bluuebunny/crossref_metadata_2025_split huggingface dataset:
Density of States Model for the Lattice Transformation in A‐15 Compounds. Application to the Magnetic Susceptibility of V3Si
Authors: Pietrass B. , Handstein A. , Behr G. 
Published: July 2007

AbstractThe cubic‐tetragonal lattice transformation in A‐15 compounds is described by an empirical model in which the density of states function near the Fermi energy is characterized by a two‐parametric peak in addition to the constant part. Two types of peak splitting under tetragonal deformation are considered, leading to qualitatively different results about the phase transition. Results are given for the order parameter, the phase stability, the soft elastic modulus, and the paramagnetic spin susceptibility. Comparing with measurements of the magnetic susceptibility of V3Si single crystals near the phase transition a better agreement is obtained for a twofold degenerate density of states peak than for a threefold degenerate one.
Stress Dependence of Anomalous Hall Effect in n‐InSb
Authors: Biernat H. , Kriechbaum M. 
Published: July 2007

AbstractConsistent inclusion of the vector potential and the nonparabolicity in the impurity scattering leads to anomalous contributions in the Hall effect of n‐InSb in the magnetic freeze‐out regime. Their dependence on uniaxial stress is calculated. A measurable effect is found for stress up to 5 kbar.
Statistical Model and Experiments on Low‐Dimensional Exciton Transport
Authors: Erdle E. , Möhwald H. 
Published: July 2007

AbstractA statistical model is presented to calculate the concentration dependence of the ESR line width of triplet excitons in mixed CT crystals. A comparison between computation and experiments yields the anisotropy of energy diffusion. As experimental example data on the charge‐transfer crystal anthracenec–phenanthrene1–c–TCNB (0 ≦ c ≦ 1) are presented. It is shown that triplet excitons move by a factor of 15 to 60 faster along one distinct direction than perpendicular to it.
Thermal Phonon Scattering in n‐Ge. Effect of Uniaxial Stress
Authors: Kobayashi A. , Suzuki K. 
Published: July 2007

AbstractThe thermal phonon scattering, at low temperatures, due to isolated donor impurities in Ge under uniaxial stress is studied theoretically. The calculation shows that the piezo‐thermal conductivity depends on the chemical species of impurities and this dependence arises from the difference in the electronic structure of their ground states. A comparison with the experiment is also given.
An Analytical Solution to Fick's Equations in the Case of the Dissociative Diffusion Mechanism
Authors: Edelin G. 
Published: July 2007

AbstractThe Fick's equations are solved by the Laplace transformation method in the case of an impurity diffusing by the dissociative mechanism into a semi‐infinite solid at constant surface concentration. The only assumption made in the calculation is that the interstitial diffusivity is very high. The form of the substitutional and vacancy concentration profiles and the influence of dislocations on these profiles are discussed. It is pointed out that under certain circumstances the tails on diffusion profiles can be due to the dissociative mechanism.
Lattice Dynamics and Elastic Properties of GaSe
Authors: Altshul V. Ya. , Bashenov V. K. , Marvakov D. I. , Petukhov A. G. 
Published: July 2007

AbstractLattice dynamics of gallium selenide is studied by using both, the Born‐von Karman model with 22 interatomic force constants and the central two‐body‐force model with 10 constants ignoring completely any long‐range interaction. The second model including four equilibrium conditions leads to a good description of the elastic properties. The isolated layer dynamics is also considered. The striking feature of the acoustical modes appearing in an isolated layer is the quadratic dispersion of the out‐of‐plane acoustical mode in a small part of the Brillouin zone.
New Mechanism of Electric Field Influence on Defect Creation in Non‐Metallic Crystals
Authors: Chaika G. E. , Vinetskii V. L. 
Published: July 2007

AbstractThe mechanism of radiation defect creation in crystals below threshold is considered. Such defects may be due to impurity atoms capable of occurring at intersites, the latter being acceptors. The probability of lattice site–intersite transition for an impurity atom is calculated by statistical and quantum mechanical methods. This transition is accompanied by band electron (hole) capturing at the level of the created defect. When calculating by quantum mechanical methods the impurity atomic mass is supposed to be smaller than those of the host atoms. Such an assumption enables one to apply the adiabatic approximation twice: host atoms–impurity atom–electron. The upper value of the above transition probability corresponds to an electron energy level higher than the band minimum. Thus the heating by an electric field (or, perhaps, by the light of a discrete spectrum), causing the electron density to increase in the high energy tail region, may enhance appreciably the defect creation efficiency.
Reduction Symmetry Method in Crystal Field Theory (IV)
Authors: Kustov E. F. 
Published: July 2007

AbstractThe rotation groups of the type R[γ]γ and branch rules for the representations of the groups (unitary and point) are introduced. Relations between the SC and the 6U, 6r coefficients are developed by using the graph technique. The main formulas for the matrix elements of one‐particle operators between states of complex configurations and the eigenvalues of the Casimir operators are given.
Commensurate‐Incommensurate Transition in the Quasi‐One‐Dimensional Fröhlich Model with a Nearly Half‐Filled Band
Authors: Mertsching J. , Fischbeck H. J. 
Published: July 2007

AbstractThe mean‐field approximation of the commensurate‐incommensurate (C‐IC) phase transition in the one‐dimensional Fröhlich model with a nearly half‐filled band is studied near Leung's triple point, including up to 19 harmonics of the charge‐density wave. The C‐IC transition appears to be discontinuous, and the C and 1C phases coexist in a small region of the temperature‐density plane.
Theory of Core Excitons in Semiconductors
Authors: Bechstedt F. , Endeblein R. , Koch M. 
Published: July 2007

AbstractCore exciton binding energies are calculated for the Ga 3d‐X6 conduction band transition inGa‐V compounds and the Si 2p‐Δ6 transition in Si. Various corrections to the Wannier‐Mott theory are considered. Realistic core hole charge distributions, q‐ and ω‐dependent dielectric screening and an‐isotropic electron effective masses are taken into account. In the case of Ga‐V compounds, binding energies from the calculation are considerably larger than the Wannier‐Mott values, and close to experimental data. Smaller changes result for Si. The large discrepancies between theory and experiment cannot be resolved in this case.
Variations in the Exciton Spectra of CdTe and ZnTe Thin Films with Pressure and Temperature
Authors: Brothers A. D. , Brungardt J. B. 
Published: July 2007

AbstractExciton peak positions in thin films (≈ 700 Å) of CdTe and ZnTe are measured as a function of temperature between 90 and 300 K and hydrostatic pressures to 3500 atm at 90 K. The value of (∂E/∂T)P in the CdTe films for the E1 and E1 + Δ1 peaks is –2.3 ×10−4 eV/K and –1.7 ×X 10−4eV/K, respectively. For the ZnTe films these values are determined to be –2.5 ×10−4 eV/K and –1.4 ×10−4 eV/K, respectively. In CdTe films the values of (∂E/∂T)T are 7.4 ×10−6 eV/atm and 8.9 ×10−6 eV/atm, respectively, and for ZnTe films both are 8.3 ×10−6 eV/atm. A comparison of these results with previous results, and comments on the nature of the band structures of these materials are made.
A Contributory Mechanism to the Ground State Splitting of Gd3+ in C3h Symmetry
Authors: Dixon J. M. , Chatterjee R. 
Published: July 2007

AbstractA contribution to the zero‐field splittings of Gd3+ 4f7(8S7/2) in lanthanum ethylsulphate is calculated using a spin correlated crystal field. A particular mechanism is provided and estimated the sign and magnitude of the coupling coefficient. It is found, that the sign is positive and the contribution to the zero‐field splitting is of the correct sign.
Ag Centres in KCl:Ag Crystals. A Thermoluminescence Study
Authors: Sridaran P. , Bhuniya R. C. , Ratnam V. V. 
Published: July 2007

AbstractThe optical transformation and thermal stability of Ag centres in KCl:Ag crystals stabilized in different valence states after X‐irradiation are studied using thermoluminescence (TL) as the tool. The much higher sensitivity of TL over optical absorption enables to monitor the transformation processes with the help of the data obtained from TL spectra. It is shown that the 555 nm recombination luminescence emission predominant in the 90 °C glow peak is due to Ag0 atoms at cation sites while the 543 nm emission predominant in the 135 °C glow peak is due to Ag+k: F centre complex. The results further reveal that electrons trapped by Ag+ ions during X‐irradiation are mostly not destroyed during optical bleaching but undergo transformation and stabilize the Ag+ ions in different valence states both in cationic and anionic sites. Results also indicate that Ag0 atoms in anion sites are non‐thermoluminescent.
Higher Harmonics of Spontaneous Radiation of Ultrarelativistic Channeled Particles
Authors: Kumakhov M. A. , Trikalinos Ch. G. 
Published: July 2007

AbstractThe case of spontaneous radiation of channeled ultrarelativistic particles is considered when the dipolarity condition is not satisfied. The change of the particle longitudinal velocity affecting the maximum radiation frequency is included. The angular and frequency characteristics of the radiation for superhigh energies are studied for the first time. It is shown that there is an optimum energy at which the radiation density is maximum. The influence of the angle at which electrons enter a crystal and of the beam divergence on the radiation is investigated. The problem of quasi‐channeled particle radiation and also the radiation in axis‐plane transitions are considered.
Sublattice Displacement Effects in the Electromodulation Spectra of Zincblende‐Type Crystals
Authors: Suisky D. , Enderlein B. , Lange H. 
Published: July 2007

AbstractExpressions are derived for the deformation potential constants for pure piezomodulation (PM) and piezoelectrically induced linear electromodulation (LER EM), taking into account the difference in sublattice displacements caused by strain and field calculated in a previous paper. It is shown that in case of star degeneracy the sublattice contributions to the deformation potential constants C and C differ in LER EM and PM. The theory is applied to the experimental PM and LER EM spectra at the E1 E1 + Δ1 transitions of GaAs reported in the literature. In agreement with the predictions of the theory, the deformation potential constant C extracted from the LER EM data is found to be much greater than that obtained from PM spectra.
Lattice Dynamics of Si and Ge under Pressure
Authors: Soma T. 
Published: July 2007

AbstractThe lattice dynamics of Si and Ge under pressure is investigated using the higher‐order perturbation and the local Heine‐Abarenkov model potential. Then, the dispersion curves at the metallic‐transition pressure are estimated using the Grüneisen parameters of the individual modes of phonons in the phenomenological theory where the experimentally observed temperature dependence of the thermal expansion coefficient, i.e. the Grüneisen constant is reproduced.
Photoemission Cross‐Sections of Oriented Orbitals
Authors: Bartosš I. , Máca F. 
Published: July 2007

AbstractExpressions for photoemission cross‐sections of oriented orbitals are derived in the surface Green function formalism. Centres, described by short‐range spherically symmetric potentials, are treated and results for 2s and 2p levels of Al are given and discussed in context with the experimental data for solids.
Fermi Energy, Density of States, and Electronic Properties of Alkali Metals Exchange and Correlation Effects
Authors: Thakur J. 
Published: July 2007

AbstractFermi energy density of states, electrical resistivity, and thermoelectric power of liquid alkali metals are computed using first principle pseudopotential. Effect of various forms of dielectric screening procedures are also investigated. Slater's value of electronic exchange parameter α in the Xα‐exchange with unmodified orthogonalization hole potential (Vopw) presents a good picture.
Untersuchungen zum elektrischen Widerstand von Versetzungen in Metallen II. Anwendung auf Stufenversetzungen in Kupfer
Authors: Rauh H. 
Published: July 2007

AbstractDie in einer vorangehenden Arbeit entwickelte Theorie zur Berechnung des elektrischen Restwiderstands wird auf Stufenversetzungen in Kupfer angewandt. Das Störpotential der betrachteten Kristallfehler wird hierbei als lineare Superposition eines starken, auf das Gebiet des Versetzungskerns begrenzten und eines schwachen, ausgedehnten Anteils beschrieben. Der Einfluß dieser exakt bzw. störungstheoretisch behandelten Anteile sowie derjenige des gesamten Potentials auf den Widerstand werden im einzelnen untersucht. Dabei zeigt sich, daß beide Anteile Widerstandsbeiträge derselben Größenordnung liefern. Die experimentell bekannte Widerstandsanisotropie kann im Rahmen dieses Modells gedeutet werden, welches insbesondere die Bestimmung phänomenologischer Parameter gestattet. Die für den Widerstand selbst erhaltenen Werte erweisen sich jedoch als zu klein verglichen mit experimentellen Daten.
Surface Dipole Barrier of Metals
Authors: Taut M. , Eschrig H. , Schubert M. 
Published: July 2007

AbstractThe surface dipole barrier of simple and transition metals up to atomic number 50 is calculated by a simple scheme using only parameters of the bulk band structure. Good agreement with semiempirical values is reached and the trend over the 3d and 4d series is explained. The results prove that the charge density of surface atoms can be derived from bulk atoms, but not from free atoms.
Lattice Stability and 2kF Anomaly in a Quasi‐One‐Dimensional System
Authors: Kato K. , Iguchi K. , Itoh R. 
Published: July 2007

AbstractThe lattice stability and the phonon dispersion of a quasi‐one‐dimensional systems are studied using the tight‐binding approximation. The dependence of these properties on the electron—phonon coupling constant λ, the electron—electron interaction, and the temperature are elucidated. The dip in the phonon dispersion curve increases with increasing λ, the repulsive electron—electron interaction suppresses the Peierls instability as well as the Kohn anomaly, while the attractive electron—electron interaction raises them. For K(q; ω) > 1 (dielectric constant) the phase transition does not occur even in a one‐dimensional system. The temperature dependence of the curves are in good agreement with the experiments on TTF‐TCNQ.
Exciton Effects in Photoconductivity of GaAs
Authors: Kravchenko A. F. , Nazintsev V. V. 
Published: July 2007

AbstractPhotoconductivity (PC) and photoluminescence (PL) spectra are investigated on epitaxial GaAs at T = 2 to 50 K. According to the way excitons manifest themselves, two types of crystals, A and B, are discovered in the PC spectra. In crystals of A‐type, the photocurrent maximum corresponds to the exciton maximum in absorption spectra; in crystals of B‐type, vice versa, the photocurrent minimum corresponds to the exciton maximum in the absorption spectra. In crystals of A‐type the position of the earlier observed lines b (1.5154 eV) and d (1.5175 eV) is defined more precisely, and new lines a (1.5141 eV), c (1.5167 eV), and e (1.5185 eV) are registered. An identification of the observed lines is carried out. The influence of temperature and additional illumination on the PC spectra of crystals of both types is studied. The results of investigation show the decisive role of the recombination processes in the volume and on the surface of a crystal in the formation of excitons in PC spectra.
The Two‐Phonon Resonant Effect in Far‐Infrared Reflectivity of HgSe
Authors: Witowski A. M. , Grynberg M. 
Published: July 2007

AbstractReflectivity spectra of HgSe with various carrier concentrations are measured in the spectral region from 80 to 600 cm−;1 at 6, 80, and 300 K. Their features are well explained by the theoretical dynamic dielectric function including the dispersive interband part. This part is evaluated using Kane's model of band structure. The properties of an additional mode observed in zero gap semiconductors can be well explained by means of two‐phonon resonant process.
On the Phase Transition between the Commensurate and Incommensurate Charge‐Density Wave States of the Nearly Half‐Filled Fröhlich Model
Authors: Fischbeck H. J. , Mertsching J. 
Published: July 2007

AbstractThe commensurate—incommensurate phase transition of the nearly half‐filled one‐dimensional Fröhlich model is studied by numerical calculations of the grand potential in the mean‐field approximation. The phase diagram in the μ, T and the n, T plane is calculated using one and three order parameters of the incommensurate phase. The question whether or not the discontinuous phase transition becomes continuous at zero temperature with inclusion of an infinite number of order parameters remains open.
Semi‐Empirical Calculations of the Configuration and Electronic Structure of Lithium‐Related Defects in Silicon
Authors: Singh Vijay A. , Weigel C. , Corbett J. W. 
Published: July 2007

AbstractA modified extended Hückel theory method is employed to perform calculations for the lithium defect in silicon model crystals with and without vacancies. The energetically stable positions for the lithium atom appear to be the tetrahedral interstitial in models without vacancies; in the case of vacancies the substitutional position is preferred. The migration energy is found to be in the same range as experimental predictions. In models with no vacancy defects the electronic defect level is established to be a shallow donor.
Shielding by an Electron Gas in a Semiconductor in a Magnetic Field
Authors: Krupski J. 
Published: July 2007

AbstractThe macroscopic static dielectric function is used to study the effect of anisotropy of the electron effective mass on the screened Coulomb potential of a point charge impurity in semiconductor in a uniform magnetic field. Formulae for both degenerate and classical statitsics are derived. It is also shown how the positions of Kohn anomalies change due to the orientation of the crystal with respect to the magnetic field.
A New Infrared Luminescence of Nickel‐Doped ZnS and Its Interpretation by Means of Absorption Spectroscopy with Ni2+ Ions
Authors: Roussos G. , Schulz H.‐J. 
Published: July 2007

AbstractAt low temperatures, a new emission band is detected with Ni‐doped ZnS crystals. Zero‐phonon transitions at 4379 and 4199 cm−;1 and phonon side bands are resolved. The luminescence is interpreted as a 3T2(F) → 3T1(F) transition of substitutional Ni2+(d8) ions in a tetrahedral crystal field. This assignment is verified by the coincidence of (i) the fine structure in the emission and (ii) its excitation spectrum with the known absorption spectrum of the Ni2+ ion. The crystals exhibit all of the known internal absorption transitions of ZnS:Ni2+ and some weaker additional finestructured details which are in accord with the proposed interpretation.
Luminescence of Cs2NaYCl6—Bi3+ (6s2)
Authors: Van Steen A. C. Der 
Published: July 2007

AbstractThe luminescence properties of Bi3+‐activated Cs2NaYCl6 crystals are presented. The Bi3+ ion (6s2) occupies an Y3+ site which has cubic symmetry. Excitation in the A absorption band yields 3T1u emission. Excitation in the C absorption band, however, yields 3T1u and 3A1u emission, because both levels are populated by nonradiative processes from the 1T1u excited state. The emission and excitation spectra show vibrational structure. The vibronic lines are assigned and discussed.
Molecular Model Parameters for the Saddle‐Point Configuration of F, FA, FB, and FH Centres in the Alkali Halides
Authors: Kung A. Y. S. , Lagowski J. , Vail J. M. 
Published: July 2007

AbstractA molecular model for the saddle‐point configuration of F‐type centres, which previously led to the correct prediction of type II emission for FA centres in RbF:Li and RbF:Na, based on an empirical parameter Z, is extended to other impurity F centres in the alkali halides. CsF:Li and CsF:Na are predicted to have type II FA centres, and a number of triangular FB centres in the NaCl structure are also predicted to be type II, particularly in materials with small host anions combined with Li+ or Na+ impurities. Materials having small Z values, presumed to favour type II behaviour, are also identified, for FH centres with large host anions and H−; or F−; impurities, and for FA and triangular FB centres in the CsCl structure containing Li+ or Na+ impurities, where the FB centre which has impurities on adjacent corners of a unit‐cube face is strongly favoured.
Two‐Phonon Resonance Raman Scattering in Polar Semiconductors
Authors: Giner C. Trallero , Lang I. G. , Pavlov S. T. 
Published: July 2007

AbstractIndirect creation and annihilation probabilities are obtained for a Wannier‐Mott excition with arbitrary kinetic energy which interacts with longitudinal lattice vibrations (LO‐phonons). An analysis is made of the discrete and continuous spectra of the exciton intermediate (virtual) state contribution to these probabilities. These results are applied to the calculation of the two‐phonon resonance Raman scattering (RRS) cross‐section, which is directly proportional to Fröhlich's exciton—phonon coupling constant αexc. It is shown that the greatest contribution of intermediate states to the indirect hot‐exciton creation and annihilation probabilities is that one due to the continuous spectrum.
Phonon Coupling and Ferroelectric Phase Transition in Mixed As0.1Sb0.9SI Crystals
Authors: Valakh M. Ya. , Veshka Y. A. , Lisitsa M. P. , Svechnikov G. S. , Pinzenik V. P. 
Published: July 2007

AbstractThe Raman spectra of AsxSb1‐xSI (x = 0.1 and 0.05) are studied experimentally. The resonance interaction between soft mode and low frequency phonon excitations is observed. The effect appears to be stronger in mixed crystals, than in pure SbSI. The soft mode temperature dependence indicates that the Curie temperature falls when the As concentration x is raised. This effect is due to the increase of the anharmonicity in the mixed crystal lattice.
Analysis of the Phonon Drag Thermoelectric Power of the Doped Semiconductor at Low Temperatures Application to p‐Doped Ge
Authors: Dubey K. S. 
Published: July 2007

AbstractThe phonon drag contribution to the thermoelectric power of five phosphorus doped Ge samples with carrier concentrations of 1.2×1023 to 1.1×1024 m−;3 are studied in the temperature range 1 to 5 K. The variation of the phonon drag thermoelectric power with the reduced Fermi energy η*, the density of the states effective mass m*, the carrier concentration n, and the deformation potential Ed are also studied to see the role of the electron—phonon scattering relaxation rate in the analysis of the phonon drag contribution of the thermoelectric power of the doped semiconductor. The variation of the thermoelectric power with the lattice thermal conductivity is also reported in the entire temperature range of study. An analytical expression is also formulated to calculate an approximate value of the phonon drag thermoelectric power of the doped sample at low temperatures.
On the Use of Monte Carlo Techniques for the Calculation of Transient Dynamic Response in Semiconductors
Authors: Ferry D. K. , Barker J. R. 
Published: July 2007

AbstractThe transient dynamic response in InAs and GaAs is calculated by both, a drifted Maxwellian approach and a Monte Carlo approach. While previous calculations by the latter method yield results that differ from those obtained using the Maxwellian approach, using an ensemble Monte Carlo technique, which is free from errors introduced by velocity estimators, it is found that the results are extremely sensitive to the value of Γ, the self‐scattering parameter. However, when Γ is selected so that <Δt> = 1/Γ « >τ>, comparable results are obtained for the two techniques.