bluuebunny/crossref_metadata_2025 huggingface dataset:
Resonance Scattering of Hard Synchrotron Radiation and Neutrons by Nuclei in Crystals
Authors: Haas M. A. , Hizhnyakov V. V.
Published: July 2007

A resonant scattering of hard synchrotron radiation and neutrons by nuclei in a crystal is considered at a recoil energy of R≫ ℏ\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \omega \limits^ \sim $\end{document} and the lifetime of the compound nucleus τ0 ≈︁ 2π/\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \omega \limits^ \sim $\end{document}, with \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \omega \limits^ \sim $\end{document} being the characteristic phonon frequency. In these cases the main contribution to the scattering is made by the secondary particles emitted in the relaxation process of the recoil energy of the compound nucleus. This emission is called hot nuclear fluorescence (hot emission of neutrons). Numerical calculations are performed to show the strong dependence of this type of resonant scattering spectra on the parameters R/ℏ\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \omega \limits^ \sim $\end{document}, \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \omega \limits^ \sim $\end{document}τ0, and local lattice dynamics. The requirements for the corresponding experiments, following from this study are considered. A possible set‐up for an experiment is proposed which allows to study the hot nuclear fluorescence without spectrometer.
Polarized Electronic Absorption, Emission, and Excitation Spectra of Cs2CdCl4:Ni2+ Single Crystals
Authors: Ghosh B. , Mukherjee R. K.
Published: July 2007

The polarized absorption spectra are reported of Ni2+ doped in Cs2CdCl4 single crystals at 295 and 77 K in the range 5000 to 25000 cm−1. Emission and excitation spectra are also reported in the range 11000 to 25000 cm−l. The Ni2+ ions occupy the Cd2+ sites in octahedral geometry and the spectra are satisfactorily interpreted in terms of a cubic ligand field model including spin‐orbit coupling. The ligand field parameters evaluated to best fit the observed spectra are Dq = 600 cm−1, F2 = 1260 cm−1, F4 = 87 cm−l, und λ = 290 cm−l. No strong spectral evidence for tetragonal distortion is observed.
Reduction of the Energy Splitting of an E‐State by Jahn‐Teller Coupling and by Covalency
Authors: Biernacki S. W.
Published: July 2007

A semiempirical LCAO method is used for the calculation of the spin‐orbit and spin‐spin splitting parameter K of the 5E state of Fe2+ in ZnS. The estimated reduction due to covalency effect of the spin‐orbit parameter is 15% and the reduction of the angular orbital momentum is 20%. The calculated value of the Jahn‐Teller energy on the base of the multimode model of coupling is 7.0 em−1.
ESR and NMR Study of Mixed Yttrium–Lutetium–Aluminum Garnets
Authors: Asatryan H. R. , Petrosian A. G. , Sharoyan E. G. , Wósjcik M. , Zbieranowski W. T.
Published: July 2007

ESR of Mo3+ ions and NMR of 27Al nuclei is investigated in mixed single crystals of yttrium‐lutetium‐aluminum garnets (Y1−xLux)3Al5O12, where O ≦ x ≦ 1. Several new centres of Mo3+ and 27Al compared with Y3Al5O12 and Lu3Al5O12 single crystals are revealed associated with symmetry and crystalline field parameter changes at isomorphous substitution of Y3+ ions in the rare‐earth sublattice of the garnet by those of Lu3+. Symmetry, nearest coordination, and parameters of spin‐Hamiltonians are estimated concerning all of Mo3+ and 27Al centres in (Y1−xLux)3Al5O12, at x < 0.15.
Quadratic Response of the Electron Gas. Inclusion of Local Field Corrections
Authors: Paasch G. , Heinrich A.
Published: July 2007

For the description of the static quadratic response of the electron gas several quadratic response functions are defined in analogy to the linear response theory. These response functions can be determined self‐consistently using the known quadratic response function for non‐interacting electrons. Local field corrections describe the influence of exchange and correlation beyond the random phase approximation. They are included in the self‐consistent procedure in the framework of the Hubbard‐Singwi approach.
Comments on Many‐Body Dielectric Relaxation in Solids
Authors: Jonscher A. K. , Dissado L. A. , Hill R. M.
Published: July 2007

A discussion is given elaborating some salient features of a recently proposed many‐body theory of dielectric relaxation in solids. It is pointed out that orientational polarisation involves disorder as an essential element and this leads to important conclusions regarding the relaxation processes. Three types of transitions, outlined in the original theory, are discussed in some detail and distinctions are made between “large” and “small” transitions. The physical nature of correlated states is discussed and some comments are made about energy loss processes involved in the many‐body model of dielectric relaxation, with particular reference to the frequency‐independent ratio of energy lost per cycle to energy stored in polarisation.
Scattering of Phonons by Charge Carriers and Peripheral Phonons and Lattice Thermal Conductivity of a Metal act Low Temperatures. Application to Sb
Authors: Dubey K. S.
Published: July 2007

The role of the scattering of phonons by charge carriers (electrons and holes) and peripheral phonons in the calculation of the lattice thermal conductivity of a metal at low temperatures is studied. The entire study is made in the frame of the Callaway integral using the Ziman expression for the scattering relaxation rate of phonons by the charge carriers, Sb is taken as an example. The percent contributions due to non‐peripheral and peripheral phonons are also calculated and it is found that the percent contribution due to peripheral phonons increases with increasing temperature. The separate contributions due to each scattering process to the total lattice thermal resistivity are studied and it is found that at low temperatures, the lattice thermal resistivity of Sb is mainly due to the charge carriers. The effect of the characteristic temperature θ* which differentiates the peripheral phonons from non‐peripheral phonons, on the lattice thermal conductivity is also studied by calculating the total lattice thermal conductivity of Sb for different values of θ*. The contribution of the correction term due to the three‐phonon normal processes to the total phonon conductivity of Sb is studied and it is reported that the contribution due to the correction term is very small compared to the total lattice thermal conductivity, so one can neglect its contribution.
Orientational Population of Quantum States for Fast Electrons in Planar Channeling
Authors: Plotnikov S. V. , Popov D. E. , Rozum E. I. , Kostareva O. G. , Vorobiev S. A.
Published: July 2007

The strong orientation dependence of angular distributions for 4.9 MeV electrons channeled along the (110) atomic planes through crystalline Si is observed and investigated in detail. For electron transmission along the 〈111〉 axis and (110) planes a considerable increase of the X‐ray yield is observed. These experimental results are explained by the orientation population of the different quantum states for channeled electrons.
Decay of Magnetic Fluctuations in Thin Films
Authors: Duszewski J.
Published: July 2007

The dynamic behaviour of fluctuations in magnetization is considered in inhomogeneous systems represented by thin films. The presented approach is a generalization of Oguchi's method's for the description of the spin correlation decay. The time‐dependent correlation function is obtained for thin films. In the case of infinite sample it is reduced to the Ornstein‐Zernike form. The damping and the diffusion coefficients are evaluated. The spin correlation time is of a local character and may be treated as a parameter for the determination of the surface fluctuations observed in experiments.
Galvanomagnetische und thermoelektrische Transportuntersuchungen an Sb2Te3
Authors: Simon G. , Eichler W.
Published: July 2007

Es werden erstmalig alle zwölf galvanomagnetischen Schwachfeldtransportkoeffizienten sowie die beiden Seebeck‐Koeffizienten von Sb2Te3 im Temperaturbereich von 100 bis 360 K angegeben. Ferner wird die Änderung einiger dieser Effekte bei Pb‐Dotierung beobachtet. Ausgehend von qualitativen Unterschieden im Transportverhalten von Sb2Te3 und der Analogiesubstanz Bi2Te3 werden Modelle zur konsistenten Beschreibung der Transporteigenschaften von Sb2Te3 diskutiert.
An Ising Model Analysis of Dielectric Polarization. I. Analysis for the Dielectric Response of Infinite and Finite Dipolar Chains in Dielectrics
Authors: Bozdemir S.
Published: July 2007

An analysis of the dielectric polarization for a model system consisting of a one‐dimensional chain of dipoles with nearest neighbour interaction only is presented. In this model, each dipole is assumed to have two components: One is normally oriented between two localized states in a plane perpendicular to the chain axis, while the other is oriented along the chain. The model further presumes that the reorientation probability of any dipole located on the site chain has a time‐dependent parameter, depending at any instant upon the momentary orientation of neighbouring dipoles. Glauber's time‐dependent Ising model formalism is applied to this situation. It is shown that the decay function of a single dipole located in either an infinite or a finite chain results in a non‐Debye‐type form, due to the many‐body nature of the induced molecular moments.
Three‐Body Interaction in the Fluorite Structure Ionic Crystals
Authors: Basu A. , Sengupta S. , Basu A. N.
Published: July 2007

The importance of the three‐body interaction in the study of simple ionic solids with centrosymmetric structure is both, theoretically and empirically well established. But so far there is no attempt to investigate its significance in the properties of ionic crystals belonging to fluorite and antifluorite structures. In contrast to said alkali halides the absence of the centre of symmetry for this structure implies complications which make a direct estimate of this effect quite difficult. From an analysis of the elastic data the inadequacy of a two‐body central interaction to describe the elastic constants of such crystals is demonstrated. An order of estimate is made of the three‐body interaction in the elastic properties of the calcium fluorite crystal from the HF wavefunctions of the ions. For the other crystals where the Clementi wavefunctions for the ions are not available the estimate is done directly from the elastic constants. The order of magnitude of this interaction obtained for the different crystals is comparable and lies in the range observed for other ionic solids. Further this investigation apart from indicating the importance of the three‐body interaction also accounts for the anomalies in the previous calculations. Finally some of the limitations of the present calculation are pointed out.
Electrical Conductivity Mechanism in Zinc and Copper Substituted Magnetite
Authors: Srinivasan G. , Srivastava C. M.
Published: July 2007

The electrical transport properties in polycrystalline ferrous zinc ferrites, ZnxFe3−xO4 (x = 0, 0.2, 0.4, 0.6) and ferrous zinc–copper ferrites, ZnxCu0.1Fe2.9‐xO4 (x = 0, 0.1, 0.2, 0.3, 0.4), are studied by measuring the conductivity and the Seebeck coefficient. The conductivity is shown to arise from the phonon‐induced tunneling of electrons from one B site to another in the cubic phase of these ferrites.
Anisotropy of Exciton Polaritons and Polariton‐Phonon Interaction in 2H‐PbI2 Crystals. II. Anisotropy of the Photoluminescence of 2H‐PbI2
Authors: Biellimann J. , Gubanov V. , Meyer B. , Schwab C.
Published: July 2007

A detailed investigation of the anisotropy of the photoluminescence spectra of 2H–PbI2 as a function of the orientation of the electrical and propagation vectors of the emitted light is reported. The results are analysed in terms of exciton polariton emission and polaron mass anisotropy.
The Incommensurate Peierls Phase of the Quasi‐One‐Dimensional Fröhlich Model with a Nearly Half‐Filled Band
Authors: Mertsching J. , Fischbeck H. J.
Published: July 2007

The one‐dimensional Fröhlich model with a nearly half‐filled band is solved in the mean‐field approximation for finite temperatures, extending a recent ground‐state calculation by Brazovski et al. The commensurate–incommensurate phase transition is shown to be continuous, and the corresponding transition temperature is calculated as a function of the chemical potential or the electron density.
Phonon Dispersion Relations in the Bi0.95Sb0.05 Alloy
Authors: Sosnowski J. , Bednarski S. , Bührer W. , Czachor A. , Maliszewski E.
Published: July 2007

Neutron inelastic scattering experiments are made using triple‐axis spectrometers at the EWA and DIORIT reactors to determine the phonon dispersion relations in dilute Bi0.95Sb0.05 alloy at room and liquid nitrogen temperatures. The shifts of phonon frequencies for the Γ–T, Γ–X, and Γ–L directions are determined.
Vk Center in Cesium Halides by the MSXα Method
Authors: Oliveira P. M. , Maffeo B.
Published: July 2007

The electronic structures of the Vk center in CsCl, CsBr, and CsI are calculated using the MSXα method. Comparison with two experimental energy values is made, and very good agreement is found. The internuclear distances in the halogen molecular ion are estimated and the results compared to those obtained by other workers.
Optical and Thermal Stability of Ag Centres in RT X‐Irradiated KCl:Ag Crystals
Authors: Sridaran P. , Bhuniya R. C. , Ratnam V. V.
Published: July 2007

The optical absorption, thermoluminescence (TL), monochromatic TL, and TL spectra of potassium chloride crystals doped heavily with silver are measured after X‐irradiation at RT. The effect of optical bleaching on X‐irradiated crystals with light in the F, E, and B bands both, separately and together, as well as thermal annealing effects of the defect centres are studied. It is found that in the heavily doped crystals the role of holes in the form of doubly charged impurity ions (Ag++) is predominant compared to holes of the host lattice in the form of Cletc. The Ag ions stabilised only at cation sites in different valence states are involved in the recombination‐luminescence process. From the TL spectral data of the glow peaks preferential redistribution of the excess electron centres on optical bleaching is evident. The results support that tunnelling of electrons is responsible for the observed TL and TL spectral data.
Vacancy Formation Enthalpy in Cadmium by Positron Lifetime Measurements
Authors: Mascher P. , Breitenhuber L. , Puff W.
Published: July 2007

Because of a strong prevacancy effect in cadmium the assumptions of the trapping model seem to be fulfilled rather badly. Therefore the formation enthalpy of monovacancies is also determined by methods using the trapping model only to some extent or not at all. H is obtained as (0.39 ± 0.04) eV (from the trapping model), H = (0.42 ± 0.02) eV (from the inflection point), and H = (0.45 ± 0.08) eV (from the threshold temperature).
Liquid Metal Pair‐Correlation Functions from Empirical Pair Potentials
Authors: McGurn A. R. , Esterling D. M.
Published: July 2007

The pair‐correlation functions of liquid Fe, Cu, Ag, Au, and V are calculated from empirically determined potentials obtained from the solid state of these substances. The calculations use Percus‐Yevick theory, and comparison is made between the results using the empirical potentials obtained by Esterling‐Swaroop and those of Johnson and Wilson. Reasonable agreement with the experimentally determined pair‐correlation functions is obtained for Fe, Cu, and Ag with both sets of potentials. However, the results for Au and V with the Esterling‐Swaroop potentials are not satisfactory. It is noted independent evidence suggests that the pair potential approximation is inadequate for these two metals. In addition, the pair‐correlation function serves as a discriminator between two pair potentials for iron derived from the same phonon data.
Temperature Dependence of Electrical Resistivity of Zn, Cd, Hg, Al, In, Tl, and pb by Nonlocal Harmonic Model Potential
Authors: Sahay B. B. , Srivastava P. L. , Mitra N. R.
Published: July 2007

The harmonic model potential is used in its nonlocal form to study the temperature variation of the electrical resistivity of liquid Zn, Cd, Hg, Al, In, Tl, and Pb. The variation of the electrical resistivity with temperature is well demonstrated by the model and the numerical values are consistent with the experimental measurements in all the cases, except Hg.
The Validity of the Column Approximation in Image Contrast Calculations of Crystals Containing Stacking Faults
Authors: Jap B. K. , Sheinin S. S.
Published: July 2007

The validity of the column approximation is assessed for image contrast calculations of stacking faults in plate shaped crystals. The basic approach is based on application of the appropriate boundary conditions at the fault to determine the exact wave functions describing the electrons both above and below the fault and does not involve the differential equation approach used in non‐column approximation calculations in the past. In order to assess the validity of the column approximation, a validity assessment parameter, based on the two‐beam theory, is defined. The results obtained show that the validity domain of the column approximation, for a particular stacking fault inclination, decreases with increasing deviation from the Bragg condition, and increases with increasing electron energy. Direct comparison of many‐beam profiles in the noncolumn and column cases show that significant differences in profile shape can be obtained for weak beam diffraction conditions even when the stacking fault inclination is less than 45°.
The Configuration ƒN in Cubic Symmetry: A Symmetry Adapted Weak‐Field Approach
Authors: Kibler M. , Grenet G.
Published: July 2007

The symmetry adapted weak‐field model recently introduced by the authors is applied to the case of the configuration ƒN in cubic symmetry. This leads to a 29‐parameter model which parallels the 32‐parameter strong‐field model.
Correlation Factors for Diffusion in Binary Alloys with Short‐Range Order
Authors: Stolwijk N. A.
Published: July 2007

A method is presented for the calculation of the diffusion kinetics in binary alloys with only short‐range order. The method may be considered as an extension of Manning's theory on random alloys. Effects from atom‐vacancy exchanges on local order are taken into account in detail. The model is tested by comparing its results for alloys with nearest‐neighbour interactions with correlation factors obtained by computer simulation. For all sets of interatomic energies very good agreement is obtained over the entire temperature range. The present treatment of correlation effects may also be applied to more extended alloy models or to multicomponent systems.
Electrical Conduction of GeSe at Low Temperatures
Authors: Ishihara Y. , Nakada I.
Published: July 2007

The Hall coefficient and resistivity of germanium monoselenide were measured between 320 and 1.5 K. The ionization energy of the acceptor is estimated from the temperature dependence of the Hall coefficient. It changes from 3.9 to 5.3 meV according to the heat treatment. The impurity conduction is found to occur at low temperatures. There appear two activation energies corresponding to impurity conduction, the first of about 1.5 meV and the other of about 0.5 meV. The former value can be associated with the thermal excitation of holes from the Fermi level to a mobility edge in the upper Hubbard band.
Evaluation of Third‐Order and Fourth‐Order Elastic Constants of Cesium Halides and Thallium Halides
Authors: Shanker J. , Singh J. P. , Jain G. D.
Published: July 2007

The third‐order and fourth‐order elastic constants for CsCl, CsBr, CsI, TlCl, and TlBr crystals are calculated taking into account the effect of Lundqvist's three body potential. The nearest neighbour and next‐nearest neighbour repulsive interactions and the Van der Waals interactions are also included according to a recent scheme developed for NaCl‐structure alkali halides. The three body charge transfer parameter and its derivatives are evaluated using an exponential form suggested by Cochran. The pressure derivatives of second‐order and third‐order elastic constants are also calculated for the crystals under study. The results obtained are found to be in reasonable agreement with available experimental data.
Non‐Markovian Evolution of Crystal Electrons in a Strong Electromagnetic Wave Field
Authors: Kruglov V. I.
Published: July 2007

The non‐Markovian kinetic equations describing the interaction of two multi‐particle subsystems are defined and an approximate calculation procedure of the electron—phonon crystal system wave functions in an external electromagnetic field is suggested. A kinetic non‐Markovian equation for the electron density matrix is derived on the basis of results obtained without using perturbation theory. The general solution of the non‐Markovian kinetic equation describing multiphoton processes and the high‐frequency oscillations of the electron distribution function is obtained for the case of weak binding.
Free Carrier Compression and Galvanomagnetic Luminescence of Germanium at High Lorentz Fields
Authors: Kessler F. R. , Mangelsdorf J. W.
Published: July 2007

A local variation in carrier concentration occurs in intrinsic semiconductors in the presence of crossed electric and magnetic fields which leads partly to an enhancement (“compression”) and partly to a depletion. In connection with these displacements from thermal equilibrium luminescent radiation can be observed which, when related to the thermal radiation under equilibrium conditions, is positive in enhanced and negative in depleted regions. The luminescent radiation spectrum in the region of the fundamental absorption edge is directly related to the free carrier concentration profile in the sample. The report deals with theoretical and experimental results obtained with germanium exposed to Lorentz field strengths of up to 20000 TV/m (or B ≦ 10 T) at 400 K. Non‐linear surface recombination must thereby be allowed for. The corresponding semiconductor parameters are given. The modulated galvanomagnetic luminescence exhibits the expected antiphase component at longer wavelengths, corresponding to an increase in the separation of the quasi fermi level from the band edges for constant lattice and electron temperatures.
On the Experimental Determination of Many‐Particle Effects at Interband Transitions
Authors: Jungk G.
Published: July 2007

The energy‐derivative spectra of the real and imaginary part of the dielectric function ε(ω) = ε1 + iε2 in the range of critical interband transitions can be used to determine a parameter which describes the influence of many‐particle effects. Afterwards the computation of the one‐electron spectra becomes possible from experimental spectra, which are modified by many‐particle interactions. The application of this procedure to ellipsometrically determined spectra of GaP and GaAs for the E1 transition results in the predominant influence of the continuum—exciton effect in accordance with theoretical predictions of Hanke and Sham.
Calculation of the Compton Profile of Beryllium
Authors: Rennert P.
Published: July 2007

Starting from a pseudopotential calculation for h.c.p. beryllium the Compton profiles are calculated for the directions 〈101〉, 〈102〉, 〈111〉, and 〈112〉. The profiles for 〈001〉, 〈100〉, and 〈110〉 are improved by detailed considerations on the orthogonalization corrections. A strong anisotropy is found for I〈001〉 — I〈102〉 and I〈001〉 — I〈112〉, respectively. The contribution from the correlation tail in the momentum distribution is estimated. It must be included, if the calculated profiles are compared with high resolution measurements.
Influence of Dielectric Screening and Band Nonparabolicity on Ionized Impurity Scattering in Doped Semiconductors
Authors: Neumann H. , Tsipivka Yu. I. , Unger K.
Published: July 2007

Dielectric screening beyond the Thomas‐Fermi approximation and band nonparabolicity are included in the theory of ionized impurity scattering in semiconductors. The resulting mobilities are always smaller than the Brooks‐Herring mobility. The corrections to the Brooks‐Herring mobility increase with increasing nonparabolicity. Numerical results are given for the electron mobility due to ionized impurity scattering in n‐type GaAs, InAs, and InSb.
Luminescence et interaction phonon—électron dans le luminophore MgS:Bi3+. II. Théorie sur le mélange entre les états 3T1u et 3A1u
Authors: Asano S.
Published: July 2007

Theoretical considerations are made on the mechanism of the admixture between the 3T1u and 3A1u states of Tl+‐type ions, which is realized for Au− ions in alkali halides and Pb2+, Bi3+ ions in alkali‐earth chalcogenides. It is shown that the ordinary electric electron‐phonon interaction has no effect on the admixture between both the states. A new model containing the magnetic interaction with the localized τ1g vibrational mode is proposed in order to explain this admixture by the use of the two‐electron wave functions.
Host Spin—Lattice Relaxation Narrowing in Sm2Co3(NO3)12 · 24 H2O:Mn2+, Gd3+ Single Crystals
Authors: Jain V. K.
Published: July 2007

The electron paramagnetic resonance of Mn2+ and Gd3+ in single crystals of Sm2Co3(NO3)12 · 24 H2O is studied in the X‐band at 300 and 90 K. The spin‐Hamiltonian parameters are evaluated. The observation of resolved Mn2+ and Gd3+ spectra at 300 K and their broadening on lowering the temperature is discussed in terms of host spin—lattice relaxation narrowing.
Defects Induced in RbMgF3 Crystals by X‐ and UV‐ Irradiation
Authors: Trieman B. , Kristianpoller N.
Published: July 2007

The effects of X‐ and UV‐irradiation on pure and Pb‐doped RbMgF3 single crystals are studied. The temperature dependence and spectral composition of X‐luminescence (XL) as well as TSL, TSC, and optical absorption are measured. The XL shows main emission bands at 270, 305, 410, 430, 495, and 560 nm. Prolonged X‐irradiation at 80 K causes the appearance of absorption bands at 245, 315, 330, and 378 nm which are attributed to interstitial aggregates, F centers, VK centers, and F2 centers, respectively. Some of the TSL peaks which appear after X‐irradiation, appear also after monochromatic VUV irradiation. VUV excitation spectra of the TSL show maxima at 127 and 160 nm. The results indicate that a radiolysis process may be responsible for defect formation in both, the × and VUV irradiated samples, it appears, however, that this process is suppressed in the Pb‐doped samples.
Self‐Trapped Particles in Complex Oxide Crystals
Authors: Vakhidov Sh. A. , Ibragimova E. M. , Nuritdinov I. , Rakov A. F. , Ikramov G. I.
Published: July 2007

Self‐trapped hole (STH) and self‐trapped exciton (STE) states which are formed in Y3Al5O12, Y2SiO5, and TR2Si2O7 crystals under γ‐irradiation in the temperature interval of 77 to 200 K are investigated. The STH is shown to be molecular O, absorbing at 1.6 eV (for Y3Al5O12) and at 1.65 eV (for Y2SiO5) and causing the eleven‐component EPR signal; the corresponding STE emits at 3.9 and 3.6 eV. In metal‐doped crystals the exciton and hole delocalization lead to a decreasing of the emission energy, to a short‐wave shift of the absorption band, and to the growth of the anneal temperature. At the self‐localization temperature excitons are proved to migrate by jump diffusion and to transfer energy to the impurity ions exciting their emission.
Properties of the Rn and IR‐1 Luminescence Bands in Cadmium Sulfide Irradiated with Thermal Neutrons
Authors: Ermolovich I. B. , Gorbunov V. V. , Matvievskaya G. I.
Published: July 2007

Specific features of Rn (λmax equals; 728 nm) and IR‐1 (1040 nm) luminescence bands in CdS single crystals irradiated by thermal neutrons with doses 1013 to 1019 n/cm2 were studied. The joint investigations of luminescence and photoconductivity dependences on temperature and on both the intensity and the wavelength of excitation confirm the Rn and IR‐1 centre models proposed earlier, (VCd · VS) and (VCd · InCd), respectively. The electron‐phonon interaction at radiative carrier capture on Rn‐centres are investigated, its parameters are obtained. At the first time it is found that at sufficiently low temperatures (≧ 160 K) the photosensitivity centres in monopolar, photosensitive semiconductor with wide band gap are the centres of effective nonradiative recombination due to high electron‐phonon interaction.
Dielectric Relaxation of Chalcogen—Vacancy Centres in Potassium Halide Crystals
Authors: Kokott Ch. , Fischer F.
Published: July 2007

O−−, S−−, Se−−, and Te− ions dissolved in potassium halides form electric dipoles by association with an anionic vacancy. Reorientation stops below characteristic temperatures. They are measured by TSD (ITC) techniques. Crystals, not optimally quenched, can have additional TSD bands which are regarded as belonging to dipole‐impurity associates. Measured activation energies favour the chalcogen‐vacancy jump as the dominating relaxation mechanism at lower temperatures. Additional dielectric loss results above room temperature are compared with TSD data.
Free Exciton Energy Transfer in KrAu Sandwiches
Authors: Schwentner N. , Martens G. , Rudolf H. W.
Published: July 2007

The photoelectron yield of KrAu sandwiches caused by energy transfer of Kr excitions to the Au substrate is measured. The range for energy transfer of Kr excitons is determined from the dependence of the yield on the thickness of the Kr overlayer for several excitation energies within the n equals; 1, n′ equals; 1, and n equals; 2 exciton bands. The derived diffusion lenghts of free excitons depend strongly on the individual exciton state and increase monotonically with the exciton energy within one exciton band as well as to higher exciton states from 30 Å for the n equals; 1 up to 300 Å for the n equals; 2 excitons. The efficiency for electron emission due to exciton decay exceeds the usual photoelectron yield of Au by a factor of ten.
Temperature Dependence of the Isothermal Elastic Constants of Alkali Metals
Authors: Soma T. , Kagaya S. , Matsuo H.
Published: July 2007

The temperature dependence of the isothermal elastic constants of alkali metals are calculated using second order perturbation theory and the local Heine‐Abarenkov model potential. The theoretical results are in quantitatively good agreement with available experimental data. The, the qualitative temperature dependence of elastic constants in the dynamical treatment using the expression for the temperature dependent two‐body interactions is obtained.
On the Pseudopotential Calculation from First Principles
Authors: Altshuler A. , Bezryadin S. N. , Kh. Vekilov Yu. , Verner V. D.
Published: July 2007

The dependence of the pseudopotential of free ions on the ion core electron structure approximation and on the description of the exchange and correlation scattering and pseudopotential nonlocality are discussed. An analysis is made of the Phillips‐Kleinman method. The formfactors for 17 elements are calculated. The problem of the pseudopotential ambiguity is discussed on the basis of the Hartree‐Fock Hamiltonian with nonorthogonal one‐particle wave functions. It is shown that in the weak bond approximation the effective potential is unambiguous.
Specific Heat of Ar‐Xe Solid Solutions at Low Temperatures
Authors: Tiwari M. D.
Published: July 2007

The measured specific heat of argon with solid solutions of xenon containing 5.01 and 10.88 at% Xe are analyzed on the basis of low concentration Green's function theory. Maxima are observed at about 4 K in the relative variation ΔC(T)/C(T) of the solid mixture. The maxima are related to the appearance, in the solid mixture phonon spectrum, of quasilocal oscillations due to introduction of heavy Xe impurity atoms into the Ar lattice. The changes in mass at the impurity site as well as changes in the closest‐neighbour force constants are taken into account in performing the computations. The force constants for the interaction between the impurity atom and its nearest neighbours are larger than the atomic interaction constants in the initial lattice. For the Ar‐10.88 at% Xe system the low‐concentration theory is modified. Reasonably good agreement with the experimental data is obtained.
Model of the Excitonic Surface Layer in Normal Incidence Reflection
Authors: Stahl A.
Published: July 2007

A pair of semiclassical wave equations describing exciton polaritons of Wannier type is set up and solved for half‐space geometry under certain simplifying assumptions. The main results are: (i) the polarization as a function of the distance from the boundary; (ii) an energy dependence of the depth of the transition region; (iii) evidence for a possibly non‐monotonous behaviour of the polarization near the boundary if the frequency is above resonance; (iv) reflection curves that for certain parameter sets give spikes for ω > ωL.
Paraelastic Alignment and Electric Dipole Relaxation Behavior of Off‐Center Ag+ Defects in RbI
Authors: Jimenez R. V. , Lüty F. , Siu Li M. , De Souza M.
Published: July 2007

Substitutional Ag+ defects are investigated for the first time in RbI host material. The absorption spectrum of isolated defects – obtainable only after quenching and rapid cooling of the crystals – consists of three UV absorption bands at 4.81, 4.94, and 5.13 eV. Uniaxial stress application produces characteristic increases or decreases of these absorptions for 〈111〉 and 〈110〉 stress, due to elastic dipole alignment following a Curie (1/T) law, while dichroism is absent under 〈100〉 stress. This stress alignment is possible only above 27 K demonstrating freezing‐in of dipole reorientation below this temperature. In agreement with this, ITC measurements show a peak of the depolarization current at 23.4 K, yielding an activation energy for reorientation of 53 meV and an electric dipole moment of 0.64 eÅ. For interpretation of the elasto‐optical data, two models involving pure T2g elastic dipole reorientation are dipole reorientation are discussed: the normal 〈111〉 dipole model, and a restricted 〈110〉 dipole model, in which strong and immobile Eg distortions allow dipole reorientation only among four orientational states in a (100) plane. It is shown that both models cannot be distinguished in the linear range of the elasto‐optical effect and that both can be fitted well to the observed data. Several arguments, however, favor the 〈111〉 model with deep off‐center wells of Ag+ in RbI.
Stimulated resonant Raman scattering of light in anthracene crystals
Authors: Maksimov A. A. , Tartakovskii I. I.
Published: July 2007

The investigation of stimulated resonant Raman scattering of light (SRRS) is carried out on thin plane‐parallel anthracene crystals (d = 2 to 45 μm) at low temperatures (T = 1.5 to 40 K). The resonance excitation at the bottom of the lowest exciton band is produced by a pulsed tunable dye laser. It is shown that under resonance excitation at optical pumping levels P ≈︁ 3 MW/cm2 up to nine SRRS Stokes components of intramolecular vibrations 395, 1167, and 1402 cm−1, are observed, the three Stokes components of 1402 cm−1 vibrations being the most intensive ones. Characteristic dependences of the intensity of SRRS Stokes components on pumping level and crystal tempe ature for different exciting frequencies are obtained. An anomalous intensity increase of the 49 cm−1 RS Stokes component is found attributed to RS on nonequilibrium phonons of the lowest optical branch. The results of the measurements are compared with the data on spontaneous resonant RS of light in anthracene crystals.
The influence of a magnetic field on the ground and excited states of bound exciton complexes in ZnO
Authors: Blattner G. , Klingshirn C. , Helbig R. , Meinl R.
Published: July 2007

The Zeeman splittings of those luminescence and absorption lines of ZnO are investigated which are due to excitons bound to impurities. Additionally the thermalization of the Zeeman components is studied. The results are discussed in terms of excitons bound to neutral donors and acceptors. The g‐values for the different lines are determined and discussed. Excited states of the complexes, which are investigated by means of excitation spectroscopy, are identified by their magnetic field behaviour, as being due to a hole from a deeper valence band and excited states of the envelope function.
Optical properties of the surface plasmon of n+ silicon
Authors: Robusto P. F. , Braunstein R.
Published: July 2007

The optical properties of the surface plasmon of n+ silicon are determined by a least‐squares curve fit of the Drude intraband model to the ATR reflection spectra. The surface plasmon resonance of n+ silicon is highly damped ( ωpτ = 2.69), and causes the ATR dispersion curve calculated on the real frequency axis to exhibit back‐bending for its complex frequency‐like solutions; whereas the theoretical dispersion curve exhibits the standard wave vector divergence at the surface plasmon frequency. This discrepancy is rectified by converting the optical properties of n+ silicon into functions of complex frequency, and using them to calculate the ATR dispersion curve in the complex frequency plane. A comparison of the Drude dielectric function as a function of real and complex frequencies is analyzed. The comparison shows that the difference between their values is small at high frequencies and deviate the largest in the region near the surface plasmon resonance.
Investigations on a two‐valence band model for Sb2Te3
Authors: Simon G. , Eichler W.
Published: July 2007

A two‐valence band model with a single‐and six‐valley structure is developed for the interpretation of galvanomagnetic effects in p‐type mixed crystals of the system (BixSb1−x)2Te3(0 ≦ x ≦ 1), especially for x = 0 under the assumption of a purely anisotropic scattering in each band, neglecting interband and intervalley scattering. This model, refering to results from Shubnikov‐de Haas investigations on Sb2Te3 at 4 K, is tested with galvanomagnetic data of undoped Sb2Te3 in the temperature region 100 K ≦ T ≦ 360 K. It is, however, not possible to fit such a two‐valence band model to these data sufficiently well due, possibly, of a more complicated scattering process of charge carriers.
Nuclear magnetic resonance in liquid InGa alloys
Authors: Ploumbidis D. , Böss E.
Published: July 2007

Measurements of the Knight shift of 115In and 71Ga in liquid InGa bulk samples are carried out as a function of temperature from 263 to 523 K and concentration from 0 to 100 at% Ga. It is shown that bulk and particle samples give, within the experimental error, the same Knight shift values. The results are compared with contradictory experimental data in the literature, and it is found that they agree with those of one of the earlier authors. A further important result based on these measurements extended over a broad temperature range is the determination of the temperature coefficient of the Knight shift of both isotopes 115In and 71Ga as a function of concentration. The 115In temperature coefficient decreases with increasing Ga concentration whereas the 71Ga one remains almost constant over the entire concentration range. Comparisons between the experimental and the theoretical results show satisfactory agreement in some cases but strong discrepancies in others.
Boltzmann equation and force–force correlation function for electrical resistivity
Authors: Sorbello R. S.
Published: July 2007

The frequency‐dependent electrical resistivity is investigated through the Boltzmann equation and the Kubo formalism in the low‐frequency weak‐scattering regime where the Boltzmann equation is known to be valid. A commonly used force‐force correlation‐function formula for dc resistivity is shown to be derivable from the Boltzmann equation as well as from the Kubo formalism. The derivation assumes that expansions used in the ωτ ≫ I regime for the “memory function” or for the inverse of the relaxation time τ are valid in the limit as the frequency ω goes to zero. This procedure and the correlation‐function formula are shown to give incorrect results even for the zero‐temperature case if the scattering is anisotropic, i.e., if τ varies over the Fermi surface. Thus the previous criticism of the force‐force correlation function is extended to the anisotropic scattering regime, and the direct connection between this function and the Boltzmann equation is shown.
Self‐trapping and hot luminescence of excitons in rare gas solids
Authors: Kink R. , Lôhmus A. , Selg M.
Published: July 2007

The mechanism of intrinsic luminescence of excitons in crystalline Xe and Ar is treated. The band at 9.7 eV in Ar is shown to be non‐elementary. The height of the exciton self‐trapping barrier in Ar is determined experimentally (ϵ = 3.5 meV). An experimental and theoretical study of hot luminescence of self‐trapping excitons in rare gas crystals is carried out. The contribution of hot luminescence to the total light sum increases in the series XeArNe.
Calculation of atomic relaxation near the (111) 1 × 1 surface of covalent semiconductors: Tight‐binding Green's function approach
Authors: Masuda K.
Published: July 2007

The atomic relaxations near the (111) 1 × 1 covalent semiconductor (C, Si, and Ge) surfaces are calculated using a tight‐binding Green's function approach and compared with the results of LEED experiments as well as those of other theoretical calculations. The present calculation takes into account the repulsive interaction energies between adjacent atomic sites and uses a total energy minimization procedure. It is shown that the change in the topmost interlayer spacing δ0 depends strongly on the material and subsurface relaxation is unimportant. The value of δ0 increases rapidly as going C(≈︁ 1%) → Si(≈︁ 5%) → Ge(≈︁ 13%). Simple physical interpretation for this behaviour is also given.
On the theory of resonance Raman scattering in heavily doped degenerate semiconductors
Authors: Quang Doan Nhat , Esser B. , Keiper R.
Published: July 2007

The influence of the random impurity potential on the dispersion of the one‐phonon resonance Raman scattering of a heavily doped p‐type degenerate semiconductor is investigated. It is proved that a local scattering amplitude representable by the difference of local dielectric functions may be introduced. The local coordinate dependence is due to the fluctuations of the impurity potentia. The resonance scattering cross‐section of the system is shown to be proportional to the modulus square of the difference of configurational averaged dielectric functions. The dispersion curve is dominated by the peaks occurring at the energy of the Burstein‐Moss shift in the real part of the dielectric function.
Study of the ghost phenomena in mathematical texture analysis by means of standard functions
Authors: Matthies S. , Wagner F.
Published: July 2007

Questions connected with ghost phenomena in reduced orientation distribution functions are studied with the help of the standard functions introduced recently into the mathematical texture analysis.
Quantum transport theory of impurity and electron‐electron scattering resistivity in n‐type semiconductors using the correlation function method
Authors: Röpke G. , Höhne F. E.
Published: July 2007

The quantum transport theory of electrical conductivity of a model system of electrons interacting with fixed ions should unify the usual theories of electrical conductivity of doped semiconductors, liquid metals, and dense ion plasmas. Starting from the method of nonequilibrium statistical operator, the conductivity is expressed by correlation functions which can be evaluated using the Green's function technique. Especially, the influence of electron‐electron scattering on the conductivity is considered. Results are given for arbitrary degree of degeneration and are compared with results obtained from the solution of the Boltzmann equation by standard methods.
Crystal growth, EPR, and luminescence of BaZnF4:Mn
Authors: Recker K. , Wallrafen F. , Büscher R. , Lehmann G.
Published: July 2007

Pure and doped crystals of BaZnF4, are grown in graphite crucibles using the Bridgman technique. EPR measurements at Q‐band show one center of Mn2+ with b = −301 ± 10; b = −185 ± 20 and A = −88.1 (all in units of 10−4 cm−1). The latter value indicates exclusive occupation of Zn sites. For the first time different values of the intrinsic ZFS splitting parameter \documentclass{article}\pagestyle{empty}\begin{document}$\overline {b_2 }$\end{document} for bridging and nonbridging F−ions are required for the superposition analysis, but both values are close to those for Mn‐F in other systems. For low energy excitations a second low energy emission band is observed. In accordance with previous results it can be explained by the large distortion of the [MnF2F4/2]2− units.
Far‐infrared reflectivity spectra of KH2PO4 between 300 and 400 K
Authors: Brehat F. , Wynckk B. , Hadni A.
Published: July 2007

The far‐infrared reflectivity spectra of a KDP single crystal in the temperature range 300 to 400 K are explained in terms of six lattice modes predicted by group theory and two extra modes: i) for E ‖ c, a lattice mode (ω = 183 cm−1) is coupled to an overdamped extra‐mode (ω1 = 76.5 cm−1), ii) for E ⟂ c, five lattice modes and an overda mped extra mode without any coupling, are needed tolexplain the reflectivity data. The extra‐modes ω1 = 76.5 cm−1 (B2) and Ω1 = 65 cm−1 (E) are probably the proton tunneling modes.
Electron momentum distribution and charge transfer study of FeAl, CoAl, and NiAl
Authors: Manninen S. , Sharma B. K. , Paakkari T. , Rundqvist S. , Richardson M. W.
Published: July 2007

Charge transfer and electron momentum distribution of transition metal alloys FeAl, CoAl, and NiAl are studied using the γ‐ray Compton scattering technique. The results support the model where the charge transfer takes place from aluminium to the transition metal. A proper solid state calculation is, however, required in order to explain the details of the electronic properties of these alloys.
Some peculiarities of the temperature dependence of the electronic conductivity in charge‐ordered crystals
Authors: Manakova L. A. , Zemskov B. G. , Ionov S. P.
Published: July 2007

A system of localized electrons capable of passing into the charge‐ordered state is found to modify substantially the properties of crystals. In the calculations the finite compressibility of the crystals is taken into account. The lattice parameters are shown to vary under definite conditions, giving rise to a temperature dependence of the electron conductivity differing from that observed in metals. For properly chosen compounds this effect can amount to tens of percents.
LO‐Phonon‐Plasmon Dispersion in GaAs Hydrodynamical Theory and Experimental Results
Authors: Nowak U. , Richter W. , Sachs G.
Published: July 2007

Measurements of the LO‐phonon‐plasmon dispersion in GaAs epitaxial samples are performed in the wave vector range K ≈︁ 0 to 106 cm−1, by using VIS, IR Raman scattering, and FIR reflectivity. For analysis the simple hydrodynamical theory for the free carrier electric susceptibility is used. Good agreement with the experimental data is obtained.
Double Spin Flips in Nuclear Double Resonance Calculated Cross‐Relaxation Rates for the Alkali Halide Structure
Authors: Whitaker M. A. B.
Published: July 2007

A general expression for the rate of double spin flips in nuclear double resonance, produced in a previous paper, is evaluated for crystals of an alkali halide structure. A Gaussian approximation is used, and a number of lattice summations performed in order to obtain numerical answers for any given case. Reasonable agreement is found with the experimental values of Kunitomo and co‐workers. A statement by other workers concerning the location of the absolute maximum of the resonance is modified.