bluuebunny/crossref_metadata_2025 huggingface dataset:
On Non‐Equilibrium Effects in Solid State Rate Processes
Authors: Geszti T.
Published: July 2007

At temperatures high enough to make thermally activated hopping sufficiently fast and at correspondingly high frequencies, inelastic or dielectric relaxation (damping) due to point defects may show the following deviations from the predictions of equilibrium theory: a) the main damping maximum appears at a frequency lower than predicted by equilibrium theory, b) the intensity of the main maximum is reduced, c) secondary damping maxima appear at eigenfrequencies of the energy exchange between defect and surroundings. The analysis shows that experimental detection of these effects is most easily realizable on defect systems with slow energy exchange with the surrounding crystal, and low activation energy.
Vineyard's Theory of the Kinetics of Ordering and Lidiard's Consistency Conditions
Authors: Sohoijet M.
Published: July 2007

Lidiard's consistency conditions are extended to the case of alloys of face centered cubic structure. By separating the jump rates into a part originating in the saddle point atoms and a part originating in the other neighbors it is shown that a Vineyard type of theory does not verify Lidiard's consistency conditions except in the limiting cases of complete order and complete disorder.
On the Experimental Observation of Small Polarons in Rutile (TiO2)
Authors: Bogomolov V. N. , Firsov Yu. A. , Kudinov E. K. , Mirlin D. N.
Published: July 2007

A careful analysis of certain observations concerning the polaron nature of current carriers in rutile is presented. The criticism of our paper [1] given in [2] is shown to be unfounded.
The Electrical Resistance of Palladium and Palladium–Gold Alloy (50 wt% Au and Pd) in Gaseous Hydrogen up to 24000 at at 25 °C
Authors: Baranowski B. , Wiśniewski R.
Published: July 2007

The outline of a high‐pressure advice for gaseous hydrogen as a double piston‐cylinder system is given. Any contact between the gaseous volume and the pressure‐transmitting liquid is avoided. The electrical resistance of Pd and Pd–Au (50 wt%) foils was measured at (25 ± 0.1) °C up to 24000 at of gaseous hydrogen. A linear relationship of relative electrical resistance versus the logarithm of the hydrogen fugacity is observed. The relative electrical resistance of Pd as function of the atomic ratio H:Pd is estimated.
On the Influence of Surface Roughness on the Magnetization Ripple in Ferromagnetic Thin Films
Authors: Maksymowicz A. , Maksymowicz L. , Lubecka M.
Published: July 2007

A model is proposed in which the decisive influence on magnetization ripple is exerted by demagnetizing fields produced by surface charges due to the roughness of the surface of the thin film. The model predicts periodical fluctuations of the magnetization vector around the mean magnetization direction. The expressions obtained for the ripple amplitude and periodicity are where
equation image
a is the effective value of the surface roughness and t the thickness of the film. The theoretical results are in agreement with the experimental data of other authors.
Phonon Bottleneck Investigation Using a Quantum Statistical Method
Authors: Böttger H.
Published: July 2007

Using a density‐matrix formalism equations are derived describing the time dependence of spin and phonon temperatures of a paramagnetic crystal with a phonon bottleneck. The derived equations are compared with the usual rate equations describing a phonon bottleneck.
Compensation of Trivalent Europium and Ytterbium Ions in Calcium Fluoride by Interstitial Hydride Ions
Authors: Chambers D. N. , Newman R. C.
Published: July 2007

Hydrogen has been diffused into calcium fluoride crystals doped with Eu, Yb and other Rare Earths. The local mode absorption from H− ions has been measured before and after X‐ or γ‐irradiations and a detailed study has been made of the new electronic transitions of Yb3+ ions near 1 μm which appear after the irradiation. It is concluded that for Eu and Yb dopings, RE3+—H−(i) pairs are produced which are thermally unstable. In CaF2:Yb crystals, a second centre involving two hydride ions has also been identified.
Dynamical Theory of Hydrogen Diffusion in Cubic Metals
Authors: Lepski D.
Published: July 2007

Starting from a criticism of the classical rate theory for diffusion processes and its quantum derivatives a dynamical theory for the diffusion of light interstitial impurities in crystals based on Kubo's work is derived and applied to an one‐dimensional model for hydrogen diffusion in cubic metals. It appears that hydrogen diffusion in the b.c.c. metals must be treated quantum mechanically in a band model, whereas for f.c.c. metals a classical theory seems more suitable. In the quantum (b.c.c.) case we obtain a remarkable isotope effect in the activation energy, which depends strongly on the model potential used, and a pre‐exponential factor, D0, approximately proportional to the inverse of the particle mass.
Potential Fields of Parallel Edge Dislocation Arrays
Authors: Neubert D.
Published: July 2007

The equipotential lines for a free test dislocation in the stress field of fixed parallel edge dislocation arrays are calculated from linear elasticity theory. The potential fields determine the path a free dislocation will take under ideal conditions. The well known fact is demonstrated that from an energetic point of view edge dislocations prefer to arrange in a wall rather than in a glide plane, namely by the positions of the calculated potential valleys which give the stable positions for the free test dislocation. Calculations are presented for characteristic arrays with a small number of dislocations. As the qualitative features of the results will hold also for arrays with a large number of dislocations some conclusions are drawn on the process of polygonization and a comparison with properties of edge dislocation arrays in silicon is made.
On the Theory of Excitons in High Magnetic Fields
Authors: Fritsche L. , Heidt F. D.
Published: July 2007

It has been shown in a previous paper the excitonic optical absorption spectra in GaSe at high magnetic fields can be explained on the basis of a theory developed by Elliott and Loudon. In the present paper this theory is generalized by including the effects of dielectric anisotropy and non‐spherical bands. As can be expected in view of the layer‐structure of GaSe the treatment yields a considerable improvement in fitting the experimental data, especially those of the so‐called satellite lines of the exciton absorption spectrum above 30 kG.
Electron Energy Bands of Two Solids in Contact
Authors: Gossick B. R.
Published: July 2007

An algorithm is outlined for determining the amplitude and phase of the electronic wave function as a function of energy and distance from the boundary between two different crystals.
On the Energy Transmission of Paramagnetic Ions into the Lattice through Rapidly Relaxing Centres
Authors: Skrebnev V. A.
Published: July 2007

A investigation is made of the spin‐lattice relaxation in crystals having two kinds of paramagnetic centre whose resonance frequencies ae nearly the same and whose spin‐phonon interaction differs essentially. The concentration of centres with slower relaxation rate is considered to be greater than the concentration of rapidly relaxing centres. It is assumed that the spin‐phonon coupling of the rapidly relaxing centres is much less than the spin‐spin interactions of these centres with the other paramagnetic centres. The dependence of the spin‐lattice relaxation time of centres which ae weakly bounded to the lattice and which relax through rapidly relaxing centres on the splitting difference of their spin levels, on the value of spin‐spin interactions between them, on their concentration, and on the value of the spin‐phonon interaction of the rapidly relaxing centres is established.
The Nature of DC Field Effect Relaxation in Photoconducting CdS
Authors: Weber E.‐H.
Published: July 2007

It is shown that the real surface of photoconducting CdS crystals is usually contaminated by CdSO4. From de field effect and photocurrent measurements it can be concluded that CdSO4 has a donor‐like action at the surface which leads to a reduced recombination rate for photocarriers near or at the surface. Apparently no slow surface states are present on a contaminated surface; the slow relaxation of field effect seems to be determined mainly by volume trapping centres within the space‐charge region.
Magnetic Properties of FeCr2S4 and CoCr2S4
Authors: Gibart P. , Dormann J.‐L. , Pellerin Y.
Published: July 2007

New measurements of magnetic properties of pure FeCr2S4 and CoCr2S4 have been carried out. The g‐factors of cobalt, iron, and chromium in these compounds were evaluated. Exchange interactions were deduced from computation of the experimental paramagnetic and magnetization curves.
Deformation of Molecular Crystals at Electronic Excitation
Authors: Davydov A. S.
Published: July 2007

In this article an investigation is made of deformation of the molecular crystal due to electronic excitation. It is shown that in a three‐dimensional crystals at a sufficiently large resonance interaction between molecules the states of free excitations with positive effective mass correspond to minimum of the total energy of the crystal. The transition to local excitations requires activation energy. The states of the free excitons with negative effective masses in three‐dimensional and one‐dimensional crystals are unstable. Exciton states with positive effective masses in one‐dimensional crystals are represented as modulated plane waves. Distribution of the excitation along some length of the crystal corresponds to these waves. The stronger is the resonance interaction between molecules, the more is this length.
Die Deutung sekundärer Eigenschaften des Bordoni‐Maximums in einem Mehrmuldenmodell der Doppelkinkrelaxation
Authors: Engelke H.
Published: July 2007

Ein in einer vorangegangenen Arbeit abgeleitetes Modell für die Bewegung von Versetzungsbögen im Peierls‐Potential wird in vereinfachter Form dazu benutzt, mechanische Dämpfungsmaxima im amplitudenunabhängigen Bereich zu berechnen. Ein Vergleich mit gemessenen Bordoni‐Maxima ergibt gute Übereinstimmung für die Relaxationsstärke und den präexponentiellen Faktor der Relaxationszeit. Bei Annahme plausibler Verteilungen der Bogenlängen und der inneren Spannungen erhält man näherungsweise eine von D. O. Thompson gefundene Λ2‐Abhängigkeit der Relaxationsstärke (Λ mittlere Bodenlänge) und Temperaturverschiebungen der Maxima in der richtigen Größenordnung. Obwohl die berechneten Maxima gegenüber einfachen Relaxationsmaxima erheblich verbreitert sind, scheint eine Deutung der vollen Breite des Bordoni‐Maximums eine strengere Behandlung des Modells zu erfordern.
Polishing Damage and Luminescence in p‐Type GaAs
Authors: Tuck B.
Published: July 2007

The photoluminescence of zinc‐doped GaAs has been studied for different surface preparations. Mechanically polished specimens fluoresced less than chemically prepared ones. Etch‐pit studies using a dislocation etch indicated that mechanical polishing introduced dislocations and samples showing the largest number of etch pits showed the weakest photoluminescence. It was also shown that diffusing a large concentration of zinc into n‐type GaAs introduces dislocations, and it is suggested that this is the reason for the low photoluminescence efficiency of zinc‐doped GaAs for concentrations in excess of 1019 cm−3.
Radiative Recombination in Silicon p‐n Junctions
Authors: Michaelis W. , Pilkuhn M. H.
Published: July 2007

The electroluminescence of silicon was investigated in the temperature range between 300 and 77 °K. The near edge emission is due to indirect band‐to‐band transitions associated with TO and TA phonon emission/absorption. The intensity‐voltage relation shows that this emission is connected with the diffusion current. At low voltages, additional long wavelength emission is observed which is connected with recombination in the space charge region. An absolute measurement of the internal quantum efficiency yields a room temperature value of 2 × 10−6 for the band‐to‐band emission. This value is well described by a theoretical radiative lifetime derived from van Roosbroeck‐Shockley statistics and by an experimental non‐radiative lifetime.
Far Infrared Reflectivity of SbSI
Authors: Petzelt J.
Published: July 2007

Far infrared reflectivity of SbSI bulk crystals in a polarized light was measured in the temperature region between −185 and 80 °C and frequency from 400 up to 15 cm−1. The optical constants and dielectric constant were calculated using Kramers‐Kronig analysis. The experimental data were compared with the results of the group‐theoretical analysis of normal vibrations. Soft mode behaviour was observed in the lowest frequency region (below 100 cm−1) and parameters of the corresponding oscillator were calculated. The mode frequency shifts from 32 cm−1 at 60 °C to 22 cm−1 at 25 °C. The oscillator strength is not high enough to explain the whole value of the static dielectric constant so that still another lower frequency resonance as observed by Grigas and Karpus in the centimetre region or a relaxation as observed by Vu Huy Dat in megacycle region should exist.
Effect of Three‐Body Forces on the Shell Model of Alkali Halides: Application to KBr and KI
Authors: Singh R. K. , Verma M. P.
Published: July 2007

The three‐body coupling coefficients computed in an earlier paper [14] have been injected in the shell model of ionic solids treating both the ions as polarizable. This modified shell model has been used to compute the dispersion curves and the two phonon combined density of states (C.D.S.) curves of KBr and KI. Excellent agreements have been obtained with the results of neutron scattering and Raman scattering experiments.
Die Behandlung von Fehlern im Fußliniengitter der Supraleiter 2. Art in der Nähe von Hc2
Authors: Brandt E. H.
Published: July 2007

Abrikosovs Methode zur Berechnung der Energie und Struktur eines regelmäßigen Flußliniengitters in Supraleitern 2. Art in der Nähe von Hc2 mit Hilfe der linearisierten Ginsburg Landau‐Gleichungen wird auf die Behandlung von Störungen im Flußliniengitter erweitert. Die Fehlerenergie kann als Integral über den ganzen Supraleiter geschrieben werden. Durch Variation dieses Ausdrucks erhält man das Verschiebungsfeld des Fehlers. Der Schubmodul des Flußliniengitters wird berechnet. Sowohl die Fehlerenergie als auch der Schubmodul gehen für Ha → Hc2 wie (Hc2Ha)2 gegen Null.
Low‐Temperature Internal Friction in Deformed Single Crystals of Niobium and Niobium‐Molybdenum Alloys
Authors: Amateau M. F. , Mitchell T. E. , Gibala R.
Published: July 2007

The low‐temperature internal friction spectrum has been measured on single crystals of Nb and Nb‐Mo alloys deformed in tension. The α‐peak height is found to increase in proportion to the square of the work‐hardening stress and, therefore, in direct proportion to the dislocation density. The addition of interstitial impurities or substitutional molybdenum is found to increase the frequency factor of the α‐peak without changing the activation energy. The maximum peak height is decreased substantially both by impurities and by decreasing the deformation temperature. It is concluded that the α‐peak is similar to the Bordoni peak in f.c.c. metals and is due to either an intrinsic dislocation mechanism (most likely kink nucleation on non‐screw dislocations), which is sensitive to impurities, or an extrinsic mechanism in which impurities are more directly involved. Some preliminary observations on the β‐peak are also presented.
Effect of Copper Layers on the Coercive Force of Permalloy Films
Authors: Grishechkin M. I. , Telesnin R. V. , Durasova Yu. A. , Osukhovskii V. E.
Published: July 2007

Three mechanism of the effect of a copper layer on the coercive force of films are studied in this work: variation in the “roughness” of the substrate; diffusion of the copper into the permalloy; variation in the energy of exchange interaction between permalloy films separated by a copper layer. It is found, that an increment of the coercive force (ΔHc) with time is directly proportional to the effective diffusion depth, Δd. The results of experimental investigations on the condensation of metallic film make it possible to single out the following stages of this process: the formation of stable nuclei, the coalescence of discrete nuclei to a continuous layer; the growth of crystallites with a further increase of the thickness of continuous films. Observation of structures of interlayers under an electron microscope indicates that in wide ranges of thickness and deposition temperatures the interlayer consists of individual stable nuclei. The presence of exchange interaction between separated magnetic layers due to their direct contact makes it possible to explain the experimental results.
The Overshoot Phenomena in Single Crystals of Cu‐15 at% Al Tested in Tension. II. Orientation and Temperature Dependence of the Overshoot
Authors: Tisone T. C. , Brittain J. O. , Meshii M.
Published: July 2007

Overshooting in Cu‐15 at% Al single crystals was studied as a function of quenching temperature, testing temperature, and initial tensile axis orientation. Overshooting was found to be independent of orientation and test temperature but the degree of overshoot appeared to increase with increasing quench temperature. It was concluded that the overshoot was not a direct function of the stacking fault energy in the range of 5 to 10 erg/cm2 for a Cu‐15 at% Al alloy. A model for overshoot was developed based on the collapse of Lomer‐Cottrell dislocations under the line tension of bowed out conjugate dislocation segments.
Electrical Properties of Dislocations in Ge and Si
Authors: Schröter W. , Labusch R.
Published: July 2007

The occupation statistics of the energy levels which are introduced by dislocations in Ge and Si are carried out taking into account that charged dislocations are a strong perturbation for the energy levels of the valence and the conduction band. The result is a theoretical relation between the line charge of the dislocation and the apparent experimental Fermi energy which is obtained from the number of free carriers. Comparing this relation with Hall effect measurements the position of the neutral dislocation level in the energy gap and the dislocation length per unit volume that is electrically active can be determined. Possible mechanisms for the screening of charged dislocations are discussed. It turns out that former screening models are appropriate only at very low temperatures and that for a wide range of experimental conditions the screening is done by a rearrangement of free carriers.
Thermodynamic Calculations of the Debye‐Waller Frequency Integrals of Alkaline Earth Fluorides
Authors: Brade R. M. , Yates B.
Published: July 2007

The maximum frequencies of the Debye distributions having the same n‐th moments as the vibrational frequency spectra in CaF2, SrF2, and BaF2, calculated from specific heat, thermal expansion, and elastic constant data, have been applied in the quasi‐harmonic approximation to calculate the Debye‐Waller frequency integrals of these solids. High‐and low‐temperature series expansions and Padé approximants have been employed to calculate these parameters as functions of temperature between 0 and 300 °K. Good agreement is observed between the values calculated for CaF2 and BaF2 at room temperature and those based upon neutron diffraction studies.
A. Semi‐Empirical Model for the Valence Band Structure of Tellurium
Authors: Betbeder‐Matibet O. , Hulin M.
Published: July 2007

A simple model for the valence band structure of tellurium, in the neighbourhood of its maximum, has been derived. It takes account of spin‐orbit coupling and depends upon a restricted set of parameters which can all be determined from experimental data. Most of the qualitative features of electronic properties (Shubnikov‐de Haas effect, cyclotron resonance, and optical absorption) can be explained by this model, and a quantitative agreement between theory and experiments can be obtained.
Dichroïsme linéaire sous contrainte des matrices cubiques dopées
Authors: Duran J.
Published: July 2007

On envisage l'extension de l'étude des effets piézospectroscopiques aux raies d'absorption larges. On analyse les différents facteurs intervenant dans le dichroïsme linéaire sous contrainte des matrices cubiques contenant des centres possédant la dégénérescence d'orientation et (ou) électronique. On démontre et on vérifie expérimentalement des relations valables dans tous les types de centres entre les dichroïsmes mesurés pour différentes directions de pression et d'observation parallèles aux axes d'ordre 2, 3 et 4 du cube. On donne un tableau général des dichroïsmes linéaires calculés pour tous les types de centres anisotropes susceptibles d'exister dans les matrices cubiques. Enfin l'examen des effets de la température et des mélanges des fonctions d'onde par la pression permet de donner une formulation générale du dichroïsme linéaire sous contrainte analogue à celle du dichroïsme circulaire magnétique.
Mössbauer Effect for Fe57 in CoCl2 and CoF2
Authors: Cavanagh J. F.
Published: July 2007

The Mössbauer effect for Fe57 in CoCl2 and CoF2 has been measured by using them as sources in a resonant absorption experiment. While the CoCl2 spectra indicate only a 2+ charge state for the Fe57 ion, the CoF2 spectra indicate both a 3+ and a 2+ charge state. When a sample of CoF2 is used as an absorber doped with a small amount of iron enriched in Fe57, however, only 2+ charge state lines appear in the absorption spectra. This is interpreted as resulting from a local environment change associated with Auger aftereffects following K‐capture. The internal magnetic field has been estimated for each compound below its Néel temperature. Values of (49 ± 2) kOe for CoCl2 and (245 ± 2) kOe for CoF2 were found at 10 and 11 °K, respectively, for the field at an Fe2+ nucleus.
Temperature Distribution and Its Kinetics in a Semiconducting Sandwich
Authors: Böer K. W. , Döhler G.
Published: July 2007

The temperature distribution and its change in time is calculated for a semiconducting sandwich between two metal electrodes by solving the thermal balance equation including Joule's heating for one spatial coordinate and neglecting space‐charge effects. As boundary conditions, three cases are analysed: perfect cooling and Newton's cooling of the metal electrodes, however neglecting a temperature drop in the metal layers, or including a finite heat conductivity of the electrodes.
The Dependence of Cd Diffusion and Electrical Conductivity in CdS on Cd Partial Pressure and Temperature
Authors: Shaw D. , Whelan R. C.
Published: July 2007

The diffusion coefficient of Cd in undoped single crystal CdS has been measured at 850 °C as a function of Cd pressure, pCd, by a radiotracer method. The electrical conductivity of similar CdS samples has also been measured as a function of pCd in the temperature range 660 to 950 °C. It is concluded that the defects V″Cd and Cd are responsible for Cd diffusion at 850 °C and that a satisfactory account of the results can be given in terms of Cd interstitials and vacancies plus a residual shallow foreign donor. A model for the defect structure in CdS at 850 °C is presented in terms of Cd vacancies and interstitials.
Exciton Diffusion and Multimode Behaviour in Electron‐Beam‐Pumped CdS Lasers
Authors: Bille J.
Published: July 2007

From CdS platelet crystals coherent radiation can be obtained resulting from the decay of free excitons to photons and longitudinal optical phonons (line ALO). In semiconductor lasers as CdS with a homogeneously broadened spontaneous emission line spatial inhomogeneity of the inverted population can lead to multimode oscillation. The number of axial modes oscillating simultaneously for a given excitation value above the threshold depends on the diffusion velocity of the inverted carriers, whereby the diffusion is smoothing out the spatial inhomogeneities. The fitting of the experimental data by the theory of Statz and Tang enables us to determine the exciton diffusion length at liquid‐air temperature; we find LDiff = 0.1 μm.
A Calculation of the Formation and Migration Entropies of Surface Defects in Copper
Authors: Wynblatt P.
Published: July 2007

Formation entropies, frequency factors, and associated migration entropies have been calculated on copper surfaces of (100), (110), and (111) orientations for both terrace vacancies and adatoms, using a discrete vibrational approach. The vibrational spectra for the various defect configurations have been obtained using a quasi‐harmonic Einstein model in conjunction with a modified Morse function force law. ‐ The calculated quantities have been used to estimate Arrhenius D0's for intrinsic, single‐defect‐controlled diffusion. When these quantities are taken together with previously calculated activation energies for surface self‐diffusion, it is possible to obtain theoretical Arrhenius plots for each defect on a given surface orientation. The results are also helpful in the evaluation of earlier mechanistic interpretations of the observed curvature in the experimental Arrhenius plots.
The Infrared Absorption of the FCl− Heteronuclear Molecule Ion in KCl
Authors: Susman S.
Published: July 2007

Single crystals of KCl doped with KF and exposed to high dosages of Co60 γ‐radiation develop a simple doublet absorption on the high frequency edge of the KCl reststrahl. This 403.7—399.8 cm−1 doublet is assigned to the fundamental internal vibration of the FCl− heteronuclear molecule ion. The doublet separation, intensity ratio, thermal decay, optical bleaching and polarization properties support this assignment. The internal stretching frequency of FCl− in KCl is not markedly different than would be approximated from gas phase data for the neutral species.
Electron Metallography of a Non‐Classical Order—Disorder Transition
Authors: Swann P. R. , Duff W. R. , Fisher R. M.
Published: July 2007

Transmission electron metallography has been used to resolve the microstructural changes which occur during the D03⇄L20 transition in an Fe26.5at%Al alloy. The micrographs show evidence for a) long‐range‐order fluctuations near the critical temperature, b) local lowering of a critical temperature in the neighborhood of domain boundaries, and c) absence of a stable two‐phase field separating the D03 and L20 phases. From these results it is concluded that the subject transition is not a classical (nucleation and growth) phase change.
Magnetic Anisotropy in F.C.C. Single Crystal Cobalt—Nickel Electrodeposited Films. I. Magnetocrystalline Anisotropy Constants from (110) and (001) Deposits
Authors: Lord D. G. , Goddard J.
Published: July 2007

A study of the magnetocrystalline anisotropy of electrodeposited (001) and (110) single crystal f.c.c. Co—Ni films of thicknesses between 100 and 1000 Åhas been carried out, at 20 °C, by torque magnetometry. The composition dependence of K1 from the thicker films is found to agree with previous results from bulk alloys of the Ni‐rich compositions, but, apart from the work of Andrä and Spinarke (1969), differs from previous results from thinfilms. The constants K2 and K3 have been measured and have both been found to be negative over the whole composition range.
A Comparison of the Effects of Systematic Reflections on Extinction Contours in Bright‐ and Dark‐Field Images of Wedge Crystals
Authors: Sheinin S. S.
Published: July 2007

The dependence of the fringe spacing of extinction contours on crystal orientation has been studied in bright‐field images of wedge crystals of silicon. Crystal orientations were chosen so that either the (111) or (220) set of systematic reflections was excited. Comparison of the results obtained with extinction contours in (111) and (220) dark‐field images shows that when effects of systematic reflections are weak, as in the (220) case, there are no significant differences between bright‐and dark‐field contours. When effects of systematic reflections are strong however, as in the (111) case, bright‐ and dark‐field extinction contours are markedly different. Thus, for example, at certain crystal orientations the brightfield intensity profiles show the complex structure characteristic of the effects of multiple reflections whereas the dark‐field images, for the same diffracting conditions, are two‐beam in character.
Observation of X‐Ray Stacking Fault Fringes in the Plane Wave Case
Authors: Sauvage M. , Malgrange C.
Published: July 2007

X‐ray stacking fault fringes in a silicon wafer are observed in the plane wave case by use of a double crystal spectrometer. Agreement with the theory is checked for two different radiations (AgKα and CuKα) and various values of the departure from Bragg angle. The nature of the fault, previously studied by X‐ray topography, is determined on the basis of the first extremum criterion in high absorption conditions. As expected, the results are closely related to those obtained in the electron case.
Lattice Vibrations of Cu2O at the Long Wave Limit
Authors: Carabatos C.
Published: July 2007

A study of the lattice dynamics of cuprite at the centre of the Brillouin zone is made and the force constants and the effective charge deduced. The energies of the optically inactive phonons are calculated and their symmetry determined. The symmetry of the upper valence band of the crystal is identified.
Electron Microscopic Investigation of the Dislocation Structure in Molybdenum Single Crystals Deformed in Tension at 293 and 493 °K
Authors: Luft A. , Kaun L.
Published: July 2007

The dislocation structure of high purity molybdenum single crystals after weak tensile deformation at 293 and 493 °K is studied by transmission electron microscopy. The transition from parabolic stress—strain behaviour to three‐stage hardening which occurs between the considered temperatures is associated with a basic change in the deformation substructure. Crystals deformed at 293 °K contain a uniform distribution of long primary and secondary screw dislocations. On the contrary, the dislocation structure in stage I at 493 °K consists mainly of isolated clusters of primary edge dipoles. It is concluded that the effect of temperature on the mobility of screw dislocations is responsible for the change observed both in work‐hardening characteristics and related dislocation structures.
Temperature Dependence of the Davydov Splitting in Anthracene
Authors: Kurik M. V. , Piryatinskii Yu. P. , Popel O. M. , Frolova E. K.
Published: July 2007

The Davydov splitting for photoconductivity and absorption in anthracene has been measured in a wide temperature range. A phenomenological theory is developed which explains qualitatively the observed regularities.
DC Ionic Conductivity of Potassium Azide
Authors: Maycock J. N. , Verneker V. R. Pai , Gorzynski C. S.
Published: July 2007

The electrical conductance of both single crystal and pressed pellets of potassium azide has been measured. The ionic conductance parameters of KN3 were calculated from samples containing known amounts of Ba2+ ion impurity. The conventional theory of association was found to be adequate to describe association between Ba2+ and cation vacancies. A value of 0.2 eV was determined for — ζ, where ζ is the free energy of association of complexes. The following point defect parameters were determined: h, the enthalpy change for the formation of a defect pair = 1.25 eV, Δh, the enthalpy for migration of a cation vacancy = 0.76 eV, s, the entropy change on the formation of a defect pair = 0.119 × 10−3 eV deg−1. Equations describing X0, the number of thermally produced defects in a pure crystal, and μ, the mobility of the cation vacancy, both as a function of temperature have been derived.
Domain Structure of Uniaxial Antiferromagnets. The Problem of Nucleation
Authors: Mitsek A. I. , Gaidanskii P. F. , Pushkar V. N.
Published: July 2007

The dependence of the energy γ180 and the halfwidth δ180 of 180° L‐domain walls in antiferromagnets on the magnetic field H is calculated for low fields. At H → H0 (H0 is the critical field of the spin‐flop transition) the walls expand and their energy γ180 decreases. In the spin‐flop region 90° domain structure appears. γ90 and δ90 are determined by the value of fourth‐order anisotropy constant K2. The calculation of the metastable state (K2 <0) region shows that its boundaries may be approximated by the astroid at |K2| ≪ K1 only. The wall displacement in the spin‐flop region (K2 ≪ 0) and the domain structure at K2 > 0 are discussed. The problem of the new magnetic phase nucleation is considered.
Excitonic Electroreflectance of CuCl
Authors: Mohler E.
Published: July 2007

Transverse electroreflectance measurements have been performed on CuCl single crystals in the region of the exciton bands. The observed changes of reflectivity can be separated into two components corresponding to a linear and a quadratic Stark effect of the excitons. The linear Stark effect is due to a splitting of the valence bands of CuCl, whereas in the case of the quadratic Stark effect the relative motion of the electron–hole pair is influenced by the electric field.
Anisotropy Investigations by Electrical Potential Measurements on Surfaces of P‐ and As‐TCNQ Single Crystals
Authors: Zosel D. , Ritschel H. , Hänsel H.
Published: July 2007

A one‐probe measuring method has been used for electrical potential measurements on different planes of naturally grown single crystals of triphenylmethylphosphonium 7, 7, 8, 8‐tetracyanoquinodimethane (P‐TCNQ) and triphenylmethylarsonium 7, 7, 8, 8‐tetracyanoquinodimethane (As‐TCNQ). Potential distributions which result from using pairs of circular and straight plate electrodes in different arrangements on the crystal planes have been investigated. The explanation and description of the measured plots of the equipotential lines with a model is possible in a simple way for the (100) plane by using an anisotropic resistance net because in this case it is possible to reduce the three‐dimensional potential problem to a plane one. The electrical potential measurements give another contribution to the explanation of the interrelations between the crystal structure and anisotropic electrical properties of P‐ and As‐TCNQ.
Hole Effective Masses in Highly Doped CdSb Determined from Infrared‐Plasma‐Reflectivity Measurements
Authors: Rheinländer B.
Published: July 2007

The infrared plasma reflectivity is measured on heavily Ag‐doped CdSb with hole concentrations of p = (0.7 to 3.0) × 1019 cm−3 in the spectral region λ = 3 to 30 μm at T = 85 and 300 °K. Conductivity effective masses and relaxation times of holes are determined from the plasma frequencies obtained by fitting experimental and theoretical reflectivity spectra. The masses are strongly anisotropic and weakly temperature dependent. The relaxation times for optical frequencies are slightly greater than those according to Hall mobilities. Scattering of holes on ionized impurities is concluded to be predominate in the relaxation mechanism.
Charge Carrier Injection by Excitons at a Tetracene (Anthracene) – Electrolyte Interface
Authors: Vaubel G.
Published: July 2007

The influence of oxygen in electrolytic contacts on extrinsic photocurrents in tetracene and anthracene crystals is investigated. By adding Na2SO3 to the electrolytic electrode it is possible to vary the O2 partial pressure by orders of magnitude. It is found that triplet induced hole currents are controlled by a reaction of triplet excitons with oxygen, while singlet exciton induced hole currents must be produced by a specific exciton‐water reaction. On the other hand it is found that Na2SO3 stimulates an electron injection i.e. sulfit ions can act as electron donor upon interaction with triplet excitons. A kinetic analysis of the results is presented.
Dislocation Invisibility in Dark‐Field Electron Microscopy
Authors: Dingley D. J.
Published: July 2007

A study has been made of conditions governing dislocation invisibility in dark‐field electron microscopy when the usual invisibility criterion g · b = 0 is not satisfied. Experiments were conducted on f.c.c., b.c.c., and h.c. p. metals. Anomalous invisibilities of dislocations were observed in each case and also when using high order or low order reflection s. Computer produced dislocation profiles indicated that the occurrence of anomalous invisibility is strongly dependent on the foil thickness to extinction distance ratio. The effects of this on the validity of past measurements of Burgers vectors using electron microscopy techniques are discussed. It is concluded that although errors must have been incurred in the past, they would only constitute a minor fraction of the data obtained.
Crystal Field Parameters of Ho3+ in YPO4
Authors: Becker P.‐J.
Published: July 2007

Sets of crystal field parameters are derived to describe the splittings of the 5F', the 3K'8, the 5G'6, and the 5G'4,5 levels of Ho3+ in YPO4 separately. The differences of the A〈r2〉 parameter for different levels by a factor of about 20 are explained qualitatively by different shielding factors for electrons in different LS‐states.
Double‐Plasmon Excitation in a Free‐Electron Gas
Authors: Ashley J. C. , Ritchie R. H.
Published: July 2007

The interaction of a fast charged particle moving in a free‐electron gas is described in the random phase approximation (RPA). The mean free path for the second order process of double‐plasmon excitation in the free‐electron gas is calculated. We find that the inverse mean free path for the double‐plasmon excitation process is related to the inverse mean free path for single plasmon excitation by λ = 0.0103 rλ−1p. Thus, for electron densities corresponding to those in a real metal (1 < rs < 6) double‐plasmon excitation may be important in the interpretation of certain experimental results as, for example, characteristic energy loss measurements.
The Effective Mass Tensor in Uniaxially Stressed n‐Type InSb
Authors: Zukotński S. , Saleh N.
Published: July 2007

In a previous paper [1] the plasma minimum in anisotropic semiconductors was theoretically analysed. In the present paper, degenerate n‐type InSb is considered and the anisotropy is induced by applying uniaxial stress. Using the theory developed by Bir and Pikus [2] the effective mass tensor is derived for stress applied in the [110], [100], and [111] directions. Measurements of the plasma minimum for samples stressed along the [100], [110], and [111] directions are presented and the effective masses are calculated. The results are used to obtain the value of the deformation potential (−40.8 eV) and of the band parameters a, b, and d (−88, −0.17, and −4.6 eV).
Magnetic Domain Wall Motion and Increase of Coercive Field
Authors: Bostanjoglo O.
Published: July 2007

The magnetic reversal in inhomogeneous iron and coarse grained cobalt films was investigated at 300 and 4 °K by Lorentz microscopy. The strong increase of the wall coercive field with decreasing temperature results in nucleation of numerous reversed domains at low temperature thus considerably changing the wall motion.
Optical Modulation Spectra of Selenium and Their Dependence on the Uniaxial Stress
Authors: Tuomi T. O.
Published: July 2007

Wavelength‐ and stress‐modulated reflectance and transmission spectra of selenium are measured at 77 °K in the photon energy range from 1.7 to 3.7 eV. New structure is discovered, e.g. a peak at 2.0 eV in the wavelength‐modulated reflectance spectrum with light polarized parallel to the [0001] direction. Unusually large linear stress coefficients of the peaks are found. The stress coefficient of the sharp exciton peak at 1.97 eV in the wavelength‐modulated reflectance spectrum with light polarized perpendicular to [0001] is +(2.5 ± 0.4) × 10−11 eV cm2 dyn−1 for the uniaxial compression along the [0001] direction, and −(6.7 ± 0.5) × 10−11 eV cm2 dyn−1 for the compression along [1000].
Symmetry Properties of the Antiferromagnetic Structure of CuCl2·2H2O
Authors: Joshua S. J.
Published: July 2007

New experimental data [12] have indicated that CuCl2 · 2H2O may be a four sublattice canted antiferromagnet in accordance with Moriya's predictions [17]. However, the data obtained are too few and too weak to confirm Moriya's model. We show by using group theoretical arguments that CuCl2 · 2 H2O has in fact a canted structure with the spins canting in the x‐z plane.
Landau Damping of Magnetoplasma Excitations in Many‐Valley Semiconductors
Authors: Wallace P. R.
Published: July 2007

Theoretical calculations are made of the effect of Landau damping and Doppler‐shifted cyclotron damping on the transverse (helicon‐like) and longitudinal (plasma) excitations of a many‐valley semiconductor such as PbTe or Ge in an external magnetic field, in the Faraday configuration. It is shown that Landau damping dominates only for low‐frequency helicon modes. For higher‐frequency modes, Landau damping is present, but generally occurs only in the frequency ranges in which Doppler‐shifted cyclotron damping is already present.
The Fine Structure of Spots in Electron Diffraction Resulting from the Presence of Planar Interfaces and Dislocations. V. Observations on Coherent Domain Boundaries
Authors: de Ridder R. , van Landuyt J. , Gevers R. , Amelinckx S.
Published: July 2007

Observations of the fine structure of electron diffraction spots due to the presence of coherent domain boundaries in ordered Ni4Mo are compared with theoretical results derived in part III of this paper. It is shown that the predicted fine structure consisting of satellites lying in a direction perpendicular to the image fringes can be observed. How‐ever, in general, only one or two out of the four predicted satellites are registered, the intensity of the other ones being too small. Analysis is made of the fine structure and excellent agreement between theory and experiment is found. Identification of the satellites, based among others on intensity considerations is possible and illustrated on an example. Moreover, the orientation parameters such as s, Δs, and the extinction distance can be estimated from the geometry and a method is outlined allowing to calculate the absorption length from the measured intensities of the satellites.
Interatomic Interactions in Alkali Halides
Authors: Abarenkov I. V. , Antonova I. M.
Published: July 2007

Using free ion orbitals two‐body and three‐body potentials between nearest and next‐nearest neighbours in several alkali halides have been calculated. The two‐body potentials have been calculated without any expansion in power‐series of overlap integral S. The three‐body potentials have been calculated approximately, only terms of the order S2 being retained. The results show that the use of the free ion orbitals leads to somewhat too strong repulsion between the ions.
Ionized Impurity Scattering in Polar Semiconductors at Strong Electric Fields
Authors: Licea I.
Published: July 2007

Ionized impurity scattering processes by a strong electric field in semiconductors with an arbitrary non‐parabolicity of spherical‐symmetric conduction band are considered in the electron temperature approximation. Using the energy and momentum conservation equations, established for this case, the warm electron temperature and mobility in a polar semiconductor with a non‐parabolic energy dispersion law as that of n‐type InSb are studied. The effect of non‐parabolicity is pointed out and a comparison with the parabolic case is made.
Current Transients in the Insulator Determined by Space Charge and Diffusion
Authors: Rosental A. , Lember L.
Published: July 2007

The mathematical problem of one‐carrier space‐charge‐limited current (SCLC) step‐response in a perfect insulator is solved with a digital computer taking carrier diffusion into account. Curves of forward‐current density vs. time are presented with an error analysis and a brief discussion of the parameter influence for the case of a dielectric diode under different values of applied pulse voltages in the steady‐state current range where a square‐law behaviour begins to show up and inclusion of diffusion in the treatment is indispensable. The lowering of the voltage in this range deprives gradually the mean features of the SCLC transient ascertained for the diffusion‐neglected case. Last of all only the diffusion‐dominated current in the very beginning of the transients remains. The maximum time for observing the diffusion contribution to the pulse current estimated by Schilling and Schachter proves to be understated.
Thermal Expansion Coefficient and Grüneisen Parameter of Na and K Based on Toya's Electron—Phonon Interaction
Authors: Srivastava R. S. , Singh K.
Published: July 2007

Phonon dispersion relation derived by Toya and based on the Hartree‐Fock method has been used for computation of phonon frequencies, Grüneisen parameter, and thermal expansion coefficients for sodium and potassium. The Brillouin zone was divided into 1000 miniature cells. Phonon frequencies and Grüneisen parameter corresponding to the centre of the miniature cells were computed and used for studying the variation of γM — the mean value of the Grüneisen parameter — with temperature. Variation of the thermal expansion coefficient with temperature was also studied in the manner of Wallace. It is found that the pseudopotential approach by Wallace gives practically the same results as Toya's theory, at least so far the variation of the thermal expansion curve is concerned. Similar calculations have been done by Buyers and Cowley on the basis of anharmonic effects.
On the Theory of Hot Luminescence and Resonant Raman Effect of Impurity Centres
Authors: Hizhnyakov V. , Tehver I.
Published: July 2007

For an impurity centre the resonant secondary radiation spectrum, consisting of luminescence, Raman scattering, hot luminescence, and interference terms, is studied at low temperatures using the model of one local or pseudolocal mode, active in the electronic transition and taking into account the change of the equilibrium position and frequency of this mode. It is shown that the latter plays an essential role in the problem of the classification of the resonant Raman scattering and hot luminescence. The anti‐Stokes region of the spectrum is analysed in detail for three cases of excitation: monochromatic, “white”, and intermediate excitation. The influence of the interference of different relaxation channels on the intensity, width, and shape of the lines is considered.
Hall Mobility of Electrons in Anthracene Crystals
Authors: Schadt M. , Williams D. F.
Published: July 2007

The Hall mobility for electrons has been measured in anthracene along different crystallographic axes. The electrons were injected into the crystals with solid electrodes containing anthracene negative ions (Na‐anthracene). To avoid any magnetic effects arising from photoconductivity, all experiments were performed in the dark and great care was taken to avoid double injection. The Hall mobilities for electrons at room temperature are ≈ 9 cm2 V−1s−1 (a‐axes), ≈ 7 cm2V−1s−1 (b‐axes), and < 2 cm2V−1s−1 (c′‐axes; no sign could be determined). The anomalous Hall mobilities predicted by the narrow band description of carrier transport in anthracene were not found.
Pair Formation and Tetrahedral Coordination of Co2+ in AgCl and AgBr
Authors: Koswig H. D. , Ulrici W.
Published: July 2007

The analysis of the optical absorption spectra (measured at 20 °K) of Co‐doped (< 800 ppm), quenched AgCl and AgBr crystals shows that in addition to octahedrally coordinated Co2+ (incorporated on cation sites) there are also tetrahedrally coordinated Co2+ ions. Tetrahedrally coordinated Co2+ arises from pairs of Co2+ ions on cation sites in which one of both Co2+ jumps on an interstitial site when both the charge compensating cation vacancies are situated in the neighbourhood of the pair. The concentration of pairs is determined by the probability to find a Co2+ ion in the neighbourhood of another one. In Co‐doped crystals additionally doped with other divalent cations the Co2+ ion jumps on an interstitial site also in that pairs in which the second cation is not Co2+. This leads to an enhancement of the concentration of tetrahedral Co2+ centres related to crystals without additional doping. The investigation of this enhancement as a function of the cation concentrations provides the spatial arrangements of the cations in the pair leading to tetrahedral Co2+ centres in the different cases.