bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Quasi‐Harmonic Calculation of Lattice Dynamics for Na
Authors: Ho P. S. , Ruoff A. L. 
Published: July 2007

AbstractWe have applied a phenomenological model for a quasi‐harmonic calculation of the lattice dynamics for Na. The lattice potential is separated into the electrostatic energy, the ion‐core exchange repulsion and the screened electron‐ion potential. The ion exchange term is taken to be the Born‐Meyer type potential. The model pseudopotential suggested by Heine and Abarenkov is used for the screened potential. The model parameters are determined from the elastic constants. First we calculate the dispersion curves at 90 °K which agree very well with the neutron scattering data. Then the calculation is extended to the temperature and pressure dependences of dispersion curves. Our result indicates that the phonon frequencies are almost inversely proportional to the volume, a fact which is needed in the Grüneisen equation of state for solids. The martensitic transformation of Na is discussed according to the temperature dependence of the [1110] shear waves along [110] direction. Some related electronic properties such as the Fermi surface distortion and the liquid metal resistivity have also been calculated as a function of pressure.
Coupling of Magnons and Phonons at High Frequencies
Authors: Lord A. E. 
Published: July 2007

AbstractA calculation is given describing the coupling of magnons and phonons, for a general wave vector, in a simple cubic ferromagnetic lattice. The source of magnetoelastic coupling is taken as the strain (or displacement) dependence of the magnetic dipole‐dipole energy, or Van Vleck's pseudodipolar energy. Particular solutions of the secular equation, describing the dispersion relation, are given for k ‖ z, z being the direction along which the spins are aligned.
Fine Structure of Weak Kinematical Electron Diffraction Beams for a Foil Containing Stacking Fault or Anti‐Phase Boundaries ‐ Two‐Beam Case
Authors: Gevers R. , van Landuyt J. , Amelinckx S. 
Published: July 2007

AbstractA calculation is made of the fine structure of weak kinematic electron diffraction spots arising from small areas containing stacking faults. It is assumed that the illumination conditions are such that there are only two strong beams, i.e. the transmitted beam and a scattered beam. The calculation allows for the fact that the electrons propagating in the weak beam directions originate from these two beams at all depths below the entry surface. The anomalous absorption is considered in the usual phenomenological manner. The analysis leads to four satellites for every weak beam occurring for the two‐beam situation. The intensities of the satellites can, however, vary considerably due to the anomalous absorption. It is then apparent why only a single satellite is usually observed which is in agreement with the simple one‐beam kinematic treatment, which is strictly speaking incorrect. Observations on stainless steel foils are discussed and it is shown that in fact, under good two‐beam situations, there are more complicated satellite configurations as predicted by the refined kinematic treatment.
Estimation of the Peierls Stress in Alkali Halides
Authors: Gutmanas E. Yu. , Nadgornyi E. M. 
Published: July 2007

AbstractThe data obtained for the velocities of individual dislocations and for the mechanical properties of “pure” NaCl and LiF crystals indicate that the effect of small impurity is very great whilst the effect of temperature is small. Examination of the results on the basis of a double kink mechanism shows that this mechanism cannot describe the dislocation motion in the crystals under consideration at screw dislocation velocities greater than about 10−3 cm/s. Therefore, the upper limit of the Peierls stress in the crystals may be estimated to be not more than some tens of p/mm2.
Electrode‐Limited to Bulk‐Limited Conduction in Silicon Oxide Films
Authors: Stuart M. 
Published: July 2007

AbstractThe current‐voltage behaviour of evaporated silicon oxide films, several microns thick, have been investigated. At low voltages conduction is determined by contact barriers at the electrodes. At high voltages conduction is bulk‐limited and obeys a modified Poole‐Frenkel equation.
Akzeptorbildende Gitterdefekte im Tellur
Authors: Hörstel W. , Kretzschmar G. 
Published: July 2007

AbstractAus Abschreck‐ und Ausheiluntersuchungen an Tellureinkristallen ergibt sich die Gleichgewichtskonzentration thermischer Akzeptoren zwischen 380 und 550 °K zu [V′Te] = 7 × 1024 exp (−0,8 eV/kT) cm−3 ± 50%. Unter Zugrundelegung eines Zweibandmodells mit konstanten effektiven Massen und konstantem Beweglichkeitsverhältnis folgt daraus, daß thermische Akzeptoren bei etwa 580 °K eine „anomale”︁ Vorzeichenumkehr des Hallkoeffizienten bewirken müßten. Die Wanderungsenthalpie der eingefrorenen thermischen Akzeptoren wird zu (0,31 ± 0,02) eV bestimmt. Während des Ausheilens der thermischen Akzeptoren scheinen sich größere Assoziate zu bilden.
Growth of Zinc and Cadmium Whiskers from the Vapour Phase on a Single Crystal Substrate of the Same Material
Authors: Nanev Chr. , Iwanov D. 
Published: July 2007

AbstractA determination is made of the crystallographic orientation of zinc and cadmium whiskers grown on single crystal substrates of the same substances which have well‐formed faces, edges and tips. Zinc and cadmium whiskers grown in this way in the presence of hydrogen or argon are oriented as 〈1120〉, however zinc whiskers grown in vacuum have the orientation 〈1123〉. These are in fact the directions of the screw dislocations in the lattice. These and other results indicate that the whiskers grow preferentially via a screw dislocation mechanism. Some cases are observed in which zinc “whiskers” grow at large supersaturations without involving a surface diffusion mechanism as required by the classical theory of whisker growth. Possible causes for the appearance of whiskers on a single crystal substrate are discussed, as well as the factors which determine their orientation.
De Haas‐van Alphen Effect in White Tin
Authors: Stafleu M. D. , de Vroomen A. R. 
Published: July 2007

AbstractThe de Haas‐van Alphen effect in white tin is measured using the field modulation technique. The results contain much more detail than those reported by Gold and Priestley. The smaller parts of the Fermi surface can be constructed directly from the measurements; the construction of the larger parts will be described in a separate paper.
Fermi Surface and Pseudopotential Coefficients in White Tin
Authors: Stafleu M. D. , de Vroomen A. R. 
Published: July 2007

AbstractThe de Haas‐van Alphen measurements previously reported are used to determine the shape of the Fermi surface in white tin, and to calculate the pseudopotential coefficients. The present results give much better agreement with the model potential of Animalu and Heine than does the recent band calculation by Weisz.
Influence de l'organisation en domaines du titanate de baryum sur sa température de transition
Authors: le Traon A. , le Traon F. , le Montagner S. 
Published: July 2007

AbstractOn propose de compléter, dans le cas d'un ferroélectrique du type BaTiO3, l'expression de l'enthalpie libre, pour tenir compte de facteurs propres aux domaines de polarisation: on en déduit une formule reliant la température de transition para‐ferroélectrique à un paramétre caractéristique de cette structure en domaines. Les températures généralement données pour BaTiO3 correspondraient alors à des domaines de dimensions moyennes supèrieures à 0,2 μm.
Electronic Structure of F‐Centers in Alkaline Earth Fluorides
Authors: den Hartog H. W. , Arends J. 
Published: July 2007

AbstractThe isotropic hfs constants of F‐centers in alkaline‐earth fluorides and the g‐shift in CaF2 are calculated using various published wave functions. The computed results of these calculations are then compared with experiment in order to assess the validity of the wave functions. The wave functions studied give the correct order of magnitude for the isotropic hfs constants of the first shell of F− ‐ions surrounding the vacancy. For the second shell of F−‐ions a few wave functions give values in agreement with experiment.
A New Type of X‐Ray and Electron Diffuse Scattering and Corresponding Strain Contrast on Electron Microscopic Images
Authors: Khachaturyan A. G. , Usikov M. P. 
Published: July 2007

AbstractA kinematic theory is developed for electron elastic diffuse scattering by static distortions, caused by coherent particles in the new phase. It is suggested that the lattice of the new phase differs from the matrix lattice in an arbitrary way. The theory is valid in cases when the matrix and the particles are elastically anisotropic and possess equal moduli. The values of the elastic displacements determining the diffuse scattering are obtained from anisotropic elasticity theory. The isodiffuse surface cross‐sections of the reciprocal lattice planes are calculated for the anisotropic ageing alloy CuBe and the isotropic alloy TaO. These alloys show the precipitation of tetragonal and rhombic phases respectively. The isodiffuse surface sections are in good agreement with the structure of the reciprocal lattice points, obtained on the diffraction patterns; the scattering in these cases also differs considerably from Huang scattering which arises when particles are dilatation centres. A kinematic theory is also developed for the strain contrast caused by the distortions in a solution due to the new phase particles. When the particles are not only centres of dilatation but also centres of an arbitrary deformation, the strain contrast differs from Ashby contrast to the same extent as the diffuse scattering differs from Huang scattering. A comparison is made between the contrast calculated theoretically and that obtained on the micrographs of the alloy TaO.
Group‐Theoretical Classification of Electronic States in Crystals Composed of Pairs and Complexes of Bound Impurity Ions
Authors: Vonsovskii S. V. , Cherepanov V. I. , Men A. N. , Nikiforov A. E. 
Published: July 2007

AbstractA group‐theoretical method is suggested for determining allowed type states of pairs and complexes of impurity ions in ionic crystals. Two cases are discussed in detail. In the first case the energy of the electrostatic interaction Veint between electrons of different impurity ions is greater than that of the internal magnetic interactions Hm0 and in the second case Veint is less than Hm0. For both cases Veint is assumed to be smaller than the total energy of the internal electrostatic interactions and the energies of a crystal field produced by the remaining ions of the crystal. As an example the I—V order pairs of the equivalent ions Cr3+ in corundum are examined.
Transient Behaviour of Space‐Charge‐Limited Currents in p‐Type Silicon
Authors: Lemke H. , Müller G. O. 
Published: July 2007

AbstractCalculation of the leading transients of space‐charge‐limited currents, neglecting diffusion, predict a “cusp”‐type behaviour which until now has only been confirmed on low mobility materials under optical excitation. On Si samples with p+‐contacts and on Pt‐contacted uncompensated (trap‐free) 60 kωcm crystals it is possible to obtain quantitative agreement at least after the first few ns. This provides a good method for measuring majority carrier mobilities. The origin of an order of magnitude deviation for times small compared with the transit time seems uncertain.
Ferromagnetische Hochtemperaturnachwirkung an Eisen‐Silizium‐Legierungen bei gleichzeitiger plastischer Verformung
Authors: Krings F. J. 
Published: July 2007

AbstractDurch plastische Verformung wird in Eisen und Eisenlegierungen mit einigen Gew‐% Si unterhalb 400 °C eine starke magnetische Nachwirkung erzeugt. Der Aufbau der Defekt‐konzentration wird während der Verformung gemessen. Meßparameter sind die Temperatur (275 bis 360 °C), die Verformungsgeschwindigkeit (2,8 × 10−7 bis l,0 × 10−5 s−1) und der Si‐Gehalt (0,1,1,2,4 und 3,3 Gew‐%Si). Das Erholungsverhalten der Defekte wird untersucht. Die Ergebnisse lassen sich mit einem Modell deuten, bei dem die Nachwirkung durch Einzelleerstellen hervorgerufen wird, deren Erholung über Doppelleerstellen abläuft. Eine Deutung durch Umorientierung von Si‐Paaren erscheint nicht möglich.
Magnetoconductivity of Trigonal Selenium Single Crystals
Authors: Mell H. , Stuke J. 
Published: July 2007

AbstractSix of the eight magnetoconductivity components of trigonal Se are measured up to 30 kG over the temperature range 83 to 300 °K. Unlike the Hall mobility, which increases exponentially with temperature, the magnetoconductivity mobility decreases with rising temperature and, at high temperatures, is approximately proportional to T−3/2. At 300 °K a value of 28 cm2/Vs is obtained for the mobility in the chain direction, whilst the Hall mobility at the same temperature is only about 0,2 cm2/Vs[1]. This discrepancy can be explained by assuming a strongly inhomogeneous hole concentration. The directional dependence of the magnetoconductivity is interpreted using a six‐ellipsoidal model. From this the ratio of the mobilities parallel and perpendicular to the chain direction is about 3.5.
The Range of g‐Factors and the Breakdown of Motional Narrowing in Conduction Electron Spin Resonance
Authors: Dupree R. , Holland B. W. 
Published: July 2007

AbstractIt is suggested that the recent measurements of electron spin resonance in aluminium [1] indicate that motional narrowing is absent at low temperatures and the linewidth is deter‐mined by the spread in g‐factors over the Fermi surface. Using first order perturbation theory an upper limit to the g‐shift as a function of position on the Fermi surface is derived, and its consistency with all the g‐shift observations on metals to date is demonstrated. An upper limit to the range of g‐factors over the Fermi surface of aluminium is estimated and is found to give strong support to the hypothesis that motional narrowing is absent at low temperatures. It is pointed out that the usual simple theories of motional narrowing are not applicable and some implications for other metals are discussed.
Shell Model Treatment of the Vibrations of Crystals Containing Substitutional Defects I. U‐Center Localized Modes
Authors: Page J. B. , Strauch D. 
Published: July 2007

AbstractA shell model treatment of the harmonic vibrations of lattices containing substitutional defects is given and is applied to the problem of the infrared‐active localized modes of U‐centers in alkali halide crystals. Long‐range effects due to the shell motions and to altered core and shell charges are included, as are the effects of spherical deformations of the ions. For a U‐center polarizability of 1.9 Å3 and a shell charge of −e it is found that the fractional decreases in the defect's nearest neighbor shell‐shell and isotropic core‐shell spring constants are between 0.30 and 0.55 and greater than 0.75, respectively, for U‐centers in nine different alkali halides.
Transient Acousto‐Electric Phenomena in Semiconducting Piezo‐Electric Crystals
Authors: Autin B. 
Published: July 2007

AbstractIn a semiconducting piezo‐electric crystal the intensity of the current remains proportional to the applied voltage during an incubation time under acoustic gain conditions. The departure from Ohm's law is ascribed to two processes relevant to the build‐up of the acoustic flux: a strong acousto‐electric current and a negative differential conductivity. The onset times of these two processes are calculated by assuming that the electric field is uniform inside the crystal. It is shown that the incubation time is of σdiff < 0 type if the electron drift velocity is slightly higher than the sound velocity and changes into acousto‐electric current type for higher drift velocities.
Studies on the Nature of CdS Single Crystal Sensitization by Etching
Authors: Sheinkman M. K. , Tyagai V. A. , Snitko O. V. , Ermolovich I. B. , Belenky G. L. , Nbondakenko V. 
Published: July 2007

AbstractThe sensitizing of CdS single crystals by etching in a KOH (NaOH) solution is investigated by several photoelectric and luminescence methods. It is shown that the sensitizing is mainly due to the creation of slow sensitizing r‐centres of recombination with parameters identical to those of recombination centres in naturally photoconductive crystals. Two mechanisms are proposed to explain the sensitizing and these take into account the dif‐fusion of vacancy complexes and hydroxyle groups.
Application of the S.C.F. Method of Lattice Dynamics to the Coulomb Lattice
Authors: Pietrass B. 
Published: July 2007

AbstractAnharmonic effects of the Coulomb‐lattice vibrations are investigated by the time‐deendent s.c.f.‐method. In contrast to the traditional treatment using the lattice theory of Born there are higher branches in the dispersion relation of the lattice vibrations which represent anharmonic elementary excitations. In the harmonic oscillator approximation for the low s.c.f.‐states, which is justified for sufficient lylow density, Kohn's sum rule is generalized to include the anharmonic branches. Taking into account anharmonic branches, the instability of the lattice state above a certain density is indicated by imaginary eigenfrequencies in the transverse vibration mode. The contribution of the anharmonic branches to the zero‐point energy is evaluated.
ESR Studies of Different Se Centres in Silver Halides
Authors: Höhne M. , Stasiw M. 
Published: July 2007

AbstractThe ESR spectrum of AgBr:Se crystals which have been irradiated at 120 °K with green light is changed by heating the crystals to 170 °K. The spectrum obtained after heating was recently investigated and attributed to a Se centre. In the present paper the spectrum observed before heating is analyzed with regard to g‐values, and superhyperfine and hyperfine structure. This spectrum is also found to be due to a Se centre of ortho‐ rhombic symmetry The two centres differ in their surroundings and a model of this situation is developed. The investigations are extended to AgCl:Se.
Forward Current Injection Modulation of Photocurrent in p‐n Heterojunctions
Authors: Tansley T. L. 
Published: July 2007

AbstractThe effect of applied forward bias upon the photocurrent observed in p‐n heterojunctions has been investigated in the systems GaAs‐Ga(AsP) and (GaIn)As‐GaAs. In all the heterodiodes measured the photocurrent was found to cut‐off sharply at a well defined bias and this cut‐off voltage proved extremely sensitive to temperature. The observation that the excess photocurrent is simply related to the dark‐current leads to a model in which photo electrons may rapidly thermalize in the conduction band notch if the equilibrium injected population is sufficiently large.
Elektronenmikroskopische Untersuchung von Fehlstellenagglomeraten in ionenbestrahlten Kupferfolien II. Entstehung der Agglomerate
Authors: Diepers H. 
Published: July 2007

AbstractDer Entstehungsmechanismus der in Cu‐Folien durch Beschuß mit Ar‐Ionen erzeugten Zwischengitteratomagglomerate wird untersucht [1]. hierzu wird einerseits die Abhängigkeit der Tiefenverteilung der Agglomerate von der Orientierung der Folie und der Energie der Ionen, andererseits die Abhängigkeit der Agglomeratdichte von der Ionendosis (Dosis‐kurven) bei verschiedenen Folientemperaturen gemessen. Es ergab sich, daß die Agglomerate aus Eigenzwischengitteratomen des Cu aufgebaut sind, die durch gerichtete Stoßprozesse in Form dynamischer Crowdionen ins Gitter eindringen. Der Mechanismus der Agglomeration wird an Hand der Dosiskurven, der Tiefenverteilungskurven und weiterer Experimente zur Bestimmung der Agglomeratgröße in Abhängigkeit von der Dosis, der Temperatur und der Tiefenlage diskutiert.
Experimentelle Ergebnisse zur Temperaturabkängigkeit der Sekundärelektronen‐Emission an polykristallinem Nickel im Intervall 100 ≦ T ≦ 600 °C
Authors: Hölzl J. , Heimann B. 
Published: July 2007

AbstractAn einer 99,9% reinen, polykristallinen Ni‐Zielplatte wird im UHV die Sekundärelektronen‐Emission im Energiebereich der Primärelektronen 50 ≦ Vp ≦ 1000 eV gemessen. Im einzelnen werden folgende Untersuchungen durchgeführt: 1. Bei konstanter Primär‐energie wird die Temperaturabhängigkeit der Koeffizienten der Sekundärelektronen‐Emis‐sion σ, δ und η im Temperaturintervall 100 ≦ T ≦ 600 °C gemessen. Der Widerspruch in bisherigen Ergebnissen älterer Arbeiten bezüglich einer Temperaturabhängigkeit von σ konnte dahingehend entschieden werden, daß σ und δ, nicht hingegen η am ferromagnetischen Curie‐Punkt eine reproduzierbare Anomalie zeigen. 2. Die Energieverteilung von Sekundärelektronen wird einerseits im ferromagnetischen, andererseits im paramagnetischen Zustand der Probe gemessen. Es ergeben sich bei konstanter Primärenergie für beide Probenzustände unterschiedliche Energieverteilungskurven. — Ein Vergleich der unter 1. und 2. mitgeteilten Ergebnisse mit denen einer Modellrechnung, die den Einfluß oberflächlicher magnetischer Streufelder auf niederenergetische Sekundärelektronen abschätzt, zeigt, daß die Anomalie in σ resp. δ nicht ausschließlich als Folge eines oberflächlichen Streufeldeffektes zu interpretieren ist.
Electrical Properties of n‐Type CdSe
Authors: Btirmeister R. A. , Stevenson D. A. 
Published: July 2007

AbstractThe electrical properties of n‐type CdSe were studied over the temperature range of 4.2 to 300 °K. Measurements were made in both as‐grown crystals and crystals annealed under controlled Cd pressures. Hall effect measurements on low resistivity specimens indicate the presence of a donor level 0.014 eV below the conduction band, with concentrations typically ≈︁ 1016 cm‐3. Analysis of the Hall mobility data indicates that the predominant scattering mechanism at room temperature and above is polar optical mode scattering. The magnetoresistance effects observed are consistent with the energy structure determined by previous optical studies. The transport properties exhibited typical characteristics of impurity band conduction at low temperatures (< 77 °K), including negative magnetoresistance.
Magnetoresistivity of Metals I. General Theory
Authors: Seeger A. , Mann E. , Clauseckek K. 
Published: July 2007

AbstractA general theory is given for the low‐temperature magnetoresistivity of metals. This is valid for arbitrary shapes of the Fermi surface, for arbitrary elastic scattering mechanisms, and for all magnetic field strengths with the exception of the so‐called quantum limit. The derivation of the Boltzmann equation and the necessary conditions on the scattering probabilities and potentials are carefully treated. It is shown that the electrical conductivity in a magnetic field (including the Shubnikov‐de Haas effect) can be calculated exactly if the scattering of the electrons is formulated in terms of Wannier functions. The simplifications of the general case due to symmetries are discussed.
Distortion Correction in Anomalous Absorption Coefficients
Authors: Kubiyama M. 
Published: July 2007

AbstractBased on a recent theory of X‐ray diffraction by a distorted crystal completed by the present author, the temperature and distortion corrections in anomalous absorption coefficients have been studied in the case of a single symmetric Bragg reflection in transmission (symmetrical Laue case). If the distribution of atomic displacements is given, then the anomalous absorption coefficient has a distortion correction of the same form as the Debye‐Waller factor in terms of the second moment of the distribution. If the displacement of atoms in a distorted crystal is replaced by a proper time‐average value of the thermal motion of atoms, then the temperature correction in the absorption coefficient is given by the Debye‐Waller factor multiplied by the structure factor.
On the adiabatic potential of a complex system
Authors: Ledovskaya E. M. 
Published: July 2007

AbstractThe energy of an electronic state of a complex system, consisting of a number of interacting subsystems, is considered. The interaction of these subsystems is taken as a perturbation and the calculation of the adiabatic potential uses the iterative method of perturbation theory for nonorthogonal functions. The second order correction to the energy is determined.