bluuebunny/crossref_metadata_2025_split huggingface dataset:
Defect Formation in LiF by Low Energy Ion Implantation
Authors: Afonso C. N. , Ortiz C. , Clark G. J. 
Published: July 2007

AbstractThe defect formation is studied in LiF by 100 to 290 keV 1H, 4He, 11B, 16O, and 20Ne ion implantation. Room temperature optical absorption is used to study the F‐center aggregates as well as colloid formation. 2 K optical absorption is performed to analyse the zero phonon lines (ZPL) associated with the higher aggregates. The induced damage versus the ion mass, energy, and dose is studied. The influence of impurities such as Ni and Co, as well as pre‐existing defects due to γ irradiation is analysed. It is observed that the induced damage decreases as the implanted ion mas increases and that negatively charged aggregates such as R' and M' are not formed by ion implantation.
Magnons in an Anisotropic Ferromagnetic Heisenberg Chain with One Static π‐Kink
Authors: Fischer K. G. , Heber G. 
Published: July 2007

AbstractA ferromagnetic Heisenberg spin chain with an anisotropic exchange interaction of the easy axis type is considered. The chain has a π‐kink structure. The energy of one‐magnon‐states and their localization is calculated, depending on the relative anisotropy, for nearest neighbour interactions in the continuum approximation.
The Refractive Index and the Exciton Transition Oscillator Strength of CdSe Single Crystals
Authors: Terekhova S. F. , Onishchenko N. A. , Talenskii O. N. , Pendur S. A. 
Published: July 2007

AbstractThe dependences of the refractive index and the group velocity of light on the photon energy are obtained near the exciton transitions of CdSe single crystals at 5 K by the method of twobeam interferometry. The independence of the oscillator strength on the sample thickness is determined for the exciton transitions in CdSe. The results are compared with the data obtained by other's methods in recent papers.
Stimulated Raman Scattering and Raman Instability of an Intense Helicon Wave in Longitudinally Magnetized n‐Type Piezoelectric Semiconducting Plasma
Authors: Ghosh S. , Dixit S. 
Published: July 2007

AbstractA detailed analytical investigation is made of the Raman instability of the Stokes component of the scattered helicon wave in longitudinally magnetized n‐type nondegenerate cubic piezoelectric semiconductor crystal belonging to the class 43m. The general dispersion relation is obtained by using coupled mode theory and considering that the scattering is due to both the molecular vibrations produced due to the pump wave at a frequency equal to that of the transverse optical phonons and the electron plasma wave. The dispersion relation is solved for both the cases of scattered helicon waves (i.e. in the cases of left‐hand and right‐hand circularly polarized waves). The threshold value of the pump amplitude necessary for the onset of instability and the growth rate well above the threshold are obtained analytically for both the modes. The analysis is applied to a specific semiconductor, n‐InSb at 77 K duly irradiated by a high‐power helicon wave for numerical estimations. The laser wave intensities used are in the range of 109 to 1012 Wm−2 which is assumed to be less than the damage threshold of the InSb crystal. The order of wave amplitude is feasible presently.
Evaluation of Suitable Mean‐Field (Hartree‐Fock) Representations for Perturbational Studies of Disordered Solids
Authors: Böhm M. C. 
Published: July 2007

AbstractA unitary transformation scheme in Hartree‐Fock (HF) space is derived allowing for the definition of a “mixed” representation of the mean‐field operator which forms a suitable self‐consistent‐field (SCF) HF basis for perturbational studies of disordered solids and polymers. The transformed HF operator contains only a small number of off‐diagonal Lagrange multipliers (i.e. coupling terms) between properly defined “defect state(s)” in the filled or empty HF space and the remaining one‐particle functions of the Fermion system which are collected into a prediagonalized subspace. The unitary transformation scheme requires two numerical operations; in the first one the canonical one‐electron functions are transformed into a set of localized valence‐bond‐type orbitals. This one‐particle representation is then transferred into a mixed basis via elementary matrix diagonalizations and multiplications. The relevant theoretical steps are outlined in a few simple examples.
The Behavior of Active Centers in a Laser Host. A Crystal Field Investigation on Nd3+ and Er3+ in LaF3 Single Crystals
Authors: Neogy D. , Purohit T. 
Published: July 2007

AbstractThe effects of the well known laser host, LaF3, on the triply ionized rare earth (RE) ions, Nd3+ and Er3+, are studied in detail theoretically. The theoretical results deduced with a field of D3h symmetry obtained from absorption spectra, are in good agreement with available experimental results on the magnetic susceptibilities of these two ions in similarly constituted compounds with identical nearest neighbor environments. The effective Hamiltonian which includes the crystal field and spin‐orbit interactions is diagonalized in the complete basis of the 4I term which inherently includes J‐mixing; intermediate coupling effects are also considered. Hyperfine properties arising from nuclear level splitting under the influence of the crystal field are worked out.
Physical Properties of Ion‐Implanted Laser Annealed n‐Type Germanium
Authors: Contreras G. , Tapfer L. , Sood A. K. , Cardona M. 
Published: July 2007

AbstractAn investigation is made of the impurity distribution and carrier concentration in n‐type germanium layers doped with P, As, and Sb by ion implantation and recrystallized by laser annealing. The impurity distribution is determined with SIMS. The electron concentration is obtained from Hall effect and from ir reflectivity measurements. Impurity concentrations as high as 2 × 1021 cm−3 are reached, with carrier concentrations Ne as high as 2.4 × 1020 cm−3, much higher than in bulk doped samples (Ne ≦ 4 × 1019 cm−3). For the P‐doped samples the implanted layers are found to have a lattice constant larger than the substrate for small implantation doses and smaller for larger doses. An analysis of these data leads to the conclusion that most of the ions are implanted substitutionally and, at high concentrations, they are compensated by pairing defects, probably vacancies. With this hypothesis it is also possible to interpret the dependence of the strength of the phosphorus local mode on implantation dose, as found with Raman spectroscopy. The softening of the Raman phonon with dose observed experimentally is also compatible with this hypothesis. A softening of the acoustic phonons with dose found with Brillouin spectroscopy is also reported and discussed.
The Nature of Two Intense Si–H IR Stretching Bands in FZ‐Si:H
Authors: Shi T. S. , Xie L. M. , Bai G. R. , Qi M. W. 
Published: July 2007

AbstractBased on the isotope effect, two H‐defect complexes: tetrahedral interstitial silane (SiH4)Td and hydrogenated 〈100〉 split interstitials (Isp · 2 H) are proposed to account for the two strong Si–H IR stretching bands in FZ‐Si grown in H atmosphere (2210 cm−1, 1946 cm−1). A series of experimental facts, including the vibration frequency, the correlation with Si–H IR bands in the bending‐wagging region, the temperature dependence of band‐width and the annealing behaviour are presented, which support the proposed model. The results coincide with the view that the self‐interstitial is the dominate thermal defect in crystalline silicon at high temperature.
Secondary Emission Spectra and Energy Relaxation of Polaritons in Layer Polar Semiconductors
Authors: Brodin M. S. , Blonskii I. V. , Gushcha A. O. , Tishenko V. V. 
Published: July 2007

AbstractThe main processes of energy relaxation of polaritons in dependence on their initial energy and temperature are determined for the layer polar semiconductors 2H‐PbI2 and red HgI2. It is shown that thermalization of the polaritons is reached due to the “thermal barrier” effect.
Charge Self‐Consistent Tight‐Binding Parameters. Application to III‐V Compound Semiconductors
Authors: Strehlow R. , Hanke M. , Kühn W. 
Published: July 2007

AbstractThe description of defects (impurities, surfaces, etc.) in the framework of empirical tight‐binding method (ETBM) suffers from the drawback that already the TB parameters of the unperturbed crystal are not uniquely defined when obtained from pure fitting to existing band structures. Such an uncertainty enters the defect model via both, the unperturbed problem itself and the defect potential. It is suggested to overcome these difficulties by determining the diagonal TB parameters and orbital populations always self‐consistently. In the present paper and as the first step a method is developed to construct such charge self‐consistent TB parameter sets for the pure crystal within the framework of a special fitting procedure including up to second‐nearest neighbour interactions. With this additional self‐consistency requirement band structures are obtained being even better than those calculated from other parameter sets. The method is applied to the III‐V compound semiconductors GaP, GaAs, GaSb, InP, InAs, and InSb. Chemical trends are discussed.
Stochastic Liouville Equation Model for Nonperiodic Systems and Finite Temperatures
Authors: Čápek V. , Szöcs V. 
Published: July 2007

AbstractTheoretical background leading to the recently proposed generalization of the stochastic Liouville equation model of the excitation transfer to nonperiodic systems and finite temperatures is reformulated here using the time‐convolutionless generalized master equations. In the lowest order and for linear coupling to phonons, the Haken‐Strobl‐Reineker parametrization becomes acceptable after a short initial time‐interval following the creation of the excitation, but with time‐dependent parametrization, the theory applies to arbitrarily short time‐intervals. For separable initial conditions, the time development of the excitation is calculated numerically for onedimensional models describing the dynamics of the excitation near traps, trap‐luminescence etc. provided that the time‐development in the initial time interval is negligible. The equations correctly provide non‐equal asymptotic site‐occupation probabilities for non‐equal sites if the excitation lifetime is infinite.
Phonons and the Electron‐Phonon Interaction in Multi‐Layer Systems
Authors: Fomin V. M. , Pokatilov E. P. 
Published: July 2007

AbstractA theory of the potential due to the slow polarization field is developed for multi‐layer systems with an arbitrary number of layers. The general expression of the potential is specialized for three‐ layer and periodic systems. As result of diagonalization of the energy of the polarization vibration field, the bulk and surface vibrations are separated and the spectrum of their eigenfrequencies is determined both, for systems with a finite number of layers (inparticular, for a layer of a heteropolar semiconductor between a substrate of an ionic crystal and a homopolar dielectric medium) and for periodic systems. Finally, the exact electron‐phonon interaction Hamiltonian for multilayer systems is obtained in the second quantization representation.
Evaluation of the First‐ and Higher‐Order Volume and Pressure Derivatives of Dielectric Constants of Alkali Halide Crystals
Authors: Dutt N. , Agrawal G. G. , Shanker J. 
Published: July 2007

AbstractAn analysis of first and higher order volume and pressure derivatives of low frequency or static dielectric constant is presented for sixteen alkali halide crystals with NaCl structure using seven different potential forms for the short range overlap repulsive energy. The potential parameters are calculated using recent values of van der Waals potentials and taking proper account of the thermal contribution derived from consistent experimental ultrasonic data. Calculated values of volume derivatives of dielectric constant and optic mode Grüneisen parameters are compared with available experimental data. The results obtained from some potential forms present distinctly better agreement with experiment in comparison of others. The usefulness of such potential forms is demonstrated in predicting the higher order pressure derivatives of dielectric constants of ionic crystals.
Some Remarks on the Random Field Ising Model on a Lattice
Authors: Nattermann T. 
Published: July 2007

AbstractIt is suggested that domain wall roughening due to random fields in lsing‐like systems is different for lattice and continuum models. It is shown quite generally, that this is incorrect for dimensions d ≦ 3; on a sufficiently large scale the scale dependence of the wall roughness and the interface tension are identical for both types of models. This may have consequences for metastability and hysteresis effects.
Acoustic and Optical Deformation Potentials in Cubic IV‐VI Compounds
Authors: Enders P. 
Published: July 2007

AbstractAcoustic and optical deformation potentials (DP) in cubic IV‐VI compounds are calculated by diagonalizing the p‐model Hamiltonian including finite lattice distortions at the L‐ and T‐points of the Brillouin zone. A very pronounced and even non‐monotonous dependence is found of some DP upon the very lattice deformation and, most surprisingly, Ξ2(L) < 0 for the optical DP. This may explain the wide variance of experimental data for different samples and experimental conditions.
Localized Impurity Level and Carrier Concentration in Self‐Intercalated TiS2 Crystals
Authors: Inoue M. , Koyano M. , Negishi H. , Ueda Y. , Sato H. 
Published: July 2007

AbstractThe a‐ and c‐axis resistivities and Hall coefficients of self‐intercalated IT‐CdI2, type layered crystals of TiS2, are measured over the temperature range 1.5 to 300 K. The temperature dependence of the carrier concentration at low temperatures T < 150 K can be explained by a simple model which takes into account both, the host Ti 3d conduction band and a localized impurity level Ei due to excess Ti atom. The position of Ei is found to lie by about 5 meV above the Fermi energy. The self‐intercalated Ti atoms become ionized impurity scattering centers as Ti4+ and Ti3+ ions, whose relaxation times are calculated to give a good fit to the observed residual resistivity vs. carrier concentration curve.
Effect of Lattice Anharmonicity on Specific Heat of Alkali Alloys
Authors: Soma T. , Higuchi H. , Kagaya H.‐Matsuo 
Published: July 2007

AbstractUsing the expression by Trivedi in the high‐temperature limit with nearest‐neighbour central‐force interaction, the anharmonic contributions to the specific heat of the alkali alloys are studied theoretically. The concentration x‐dependence of the anharmonic coefficient for the specific heat A, defined by CΩ/3Nk = 1 + AT, is calculated for CS1−xKx, CS1−xRbx, and Rb1−xKx solid solutions.
Structural Phase Transformamtion and the Equation of State of CsCI, CsBr, and CsI Crystals
Authors: Narain J. , Dwivedi N. K. , Agrawal G. G. , Shanker J. 
Published: July 2007

AbstractThe structural phase transformation of CsCl crystals under the effect of high temperature is investigated using an interionic potential model which takes account of repulsive interactions up to second neighbours and of van der Waals (vdW) interactions between dipole‐dipole and dipole‐ quadrupole. It is found that the transition temperature at which the CsCl crystal transforms from B2 (CsCI) to B1 (NaCl) structure can be predicted correctly only if larger values of vdW potentials are used in calculations. The same potential parameters are used to predict the high pressure equation of state for CsCl, CsBr, and CsI crystals. The use of overlap integrals in the Born‐Mayer potential form yields good agreement between theory and experiment for the high pressure compression data.
Defect Clusters and Subcascades. I. The Distribution of Mean Free Paths of PKA and Splitting Function
Authors: Melker A. I. , Romanov S. N. , Tarasenko N. L. 
Published: July 2007

AbstractA theory of displacement cascade splitting is developed. The free path distribution of PKA is obtained in which inelastic energy losses are included. On this basis an equation for the number of subcascades per PKA is suggested.
Copuling of a Structural and a High‐Spin‐Low‐Spin Transition in MnAS1−xPx Compounds
Authors: Bärner K. , Gmelin E. 
Published: July 2007

AbstractUnusual temperature dependences of the orthorhombic distortion η, of the hs fraction γ, and of the specific heat capacity cp suggest a coupling between the high‐spin‐low‐spin and the structural transitions of MnAs1−xPx crystals. A mutual dependence of the coupling constants and the static order parameters is assumed and its effect on η, γ, and cp is evaluated.
X‐Ray Spectroscopic Studies of Azurite Mineral
Authors: Hemachandran K. , Chetal A. R. 
Published: July 2007

AbstractThe K‐absorption of copper in azurite and in some copper systems is studied using a Gauchois‐type X‐ray spectrograph. It is established that copper is in the divalent state and behaves as a cation in azurite. The two structures, B and C, observed in the Cuk edge of the mineral are assigned to the transitions 1s → 2a2u and 1s → 3eu on the basis of the molecular orbital theory.
Parametrization of Crystal Field Spectra of Mn2+ in ZnSe and ZnS
Authors: Biernacki S. W. 
Published: July 2007

AbstractA new parametrization scheme is proposed of the optical spectra of Mn2+ in ZnSe and ZnS considering the symmetry dependent deformation of the radial wave function and the dependence of one electron energies on spin orientations. It is found that the covalent bonding between d states of symmetry t2 and e with ligand states gives the main contribution to the splitting of the free ion terms in a crystalline environment.
Influence of Local Environment on Bound Excitons and Bound Excitonic Mqlecules in III‐V Alloys. II. Numerical Results for GaxIn1−xP:N and the Role of Disorder Topology for the Optical Spectrum
Authors: Müller H. ‐J. 
Published: July 2007

AbstractThe binding energy, the oscillator strength, and the broadening of bound excitons and bound excitonic molecules in GaxIn1−xP:N are calculated considering an x‐dependent multi‐valley band structure, the mutual particle interaction, the isoelectronic nature of the impurity, and the influence of disorder in the local environment. A satisfactory agreement with available experimental data is obtained. The results for the spectra of GaAs1−xPx:N and GaxIn1−xP:N prove the relevance of the disorder topology for the description of the shape of the spectra.
Dielectric tails in K2ZnCl4: No evidence for an intrinsic chaotic state
Authors: Nattermann T. 
Published: July 2007

AbstractIt is shown, that the increasing dielectric tail found recently for decreasing impurity concentration Ni in the incommensurate system K2ZnCl4 does not indicate the existence of an intrinsic chaotic state. Using a simple model for the pinning of solitons by impurities (but more realistic than those used previously in this context) it is shown, that the dielectric tails grow with growing soliton density ns but with dropping Ni. The precise dependence on Ni depends on the pinning mechanism (i.e. weak or strong pinning).
The structural disorder model: Pressure induced transitions in the semiconductors Si and Ge
Authors: Dixit P. K. , Vaid B. A. , Sharma K. C. 
Published: July 2007

AbstractThe structural disorder model, recently proposed by the authors to explain the thermodynamic properties near the transitions of first order, is generalized to include the pressure induced transition in the semiconductors Ge and Si. The calculated values show at least a in order of magnitude agreement with the experimental data.
Calculation of thermal expansion and phonon frequency shift in deuterated naphthalene
Authors: Jindal V. K. , Kalus J. 
Published: July 2007

AbstractA calculation of the implicit shift to the phonon energies for phonons in deuterated naphthalene at q = 0 is presented, the “explicit shift” having been already described in an earlier paper. With this the calculation of the shift in the phonon energies due to temperature becomes complete and consistent, ready for direct comparison with the measured results of the shift obtained by neutron scattering experiments. The results for the total calculated shift in the phonon energies, arising from both, the explicit anharmonic terms and the implicit (i.e. the volume dependent) shift are presented and compared with the experimental neutron scattering results. The calculations of thermal expansion, compressibility, and the Grüneisen constants which naturally enter the calculation of the implicit shift, are also described and a comparison with the experimental neutron scattering results of these also is made. All the results are very satisfactory, strengthening the faith in the assumption for the model of the molecular crystals.
Electromigration in niobium. A finite‐cluster‐model study
Authors: Brand M. G. E. , Lodder A. 
Published: July 2007

AbstractThe windforce acting upon a host atom and the impurities Ta, Cr, and Ni in niobium is calculated in a finite cluster model. In this model all strong and multiple scattering effects up to lmax = 2 are preserved. Special attention is given to the influence of the vacancy, the cluster size, and of charge transfer. A positive windforce is found, in accordance with experiment, so that this appears to be not directly related to a hole current contribution, contrary to what is believed commonly.
CDW‐SDW transition in the extended hubbard model
Authors: Zhong Jian , Zhang Kaiyi , Chao K. A. , Micnas R. , Robaszkiewicz S. 
Published: July 2007

AbstractThe ground state phase diagram of the extended Hubbard model for arbitrary electron density is investigated with the broken‐symmetry Hartree approximation. It is found that for two‐sublattice orderings, only the charge‐order and the antiferromagnetism exist without the mixed phase.
Detailed low‐field magnetic properties of rare‐earth ion states in cubic crystal fields
Authors: Fischer G. , Herb A. 
Published: July 2007

AbstractThe effect of a cubic crystal field on rare‐earth ions is calculated and presented in a graphical form representing the individual magnetic moment and Van Vleck susceptibility of the lowest‐lying sub‐state, for J = 3.5; 4; 4.5; 6; 7.5; 8. This is a practical guide for analyzing the moderate‐field part of the magnetization. The results are given for the three principal directions. In order to analyze susceptibility measurements, the calculated Curie constant (or the Van Vleck susceptibility) of the fundamental multiplet is also represented.
The second‐order correction to field‐electron‐emission formulae for an extended temperature range
Authors: Workowski C. J. 
Published: July 2007

AbstractCorrected formulae for the total energy distribution, the emission current density, and the inversion temperature are derived under the condition that the field‐electron emission takes place from a free‐electron metal. The corrections relate to the series truncation approximating the WKB phase integral inherent in the analytic approximation of the electron tunneling probability. The assumed approximation for the phase integral takes into account not only the zero and first order terms, present in the existing theory, but also the quadratic term. The expression for the total energy distribution, obtained on this basis, is in typical circumstances valid for field emission in the electron energy range of |ε| ≦ 1.5 eV with respect to the Fermi energy. The accuracy of the approximations used is also discussed.