bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical Absorption in Electric and Magnetic Fields
Authors: Spector H. N.
Published: July 2007

The theory of optical absorption in electric and magnetic fields is extended to treat the case where the relative orientation of the fields is arbitrary. The treatment is valid within the limits of the effective mass approximation. For the cases where one of the fields is absent or where the electric and magnetic fields are perpendicular to each other, the theory yields the results previously derived. However, for the case of parallel magnetic and electric fields, the theory yields the result that the absorption edges and peaks are broadened due to the field induced tunneling between the bands. The effect of the parallel fields on phonon‐assisted transitions is also calculated. It is found that steps in the optical absorption which normally occur are broadened due to the field induced tunneling.
Variations of Young's Modulus throughout the Mixed State in Niobium
Authors: Kramer E. J. , Bauer Ch. L.
Published: July 2007

Variations of Young's modulus throughout the mixed state in niobium have been measured as a function of external magnetic field. The variations then are converted to magnetization values utilizing the two‐phase model of the mixed state. Results are in satisfactory agreement with the measured magnetization curve, and thus support the applicability of the two‐phase model.
On the Isotope Effect in Interstitial Diffusion
Authors: Pegel B.
Published: July 2007

Following an idea of Prigogine and Bak the frequency factor of interstitial diffusion is calculated for a classical, one‐dimensional model of a crystal. An isotope effect is found which is more complicated than that obtained from rate theory. This effect depends very strongly on the lattice spectrum. The model explains qualitatively recent experimental observations on the isotope effect.
Colour Centres in Ruby Crystals
Authors: Arkhangelskii G. K. , Morgenshtern Z. L. , Neustruev V. B.
Published: July 2007

An investigation is made of the absorption spectra, the spectral dependence of the luminescence quantum output, glow curves, and the radiation spectra of the glow curves of ruby crystals. These crystals are coloured by intense light flashes or by γ‐rays from Co60. It is found that the absorption is greater in coloured crystals while the luminescence quantum output is smaller. The thermal decoloration of crystals is accompanied by a luminescence in the R‐line region. A decrease in the Cr3+ ion concentration is detected in coloured crystals by ESR measurements. The similarity of all the characteristics obtained allows a conclusion about the identity of the colour centres arising under optical and γ‐irradiation of the crystals. The results obtained here and published data suggest that Cr2+ and Cr4+ act as colour centres, and that their formation under optical coloration is duo to Cr3+ ion ionization via a two‐step process. It is shown that the gradual increase of the ruby generation threshold observed experimentally, which gives laser operation, is due to the formation of colour centres which cause a parasitic absorption of the pumping light.
On the Possibility of Existence of Quantum Electromagnetic Waves in Metals
Authors: Kaner E. A. , Skobov V. G.
Published: July 2007

The electromagnetic properties of a metal are considered theoretically for strong quantization of the electron states in a magnetic field. It is shown that a large number of quantum waves should occur with velocities close to the discrete velocities of the electrons on the Fermi surface. The extensce of these waves is due to the absence of Landau damping in the interval between giant oscillation maxima.
Stacking Faults in a Non‐Stoichiometric Face‐Centred Cubic TaC
Authors: Martin J. L. , Jouffrey B. , Costa P.
Published: July 2007

Stacking faults are observed by transmission electron microscopy in face centred cubic TaC0.75. These stacking faults have the same contrast as intrinsic faults in face centred cubic metals; they do not exist in nearly stoichiometric carbides. No metallic plane relaxation is detected in the neighbourhood of a fault. It seems that another carbide phase precipitates along the fault planes in a Widmanstätten structure.
Surface Spin Waves in Hexagonal Cobalt Thin Films
Authors: Puszkarski H.
Published: July 2007

It is shown that excitation of acoustic surface spin waves is possible for certain intervalls of the parameter A which describes the degree of spin pinning. The resonance absorption obeys the k−1 rule. The first resonance spin‐wave mode, weaker than the next one, is expected to have a surface spin‐wave nature.
Effects of Fast Neutrons on Electric Properties of NiO Single Crystals
Authors: Cojocaru L. N.
Published: July 2007

A study is made of the effect of fast neutrons on the electric conductivity and thermo‐electric power of NiO single crystals. It is found that the conductivity and thermo‐electric power are reduced after an irradiation of about 1017 nvt. This is explained by assuming that the defects introduced into the NiO lattices act as acceptors and not as trapping centres for holes. The decrease of the electric conductivity is due to the mobility decrease whilst the decrease in the thermo‐electric power arises from the increase of the hole concentration.
On Energy Bands of Crystals with Lowered Point Symmetry
Authors: Frei V.
Published: July 2007

The special case of those subgroups of space groups that have the same translational symmetry but lowered point symmetry is discussed from the crystallographic, group‐theoretical and physical points of view. Consequences are studied concerning the energy band structure (degeneracies, zero slopes of E(k), dipole selection rules, etc.). It is shown preliminarily that the theory of space subgroups [3] is important here and that the case of lowered point symmetry is especially simple and physically interesting.
Calculation of Light‐Stimulated Luminescence and Current Transients in Phosphors. (Release of Trapped Carriers by Light)
Authors: Bráunlich P.
Published: July 2007

The paper discusses light‐stimulated luminescence and conductivity in phosphors using a model proposed by Schön [1]. This model was previously used for the calculation of thermoluminescence on thermally stimulated current [2]. It considers transitions between defect levels and both bands (conduction band and valence band) and is, therefore, suited for the calculation of light‐stimulated recombination phenomena in phosphors in cases where the energy distribution of light allows a simultaneous release of trapped carriers from electron and hole traps. Approximate solutions are presented. In one case the approximate solutions are compared with numerical solutions of the rate equations which govern the recombination kinetics. A method for the determination of the cross‐section of hole traps for light absorption is discussed.
A Thermodynamic Investigation of the Conditions for the Generation of Oscillations of an Electric Current Flowing through a Non‐Ohmic Medium
Authors: Pastrňák J.
Published: July 2007

Previous experimental and theoretical work on instabilities of the electric current have been mostly limited to various special cases. A better approach would be to treat the problem generally in terms of phenomenological non‐equilibrium thermodynamics. This would lead to some general conclusions which would be independent of the microphysical origin of the instabilities. It is shown here that even the restricted approach of taking the electric field as the thermodynamic force yields some general results of this nature which provide new information on this problem.
Spontaneous Recombination of Frenkel Pairs in Neutron‐Irradiated Solids
Authors: Dettmann K. , Leibfried G. , Schroeder K.
Published: July 2007

The accumulation of Frenkel defects in neutron‐irradiated solids is studied using a simple model of a displacement cascade. The lowering of the damage rate by spontaneous recombination of unstable Frenkel pairs is taken into account. The general equations are solved using the superposition approximation in which third‐order correlations are replaced by products of second‐order correlations. The saturation density of defects and the damage rate as a function of the density are calculated. By comparison with experiment the annealing and cascade volumes can be deduced for various metals.
Electrical and Optical Properties of Titanium‐Doped Lithium Fluoride Crystals
Authors: Jain S. C. , Sootha G. D.
Published: July 2007

Measurements are made of the electrical conductivity and optical absorption of LiF crystals doped with Ti. The plot of log (σ T) as a function of 1/T shows the usual intrinsic and extrinsic regions. In the extrinsic region, the behaviour of titanium is found to be similar to that of magnesium but different from that of manganese. The results indicate that most of the titanium is present in a highly aggregated form. However, a small fraction of the titanium is atomically dispersed in the form of doubly positively charged centres, either as Ti2+ or as stable pairs of Ti3+ and a cation vacancy. The values of the energies derived from the conductivity plot are W = 2.74 eV for the energy of formation of a separated pair of vacancies, E = 0.70 eV for the activation energy for the migration of a cation vacancy, and Wa = 0.48 eV for the energy of association of a cation vacancy with a titanium centre. Unirradiated LiF:Ti crystals show an optical absorption band, designated as the E‐band, at 207 nm with a half‐width of 0.72 eV. On X‐irradiation, this band decreases, and the F‐band and two new bands are observed. The new bands are designated as the H‐ and G‐bands. The H‐band occurs at 240 nm with a half‐width of 0.20 eV and the G‐band at 270 nm with a half‐width of 0.25 eV. The rate of growth of the F‐band on X‐irradiation is enhanced considerably by titanium impurity. Possible models of the E‐, G‐ and H‐centres are discussed and approximate values of the appropriate oscillator strengths are: fF = 0.32, fE = 0.23, and fG = 0.07. Attempts to distinguish between Ti2+, and Ti3+ plus a cation vacancy, by ESR absorption measurements are not successful because the titanium in highly aggregated form gives a very strong, complicated, and temperature independent background to the ESR absorption. Experiments are suggested which would distinguish between the two possible models of the titanium centres.
Phonon Green Functions by Functional Methods
Authors: Wehner R. K.
Published: July 2007

The time‐ordered many‐time Green functions are studied for a general lattice Hamiltonian which includes effects of a static electric field and of homogeneous deformations. The structure of the self‐energy part is investigated, and integral equations are derived for a cubic and a quartic vertex part.
Epitaxial Growth of Vacuum‐Evaporated Co on NaCl. I. Conditions Leading to Epitaxy
Authors: Otsuka K. , Wayman C. M.
Published: July 2007

Conditions necessary for complete epitaxial growth ((001) [100] Co // (001) [100] NaCl) of f.c.c. Co on NaCl were investigated. Both high‐evaporation rates and vacuum cleavage were found necessary, which indicates the importance of substrate cleanliness. It also appears necessary to avoid the nucleation of h.c.p. Co in order to obtain epitaxial growth of the f.c.c. phase. The development of “abnormal” h.c.p. crystals of Co in fiber texture orientation (00.1) h.c.p. // (001) Nacl is discussed. It is suggested that contaminants aid the occurrence of h.c.p. Co in preference to the f.c.c. form.
The Structure of Silicon Oxide Films
Authors: Coleman M. V. , Thomas D. J. D.
Published: July 2007

The scattering of electron waves by an amorphous material is partly dependent on its structure. The variation of this scattered intensity with angle may be mathematically transformed to give a radial distribution function (r.d.f.) which describes both the position and co‐ordination of sets of atoms. The methods used to obtain the r.d.f. from the structurally dependent intensity and the elimination of errors are described. To determine the scattered intensity experimentally, the electron diffraction pattern is scanned across a small aperture and the open circuit voltage developed in a silicon solar cell is measured. The structure found for amorphous silica films is similar to that determined by X‐rays and amorphous silicon has the expected tetrahedral bonding. It is shown that glow discharge and evaporated silicon oxide films, whose average composition lies between silicon and silica, consist of a mixture of these latter two materials.
Mössbauer Study of β‐ and δ‐FeOOH and their Disintegration Products
Authors: Dézsi I. , Keszthelyi L. , Kulgawczuk D. , McInár B. , Eissa N. A.
Published: July 2007

β‐FeOOH and δ‐FeOOH are studied by Mössbauer effect measurements. The Néel point of β‐FeOOH is TN = (295 ± 4) °K. Above this temperature the material is paramagnetic with quadrupole splitting and it decomposes to α‐Fe2O3 at 670 °K. The transition at this temperature takes 12 hours. The two internal magnetic fields observed in δ‐FeOOH are found to correspond to Fe3+ ions in octahedral and tetrahedral positions. δ‐FeOOH decomposes to intermediate products at 370 °K below its Curie Temperature and it disintegrates to α‐Fe2O3 at approximately 510 °K.
Das Erholungsspektrum von Kobalt
Authors: Bilger H. , Kronmüller H.
Published: July 2007

An plastisch verformten Kobalt‐Einkristallen wurden Erholungsmessungen des elektrischen Widerstandes im Temperaturbereich zwischen 4 und 550 °K durchgeführt. Ein Vergleich dieser Messungen mit Ergebnissen anderer Autoren ermöglicht eine vorläufige Deutung des Erholungsverhalten von Kobalt. Es zeigt sich dabei, daß zwischen dem Erholungsverhalten des hexagonalen Kobalts und der kubisch‐flächenzentrierten Metalle eine weitgehende Analogie besteht. Unter anderem wird die Stufe II in Kobalt der Annihilation weit entfernter Frenkelpaare, Stufe III der Annihilation freier Zwischengitteratome an Leerstellen und Stufe IV der Wanderung von Leerstellen zugeschrieben. Die Experimente weisen ferner darauf hin, daß im Temperaturbereich der Stufe III auch die Wanderung von Doppelleerstellen eine Rolle spielen kann.
Der Einfluß der Magnetostriktion auf die magnetische Bereichsstruktur einachsiger Kristalle, insbesondere des Kobalts
Authors: Hubert A.
Published: July 2007

Die Bereichsstrukturen, die auf der Basisebene eines Kobalteinkristalls auftreten, wurden experimentell und theoretisch untersucht. Die Vielfalt der Erscheinungen läßt sich deuten, wenn man zu den bisher betrachteten Energietermen noch die magnetostriktive Eigenenergie hinzunimmt. Diese Energie beherrscht vor allem die Strukturen in dickeren Kristallen (> 10 μ m) und in höheren Magnetfeldern. Die Bereichsstrukturen dünnerer Kristalle werden zwar primär von der Wandenergie bestimmt, doch spielt auch hier die magnetostriktive Energie noch eine bedeutsame Rolle, vor allem für die Keimbildung in hohen Feldern. So muß das sog. Wabenmuster in dünneren Kristallen nach unseren Ergebnissen neu interpretiert werden. Auf Anwendungsmöglichkeiten zur Untersuchung plastisch verformter Metalle wird hingewiesen.
Non‐Equilibrium Vacancy Concentrations in Metals Subject to Thermal Gradients and Electric Fields
Authors: Blackburn D. A.
Published: July 2007

Gradients of temperature and electric fields may be used to cause vacancy currents in metals. If vacancies are supposed to migrate between randomly distributed, fixed sources and sinks, a metal subject to an internal electric field E, parallel to a temperature gradient ∂T/∂x, should suffer a vacancy supersaturation given by q = Ce r Lambda;2/k2 T4 [(Ef(Ef + Em + Et ‐ 2 kT) + Et (Em ‐ 2 kT)) (∂T/∂x)2 ‐ Z e E T (Ef + Em ‐ kT) ∂T/∂x ‐ Z e kT3 ∂E/∂x + Et kT2 ∂2T/∂x2], where Ce denotes the equilibrium vacancy concentration appropriate to the temperature T at any point x, and Lambda; is the mean free path of a vacancy during migration between source and sink. Ef, Em, and Et are the energies for formation, motion, and transport of vacancies, Z e is the effective electrical charge carried by a vacancy when diffusing, and r is a geometrical constant (1/6 in f.c.c.).
Absorption of Ultrasound in Indium Antimonide
Authors: Hrivnák L. , Kovár J.
Published: July 2007

The frequency dependence of the attenuation coefficient for longitudinal ultrasonic waves in InSb is determined over the range 50 to 210 MHz for temperatures between 200 and 600 °K. The experimental results are interpreted using the Woodruff‐Ehrenreich theory. It is shown that above 200 °K the attenuation coefficient decreases with increasing temperature according to the function A/(1 + β T) and therefore the lattice thermal conductivity decreases as the function B/T (1 + β T), in accordance with theories of lattice thermal conductivity.
Mössbauer Spectra in the Presence of Electron Spin Relaxation (I)
Authors: Gabriel H.
Published: July 2007

The effect of time‐fluctuating electronic spins (magnetic fields) on the hyperfine splitting of the Mössbauer spectra is investigated. The author's previous formal theory, which utilizes the Liouville formalism due to Zwanzig, is briefly outlined and extended by considering relaxation effects in more detail. The solution for large times involves a superposition of frequency‐shifted Lorentzian lines with modified line widths. The frequency shift and the change in line width are obtained as functions of the nuclear spins, the magnetic quantum numbers, the magnetic moments, and of correlation functions defined in terms of the fluctuating spins.
Rubans d' aimantation dans les lames minces de fer pur
Authors: Bourret A. , Kleman M.
Published: July 2007

Le modèlé de répartition de l'aimantation dans les domaines en rubans (stripe domains) des lames minces de fer monocristallines d'orientation (111), est ici repris et appliqué è la géométrie particulière de la lame. Les équations linéarisées ainsi obtenues donnent une expression algébrique des composantes de l'aimantation dans la lame. Celles‐ci sont ensuite utilisées pour le calcul des divers contrastes de diffraction attendus, par résolution des équations de Howie et Whelan dans l'approximation á 2 ondes. Ces contrastes sont en bon accord avec les résultats expérimentaux.
Autodiffusion au joint de grains de bicristaux d'argent soumis à une pression hydrostatique
Authors: Martin G. , Blackburn D. A. , Adda Y.
Published: July 2007

L'autodiffusion au joint de grains de bicristaux d'argent à forte désorientation a été mesurée sous des pressions hydrostatiques comprises entre 0 et 8 kbar. On observe une variation de vitesse de diffusion correspondant à un volume d'activation de (11,5 ± 2,5 cm3/g‐at) soit (1,1 ± 0,2) fois le volume atomique.
Anisotropy of Thermomagnetic Effects in n‐Ge
Authors: Samoilovich A. G. , Buda I. S. , Dakhovskii I. V.
Published: July 2007

A generalization of the theory of the anisotropic scattering of current carriers is proposed for the case of a phonon‐drag effect. For two selected versions of phonon‐phonon scattering theory it is possible to determine the nonequilibrium partition‐function of the phonons. Calculations are made of the longitudinal and transverse Nernst‐Ettinghausen effects in n‐Ge on the basis of anisotropic scattering and a phonon‐drag effect. The results are compared with experimental data [1], and it is found that the present theory agrees well with experiment.
Spectral Response of p‐n Heterojunctions
Authors: Tansley T. L.
Published: July 2007

Semiconductor heterojunctions have been grown by the deposition of III‐V solid solutions on GaAs substrates and their optical properties studied in detail. While the general picture is that deduced from simple theory, some interesting second order phenomena have been observed. Effects considered include absorption in the wide gap material, loss of photocurrent due to the conduction band spike and notch and high field absorption effects in the narrow gap material transition region. Experimental results are presented and the incidence of these effects in real heterojunctions discussed.
Optical Measurement of Compensation in Highly Doped Silicon
Authors: à la Guillaume C. Benoit , Voos M.
Published: July 2007

The radiative recombination spectrum of silicon which is highly doped with 7 × 1018 cm−3 Sb atoms is analysed between 4.2 and 110 °K. From these measurements, it can be deduced that the silicon is compensated, and it is also possible to determine the nature of the compensating impurity. It is shown that the compensating impurity concentration can be obtained from the Shockley‐Read theory which allows a calculation to be made of the ratio of the hole and electron capture probabilities for such a recombination centre.
Energy Band Structures of Cubic ZnS, ZnSe, ZnTe, and CdTe (Korringa‐Kohn‐Rostoker Method)
Authors: Eckelt P.
Published: July 2007

The energy band structures of cubic ZnS, ZnSe, ZnTe, and CdTe are calculated by the KKR (Korringa‐Kohn‐Rostoker)‐method. The “muffin‐tin” potential, on which the calculations are based, is described in detail. The calculated energy splittings at critical points are compared with data from optical measurements.
Thermoluminescence Investigations on Doped Alkaline Earth Fluorides
Authors: Görlich P. , Karras H. , Kötitz G. , Ullmann P.
Published: July 2007

The thermoluminescence spectra and glow curves of MeF2: Y, MeF2: Tm (Me:Ca, Sr, Ba), and CaF2: Sm single crystals are measured over the temperature region from 89 to 300 °K and compared with earlier results obtained above room temperature. It is established that temperature has a considerable effect on the spectral intensity distribution of the thermoluminescence emission and effects are observed which arise from both the activator concentration and a charge compensation by NaF. A brief discussion is given of the results.
On Lindemann's Melting Criterion
Authors: Pal S. , Sharma P. K.
Published: July 2007

The ratio ηm of the mean square amplitude of thermal vibration to the square of the interatomic spacing at the melting point are calculated for a number of cubic metals using de Launay's electron gas model. The computation uses Blackmann's sampling technique. In contrast to Lindemann's hypothesis of constant ηm for all solids, the calculated ηm varies widely from one group of the periodic table to another.
Dynamical Scattering Theory for Crystals with Point Defects
Authors: Dederichs P. H.
Published: July 2007

Dynamic scattering theory is generalized to crystals containing statistically distributed point defects. Various absorption mechanisms are discussed, 1. inner shell absorption modified by a generalized Debye‐Waller factor and, 2. several corrections to this arising from correlations of static and thermal atomic displacements, due to fluctuations of the atomic scattering factors at the lattice points and due to defect clustering.
Growth and Optical Properties of Wurtzite and Sphalerite CdSe Epitaxial Thin Films
Authors: Ludeke R. , Paul W.
Published: July 2007

Growth of epitaxial thin films of sphalerite and wurtzite CdSe on cleaved BaF2 substrates is reported. Optical transmission measurements to 6.5 eV in the ultraviolet at 300 and 80 °K were made. The spin‐orbit splitting of the A3‐;A1 transitions in cubic CdSe is 0.26 eV, in close agreement with seemingly spin‐orbit split transitions of 0.28 eV in the hexagonal phase, attributed to transitions along the Δ‐axis (the c‐axis of the hexagonal Brillouin zone). Our findings substantiate this identification. Other optical structure is reinterpreted based on our measurements and some recent band calculations of wurtzite compounds. A band structure for wurtzite CdSe is proposed.
Effect of Storage Temperature on the Time Dependence of Charge Density in Carnauba Wax and Methyl Polymethacrylate Electrets
Authors: Hilczer B. , Blaszczyk B. , Goderska S.
Published: July 2007

An investigation is made of the effect of storage temperature on the transition time for the heterocharge to homocharge transition in electrets of Carnauba wax and methyl polymethacrylate. The transition time is found to decrease as the temperature is raised. The transition time is also strongly dependent on the electric field strength applied during polarization and decreases as the field strength is increased.
The Reflection Coefficient of Optically Inhomogeneous Solids
Authors: Subashiev V. K. , Kukharskii A. A.
Published: July 2007

The optical reflectivity of some optically inhomogeneous solids is considered and the appropriate general reflectivity formulae are determined. Some particular cases of these formulae are also discussed. The infrared reflectivity spectra of epitaxial and diffused semiconductor layers are calculated as examples.
Nucleation of Zinc Crystals in Multilayer Adsorption
Authors: Gretz R. D.
Published: July 2007

The adpopulation of zinc which is critical for an appreciable nucleation rate of crystallites on clean tungsten field emitter tips has been measured. This critical adconcentration is 2.7 monolayers for zinc, independent of temperature from 75 °K to above room temperature. This phenomena can be described by none of the existing theories of heterogeneous nucleation because all of these theories presuppose that adsorption prior to nucleation is less than a monolayer. For concentrations greater than a monolayer, the exact supersaturation at the substrate becomes indeterminate.
Visualization of Dislocations on Basal Planes of GaSe Single Crystals
Authors: Guseinov G. D. , Ramazanzade A. M.
Published: July 2007

Screw and linear dislocations are investigated on the (0001) planes of GaSe crystals. From the measured parameters of the regular growth spirals, calculations are made of the critical nuclear radius, the supersaturation, and the step translation rate. An optimum chemical etching solution (1 HF + 2 HNO3 + 7 HCl) for the (0001) plane of GaSe crystals is established. The density of screw and linear dislocations is determined. The statistical density of screw dislocations is found to be less than 104 cm−2, whilst the density of linear dislocations varies from 2.3 × 105 to 1.3 × 106 cm−2 depending on the mode of rotation.
Étude d'eutectiques supraconducteurs plomb‐étain à lamelles orientées
Authors: Dobrosavljevic L. , Dupuis C.
Published: July 2007

Nous avons étudié les propriétés magnétiques d'eutectiques Pb/Sn á lamelles orientées, le champ magnétique H étant toujours dans le plan des lamelles. Nous avons surtout mesuré la perméabilité superficielle en radiofréquence: les seuls grains intervenant dans ces conditions sont ceux qui sont à la surface de l'échantillon pour lesquels le flux pénétre beaucoup plus réversiblement que dans les régions intérieures. L'épaisseur des lames (Sn) est dans la plupart des cas assez notablement supérieure à la longueur de cohérence. Dans ces conditions, dès que le champ statique H est plus grand que le champ critique de l'étain, le flux pénètre dans chaque lame d'étain. La surface traversée par le flux dans une lame peut être mise sous la forme δ × 2 (d ‐ ϱ) où δ représente le diamètre des grains, 2 d l'épaisseur de la lame d'étain et ϱ un terme correctif dû aux effets de proximité. Les valeurs et les variations, avec T et H, de ϱ sont en accord qualitatif avec les prévisions théoriques. Les comparaisons quantitatives sont compliquées par certains effets de migration atomique aux interfaces, qui se traduisent en particulier par des phénomènes de vieillissement.
A Method for Describing a Flexible Dislocation
Authors: Bacon D. J.
Published: July 2007

A procedure for determining the equilibrium shape of a dislocation under the influence of both internal and external stress fields is described. The method, which is an extension of that used by Brown to determine the shape of extended nodes, does not require the explicit numerical integration of line integrals to obtain the self‐stress, and line shapes are therefore computed with comparative simplicity. The procedure has been used to study the bowing characteristics and the critical shapes and stresses of Frank‐Read sources of various lengths and orientations, and the results are compared with those of the line tension model. The effects on the critical features of an orientation‐dependent friction stress have also been studied. Similar results on the bowing characteristics of a dissociated dislocation in the f.c.c. structure and their dependence on stacking fault energy are also presented.
Thermally Activated Deformation of Potassium
Authors: Bernstein I. M. , Li J. C. M.
Published: July 2007

The thermally activated deformation of single crystal and polycrystalline potassium is examined. It is shown that the activation parameters describing low‐temperature deformation can be correlated reasonably well with the b.c.c. transition metals on the basis of their respective shear moduli. This supports the suggestion that the same general mechanism controls low‐temperature deformation for all b.c.c. materials. The possibility of this mechanism being either impurity or lattice controlled is examined and it is shown that the Peierls‐Nabarro lattice resistance model adequately explains the experimental behavior. The possible role of impurities at low temperatures is briefly considered.
A Pseudopotential Approach to the Electron Band Structure of Tellurium
Authors: Picard M. , Hulin M.
Published: July 2007

A semi‐empirical pseudopotential, derived from a study of the lead salts PbS, PbSe, PbTe, is used to compute some features of the band structure of Se and Te. For Te, this calculation confirmes previous results as the location of the band extrema. The effects of spin‐orbit coupling near the band extrema are evaluated and this yields a satisfactory picture of the main features of the band structure.
Contribution to the Determination of Gold Centre Cross Sections in Single‐Crystal Germanium by Double Injection Experiments
Authors: Hennig H.‐P.
Published: July 2007

The negative resistance region in Au‐doped double injection Ge diodes is investigated at 77 °K. The observed relaxation oscillations are typical of the 0.15 eV and 0.2 eV levels of gold in germanium. The time constants for the filling and emptying of the traps are determined from the mode of oscillation. The cross sections of the traps are then found by using concentration parameters derived from Hall effect measurements. These values of the cross sections agree with data available from the literature.
The Orientation Dependence of the Spin Wave Damping in Ferromagnetic Insulators with Spinel‐Structure
Authors: Voigt F.
Published: July 2007

Measurements are made of the relaxation frequencies of magnons at the minimum of the butterfly curve in parallel‐pumping experiments for some single crystals of ferrites and also for lithium ferrite. It is found that the anisotropic contribution to the relaxation frequency contains a large term of the sixth degree in the direction cosines of the magnetization with respect to the crystal axes. Callen and Pittelli have calculated the anisotropic ferromagnetic resonance line width in ferrites arising from the random variation of the intra‐atomic spin‐spin and spin‐orbit coupling parameters of the disordered ions. Their theory predicts a larger line width in the disordered state with a maximum in the [111] direction. The anisotropic contribution to the line width only contains a term of the fourth degree.
Photoconductivity in Amorphous Germanium
Authors: Grigorovici R. , Croitoru N. , Dévényi A.
Published: July 2007

The spectral dependence of the photosensitivity of amorphous germanium (a‐Ge) layers is measured at 106 °K and room temperature. The experimental data are correlated with those obtained from the optical absorption of a‐Ge. The high values and the temperature dependence of the time constant are attributed to the presence of a high density of trapping centres within the energy gap of a‐Ge.
Elektronenspin‐Resonanz von Triplett‐Exzitonen in Anthrazen
Authors: Haarer D. , Schmid D. , Wolf H. C.
Published: July 2007

Wir berichten über die Beobachtung zweier metastabiler ESR‐Linien in optisch angeregten Anthrazen‐Kristallen bei Zimmertemperatur. Die Linien wurden mit einem hochempfindlichen K‐Band‐Spektrometer (24 GHz) nachgewiesen. Durch Verwendung von moduliertem Anregungslicht (80 Hz) wurde eine Effektmodulation erzielt. Die Winkelabhängigkeit der ESR‐Linien kann mit Hilfe des von Sternlicht und McConnell angegebenen Spin‐Hamiltonoperators für Triplett‐Exzitonen analysiert werden. Die kristallographische b‐Achse ist eine der Hauptachsen des Feinstrukturtensors. Die Meßwerte für die Feinstrukturkonstanten sind D* = −(0,0058 ± 0,0015) cm−1 und E* = (0,0327 ± 0,0020) cm−1. Damit kann man die Feinstrukturkonstanten isolierter Anthrazen‐Moleküle berechnen: D = (0,0688 ± 0,0040) cm−1, E = −(0,0081 ± 0,0020) cm−1. Auf Grund der Zahlenwerte von D und E, der Zahl der ESR‐Linien und ihrer Winkelabhängigkeit schließen wir, daß es sich um ESR‐Spektren von Triplett‐Exzitonen handelt.
Cathodoluminescence Yields in Highly Excited CdS
Authors: Egorov V. D. , Müller G. O. , Weber H. H.
Published: July 2007

An inner energy yield between 0.15 and 0.35 is obtained for the exciton emission, 489 and 493 nm, of CdS crystals at liquid nitrogen temperature under pulsed 9 ke V electron excitation at a pair‐production rate of about 1025 cm−3 s−1 below the lasing threshold. The CdS crystals were grown without deliberate doping. Emission at other wavelengths is less than 10%; the angular dependence of the radiation is of the form expected from classical optics. According to available experimental and theoretical data the pair‐production energy is equal to about three times the energy gap, hence the observed maximum energy yields correspond to a quantum yield of one. Therefore it would be expected that the transition to stimulated emission should be accompanied only by a spatial and spectral redistribution and not by an increase in efficiency.
On the τ‐Approximation in the Quantum Theory of the Conductivity Tensor
Authors: Stolz H.
Published: July 2007

In the framework of the random phase approximation a relaxation time is introduced into the quantum mechanical calculation of the conductivity tensor for a degenerate system of free electrons being elastically scattered by randomly distributed impurities. The result satisfies the requirements of gauge invariance and particle conservation and accounts for the modification of the level density by the scattering processes. In the special case of a weakly varying field the result obtained by Mertsching [6] is retained under certain conditions. Mertsching's semiphenomenological treatment is based on a heuristic formulation of the equation of motion for the statistical operator. The result is retained here if the Landau‐condition for the level width is met (i.e. the level width is much less than the Fermi energy). In the optical limit of zero wave number the Drude expression for the conductivity is obtained only for energies considerably less than the Fermi energy, otherwise a frequency‐dependent optical mass can be introduced.
Photoconductivity Oscillations in InP
Authors: Kovalevskaya G. G. , Nasledov D. N. , Slobodchikov S. V.
Published: July 2007

The oscillatory photoconductivity effect is found in n‐ and p‐type InP (n = 2 × 1015 cm−3, p = 1014 cm−3 at T = 300 °K) at 4.2 °K for the incident photon energy range 1.4 to 2.6 eV. The oscillations are the result of a strong interaction not only with longitudinal (in the photon range 1.4 to 1.58 eV) but also with the transverse (in the photon range 1.58 to 1.71 eV) optical phonons. For the incident photon range 1.7 to 2.6 eV the photoconductivity oscillations are considered to be connected with the emission of two phonons, probably TO(x) + TA(x). A possible explanation of the results is given. The interaction with the transverse mode is considered to arise from the fact that the constant‐energy surfaces in k‐space are not spherical and from the contribution of U‐processes.
On the Problem of Static Domains in Hot Electron Semiconductors
Authors: Bonch‐Bruevich V. L.
Published: July 2007

A qualitative study is made of the possible types of static inhomogeneous charge and field distributions in hot electron semiconductors. Both continuous and discontinuous solutions are considered, the discontinuities in the displacement vector occurring either at the contacts or inside the sample.
Invariance of Sound Velocity Sums in Crystals
Authors: Fitzgerald E. R. , Wright T. W.
Published: July 2007

A relation between the lattice dissociation energy D of a monatomic crystal, the atomic mass m, and a mean crystal sound velocity csrecently suggested by Fitzgerald in connection with his particle‐wave description of non‐elastic deformation in solids is reviewed. The cited relation D=m c2s implies that certain sound velocity sums in crystals are invariant and this is shown to be the case for crystals in which small atomic displacements can be described by linear elasticity. The proposed relation between lattice dissociation energy and a mean squared sound velocity is therefore entirely consistent with classical elasticity theory although, of course, not predicted by it.
Plastic Deformation of the Intermetallic Compound MgZn2
Authors: Paufler P. , Schulze G. E. R.
Published: July 2007

The behaviour of single crystal specimens of MgZn2 deformed by basal slip is investigated by both dynamic and creep tests at temperatures between 250 and 500 °C. With the dynamic experiments a smooth upper yield point is observed. The temperature dependence of the critical resolved shear stress and of the secondary creep rate, together with the stress dependence of the latter, are discussed in terms of a Peierls mechanism of plastic deformation. Some observations concerning slip band density, length, and height are given. It is concluded that the brittleness of MgZn2 is probably a consequence of its complex atomic structure.
A Method of Measuring Effective Electron Mass in Thin Insulating Films
Authors: Antula J.
Published: July 2007

MA method is proposed for calculating the electron effective mass in thin insulating films (less than 100 Å) from the tunnel‐ and Schottky currents. In this method the slope of the Schottky characteristic provides the effective film thickness, and the slope of the tunnel characteristic leads to the electron effective mass. It is shown that, for uneven films, this method may provide better results than the calculation using the capacitance film thickness. The method is used to calculate the electron effective mass in a thin Ta2O5 film.
Zum dielektrischen Verhalten von Seignettesalz im Bereich der Decimeter‐ und Zentimeterwellen
Authors: Müser H. E. , Potthaest J.
Published: July 2007

Es wird über Messungen der komplexen Dielektrizitätskonstante von Seignettesalz zwischen 0,5 und 4,5 GHz in der Umgebung des oberen Curie‐Punktes berichtet. Die Dielektrizitätskonstante folgt einer einfachen Debye‐Relaxation mit einer Relaxationsfrequenz, die oberhalb des Curie‐Punktes linear mit der Temperatur ansteigt. Die Relaxationsfrequenz für den Dielektrizitätsmodul ist praktisch temperaturunabhängig. Hieraus folgt durch eine einfache thermodynamische Betrachtung das von anderen Autoren bei hohen Frequenzen beobachtete Minimum der Dielektrizitatskonstante am Curie‐Punkt.
About the Fowler‐Nordheim Plots of Germanium Field Emitters
Authors: Ernst L.
Published: July 2007

Fowler‐Nordheim plots are obtained for tips of n‐type Ge with a resistivity of 5 Ωcm at room temperature. Atomically clean tip surfaces are obtained by field evaporation. The field‐current density vs. field strength characteristics are given, using the data obtained by Arthur regarding the field strength necessary for the field evaporation of Ge. These are compared with characteristics computed from Stratton's theory of field emission from semiconductors by using plausible values for the surface states parameters. The comparison shows that for Ge the effective work function for field emission is appreciably higher (≈︁5.8 eV) than would be expected from the literature. A value of Na < 1.7 × 1013 cm−2 is found for the density of surface acceptor states.
Electron Microscopic Contrast Effects at the Interface between Two Different Polytypes
Authors: Fourdeux A. , Gevers R. , Amelinckx S.
Published: July 2007

A description is given of the δ‐type fringe pattern produced at the interface between a cubic and a hexagonal region within the same crystal. A discussion is given of the information which can be derived from a study of the nature of the outer fringes. Observations on a cobalt‐chromium 10% alloy are used to illustrate the theory. In this alloy the c/a ratio is found to be smaller than the ideal value. The stacking faults are found to be intrinsic.
Elektronenmikroskopische Untersuchung von Fehlstellen‐agglomeraten in ionenbestrahlten Kupferfolien. I. Analyse von Agglomerattyp und ‐konfiguration
Authors: Diepers H.
Published: July 2007

Epitaktisch gezüchtete Cu‐Einkristallfolien wurden mit monoenergetischen Ar‐Ionen (5 keV) bestrahlt. Dabei werden Fehlstellenagglomerate erzeugt, die im Elektronenmikroskop als kleine, nicht näher auflösbare Punktkontraste sichtbar sind. Die Tiefenlage der Defekte in der Folie wurde mit Hilfe von Stereoaufnahmen ermittelt. Das hierzu verwendete Verfahren wird im einzelnen beschrieben. Der Defekttyp dieser Fehlstellen (Leer‐stellen‐ oder Zwischengitteratomagglomerate) und ihre Konfiguration werden auf Grund der Kenntnis ihrer Tiefenlage unter Anwendung der dynamischen Theorie des Kontrastes (Rühle et al.[2, 12]) bestimmt. Die Agglomerate sind aus Zwischengitteratomen aufgebaut und liegen überwiegend in Form Frankscher Versetzungsringe vor. Sie liegen alle in einem schmalen Tiefenbereich unterhalb der bestrahlten Oberfläche der Folie.
Röntgenwellenfelder in einem Dreistrahlfall
Authors: Hildebrandt G.
Published: July 2007

Geburtstag gewidmet Die Grundgleichungen der dynamischen Theorie werden auf den Dreistrahlfall (000, 111, 11l) angewendet und gelöst. Es zeigt sich, daß die Dispersionsfläche aus drei Schalen‐paaren besteht, von. denen zwei ähnliche Eigenschaften haben wie die Schalenpaare des Zweistrahlfalles; insbesondere ist die zugeordnete Absorption stark erniedrigt bzw. erhöht, aber der minimale Koeffizient μ(3)⟂min ist weit kleiner als μ(2)⟂min des Zweistrahlfalles(000, 111). Die Wellenfelder des dritten Schalenpaares unterliegen etwa normaler Absorption. Folgende Eigenschaften symmetrischer Felder werden untersucht: Polarisation, Wellenlängen‐ abhängigkeit von μ(3)⟂min und μ(3)‖min, Intensitätsverteilung innerhalb der Felder mit μ(3)min und μ(3)max, Anpassung des Feldes mit μ(3)⟂min ans Gitter. Die Ergebnisse der Rechnungen stehen in befriedigender quantitativer übereinstimmung mit dem Experiment.
A Theory of X‐Ray Diffraction from an Ordered Alloy Containing Antiphase Domains
Authors: Roessler B. , Flinn P. A.
Published: July 2007

The theory of X‐ray diffraction from an ordered alloy containing antiphase domains is developed by expressing the Fourier coefficients that represent the diffracted intensity in a powder pattern in terms of a domain size distribution function. The size distribution function is expressed in terms of the second derivative of the Fourier coefficients and, hence, can be determined from experimental measurements of the superlattice peak shape. A comparison of these results to those of previous treatments of this problem shows that valuable additional information about the domain size distribution is accessible by means of the procedures presented here.
The Small Polaron Problem with an Application to Optical and DC Data of Reduced Barium Titanate
Authors: Reik H. G. , Heese D.
Published: July 2007

Reflectivity data from 1 to 12 μm for four samples of reduced BaTiO3 with dc conductivities between 20 and 240 (Ωcm)−1 are analysed in terms of small a polaron theory. Quantitative agreement between theory and experiment is found except for the sample with the highest conductivity. By fitting the optical data it is found that the parameters of the theory the average frequency of the optical phonons, Ω0, and the number η of phonons in the polarization cloud, have the values Ω0 = 1.265 × 1014 s−1 and η = 7. These parameters also determine the temperature dependence of the dc mobility. A weak temperature dependence of the mobility is found theoretically and is in agreement with the experimental data.
Piezowiderstandseffekt an Tellur. I. Experimente mit uniaxialem Druck parallel zur c‐Achse
Authors: Herrmann K. H. , Oelgabt G.
Published: July 2007

An Tellureinkristallen mit Akzeptorkonzentrationen zwischen 2,4 × 1014 und 6 × 1017 cm−3 werden die Piezowiderstandskoeffizienten π1133 und π3333 statisch gemessen. Im Eigenleitungsgebiet können die experimentellen Ergebnisse mit Hilfe des Deformationspotentialmodells quantitativ beschrieben werden. Im Störleitungsgebiet ist der Effekt temperaturunabhängig das spricht gegen das Auftreten zufälliger Entartungen im Valenzband.
Theory of Electric field Gradient due to Conduction Electron Charge Density Redistribution around Screw Dislocations in Metals
Authors: Ogurtani T. O. , Huggins R. A.
Published: July 2007

The electric field gradient due to conduction electron charge density redistribution around screw dislocations in metals is calculated. It is found that the electric field gradient behaves as r−5/2 cos(2 kF r + ϕ), where kF is the Fermi wave number and ϕ is the phase. The Bloch enhancement factor is computed using the orthogonalized plane wave procedure, and is found to be 7.62 for a screw dislocation in copper. These results are in agreement with nuclear magnetic resonance experiments in plastically deformed copper.
Magnetic Resonance in Higher Harmonics Generated by Free Carriers in Semiconductors
Authors: Kołodziejczak J.
Published: July 2007

An effect of higher harmonics generation by free carriers in semiconductors is discussed. It is shown that a large enhancement of nonlinear effects due to resonance at high magnetic fields can be observed. The effects discussed in the paper are associated with a non‐parabolicity of the band.
Derivation of Nucleation Kinetics in Solids by Examination of Plane Sections through the Samples
Authors: Toschev S. , Gutzow I.
Published: July 2007

Using a statistical approach, the basic formula is derived which relates the size distribution of spherical non‐communicating second phase particles embedded in a solid matrix to the distribution of their circular intersections revealed on an arbitrary plane through the specimen. Four types of crystallization kinetics are treated: steady state nucleation, transient nucleation, heterogeneous nucleation, and transient heterogeneous nucleation. The linear rate of crystal growth is assumed to be time‐independent in all cases. The corresponding size distribution functions in the volume and on the surface are derived. Their analysis permits the evaluation of important crystallization parameters from experimental data.
On the Phonon Drag Effect Contribution to Thermomagnetic Phenomena
Authors: Plăvttu C. N.
Published: July 2007

Calculations are made of the acoustic and optical phonon drag effect contributions to some of the isothermal thermomagnetic coefficients. The scattering is considered to be a mixture of acoustic, optical, and ionized impurity scattering. It is found that the optical phonon drag is of more importance for the thermomagnetic effects than for the thermoelectric effects.
The Dielectric Permeability of Molecular Crystals
Authors: Davydov A. S. , Onishchuk V. A.
Published: July 2007

The quantum theory of the dielectric permeability of molecular crystals is developed on the basis of the quantum field equations and electronic excitation states of the crystals. The interaction between the molecules is considered to take place only through the field. The Green's function formalism is used.
Neutron‐Diffraction Study of AntiferroFerromagnetic Transition in a System of Ordered Fe(PdxPt1−x)3 Alloys
Authors: Kelarev V. V. , Sidorov S. K. , Klyushin V. V. , Abdulov R. Z.
Published: July 2007

Some conclusions are made regarding the transition from antiferromagnetic to ferromagnetic structure in the ordered alloys of the system Fe(Pdx Pd1−x)3. This is based on an analysis of an experimental dependence of the intensity of the (100) ferromagnetic reflexion on the average magnetic moment per atom of the alloys of the system. It is concluded that the transition takes place through a set of complex magnetic structures with a noncollinear orientation of the atomic magnetic moments of the components.