bluuebunny/crossref_metadata_2025_split huggingface dataset:
Resonant Secondary Emission Spectroscopy
Authors: Kanehisa A. , Balkanski M. 
Published: July 2007

AbstractA prospective view is taken of a new field of optical spectroscopy, unifying resonance Raman scattering and luminescence, with main emphasis on conceptual and theoretical aspects. The method consists in explicitly exploiting two independent sets of probes, (e, ω, k) and (e′, ω′, k′), i. e. polarization, frequency, and wave vector of incident and scattered photons, respectively. As compared with absorption spectroscopy, where one has only one set of probes (e, ω, k), the secondary emission spectroscopy gives higher information about the dynamics of the material: interaction in the intermediate states or relaxation, characterized experimentally and theoretically by the secondary emission intensity Is(e, ω, k; e′, ω′, k′), which is a measure of polarization‐, energy‐, and momentum‐correlation of incident and scattered photons.
Spectroellipsometric Investigation of PbI2 Single Crystals
Authors: Ghiţă C. , Ghiţă L. , Baltog I. , Constantinescu M. 
Published: July 2007

AbstractThe complex dielectric and optical constants of PbI2 single crystals are determined in the spectral range 240 to 630 nm by ellipsometric measurements for the first time. The calculated derivatives of the dielectric functions with respect to energy are consistent with the energy band structure of PbI2 reported in the literature.
Estimation of Covalency Effects in the Optical Spectra of Crystals Containing Iron Group Ions (I)
Authors: Kustov E. F. , Uskova L. I. 
Published: July 2007

AbstractIn the limits of a semi‐empirical theory, the influence of covalency effects on the optical spectra of crystals, containing iron group ions is investigated. The general matrices for the calculation of these effects are derived, taking into consideration the configurations of central ion and ligand electrons. Using the unitary group method, ML6, cluster states and states of tensor operators of single and double electron interactions are classified.
Detrapping of Charge Carriers by Singlet Excitons in Naphthalene Single Crystals
Authors: Nakagawa K. , Kotani M. , Tanaka H. 
Published: July 2007

AbstractThe detrapping of charge carriers by singlet excitons in naphthalene crystals is investigated at 300 K. Singlet excitons are generated homogeneously in the bulk of the crystal by two‐photon absorption and the detrapped charges ere observed as pulsed photocurrent. From the wave form and the effect of the pulse to pulse interval the amount and the spatial distribution of trapped, as well as detrapped, charges are determined. The bimolecular rate constant for the detrapping is found to be (8 ± 6) × 10−10 cm3 s−l. The result indicates that, in naphthalene crystal, the probability of the detrapping reaction is high, close to the diffusion limit, whereas that of the singlet‐singlet annihilation is lower.
Acceptor Pair‐Bound Exciton Complexes in Semiconductors
Authors: Molva E. , Magna N. 
Published: July 2007

AbstractThe evolution of the principal bound exciton (PBE) line, for bound exciton‐neutral acceptor(s) complex(es), between low (≦ 1016 cm−3) and high (>1017cm−3 acceptor concentrations in semiconductors, is studied. Photoluminescence experiments are performed in ZnTe, for the five wellknown acceptors Li, Na, Ag, Cu, Au and for several doping levels. High concentrations provide an asymmetric broadening with undulations and a shift to lower energies of the PBE line. Semiempirical calculations are made for the neutral acceptor pair‐bound exciton complex. In ZnTe good agreement is obtained with experiment. The calculations demonstrate that the empirical relation ΔE(R) = E0, exp (−R/R0)3 is a good and simple analytical approximation of the bound exciton localization energy shift, when the exciton is bound on a neutral acceptor pair, with a pair separation R. These calculations permit to evaluate the energy shift of the PBE line maximum for acceptors in highly doped semiconductors.
Variational Treatment of Anisotropic Heisenberg Antiferromagnets
Authors: Figueiredo W. , Gitahy V. H. , Salinas S. R. 
Published: July 2007

AbstractA simplified version of Falk's variational treatment of the isotropic Heisenberg antiferromagnet is extended by taking into account both, exchange and single‐ion uniaxial and orthorhombic anisotropic interactions. Expressions are obtained for the low‐temperature canted‐paramagnetic phase boundary. For uniaxial anisotropies the expression is of the form Ã – B̃T3/2 – C̃T5/2 – …, and for orthorhombic anisotropies it is of the form \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \alpha \limits^ \sim $\end{document} – \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \beta \limits^ \sim $\end{document}T2 – …. The structure coefficients Ã, B̃, \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \alpha \limits^ \sim $\end{document}, and \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \beta \limits^ \sim $\end{document} agree with previous spin‐wave calculations.
Electronic Properties of Amorphous SixGe1−x:H Films
Authors: Hauschildt D. , Fischer R. , Fuhs W. 
Published: July 2007

AbstractAmorphous SixGe1−x:H films are prepared by decomposition of SiH4/GeH4 mixtures in a rf glow discharge. With increasing Ge‐content the optical gap as well as the energy and the half width of the luminescence peak decrease linearly. It is concluded that by admixture of Ge the tail state distribution becomes steeper and that the concentration of defects is considerably enhanced. Already small amounts of Ge lead to a drastic decrease of the photoconductivity (ημτ‐product).
Theory of Tunneling into Size‐Quantised Films with Application to Lead
Authors: Cottey A. A. 
Published: July 2007

AbstractElectrons tunneling through an oxide layer into a sufficiently thin metal or semiconductor film can resonate with the discrete “particle‐in‐a‐box” energy levels in the film. The theory of this effect is given in the case that the electrons couple with only one “standing Bloch wave”. It is possible to deduce from experiment five parameters of the relevant group of electrons. These are the energy, velocity, effective mass, surface scattering phase shift η, and dη/dk (𝒽𝓀 crystal momentum). Values of the energy, velocity, and phase shift for Pb are presented, deduced from experimental data of Jaklevie and Lambe, and an approximate value of the effective mass. (The value of phase shift published earlier by the present author is revised).
On the Statistical Distribution Functions of the Anharmonic Crystal
Authors: Olkhovskii† I. I. 
Published: July 2007

AbstractThe solution technique of the BBGKI equation set for symmetric distribution functions of equilibrium systems is considered. The solution of the integral equations of the first and second approximations with respect to temperature is demonstrated. The equations of state generalizing the corresponding equations in the thermodynamic perturbation theory are obtained. It is also shown that the major contribution to the equations is correlated with the distribution function coefficients which are independent of the distances between crystal lattice points. The coefficients dependent on the distance between the crystal lattice points, and giving appreciable corrections in the equations of state, are obtained.
Modified Fielek Schemes and Phonon Dispersion in Noble Metals
Authors: Agrawal R. M. , Rathore R. P. S. 
Published: July 2007

AbstractRelations for phonon dispersion in noble metals are derived on the basis of three simplified and improved Fielek schemes. These schemes assume the core‐core interaction to be central pairwise. First of these schemes assumes the interaction among the neighbouring d‐shells to be angular, while the second scheme describes these as purely radial. The third scheme incorporates the volume interactions in the Fielek scheme on the lines of the modified Bhatia scheme. First and second models are further made to incorporate the equilibrium condition on simple and realistic lines. The dispersion relation in noble metals predicted by these schemes are compared (a) mutually and (b) with the experimental data to arrive a t the conclusions regarding the nature and range of the interactions coupling the various constituents of the non‐simple metals, like noble metals.
Interband Absorption in the Coloured Intermetallic Compounds PdIn
Authors: Nomerovannaya L. V. , Kirillova M. M. , Shaikin A. B. 
Published: July 2007

AbstractThe refractive, 𝓃, and absorption, 𝓀, indexes of six intermetallic PdIn compounds are measured in the spectral range of 0.248 to 17 μm by Beattie's polarimetric method, the indium concentra‐tion being 42, 44, 46, 48, 50, and 52 at%. All the compounds are single crystals. It is shown that as the indium concentration increases from 42 to 52 at%, the interband absorption peaks found at 0.15 to 0.17, 0.6 to 0.7, 2.2 to 2.65, and 2.6 to 3.2 eV shift towards lower energies, while that at 4.6 eV does not change its position with temperature and indium concentration. Comparison of the high‐frequency conductivity σ(ω) dispersion and the energy bands of equiatomic β′‐PdIn shows that the interband absorption at 𝒽ω < 3 eV is caused by the electronic transitions from the Fermi level to vacant sp conductive states. The value of the spin‐orbit band splitting along the T‐direction of the Brillouin zone is estimated to be 0.15 to 0.17 eV.
The Influence of the Environment of the Absorbing Atom on the Photoelectric Yield Spectra of Beryllium Compounds in the Soft X‐Ray Region
Authors: Blokhin M. A. , Orlova E. G. , Schweitzer I. G. 
Published: July 2007

AbstractThe photoelectric yield spectra (PYS) of beryllium compounds are investigated experimentally. The BeK absorption edge energy position is shown to be affected by the composition not only of the first coordination sphere, but also of the second one. It is found, that the fine structure of the BeK PYS of beryllium fluoride, hydroxide, and acetate is determined by the first coordination sphere and can be interpreted on the basis of electronic structure calculations for the corresponding structure‐forming tetrahedra, taking into account their distortions in the real crystal lattice. An essential difference is revealed in the fine structure of the initial region of the BeK photoelectric yield spectra of the compounds Na2BeF4, K2BeF4, BeO, BeSO4 · 4 H2O, BeSiO3, and Be3(PO4)2 as compared with the spectra of BeF2, Be(OOCCH3)2 and Be(OH)2. This difference is displayed in the presence of a second line group at a distance of 4 to 5 eV from the first near‐the‐edge group and is due to a strong influence of the second coordination sphere atoms on the formation of fine structure near the beryllium K absorption edge.
Selection Rules and Absorption Lineshapes for Electron Transitions Between Minizones in a Superlattice
Authors: Dubrovskii G. B. , Belyavskii V. I. 
Published: July 2007

AbstractTheoretical analysis of the selection rules and absorption line shapes is presented for inter‐minizone transitions of electrons in a superlattice. Impurity absorption associated with electron transitions from the donor level is also considered. The results show good agreement with the experimental data on the optical absorption in SiC crystals known as natural electronic superlattices.
Simple Two‐Band s–d Model for Ferromagnetic Semiconductors with Hybridization. II. Further Development and Optical Properties
Authors: Szőcs V. , Čápek V. , Velický B. 
Published: July 2007

AbstractThe two‐band model of electronic states proposed previously for the conduction band of some types of ferromagnetic semiconductors like chromium chalkospinels is discussed and used to prove the significance of the higher order spin‐flip processes. On the basis of this model a simple valence‐to‐conduction band absorption is investigated at a level of the self‐consistent CPA. The inadequacy of such mechanism for the explanation of the absorption edge at least in CdCr2Se4 is shown. The lowest order mean‐field approach to the d‐states is illustrated to yield a spurious agreement with the experiment.
The Effect of Rare‐Earth Impurities on the Electronic Transition in Ce
Authors: Korshunov A. N. , Fedorov V. M. , Sharshakov I. M. , Grokhotov V. T. 
Published: July 2007

AbstractA model of the α‐γ transition in Ce1−xRx alloys where R is a rare earth is presented which is based on the Ramirez‐Falikov (RF) zone model. It is shown that the decrease in the temperature region of the α‐γ transition in cerium when impurities are added depends in particular on the spin degeneracy (2J + 1) of the impurity element ion. The amount of the impurity added affects the conditions under which the α‐γ transition of type I in pure Ce proves to be a transition of type II in Ce1−xRx alloys. A comparison with experimental results is given.
Isochromat and SXAPS Measurements on Hafnium, Tantalum, and Tungsten
Authors: Dose V. , Scheidt H. 
Published: July 2007

AbstractThe density of unoccupied states in the conduction band of hafnium, tantalum, and tungsten is measured employing soft X‐ray appearance potential (SXAPS) and bremsstrahlung‐isochromat spectroscopy (BIS). The MV core levels of Hf, Ta, and W with binding energies of 1662, 1735, and 1809 eV, respectively, are used for the SXAP measurements. Since the MV spectra of these elements exhibit rather poor signal to noise ratios, a novel self‐tuning SXAP spectrometer which provides the necessary stability for the required long term measurements, is employed. Isochromat spectra are taken using the very same SXAP spectrometer with an additional aluminium absorption foil in front of the X‐ray photodetector. As described previously this setup provides a BI‐spectrometer with a monochromator energy equal to the K‐absorption energy of 1560 eV of the aluminium foil. Experimentally obtained density of state (DOS) functions from BIS and deconvoluted SXAP spectra compare favourably with each other and with theoretical calculations.
Multiple Scattering in Disordered Materials III. Compact Representation of the Wave Number and Introduction of Local Currents
Authors: Lenk R. 
Published: July 2007

AbstractSome general conclusions are drawn from the basic mathematical structure of a theory developed in a preceding paper. Employing a proper normalization of the strength coefficients which are introduced there together with a reference function to get a general representation of the incident fields, these coefficients as well as the reference function get an enhanced physical meaning. With the normalized strength coefficients a compact representation for the wave number of the medium is derived. Especially the attenuation term Im k2 shows a close correspondence to the kinematic expression on the one hand and to the local loss currents, on the other hand. Via the introduction of these currents a deeper understanding of the loss mechanism and the possibility to analyse the angular distribution of these currents is achieved. The fields for a half‐space and a slab are determined. The results exhibit the shortcomings of a macroscopical‐optical analysis in the case of anisotropic scattering at single scatterers.
Theoretical Investigation of Current Amplitudes of Niobium–Lead Tunnel Junctions
Authors: Meyer H.‐G. , Seidel P. 
Published: July 2007

AbstractThe current amplitudes in Werthamer's general expression for the current in Josephson tunnel junctions are investigated with the help of the proximity‐effect model developed for superconducting niobium tunnel junctions. Numerical calculations of these amplitudes as functions of frequency and temperature are presented for different systems forming the proximity electrode. In agreement with experiments marked differences can be stated between the proximity model and the commonly used standard BCS model also in the ac properties of the tunnel junction.
57Fe Absorption and Emission Mössbauer Spectroscopy in Co (III) Acetylacetonate
Authors: Sanchez J. P. , Friedt J. M. , de Jesus Filho M. F. 
Published: July 2007

AbstractThe results of a comparative investigation of the electronic behavior of 57Fe impurities diluted in Co (III) acetylacetonate is reported for conditions in which these impurities are introduced either chemically or by 57Co electron capture decay. The 57Fe absorber experiments provide evidence for a ± 1/2 electronic ground state in this host. The 57Co source experiments show that a fraction of the EC decay products stabilizes as substitutional Fe3+ sites, while another part occupies defect sites both, as Fe3+ and aliovalent Fe2+ ions. The anomalous Fe3+ component does not reveal the expected paramagnetic relaxation effects. This behavior is attributed to the creation of paramagnetic radicals as a consequence of the self‐radiolysis associated with the Auger deexcitation. A comparative discussion of the after‐effects of the 57Co decay in different chemical environments is presented.
Isotropic EPR Spectra of Vanadium in Alkali Chlorides
Authors: Van Steen F. , Vanhaelst M. , Matthys P. , Boesman E. , Schoemaker D. 
Published: July 2007

AbstractSome new EPR spectra of alkali chloride containing vanadium are reported. The paramagnetic complex V2+–vacancy, which dominates in quenched crystals, decomposes under X and γ irradiation at room temperature (in NaCl and KCl) and under high uniaxial pressure (in KCl and RbCl). The study of the resulting isotropic EPR spectra proves that the new paramagnetic centre consists of a V2+ ion in a cubic environment. The conversion under pressure is due to running dislocations, which absorb the charge compensating vacancy. With X irradiation, the conversion is one order faster in KCl than in NaCl.
Virtual Surface States of Thin Films
Authors: Jerrard R. J. , Ueba H. , Davison S. G. 
Published: July 2007

AbstractThe surface Green function for a two‐interface system, obtained by the factorization method, is used to study the virtual surface states, which arise when a linear field is applied to a semiconductor thin film. The energies of the surface states are evaluated as a function of the film thickness. The surface density‐of‐states calculation gives a means of distinguishing the surface states according to the surface on which they are localised. It is also shown that the interaction between the states restricts their existence to certain regions of the energy gap.
Anisotropy of Exciton Polaritons and Polariton–Phonon Interaction in 2H‐PbI2 Crystals I. Structure of the Fundamental Excitonic Emission
Authors: Biellmann J. , Meyer B. , Schwab C. 
Published: July 2007

AbstractA procedure is described which allows to prepare optical faces parallel to the c‐axis by processing bulk 2H‐PbI2 crystals grown from the melt. Its effectiveness is checked by a simultaneous investigation of the reflection and photoluminescence spectra, whose main features compare well to former results obtained on cleaved or natural faces.
IR Absorption and Raman Scattering Spectra in Mixed Cuprous Halides
Authors: Talwar D. N. , Vandevyver M. , Kunc K. , Zigone M. 
Published: July 2007

AbstractGreen's function theory for the low concentration of point defects is used to calculate the impurity induced ir absorption and Raman scattering spectra in mixed cuprous halides. The same perturbation parameters extracted from the impurity mode study provide reasonable correspondence to the Raman structure data in the band mode region recently observed by Murahashi et al. and Vardeny et al.
Propagation of Displacement Pulses in Harmonic Crystals
Authors: Czachor A. , Holas A. 
Published: July 2007

AbstractThe time evolution of the displacement field due to a localized initial pulse is calculated for a harmonic crystal. It is analyzed in detail for some simple phonon dispersion relations and for propagation in symmetric directions. The front of the pulse usually travels with sound velocity, except the case of a concave dispersion relation – the velocity is then different (higher). A “thought” experiment in which the dispersion relation may be determined from the analysis of the time profile of the arriving signal is considered.
Theory of the Static Atomic Displacements in Ordinary Metals with Isoelectronic Impurity Atoms
Authors: Zhernov A. P. , Mamedov T. A. 
Published: July 2007

AbstractUsing the many‐electron theory of metals an equation is obtained for the determination of the field of atomic displacements ζm for the case of an isoelectron impurity atom. Besides the force parameters of the first order, those of the second and the third orders are also explicitly regarded in relationship for the effective force Fm, determining the static distortions of the crystal lattice near the defect. The appropriate force parameters are found in an arbitrary order using the pseudopotential theory. Regarding those terms of Fm, proportional to the force parameters of the second and third order, is shown to significantly affect the ζm values for Rm ≫ a (a is the lattice parameter).
Investigation of the Dislocation Spin System in Silicon as Model of One‐Dimensional Spin Chains
Authors: Grazhulis V. A. , Kveder V. V. , Osipyan Yu. A. 
Published: July 2007

AbstractMagnetic properties of the dislocation dangling bond (DDB) spin system in silicon crystals are investigated by means of the EPR technique at T = (1.3 to 150) K. Experimental results are obtained which enable one to develop a one‐dimensional model of the spin system according to which the DDB chains are unstable with respect to the pairing of the neighbouring bonds (S = 1/2) to form singlet pairs (S = 0) at T ≦ 50 K, and, apart from that, possess a softened phonon spectrum. It is shown that both these peculiarities in the DDB chain properties can give rise to strong anomalies in the behaviour of the DDB‐EPR spectrum.
Peculiarities of an Electromotive Force Arising in a Semiconductor in a Non‐Homogeneous Magnetic Field (I)
Authors: Gulamov Sh. A. , Katulevskii Yu. A. , Muminov R. A. 
Published: July 2007

AbstractThe possibility of arising of both, longitudinal and transverse electromotive forces (e. m. f.) in a semiconductor placed only into a non‐homogeneous magnetic field is shown firstly. The appearance of the e. m. f. is due to the interaction of the spin and orbital magnetic moments of current carriers with an external non‐homogeneous magnetic field. The spatial distribution of current carriers, that of the electric field, and the expressions for the longitudinal and transverse e. m. f. are found by using the magnetohydrodynamical approximation.
Electroreflectance of InN Semimetallic Thin Films
Authors: Tyagai† V. A. , Snitko O. V. , Evstigneev A. M. , Krasiko A. N. 
Published: July 2007

AbstractPlasma electroreflectance spectra (1.2 to 2.2 eV) and the bias dependence of capacitance are presented for InN semimetallic (N ≈ 3 × 1020 cm−3) thin films. The interference patterns in the electroreflectance spectra are analysed and grouped into two types according to the form of the electroreflectance undulations. From capacitance measurements the Fermi energy is determined to EF = (0.4 ± 0.1) eV. The contribution of Friedel oscillations to the capacitance is also discussed.
Impurity Photoconductivity of γ‐Irradiated LiF
Authors: Lee R. S. , Merklin J. F. , Marrs C. D. , Richter M. H. 
Published: July 2007

AbstractThe photoconductivity and absorbance of three batches of γ‐irradiated LiF crystals with different impurity levels are measured. Impurity levels are determined by neutron activation analysis. In absorbance experiments using polarized light, dichroism with 〈110〉 symmetry is observed in the region of a shoulder on the low‐energy side of the F band. The shoulder occurs in the spectral region where a photoconductivity peak is observed. It is shown that the same defect center produces the shoulder and the photocurrent peak. The data indicate that the center responsible for the photoconductivity is the Fz1 center.