bluuebunny/crossref_metadata_2025_split huggingface dataset:
Directional Dispersion of Extraordinary Optical Phonons of α‐Quartz
Authors: Merten L. 
Published: July 2007

AbstractIt is shown that eight ordinary and twelve extraordinary branches of long optical phonons exist in α‐quartz. The ordinary phonons are always transversal and characterized by orientation independent frequencies; the extraordinary phonons are mixed transversal‐longitudinal for general orientations and characterized by orientation dependent frequencies. The extraordinary branches are divided in: two (t → t)‐branches, two (1 → 1)‐branches, six (t → 1)‐branches, and two (1 → t)‐branches (t: transversal, l: longitudinal). The orientation dispersion of these extraordinary branches is quantitatively calculated. The results are compared with hitherto presented data of the orientation dispersion in the Raman spectrum. The agreement is partly excellent.
Lattice Disorder in Alkali Halides X‐Irradiated at Room Temperature
Authors: Balzer R. , Peisl H. , Waidelich W. 
Published: July 2007

AbstractCombined measurements of lattice parameter and length change give evidence that in the alkali halides KBr, LiF, KCl, NaF, and NaCl Frenkel disorder is present after X‐irradiation at room temperature.
Some Effects of Material Inhomogeneities on the Near‐Field Pattern of GaAs Diode Lasers
Authors: Hatz J. 
Published: July 2007

AbstractStudies are made of the near‐field patterns of diode lasers fabricated from slices of Czochralski‐grown GaAs crystals with dislocation densities between 105 cm−2 and zero per slice. Four of the crystals were Te‐doped, the fifth Si‐doped, to 2 × 1018 atoms cm−3. Comparison of the crystal qualities with the near‐fields shows that filamentary emission is not an intrinsic property of diode lasers. With decreasing dislocation density the near‐fields become more homogenous. Diodes made from dislocation‐free material, having in addition almost perfect mirrors, emit uniformly over nearly the whole width of the diode at 1.5 times threshold current. The emission from diodes having a high dislocation density (higher than 104 cm−2) in the active region was strongly filamentary and in some cases the intensity difference between both ends of a filament was as high as 25%. This difference has been accounted for by a simple model of the cavity, which allows for variations of absorption and gain along the optical path.
Effect of Applied Electric Field on EPR Spectra of Crystal Impurity Centres
Authors: Sherstkov Yu. A. , Nepsha V. I. , Vagenin V. A. , Nikiforov A. E. , Krotkii A. I. 
Published: July 2007

AbstractThe spin‐Hamiltonian term which describes the linear effect of an applied electric field on EPR spectra of impurity ions is suggested to be expressed by irreducible tensor operators of the spin and electric field. The method of determining the number of the linear independent coefficients which describe the shift of EPR signals in electric fields is given for 3 dn and 4 fn ions in sites lacking inversion symmetry. The experimental results of the “pseudo‐Stark splitting” for Fe3+ ions in α‐Al2O3 with the electric and magnetic fields parallel and perpendicular to the C3−crystal axis are considered. It is established that the transverse pseudo‐Stark‐effect for Fe3+ ions in α‐Al2O3 is more pronounced than the longitudinal one and exceeds the corresponding effect for Cr3+ in α‐Al2O3.
Dynamical Treatment of the Thermal Diffuse Scattering of X‐Rays
Authors: Afanasev A. M. , Kagan Yu. , Chukhovskii F. N. 
Published: July 2007

AbstractA dynamical theory of the thermal diffuse scattering of X‐rays from thick crystals is developed which consistently takes into account the Bragg scattering of both the incident and diffusely scattered X‐rays. Special attention is paid to the analysis of the intensity distribution of the diffusely scattered waves near the Bragg peak. The known singularity of the one‐phonon scattering of type 1/q2, where q is the phonon wave vector, is shown to be transformed at small q to the more weak singularity of type1/q| for the case of the Bragg diffraction (here,q| is the projection of the vector q ona plane parallel to the crystal surface).
Electron Diffraction and Electron Microscopic Study of Long‐ and Short‐Range Order in Ni4Mo and of the Substructure Resulting from Ordering
Authors: Ruedl E. , Delavignette P. , Amelinckx S. 
Published: July 2007

AbstractThe ordering process in Ni4Mo gives rise to three different classes of interfaces within a single crystal of the basic structure. The geometry of these interfaces and the diffraction effects to be expected from them are discussed. Evidence for the different classes of interfaces is given. The interfaces resulting from slip are discussed and compared with the observations. Quenched specimens exhibit short range order. A model for short range order in this alloy is presented. Preliminary experiments indicate that quenched Ni3Mo also shows short range order of a similar type as Ni4Mo.
360° Walls and Strong Stripe Domains in Permalloy Films
Authors: Ferrier R. P. , Puchalska I. B. 
Published: July 2007

AbstractIn permalloy films evaporated at oblique incidence weak stripe domains [1, 11, 12, 13] and a new type of stripe domains designated “strong stripe domains” can coexist in the same film when the angle of incidence is in range40 to 50°. The creation of the strong stripe domains proceeds either by the formation of 360° walls and their multiplication and subsequent realignment or they may be nucleated directly in the Bloch walls and grow from these nuclei. These two mechanisms are discussed in detail and models for the spin configurations in the films are proposed.
Theory of Orientation Contrast from Inclusions
Authors: Guyot P. 
Published: July 2007

AbstractThe diffraction contrast in transmission electron microscopy for non‐diffracting inclusions in a diffracting matrix not distorted around the inclusion is calculated on the basis of the two‐beam dynamical theory. The normal and anomalous absorption in the matrix and the normal absorption in the inclusion are taken into account. The computed intensity profiles are given for several values of the parameters, i.e. foil thickness, deviation from the Bragg condition, inclusion thickness, inclusion position, absorption coefficients of matrix and inclusion.
On the Double Injection Current Noise in Solids
Authors: Fazakas A. B. , Friedman A. 
Published: July 2007

AbstractCurrent noise in dielectrics and semiconductors is investigated under the following conditions: double injection, negligible traps and recombination centre effects, space‐charge‐limited region, negligible diffusion and direct electron‐hole recombination. A method of calculating the spectral noise density based on the Lax approach and the Debye‐Hückel position correlations between carrier densities is used. Expressions for low and high frequencies are given in closed form; an enhancement effect is found at low frequencies. In the limit of the quasineutral (ambipolar) region, a small correction to the Hill‐van Vliet formula is obtained.
The Normal Spectral Emissivity of Tungsten‐Molybdenum Alloys
Authors: Thomas L. K. 
Published: July 2007

AbstractResults of investigations of the normal spectral emissivity of W‐Mo alloys are reported. The measurements were made at 2000, 2200, and 2400 °K with the wavelength range being 0.4 to 4 μm. Emissivity values of the alloys lie in between those of the pure constituents. The temperature coefficient of the emissivity and the x‐point position change with composition. The results are discussed in terms of the rigid band model.
Storage Effects in Photoconducting GaPCu
Authors: Grimmeiss H. G. , Olofsson G. 
Published: July 2007

AbstractExperimental evidence is given that charge storage exists in photoconducting GaPCu after excitation with both intrinsic and extrinsic light. Appreciable storage is still observed one hour after excitation even at roomtemperature. Measurements of stored charge as a function of ir photon energy, external voltage, and excitation density confirm that such effects as supralinear photoconductivity, etc., are governed by optical charge exchange in agreement with previous investigations.
Multiphononabsorption von Kristallen mit Punktdefekten im starken Strahlungsfeld
Authors: Böttger H. 
Published: July 2007

AbstractEs wird die Gitterabsorption durch Summenprozesse in Kristallen mit einer lokalisierten Schwingung im starken Strahlungsfeld unter Verwendung einer Diagrammtechnik untersucht. Für die hochfrequenten Seitenbanden der lokalisierten Schwingung von H−‐Defekten in Alkalihalogeniden wird die kritische Feldstärke, in deren Nähe die betrachtete Absorption rapide anwächst, zu ca. 106 V/cm abgeschätzt.
Surface Photoconductivity of CdS Influenced by Chemisorption and Desorption of Oxygen
Authors: Weber E.‐h. 
Published: July 2007

AbstractUsing investigations of the spectral dependence of photoconductivity and of the influence of oxygen on photoconductivity a method is developed to test the properties of space‐charge layers at the surface of CdS, at least in some extreme cases. The surface space‐charge layer of thick CdS platelets with a photoconductivity greatly sensitive to an oxygen atmosphere is found to be of accumulation type. This makes a re‐interpretation necessary of the models so far accepted for the chemisorption and desorption processes. As their rate‐ limiting steps the direct capture of electrons and holes by neutral and negatively charged oxygen, respectively, is assumed. Theoretical calculations on the basis of this model show qualitative agreement with the experimental results, but desorption seems to be a process more complex than pure photodesorption.
Long‐Wavelength Longitudinal Phonons of Multi‐Mode Crystals
Authors: Chang I. F. , Mitra S. S. , Plendl J. N. , Mansur L. C. 
Published: July 2007

AbstractIt is shown that the application of the so‐called Drude's rule in obtaining the k ≈︁ 0 longitudinal optic mode frequencies (LO's) of multi‐resonance damped oscillators is not correct, although it may be used as an approximate method only when a few oscillators, all of appreciable strength, are present. A rigorous procedure suitable for all cases, single or multi‐resonance, is shown to be to identify the frequencies at which the minima of the modulus of the complex dielectric constant (|ϵ|) occur with the LO modes. The frequencies of the maxima of |ϵ|, on the other hand, approximately represent the k ≈︁ 0 transverse optic modes. It is also shown that for a general n‐mode crystal it is possible to obtain the LO frequencies individually provided that all the parameters of the Lorentz oscillators needed to represent an observed optical property are known. In the case of a single resonance oscillator the equations reduce to the well‐known Lyddane‐Sachs‐Teller relation. Examples are given where LO's are obtained by the above methods using reflectivity data and compared with whatever available directly measured experimental LO values, e.g., from Raman or neutron scattering measurements.
Phase‐Dependent Superconductive Current Density in a Superconductor _ Normal Metal _ Superconductor Junction at T = TCN
Authors: Yeh R. H. T. , Mechetti H. 
Published: July 2007

AbstractA general equation for the phase‐dependent supercurrent density across the weak‐link is obtained, from which we find that Jmax at T = TCN decreases very slowly with dN when compared with Jmax at T near TCS.
On the Problem of Recombination Autooscillations
Authors: Bonch‐bruevich V. L. 
Published: July 2007

AbstractThe conditions are studied under which autooscillations of the concentration of free carriers may take place. A unipolar semiconductor sample is considered containing besides the standard doping impurity some traps of one or of two types. The criteria of the soft self‐excitation of the oscillations in question are stated explicitly, together with the conditions of the fluctuational stability of the system. The decisive role of extrinsic illumination is pointed out.
Stability of Surface‐Barriers in Semiconductors
Authors: Fazakas A. B. , Handel P. H. 
Published: July 2007

AbstractIn order to test a recently proposed recurrence method for studying the stability of the semiconductor surface‐barrier, we apply it to the currentless state up to second order. We obtain the expected stability at arbitrary values of the surface potential. Furthermore, we investigate the stability in the presence of an applied electrical field at sufficiently small values of the surface potential and restrict ourselves to the first order calculation. The obtained critical field exceeds the breakdown value. Thus, at least for small values of the surface potential (|V8| ≤ 0.75 kT) stability prevails.
Conductivity of Intrinsic InSb in High Electric Fields
Authors: Weissglas P. , Blötekjaer K. 
Published: July 2007

AbstractA theory is developed for the carrier transport properties and impact ionization rate in an intrinsic polar semiconductor with high carrier density. Polar scattering prevails in weak fields but it is shown that intercarrier interactions become important at higher field strengths. The carrier concentration is found to vary approximately exponentially with applied field. Numerical results for data representative of InSb are presented.
Role of Gradual Capture in the Photoelectromagnetic and Photoconductive Effects
Authors: Dolocan V. 
Published: July 2007

AbstractA theoretical study is made of the role of the gradual capture in the photoelectromagnetic and photoconductive effects. The results obtained show that the photoelectromagnetic lifetime is not affected, while the photoconductive lifetime is affected by gradual trapping. The gradual recombination affects both the photoelectromagnetic and photoconductive lifetime.
On the Origin of High Photovoltages in Semiconductors
Authors: Zhadko I. P. , Romanov V. A. 
Published: July 2007

AbstractA new possible mechanism is proposed for explaining the high photovoltage arising in semiconductor films assuming an anisotropic conductivity of the photosensitive crystallites of which the films consist. In this case the high photovoltage is the sum of the elementary transverse Dember photo‐e.m.f.'s. This model may explain practically all peculiarities of the high‐photovoltage effects.
The Theory of Cohesion of Noble Metals (II)
Authors: Nikulin V. K. , Trzhaskovskaya M. B. 
Published: July 2007

AbstractOn the basis of the results obtained in previous papers a calculation is made of the cohesive energy, Wigner‐Seitz sphere radius, and compressibility of Cu and Ag using the nonlocal model potential. An isotropic band effective mass is also estimated for these elements.
Exciton Theory in Crystals with Complicated Band Structure with Electron‐Phonon Interaction
Authors: Kudykina T. A. , Tolpygo K. B. , Zubkova S. M. 
Published: July 2007

AbstractThe theory of the exciton is developed on the basis of the many‐electron model. It is supposed that the excited electron can pass from any occupied state of one atom to a free state of this atom or of another one. Two limiting cases are considered: the large‐radius exciton in many‐valley semiconductors with the value of the many‐valley splitting of its level being estimated, and the small‐radius exciton in alkali halide crystals. In the last case the energy of the exciton, composed of Känzig's autolocalized hole and an electron, moving over ten nearest neighbours, is calculated.
Effect of Lattice Distortions on the Magnetic Behaviour of Perovskite‐Type Manganites
Authors: Bokov V. A. , Grigoryan N. A. , Bryzhina M. F. , Tikhonov V. V. 
Published: July 2007

AbstractSome series of solid solutions with perovskite‐type structure are synthesized and investigated, viz. the binary systems Nd1−x, MexMnO3 where MeCa2+, Sr2+, Ba2+, and the ternary systems (Bi1−xLax)0.5Ca0.5MnO3 and Bi0.5(Ca1−xMex)0.5MnO3 where MeSr2+, Pb2+, Ba2+. Distortions from the cubic perovskite structure are detected at room and liquid nitrogen temperature. Magnetic measurements are made in the temperature interval 77 to 800 °K. For all the compounds, a correlation between lattice distortions and magnetic behaviour is observed; 1. cubic and slightly distorted compounds exhibits a pure ferromagnetism; 2. distortions from the cubic structure give reduced spontaneous moments and in some cases antiferromagnetism developes. The ferromagnetic nature of the Mn3+ O2−Mn3+ and Mn3+O2−Mn4+ interactions which are found in the non‐distorted compounds is interpreted according to the Goodenough‐Kanamori rules assuming that the quasi‐static hypothesis is satisfied. The lattice distortions observed are thought to give rise to a static distortion in the Mn3+ ion environment and an ordering of covalent bonds. As a result, some part of exchange couplings becomes antiferromagnetic. The influence of the decreased subtended angle in the MnO2−Mn linkage is discussed. This angle decreases from 180° when the lattice becomes distorted and this fact disturbs the orbital orthogonality. This results in an increase of the antiferromagnetic t2g−t2g interaction via σ‐bonding and in the occurence of the other superexchange antiferromagnetic interactions which couple both the eg and t2g orbitals and the t2g and t2g orbitals via π‐bonding. The contribution of double exchange to the ferromagnetism of mixed manganites is believed to be not important.
Investigation of the Mössbauer Effect in Some Fe–Al Alloys
Authors: Nemoshkalenko V. V. , Rasumov O. N. , Gorskii V. V. 
Published: July 2007

AbstractFrom a general consideration of the isomeric shift and the parameters of the X‐ray emission K‐spectra of Al and Fe in FeAl2 alloy it is concluded that the transition from Fe3Al to FeAl is accompanied by an electronic transition from the Al atom to the Fe atom with the filling of the 3d states; this process seems to be complete in the equi‐atomic alloy. Further increasing of the Al content in the alloy (transition from FeAl to FeAl2) leads to an increase in the p‐shell population in the Fe atoms.
Mössbauer Effect in Antimony–Organic Compounds
Authors: Gukasyan S. E. , Shpinel V. S. 
Published: July 2007

AbstractThe isomeric chemical shifts (IS) of the Mössbauer 37.2 keV γ‐line of the Sb121 nucleus in organic compounds of antimony (type Ar3SbX2, Ar4SbX, and Ar3Sb) have been measured. The spectra of the resonance absorption are mainly found to be broadened single lines with appreciable asymmetry. The results obtained are interpreted on the basis of the semi‐empirical method of hybrid orbitals.
Analysis of Point Defect States in Copper I. The Influence of the Point Defect State on the Irradiation Damage Rate at 80 °K
Authors: Dworschak F. , Schuster H. , Wollenberger H. , Wurm J. 
Published: July 2007

AbstractThe present measurements of the irradiation damage rate at 80 °K and those from the literature demonstrate the validity of the unsaturable trap model of Walker for copper over a wide range of trap concentrations and radiation induced defects. These results imply the free migration of interstitials below 80 °K. By damage rate measurements at 80 °K effective concentrations of vacancies and interstitial traps introduced by any pretreatment can be determined.
Temperature Dependence of the Magnetocrystalline Energy Constants K1, K2, and K3 of Iron
Authors: Gengnagel H. , Hofmann U. 
Published: July 2007

AbstractThe magnetocrystalline energy constants K1, K2, and K3 of spherical iron single crystals are determined by the torque method in the temperature range 20 to 800 °K. The temperature dependence of K1 is in good agreement with recent measurements of other authors. The constants K2 and K3 are very small as compared to the constant K1. K2 is always negative and K3 is positive within the whole temperature range.
Pressure Dependence of the Elastic Constants of Single Crystalline Aluminum Oxide
Authors: Gieske J. H. , Barsch G. R. 
Published: July 2007

AbstractThe six single crystal elastic constants of aluminum oxide have been measured by the ultrasonic pulse superposition method at 25 °C as a function of hydrostatic pressure up to 10 kbar. A linear pressure dependence has been found in all cases. The results are compared and found to agree approximately with theoretical data for the hexagonal close‐packed structure with nearest neighbor central forces. They are also used to calculate the pressure dependence of the lattice parameters from Thurston's equation of state. The agreement with directly measured experimental data of Hart and Drickamer is excellent for one, and poor for the other lattice parameter.
Optical Energy Gap in TlSe
Authors: Pickar P. B. , Tiller H. D. 
Published: July 2007

AbstractThe results of a study to characterize samples of single crystals of TlSe grown by the Bridgman‐Stockbarger and zone recrystallization techniques are given. The X‐ray diffraction patterns were indexed as a tetragonal lattice whose parameters were a = 8.02 Å and c = 7.00 Å. The absorption and transmission measurements in the region from 0.64 to 1.20 eV yield an estimate for the band gap for the indirect transition as 0.73 eV, which agrees with that obtained from photoconductivity experiments.
Properties of Exciton States in NaI I. The Intrinsic Photoluminescence
Authors: Fontana M. P. , Blume H. , van Sciver W. J. 
Published: July 2007

AbstractThe efficiency and the decay time of the intrinsic photoluminescence of NaI have been investigated as a function of temperature and uv excitation energy. Upon excitation in the band‐to‐band region, the efficiency and the decay time are constant at low temperatures and decrease above 77 and 60 °K, respectively. The decrease in the decay time is not correlated to radiationless transitions occurring within the luminescent center. Upon excitation in the exciton region, the luminescence efficiency reaches a maximum at 60 °K and decreases at both higher and lower temperatures. The high temperature behavior is similar to that produced by band‐to‐band excitation. At 5 °K the luminescence efficiency for exciton excitation is negligibly small. The low temperature behavior of the luminescence is explained in terms of localized exciton states and temperature activated transitions among them.
Elektrische Leitfähigkeit und Halleffekt von mangandotiertem Germanium und der Einfluß von Wärmebehandlungen auf den Einbauzustand des Mangans
Authors: Gläser H. J. , Geist D. 
Published: July 2007

AbstractDurch verschiedene Wärmebehandlungen kann der Zustand des Mangans in Germanium‐Einkristallen geändert werden. Diese Änderung beeinflußt nicht nur die Trägerkonzentration, sondern auch die Beweglichkeit. Die Ergebnisse werden durch das Verhalten des Spektrums der paramagnetischen Elektronenresonanz des substitutionell eingebauten Mangans bestätigt.
Determination of the Electron Spin–Lattice Relaxation Time T1 in the Direct Process
Authors: Pfeuffer K. 
Published: July 2007

AbstractIn the standard investigation methods of the spin–lattice relaxation of paramagnetic ions in crystals the measured time constant of the relaxation process is the spin–bath relaxation time Teff. If a phonon bottleneck exists, the spin–lattice relaxation time T1 does no longer equal Teff. A method is proposed for determining T1, which is still valid if a phonon bottleneck exists.
Magnetic Properties of ZrFe2 and TiFe2 within Their Homogeneity Range
Authors: Brückner W. , Perthel R. , Kleinstück K. , Schulze G. E. R. 
Published: July 2007

AbstractThe magnetic properties of TiFe2 and ZrFe2 are investigated within their homogeneity range in dependence on the concentration. TiFe2 is antiferromagnetic at titanium excess and at stoichiometric composition and it is ferromagnetic at iron excess. ZrFe2 is ferromagnetic throughout the whole homogeneity range. The dependences of the Curie temperatures and of the saturation magnetizations on the concentration are determined. By the present studies the discrepancies of the magnetic data of ZrFe2 and TiFe2 existing in the literature can be attributed to the existence of a homogeneity range.