bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Simple Approach to the Energy of Bound Exciton Complexes
Authors: Loose P. , Wöhlecke M. 
Published: July 2007

AbstractFrom some basic properties of excitons bound to ionized impurities a rough estimate and an approximation is obtained of the energy of the complex. Especially the upper limit of the estimate reflects the available experimental data quite well. The critical σ = me/mh value, above which the complex becomes unstable, is found to be 0.462 ≦ σc ≦ 0.576. For the region σ ≦ 1 we compute both upper and lower limits and an approximation of the energy of excitons bound to neutral impurities. From the limiting cases σ → 0, ∞ the forbidden region 2.1 ≦ σF ≦ 12 is obtained where the upper value is certainly too large.
Determination of the Conduction Band Effective Masses of the Germanium—Silicon Alloy by Infrared Cyclotron Resonance
Authors: Fink D. , Braunsteih R. 
Published: July 2007

AbstractCyclotron resonance measurements have been performed on the conduction bands of germanium‐silicon alloys at 891 GHz (337 pm) using an infrared laser. This has enabled measurement of the longitudinal and transverse effective masses to within 4 at% of each side of the alloy composition at which the conduction band edge switches from the [111] to the [100] direction (15 at% Si in Ge). The masses do not appear to change from their values in the pure constituents, although only the transverse mass of the [111], Ge‐like, minimum was measured with good accuracy. Within 3 at% of the switch‐over concentration, intervalley scattering becomes predominant; throughout the rest of the alloy system, disorder scattering predominates and the scattering frequency obeys an x(1 − x) law.
Quantum Theory of Rosette‐Motion Channeling
Authors: Tamtura A. , Kawamura T. 
Published: July 2007

AbstractA previous quantum theoretical study of rosette‐motion channeling is developed assuming a realistic string potential of a Coulombic form and using a proper boundary condition. The quantization of channeling electrons is performed on the basis of a certain hypothetical, two‐dimensional atom model. Wave functions of bound states around a string and their excitation probabilities are calculated in analytical forms. The calculated channeling profiles agree fairly well with experimental ones.
Anwendung gruppentheoretischer Methoden zur Lösung des Grundgleichungssystems der elastischen Elektronenstreuung in Einkristallen (Si)
Authors: Hansen‐Schmidt J. 
Published: July 2007

AbstractDas Grundgleichungssystem der dynamischen Theorie der Elektronenstreuung wird mit Hilfe von Projektionsoperatoren in einer der Symmetrie des Problems angepaßten Art in zwei Spezialfällen (Primärstrahl in [lll]‐Richtung, Anregung des symmetrischen 6‐Strahlfalls) formuliert und exakt gelöst.
The Influence of the Electron–Hole Exchange Interaction on the Biexciton Ground State in CuCl and CuBr and Related Optical Transitions
Authors: Ekardt W. , Sheboul M. I. 
Published: July 2007

AbstractThe influence of the electron‐hole exchange interaction on the biexciton ground state is recalculated. Due to the analytical and nonanalytical parts of the electron‐hole exchange interaction of the single exciton there exist two analytical parts. Both can be quite different in the order of magnitude. General formulas for s‐type states in cubic crystals are derived and numerical results for the ground states in CuCl and CuBr are given. Finally the results are compared with experimental data.
Effect of Damping on the Plasmon‐Phonon Coupling in CdS and Gap
Authors: Giehler M. , Jahne E. 
Published: July 2007

AbstractThe influence of dampings of the free carrier motion and polar lattice vibration on the coupled plasmon‐phonon states is studied both semi‐phenomenologically and experimentally. It turns out that the correct frequencies and damping rates of the normal modes are the roots of the dielectric function ε(ω) for complex ‐values and the dielectric function takes a factorized form. Scattering of the free carriers mainly counteracts the well known coupling mechanism by the electric fields of the two subsystems, and reduces the forbidden frequency gap. Infrared reflection spectra of differently doped CdS and GaP samples and Raman spectra of GaP are analyzed by fitting the optical spectra end calculating the complex roots of ε(). The analysis shows that the shifts of the normal mode frequencies due to the high scattering rates of free carriers in these materials is beyond the limits of experimental error and that the effect of coupling is completely suppressed in heavily doped Gap. An overall fit of the reflection spectra with a frequency‐independent free carrier damping rate fails in the frequency region of the coupled plasmon‐Phonon modes and at frequencies below them.
Cation Distribution and Magnetic Exchange Interactions in MgFe2O4 Studied by the Mössbauer Effect
Authors: De Grave E. , Dauwe C. , Govaert A. , De Sitter J. 
Published: July 2007

AbstractThe quenching temperature dependence of the magnetic hyperfine fields at the Fe57 nucleus in magnesium ferrite has been investigated by the Mössbauer effect technique. Since the outer absorption lines are broad and asymmetric, the average magnetic hyperfine field is calculated from the two most inner lines. Using a molecular field model and an equilibrium distribution law and taking into account the difference in covalency for the A‐ and B‐site Fe3+ ions, reliable results are obtained concerning the magnetic exchange interactions and the ionic distribution in MgFe2O4.
Electroreflectance and Wavelength Modulation Study of the Direct and Indirect Fundamental Transition Region of In1−xGaxP
Authors: Lange H. , Donecker J. , Friedrich H. 
Published: July 2007

AbstractThe direct Eo, Eo + Δo and indirect EΓ−X transition energies of In1−xGaxP crystals are studied by electromodulation and wavelength modulation methods at 77 K and room temperature. The Eo energy at 77 K and room temperature obeys a parabolic relation as a function of composition x with a bowing parameter of b = 0.764 and 0.76 eV, respectively. The EΓ−X energy at 77 K can be expressed by a linear x‐dependence with slope 0.072 eV. The crossover point at 77 K is determined as xc = 0.72 ± 0.015; Ec = (2.300 − 0.003) eV. The spin‐orbit splitting Δo shows an upward bowing with bowing parameter −0.060 eV.
Frequency‐Dependent Exchange Correction to the Dielectric Function of the Electron Gas
Authors: Brosens F. , Lemmens L. F. , Devreese J. T. 
Published: July 2007

AbstractThe equation of motion of the Wigner distribution function in the homogeneous electron gas is decoupled using the Hartree‐Fock prescription. After linearization, the variational procedure, used by Rajagopal and Jain and by Langreth is applied. The transverse and the longitudinal dielectric functions in the Hartree‐Fock approximation are derived, and the consistency of the equations for the charge density and the current density is examined. Several limits are calculated. The slope of the plasmon mode is substantially lowered by the exchange interactions, and the damped acoustic mode disappears for the densities that give a negative bulk modulus in the Hartree‐Fock approximation. The exchange interaction only slightly influences the dispersion of the transverse collective modes.
Über die Berechnung des elektrostatischen Potentials in Kristallgittern: I. Grundlagen der Berechnungsmethode
Authors: Matthies S. 
Published: July 2007

AbstractEine Methode zur Berechnung des elektrostatischen Potentials in Gittern punktförmiger Multipole wird vorgeschlagen. Die Grundformeln der Berechnungsmethode werden abgeleitet. Die Methode benutzt Größen vom Typ eines Formfaktors der Basis der Elementarzelle und bestimmte Gittersummen über die einfachen Bravaisgitter, die, wenn sie in tabellarisierter Form vorliegen, die Berechnung des Potentials mit vorgegebener Genauigkeit merklich vereinfachen.
A New Approach to Exciton‐Phonon Interaction and Some Consequences
Authors: Kapor D. V. , Stojanović S. D. , Čkrinjar M. J. , Tošić B. S. 
Published: July 2007

AbstractIn the present paper a new definition of the exciton‐phonon interaction is given, whose basic idea is that even the exciton operators are expanded in molecular displacements. The interaction Hamiltonian defined in this way gives the value of Urbach's coefficient which is in good agreement with the experimentally measured values. Another good agreement between theory and experiment is obtained if this new approach to the exciton‐phonon interaction is used in the calculationof the level shift and exciton absorption line broadening.
ESR Analysis of IIB‐IV‐V2 Semiconductors with Mn2+ as a Paramagnetic Probe
Authors: Kaufmann U. , Räuber A. , Schneider J. 
Published: July 2007

AbstractThe electron spin resonance spectra of Mn2+ impurities in the chalcopyrite semiconductors ZnSiP2, CdSiP2, and ZnSiAs2, have been analysed. These impurities are used as a paramagnetic probe to demonstrate the magnetic non‐equivalence of the two group IIB sites in the unit cell of a IIB‐IV‐V2 compound. The 55Mn2+ hyperfine constants A observed here are very close to those in the binary analogs GaAs and GaP indicating that bond ionicities in both classes of semiconductors are quite similar. The ESR line widths of Mn2+ in the ternary compounds are considerably smaller than those in GaP and GaAs and anion ligand hyperfine structure is resolved. These results suggest that cation ligand hyperfine interaction and/or strains are an important ESR line broadening mechanism in III‐V semiconductors.
Mean‐Square Displacements for NH4Cl and ND4Cl Crystals
Authors: Kurittu J. , Merisalo M. 
Published: July 2007

AbstractThe mean‐square displacements for NH4Cl and ND4Cl crystals at various temperatures between 85 K and 165 K have been calculated from the eigenfrequencies and eigenvectors of the phonon states as obtained from a rigid ion‐rigid molecule model of lattice dynamics, and from the internal vibrations of ammonium ions. The calculated results are discussed in relation to available experimental data.
Mössbauer Effect and Raman Studies of the Structural Phase Transitions in K2[SnCl6]
Authors: Winter J. , Rössler K. , Bolz J. , Pelzl J. 
Published: July 2007

AbstractThe 110Sn Mössbauer spectrum and the Raman phonons in polycrystalline samples of K2[SnCl5] have been investigated in the temperature range from 4 and 150 K, respectively, to 300 K. With decreasing temperature a discontinuous increase of the halfwidth of the Sn‐Mössbauer line and a concommitant change in the isomeric shift are observed. The former is attributed to the appearance of a quadrupole splitting at the first order crystallographic transition at T1 = 262 K. The Raman spectrum of the low‐symmetry phase exhibits an external lattice mode located at 33 cm−1 at 150 K. It shows a pronounced softening following the relation ω(T) ∼ (T0 − T)1/2 where T0 is close to T1. Two models are discussed in which alternatively a zone centre and a zone boundary rotary mode is considered to drive the crystallographic transition.
The Critical Voltage Effect in Transmission Electron Microscopy: VI. Renormalized Perturbation Theory for the Treatment of Absorption
Authors: David M. , Gevers R. , Serneels R. 
Published: July 2007

AbstractFor a study of the critical voltage effect (CVE) with absorption, treating the latter as a perturbation, one has to apply degenerate perturbation theory to a non‐Hermitean perturbation. It is pointed out that the perturbation expansion may then become divergent under certain illumination conditions. A renormalization technique is developped to remove the divergence. The following conclusions result: In all centrosymmetric crystals where the CVE occurs, and in certain noncentrosymmetric ones, the dynamical matrix with absorption becomes degenerate at a voltage close to the usual CV and for two small misorientations which are symmetrical with respect to the exact Bragg orientation for the second order reflection. At the degeneracy the diagonalizing matrix is singular. Nevertheless the renormalized perturbation theory yields for the latter a simple and very accurate approximative expression which is valid even at the singularity.
Influence of Self‐Consistency on the Relaxation near a Vacancy or a Surface in Transition Metals
Authors: Allan G. , Lannoo M. 
Published: July 2007

AbstractIn the tight‐binding approximation a complete intra‐atomic screening of the charge is assumed to evaluate the self‐consistent potential near a defect in a transition metal. The importance of this potential on the relaxation near a defect is demonstrated. It can, for instance, invert the sign of the displacements for a nearly empty or full d band where the screening by the d electrons is less efficient. The agreement with the experimental results is notably improved for the vacancy formation volume of platinum.
The Tensor of the Drift Mobility of Electrons and Holes in the Anthracene‐1,3,5,‐Trinitrobenzene Charge Transfer Complex
Authors: Zboiński Z. 
Published: July 2007

AbstractThe mobilities of electrons and holes in differently orientated crystals of anthracene‐1,3,5‐trinitrobenzene are studied as a function of temperature over the range 275 to 355 K. The mobilities of both electrons and holes are found to increase linearly with temperature; the mobility of holes being markedly higher and its temperature dependence weaker than that of electrons. The most probable process for the migration of an excess electron occurs along infinite columns formed by donors and acceptors stacked alternatively plane to plane; the direction of the highest hole mobility deviates from that of electrons by an angle of about 33°.
On the Electronic Molecular Structure of the Organic Semiconductor Copper Phthalocyanine
Authors: Malter H. 
Published: July 2007

AbstractThe electronic eigenvalue problem of the molecule of copper phthalocyanine is approximated using the molecular orbital formalism. The symmetry of the molecule allows a group theoretical reduction of the secular equations and a classification of the eigenvalues and eigenfunction coefficients. The model statements are compared with the experimental molecular spectra in the vapour phase and in solution from the near UV to the near IR.
Crystal‐Field‐Induced Surface Anisotropy in Thin Magnetic Films
Authors: Duda A. 
Published: July 2007

AbstractThe general form of the spin Hamiltonian for the (001), (111), and (110) surfaces of cubic crystals is derived on the basis of symmetry requirements. The resulting angular dependence of the spin‐wave spectrum is considered. For rare‐earth ions, the surface anisotropy is shown to be related with the crystal field parameters.
Nucleation Phenomena in Electron‐Hole Drop Formation in Ge and Si: I. Nucleation Rates
Authors: Westervelt R. M. 
Published: July 2007

AbstractA general nucleation theory for liquids possessing finite lifetimes, specifically for the condensation of electron‐hole drops (EHD) from a gas of free excitons (FE), is presented. The theory is developed for both homogeneous and inhomogeneous nucleation in Ge and Si. In Part I explicit expressions are derived for the steady‐state rates of formation J+ and breakup J− of macroscopic EHD, and for the EHD size distribution in dynamic equilibrium. It is found that the FE‐EHD system above T ≈ 1.3 K in Ge is characterized by metastable states for which the equilibration time is extremely long. The expressions for J+ and J− yield two sharp excitation thresholds. In Part II these results are applied to quantitatively predict for EHD the metastable time behavior, a procedure for measuring the surface tension, the phase diagram, and the EHD radius as a function of temperature. In Part III experimental luminescence data are presented for Ge which support this theory and accurately determine the surface tension.
Deformation‐Induced Exciton Luminescence of Alkali Halide Crystals
Authors: Markova‐Osorgina I. A. , Shmurak S. Z. 
Published: July 2007

AbstractLuminescence due to deformation is found in ionic crystals coloured at 77 and 193 K and the spectral characteristics of the process are investigated. It is shown that the deformation is accompanied by electron and hole capture by moving dislocations. Electron recombination with impurity ions and VK centres results in impurity and autolocalized exciton luminescence, respectively. Hole transfer by dislocations gives rise to a change of the F‐stimulated luminescence after deformation. New previously unknown luminescence bands occurring seems to be associated with exciton recombination in the dislocation field.
Chemical Shifts in the K X‐Ray Absorption Discontinuity of Arsenic
Authors: Kondawar V. , Mande C. 
Published: July 2007

AbstractThe K X‐ray absorption discontinuity of arsenic has been studied in the pure element and in several transition metal arsenides. It is observed that the discontinuity shifts towards the low energy side in the arsenides, indicating charge transfer from the metal to the arsenic atoms. The magnitudes |ΔE| of the shifts are found to be smaller than those observed for the arsenic discontinuity in some other compounds, where the arsenic atom is incorporated as a cation.
On the Pressure Dependence of Electron Transport in Noble Metals
Authors: Bansal O. P. 
Published: July 2007

AbstractFrom experiment, it is known that the logarithmic derivative of the electron‐phonon interaction parameter K with volume V is negative for the noble metals. A previous interpretation of this anomalous behaviour is based on the assumption that the Fermi surface distortions increase with increasing pressure. An alternative simpler explanation is presented in terms of the properties of the pseudopotential form factors.
Low‐Lying Collective Electronic Excitations in Semiconducting Charge‐Ordered Crystals
Authors: Lubimov V. S. , Ionova G. V. , Pachev O. M. , Manakova L. A. , Makarov E. F. , Ionov S. P. 
Published: July 2007

AbstractThe properties of the excited states of a charge‐ordered crystal with arbitrary band width are analysed. It is shown that the collective excitations in such systems are within the energy gap of the one‐particle spectrum, if the intra‐site electron correlation corresponds to the attraction and prevails over the inter‐site repulsion. For two kinds of collective excitations, the dispersion relations are found and the lower spectral boundaries are determined.
Magnetization and Susceptibility in the Truncated Anderson Model
Authors: Debnath G. , Rudra P. 
Published: July 2007

AbstractThermodynamic Green's functional method is used to obtain the expression for the spin polarization of the conduction electrons and the d‐electrons in the presence of an external magnetic field for systems described by the truncated Anderson Hamiltonian. The behaviour of the susceptibilities χc and χd at low and high temperatures is determined.
The Initial Susceptibility of Cobalt after Electron Irradiation at 4.2 K
Authors: Schaefer H. E. , Dander W. 
Published: July 2007

AbstractAfter electron irradiation at 4.2 K the initial ferromagnetic susceptibility of cobalt shows a marked decrease (“susceptibility dip”) of about 50% when the specimen is annealed between 20 and 30 K and regains its initial value in recovery stage Ic of the electrical resistivity between 40 and 50 K. Similar, yet smaller “susceptibility dips” are observed at 5, 55, 70, and 150 K. The 30 K decrease of the initial susceptibility is tentatively ascribed to the pinning of domain walls by interstitial atoms of hexagonal symmetry in the [0001]‐dumbbell configuration which, however, may be stable only under the influence of close Frenkel pairs in their neighbourhood. This model is in good agreement with simultaneous electrical resistivity and magnetic after‐effect measurements reported elsewhere which indicate that the anisotropy axis of the freely migrating interstitial atom has a component parallel to the basal plane.
Quantitative Analysis of Interference Structures in the Transmission Spectrum of Very Thin CdS Platelets
Authors: Voigt J. , Senoner M. , Rückmann I. 
Published: July 2007

AbstractA quantitative analysis is given of interference structures appearing in very thin CdS single crystals of high perfection at 1.8K on both sides of the A ground‐state exciton. It is shown that the structures are due to Fabry‐Perot interferences of polaritons of the lower and upper branch, respectively. From the analysis of the interferences the energy of the transversal exciton is determined with high precision to be Et = 2.5528 eV, shifted from the transmission minimum by 0.8 meV in the low energy direction. This is to be expected in the polariton model.
Mössbauer Spectrum near the Critical Point
Authors: Selyutin G. Ya. 
Published: July 2007

AbstractIt is shown theoretically that the exchange narrowing of the Mössbauer line is induced by the magnetic phase transition in crystals. The discontinuity of the shift, the intensity of the Mössbauer spectrum, and the spin correlation function 〈SiSj〉 near the critical point are determined.
Far‐Infrared Single Crystal Studies of TTF–TCNQ
Authors: Coleman L. B. , Fincher C. R. , Garito A. F. , Heeger A. J. 
Published: July 2007

AbstractPolarized and unpolarized far‐infrared (12 to 100 cm−1) reflectance data are presented for TTF‐TCNQ. The results confirm the existence of the energy gap, in the conducting state at 100 K, and in the dielectric regime at 4.2 K and provide a quantitative measure of the residual conductivity in the gap region. The data are discussed in terms of the Peierls‐Fröhlich model. Analysis of the results yields an estimate for the Frohlich mass of approximately 1500 times the band effective mass and a value for the pinning frequency in the dielectric regime, ωF ≈ 2 cm−1.
The Influence of the Hyperfine Range Magnetic Field on Charge Transfer States at the Metal–Organic Semiconductor Interface
Authors: Kaulach I. S. , Silinsh E. A. 
Published: July 2007

AbstractHyperfine range (HFR) magnetic field (H < 300 Oe) induced increase of photoconductivity and decrease of dark conductivity are observed in thin‐layer sandwich type Au‐tetrathiotetracene‐Al systems. The experimental results are interpreted in terms of HFR magnetic field influence on single‐triplet transition rate of charge transfer (CT) states at metal (Me)‐organic semiconductor (OS) interface in the framework of Merrifield's et al. hyperfine interaction model. It is suggested that in the case of photoconductivity, triplet 3CT states are initially formed by molecular triplet exciton dissociation at the Me‐OS interface, whereas in the case of dark conductivity, singlet 1CT states are initially formed in the process of non‐equilibrium hole injection from the Me electrode. The HFR magnetic field reduces the 1CT–3CT transition rate and is thus assumed to cause the observed increase of photo‐ and decrease of dark conductivity. The possible role of the inhomogeneous local magnetic field caused by the charge carriers trapped near the Me‐OS interface on the rate of 1CT–3CT transition is also briefly discussed.
Computation of the Two‐Centre Molecular Integrals Involved in the Exchange Interaction Between Ligand and Metal Electrons for the [VF6]4− Cluster in KMgF3
Authors: Emery J. , Fayet J. C. 
Published: July 2007

AbstractIn order to make an advance in the analysis of recent Spectroscopie studies on the [VF6]4− cluster the matrix elements are computed involved in the exchange interaction between the electrons of the metal and the electrons of the ligand, when a molecular orbital model is used. In comparison with [NiF6]4− and apart differences arising from different electronic configuration, the widely spread atomic orbitals of V2+ result in a noticeably larger interaction.