bluuebunny/crossref_metadata_2025_split huggingface dataset:
The attenuation length of photoelectrons in thin films of uranium
Authors: Lea C. , Mee C. H. B. 
Published: July 2007

AbstractFilms of uranium up to about 1000 Å thick were evaporated on to quartz substrates at pressures less than 5 × 10−10 Torr. The attenuation length L of photoelectrons in the films was estimated by comparing the photoelectric emission current when the film was illuminated from the vacuum side (i1) to that when the film was illuminated from the substrate side (i2). Theory indicates a linear relationship between log (i1/i2) and thickness, and this was confirmed by experiment for illumination with light of photon energies from 3.5 to 5.0 eV. The constants of the relationship yield values for L between 60 and 120 Å, the attenuation length decreasing with increasing photon energy. Measurements of the electrical conductivity of the films as a function of thickness yielded a value for the mean free path of the conduction electrons of about 290 Å. The results suggest that the principal energy‐loss mechanism for the excited electrons is one of electron‐electron scattering.
Photoconductivity of CsBr single crystals containing F ‐ and M‐centres
Authors: Pelsers L. , Jacobs G. 
Published: July 2007

AbstractThe photoconductivity of additively coloured CsBr crystals was measured in function of wavelength and temperature. The temperature dependence of the quantum efficiency for the two main components of the F‐band is found to be identical. A possible explanation is given following Fowler's suggestion about a diffuse relaxed excited state after absorption. When the temperature dependence of the mobility is taken into account and the expression of Swank and Brown for η is used, a theoretical curve of η w as a function of temperature can be fitted to the experiment with a thermal ionization energy of 0.065 eV. F‐aggregate centers are formed when the F‐band is optically bleached at _ 100 °C. The temperature behaviour of the photoresponse and the spectral distribution at LHT and LNT have been investigated while the F‐band is systematically bleached.
Contributions to the kinematical theory of diffraction contrast from screw dislocations
Authors: Coghlan W. A. , Nix W. D. 
Published: July 2007

AbstractThe images of screw dislocations have been evaluated with the kinematical theory of electron diffraction using numerical techniques. The advantage of this method is that the periodic term in the diffracted intensity can be treated. It is found that because of this periodic term a screw dislocation for which n = g · b = 1 will be nearly invisible for certain foil thicknesses, deviations from the Bragg angle, and dislocation positions in the foil. On the basis of these findings, it is proposed that errors in Burgers vector determinations are possible.
Optische und elektrische Messungen an dünnen Thallium(III)‐Oxydschichten
Authors: Geserich H. P. 
Published: July 2007

AbstractDurch Kathodenzerstäubung wurden dünne polykristalline Tl2O3−Schichten hergestellt. Sie besaßen auf Grund eines stark unterstöchiometrischen Sauerstoffanteils eine hohe Konzentration freier Elektronen (ne ≈︁ 7 × 1020 cm−3). An Schichten mit genügend hoher Elektronenbeweglichkeit (μ = 75 bis 100 cm2/Vs) wurden die optischen Konstanten zwischen 0,2 und 4,5 μm ermittelt. Aus dem Dispersions‐ und Absorptionsverlauf im Ultraroten wurden die effektive Masse im Leitungsband (m* = 0,32 m0) und der Einfluß des Fermi‐Niveaus auf die Absorption durch freie Ladungsträger beim entarteten Halbleiter bestimmt. Aus dem Absorptionsverlauf im sichtbaren und ultravioletten Spektralbereich ergaben sich Bandabstände für direkte (ΔEdirekt = 2,25 eV) und indirekte Übergänge, letztere modifiziert durch den Burstein‐Effekt (ΔEindirekt + ξ ≈︁ 1,4 eV).
Consistent Treatment of Symmetry in the Tight Binding Approximation
Authors: Egorov R. F. , Reser B. I. , Shirokovskii V. P. 
Published: July 2007

AbstractThe form of Hamiltonian matrix components in the tight binding approximation are deduced group‐theoretically taking into account the space symmetry of the problem, time‐reversal symmetry and hermiticity of the Hamiltonian. This method enables the calculations for any complicated crystal structure, when the spin is included respectively not regarded. Calculations for hexagonal close‐packed structure illustrate the procedure.
Notes on a Valence Electron Model of Atoms
Authors: Kunz A. B. 
Published: July 2007

AbstractThe exact solutions to the “valence‐electron model Hamiltonian” are considered. This model was suggested in recent articles by Wang. It is shown that for a certain range of C in the potential term –C r−2, solutions to the problem exist which are formally identical to the usual solutions for the hydrogen atom problem. It is also seen that for a wide range of the parameter C, there exist no solutions for which the Hamiltonian is Hermitian. The implications of this are discussed, and uses of this model considered.
The Ionic Conductivity of CsCl Doped with K+, Rb+, and Br−
Authors: Arends J. , Nijboer H. 
Published: July 2007

AbstractIonic conductivity measurements are made on single crystals of CsCl doped with Rb+, K+, and Br−. The results indicate that small concentrations of these monovalent ions have a marked effect on the activation energies in the NaCl and the CsCl phases and also on the hysteresis behaviour. It is shown that the decrease of the activation energies in crystals doped with Rb+ and K+ and the independence of these energies of the Br− content, can be described in terms of the size of the ions. The decrease of the pre‐exponential factor in crystals doped with K+ or Rb+ is probably due to a change in the frequency spectrum of the lattice vibrations.
A Possibility for Band Structure Determination: Intraband and Donor‐Band Transitions of Crystal Electrons in High Electric Fields
Authors: Döhler G. , Hacker K. 
Published: July 2007

AbstractThe electron states of a crystal in an electric field are Kane functions, the Wannier‐Stark levels are the corresponding energy levels. Electromagnetic transitions between them in the infrared region are considered. From the probability of spontaneous transitions as well as from the hf current produced when the field is changed abruptly the band structure can be determined. The absorption constant for donor‐band transitions shows steps as a function of frequency, the tunneling probability shows steps as a function of the field. Both facts can be used to prove the existence of the Wannier‐Stark levels. The absorption threshold is shifted (Franz‐Keldysh effect). The influence of phonons, imperfections and the electron‐electron interaction is estimated.
Planar Hall Effect in Ferromagnetic Films
Authors: Ky Vu Dinh 
Published: July 2007

AbstractThe planar Hall effect of Ni, Fe, Co and Ni‐Fe films with thicknesses between 100 and 1500 Å is investigated in the temperature range 77 to 293°K. It is shown that the experimental data obtained may be explained by assuming that the mechanism of scattering and reflection on film surfaces does not give an appreciable contribution to the planar Hall effect.
Calculation of the Width of the Second Conduction Band in Anthracene Crystals from Photoemission Data
Authors: Baessler H. , Riehl N. , Vaubel G. 
Published: July 2007

AbstractThe spectral dependence of the photoemission of electrons from a metal into a narrow conduction band of a crystal is calculated qualitatively. It is shown that the Fowler relation jph ∼ (h v–χ)2 holds for χ ≦ h v ≦ χ + δ where χ denotes the energy difference between the Fermi level of the metal and the bottom of the conduction band and δ the band width. For h v ≧ χ + δ the current approaches a saturation value. The model is applied to the description of the photoemission of electrons from a Na and a Ca cathode into the first and the second conduction band of an anthracene crystal. The width of the second band is found to be (0.5 ± 0.1) eV. The energy gap between the top of this band and the next higher (third) conducting state is at least 0.6 eV.
Some Unifying Relations for Moving Dislocations
Authors: Beltz R. J. , Davis T. L. , Malén K. 
Published: July 2007

AbstractLothe's formula for the self‐force on a bent dislocation and Brown's formula for the stress in the plane of a planar loop are generalized to be valid for uniformly moving dislocations when the energy factor is replaced by the Lagrangian factor. Application to straight dislocations in isotropic media shows that the screw dislocation becomes unstable with regard to bends at high velocities. The Lagrangian factor is also used to extend Lothe's representation of the energy flow along a moving straight dislocation and to show the relationship between the mass, the back stress in acceleration, and the energy radiation from an oscillating straight dislocation.
On Electron Mirror Microscopic Observations of the Details of p‐n Junction Regions in Si
Authors: Igras E. , Warmińaski T. 
Published: July 2007

AbstractElectron mirror microscopic observations of lithium p‐n and p‐i‐n junctions in Si show that the contrast of the junction boundary strongly decreases after being irradiated with electrons. Simultaneously the process of saturation with lithium of the micro‐cracks present on the surface in the neighbourhood of the junction line is observed. The observed process is interpreted in terms of the field extraction of lithium ions from the deeper lying positions into the surface. The electric field responsible for the extraction of lithium ions originates from the electrons impinging on a high resistive solid polymer film formed on the crystal in the course of observation. A similar process, though with slower rate, was observed on p‐n junctions obtained by the diffusion of aluminum into n‐type silicon.
Contrast of a Stacking Fault on X‐Ray Topographs
Authors: Authier A. 
Published: July 2007

AbstractThe contrast of the image of a stacking fault on a section topograph is discussed in detail. The intensity distribution of the X‐rays reflected by a crystal containing a stacking fault is the sum of three terms: the first one is due to interferences between waves which have suffered no interbranch scattering, the third term is a cross term due to interferences between waves of both types. The latter is shown to be the predominant term when the crystal is absorbing. This is confirmed by experiment. The derivation has been done using Kato's spherical wave approach and the stationary phase method. The expressions are given for an absorbing crystal and an asymmetrical orientation of the reflecting planes and the stacking fault with respect to the crystal faces. There is good agreement between the calculated intensity distribution and that observed in the image of a stacking fault.
Studies of the Effect of Annealing on Extended Dislocation Nodes in Silver‐Tin Alloys
Authors: Ives L. K. , Ruff A. W. 
Published: July 2007

AbstractExtended dislocation nodes have been observed by transmission electron microscopy and measured in several solid solution silver‐tin alloys after annealing at elevated temperatures. The intrinsic stacking fault energies were determined and compared with previously reported values for freshly deformed specimens. Only small irreversible changes in the fault energy were found after annealing up to 600°C, in contrast to results found in some other alloy systems. The effect of oxygen on the node extensions in pure silver was also studied.
Motion of Markers and Bubbles in Solids by Self‐Diffusion in a Temperature Gradient
Authors: Biersack J. , Diez W. 
Published: July 2007

AbstractIn a pure substance a temperature gradient gives rise to a current of atoms relative to the lattice planes. This current is compensated by the motion of lattice planes in the end face system. It is shown that markers or bubbles are not fixed to the lattice planes in the case of a free surface boundary condition. Thus such markers do not indicate the motion of lattice planes as was formerly supposed. Another mechanism for the motion of such markers is therefore proposed: the disturbance of the temperature gradient in the vicinity of the marker generates an uncompensated current of atoms, which causes the marker migration. The velocity of elliptical markers can be calculated analytically. The calculation is carried out for spherical bubbles in metals and ionic crystals. Spheres are found to be an equilibrium form of moving bubbles.
Field Effect on Photocarriers in Copper Phthalocyanine Single Crystals
Authors: Devaux P. , Schott M. 
Published: July 2007

AbstractThe photoconductivity of copper phthalocyanine single crystals changes when a high electric field is applied perpendicular to the illuminated surface. The ionization rate of excitons at the surface and the lifetime of the generated carriers change as a result of the variation of the surface charge; lifetime variation alone cannot explain the experimental results. In all the crystals studied the majority carriers for photoconduction are holes at 300°K. The densities of surface acceptors are higher than 1011 cm−2. A different photogeneration mechanism exists for the bulk throughout the investigated range from 3650 to 8150 Å. It dominates, at least under intense excitation, for light being absorbed only weakly.
Untersuchungen zur aktiven Kristallänge im Fließbereich neutronenbestrahlter Kupfereinkristalle. II. Die aktive Kristallänge
Authors: Neuhäuser H. 
Published: July 2007

AbstractKinematographische Messungen der aktiven Kristallänge la im Fließbereich neutronenbestrahlter Kupfereinkristalle in Abhängigkeit von Verformungsgeschwindigkeit ( = 2 × 10−6 bis 4 × 10−12mm/s), Temperatur (90 bis 360°K) und Bestrahlungsdosis (5 × 1017 bis 7 × 1018 n/cm2) ergeben Werte für la zwischen 20 und 2000 Å. Bei fester Temperatur und Dosis wächst die aktive Kristallänge mit der Abgleitgeschwindigkeit gemäß la = la 0–la 1/(1 + t0 ) [2]. Von den Parametern la 0, la 1 und t0 nimmt t0 mit zunehmender Temperatur und Dosis ab. Für ⪆ 10−4 mm/s zeigt sich eine deutliche Abweichung von der Proportionalität zwischen Abgleitgeschwindigkeit und Verformungsgeschwindigkeit . Bei fester Dehngeschwindigkeit variiert sowohl mit der Temperatur wie mit der Dosis: la nimmt mit zunehmender Temperatur und zunehmender Dosis ab. Die Abhängigkeiten werden qualitativ diskutiert.
Mössbauer Spectra in the Presence of Electron Spin Relaxation (II)
Authors: Gabriel H. , Bosse J. , Rander K. 
Published: July 2007

AbstractBasing on the simple model of spin‐lattice relaxation used by Afanasev and Kagan [3], we have investigated the modifications of the Mössbauer line shape due to relaxation effects. Utilizing Zwanzig's formalism as in I, we eliminate the bath (lattice) variables and retain only the Hamiltonian for the entire Mössbauer ion in the final formal expressions for the line shape. The essential difference compared to I is that in the present paper the electronic shell of the respective nucleus is included in the quantum mechanical subsystem. Therefore this theory is applicable to all relaxation rates. This has already been pointed out in [3] and is elucidated here by making evident that all results found by the solution of rate equations or by stochastic model treatments are special cases of the present theory.
Rare‐Gas Diffusion in Neutron‐Irradiated Rubidium Halides
Authors: Felix F. W. 
Published: July 2007

AbstractThe release of radioactive Kr from neutron‐irradiated single crystals of Rb halides is measured at temperatures ranging from 150°C up to the melting point. The release behaviour is similar to earlier results on the K halides [1]. The activation energies for RbCl, RbBr, and RbI at higher temperatures are 0.56, 0.30, and 0.31 eV, respectively. It is assumed that Kr diffuses by an interstitial mechanism. At lower temperatures a stronger dependence is found, which is attributed to the interaction of the gas atoms with defects. The activation energies in this region are 2.04, 1.68, and 1.41 eV, respectively. RbF shows only a single activation energy of 1.38 eV. In RbI the simultaneous diffusion of Kr and Xe is investigated.
Dislocations and Persistent Slip Bands in Copper Single Crystals Fatigued at Low Stress Amplitude
Authors: Lukáš P. , Klesnil M. , Krejčí J. 
Published: July 2007

AbstractPersistent slip bands in fatigued copper single crystals are studied by means of transmission electron microscopy of surface thin foils, both parallel and nonparallel to the surface. Comparing the observations from the different nonparallel sections a three‐dimensional model of the internal structure may be constructed. Dislocations with all six possible Burgers vectors of the type 1/2 〈0011〉 are found in the structure. This demonstrates the microscopic action of the secondary slip systems during the low stress fatigue. The macroscopic action of the secondary systems, which is connected with the cell structure formation, is typical for the high stress fatigue. Surface extrusions are found to be related to the dislocation structure below the surface.
Diffusion of Mn2+ in AgCl and AgBr Crystals
Authors: Süptitz P. , Weidmann R. 
Published: July 2007

AbstractThe diffusion of Mn2+ in undoped and Mn‐doped AgBr and AgCl crystals is measured in dependence on temperature with the aid of radioactive tracers (Mn54). For AgBr:Mn the concentration dependence of the diffusion coefficient D is determined, there is a qualitative correspondence to the assumption of Mnc □c associates and a migration of the foreign ions via cation vacancies. The enthalpies for association (Ha = 0.22 eV for AgBr and 0.28 eV for AgCl) and for migration (Hm = 0.74 eV for AgBr and 0.56 eV for AgCl) are approximatively determined from the temperature dependence of D.
Interstitial Solute Trapping in Irradiated and Quenched Iron
Authors: Wuttig M. , Stanley J. T. , Birnbaum H. K. 
Published: July 2007

AbstractThe interaction of interstitial carbon and nitrogen solutes with defects produced by low temperature neutron irradiation and by quenching was studied in high purity and Ferrovac E iron. Magnetic disaccommodation techniques were applied to determine the interstitial solute content after irradiation and upon annealing. Doses of about 1017 neutrons/cm2 caused the trapping of about 20 ppm (atomic) interstitial solutes at 65 (carbon) and 40°C (nitrogen). Trapping of carbon in a Ferrovac E iron alloy occurred during a fast quench from 880°C. After trapping, the interstitial solutes reappeared in solid solution at 300 (carbon, neutron irradiation), 200 (nitrogen, neutron irradiation), and 620°C (carbon, quenching). Various possibilities for the defect traps were considered and it was concluded that trapping of the interstitial solutes occurred at iron interstitial clusters after neutron irradiation and at vacancy type defects after quenching.
Pseudopotentials and the Knight Shift
Authors: Holland B. W. 
Published: July 2007

AbstractAn expression for the Knight shift, accurate to zero order in the pseudopotential, is derived and tested by calculations for Li, Na, Al, Ga, and Cs. The calculations take at most a few hours, and can be used to decide rapidly for any metal whether the pseudopotential method is likely to prove fruitful in general for that metal. In particular the results indicate whether in a more accurate calculation of the Knight shift or change in Knight shift with temperature, pressure or alloy composition, the pseudopotential approach would be appropriate, and whether relativistic, orbital or core polarisation effects might be significant.
Elastisches und thermoelastisches Verhalten von MgF2 und MnF2
Authors: Haussühl S. 
Published: July 2007

AbstractDie elastischen und thermoelastischen Konstanten von MgF2 und MnF2 wurden mit dem verbesserten Schaefer‐Bergmann‐Verfahren gemessen. Die beobachtete Anisotropie und auch der kleine Scherwiderstand (c11 ‐ c12)/2, der die geringe mechanische Festigkeit des Rutiltyps bewirkt, lassen sich qualitativ aus dem Verlauf der Hauptbindungsketten deuten. Die thermoelastischen Eigenschaften, die Abweichung von den Cauchy‐Relationen und auch die Kompressibilität entsprechen dem Verhalten anderer isotyper Kristalle. Aus dem Vergleich der Kompressibilität von Rutil und MgF2 ergibt sich ein Hinweis auf eine Schwächung der polaren Bindung im Rutil zugunsten eines kovalenten Anteils.
Paramagnetic Resonance Spectrum of Gadolinium in CdWO4 Single Crystals
Authors: Kratêna L. , Žďánský K. , Šik V. 
Published: July 2007

AbstractThe paramagnetic resonance spectrum of Gd3+ in CdWO4 is measured at 24 GHz at room temperature. The parameters of the spin Hamiltonian are determined by fitting of the angular dependence of the spectrum. The values of the zero‐field splitting of Gd3+ and Mn2+ in CdWO4 and CaWO4 are compared and an appropriate mechanism for explaining these values is discussed.
The Growth and Electrical Characteristics of Epitaxial Layers of Zinc Selenide on p‐Type Germanium
Authors: Calow J. T. , Owen S. J. T. , Webb P. W. 
Published: July 2007

AbstractThe experimental details are given of an evaporation technique for producing epitaxial layers of zinc selenide on 0.1 Ωcm p‐type germanium substrates. The degree of crystal order in the deposited layer is presented and the results show that, whilst the (100) orientation readily produces epitaxial layers of zinc selenide, the (110) and (111) orientations are more restricted. The preliminary electrical characteristics of the devices formed on the (100) substrate indicate that, at the higher growth temperatures, an interface layer is formed between the germanium and zinc selenide.
Specific Heat of Ice near the “Ferroelectric” Transition Temperature
Authors: van den Beukel A. 
Published: July 2007

AbstractAccording to Dengel et al. [1] a transition (believed to be ferroelectric) occurs in ice near 100 °K. Specific heat measurements in this temperature range show the existence of two peaks, at 104 and132 °K, respectively. The excess heat and the transition entropy corresponding to these peaks amount to (4.3 ± 0.8) cal/mol and to about 0.04 cal/mol °K, respectively.
A Curvature in the In D versus 1/T Plot for Self‐Diffusion in Nickel at Temperatures from 980 to 1400°C
Authors: Bakker H. 
Published: July 2007

AbstractA rather gradual curvature was found for the In D versus 1/T plot for tracer‐self‐diffusion in nickel single crystals at temperatures from 980 to 1400 °C. The activation energies and frequency factors at the highest and lowest temperatures were in agreement with values measured by other investigators in a similar temperature region. It proved to be possible to analyse the curve in terms of contributions of single and multiple vacancies. Especially accurate values of the characteristic quantities for the diffusion via single vacancies were obtained. Other possible explanations of the curvature were investigated, but rejected.
Polaronic Impurity Hopping Conduction
Authors: Schnakenberg J. 
Published: July 2007

AbstractImpurity hopping conduction in polar lattices and amorphous substances is investigated by application of the canonical transformation of the small polaron theory. In the case of acoustic coupling only, the results of Miller and Abrahams and Gosar for one‐phonon processes are recovered and compared with the contributions of multi‐phonon processes. In the polar case the assisting roles of acoustic and polar phonons are discussed seperately at temperatures T > θ/2 and T <θ/2 (θ being the Debye temperature). The type of the temperature dependence of the conductivity is determined.
On the Problem of Kinematic Interaction in the Quantum Theory of Magnetism
Authors: Lalović D. I. , Tošić B. S. , Žakula R. B. 
Published: July 2007

AbstractThe work considers the problem of the kinematic interaction of elementary excitations in the quantum theory of magnetism. In order to avoid the appearance of so‐called non‐physical states, a generalization of the Holstein‐Primakoff representation is suggested. It is shown that in calculating dynamic characteristics of magnon systems the Holstein‐Primakoff representation can be applied consistently only up to terms of the order 2 S, and not up to terms of the order 2 S +1, as it is tacitly assumed. In addition, a Pauli representation of spin operators for spins S = 1 and S = 3/2 is given.