bluuebunny/crossref_metadata_2025_split huggingface dataset:
ESR‐Untersuchungen zur Aggregation von F‐Zentren in RbCl
Authors: Ehret P. , Wolf H. C. 
Published: July 2007

AbstractOptisches Bleichen vermindert die Auflösung der teilweise aufgelösten Hyperfeinstruktur im ESR‐Spektrum der (restlichen) F‐Zentren in RbCl. Messungen von T1 T2 und T1 bei Sättigung ergeben für T2 näherungsweise T2 = 2 × 10−8s (ungebleichte F‐Zentren) und T2 = 2,5 × 10−9 s (F‐Zentren nach optischem Bleichen bei Zimmertemperatur). Rechnungen zeigen, daß T2 einen Wert von 3 × 10−9s haben muß, um die Verminderung der Auflösung des Hyperfeinspektrums zu erklären. Es wird angenommen, daß der Abfall von T2 durch eine optisch‐induzierte, lockere Ansammlung von F‐Zentren herrührt. Der gemessene Wert von T2 entspricht dem Mittel von fünf Abständen zwischen den Ionen der F‐Zentren in den Agglomeraten, wenn nur Dipol‐Dipol‐Wechselwirkung berücksichtigt wird.
Thermoluminescence and Thermoluminescence Spectra of Calcium Fluoride Crystals Irradiated by X‐Rays
Authors: Ratnam V. V. , Bose H. N. 
Published: July 2007

AbstractThe glow curve pattern obtained for CaF2 crystals irradiated by X‐rays at room temperature is markedly affected by even a small rise (say 30 °C) in the temperature of irradiation. This is presumably due to the neutral fluorine atoms which are produced by the holes trapped by the fluorine ions during X‐ray irradiation and which, at elevated temperatures of irradiation, form molecular complexes or diffuse out of the crystal. The spectral composition of the thermoluminescence obtained with samples irradiated at room temperature is similar for the first three glow peaks, except for minor changes in the relative intensities of the emission peaks; for the fourth glow peak however it is markedly different. Further, the first three glow peaks attain saturation with X‐ray dose similar to the colour bands, but no such tendency is observed for the fourth glow peak. These results indicate that the traps and emitting centres responsible for the first three glow peaks are different from those of the fourth glow peak.
Untersuchungen über die energetische Verteilung der Haftsteller für Defektelektronen in Anthracenkristallen
Authors: Bässler H. , Becker G. , Riehl N. 
Published: July 2007

AbstractBeim Anlegen einer Spannung stellt sich in einem Anthracenkristall eine räumlich unsymmetrische Besetzung der Haftstellen mit Defektelektronen ein. Beim Abschalten des Feldes entsteht deshalb ein Rückstrom. Seine Zeitabhängigkeit liefert Informationen über die beteiligten Haftstellen. Es wird gezeigt, daß energetisch benachbarte Haftstellen für Defektelektronen existieren müssen (Energieabstand ca. 0,01 eV), deren Dichte exponentiell mit der Energie abnimmt. Numerische Abschätzungen führen zu dem Schluß, daß diese Haftstellenverteilung mit der früher als kontinuierlich postulierten exponentiellen Verteilung identisch ist.
Determination of Activation Energy from Step Annealing
Authors: Bell F. , Sizmann R. 
Published: July 2007

AbstractThe activation energy Q can be determined for processes of type dx/dt = F(x) exp (–Q/RT) from linear heating data or from the point sequence of step annealing (time and temperature intervals are constant). Q may be evaluated at each point x if two samples are available. With only one sample Q can be found at some isolated points by applying cycling temperature procedures.
Über die Anregung von Rumpfelektronen durch Stoß mit schnellen Primärelektronen in Metallen
Authors: Fischbeck H. J. 
Published: July 2007

AbstractDie Energieverteilung der Anregung von fest gebundenen Metallelektronen durch Stoß mit schnellen Primärelektronen wird in Bornscher Näherung berechnet. Die Anfangszustände der Rumpfbänder des Metalls werden durch Blochsummen und die Endzustände der angeregten Elektronen durch orthogonalisierte ebene Wellen approximiert. Als Anwendungsbeispiel wird die Energieverteilung der Anregung aus den Rumpfbändern des Natriums numerisch berechnet und im Hinblick auf die Sekundärelektronenemission diskutiert. Es ergibt sich, daß die Anregung aus dem Rumpf für die Sekundäremission des Natriums von weit größerer Bedeutung als die Anregung aus dem Leitungsband ist.
Transporteigenschaften von HgTe
Authors: Wagini H. , Reiss B. 
Published: July 2007

AbstractAn zwei HgTe‐Proben wurden zwischen 100 und 300 °K die Transportkoeffizienten im schwachen transversalen Magnetfeld gemessen und vergleichshalber in der Nähe der Eigenleitung Rechnungen für Streuung an akustischen und optischen Phononen sowie an Ionen durchgeführt. Legt man der Theorie eine Abart des von Groves und Paul [1] für graues Zinn entwickelten Bändermodells (ΔE = 0, nichtparabolisches Leitungsband Kanescher Form) zugrunde und berücksichtigt die aus optischen Untersuchungen gewonnenen Daten, (mn = 0,017 mo sowie |ε| = 0,15 eV) von Verié und Decamps [2], so ergibt sich nahe der Eigenleitung im Bereich der Zimmertemperatur für vorwiegend optische Streuung der Elektronen gute Übereinstimmung mit dem Experiment.
Nachweis von Frenkeldefekten in röntgenbestrahltem LiF
Authors: Balzer R. , Peisl H. , Waidelich W. 
Published: July 2007

AbstractLiF‐Kristalle wurden bei Zimmertemperatur röntgenbestrahlt. Die dabei erzeugten Farbzentren wurden durch Messung der optischen Absorption nachgewiesen. Zur Untersuchung der Störung des Kristallgitters durch die erzeugten Punktdefekte wurden die relative Gitterkonstantenänderung und die relative Änderung der makroskopischen Dichte der Kristalle nach der Bestrahlung bestimmt. Durch Vergleich dieser beiden Änderungen wird gezeigt, daß bei der Bestrahlung Frenkeldefekte gebildet wurden.
Contribution à la théorie statistique de la ferroélectricité
Authors: Godefroy L. 
Published: July 2007

AbstractL'étude statistique du modèle ferroélectrique basée sur l'existence de puits de potentiel rigide à deux minimums est étendue à la dynamique du switching. On montre que si les résultats obtenus avec un tel modèle étaient valables en statique, ils ne le sont plus du tout en dynamique. Il semble que I'hypothèse de la rigidité du puits de potentiel soit à incriminer.
Electron Interaction Effects on Recombination Spectra
Authors: Landsberg P. T. 
Published: July 2007

AbstractThis note suggests a possible origin of low energy tails observed in radiative recombination when at least one of the participating bands is degenerate. An order‐of‐magnitude calculation is made which shows that the effect can have the same origin as similar effects in the soft X‐ray emission spectra of metals. Furthermore, it is suggested that the analysis of experimental tails can lead to information about the screening lengths in the Coulomb interaction between electrons in bands.
Optical Properties and Electronic Structure of Amorphous Germanium
Authors: Tauc J. , Grigorovici R. , Vancu A. 
Published: July 2007

AbstractThe optical constants of amorphous Ge are determined for the photon energies from 0.08 to 1.6 eV. From 0.08 to 0.5 eV, the absorption is due to k‐conserving transitions of holes between the valence bands as in p‐type crystals; the spin‐orbit splitting is found to be 0.20 and 0.21 eV in non‐annealed, and annealed samples respectively. The effective masses of the holes in the three bands are 0.49 m (respectively 0.43 m); 0.04 m, and 0.08 m. An absorption band is observed below the main absorption edge (at 300 °K the maximum of this band is at 0.86 eV); the absorption in this band increases with increasing temperature. This band is considered to be due to excitons bound to neutral acceptors, and these are presumably the same ones that play a decisive role in the transport properties and which are considered to be associated with vacancies. The absorption edge has the form: ω2ϵ2∼(hω−Eg)2 (Eg = 0.88 eV at 300 °K). This suggests that the optical transitions conserve energy but not k vector, and that the densities of states near the band extrema have the same energy‐dependence as in crystalline Ge. A simple theory describing this situation is proposed, and comparison of it with the experimental results leads to an estimate of the localization of the conduction‐band wavefunctions.
Fine Structure of Emission Spectra of the Red AIN:Mn Luminescence
Authors: Karel Fr. , Pastrňák J. , Hejduk J. , Losík V. 
Published: July 2007

AbstractThe luminescence of aluminium nitride, activated by manganese, is described. A structure with equidistant peaks, clearly resolved at low temperatures, is found in the emission band 580 to 620 nm. This structure is interpreted in terms of phonons using the Pekar theory. The energy of the phonon involved is 0.023 eV. The luminescence decay is exponential with a time constant τ = 1.0 × 10−3 s over a wide temperature range. It is suggested that the luminescence is due to transitions between metastable and basic levels of the tetravalent manganese ion.
Growth of Hexagonal Crystallites in CdTe Thin Films
Authors: Spînulescu‐Carnaru I. 
Published: July 2007

AbstractIt is shown that the crystal structure of CdTe thin films is strongly affected by a variation in the relative concentration of the metallic and non‐metallic constituents. Optimum conditions are found which lead to CdTe thin films with a pure hexagonal structure. The constants of the CdTe cubic and hexagonal cells are computed.
Electrical Pinch in Elastically Deformed Germanium
Authors: Rashba E. I. , Romanov V. A. , Boiko I. I. , Zhadko I. P. 
Published: July 2007

AbstractThe phenomena accompanying the flow of an electric current through uniaxially compressed plates of intrinsic Ge are investigated. The plates are cut with definite orientations relative to the main crystallographic axes so that the directions of the current and field do not coincide. Under these conditions transverse gradients of the nonequilibrium carrier concentration arise in specimens long carrier lifetimes, this results in a modulation of the conductivity, emergence of rectifying characteristics, etc. In strong field the carriers and current are concentrated in a narrow layer close to one of surfaces, the carriers being almost completely removed from the rest of the specimen (the electrical pinch in an electron‐hole plasma). The redistribution of carriers across the sample and the current‐voltage characteristics are investigated experimentally for these pinch conditions. For fields of about 100 V/cm an increase and decrease of concentration is observed, giving an extremely nonlinear current‐voltage characteristic if opposite plate surfaces have different surface recombination velocities. A rectification ratio of about 50 may be obtained in this way. Under electrical pinch conditions the dependence of the resistance of the specimen on compression exceeds the ordinary piezoresistance by an order of magnitude.
The Migration of Double Positioning Boundaries During the Growth of Epitaxial (111) Gold Films
Authors: Stowell M. J. , Law T. J. 
Published: July 2007

AbstractA study has been made of the migration of double positioning boundaries during continuous growth of (111) gold films inside an electron microscope. The boundary mobility is shown to be temperature dependent and the results indicate that double positioning boundary migration is a thermally activated process. The influence of rate of coalescence of deposit islands and of deposition rate on the size of double positioning domain structures in (111) gold films is discussed and the conclusions are extended to other multiply positioned and polycrystalline structures formed by vacuum evaporation.
Excitonic Effects in the Interband Absorption of Semiconductors
Authors: Velický B. , Sak J. 
Published: July 2007

AbstractElliott's work on exciton effects at the direct absorption edge is extended to include other van Hove singularities and deviations from the effective mass approximation. The sum rule which replaces the f‐sum rule in this case is derived. The Koster‐Slater and Coulomb interactions are treated as limiting cases. Due to the electron‐hole interaction, the M0 and M1 branch‐points of ϵ2 are enhanced and sharpened, whilst the M2 and M3 branch‐points are weakened and smoothed out. Only the M0 points generate (quasi) discrete levels; no evidence for these is found near the M1 points. For a very prolate M1 singularity, certain branch‐points appear asymptotically below the critical energy.
EPR Measurements on Diatomic Halogen Centers in Alkali Halides
Authors: Dreybrodt W. , Silber D. 
Published: July 2007

AbstractEPR spectra of diatomic halogen centers in alkali halides are investigated. Centers of the type FBr−, FJ−, and CIJ− are identified. The constants of the spin Hamiltonian are derived from the FBr‐ spectra by a perturbation calculation up to fourth order. By studying the photochemical properties of centers of the type X and XY− information regarding the formation mechanismus of the FCl− and FBr− centers are obtained.
A Model for the Change in Elastic Modulus of a Solid Caused by Point Defects
Authors: Melngailis J. 
Published: July 2007

AbstractPoint defects introduced into copper at low temperatures by irradiation are known to produce bulk expansion. We suggest here that an external stress might cause the defect (represented as oversized spherical inclusions) to relax. This would change the expansion produced by the defects so that the deformation due to the stress would be greater and the elastic modulus would thus appear smaller. This relaxation is represented by a small deformation of the spherical inclusions, and elastic energy considerations are used to calculate the change in the elastic modulus of Cu due to such defects. If the radius of the inclusions is chosen to be two lattice constants, the experimentally observed value of 18% for the decrease in the elastic modulus at saturation density of defects is obtained.
The Interaction of Two Excitons in a Crystal
Authors: Bobrysheva A. I. 
Published: July 2007

AbstractThe energy of the exciton—exciton interaction is calculated as a function of the distance between their centres of mass for the atomic model of a semiconductor. Computed numerical results are presented for various values of the parameters of the atomic functions, relative‐motion functions, and the electron‐hole‐effective mass ratio. The binding energy of two excitions is obtained by the Green's function method assuming that the exciton‐exciton interaction is less than the interaction of the excitons with optical and acoustic phonons. The role of the direct exciton‐exciton interaction and the indirect interaction, via optical or acoustic phonons, in the formation of a biexciton is studied. The results are given of calculations of the cross‐section for elastic scattering between two excitons using the Born approximation.
On the Theory of Anisotropic Thermoelectric power in Semiconductros
Authors: Samoilovich A. G. , Nitsovich M. V. , Nitsovich V. M. 
Published: July 2007

AbstractPossible mechanisms for the appearance of an anisotropic thermoelectric power in semi conductors are examined using simple models. It is shown that an anisotropic thermoelectric power may arise both as a result of combined phonon and impurity scattering, and in the presence of two types of carriers if at least one type of carrier has an anisotropic effective mass. The effect of different parameters on the magnitude of the anisotropy in the thermoelectric power is examined and it is shown that for reasonable values of these parameters the anisotropy may be significant.
On the Colour Centres and X‐Ray Luminescence of Calcium Fluoride Crystals
Authors: Ratnam V. V. 
Published: July 2007

AbstractA study is made of differences in the colouration spectrum of calcium fluoride cyrstals obtained by X‐ray irradiation at different temperatures and by electrolysis. The changes occuring in the X‐ray luminescence spectrum due to the use of different irradiation temperatures are also considered. It is shown that the α‐ and β‐bands, usually only observed in additive and electrolytic colouration, can also be produced by X‐ray irradiation if the irradiation temperature is between 180 and 250°C. The formation of the α‐ band (the F‐band of this system) is difficult to detect at lower irradiation temperatures because of 1. the small number of free negative ion vacancies at these temperatures and 2. the low oscillator strength associated with this band. The changes observed in the X‐ray luminescence spectrum for different irradiation temperatures are explained and the associated electronic processes are discussed briefly.
Mössbauer Effect in Some Polyatomic Crystals
Authors: Iosilevskii Ya. A. 
Published: July 2007

AbstractExpressions are obtained for the probability of the Mössbauer effect and the thermal shift in the energy of a γ‐photon for binary crystalline compounds ABr−1. These compounds include crystals of the type NaCl or CsCl, crystals of completely ordered alloys (AuCu3, AlFe3 etc.), and monatomic crystals with isolated impurity atoms. It is assumed that the force constants depend only on the differences of the position vectors of the atoms. The treatment includes the two cases in which nucleus A or nucleus B is resonant. The case in which atom A (mass M0) and atom B (mass M) differ considerably in mass is analysed in greater detail. For M0/M ≪ 1 or M0/M ≫ 1 the fraction e of recoilless emissions (or absorptions) of γ‐rays by atom A and the thermal shift δE0 are independent of M0/M for given interatomic forces. Values of these quantities are hence determined by the appropriate limiting expressions (M0 = const, M → ∞ or M → 0). Thus the finite Mössbauer effect for an atoms surrounded by light atoms is independent of the mass of the latter. In addition there exists a limit to the gain in the probability of the Mössbauer effect and in the thermal shift for an atom which can be obtained by surrounding it with increasingly heavier atoms. It is also shown that the probability of the effect and the thermal shift for the atoms A, for the given interactions, are essentially independent of r. The quasiclassical expansions of Zj and δEj, for the j‐th atom in a unit cell, are obtained for more complicated compounds of the type A A … A (r1 + r2 + … rn = r) by the method of moments.
On the Critical Resolved Shear Stress of Solid Solutions Containing Coherent Precipitates
Authors: Gerold V. , Haberkorn H. 
Published: July 2007

AbstractA quantitative estimate is made of the increase Δτ0 of the critical resolved shear stress for the case of solid solutions containing spherical and coherent precipitates. The interaction between edge dislocations and the coherency strain fields is believed to be the strengthening mechanism. The calculation is applied to experimental measurements on Al‐Zn and CuCo alloys. For small particles (R/b < 20) the dislocations tend to cut through the precipitates, whereas for larger particles the Orowan mechanism becomes predominant.
General Theory of Electron Emission from Metals
Authors: Christov S. G. 
Published: July 2007

AbstractA theory of the emission of electrons from metals is developed on the basis of a general integral expression for the total transmission probability of an incident electron on the potential barrier at the metal surface. This integral is expressed as a sum of three conveniently defined integrals. In this way formulas are obtained for the current density for all temperature and field conditions of practical interest. The maximum error in the calculation of the total current by this method is about 10%. This theory includes as limiting cases thermionic and field emission as well as some earlier results for the emission over a narrow intermediate range of conditions. The limits of applicability of the theory in its general form are outside those of practical importance and include temperatures from 0 to 3500 °K and fields from 0 to 108 V/cm.
Electrisation du polyéthylène et du polystyrène après irradiation γ
Authors: Asch M. G. , Félix M. C. , Ongaro M. R. 
Published: July 2007

AbstractOn montre qu'après avoir été exposés au rayonnement γ, le polyéthylène et le polystyrène peuvent acquérir une électrisation superficielle stable sous l'influence d'un champ électrique. La densité superficielle de charge est calculée en admettant que l'électrisation est due au déplacement d'électrons qui, initialement piégés, sont progressivement libérés par excitation thermique. L'expression de la densité de charge ainsi obtenue est conforme aux résultats expérimentaux.
Electrical Properties of n‐Type Epitaxial Gallium Arsenide
Authors: Eddolls D. V. 
Published: July 2007

AbstractMeasurements have been carried out to determine the temperature dependence of the Hall coefficient and resistivity of n‐type epitaxial gallium arsenide in the range 4.2 to 300 °K. Such materials has in general a lower impurity concentration and a higher mobility than melt grown material. The temperature dependence of the carrier concentration is described by the expression

where gr is the degeneracy factor and Er the excitation energy of the rth excited state of the donor atom, the number of excited states depends upon the donor concentration. The ionization energy varies from 1.6 × 10−3 to 4.7 × 10−3 eV when the donor concentration changes from 5 × 1015 to 3 × 1014 cm−3. Qualitative comparison between the measured temperature variation of the Hall mobility and published theory shows reasonable agreement. The highest mobility measured was 103000 cm2 (Vs)−1 at 52 °K.
Magnetische Eigenschaften von Einkristallschichten aus Eisen, Nickel, Kobalt und deren Legierungen
Authors: Kirenskii L. V. , Pynko V. G. , Pynko G. P. , Sukhanova R. V. , Sivkov N. I. , Rusov G. I. , Edelman I. S. 
Published: July 2007

AbstractIn dieser Arbeit wird gezeigt, daß die Energie der Anisotropie der einzelnen Kristallite in Epitaxieschichten (z. B. Co‐Schichten) additiv ist. Das Feld, das während der Aufdampfung anliegt, beeinflußt die Anisotropie von einkristallinen Fe‐Schichten nicht merklich, während bei Ni‐ und β‐Co‐Schichten das Feld eine starke einachsige Komponente hervorrufen kann. Die Feinstruktur in den Domänen von einkristallinen FeNi‐ und CoNi‐Schichten mit schwacher kristallographischer Anisotropie wird beobachtet. Die Breite der Wände zwischen den Domänen in einkristallinen Schichten aus Fe, Ni und β‐Co wird elektronenmikroskopisch gemessen. Es wird gezeigt, daß in Schichten mit starker biaxialer Anisotropie die Änderung der Koerzitivkraft in Abhängigkeit von der Änderung der Richtung des magnetisierenden Feldes befriedigend durch den Ausdruck

beschrieben wird, wobei p den Druck, der durch das Feld auf die Wände ausgeübt wird, Θ1 und Θ2 die Winkel zwischen dem Feld und den Magnetisierungsvektoren auf beiden Seiten der Wand und IS die Sättigungsmagnetisierung bedeuten.
On the Reaction Order of Bimolecular Recovery Processes in Solids
Authors: Nihoul J. , Stals L. 
Published: July 2007

AbstractA general expression is derived for calculating the reaction order of recovery processes when rate equation is known. This expression is independent of the rate constant but is completely determined by the relative concentration of the defects. On the basis of this expression the reaction orders of some bimolecular recovery processes are discussed as a function of defect concentrations, the ratio of the initial concentrations and the capture radius. It is shown that, unless rather severe conditions are fulfilled, the reaction order may vary over a wide range of values, even in cases where the application of some widely‐used methods would indicate an apparently constant reaction order.
Franz‐Keldysh‐Effekt an trigonalem und amorphem Selen
Authors: Stuke J. , Weiser G. 
Published: July 2007

AbstractAu dünnen trigonalen Se‐Einkristallen und an aufgedampften Schichten von amorphem Se wird die Verschiebung ΔEg der Absorptionskante durch ein elektrisches Feld untersucht. Dabei ergibt sich, daß ΔEg recht genau proportional zum Quadrat der Feldstärke F und zum Quadrat der Steigung S der exponentiell verlaufenden Kante ist. Die spezifische Kantenverschiebung ΔEg/F2 hängt bei Kristallen stark von der Orientierung des Feldes und der Polarisation des Lichtes ab. Daraus ist zu schließen, daß die reduzierte effektive Masse in Richtung der c‐Achse um etwa den Faktor 6,5 kleiner ist als senkrecht dazu. Bei amorphem Se stimmt der Franz‐Keldysh‐Effekt qualitativ mit dem von Se‐Kristallen überein.