bluuebunny/crossref_metadata_2025_split huggingface dataset:
Zur Theorie der kooperativen Absorption (Emission) von Licht in Kristallen
Authors: Tulub A. V. , Patzer K. 
Published: July 2007

AbstractEs wird die Wahrscheinlichkeit für die Anregung von zwei Atomen durch ein Photon untersucht. Weiterhin wird die Wahrscheinlichkeit für die Energieübertragung von zwei Donatoren auf einen Akzeptor betrachtet, wobei sich die Anregungsenergien der Donatoren addieren. Durch Vergleich dieser Wahrscheinlichkeiten wird gezeigt, warum bisher die kooperative Emission experimentell nur in Anwesenheit eines Akzeptors beobachtet wurde. Der Einfluß der Kristallsymmetrie auf diese Prozesse wird berücksichtigt.
Die Magnetisierungsverteilung an der Stirnfläche zylindrischer Ferromagnetika mit Anwendungen auf die Keimbildung
Authors: Holz A. 
Published: July 2007

AbstractIn einer vorangehenden Arbeit [1] wurde dargelegt, daß der Ummagnetisierungsprozeß eines ferromagnetischen Zylinders an einer seiner Stirnflächen beginnt. Zur Berechnung der Magnetisierungsverteilung in der Umgebung der Stirnfläche wird ein für die numerische Rechnung geeignetes Verfahren entwickelt, das auf einer Diskretisierung des ferromagnetischen Kontinuums in geeignet gewählte Volumenelemente beruht. Für Fe werden für den Fall eines starken äußeren Magnetfeldes numerische Rechnungen durchgeführt. Sie ergeben große Radialauslenkungen der Magnetisierung für Probenradien größer als 1 μm sowie einen Vorzeichenwechsel der Radialauslenkung längs der Zylinderachse, welcher eine Erklärung für die in der Umgebung der Stirnfläche beobachteten Querbereiche sein könnte.
Optical Properties of α‐ and β‐TiCl3
Authors: Baldini G. , Pollini I. , Spinolo G. 
Published: July 2007

AbstractIn this paper the absorption spectra of α‐TiCl3 single crystals and α‐ and β‐TiCl3 vacuum deposited films are reported. The absorption of β‐TiCl3 films is measured from 1 up to 10 eV in the temperature range 55 to 400°K. The optical thickness of the growing film is continuously measured with interference methods. The refractive index at 7000 Å is found to be 1.85 ± 0.10. A tentative attribution of the various absorption peaks to corresponding optical transitions is made in terms of the excited states of the Ti3+ ion and of charge transfer from the Cl− ion to the Ti3+ ion.
Mössbauer Study of Hyperfine Fields in MnZn Ferritess
Authors: Cser L. , Dézsi I. , Gladkih I. , Keszthelyi L. , Kulgawczuk D. , Eissa N. A. , Sterk E. 
Published: July 2007

AbstractThe hyperfine field in Mn1−xZnx Fe2O4 ferrites is studied in dependence on x and temperature. A six‐nearest‐neighbours model used in evaluating the Mössbauer spectra leads to convex magnetization functions if the number of Zn nearest neighbours is > 3.
Hopping Recombination in Trigonal Selenium Single Crystals
Authors: Fuhs W. , Stuke J. 
Published: July 2007

AbstractThe decay of the photocurrent in trigonal selenium single crystals is investigated as a function of temperature, applied voltage, and simultaneous illumination with quenching light. At 90°K the photocurrent decays logarithmically with time. This behaviour is explained by the assumption that the recombination process is due to transitions of minority carriers, i. e. electrons, from traps to recombination centres. The decay rate is considerably enhanced when trapped minority carriers are raised to the conduction band: at higher temperature by thermal activation or at low temperature both by optical activation and by a strong electric field. Two kinds of electron traps are found, the optical activation energies of which exceed by far the thermal ones.
Stacking Faults in a Cu‐15 at% Al Alloy. I. The Short Range Order and Temperature Dependence of the Stacking Fault Energy
Authors: Tisone T. C. , Brittain J. O. , Meshii M. 
Published: July 2007

AbstractAn experimental study was made of the short range order (SRO) and temperature dependence of the stacking fault energy (SFE) for a Cu‐15 at% Al alloy using (110) single crystal foils. The SFE was determined using measurements form threefold nodes, intrinsicextrinsic fault pairs, and Frank triangles. Good quantitative agreement was obtained for the SFE determined form these three defects. A SRO dependence of the SFE was found by measuring the SFE form foils quenched from different annealing temperatures which are known to vary the degree of SRO [4]. A reversible temperature dependence of the SFE was found where the SFE increased with increasing temperature for both intrinsic and extrinsic faulting. The ratio of extrinsic to intrinsic fault energy was found to be 1.14 ± 0.08.
Direct Evidence for Dechanneling of 40 kV Gold Ions at Planar Defects in Silver and Gold
Authors: Schober T. , Balluffi R. W. 
Published: July 2007

AbstractThin single crystal sandwiches consisting of silver‐gold‐silver layers were prepared by epitaxial vapor deposition on (100) cleaved rocksalt. These specimens contained numerous (111) planar faults (coherent twins and stacking faults) extending through them at an angle of 54.7° with the surface. After bombardment along [100] with 40 ke V gold ions the middle gold layer was removed and examined by transmission electron microscopy. Zones free of radiation damage were found directly adjacent to the planar faults. These zones were a result of a shadowing effect caused by the defocusing of the incoming ions by the extensions of the planar defects into the upper silver layer (which were present during the bombardment). Evidence was also found for the production of excess defects directly at the planar defect surfaces in the gold layer due to dechanneling. The geometry of the blocking of [100] channels in a f.c.c. lattice by (111) planar faults is described.
Low‐Field Magnetoresistance and Magnetoconductivity in n‐Type Ge with Dislocations
Authors: van Weeren J. H. P. , Struikmans R. , Koopmans G. , Blok J. 
Published: July 2007

AbstractExpression are derived for specified magnetoresistance and magneto‐conductivity coefficients for n‐type Ge with an array of parallel dislocations. The obtained equations are compared with measurements at 77°K on plastically bent n‐type Ge. From the results we conclude that the electron mobility is not reduced by the dislocations for Ndisl. < 2 × 107 cm−2. The observed anisotropies in the conductivity can be attributed to the inhomogeneous distribution of the dislocations.
Phonons, Torsons, and Rotational Diffusion in Adamantane
Authors: Stockmeyer R. , Stiller H. 
Published: July 2007

AbstractThe results of neutron spectroscopic measurements on solid adamantane (C10H16) are compared to calculated frequency distributions for phonons, torsons and mixed modes in the adamantane lattice. The comparison suggests that rotational diffusion jumps are superimposed on librational motions (torsons) and vibrations of the molecular centres of masses (phonons).
The Theory of Low‐Field Oscillations of the Surface Impedance in Metals
Authors: Fischbeck H. J. , Mertsching J. 
Published: July 2007

AbstractMagnetic surface states on cylindrical parts of the Fermi surface and their relation to volume Landau states are discussed. The scattering of the surface states by a rough surface is calculated quantum mechanically, giving the classical scattering rate in a certain limiting case. Transitions between surface states give rise to small oscillations of the surface impedance, which are calculated for arbitrary orientations of the cylinder and the magnetic field, starting with the electric field distribution in the case of anomalous skin effect. The results are compared with experimental data in indium. More elaborate numerical calculations of the transition matrix elements and the surface scattering rate are required to determine the parameters of surface scattering unambiguously.
The Micromagnetic Equations of a Superconductor
Authors: Seeger A. , Kronmüller H. 
Published: July 2007

AbstractA general theory is developed for deformable superconductors containing both spontaneous strains due to the superconductivity and internal strains due to crystal defects. An intersection technique, involving five distinct states K, x′, x″, k′, and k, is employed to derive the micromagnetic equations of a superconductor (generalizations of the Ginsburg‐Landau equations) on the basis of finite strain theory.
Mechanism of Electrical Conduction in β‐FeSi2
Authors: Birkholz U. , Schelm J. 
Published: July 2007

AbstractElectrical conductivity, thermoelectric power and Hall coefficient of β‐FeSi2 doped with cobalt (n‐type) or aluminium (p‐type) are measured between 100 and 1200 °K. The conductivity of n‐FeSi2 follows an exponential dependence on temperature. The temperature dependence of the thermoelectric power cannot be interpreted on the basis of conduction in a band. With the assumption that conduction in n‐FeSi2 is caused by small polarons, the mobility at room temperature is found to be μn = 0.26 cm2/Vs. The activation energy of the mobility is 0.06 eV, the density of states N = 1.2 × 1022 cm−3. The electrical properties of p‐FeSi2 can be interpreted using the band model with a hole mobility μp ≈ 2 cm2/Vs, which varies as T−1/2 in the region of extrinsic conduction. From intrinsic conduction a band gap of 0.9 to 1.0 eV is deduced. The disappearance of the thermoelectric power at high temperature is related to the semiconductor‐to‐metal transition at 1200 °K.
Effect of Electron‐Lattice Interactions on the Spin‐Paramagnetism of Metals
Authors: Saxena V. K. , Bhattacharya D. L. 
Published: July 2007

AbstractThe effect of electron‐static‐lattice and electron‐phonon interactions on the spin‐paramagnetism of metals is studied with a Hellmantype pseudopotential as the electron‐ion interaction potential. Numerical calculations show that the electron–static‐lattice interaction produces an enhancement of about 10% in the spin‐susceptibility of sodium. Further it is found that the electron‐phonon contribution to the spin‐susceptibility is of the order of . This confirms the result of Migdal, and Quinn and Ferrell that the spin‐susceptibility of an electron gas in a metal is unaffected by the electron‐phonon interactions to order , by means of a straightforward calculation.
Diffusion of Free Excitons in Molecular Crystals
Authors: Agranovich V. M. , Konobeev Yu. V. 
Published: July 2007

AbstractA theoretical analysis of the temperature dependence of the free exciton diffusion coefficient is given. The methods of calculating the capture probability of an exciton by impurity traps are discussed in terms of the exciton mean free path, capture radius of an impurity molecule, and average separation of two impurity molecules. A comparison of the theory with the experiment is made.
Depth Distribution Measurements Using Bombardment‐Enhanced Solubility
Authors: Jech Č. 
Published: July 2007

AbstractA method is described which enables thin, uniform layers to be sectioned off from the surfaces of insulators and semiconductors. It is based on the formation of bombardment‐induced disorder in a layer of definite thickness by low‐energy ion bombardment and subsequent dissolving the disordered layer in a suitable solvent. The thickness of the layer thus removed after various times and conditions of ion bombardment is determined for silicon and mica using neutron activation analysis. The method is applied for determining the depth distribution of radon decay products injected by recoil from a planar radon source into mica.
Kinematic and Dynamic Interaction Between Elementary Excitations in Ferromagnetics with Spin S = 1/2
Authors: Tošić B. S. , Žakula R. B. 
Published: July 2007

AbstractThe magnon creation and annihilation operators satisfying the Pauli commutation relations in a ferromagnetic with spin S = 1/2 are expressed in terms of two various types of Fermi operators. The dispersion laws for fermions are obtained by twofold diagonalization of the Hamiltonian. Furthermore, these dispersion laws are used to calculate numerically the magnetization and specific heat of the magnon system. The present results are compared with those obtained by other methods as well as with experimental results.
Fine Structure Measurements in the Energy Angular Distribution of Secondary Electrons from a (110) Face of Copper
Authors: Appelt G. 
Published: July 2007

AbstractThe energy angular distribution of secondary electrons from a (110) face of copper in the (010) azimuth is measured by means of a dynamical method. The plots exhibit numerous fine structure maxima. It can be shown that the maxima corresponding to all theoretically possible directions of reciprocal lattice vectors up to the 46th order may be found in every measurement; taking the whole results, maxima corresponding to directions of reciprocal lattice vectors up to the 148th order may be detected continuously. The correlation of the maxima to the crystal structure yields experimental values of the refractive index which depends on the energy of the secondary but is independent of the energy of the primary electrons. By means of this refractive index it is possible to determine the energy band of excited states above the vacuum level in the (010) direction of the wave vector, except an integration constant.
Experiments on Fluctuations in Optically Quenched CdS and CdSe Crystals
Authors: Herczfeld P. R. , van Vliet K. M. , Pai M. D. 
Published: July 2007

AbstractMeasurements of electronic fluctuation spectra in CdS and CdSe crystals, irradiated by primary light, causing excitation, and infrared light, causing quenching, are reported. For the primary light in the tail absorption region, a marked effect is found. Even for moderate quenching, the noise often increases by an order of magnitude; moreover, a characteristic ω−5/2‐spectrum appears, as has not been observed in photoconductors hitherto. At low temperatures the relative variance is close to unity or even sub‐poissonian. At room temperature, thermal quenching presumably may enhance the noise, though in lesser degree than infrared quenching. In the fundamental absorption band, infrared quenching enhances the noise, but does not alter the spectral shape, which generally shows a diffusion behavior signified by an ω−3/2‐dependence. A qualitative discussion of these features is given. A quantitative description, particularly of the ω−5/2‐spectrum is referred to a subsequent article [3].
Electronic Processes and Fluctuations in Optically Quenched CdS and CdSe Crystals
Authors: Herczfeld P. R. , van Vliet K. M. 
Published: July 2007

AbstractA detailed analysis is given of the electronic fluctuations in a “five‐level” photoconductor, the “levels” being the conduction band, valence band. electron traps, shallow hole traps, and quenching centers. Two recombination paths are open to the electrons, viz. via the deep traps and via the quenching centers. It is assumed that the former process prevails at the surface and the latter mainly in the bulk. As a consequence fluctuations arise from diffusion to the surfaces, in addition to the effects of the electronic transitions. The various effective diffusion constants and lifetimes are complex. The resulting spectra are evaluated with the Green's function method and reveal ω−2‐, ω−5/2‐, and ω−3/2‐contributions. It is shown that the ω−5/2‐term disappears if there is no quenching, and that it is highly unlikely for this spectral dependence to appear in a more simple model than analyzed here. Surface recombination enhances the feasibility of the ω−5/2‐spectrum. The results, in as far as they can be analytically pursued, are in reasonable agreement with the previously described experimental data [1].
Production of Colloidal Calcium by Electron Irradiation of CaF2 Crystals
Authors: McLaughlan S. D. , Evans H. W. 
Published: July 2007

AbstractAfter irradiation with 75 keV electrons the optical absorption spectra of differently doped CaF2 crystals show an identical broad band peaking between 515 and 565 nm which is attributed to colloidal particles of calcium. Further evidence for the existence of a colloid is given by an ESR investigation. After irradiation most samples exhibit a narrow isotropic resonance g = 2.006 ± 0.001 which is thought to arise from conduction electron spin resonance in the particles of colloidal calcium.
Stress‐Induced Inhomogeneous Effects of the K‐Absorption in RbCl
Authors: Maier K. , Gebhardt W. 
Published: July 2007

AbstractThe change in the K‐absorption in additively coloured RbCl under applied uniaxial stress is investigated. A new technique with an ac‐stress is applied. The effects are compared with the change in the absorption shape in Ba++ doped crystals. The analysis reveals two components of the K‐absorption, K1 and K2, which behave differently under external perturbations. The K2‐component coincides with the spectral range of high photoconductivity.
Electrical and Optical Properties of Sputtered In2O3 films. II. Optical Properties in the Near Infrared
Authors: Müller H. K. 
Published: July 2007

AbstractThe influence of conduction electrons on the optical properties in the near infrared has been investigated for sputtered In2O3 films. The results are interpreted using the present theories of absorption and dispersion by free carriers. The optical properties in the investigated frequency range are considerably influenced by the anisotropy of the predominant scattering mechanism (scattering at charged defect centres) and by the low mean free time of the electrons (τ ≈ 1.5 × 10−15 s).
Comparative Investigation of the Specific Heat of KH2PO4 (KDP) and KD2PO4 (DKDP) Single Crystals
Authors: Strukov B. A. , Amin M. , Kopchik V. A. 
Published: July 2007

AbstractThe surplus entropy of the phase transition is measured for KH2PO4 and KD2PO4 crystals. The corresponding values are as follows: (0.69 ± 0.02) and (0.96 ± 0.08) for KDP and DKDP, respectively. The temperature dependence of the specific heat of DKDP shows that the phase transition in the crystal is of the first order. For the KDP crystals, the analytic form of the surplus specific heat is approximately Δcσ,E ∼ (Tc–T)−δ, δ = 0.51 ± 0.01. Theoretical estimates and experimental measurements are made of the effect of an electric field on the specific heat.
Attenuation and Amplification of Hypersound by Mott Excitons in Semiconductors with Piezoelectric and Deformational Electron‐Phonon Interactions
Authors: Lipnik A. A. , Ruvinskii M. A. 
Published: July 2007

AbstractA calculation is made of the attenuation of hypersound by Mott excitons in semiconductors with piezoelectric and deformational electron‐phonon interactions taking into account 1. the complex band structure (anisotropy, many‐valleyness, degeneracy, spin‐orbit interaction); 2. the presence of many sorts of carriers and screening of the electron‐phonon interaction; 3. the possible change in the internal state of the exciton including its dissociation and formation from a pair; 4. the possible degeneracy and Bose‐Einstein condensation of the excitonic gas. It is proved that there is a real possibility of amplification of hypersound both by the excitonic gas, due to its de‐excitation and by the electron‐hole gas, due to the formation an exciton from a pair (at rather low temperatures). The resonant character of hypersonic attenuation by the excitonic condensate may serve as an agent for detecting the latter effect. The measurement of attenuation and emission frequencies allows the exciton binding energy and the main values of its effective mass tensor to be determined.
Schottky Defects in Alkali Halides: Their Creation, Interaction, and Migration
Authors: Rao K. J. , Rao C. N. R. 
Published: July 2007

AbstractSchottky defect energies of alkali halides are calculated by the force balance method employing a modified Born model with higher than van der Waals terms and appropriately adjusted repulsive terms. The energies for various potassium and rubidium halides of NaCl structure show good agreement with the experimental values. Schottky defect energies of CsCl are calculated for the CsCl and the NaCl structures. The calculated value (≈︁ 1 eV) for the CsCl structure is in excellent agreement with the recent experimental value. The Schottky energy of CsCl in the NaCl structure is about 2 eV. The ground state interaction energy between a positive and a negative ion vacancy is determined with the inclusion of van der Waals terms. The values obtained for various alkali halides are in fair agreement with the previous ones. The migration barriers for single and pairs of vacancies in KCl and RbCl are calculated by an energy minimization procedure. The barrier heights compare nicely with the experimental value and reflect the expected trend in various parameters. The values also show that the activation energies for the migration of double vacancies and single vacancies are nearly the same; this result contradicts the generally accepted statement that migration of pairs is less energetic, but supports the recent proposal of Lidiard who obtained this result by employing different repulsive energy expressions in the different interionic regions.
An Investigation of the Electrical Resistivity of Nickel‐Rich Nickel‐Gold Alloys
Authors: Arajs S. 
Published: July 2007

AbstractElectrical resistivity of nickel‐gold alloys, containing 0.075, 0.22, 0.45, 0.68, 1.07, and 1.54 at% gold, has been measured at 4.2, 77.2, and 300.0 °K. The resistivity increase at 4.2 °K, due to 1 at% gold in nickel, is (0.33 ± 0.01) μΩcm. This value compares favorably with the result of (0.38 ± 0.02) μΩ cm due to Roberts et al., This finding implies that the disagreement between the measured and the theoretical isomer shifts, calculated by Roberts et al., for 197Au in nickel is not due to the uncertainty in the residual resistivity data. Nickel‐gold alloys exhibit large deviations from the Matthiessen rule. The longitudinal electrical magnetoresistivity at 4.2 °K in presence of an applied field of 60 kOe is positive, rapidly increases with increasing gold concentrations, and then gradually saturates at higher gold contents.
Vibrational Resonance Mode and the Temperature Dependence of Hyperfine Coupling of Mn2+ in BaO
Authors: Žďánský K. 
Published: July 2007

AbstractThe temperature dependence of the hyperfine coupling constant A of Mn2+ in BaO is measured in the temperature range 4 to 300 °K. It is shown that the theoretical temperature dependence of A given by Šimánek and Orbach [5] does not give a good agreement with the measured values. The temperature dependence of A is calculated by assuming that the interaction of the electronic states of the impurity ion with the resonance mode of vibration prevails over the interactions with the continuous phonon spectrum. To explain the discrepancy between the theoretical curve and the experimental data, the effect of anharmonic terms on the temperature dependence of hyperfine coupling is taken into account.
Electrical Conduction in Li‐Doped MnO Single Crystals
Authors: Ali M. , Fridman M. , Denayer M. , Nagels P. 
Published: July 2007

AbstractA study of the electrical properties including resistivity, Hall effect, and thermoelectric power is made on slightly Li‐doped single crystals of MnO. The temperature dependence of the conductivity is almost completely determined by the charge carrier concentration. From the results of electrical conductivity and thermoelectric power measurements it is concluded that the samples are slightly compensated. When the samples are thermally treated in an atmosphere containing oxygen in excess compared to the equilibrium pressure, more donor centres are introduced resulting in further compensation. The height of the acceptor (Li+Mn+++) level is 0.64 eV while the band gap has a value of 2.6 eV. The calculations of the density of states Nv and the effective mass m* yield a high value. These results indicate that holes move in a narrow band.
Calculation of Properties of Vacancy‐Centered Z1−Center Models in Alkali Halides
Authors: Dick B. G. 
Published: July 2007

AbstractA simple variational calculation of the ground and excited p‐state energies, wavefunctions, and transition oscillator strengths is carried out for three forms of proposed vacancy‐centered models for Z1−centres in alkali halides. The calculated excitation energies compare well with experiment for NaCl, NaBr, KCl, RbCl, KBr, and KI.