bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Absorption on Multi‐Beam Intensity Profiles of Wedge Crystals
Authors: Sheinin S. S. , Cann C. D.
Published: July 2007

The effects of absorption on multi‐beam intensity profiles of wedge crystals have been investigated. The fringe spacing has been shown to change appreciably when absorption is taken into account, particularly at high accelerating voltages. It has also been shown that the subsidiary fringes which occur at certain values of the deviation parameters s in theoretical profiles which neglect absorption, will in some cases disappear when absorption is taken into account. Good agreement was found between these theoretical predictions and experimental measurements of extinction distance in magnesium oxide and molybdenum.
Cyclotron Resonance of Holes in Si
Authors: Owner‐petersen M. , Samuelsen M. R.
Published: July 2007

Hole resonances are studied in 3900 Ωcm p‐type Si samples at temperatures from 1.2 to 5.0 °K. Measurements are performed at 45 GHz using magnetic inductions B up to 10 kG corresponding to a maximum value of m*/m0 = 0.62, and a few resonances not reported previously are observed. The experimental data are in reasonably good agreement with the Luttinger theory [1] of Landau levels in the valence band of semiconductors when a suitable set of band parameters are chosen. Numerical calculations of the levels and the matrix elements for transitions between the levels are carried out for B pointing in the crystallographic directions [001], [111] and [110]. The variation of the level positions and of the matrix elements as a function of the band parameters is examined in order to find the parameters providing the best fit to the experimental data.
ESR Detection of Self‐Trapped Holes in AgCl
Authors: Höhne M. , Stasiw M.
Published: July 2007

Ag2+ centres are produced in doped and appropriately treated AgCl crystals by irradiation with blue light at 20 °K. It is shown that the only purpose of the preceding treatment is to create a high concentration of electron traps. In chalcogen doped crystals (AgCl:S, Se, Te) electron traps are formed by pre‐irradiation with blue light above 120 °K; in iron doped crystals the incorporated Fe2+ ions are converted to Fe3+, acting as traps, either by irradiation at 20 °C or by annealing in chlorine gas. As the paramagnetic data of the localized Ag2+ centres are independent of the kind of the impurity, one must conclude that the hole is trapped in the undisturbed lattice.
Negative Space‐Charge Effect on Schottky Current in Thin Insulating Films
Authors: Antula J.
Published: July 2007

A simple theory is used to describe the effect of negative space‐charge on the Schottky current in thin insulating films. The space‐charge limited current is discussed as a limiting case. The theoretical results are applied to the measured In I (\documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt U $\end{document}) Schottky characteristics of Al‐Al2O3‐Al structures. The observed negative space‐charge effect leads to a concentration of trapped electrons nt ≈︁ 3 ×1017 cm−3.
Thermally Activated Domain Wall Movement in Nickel‐Iron Films
Authors: Craik D. J. , Wood M. J.
Published: July 2007

The slow movement of domain walls under a steady field, due to thermal activation, has been observed in a permalloy film, and a quantitative study made over the temperature range ‐39 to +77 °C. Unlike results obtained previously in another film [8], these do not conform to the simple theory. The theory is extended to include switching by a sinusoidal field, and the ac coercivities are correlated with the dc results. It is suggested that magnetic viscosity should be more pronounced in films with high magnetization dispersions. Some criticisms of the simple theory are advanced. An estimate of the frequency factor C is made from the results on both films, which is higher than theoretical predictions.
L'activation thermique des déviations sous faibles contraintes dans les structures h.c. et c.c. Par
Authors: Escaig B.
Published: July 2007

Duesbery et Hirsch ont suggéré récemment que dans les structures c.c. et h.c., la déviation d'une dislocation hors de son plan de dissociation, doit se produire à faible contrainte par un mécanisme de double décrochement. On montre ici que ce mécanisme doit se produire en dessous d'une contrainte ßc = R/b2, où R est l'énergie de recombinaison et b le vecteur de Burgers de la dislocation; de plus, il n'introduit aucune discontinuité de contrainte, d'énergie, ou de volume d'activation. On calcule l'énergie d'activation maximum de la déviation correspondantà une composante thermique de la contrainte nulle, pour laquelle on retrouve l'expression donnée par Duesbery et Hirsch. En tenant compte de l'interaction élastique des décrochements au moyen d'une tension de ligne qui varie logarithmiquement aves leur distance de séparation, on obtient un volume d'activation qui varie en σ−1 à faible contrainte σ.
Étude de l'écoulement plastique de monocristaux filamentaires de fer entre 300 et 4 °K Par
Authors: Conte R. , Groh P. , Escaig B.
Published: July 2007

On étudie du point de vue expérimental l'influence de la température et de la vitesse de traction sur la plasticité de monocristaux filamentaires de fer, dans un domaine de température allant de 4 à 300 °K. Les résultats des mesures sont comparés aux prédictions du modèle de Dorn et Rajnak (forces de Peierls) et à celles du modèle d'Escaig (dissociation‐recombinaison). Ce dernier modèle semble mieux rendre compte de l'expérience, indiquant que les “barrières de potentiel de Peierls” sont probablement dues, dans la structure cubique centrée, à un effet de dissociation des dislocations.
Quantum‐Mechanical Treatment of the Transient Processes with Three‐Magnon Non‐Linear Transitions under Perpendicular Pumping
Authors: Le Gall H.
Published: July 2007

The transient growth of spin‐wave populations with three‐magnon non‐linear processes under perpendicular pumping is studied. Calculations are made on the basis of second quantization of the magnetic system and the pumping microwave field, assuming that the magnons are in thermal distribution before the electromagnetic pulse is applied. General expressions describing transient evolution of the uniform mode and the parametric states are established in the case where the coincidence condition is satisfied (occurrence of the three‐magnon transitions at resonance). The stationary state of the parametric magnons is also determined. To test experimentally the validity of the theory an expression for the transient power absorbed by the crystal at the beginning of the parametric excitation of the quasiparticles is derived. Basing on experimental data, the limits of the applicability of the theory are discussed.
Couplage ferro‐antiferromagnétique et traînage magnétique dans des couches minces multiples CoCoO et NiNiO Par
Authors: Schlenker C.
Published: July 2007

On a étudié le couplage ferro‐antiferromagnétique sur des couches minces polycristallines, à anisotropie uniaxiale, oxydées superficiellement, du type CoCoO ou NiNiO, entre _ 190 et 20 °C. L'anisotropie unidirectionnelle s'annule à une température de transition toujours inférieure au point de Néel et liée à l'épaisseur moyenne de la couche antiferromagnétique. L'anisotropie uniaxiale n'est pas modifiée par la présence du couplage. On explique le maximum du champ coercitif et la disparition de l'hystérésis de rotation au voisinage de la température de transition en supposant que la couche antiferromagnétique “déformable” du point de vue magnétique aux basses températures, devient “rigide” aux plus hautes températures. On observe un traînage magnétique de très grande amplitude qui provient de réorientations des moments dans certains grains antiferromagnétiques et suit une loi logarithmique dans des intervalles de temps de plusieurs heures, par suite de la dispersion de la taille des grains. Les ordres de grandeur de l'anisotropie antiferromagnétique déduits de l'étude détaillée du traînage sont supéieurs à l'anisotropie magnétocristalline des oxydes à l'état massif.
Absolute Atomic Scattering Factors of Tungsten
Authors: Paakkari T. , Suortti P.
Published: July 2007

The atomic scattering factors f of tungsten are determined in the region sin θ/λ ≤ 1.1 Å−1from the integrated intensities of Bragg reflections. The reflections from a powder sample were measured at 300 °K with monochromatic MoKα radiation. The intensities are corrected for the effects of porosity and surface roughness, and for the contribution of thermal diffuse scattering. The intensities are put on an absolute scale with respect to the absolute value f(110) of iron. The mass absorption coefficient of tungsten for MoKα radiation is measured to be μQ = (101.8± 0.4) cm2/g. A value for the temperature parameter of BW = (0.183±0.008) Å2 is obtained by a measurement of the integrated intensity of a high‐order reflection both at 300 and 78 °K. This corresponds to the Debye temperature θM = (325 ∓ 7) °K. The experimental f‐values are compared with various theoretical calculations. It is found out that the Dirac‐Slater values are in excellent agreement with present results.
Empirical Third Neighbour LCAO Energy Bands of Silicon
Authors: Alstrup I. , Johansen K.
Published: July 2007

A third nearest neighbour LCAO description, including overlap integrals, is constructed for the energy bands of silicon. The overlap integrals are calculated from Slater‐type atomic orbitals, the interaction integrals and the screening parameter are determined empirically by fitting the bands to recent adjusted OPW calculations. Good overall agreement is obtained. The second nearest neighbour interaction integrals obtained cannot be derived from two‐center integrals only. Previous failures to obtain reasonable bands for diamond and silicon by the empirical LCAO scheme are briefly discussed.
Stacking Faults on {110} Planes in the B.C.C. Lattice
Authors: Pegel B.
Published: July 2007

Maximum stacking fault energies for α‐type stacking faults in the b.c.c. lattice are estimated for the group Va and VIa transition metals and iron. The half widths of glissile type split screw dislocations should be in all cases at least one total Burgers vector.
Thermal Expansion of Cubic Metals in Krebs's Model
Authors: Singh A. K. , Sharma P. K.
Published: July 2007

A calculation of the temperature dependence of the Grüneisen parameters for copper, silver, gold, aluminium, sodium, and potassium is carried out starting from the experimental values of the pressure dependence of the elastic constants using Krebs's model for the lattice dynamics of metals. Houston's six‐term integration procedure is used in evaluating the integrals over the phonon spectrum. The calculated γ‐T curves show fairly satisfactory agreement with experiment for copper, but not for other metals.
Temperature Dependence of the Diffusion of Photoexcited Holes in AgBr
Authors: Georgiev M. , Zagorska E. , Malinowski J.
Published: July 2007

A detection technique based on the bleaching of a thin silver deposit is used to investigate the diffusion of photoinduced holes between ‐35 and +35 °C. The apparent diffusion coefficient is found to follow an Arrhenius‐type temperature dependence exhibiting an activation energy of 0.53 eV. Following previous suggestions, it is again concluded that the holes become engaged in multiple trapping while migrating within the crystal lattice. Some trapping models are discussed.
Der Beitrag der Versetzungen zur Anisotropie des magnetischen Einmündungsgesetzes in Nickel
Authors: Holz A. , Kronmüller H.
Published: July 2007

Das magnetische Einmündungsgesetz bei Anwesenheit von Stufenversetzungen wird in Abhängigkeit von der Magnetfeldrichtung für Nickel als numerisches Beispiel berechnet. Die Suszeptibilität läßt sich in einen streufeldfreien Anteil und einen vom Streufeld hervorgerufenen negativen Beitrag zerlegen. Numerische Rechnungen wurden für die durch Burgersvektor, Gleitebenennormalen und Versetzungslinien bestimmten Ebenen ausgeführt. Im Bereich bis 2000 Oe wird in allen drei Ebenen eine ausgeprägte Anisotropie gefunden, die im wesentlichen durch bestimmt ist. Mit großem Magnetfeld H nimmt proportional 1/H4 ab, während nur mit 1/H3 abfällt. Im Feldbereich H ≥ 4 π Is ist deshalb die Anisotropie von X vornehmlich durch bestimmt.
Behaviour of the High‐Field Domains below the Voltage of the Nucleation Threshold
Authors: Levinstein M. E. , Shur M. S.
Published: July 2007

On the basis of the phenomenological theory it is shown that the high‐field domain in a Gunn diode does not annihilate if the applied voltage becomes lower than the threshold for domain nucleation. The dependence of the threshold for domain annihilation on the diode parameters is obtained. It is found that the domain annihilation amplitude is equal to half of the domain amplitude when the applied voltage corresponds to that at the beginning of the region of negative differential resistivity in the diode. The results obtained are important if an additional microwave voltage is applied, for example if the diode operates in a resonator.
The Correlation Function Szz (ω) for Weakly Coupled Impurity Atom Spin in a Ferromagnetic
Authors: Krivoglaz M. A. , Kvashnina L. B.
Published: July 2007

The closed chain of equations for the temperature Green's functions for the z‐th component of the spin of an impurity atom in a ferromagnetic is obtained for the case of quasi‐local spin excitations in the neighbourhood of the impurity atom. The solution of this system is obtained in explicit form for the cases of high and low temperatures and of small values of the spin of the impurity atom (S = 1/2, 1, 3/2). For these cases the spectral representation Szz(ω) of the correlation function 〈Sz(t1) − Sz, Sz(t2) − Sz〉 of the impurity atom spin is determined. It is pointed out that the quasi‐local spin states can result in a modulational broadening of the line of nuclear magnetic resonance some orders of magnitude larger than the broadening due to the spin waves in the perfect crystal.
Analysis of Point Defect States in Copper II. The Effects of Stage I and Stage III Annealing on Electron‐Irradiation‐Induced Frenkel Pairs
Authors: Dworschak F. , Schuster H. , Wollenberger H. , Wurm J.
Published: July 2007

The point defect states before and after stage I and stage III annealing are compared by means of 80 °K damage rate measurements. The results can be interpreted most easily by vacancy migration in stage III or more artificially by the conversion of the “stage III interstitial” to a third modification. The stage I annealing results in an at least partial formation of stable di‐interstitials.
Evidence of a Doubly Ionized Native Donor in CdTe
Authors: Whelan R. C. , Shaw D.
Published: July 2007

The electrical conductance of CdTe has been measured in the temperature range 490 to 950 °C as a function of the ambient partial pressure of Cd, pCd. The conductance varied as p and was interpreted in terms of a doubly ionized native donor whose associated ionization energy was estimated to be ≦ 0.24 eV. The incorporation energy of the doubly ionized donor into the CdTe lattice was (1.65 ± 0.15) eV. Defect equilibrium occurred by a bulk diffusion process possessing different characteristics to radiotracer self‐diffusion processes.
Piezoresistance of Tellurium II. Experiments with Pressures Lowering Symmetry
Authors: Herrmann K. H. , Puhlmann J.
Published: July 2007

The eight independent piezoresistance coefficients of tellurium single crystals containing acceptors with concentrations from 5.8 × 1014 cm−3 to 4.9 × 1017 cm−3 are measured. In the extrinsic region all coefficients are independent of temperature. This contradicts a many‐valley structure of the valence band. The anisotropy of the piezoresistance effect is strongly affected by structural defects.
The Electronic Structure of CdO II. Spectral Distribution of Optical Constants
Authors: Altwein M. , Finkenrath H. , Koňák Č. , Stuke J. , Zimmerer G.
Published: July 2007

The reflectivity of CdO has been measured up to 13 eV on single crystals and polycrystalline material. Moreover the absorption of thin films was studied. The frequency dependence of the optical constants evaluated by Kramers‐Kronig analysis is discussed with regard to the band structure calculated by Maschke and Rössler [1]. The investigation of the shape of the intrinsic absorption edge and the measurements of the electrical conductivity on films with low electron concentration indicate the existence of an indirect gap.
Vapour‐Pressure Investigations of Impurity Diffusion and Solubility in AII–BVI Compounds Demonstrated for the System CdS:Au:S2
Authors: Nebauer E.
Published: July 2007

It is shown that for investigations of disorder problems in AII–BVI compounds it is relevant to measure the diffusion coefficient D and the solubility S as functions of the vapour pressure p of the components. Using the tracer technique this method is exemplified in detail for a cation impurity diffusion process in the system CdS:Au:S2. The measured concentration profiles C(x) are not of Fick's type. After eliminating surface and dislocation diffusion (Fisher analysis), D(T, p, C) and also simultaneously S(T, p) can be obtained. The results are explained in a disorder model with controlled intrinsic disorder. It is found that gold diffuses in CdS via singly‐charged cadmium vacancies and acts as a singly‐charged acceptor.
A Neutron Diffraction Study on Gallium‐Substituted Magnetite
Authors: Gamari‐Seale H. , Papamantellos P.
Published: July 2007

The distribution of Ga3+ and Fe3+ ions in tetrahedral and octahedral sites, A and B, of the inverted spinel Fe3−tGatO4, with t = 0.442 and 0.628 is determined from neutron diffraction measurements on two synthetic single crystals. To avoid a great extinction effect the crystals are cut into small cylindrical fragments. The extinction correction coefficients are found by a graphical method using the extinction formula Ic = Io (A + B Ic). Because of the similarity of the nuclear scattering length of Ga3+ and Fe3+ the distribution of the ions is found only from the magnetic reflections. By applying a magnetic field in the direction of the scattering vector, it is possible to separate the magnetic from the nuclear scattering. The Ga3+ ions are found to be distributed between the two sites as follows: 93 and 76% in the tetrahedral, 7 and 24% in the octahedral site for the two crystals, respectively. A least square refinement of the corrected nuclear data yields agreement factors R = 0.03 and 0.04; the resulting oxygen parameters u = 0.369 ∓ 0.0006 and 0.369 ∓ ∓ 0.0008, respectively, indicate the usual shift for the inverted spinel from the ideal value 3/8.
Solution‐Hardening and Deformation of Niobium‐Tungsten Alloys
Authors: Harris B.
Published: July 2007

The results of some experiments on the strain‐rate and temperature dependence of the flow stress of some dilute niobium‐tungsten alloys are reported. Alloys containing 0.25, 0.5, and 2.6 at% tungsten exhibit unusual twin peaks in the strain‐rate sensitivity as a function of temperature, and this leads to abnormally high values of the activation energy of deformation in the region of 150 °K. And yet the behaviour of a 5.3 at% W alloy appears to be indentical with that normally observed for b.c.c. metals. The results suggest that two deformation mechanisms are overlapping below 150 °K, and current theories of solute hardening and deformation of b.c.c. metals are examined to provide an explanation.
Die kritische Schubspannung mit zweiwertigen Kationen dotierter Alkalihalogenide I. Nicht‐agglomerierte Fremdion‐Leerstellen‐Paare
Authors: Frank W.
Published: July 2007

Es wird gezeigt, daß bei Alkalihalogeniden, welche zweiwertige Kationen in Form von Fremdion‐Kationleerstellen‐Paaren (elastischen Dipolen) enthalten, die kritische Schubspannung τ0 durch die elastische Wechselwirkung dieser Dipole mit den Versetzungen verursacht wird. Unterhalb Raumtemperatur ist τ0 durch das thermisch aktivierte Vorbeigleiten von Versetzungen an Dipolen in der Nähe der Gleitebenen bestimmt, während oberhalb Raumtemperatur der induzierte Snoek‐Effekt der Dipole im Spannungsfeld der Versetzungen τ0 entscheidend beeinflußt. An einen temperaturunabhängigen Bereich oberhalb Raumtemperatur schließt sich ein Hochtemperaturabfall von τ0 an, zu dem neben dem induzierten Snoek‐Effekt der Zerfall der Dipole in zweiwertige Kationen und Kation‐Leerstellen beiträgt.
Nonlinear Magnetooptical Phenomena in Semiconductors (I)
Authors: Kołodziejczak J.
Published: July 2007

A theory of a nonlinear magnetooptical phenomena associated with free carriers in semiconductors is proposed. Starting from a nonlinear Boltzmann equation, the effects of optical mixing and higher harmonics generation are predicted. The calculations are carried out assuming nonparabolic energy band of ellipsoidal symmetry. Thus the results can be applied to a wide class of semiconductors as for example to all those with one energy minimum as well as to many‐valley semiconductors.
Observations de sources et de réactions entre dislocations partielles de macle sur des topographies aux rayons X
Authors: Sauvage M.
Published: July 2007

L'observation directe de dislocations partielles de macle sur des topographies aux rayons X montre que les sources sont des centres de concentration de contraintes. Le mécanisme de nucléation et croissance des macles est donc le mécanisme de „nucléation hétérogène”︁. Les interactions entre dislocations glissiles et défauts du réseau donnent naissance à des configurations particulières dont on essaie de rendre compte théoriquement.
Phonon‐Induced Hyperfine Coupling of V2+ Ion in Cubic Crystalline Fields
Authors: Shrivastava K. N.
Published: July 2007

The effect of dynamic phonon interaction on the hyperfine fields of ions with electronic configuration 3d3 has been examined theoretically. The zero‐point vibrational contribution and the temperature dependent part is discussed for both the acoustical and the optical phonons in a covalent model. As the amplitude of phonon vibrations is thermally increased a net decrease in the V2+ hyperfine interaction in octahedrally coordinated environment is predicted the temperature dependence of which is in agreement with experimental measurements in V2+ doped MgO.
Scattering Effects with Channeled Ions
Authors: von Jan R.
Published: July 2007

The angular distribution F(α) is calculated for fast ions that have traversed a lattice channel with an axis in the direction α = 0. For both axial and planar transmission channeling, intensity maxima are expected at \documentclass{article}\pagestyle{empty}\begin{document}$ |\alpha _{\max} | = \alpha _0 \sqrt {(1 - \eta ^t)/(1 - \eta ^l)} $\end{document}, where α0 is the angle of incidence, and ηt and ηl denote the relative energy loss of transverse and longitudinal motion. The scattering effects provide a direct method to measure separately longitudinal and transverse stopping powers for channeled ions.
Low‐Temperature Neutron Radiation Damage and Recovery in Beryllium
Authors: Delaplace J. , Nicoud J. C. , Schumacher D. , Vogl G.
Published: July 2007

In beryllium neutron irradiated at 4.2 °K, the defect production and subsequent recovery up to 350 °K have been studied by means of electrical resistivity measurements. The data are discussed in view of our present knowledge on point defect phenomena in other metals, in particular aluminium, which exhibits after neutron irradiation a similar recovery behaviour as beryllium.
Noise in Thin Films Metal‐Oxide‐Metal AlAl2O3Al
Authors: Lecoy G. , Gouskov L.
Published: July 2007

It is the purpose of this note to verify the existence of tunneling through the oxide layer of metal‐oxide‐metal structures. Noise measurements on thin AlAl2O3Al sandwiches (30 Å thick) yield full shot noise at high frequencies (v > 1000 Hz) and v−3/2 noise for v < 1000 Hz. From conductivity and noise measurements the dependence of each individual tunnel current on voltage and temperature is determined. Experimental values of I1/I2 are in good agreement with the Boltzmann law owing to the tunneling process.
Dislocation Theory of Susceptibility and Coercive Force of Silicon Iron
Authors: Mishin D. D.
Published: July 2007

In the present work the dislocation theory of the susceptibility and coercive force of silicon iron is developed. Calculations are made of the force between a Bloch wall of the {100}‐180° type and dislocations really existing in this material. The susceptibility and coercive force of silicon iron are calculated, and conditions are stated under which the temperature dependence of susceptibility and coercive force of this material changes markedly.
On the Problem of Depth Distributions in Oxides Following High‐Dose Labelings. (Sputtering and Depth‐Distribution Phenomena, Part III)
Authors: Kelly R.
Published: July 2007

It has been shown previously that meaningful depth‐distribution parameters can be obtained with Al, KCl, and Pt, following high‐dose labelings at ≦ 10 keV, by sputtering the targets with 2 or 3 keV ions. We present here similar data for the oxides Al2O3, MgO, NiO, SiO2, TiO2, and UO2 labeled to a high dose at 4 keV. It is found that, when the sputtering energy is 2 keV, the implied ion ranges are roughly a factor of 2 less than might be expected (shown with all oxides), while, when the sputtering energy is 8 keV, the implied ranges are smaller still (Al2O3, TiO2). Moreover, shortened ranges are also found by sputtering oxide skins (Al, Mg, Ti), by sputtering bulk materials at about −150°C (Al2O3, MgO, UO2), by applying an anodizing‐stripping technique (Al2O3), and by comparing high‐dose sticking factors (all oxides). It is concluded that the available evidence is compatible with two extreme views. Possibly the shortened ranges found with high‐dose labeled oxides are in error, for example due to bombardment‐enhanced gas motion when the sputtering technique is used, or due to excess oxide growth when anodizing‐stripping is used; alternatively they may be real, as would be true if an effect such as bombardment‐enhanced gas motion occurred during the labeling.
Self‐Diffusion in α‐Silver‐Cadmium
Authors: Gardner A. B. , Sanders R. L. , Slifkin L. M.
Published: July 2007

The diffusion of tracers of silver and cadmium has been measured in AgCd alloys over the range 31 to 37 at% Cd, thus extending the data of Schoen to compositions near to the phase boundary, and facilitating a comparison with Zener relaxation studies by Turner, Dozier, and Williams (see preceding paper). The present diffusion results fit smoothly onto an extrapolation of Schoen's data, but the decrease in activation energies with increasing cadmium content appears to flatten out at the higher concentrations. It is suggested that a temperature dependence of the short range order may contribute to the activation energies.
Temperature Dependent Spin‐Lattice Relaxation Times for Conduction Electrons in Lithium Particles in n‐Irradiated Lithium Fluoride
Authors: Watts A. J. , Cousins J. E.
Published: July 2007

Measurements of the conduction electron spin resonance linewidths of Li particles in neutron‐irradiated LiF are presented as a function of temperature and at a frequency of 9.27 GHz. A temperature range of 20 to 500°K was covered, and a genuine reversible temperature dependence of the linewidths was observed. The results are interpreted in terms of a temperature dependent surface relaxation mechanism and a temperature dependent intrinsic one. The latter has a room temperature value of 45 mG which compares favourably with the theoretical prediction of Overhauser. It is shown that the assumptions made for the analysis are compatible with the results of other workers.
Experimental Observations of the Absorption, Infra‐Red Emission, and Excitation Spectra of Cr3+ Ions in ZnWO4
Authors: Reynolds M. L. , Hagston W. E. , Garlick G. F. J.
Published: July 2007

Optical absorption, infra‐red emission, and excitation spectra have been measured for trivalent chromium ions in the zinc tungstate lattice. In contrast to the case of ruby the lowest excited state is 4T2(F) and emission results from the 4T2−4A2 transition. The emission at about 1 μm is of broad band type with a decay time of about 10−5 s and involves a significant Stokes shift. These characteristics are consistent with the strong dependence of the energy of the 4T2 state on the crystal field parameter, and a large activator‐lattice interaction. Rhombic symmetry is indicated for the Cr3+ ion site, but tetragonal distortion occurs for the excited states.
Low Temperature Neutron Radiation Damage and Recovery in Magnesium
Authors: Delaplace J. , Hillairet J. , Nicoud J. C. , Schumacher D. , Vogl G.
Published: July 2007

In magnesium neutron‐irradiated at 4.2°K the defect production and the subsequent recovery up to 350°K were studied by means of electrical resistivity measurements. Additional experimental evidence is presented from preliminary stored energy, internal friction, and electron microscope studies on neutron‐irradiated magnesium, and from electrical resistivity measurements on electron‐irradiated magnesium. The principal recovery peak occurs between 90 and 160°K.
A Stochastic Model of Creep
Authors: Feltham P.
Published: July 2007

A model of creep in solids is developed in which flow units, identified with dislocation segments in crystals, overcome energy barriers u1 ≦ u ≦ u2 with the aid of thermal activation. Each successful transition of a unit increases or decreases the barrier for the subsequent jump by a stress‐dependent increment. The continuity equation of the Markov process defined by the premise yields activation energy distributions as particular solutions. The distributions are used to derive relations for logarithmic, power‐law, and quasi‐viscous creep. The model delineates the scope of temperature cycling in the determination of activation energies.
Empirical Relationships for the Emission Energies and Lifetimes of the F‐Center
Authors: Gilbert R. L.
Published: July 2007

Empirical relations for the emission energies ϵ of the F‐center in the Na, K, Rb, and Cs halides, and for the lifetimes τ have been established with the following forms:

and

where Ko is the optical dielectric constant. Two different relations appear to exist for τ. One follows from measurements of τ at liquid helium temperature, the other follows from τ extrapolated from measurements above liquid nitrogen temperature with the Swank‐Brown curve. The implications of the existence of these curves are discussed.
Electron Diffraction Contrast from Three Parallel Overlapping Stacking Faults
Authors: Humble P.
Published: July 2007

The electron diffraction contrast to be expected from three parallel overlapping intrinsic stacking faults has been computed. It is shown that faint fringe contrast always arises from this configuration, even in the limiting case when the faults lie on neighbouring slip planes. This is contrary to previous predictions. Moreover, by comparison with experimental images, it is shown that the faint fringe contrast is generally detectable and that the actual spacing of the three faulted planes may be deduced. The effect of dislocation strain‐fields on this faint contrast is discussed and some results for the contrast from two parallel intrinsic stacking faults are presented.
Crystal Field Calculation of Principal Magnetic Susceptibilities and Anisotropy Variation with Temperature of Anhydrous Neodymium Chloride
Authors: Taneja S. P. , Puri S. P.
Published: July 2007

In the temperature range 5 to 300°K, the principal susceptibilities of single crystals of anhydrous NdCl3 have been calculated on the assumption that a single suitable trigonal field of C3h symmetry exists in the neighbourhood of the Nd3+ ion. Furthermore the variation of magnetic anisotropy with temperature is studied and found to increase with the decrease of temperature. The g‐values for the lowest level, viz., g∥ = 4.103, g⟂ = 1.746, compare well with the experimental values obtained from paramagnetic resonance absorption. The following crystal field parameters, reported by Judd, were used in these calculations: A〈r2〉 = 103.7 cm−1, A〈r6〉 = −44.51 cm−1, A〈r4〉 = −36.01 cm−1, A66〈r6〉 = 426.21 cm−1.
Some Transport Coefficients in Cadmium Sulphide
Authors: Sodha M. , Sharma S.
Published: July 2007

An investigation is made of the dependence of Hall coefficient, Hall mobility, and coefficient of magnetoresistance in CdS on electric field, magnetic field, and scattering mechanisms. The scattering of carriers by acoustic mode of lattice scattering as well as piezoelectric potential is considered.
Polarization of Optical Absorption and Emission Bands due to Donor‐Acceptor Associates in Wurtzite Type Crystals
Authors: Boyn R.
Published: July 2007

A discussion is given of the possibilities of orientation of donor‐acceptor associates in wurtzite type crystals and the polarization of absorption and emission bands due to electric dipole transitions in such associates. It is found that bands of this kind tend to be polarized more strongly if the corresponding associate contains interstitials than if two defects on lattice sites are involved.
Photoconduction in CdS Crystals Generated by a Modulated Electron Beam
Authors: Stössel W. , Zimmermann W.
Published: July 2007

A modulated photocurrent in CdS crystals is obtained by irradiation with an intensity modulated electron beam. The experimental set‐up for the irradiation is described. From the frequency dependence of the ac photocurrent a relaxation time τR is defined. τR decreases with increasing irradiation intensity B. At complete filling of the traps it reaches the value of the free electron lifetime τ. From the dependence τR(B) the approximate depth and the concentration of the traps, which are involved in the relaxation processes, are determined to Ec − EH = 0.215 eV and H = 8.5 × 1014 cm−3.
On the Trapping of Free and Release of Localized Carriers in Solids
Authors: Antonov‐Romanovskii V. V.
Published: July 2007

The effective cross‐section of trapping, σeff, and the “frequency” factor ωeff measured in experiments in the case of attractively charged localization centres may strongly differ from the real gaskinetical σk and ω, but for the ratio yields ωeff/σeff = ω/σk. The greater the difference the less is the carriers mean free path l. In this sense, for example, the alkali halides are of great interest. The free carriers distribution function with respect to the localization centres \documentclass{article}\pagestyle{empty}\begin{document}$ \overleftarrow {\eta (r)} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \overrightarrow {\eta (r)} $\end{document} in the cases of trapping and release processes, respectively, complete each other to the thermal equilibrium function ηT(r).
Reflectivity Spectra of the Rhombohedral Crystals Bi2Te3, Bi2Se3, and Sb2Te3 over the Range from 0.7 to 12.5 eV
Authors: Sobolev V. V. , Shutov S. D. , Popov Yu. V. , Shestatskii S. N.
Published: July 2007

The reflectivity spectra (polarisation E ⟂ c) of the homologous group of rhombohedral crystals Bi2Te3, Bi2Se3, and Sb2Te3 have been investigated in the range 0.7 to 12.5 eV. The complex structure of the two reflectivity main maxima, lying in the range 1 to 5 and 6 to 11 eV, respectively, and its similarity in all three crystals have been established. The energy variation of the reflectivity peaks in dependence of the atomic composition shows the anomalous decrease of the interband gaps in Sb2Te3 respective to Bi2Te3. The results obtained are discussed in terms of published bismuth telluride band structure.
The Active Slip Volume and the Temperature‐Dependent Processes in Stage I of Single Crystals of Cu Alloys
Authors: Schwink Ch. , Traub H.
Published: July 2007

Investigations of the easy glide region in single crystals of well‐known f.c.c. Cu alloys between 85 and 400°K are reported. From careful measurements of the strain rate dependence of the flow stress and from microscopic observations (static and cinematographic) of the development of the glide bands it is concluded that the “active slip volume” [1] of these crystals depends on strain rate and temperature. A detailed analysis of the results yields values for the number, the activation energy, and the activation volume of the obstacles responsible for the thermally activated process. We suggest that the obstacles are statistically distributed clusters of the atoms alloyed to copper.
Magnetization and Magnetostriction of Hexagonal Cobalt Single Crystals with Internal Stresses
Authors: Köster E.
Published: July 2007

Measurements of magnetization and magnetostrictive changes of the length were carried out on a plastically deformed cobalt single crystal at low magnetic fields. The results are in good agreement with theoretical calculations by Kronmüller et al. [1]. From this it is concluded that the magnetization processes within the closure structure of ferromagnetic domains at the crystal surface have no noticeable influence on the magnetization compared with the processes in the crystal volume.
Theory of Light Emission by Impurity Centres from Non‐Equilibrium Vibrational States
Authors: Peuker K. , Trifonov E. D.
Published: July 2007

A theoretical study is made of light emission from impurity centres of crystals in the non‐equilibrium vibrational state, which appears as a result of the excitation of one of the vibrational sublevels belonging to the excited electronic term. It is shown that owing to these processes anti‐Stokes luminescence may be observed at T = 0°K. The validity of the kinetic equation approach is proved.
The Theory of the Absorption and Infrared Emission of Cr3+ Ions in ZnWO4
Authors: Reynolds M. L. , Hagston W. E. , Garlick G. F. J.
Published: July 2007

The effect of fields of lower symmetry (in the crystal field approximation) on the energy levels of trivalent chromium ions in the zinc tungstate lattice is discussed. Calculations show that the optical spectra previously reported [1] can be interpreted in terms of a field of rhombic symmetry acting on the Cr3+ ion provided we include the effects of tetragonal distortion in the excited states.
Modulation of Near Infrared Radiation by Acoustoelectric Domains in n‐Type GaAs at Room Temperature
Authors: Boccon‐Gibod D.
Published: July 2007

Optical experiments have enabled measurements of the absorption coefficient of n‐type GaAs to be made at room temperature near the absorption edge by an acoustoelectric domain located at the anode. Moreover, the shape of the domain can be deduced and in addition the acoustic flux is shown to be an important factor in the variations of the absorption coefficient. Some results are also given of local resistivity variations in n‐type GaAs by the injection of free carriers when a GaAs laser beam is focused on the sample.
Zur statistischen Theorie der Diffusionsprozesse in kondensierten Systemen
Authors: Kowalenko N. P. , Ebeling W.
Published: July 2007

Auf der Grundlage der klassischen statistischen Mechanik und der Methode der Projektionsoperatoren von Zwanzig wird eine Diffusionsgleichung hergeleitet, die den Einfluß räumlicher und zeitlicher Dispersion berücksichtigt. Im Falle einer geringen räumlichen Inhomogenität unterscheidet sich diese Gleichung von der gewöhnlichen Diffusionsgleichung durch ihren nicht‐Markoffschen Charakter. Im Grenzfall t → ∞ wird die gewöhnliche Diffusionsgleichung erhalten. Es wird eine Methode sukzessiver Approximationen entwikkelt, die höhere räumliche Ableitungen einschließt. Auf der Grundlage der allgemeinen, nicht‐Markoffschen Gleichung wird gezeigt, daß ein Übergang von reversibler Wanderung für kleine Zeiten zu irreversibler Wanderung für große Zeiten existiert. Es wird die Lösung der nicht‐Markoffschen Gleichung für das spezielle Modell der Brownschen Bewegung untersucht.
Ultrasonic Velocity and Attenuation in Alkali Halides Containing CN− I. Experimental Results
Authors: Byer N. E. , Sack H. S.
Published: July 2007

The ultrasonic velocity and attenuation were measured in KCl, KBr, KI, and NaCl containing CN− as a function of acoustic mode, temperature, concentration, frequency, plastic deformation, and static bias stress. The results are not compatible with stress ordering of an elastic dipole tensor represented by an ellipsoid of rotation with CN− axes having 〈100〉 equilibrium positions, as had been inferred from other measurements. A thermally activated relaxation peak was observed for a CN− dimer with a barrier height of 0.008 eV. In NaCl the CN− reorients by thermal activation over a 0.035 eV barrier as opposed to the tunneling in the potassium halides.
Ultrasonic Velocity and Attenuation in Alkali Halides Containing CN− II. Theoretical Interpretation
Authors: Byer N. E. , Sack H. S.
Published: July 2007

The experimental results presented in Part I are interpreted in terms of the continuum elastic dipole theory, assuming that asymmetric lattice relaxation perpendicular to the CN− axis results in a dipole tensor with three different principal axes, one of which is the CN− axis. The equilibrium positions are [001], [110], and [110] and their equivalents. Acoustic interaction with hindered rotor states was also observed.
Zero‐Phonon Transitions of Eu++ ‐ and Sm++ ‐Doped Alkali Halides
Authors: Baldini G. , Guzzi M.
Published: July 2007

The theory of the electron‐phonon coupling for impurity centres in ionic crystals is reviewed in order to point out the most significant parameters involved in the optical properties of the zero‐phonon lines. The absorption and emission spectra of alkali halides doped with Eu++ and Sm++ have been measured for temperatures ranging from 15 up to 175°K. In general the analysis of the experimental data agrees fairly well with the theory. The Huang‐Rhys factor has been determined and also the effective frequencies which are responsible for the thermal behaviour of the spectra. However the electron‐phonon interaction alone has been found not to be sufficient in order to explain the thermal dependence of the zero‐phonon line strength and an additional mechanism for its thermal de‐excitation has been proposed.
The Spatial and Time Variation of Electric Fields in Semiconducting CdS
Authors: Gay R. K. L. , Hartnagel H. L.
Published: July 2007

A simple analysis involving the principles of energy exchange shows how high‐field domains may occur in semiconducting CdS because of electroacoustic interactions.
Intersystem Crossing and Multiple Tunnelling
Authors: Osherov V. I.
Published: July 2007

The problem of non‐adiabatic tunnelling in the system of two coupled parabolic terms interacting with the environment has been solved. The model is applied to intersystem crossing in the simple centre of luminescence. The role of multiple passage through the region of term interaction has been cleared up. Criteria of applicability depending on the width‐level splitting ratio have been ascertained.
Incorporation of Antimony into the Barium Titanate Lattice
Authors: Schmelz H.
Published: July 2007

The interest in the incorporation of Sb into the BaTiO3 lattice is based above all on the fact that small additions of Sb (below 0.2 wt% Sb2O3) yield semiconducting ceramics with a resistivity anomaly at the Curie point. Larger amounts of Sb, however, result in insulating samples. This is caused by a different kind of incorporation. In the range of high concentration only a composition as BaO + (1 − x) · TiO2 + x · 1/2 Sb2O3 (for x between 0 and 0.1) yields ceramics which show no crystalline phases other than the perovskite one. This and the structure factors determined by neutron diffraction provide a definite proof that Sb occupies Ti sites. By means of combined electron‐microprobe and X‐ray analysis it is also shown that in the case of excess TiO2 in the BaTiO3 solid solution, Sb partly substitutes Ba sites.
Indirect Energy Gap in GaSe and GaS
Authors: Aulich E. , Brebner J. L. , Mooser E.
Published: July 2007

Optical absorption measurements on thick monocrystalline samples of GaSe1−xSx show that in these mixed crystals the lowest energy gap is indirect in the complete range 0 ≦ x ≦ 1. These results are contrary to earlier reports which indicate that GaSe is a direct gap semiconductor. In the case of GaS the absorption spectra allow a tentative identification of the phonons involved in the indirect transition.
The Structure of High‐Angle Grain Boundaries in Aluminium
Authors: Levy J.
Published: July 2007

A transmission electron‐microscopy study of high‐angle grain boundaries has been made. When thin foils are cut in precisely oriented bicrystals of aluminium, some details of the grain‐boundary structure appear. Micrographs of symmetrical tilt boundaries around [001] show linear defects parallel to the tilt axis. Their properties are tightly bound to the geometry of the bicrystal: this provides a good support to the idea of a transitional lattice as a structure of a high‐angle boundary. A theoretical interpretation of these observations is developed essentially on geometrical considerations.
A Calculation of the Electronic Properties of the F′ Center in KCl
Authors: Strozier J. A. , Dick B. G.
Published: July 2007

The electronic properties of the F′ center in KCl were calculated by a variational procedure using a Hamiltonian which approximates the effects of polarization and correlation. The trial functions were orthogonalized to nearest and next nearest neighbor core functions. Values of −1.05 eV for the F′ maximum absorption and −0.49 eV for the thermal dissociation energy were obtained. By approximating the continuum states of the ionized F′ center by eigenstates of an appropriately chosen spherical square well, the shape of the F′ center by eigenstates of an appropriately chosen spherical square well, the shape of the F′ band itself was also calculated and the results compared with Lütys experimental data of F′ absorption in KCl. Fair agreement was obtained.
Infrared Absorption by Local Vibrational Modes of Boron Impurities in Germanium
Authors: Nazarewicz W. , Jurkowski J.
Published: July 2007

Local modes of boron in germanium have been observed by infrared absorption measurements in the range from 480 to 630 cm−1 at 195 and 295°K. Lithium has been used as a compensating donor impurity. The absorption spectrum contains three pairs of bands which are attributed to local modes of boron on the basis of the isotopic shifts observed. One of these pairs is associated with unpaired (isolated) boron and two others with boron in paired configuration (with lithium), as was predicted theoretically. A comparison of our data with those already known for silicon is given.
Zur Theorie des Ferromagnetismus magnetisch anisotroper Schichten mit kubischer Kristallstruktur. III. Berechnung der räumlichen Magnetisierungsverteilung und der mittleren Magnetisierung in einer Eisenschicht mit (100)‐Oberflächenorientierung
Authors: Haubenreisser W. , Brodkorb W. , Corciovei A. , Costache G.
Published: July 2007

Auf der Grundlage vorangegangener Arbeiten wird mit der Methode der Greenschen Funktion in einer modifizierten RPA die Abhängigkeit der mittleren Magnetisierung und der räumlichen Magnetisierungsverteilung in einer Fe‐Γ(100)‐Schicht von der Temperatur und der Atomlagenzahl numerisch berechnet. Die numerischen Ergebnisse verschiedener Theorien werden miteinander verglichen.
Topographic Study of 180° Domains in Triglycine Sulfate
Authors: Petroff J. F.
Published: July 2007

180° domain walls have been observed in TGS by X‐ray topography and two types of deformation revealed around these walls. A theoretical model has been used to calculate the wall thickness. There is good agreement between theoretical and experimental results. Domain nucleation and growth have been studied under an applied field by the same technique.