bluuebunny/crossref_metadata_2025_split huggingface dataset:
Study of GaSb Valence Band by Magnetoresistance and Hall Effect Measurements at Low Temperature
Authors: Pistoulet B. , Robert J. L. , Marques M. 
Published: July 2007

AbstractThe presence of light and heavy holes in GaSb has been pointed out by Becker et al.[1] and values of their effective masses have been obtained by various authors [2,3,4]. A study is made here of the Hall effect, and the longitudinal and transversal magnetoresistance of p‐type GaSb crystals at 4.2 °K, from 0 to 33 kG. Assuming that depopulation of the light‐hole band by the field is mainly responsible for the variation of the Hall coefficient and considering isotropic bands tangential at k (000), the densities, mobilities, and effective masses of the two species of holes are deduced.
Mössbauer Effect in Ga2−xFexO3 and Related Compounds
Authors: Trooster J. M. , Dymanus A. 
Published: July 2007

AbstractMössbauer investigations are reported for five different compositions of gallium iron oxide and for iron‐substitutedβ‐Ga2O3, and AlFeO3. The spectra confirm the ferrimagnetic spin‐arrangement of Ga2−xFexO3. Information is obtained on the cation distribution in iron‐substituted (β‐Ga2O3 and Ga2−xFexO3.
Hot Electron Polar Scattering in InSb
Authors: Hammar C. , Weissglas P. 
Published: July 2007

AbstractThe energy and momentum relaxation of conduction electrons by optical phonons in InSb are studied using the energy band structure calculated by Kane. For simplicity, the drifted Maxwellian approach is used and its form for an arbitrary band structure is presented. No intrinsic breakdown is obtained. On the contrary, the model gives a voltage‐controlled differential negative mobility for high fields.
Stationary State of a Semiconductor with Negative Bulk Differential Conductivity
Authors: Kagan M. S. , Kalashnikov S. G. , Zhdanova N. G. 
Published: July 2007

AbstractThe system of nonlinear equations describing the stationary state of a semiconductor with negative bulk differential conductivity is analysed in the “phase plane”. The negative differential conductivity is considered to arise from either the field dependence of the electron concentration (due to the recombination process) or the field dependence of the mobility. Possible spatial variations of the field along the sample have a step‐like form and correspond to two different values of the saturation current. The current‐voltage characteristics and the field distributions are studied experimentally in n‐type germanium samples containing partly compensated copper. It is found that the saturation current corresponds to the peak of the current‐field curve of a spatially homogeneous sample. The electric field in the low and high field regions, as well as the location of these regions in the sample, are found to be in satisfactory agreement with theory.
Umwandlung von OH‐Zentren in U‐Zentren bei KCl‐Kristallen durch elektrolytische Verfärbung
Authors: Fröhlich F. , Adametz O. 
Published: July 2007

AbstractMit hilfe von Absorptionsmessungen im UV und IR wird gezeigt, daß sich durch elektrolytische Verfärbung von KCl‐Kristallen OH‐Zentren in U‐Zentren umwandeln lassen, falls die OH‐Ionen an Ca‐Ionen gebunden im Kristall vorliegen. Die Zahl der gebildeten U‐Zentren ist der Ausgangskonzentration der OH‐Ionen im Kristall proportional und nimmt mit der durch die Farbzentren übertragenen Ladungsmenge und mit steigender Temperatur zu. Gleichzeitig mit den U‐Zentren entstehen Absorptionsbanden im UV, die dem Sauerstoff zugeordnet werden können.
Jahn‐Teller‐Effekt an Übergangsmetallionen in Silberhalogeniden. I. Ti3+(3d1) und Fe2+ (3d6)
Authors: Koswig H. D. , Retter U. , Ulrici W. 
Published: July 2007

AbstractEs werden die optischen Absorptionsspektren für den T2g → Eg‐übergang des Ti3+ und Fe2+ im AgCl und AgBr in Abhängigkeit von der Temperatur zwischen 20 und 400 °K untersucht. Die Aufspaltung dieses übergangs wird durch einen dynamischen Jahn‐Teller‐Effekt verursacht. Es wird die Temperaturabhängigkeit der Aufspaltung. der Lage der Maxima und der Flächen (Oszillatorenstärken) der Teilbanden bestimmt.
Orientation Superstructures and their Effects in Spinel Ferrites
Authors: Marais A. , Merceron T. 
Published: July 2007

AbstractOrientation superstructures are examined using the magnetic diffusion after‐effect, the squareness ratio R, and the induced anisotropy Ku, in the ferrites: Mn0.2Fe2.8O4.014, CuxMg1−xFe2O4 (0.09 ≦ x ≦ 0.69), Mn1+xO4 (0.1 ≦ x ≦ 0.8) and Fe1.95Ni0.95Cox× × Zn0.1−xO4 (0.02 ≦ x ≦ 0.1). In the temperature zones where disaccommodation occurs (due to the ionic or electronic diffusion), a uniaxial anisotropy can be formed with a corresponding increase of R. It is shown that a new type of electron transfer: Cu+ ↔ Cu2+ is responsible for the magnetic after‐effect in Mg‐Cu ferrites.
Zur Theorie der zweiphasigen Domänenstrukturen in Supraleitern und Ferromagneten
Authors: Hubert A. 
Published: July 2007

AbstractDie Bereichsstrukturen in supraleitenden sowie einachsigen ferromagnetischen Platten unendlicher Ausdehnung werden theoretisch untersucht. Charakteristisch für diese Domänenstrukturen ist, daß die Bereiche im allgemeinen von der Plattenmitte zur Oberfläche hin in einer komplizierten Weise aufgespalten, derart. daß — besonders bei dicken Kristallen — die Bereichsweite an der Oberfläche viel kleiner als diejenige im Innern ist. Dieses Ver‐halten wird mit hilfe eines neuartigen Energieansatzes abgeleitet, in den wesentlich eine mittlere. stetig veränderliche Bereichsweite eingeht. Entscheidend sind drei für das jeweilige Material zu bestimmende Energieparameter, nämlich eine Wandenergie, eine Oberflächenabschlußenergie und eine Feldenergie im Inneren der Probe. Diese Parameter wer‐den sowohl für ferromagnetische als auch für supraleitende Proben angegeben. Mit ihrer Kenntnis ist es dann auf Grund der Rechnung möglich, die Bereichsweite in ihrem Verlauf von der Probenmitte zur Oberfläche als Funktion der Dicke der Probe, der Temperatur oder der Größe eines äußeren Feldes vorherzusagen.
Magnetic Dilution of Bare‐Earth Aluminum Cubic Laves Phases RAL2
Authors: Buschow K. H. J. , Fast J. F. , van Diepen A. M. , De Wijn H. W. 
Published: July 2007

AbstractCurie temperatures and magnetizations are measured in the cubic Laves phases RxM1−xAl2 (R = Gd, Tb, Er and M = Y, La, Th). Upon dilution with Y or La a linear decrease of the Curie temperature, passing through zero for x = 0, is found. Dilution with Th results in an additional decrease of the Curie temperature. This effect is attributed to small changes of the Fermi wave‐vector. The results, as compared with Knight shifts, are discussed in terms of the Ruderman‐Kittel‐Kasuya‐Yosida theory. The exchange integral Γ is found to be of the order of −0.9 eV, and definitely negative.
Point Defects in Ferromagnets
Authors: van de Braak H. P. , Caspeks W. J. 
Published: July 2007

AbstractA calculation is made of the local magnetization of the nearest neighbours of non‐magnetic impurities in a Heisenberg ferromagnet with spin quantum number equal to 1/2. For the higher temperatures below the Curie point a molecular‐field model is used. The results for the low‐temperature region, derived by method of the double‐time temperature‐dependent Green function, show that assumptions made in a previous study are valid.
On the Nature of Oscillations in Impurity Photoconductivity Spectra of Ge
Authors: Besfamilnaya V. A. , Elesin V. F. , Kueova I. A. , Ormont N. N. , Ostboborodova V. V. 
Published: July 2007

AbstractA theoretical analysis is given which considers the strong dependence of lifetime on the carrier energy, the impurity scattering, and the very short relaxation time τop of the “hot” photocarriers due to optical phonons. The carrier energy is always smaller than the optical phonon energy and jumps from this value to nearly zero if the photon energy minus carrier ionizationsenergy is increased from just below to just above a multiple of the optical phonon energy. The main assumption made is that the lifetime of the carriers in this energy interval is solely determined by the relaxation time τac due to the acoustic phonons; the relaxation time with the equilibrium carriers τre and the lifetime rr of “cold” carriers being much greater. The relative depth η of the oscillations is calculated and is in good agreement with experiments on Ga‐doped p‐type germanium at 7 °K.
The temperature dependence of the borrmann effect in copper
Authors: Baldwin T. O. 
Published: July 2007

AbstractThe temperature dependence of the anomalous transmission of X‐rays (Borrmann effect) in copper has been measured in the temperature range 77 to 377 °K. From the slopes of the curves obtained, the apparent Debye temperature θ has been determined to be (306 ± 4) °K. This value is 3 to 4% less than that previously reported from the temperature dependence of X‐ray diffraction from powders and single crystals. Using this value of θ in the calculations of absolute Borrmann intensities, however, good agreement is obtained between calculated and experimental values. It is suggested that the difference in the θ‐values may arise from thermal diffuse scattering and/or anharmonic contributions to the temperature dependence of the Borrmann intensities.
Higher order elastic constants in H.C.P. crystals
Authors: Rose M. F. , Ramsey R. T. 
Published: July 2007

AbstractExpressions for the elastic constants for hexagonal close‐packed lattices are derived through third order, assuming, the atoms interact through a central potential function These expressions are then evaluated, using the Morse and Rydberg potential functions, for Be, Mg, Zn, Cd, and Tl. Comparisons are made between theory and experiment wherever possible. The effect of the axial ratio of the h.c.p. lattice on the eleastic constants is discussed and it is shown that both potential functions lead to lattice instabilities for Zn and Cd.
Field electron microscope study of niobium surfaces
Authors: Savage William R. 
Published: July 2007

AbstractAn account is presented of field emission experiments on contaminated and clean niobium surfaces. It is concluded that the equilibrium thermal end‐forms of niobium single crystal emitters consist of small flat regions of low index crystallographic directions smoothly joined by transition planes to give a shape close to spheroidal. Fowler‐Nordheim graphs of the voltage‐current characteristics of the thermally cleaned cathodes gave a work function of (4.1 ± 0.1) eV which agrees with the results of other measurements.
Temperature dependence of the band structure
Authors: Sak J. 
Published: July 2007

AbstractThe temperature dependent part of the self‐energy of an electron interacting with acoustic phonons is computed. At low temperatures the shifts of critical points are quadratic in temperature. Points of the type M0 and M1 shift to lower energies whereas the points M2 and M3 shift to higher energies. For levels at general points there exists a region where the shift is proportional to T4. At high temperatures the direction of shift is determined by the energy of the level. Levels lying below a certain energy shift downwards, those lying above this energy shift upwards. The shift is then linear in temperature.
Surface self‐diffusion measurements on copper
Authors: Bonzel H. P. , Gjostein N. A. 
Published: July 2007

AbstractThe decay kinetics of sinusoidal surface profiles on copper annealed in a hydrogen atmosphere were investigated in the temperature range 600 to 1030 °C in order to determine the temperature dependence of the surface self‐diffusion coefficient, Ds. Below 910 °C the surface profiles were found to be faceted resulting in an apparent discontinuity in Ds which can be understood in terms of the γ‐plot of copper. The discontinuity in the diffusion data can be expressed by the following equations: magnified image
At temperatures below 800 °C is dependent on the annealing time, and inthe vicinity of 600 °C, Ds drops drastically below the minimumvalue that can be measured. This behavior can be explained in terms of the rate theory for a bimolecular surface reation between impurities and diffusing defects. From the predicted time dependence of Ds, it is possible to estimate Ds at t=0. These Ds−values are greater than the extrapolated high temperature data, thus indicating thepossibility of a lower activation energy for surface self‐diffusion at low temperatures.
The structure of amorphous silicon nitride films
Authors: Coleman M. V. , Thomas D. J. D. 
Published: July 2007

AbstractIn an amorphous material the scattered intensity of electron waves depends, in part, on its structure. The variation of the scattered intensity with angle may be mathematically transformed to give a radial distribution function (RDF) which describes both the position, number and type of atoms around an origin atom. The methods used to obtain the RDF from the structurally dependent intensity and the elimination of errors are described. To determine the scattered intensity experimentally, the electron diffraction pattern is scanned across a small aperture and the open circuit voltage developed in a silicon solar cell is measured. These methods have been used to determine the structure of amorphous silicon nitride films prepared by the glow discharge technique. By changing the ratio of ammonia to silane gases, the average composition of the deposit may be varied from silicon to silicon nitride. The effect of these and other deposition parameters on the structure of the films is described. The structure of these films is shown to consist of a mixture of silicon and silicon nitride. The effect of inelastic scattering on the RDF is discussed and the validity of the results confirmed.
Über verbotene Reflexe bei Elektronenbeugung an vakuumaufgedampften Tellurschichten
Authors: Schüz W. 
Published: July 2007

AbstractTellur wurde polykristallin im Hochvakuum aufgedampft und mit der “Sandwich‐Methode” zu dünnen Einkristallfolien im Elektronenstrahl umkristallisiert. Im Beugungsbild zeigten 3 Hauptorientierungen mit horizontaler c‐Achse neben den erlaubten Basis reflexen 00l = 3 n (n ganzzahlig) auch die verbotenen Reflexe 00l für l ≠ 3 n. Dies läßt sich meist als Umweganregung deuten, weil die Intensität der verbotenen Reflexe in einer Vielzahl von Beispielen von der der Nachbarreflexreihen 10l, 11l und 21l übertroffen wird. Andererseits sind gelegentlich verbotene Reflexe bei besonders starker Anregung eines unmittelbar benachbarten 003‐Reflexes zu beobachten, die die oben genannten Nachbarreflexreihen an Intensität weit übertreffen. Dies kann auf einen hierbei überwiegenden Einfluß von systematischer Wechselwirkung zurückgeführt werden.
Structure and dynamics of perovskite‐type crystals
Authors: Cochran W. , Zia A. 
Published: July 2007

AbstractThe connection between Landau's theory of phase transitions and the lattice‐dynamical theory of a displacive transition in a crystal is discussed. At a second‐order displacive transition the frequency of one normal mode becomes zero. By investigating the displacements of the atoms from special positions of the lattice for a number of crystals having the distorted perovskite structure, we have shown that several modes are involved in the various transitions, except in the case of LaAlO3, where the transition is probably second‐order or nearly so, and is associated with a mode of low frequency. The wave vector of this mode is at the point (1/2 1/2 1/2) of the Brillouin zone, and its irreducible representation is Γ25.
Potential differences in NaCl crystals due to plastic deformation by indentation experiments between RT and 20 °K
Authors: Fröhlich F. , Seifert P. 
Published: July 2007

AbstractElectric potential differences due to plastic deformation by indentation are studied in pure and doped NaCl crystals as a function of temperature between room temperature and 20 °K. For CaCl2−doped crystals the potential difference over the whole temperature range can be explained by negatively charged dislocations, and for Na2O2−doped crystals by positively charged dislocations. In nominally pure crystals the potential differences change sign as the temperature is decreased. An interpretation of these results is suggested on the assumption of different temperature dependencies for trapping anion and cation vacancies in the dislocation core.
Energies of Formation of Metal Vacancies in II‐VI Semiconducting Tellurides (HgTe, CdTe, ZnTe)
Authors: Bailly F. 
Published: July 2007

AbstractThe energy of formation of metal vacancies in tellurides is calculated on the assumption that covalent bonding occurs between the Te neighbours. The model uses Morse functions to describe the bond strength between nearest neighbours and the approximation of Suchet's crystallochemical mode. The mean displacement of the atoms around the vacancy is calculated by minimizing the sum of the energy terms associated with the various interactions and is shown to be important. It is shown that, in the particular case of HgTe, this type of vacancy has a negative energy of formation (neglecting the interactions between vacancies). These defects are thus expected to occur naturally with a high concentration, and they are expected to behave as neutral defects. Previous experimental observations of “complex vacancies” support this conclusion. The bonds between Te neighbours may be broken at high temperatures, which transforms the complex vacancies into normal ones: the calculated energy of transformation is in fair agreement with experiment. In the cases of CdTe and ZnTe, the covalent bonding between Te neighbours has only a small effect on the energy of formation of a vacancy.The same kind of calculation, applied to the group IV elements, leads to an energy of formation of vacancies which is in good aggreement with other theoretical calculations and experimental determinations, and this supports the validity of the model.
Computer simulation of the plastic deformation in face‐centred cubic polycrystals and the rolling texture derived
Authors: Leffers T. 
Published: July 2007

AbstractUsing computer simulation of plastic deformation it is shown that both types of rolling texture found experimentally in f.c.c. metals and alloys may be developed by {111} <110> slip. A texture of the copper‐type is developed if the individual crystals are forced to follow the macroscopic deformation in accordance with Taylor's theory. If the grains are supposed to deform like isolated single crystals a brass‐type texture is developed.
Fehler im Flußliniengitter von Supraleitern zweiter Art
Authors: Träuble H. , Essmann U. 
Published: July 2007

AbstractDas Flußliniengitter von Supraleitern zweiter Art enthält Gitterfehler, wie sie aus der Kristallphysik bekannt sind, nämlich Versetzungen, Stapelfehler, “Punkt” fehler usw. Außerdem treten starke elastische Verzerrungen und Gitterkrümmungen auf. Die verschiedenen Gitterfehler werden an Hand von Beispielen, die durch direkte Beobachtung gewonnen wurden, beschrieben und klassifiziert.
Noncentral force model for hexagonal close‐packed crystal lattices (ii)
Authors: Metzbower E. A. 
Published: July 2007

AbstractA Born‐von Karman model of the hexagonal close‐packed crystal lattice was considered using a combination of central and angular forces between various sets of neighbors. The interactions between nearest neighbors in the plane were considered to be central forces while the interaction between both nearest and next‐nearest neighbors out of the plane were considered to be noncentral forces, i.e. the interactions involved both central and angular forces. The equations of motion were evolved and the atomic force constants were evaluated by three different methods. The atomic force constants were evaluated 1. from the elastic constants by the method of long waves, 2. from a least squares analysis of the eigenvalues of the secular equation for elastic waves propagating in certain symmetric crystallographic directions at critical points in the Brillouin zone, i.e. from a least squares analysis of the dispersion relations, and 3. from a least squares analysis of the elastic constants and the dispersion relations. The eigenvalues of the secular equation were calculated for a mesh of seven hundred thirty‐five (735) points in that portion (one twenty‐fourth) of the Brillouin zone irreducible under symmetry operations. The frequency spectrum was obtained from these eigenvalues. The lattice specific heats as a function of temperature were calculated using the appropriate frequency distribution function. The Debye and Einstein characteristic temperatures were also calculated as a function of temperature and compared to experimental values. The insensitivity of the calculated thermodynamic properties of the hexagonal close‐packed crystal lattice on the frequency spectrum is demonstrated for zinc by calculating three different frequency spectra, one for each method of evaluating the atomic force constants, and from these spectra computing the lattice specific heats as a function of temperature. The Debye characteristic temperatures do not change significantly although the details of the frequency spectra differ appreciably. The conclusion has been drawn that better agreement between theory and experiment is reached if angular forces are included in a model of the hexagonal close‐packed crystal lattice rather than simply extending the sphere of interaction to more and more neighboring atoms.
Delocalized excitons in thin anisotropic crystals
Authors: Evans B. L. , Young P. A. 
Published: July 2007

AbstractThe ordinary absorption spectrum of MoS2 contains two series of exciton absorption bands associated with direct optical transitions from a split valence band. In thick crystals the first five members of each exciton series have been detected; these exciton bands move to higher energies and show a diminishing diamagnetic shift with decreasing crystal thickness. The exciton series limit in thin crystals is determined from the oscillatory magneto absorption which occurs to the high energy side of the short wavelength series.
The effects of oxygen adsorption and low energy ion bombardment on the electrical properties of cadmium sulphide thin films
Authors: Hughes D. M. , Carter G. 
Published: July 2007

AbstractThe changes produced in the electrical properties of cadmium sulphide thin films following oxygen adsorption and low energy ion bombardment are reported. High purity cadmium sulphide thin films were prepared in an ultra high vacuum evaporating chamber and conductivity tests and adsorption and bombardment investigations were carried out without exposing the samples to atmospheric contamination. Changes in the electrical properties of the thin film samples which can be directly attributed to either oxygen contamination or radiation damage at the surface, were observed.
A model for tunneling through a Non‐Crystalline thin dielectric film
Authors: Schnupp P. 
Published: July 2007

AbstractContinuing along the lines of an earlier paper [4] on the tunneling of electrons through a thin dielectric film using a one‐dimensional δ‐well model, the tunneling through a disturbed crystalline or amorphous dielectric is considered introducing an uneven spacing of the δ‐wells. As to be expected form the work of De Dycker and Phariseau on the band structure of unlimited amorphous materials [5] the complex band structure in the forbidden band is not qualitatively changed introducing a randomness in the location of the δ‐wells. Quantitatively one observes a decrease in damping x with increasing deviation from the ordered crystal.