RhCl3 · 3 H2O are measured together with the Rh LIII absorption‐edge spectrum from RhCl3 · 3 H2O, using a 50 cm bent crystal vacuum spectrograph. The RuCl3 · nH2O spectrum exhibits a double‐peaked LII‐edge structure, while the other spectra are characterized by an intense „white line”︁ at the LII or LIII edge. The Ru LII and Rh LII,III absorption‐edge structures are discussed by referring to atomic transition energies in Ru3+, Ru4+, and Rh3+ ions calculated on the basis of a self‐consistent‐field (SCF) method. From these calculated results, it is shown that the double‐peaked LII‐edge structure can be attributed to the 2p1/2 → 4d transitions in the Ru3+ and Ru4+ ions.
X‐Ray Reflection Curves of Si Crystals with Microdefects in the Laue Case
Authors: Holý V. , Kuběna J. 
Published: July 2007

AbstractX‐ray diffraction in crystals with randomly placed microdefects, which are not resolvable topographically, is studied theoretically and experimentally. On the basis of the general theory published in a previous paper the procedure is described for computing the coherent and incoherent parts of the diffracted and transmitted intensities. Using a simple model for the defect deformation field the influence is studied of the size and the defect concentration on the computed reflection and transmission curves. The computations are compared with experimental curves measured by a triple crystal diffractometer in the symmetrical Laue case and a qualitative agreement is found.
Electronic Properties of Amorphous Semiconductors. Lattice Topology Effects
Authors: Latgé A. , Makler S. S. , Anda E. V. 
Published: July 2007

AbstractThe influence is studied of the lattice topology in the electronic properties of a tetrahedrally bonded amorphous semiconductor, typically a‐Si. The system is described by a nearest neighbour tight‐binding Hamiltonian, defined on a pseudolattice. The topology corresponding to the perfect gasket defined using hexagons as its basic structure is similar to the crystalline diamond lattice. The continuum random network is simulated by generating vacancies in the gasket lattice where dangling bonds are eliminated by saturation. The electronic density of states and the ring statistics of the disorder lattice are studied using a real space renormalization technique within the context of the Green function formalism.
Material Constants of Composites. II. An Improvement over the Coherent Potential Approximation for Crystals with Site‐Diagonal Disorder
Authors: Monecke J. 
Published: July 2007

AbstractIt is shown that the coherent potential approximation violates a fundamental requirement, called additivity in a previous work. A new approximation for the calculation of the self‐energy of crystals with site‐diagonal disorder is proposed, which interpolates between the two dilute limits of the average t‐matrix approximation and fulfils the requirement of additivity.
Electron Momentum Distribution in Silver and the Renormalised Free Atom Model
Authors: Sharma B. K. , Singh Hanuman , Perkkiö S. , Paakkari T. , Mansikka K. 
Published: July 2007

AbstractThe results are presented of a Compton profile study on polycrystalline silver. The measurements are carried out using 59.54 keV γ‐rays on three samples of different thicknesses − 0.5, 0.25, and 0.125 mm. Theoretical Compton profiles are calculated using (i) renormalised free atom model for 4d95s2 and 4d10Fs1 electron configurations and (ii) orthonormalised LCAO model approach. Best agreement between the measured and calculated values is found for the 4d105s1 configuration within the RFA model.
AC Losses in a Type‐II Superconducting Slab Including Surface Barrier Effects
Authors: Saif A. G. 
Published: July 2007

AbstractThe structure of a surface barrier, in the frame of the general critical‐state theory, of a type II superconducting slab subjected to parallel magnetic fields (in which the direction of the de bias and ac field are left arbitrary) is studied. The internal magnetic field distribution is developed. In the case of the amplitude of ac field (b0) less than the magnitude of the dc bias field (B0), analytic expressions for ac losses are obtained. Maximum values of FL cutting and flux pinning losses are also determined. A good agreement with the previous results (in this case of α0 = 0 with absence of surface barrier effects) is obtained.
Concentration Effect on Delayed Emissions: 1,4 Dibromonaphthalene Host—Pyrene Guest Mixed Crystal System
Authors: Pal A. J. , Talapatra G. B. , Misra T. N. 
Published: July 2007

AbstractIn 1,4 dibromonaphthalene (DBN) crystal, phosphorescence emission is observed in conformity with quasi‐one‐dimensional exciton motion. In pyrene doped DBN crystal, fairly intense delayed fluorescence (DF) and delayed excimer fluorescence (DEF) are observed on host singlet excitation though prompt excimer fluorescence (EF) is absent. EF emission, however, is observed on pyrene singlet excitation. These results suggest that host triplet excitons are trapped more efficiently at monomeric pyrene sites than at nascent excimeric pyrene sites. From temperature and guest concentration dependence studies of delayed emission intensities and lifetimes it is concluded that homofusion of an adventitious defect triplet and heterofusion of this defect with guest triplets produce DF and DEF at low temperature but at high temperature homofusion of guest triplets is the generative event of these delayed emissions.
UHF MC INDO Calculations of the Interstitial Hydrogen in Alkali Halides
Authors: Matos Maria 
Published: July 2007

AbstractThe applicability of a general scheme of parametrization of semiempirical methods for ionic crystalline systems is investigated in the study of pure LiF, NaF, LiCl, and NaCl crystals using different molecular clusters, and in the investigation of optical and magnetic hyperfine properties of the interstitial hydrogen (U2‐center) in these crystals. MC‐INDO (for the pure crystal) and UHF MC‐INDO (for the defect) calculations are performed to investigate the band crystalline structure and to estimate the U2‐band absorption peak energy and the electronic spin density at the nucleus of the interstitial atom. It is shown that the procedure of scaling the defect Slater‐type orbitals (STO) is not appropriate for the U2‐center and that this fact is related to the covalent nature of the binding of the interstitial atom to the crystal.
Screening of a Proton Moving through the Electron Gas III. Computation of the Momentum Distribution of the Screening Cloud
Authors: Stachowiak H. 
Published: July 2007

AbstractA formula for the momentum distribution of the screening cloud around a proton moving in an electron gas has been derived in an earlier paper of the author in RPA approximation. This formula is investigated in details and the actual momentum distribution computed in the whole range of proton velocities. For velocities κ >λ (λ = 0.83355656) singularities appear in the momentum distribution (κ is given in units of the Fermi velocity). Another drastic change of the momentum distribution occurs at κ = 1. Two properties of the momentum distribution remain, however, remarkably steady: the whole screening charge is equal to one electronic charge and its total momentum is equal to one third of the momentum of an electron moving with the velocity of the proton.
On SCCF Treatment of the Hubbard Model of 1‐D Alloys. Auger Densities
Authors: Šlechta J. 
Published: July 2007

AbstractThere is presented an application of the SCCF method to the Hubbard model of 1‐D binary alloys which makes possible to progress beyond the narrow band restriction. The Hubbard split is demonstrated upon realistic densities of states provided by SCCF. There are also studied the multicentre densities relevant, e.g., for theory of the Auger effect and shown that for the alloys studied here the shapes of those densites do not depend upon the concentration of the components of those alloys. Thus clusters of more than one atom may play a role of a kind of “letters” or “words” in the genetic code.
Nonequilibrium Dynamics of Carriers and Phonons in GaAs after High Excitation by Short Time Laser Pulses
Authors: Asche M. , Sarbei O. G. 
Published: July 2007

AbstractTaking into account the electron–hole interaction and the nonequilibrium of optical phonons, the plasma cooling in GaAs after short time excitation by a laser pulse is investigated numerically. The energy transfer from electrons to holes is essential for times up to the order of picoseconds. Results are presented for a concentration of 1018 cm−3 carrier pairs.
Self‐Consistent Tight‐Binding Investigation of Chemical Trends for Native Defects in III–V Semiconductors
Authors: Kühn W. , Strehlow R. , Hanke M. 
Published: July 2007

AbstractUsing the recently developed charge self‐consistent version of the empirical tight‐binding method (ETBM) in conjunction with the Koster‐Slater scattering‐theoretic approach the electronic properties induced by the substitutional native point defects (anion and cation antisite defect, anion and cation vacancy) in the six III–V semiconductors GaP, GaAs, GaSb, InP, InAs, and InSb are investigated. The calculations include the neutral and possible charged states of the defects. Chemical trends in the energetic position of gap states, the orbital composition, and the localization of the defect wave function are discussed and compared with other theoretical and experimental findings.
Spin Hamiltonian of Cr3+ in a Strained Ruby Crystal
Authors: Lacroix R. 
Published: July 2007

AbstractAs an application of the theory of the ligand field in a strained corundum crystal previously published, the spin Hamiltonian of Cr3+ in strained ruby is written down. Numerical calculations are performed, which show that the effect of the internal strains is by no means negligible.
Impact Parameter Dependent Electronic Energy Losses
Authors: Azziz N. , Brannon Karen W. , Srinivasan G. R. 
Published: July 2007

AbstractElectronic stopping power for an ion traveling through a cloud of electrons is calculated in the linear approximation. The formalism allows for an explicit dependence of the stopping power on the impact parameter between the ion and the electron in the medium. This will facilitate the calculation of stopping power for semiconductors where the electronic density varies appreciably. Comparison is made with Firsov, Oen‐Robinson, and Lindhard formulas by averaging over a Thomas‐Fermi electron density distribution. The consistency of the approach with those mentioned above is clearly demonstrated.
Surface Optical Polaron in Magnetic Field
Authors: Bhattacharya M. , Mukhopadhyay S. , Mitra T. K. 
Published: July 2007

AbstractAn extrinsic surface optical polaron is investigated in a magnetic field perpendicular to the surface by canonical transformation method. Ground state energies are found for different values of the coupling constant (as) and the reouced magnetic field strength (Λ). The motion in the z direction is completely isolated, and the energy due to localisation in the z direction is neglected, so that the ground state energy is due to 2D motion perpendicular to the magnetic field. The importance of the problem in relation to cyclotron resonance and magneto‐optics is discussed.
EPR Study of Cu2+ Ion in K2Cd(SO4)2 · 6 H2O
Authors: Yi‐Yang Zhou 
Published: July 2007

AbstractThe admixture of d‐orbitals in the ground state wavefunction of Cu2+ ion in K2Cd(SO4)2 · 6 H2O crystal and, further, the EPR parameters g and A are calculated with the aid of the approximate SCF d‐orbit of Cu2+ ion. The results (compared with that obtained by Satyanarayana recently) show that the admixture fitted by Satyanarayana is reasonable.
Time‐Resolved Spectroscopy of the Low‐Energy Emission Bands of Highly Doped Zn1–xMnxS
Authors: Benecke C. , Busse W. , Gumlich H.‐E. , Moros H.‐J. 
Published: July 2007

AbstractThe luminescence excitation and emission spectra of Zn1‐xMnxS with high Mn concentration (0.01 ≦ x ≦ 0.25) is studied by time‐resolved laser spectroscopy at temperatures 10 K ≦ T ≦ ≦ 300 K. Besides of the emission bands peaking at ṽ = 17000 cm−1, ṽ = 15750 cm−1, and ṽ = = 13500 cm−1 a fourth band peaking in the IR at ṽ = 10600 cm−1 is registered. This IR band is closely connected to two excitation bands in the UV peaking at ṽ = 26900 cm−1 and ṽ = 28750 cm−1 (T = 10 K, x = 0.034). Four different Mn dominated centers are distinguished, which are partly connected by energy transfer.
Thermal Properties of Tetrahedral Compounds
Authors: Kagaya H.‐Matsuo , Soma T. 
Published: July 2007

AbstractThe thermal properties of tetrahedral compounds are studied theoretically from first principle using the lattice dynamical method recently developed. Numerical calculations about the specific heat are performed for AlP, AlAs, AlSb and about the thermal expansion coefficient for AlP, AlAs, AlSb, ZnS, ZnSe, ZnTe, and CdTe.
Dispersion and Damping Properties of Plasmon Polaritons in Superlattice Structures II. Semi‐Infinite Superlattice
Authors: Haupt R. , Wendler L. 
Published: July 2007

AbstractThe dispersion and damping properties of surface plasmon‐polaritons in semi‐infinite superlattices are analyzed using a local theory with retardation. The position of the dispersion curves of the surface plasmon‐polaritons relatively to the bands of the plasmon‐polaritons in infinite super‐lattices is discussed. It is shown that in a definite range of the thickness ratio of the single‐layers in an infinite superlattice a degeneracy point of the two plasmon‐polariton bands exists which is crossed by one of two surface modes existing in semi‐infinite superlattices. An analytic expression for the damping function is derived by means of a perturbative method. The different behaviour of the damping of surface plasmon‐polaritons in various semi‐infinite superlattice structures is discussed. The dispersion curves, the electromagnetic fields, and the damping function are calculated and presented in graphical form.
Symmetry of Localized Crystalline Orbitals and Double‐Valued Band Representation
Authors: Evarestov R. A. , Smirnov V. P. 
Published: July 2007

AbstractThe double‐valued band representations of space groups are considered. The simple double‐valued band representations of the space groups Oh5, Oh7, and Td2 are generated for the first time. The tables of the induced double‐valued representations of the crystallographic point groups are given. These tables are necessary for some applications of the simple band representations of space groups in physical problems. The symmetry of localized orbitals in Ge crystals is analyzed basing on the results of the relativistic band structure calculation.