bluuebunny/crossref_metadata_2025 huggingface dataset:
Zum Mechanismus der Versetzungsätzung. II. Entstehungsbedingungen für Ätzgruben
Authors: Schaarwächter W.
Published: July 2007

Die Bedingungen für die Entstehung sichtbarer Ätzgruben an den Enden verunreinigungsfreier Versetzungslinien werden theoretisch untersucht. Ausgegangen wird von den Voraussetzungen, daß 1. die Wandneigung der Gruben zur Beobachtung ausreichend steil sein und daß 2. die an den Versetzungen bevorzugt ablaufende Auflösung die Auflösungsgeschwindigkeit versetzungsfreier Oberflächen überwiegen muß. Vorwiegend wird der Fall behandelt, daß die Auflösung längs der Versetzungslinien durch bevorzugte Keimbildung and Grund der dabei freigesetzten Energie allein des Versetzungskerns hervorgerufen wird. Dieses Keimbildungsmodell war in dem ersten Teil dieser Arbeit entwickelt worden. Die Entstehung der Ätzgruben sowie die Auflösung der versetzungsfreien Oberfläche werden im Sinne von Keimbildung und Keimausbreitung behandelt. Die Ergebnisse werden mit der experimentellen Erfahrung verglichen. Es stellt sich heraus, daß zur Ätzgrubenentstehung auf Metallen wie Kupfer das Keimbildungsmodell mit freigesetzter Energie des Versetzungskerns zutreffen sollte, daß jedoch unter den zu Ätzgruben führenden Auflösungsbedingungen der Modus der Auflösung gegenüber dem bei freier Verdampfung herrschenden verändert sein muß. Insbesondere die Oberflächendiffusion als Transportweg für die Auflösung muß unterdrückt und die spezifische Energie des Keimrandes gegenüber den Vakuumwerten stark vermindert sein.
Der Einfluß einer Deformation auf die galvanomagnetischen und thermomagnetischen Effekte in Kristallen mit kubischer Symmetrie
Authors: Lvov V. S.
Published: July 2007

Auf Grund von Symmetrieüberlegungen wird in der Näherung schwacher Magnetfelder H (ω τ ≪ 1, ω Zyklotronenfrequenz, τ Relaxationszeit) eine Beziehung zwischen dem elektrischen Feld und der Stromdichte I (oder ∇ T) in einem beliebig deformierten kubischen Kristall bei beliebigen Orientierungen von H und I (bzw. ∇ T) erhalten. Für einige Richtungen von I (oder ∇ T) werden die Winkelabhängigkeiten berechnet (H liegt dabei in einer Ebene senkrecht zu I (bzw. ∇ T), und der Kristall wird einer einachsigen Deformation längs I oder ∇ T unterworfen. Dadurch wird es möglich, die Vielfalt der in deformierten kubischen Kristallen ablaufenden galvanomagnetischen und thermomagnetischen Effekte zu analysieren. Die in die phänomenologische Theorie der Tensoreffekte eingehenden Koeffizienten werden für n‐leitendes Ge berechnet.
Modification of the Optical Properties of CaF2TR3+ Crystals by Yttrium Impurities
Authors: Bagdasarov Kh. S. , Voronko Yu. K. , Kaminskii A. A. , Krotova L. V. , Osiko V. V.
Published: July 2007

Absorption and luminescence spectra of CaF2Nd3+ (type 1) [1] crystals are investigated as a function of the concentration of added yttrium fluoride. The appearance of new lines, and a decrease in the line intensities, due to yttrium content is attributed to a shift in the equilibrium of Nd centres. Some possible models are discussed. The equilibrium of centres of rareearth ions (TR3+) in the presence of yttrium fluoride in CaF2Nd3+ crystals is calculated approximately.
Die Methode der Greenschen Funktionen in der Gitterdynamik eines Kristalls mit Defekten
Authors: Litzman O.
Published: July 2007

Es wird gezeigt, daß sich Frequenzspektrum und Debye‐Waller‐Faktor eines gestörten Gitters einfach durch die inverse Greensche Funktion [D ‐ z I]−1 ausdrücken lassen, wobei z eine komplexe Variable ist. Es werden einfache Formeln für die Gewinnung dieser Funktion gegeben. Besonders berücksichtigt wird die Bestimmung des durch einen Defekt hervorgerufenen elektrischen Dipolmoments des Gitters. Die hier vorgeschlagene Methode ist den Methoden der quantenmechanischen Greenschen Funktionen ähnlich.
Mössbauer Effect in α‐FeOOH
Authors: van Der Woude F. , Dekker A. J.
Published: July 2007

The antiferromagnetic compound α‐FeOOH is studied between 90 and 440°K by the Mössbauer technique. Analysis of the data gives a Néel temperature TN of 393.3°K and an effective magnetic field, extrapolated to 0°K, of 510 kOe. From the quadrupole splitting above and below TN and from the field gradient, calculated from the lattice positions, it is concluded that the direction of the spins of the iron ions lies along the crystallographic z‐axis. This is in agreement with susceptibility measurements. The shape of the peaks in the Mössbauer spectra is discussed and possible explanations of the shapes in the vicinity of TN are given. The temperature dependence of the sublattice magnetization is compared with the predictions of the two‐particle cluster theory for a Heisenberg magnet. If the reduced sublattice magnetization is represented as m(T) = D(1 − T/TN)f it is found that f = 0.32. Finally, a comparison is made with other experimental Mössbauer data on goethite and the discrepancies are explained.
Streuung der Leitungselektronen durch Punktfehler in Metallen
Authors: Mann E.
Published: July 2007

Die Differenzengleichung für die Koeffizienten in der Entwicklung der gestörten Wellenfunktion nach Wannierfunktionen wird als Streugleichung formuliert. Daraus wird für die Änderung σ(E) der Zustandsdichte im gestörten Kristall die allgemeine Beziehung σ(E) = − dα(E)/dE hergeleitet. α(E) ist dabei die in einer vorhergehenden Arbeit in der Konzeption diskreter Eigenwerte definierte Funktion für die Verschiebung der Energieeigenwerte. An einigen Beispielen wird die Zustandsdichteänderung diskutiert. Für die Änderung der Ladungsdichte in großem Abstand r vom Störzentrum wird die Verallgemeinerung des für freie Elektronen gültigen Oszillationsgesetzes cos (2 kFr + φ)/r3 abgeleitet.
Electron Microscope Study of Brazil Twin Boundaries in Amethyst Quartz
Authors: McLaren A. C. , Phakey P. P.
Published: July 2007

A study has been made of the diffraction contrast fringe patterns observed by transmission electron microscopy in amethyst quartz. Evidence is presented that the fringe patterns are due to Brazil twin boundaries on {1011} planes. A model for the Brazil twin boundary which does not involve the breaking of SiO bonds is proposed and shown to be consistent with the fringe patterns observed with different operating reflections.
Photoelektrische Eigenschaften von Lithiumantimonid
Authors: Gobrecht R.
Published: July 2007

Es wird über ein Verfahren zur Herstellung dünner Lithiumantimonidschichten berichtet, das die Eigenschaft des Lithiums, in heißem Zustand mit Quarz oder Glas zu reagieren, berücksichtigt. Die während der Formierung einer Schicht aufgenommene Leitfähigkeitskurve zeigt zwei Minima. Das erste Minimum läßt auf eine Verbindung noch unbekannter Zusammensetzung schließen, das zweite ist der intermetallischen Verbindung Li3Sb zuzuordnen. Auf Grund der aus der spektralen Verteilung des äußeren Photoeffekts sowie der Temperaturabhängigkeit der Leitfähigkeit von Li3Sb gewonnenen energetischen Daten ergibt sich, daß Elektronenaffinität und Grenzenergie von Lithiumantimonid größte Werte unter den Alkaliantimoniden annehmen.
Lattice Dynamics of Zinc
Authors: Gupta R. P. , Dayal B.
Published: July 2007

A tensor force model including up to sixth‐neighbour interactions is developed for zinc. The model involves a total of twenty‐three force constants of which eighteen are determined from certain room temperature experimental elastic constants. The condition for crystal equilibrium which interrelates the force constants is also satisfied, so that the model is elastically consistent. The other five constants are not determined. The theoretical dispersion curves involving only the eighteen force constants determined are computed and compared with the experimental neutron scattering results of Borgonovi et al. Good agreement is found. The theoretical results of De Wames et al. are also discussed.
Configuration of Antiphase Boundaries in Ordered AuCu3‐Type Solid Solutions
Authors: Popov L. E. , Kozlov E. V. , Golosov N. S.
Published: July 2007

The degree of order and concentrations of the components in the vicinity of the 1/2 〈110〉 {111} antiphase boundary of the L12 superstructure are calculated using a nearest neighbours approximation. Relaxation of atomic order, and component concentrations differing significantly from the stoichiometric compounds, are found near the antiphase boundary. The superdislocations under thermodynamic equilibrium are found to be rather strongly pinned. The temperature dependence of the “start” stress of the superdislocations shows a maximum at ≈ 0.8 Tk.
Ein Medium im elektromagnetischen Feld einer Laserwelle als optisches Gitter
Authors: Enderlein R.
Published: July 2007

Infolge der magneto‐ und elektrooptischen Effekte stellt ein Medium, das sich im elektromagnetischen Feld einer Laserwelle befindet, ein optisches Beugungsgitter dar. Der Durchgang von Licht durch ein solches Gitter wird mit Hilfe eines geeigneten Näherungsverfahrens zur Lösung der Maxwellschen Gleichungen untersucht. Es werden u. a. Ausdrücke für die Intensitäten der ersten Beugungsordnung erhalten.
Magnetic Susceptibilities of Gadolinium Orthophosphate (GdPO4)
Authors: Wang F. F. Y.
Published: July 2007

Gadolinium orthophosphate (GdPO4) follows the Curie‐Weiss law in the paramagnetic region. It becomes antiferromagnetic at 225°K, and exhibits weak ferromagnetism at lower temperatures. The origin of weak ferromagnetism is attributed to anisotropic exchange. A model of ferromagnetic and antiferromagnetic linkages of varied strengths fits qualitatively the magnetic properties of GdPO4.
Untersuchungen von Gittereigenschaften im System LiH–LiD
Authors: Brückner W. , Kleinstück K. , Schulze G. E. R.
Published: July 2007

Von vier Verbindungen der Mischkristallreihe LiH–LiD mit 0,50, 75 und 100 At‐% Deuterium wurden neutronographisch die Gitterkonstanten und dilatometrisch die Ausdehnungskoeffizienten gemessen. Für die Gitterkonstanten ergaben sich bei den Mischkristallen etwas größere Werte, als sie sich nach der Vegardschen Regel berechnen. Das deutet auf Korrelationen zwischen gleichen Atomen im H–D‐Teilgitter hin. Die gemessenen Unterschiede in den untersuchten Gittereigenschaften von LiH und LiD werden mit den Ergebnissen der theoretischen Betrachtungen von Ubbelohde und London verglichen und die Abweichungen kurz diskutiert.
Optical Absorption of LiF Crystals Irradiated with Neutrons at Liquid Nitrogen Temperature
Authors: Kamikawa T. , Kazumata Y. , Ozawa K.
Published: July 2007

The effects of low temperature neutron irradiation on LiF single crystals are investigated by optical absorption measurements. The crystals are irradiated and measurements made at 80°K. In the spectra obtained at 77°K, the Vk‐ and M‐bands appear prominently but the F‐band is hidden under other overlapping bands. A noticeable band found at 578 nm is suggested to be associated with the Li interstitials. During thermal annealing, three absorption peaks are observed at 415, 430, and 443 nm in the M‐band region. The new band at 415 nm shows a fine structure at 77°K. A new absorption band at 545 nm, called the S‐band, is observed to increase in thermally bleached crystals after ageing at room temperature. The experiments on doped crystals show that the divalent cation modify the characteristics of low temperature neutron irradiation. In the doped crystals, the 578 nm band due to the Li interstitials is not observed. When a very large band at about 400 nm is partially bleached, many sharp lines are observed. Their origin is discussed briefly.
Extended Dislocation Barriers on {112} Planes in Anisotropic Body‐Centered Cubic Crystals
Authors: Teutonico L. J.
Published: July 2007

Two glissile extended dislocations on intersecting {112} planes in a body‐centered cubic crystal can interact to form various stair‐rod configurations. The stability of these configurations has been determined on the basis of anisotropic elasticity theory for each of ten b.c.c. elements. The widths of the possible extended barriers in each element have been computed in terms of the stacking fault energy.
Abhängigkeit der Bereichsstruktur in Mn5Ge3 von der Kristalldicke
Authors: Wrzeciono A. , Gemperle R.
Published: July 2007

Die Abhängigkeit der Mäander‐, Wurm‐ und Wabenstruktur von der Kristalldicke T (parallel zur magnetischen Vorzugsachse), bei der eine Oberflächenstruktur auftritt, wurde für die intermetallische Verbindung Mn5Ge3 untersucht. Es wurde gefunden, daß innerhalb der gemessenen Kristalldicken (40 bis 900 μm) die Bereichsbreite und die Entfernung zwischen den Mittelpunkten zweier benachbarter Wabenzellen proportional zu T2/3 ist. Diese Beziehung stimmt mit der Theorie von Kaczér und früheren Messungen an Magnetoplumbit und Kobalt überein.
On the Electron Gas Energy Relaxation Mechanisms in n‐Type InSb at Helium Temperatures
Authors: Lifshits T. M. , Oleinikov A. Ya. , Shulman A. Ya.
Published: July 2007

The relaxation time of the electrical conductivity and the non‐linearity coefficient β in n‐type InSb in the temperature range from 1.8 to 4.1°K are studied as a function of power supplied to the sample from a d.c. source. The results are interpreted by considering energy losses by acoustic piezoelectric and deformation‐potential scattering and by optical polar scattering. The constants of piezoelectric and deformation potentials are estimated.
Longitudinal Hall‐Effect in n‐Type Germanium
Authors: Baranskii P. I. , Dakhovskii I. V.
Published: July 2007

On the basis of the anisotropic scattering theory developed by Samoilovitch et al. [1] a general expression is derived for the longitudinal Hall effect in which the carrier relaxation time is represented by a tensor. A possible method of measuring the longitudinal Hall effect in absolute (rather than relative) units is proposed. This allows experimental investigation (at room temperature) of the effect for n‐type Ge with ρ ∼ 10.5 Ωcm. A special case is considered in which the current in the sample is in the [100] direction and the magnetic field vector H is arbitrarily oriented in the plane perpendicular to the current flow. Good agreement is obtained between theory and experiment. Some suggestions are made as to possible applications of this effect.
The Effect of Phase Change on the Mechanical Properties of Cobalt Near Its Transformation Temperature
Authors: Kamel B. , Halim K.
Published: July 2007

The phase transformation of cobalt is studied from observations of the changes in the work‐hardening, creep and fracture characteristics of cobalt near its critical temperature. The parabolic work‐hardening coefficient, Xp, is found to be about four times greater for the h.c.p. than for the f.c.c. phase at the same temperature. However, the temperature coefficient of Xp remains fairly constant over the phase change and has an average value of about −0.0027 deg−1. In the presence of the two phases simultaneously during the transition stage, this thermal coefficient is increased by an order of magnitude. The phase transition is exhibited as a change in slope of the curve of the logarithm of steady state creep versus the reciprocal of the absolute temperature. Dislocation climb controlling of the steady state creep is activated by 5.6 eV in the h.c.p. phase, which is comparable with double the activation energy for self diffusion. This is attributed to the fact the height of an elementary jog in the hexagonal structure is twice an interatomic spacing. In the cubic phase, the climb process requires only 2.0 eV which is smaller than that for self diffusion by nearly double the vacancy‐dislocation binding energy.
Light‐Induced Dispersal of Cu2+ Precipitates in AgCl Crystals
Authors: Burnham D. C. , Moser F.
Published: July 2007

In order to investigate changes in the Cu2+ center in AgCl due to dark storage and subsequent exposure or thermal treatment, exposed samples and halogen‐treated samples of copper‐doped AgCl were studied by electron spin resonance (ESR) and optical techniques. The results show that the precipitation of Cu2+ ions during dark storage can be reversed by exposure to light. Evidence is presented to support the hypothesis that both electronic and ionic steps are involved. The effect of the thermal treatment of exposed samples is also discussed.
Die Plastizität von Aluminium—Zink‐Legierungen II. Zur Strukturabhängigkeit einiger Verfestigungsparameter
Authors: Haberkorn H. , Gerold V.
Published: July 2007

Für die kritische Schubspannung τ0 von Aluminium—Zink‐Legierungen mit kohärenten Ausscheidungen und im rückgebildeten Zustand werden quantitative Abschätzungen gegeben, die mit dem Experiment gut übereinstimmen. Während im übersättigten Mischkristall τ0 von der Cluster‐Bildung der Zinkatome bestimmt wird, sind im ausgehärteten Zustand die Kohärenzspannungen der Ausscheidung (Guinier‐Preston‐Zonen) maßgebend. Die bei höheren Abschrecktemperaturen beobachteten größeren τ0‐Werte sind vermutlich auf Abschreckdefekte (Versetzungsringe) zurückzuführen.
ESR‐Untersuchungen zur Aggregation von F‐Zentren in RbCl
Authors: Ehret P. , Wolf H. C.
Published: July 2007

Optisches Bleichen vermindert die Auflösung der teilweise aufgelösten Hyperfeinstruktur im ESR‐Spektrum der (restlichen) F‐Zentren in RbCl. Messungen von T1 T2 und T1 bei Sättigung ergeben für T2 näherungsweise T2 = 2 × 10−8s (ungebleichte F‐Zentren) und T2 = 2,5 × 10−9 s (F‐Zentren nach optischem Bleichen bei Zimmertemperatur). Rechnungen zeigen, daß T2 einen Wert von 3 × 10−9s haben muß, um die Verminderung der Auflösung des Hyperfeinspektrums zu erklären. Es wird angenommen, daß der Abfall von T2 durch eine optisch‐induzierte, lockere Ansammlung von F‐Zentren herrührt. Der gemessene Wert von T2 entspricht dem Mittel von fünf Abständen zwischen den Ionen der F‐Zentren in den Agglomeraten, wenn nur Dipol‐Dipol‐Wechselwirkung berücksichtigt wird.
Thermoluminescence and Thermoluminescence Spectra of Calcium Fluoride Crystals Irradiated by X‐Rays
Authors: Ratnam V. V. , Bose H. N.
Published: July 2007

The glow curve pattern obtained for CaF2 crystals irradiated by X‐rays at room temperature is markedly affected by even a small rise (say 30 °C) in the temperature of irradiation. This is presumably due to the neutral fluorine atoms which are produced by the holes trapped by the fluorine ions during X‐ray irradiation and which, at elevated temperatures of irradiation, form molecular complexes or diffuse out of the crystal. The spectral composition of the thermoluminescence obtained with samples irradiated at room temperature is similar for the first three glow peaks, except for minor changes in the relative intensities of the emission peaks; for the fourth glow peak however it is markedly different. Further, the first three glow peaks attain saturation with X‐ray dose similar to the colour bands, but no such tendency is observed for the fourth glow peak. These results indicate that the traps and emitting centres responsible for the first three glow peaks are different from those of the fourth glow peak.
Untersuchungen über die energetische Verteilung der Haftsteller für Defektelektronen in Anthracenkristallen
Authors: Bässler H. , Becker G. , Riehl N.
Published: July 2007

Beim Anlegen einer Spannung stellt sich in einem Anthracenkristall eine räumlich unsymmetrische Besetzung der Haftstellen mit Defektelektronen ein. Beim Abschalten des Feldes entsteht deshalb ein Rückstrom. Seine Zeitabhängigkeit liefert Informationen über die beteiligten Haftstellen. Es wird gezeigt, daß energetisch benachbarte Haftstellen für Defektelektronen existieren müssen (Energieabstand ca. 0,01 eV), deren Dichte exponentiell mit der Energie abnimmt. Numerische Abschätzungen führen zu dem Schluß, daß diese Haftstellenverteilung mit der früher als kontinuierlich postulierten exponentiellen Verteilung identisch ist.
Determination of Activation Energy from Step Annealing
Authors: Bell F. , Sizmann R.
Published: July 2007

The activation energy Q can be determined for processes of type dx/dt = F(x) exp (–Q/RT) from linear heating data or from the point sequence of step annealing (time and temperature intervals are constant). Q may be evaluated at each point x if two samples are available. With only one sample Q can be found at some isolated points by applying cycling temperature procedures.
Über die Anregung von Rumpfelektronen durch Stoß mit schnellen Primärelektronen in Metallen
Authors: Fischbeck H. J.
Published: July 2007

Die Energieverteilung der Anregung von fest gebundenen Metallelektronen durch Stoß mit schnellen Primärelektronen wird in Bornscher Näherung berechnet. Die Anfangszustände der Rumpfbänder des Metalls werden durch Blochsummen und die Endzustände der angeregten Elektronen durch orthogonalisierte ebene Wellen approximiert. Als Anwendungsbeispiel wird die Energieverteilung der Anregung aus den Rumpfbändern des Natriums numerisch berechnet und im Hinblick auf die Sekundärelektronenemission diskutiert. Es ergibt sich, daß die Anregung aus dem Rumpf für die Sekundäremission des Natriums von weit größerer Bedeutung als die Anregung aus dem Leitungsband ist.
Transporteigenschaften von HgTe
Authors: Wagini H. , Reiss B.
Published: July 2007

An zwei HgTe‐Proben wurden zwischen 100 und 300 °K die Transportkoeffizienten im schwachen transversalen Magnetfeld gemessen und vergleichshalber in der Nähe der Eigenleitung Rechnungen für Streuung an akustischen und optischen Phononen sowie an Ionen durchgeführt. Legt man der Theorie eine Abart des von Groves und Paul [1] für graues Zinn entwickelten Bändermodells (ΔE = 0, nichtparabolisches Leitungsband Kanescher Form) zugrunde und berücksichtigt die aus optischen Untersuchungen gewonnenen Daten, (mn = 0,017 mo sowie |ε| = 0,15 eV) von Verié und Decamps [2], so ergibt sich nahe der Eigenleitung im Bereich der Zimmertemperatur für vorwiegend optische Streuung der Elektronen gute Übereinstimmung mit dem Experiment.
Nachweis von Frenkeldefekten in röntgenbestrahltem LiF
Authors: Balzer R. , Peisl H. , Waidelich W.
Published: July 2007

LiF‐Kristalle wurden bei Zimmertemperatur röntgenbestrahlt. Die dabei erzeugten Farbzentren wurden durch Messung der optischen Absorption nachgewiesen. Zur Untersuchung der Störung des Kristallgitters durch die erzeugten Punktdefekte wurden die relative Gitterkonstantenänderung und die relative Änderung der makroskopischen Dichte der Kristalle nach der Bestrahlung bestimmt. Durch Vergleich dieser beiden Änderungen wird gezeigt, daß bei der Bestrahlung Frenkeldefekte gebildet wurden.
Contribution à la théorie statistique de la ferroélectricité
Authors: Godefroy L.
Published: July 2007

L'étude statistique du modèle ferroélectrique basée sur l'existence de puits de potentiel rigide à deux minimums est étendue à la dynamique du switching. On montre que si les résultats obtenus avec un tel modèle étaient valables en statique, ils ne le sont plus du tout en dynamique. Il semble que I'hypothèse de la rigidité du puits de potentiel soit à incriminer.
Electron Interaction Effects on Recombination Spectra
Authors: Landsberg P. T.
Published: July 2007

This note suggests a possible origin of low energy tails observed in radiative recombination when at least one of the participating bands is degenerate. An order‐of‐magnitude calculation is made which shows that the effect can have the same origin as similar effects in the soft X‐ray emission spectra of metals. Furthermore, it is suggested that the analysis of experimental tails can lead to information about the screening lengths in the Coulomb interaction between electrons in bands.
Optical Properties and Electronic Structure of Amorphous Germanium
Authors: Tauc J. , Grigorovici R. , Vancu A.
Published: July 2007

The optical constants of amorphous Ge are determined for the photon energies from 0.08 to 1.6 eV. From 0.08 to 0.5 eV, the absorption is due to k‐conserving transitions of holes between the valence bands as in p‐type crystals; the spin‐orbit splitting is found to be 0.20 and 0.21 eV in non‐annealed, and annealed samples respectively. The effective masses of the holes in the three bands are 0.49 m (respectively 0.43 m); 0.04 m, and 0.08 m. An absorption band is observed below the main absorption edge (at 300 °K the maximum of this band is at 0.86 eV); the absorption in this band increases with increasing temperature. This band is considered to be due to excitons bound to neutral acceptors, and these are presumably the same ones that play a decisive role in the transport properties and which are considered to be associated with vacancies. The absorption edge has the form: ω2ϵ2∼(hω−Eg)2 (Eg = 0.88 eV at 300 °K). This suggests that the optical transitions conserve energy but not k vector, and that the densities of states near the band extrema have the same energy‐dependence as in crystalline Ge. A simple theory describing this situation is proposed, and comparison of it with the experimental results leads to an estimate of the localization of the conduction‐band wavefunctions.
Fine Structure of Emission Spectra of the Red AIN:Mn Luminescence
Authors: Karel Fr. , Pastrňák J. , Hejduk J. , Losík V.
Published: July 2007

The luminescence of aluminium nitride, activated by manganese, is described. A structure with equidistant peaks, clearly resolved at low temperatures, is found in the emission band 580 to 620 nm. This structure is interpreted in terms of phonons using the Pekar theory. The energy of the phonon involved is 0.023 eV. The luminescence decay is exponential with a time constant τ = 1.0 × 10−3 s over a wide temperature range. It is suggested that the luminescence is due to transitions between metastable and basic levels of the tetravalent manganese ion.
Theory of the Δε‐Effect in Ferromagnetic Metals
Authors: Ky Vu Dinh
Published: July 2007

The Δε‐effect in ferromagnetic metals is explained, as for the Hall effect, in terms of the spin‐orbit interaction. A theoretical expression for this effect is obtained by using density matrices and the effective mass approximation.
Growth of Hexagonal Crystallites in CdTe Thin Films
Authors: Spînulescu‐Carnaru I.
Published: July 2007

It is shown that the crystal structure of CdTe thin films is strongly affected by a variation in the relative concentration of the metallic and non‐metallic constituents. Optimum conditions are found which lead to CdTe thin films with a pure hexagonal structure. The constants of the CdTe cubic and hexagonal cells are computed.
Electrical Pinch in Elastically Deformed Germanium
Authors: Rashba E. I. , Romanov V. A. , Boiko I. I. , Zhadko I. P.
Published: July 2007

The phenomena accompanying the flow of an electric current through uniaxially compressed plates of intrinsic Ge are investigated. The plates are cut with definite orientations relative to the main crystallographic axes so that the directions of the current and field do not coincide. Under these conditions transverse gradients of the nonequilibrium carrier concentration arise in specimens long carrier lifetimes, this results in a modulation of the conductivity, emergence of rectifying characteristics, etc. In strong field the carriers and current are concentrated in a narrow layer close to one of surfaces, the carriers being almost completely removed from the rest of the specimen (the electrical pinch in an electron‐hole plasma). The redistribution of carriers across the sample and the current‐voltage characteristics are investigated experimentally for these pinch conditions. For fields of about 100 V/cm an increase and decrease of concentration is observed, giving an extremely nonlinear current‐voltage characteristic if opposite plate surfaces have different surface recombination velocities. A rectification ratio of about 50 may be obtained in this way. Under electrical pinch conditions the dependence of the resistance of the specimen on compression exceeds the ordinary piezoresistance by an order of magnitude.
The Migration of Double Positioning Boundaries During the Growth of Epitaxial (111) Gold Films
Authors: Stowell M. J. , Law T. J.
Published: July 2007

A study has been made of the migration of double positioning boundaries during continuous growth of (111) gold films inside an electron microscope. The boundary mobility is shown to be temperature dependent and the results indicate that double positioning boundary migration is a thermally activated process. The influence of rate of coalescence of deposit islands and of deposition rate on the size of double positioning domain structures in (111) gold films is discussed and the conclusions are extended to other multiply positioned and polycrystalline structures formed by vacuum evaporation.
Excitonic Effects in the Interband Absorption of Semiconductors
Authors: Velický B. , Sak J.
Published: July 2007

Elliott's work on exciton effects at the direct absorption edge is extended to include other van Hove singularities and deviations from the effective mass approximation. The sum rule which replaces the f‐sum rule in this case is derived. The Koster‐Slater and Coulomb interactions are treated as limiting cases. Due to the electron‐hole interaction, the M0 and M1 branch‐points of ϵ2 are enhanced and sharpened, whilst the M2 and M3 branch‐points are weakened and smoothed out. Only the M0 points generate (quasi) discrete levels; no evidence for these is found near the M1 points. For a very prolate M1 singularity, certain branch‐points appear asymptotically below the critical energy.
EPR Measurements on Diatomic Halogen Centers in Alkali Halides
Authors: Dreybrodt W. , Silber D.
Published: July 2007

EPR spectra of diatomic halogen centers in alkali halides are investigated. Centers of the type FBr−, FJ−, and CIJ− are identified. The constants of the spin Hamiltonian are derived from the FBr‐ spectra by a perturbation calculation up to fourth order. By studying the photochemical properties of centers of the type X and XY− information regarding the formation mechanismus of the FCl− and FBr− centers are obtained.
A Model for the Change in Elastic Modulus of a Solid Caused by Point Defects
Authors: Melngailis J.
Published: July 2007

Point defects introduced into copper at low temperatures by irradiation are known to produce bulk expansion. We suggest here that an external stress might cause the defect (represented as oversized spherical inclusions) to relax. This would change the expansion produced by the defects so that the deformation due to the stress would be greater and the elastic modulus would thus appear smaller. This relaxation is represented by a small deformation of the spherical inclusions, and elastic energy considerations are used to calculate the change in the elastic modulus of Cu due to such defects. If the radius of the inclusions is chosen to be two lattice constants, the experimentally observed value of 18% for the decrease in the elastic modulus at saturation density of defects is obtained.
The Interaction of Two Excitons in a Crystal
Authors: Bobrysheva A. I.
Published: July 2007

The energy of the exciton—exciton interaction is calculated as a function of the distance between their centres of mass for the atomic model of a semiconductor. Computed numerical results are presented for various values of the parameters of the atomic functions, relative‐motion functions, and the electron‐hole‐effective mass ratio. The binding energy of two excitions is obtained by the Green's function method assuming that the exciton‐exciton interaction is less than the interaction of the excitons with optical and acoustic phonons. The role of the direct exciton‐exciton interaction and the indirect interaction, via optical or acoustic phonons, in the formation of a biexciton is studied. The results are given of calculations of the cross‐section for elastic scattering between two excitons using the Born approximation.
On the Theory of Anisotropic Thermoelectric power in Semiconductros
Authors: Samoilovich A. G. , Nitsovich M. V. , Nitsovich V. M.
Published: July 2007

Possible mechanisms for the appearance of an anisotropic thermoelectric power in semi conductors are examined using simple models. It is shown that an anisotropic thermoelectric power may arise both as a result of combined phonon and impurity scattering, and in the presence of two types of carriers if at least one type of carrier has an anisotropic effective mass. The effect of different parameters on the magnitude of the anisotropy in the thermoelectric power is examined and it is shown that for reasonable values of these parameters the anisotropy may be significant.
On the Colour Centres and X‐Ray Luminescence of Calcium Fluoride Crystals
Authors: Ratnam V. V.
Published: July 2007

A study is made of differences in the colouration spectrum of calcium fluoride cyrstals obtained by X‐ray irradiation at different temperatures and by electrolysis. The changes occuring in the X‐ray luminescence spectrum due to the use of different irradiation temperatures are also considered. It is shown that the α‐ and β‐bands, usually only observed in additive and electrolytic colouration, can also be produced by X‐ray irradiation if the irradiation temperature is between 180 and 250°C. The formation of the α‐ band (the F‐band of this system) is difficult to detect at lower irradiation temperatures because of 1. the small number of free negative ion vacancies at these temperatures and 2. the low oscillator strength associated with this band. The changes observed in the X‐ray luminescence spectrum for different irradiation temperatures are explained and the associated electronic processes are discussed briefly.
Mössbauer Effect in Some Polyatomic Crystals
Authors: Iosilevskii Ya. A.
Published: July 2007

Expressions are obtained for the probability of the Mössbauer effect and the thermal shift in the energy of a γ‐photon for binary crystalline compounds ABr−1. These compounds include crystals of the type NaCl or CsCl, crystals of completely ordered alloys (AuCu3, AlFe3 etc.), and monatomic crystals with isolated impurity atoms. It is assumed that the force constants depend only on the differences of the position vectors of the atoms. The treatment includes the two cases in which nucleus A or nucleus B is resonant. The case in which atom A (mass M0) and atom B (mass M) differ considerably in mass is analysed in greater detail. For M0/M ≪ 1 or M0/M ≫ 1 the fraction e of recoilless emissions (or absorptions) of γ‐rays by atom A and the thermal shift δE0 are independent of M0/M for given interatomic forces. Values of these quantities are hence determined by the appropriate limiting expressions (M0 = const, M → ∞ or M → 0). Thus the finite Mössbauer effect for an atoms surrounded by light atoms is independent of the mass of the latter. In addition there exists a limit to the gain in the probability of the Mössbauer effect and in the thermal shift for an atom which can be obtained by surrounding it with increasingly heavier atoms. It is also shown that the probability of the effect and the thermal shift for the atoms A, for the given interactions, are essentially independent of r. The quasiclassical expansions of Zj and δEj, for the j‐th atom in a unit cell, are obtained for more complicated compounds of the type A A … A (r1 + r2 + … rn = r) by the method of moments.
On the Critical Resolved Shear Stress of Solid Solutions Containing Coherent Precipitates
Authors: Gerold V. , Haberkorn H.
Published: July 2007

A quantitative estimate is made of the increase Δτ0 of the critical resolved shear stress for the case of solid solutions containing spherical and coherent precipitates. The interaction between edge dislocations and the coherency strain fields is believed to be the strengthening mechanism. The calculation is applied to experimental measurements on Al‐Zn and CuCo alloys. For small particles (R/b < 20) the dislocations tend to cut through the precipitates, whereas for larger particles the Orowan mechanism becomes predominant.
General Theory of Electron Emission from Metals
Authors: Christov S. G.
Published: July 2007

A theory of the emission of electrons from metals is developed on the basis of a general integral expression for the total transmission probability of an incident electron on the potential barrier at the metal surface. This integral is expressed as a sum of three conveniently defined integrals. In this way formulas are obtained for the current density for all temperature and field conditions of practical interest. The maximum error in the calculation of the total current by this method is about 10%. This theory includes as limiting cases thermionic and field emission as well as some earlier results for the emission over a narrow intermediate range of conditions. The limits of applicability of the theory in its general form are outside those of practical importance and include temperatures from 0 to 3500 °K and fields from 0 to 108 V/cm.
Electrisation du polyéthylène et du polystyrène après irradiation γ
Authors: Asch M. G. , Félix M. C. , Ongaro M. R.
Published: July 2007

On montre qu'après avoir été exposés au rayonnement γ, le polyéthylène et le polystyrène peuvent acquérir une électrisation superficielle stable sous l'influence d'un champ électrique. La densité superficielle de charge est calculée en admettant que l'électrisation est due au déplacement d'électrons qui, initialement piégés, sont progressivement libérés par excitation thermique. L'expression de la densité de charge ainsi obtenue est conforme aux résultats expérimentaux.
Electrical Properties of n‐Type Epitaxial Gallium Arsenide
Authors: Eddolls D. V.
Published: July 2007

Measurements have been carried out to determine the temperature dependence of the Hall coefficient and resistivity of n‐type epitaxial gallium arsenide in the range 4.2 to 300 °K. Such materials has in general a lower impurity concentration and a higher mobility than melt grown material. The temperature dependence of the carrier concentration is described by the expression

where gr is the degeneracy factor and Er the excitation energy of the rth excited state of the donor atom, the number of excited states depends upon the donor concentration. The ionization energy varies from 1.6 × 10−3 to 4.7 × 10−3 eV when the donor concentration changes from 5 × 1015 to 3 × 1014 cm−3. Qualitative comparison between the measured temperature variation of the Hall mobility and published theory shows reasonable agreement. The highest mobility measured was 103000 cm2 (Vs)−1 at 52 °K.
Magnetische Eigenschaften von Einkristallschichten aus Eisen, Nickel, Kobalt und deren Legierungen
Authors: Kirenskii L. V. , Pynko V. G. , Pynko G. P. , Sukhanova R. V. , Sivkov N. I. , Rusov G. I. , Edelman I. S.
Published: July 2007

In dieser Arbeit wird gezeigt, daß die Energie der Anisotropie der einzelnen Kristallite in Epitaxieschichten (z. B. Co‐Schichten) additiv ist. Das Feld, das während der Aufdampfung anliegt, beeinflußt die Anisotropie von einkristallinen Fe‐Schichten nicht merklich, während bei Ni‐ und β‐Co‐Schichten das Feld eine starke einachsige Komponente hervorrufen kann. Die Feinstruktur in den Domänen von einkristallinen FeNi‐ und CoNi‐Schichten mit schwacher kristallographischer Anisotropie wird beobachtet. Die Breite der Wände zwischen den Domänen in einkristallinen Schichten aus Fe, Ni und β‐Co wird elektronenmikroskopisch gemessen. Es wird gezeigt, daß in Schichten mit starker biaxialer Anisotropie die Änderung der Koerzitivkraft in Abhängigkeit von der Änderung der Richtung des magnetisierenden Feldes befriedigend durch den Ausdruck

beschrieben wird, wobei p den Druck, der durch das Feld auf die Wände ausgeübt wird, Θ1 und Θ2 die Winkel zwischen dem Feld und den Magnetisierungsvektoren auf beiden Seiten der Wand und IS die Sättigungsmagnetisierung bedeuten.
On the Reaction Order of Bimolecular Recovery Processes in Solids
Authors: Nihoul J. , Stals L.
Published: July 2007

A general expression is derived for calculating the reaction order of recovery processes when rate equation is known. This expression is independent of the rate constant but is completely determined by the relative concentration of the defects. On the basis of this expression the reaction orders of some bimolecular recovery processes are discussed as a function of defect concentrations, the ratio of the initial concentrations and the capture radius. It is shown that, unless rather severe conditions are fulfilled, the reaction order may vary over a wide range of values, even in cases where the application of some widely‐used methods would indicate an apparently constant reaction order.
Franz‐Keldysh‐Effekt an trigonalem und amorphem Selen
Authors: Stuke J. , Weiser G.
Published: July 2007

Au dünnen trigonalen Se‐Einkristallen und an aufgedampften Schichten von amorphem Se wird die Verschiebung ΔEg der Absorptionskante durch ein elektrisches Feld untersucht. Dabei ergibt sich, daß ΔEg recht genau proportional zum Quadrat der Feldstärke F und zum Quadrat der Steigung S der exponentiell verlaufenden Kante ist. Die spezifische Kantenverschiebung ΔEg/F2 hängt bei Kristallen stark von der Orientierung des Feldes und der Polarisation des Lichtes ab. Daraus ist zu schließen, daß die reduzierte effektive Masse in Richtung der c‐Achse um etwa den Faktor 6,5 kleiner ist als senkrecht dazu. Bei amorphem Se stimmt der Franz‐Keldysh‐Effekt qualitativ mit dem von Se‐Kristallen überein.
Photoconductivity of Anisotropically Deformed Intrinsic Germanium
Authors: Romanov V. A. , Zhadko I. P. , Boiko I. I.
Published: July 2007

Theoretical and experimental investigations are made of the photoconductivity in anisotropically deformed germanium in conditions favourable to the occurrence for electrical pinch. A saturation of the photocurrent for sufficiently high electric fields is predicted and observed. The effect of the electric field on the spatial distribution of the carriers in an illuminated crystal is investigated using the infrared spot method. Similar values of the surface recombination velocities are obtained from the current‐voltage and relaxation characteristics.
Mössbauer Effect in α‐Fe2O3
Authors: van der Woude F.
Published: July 2007

Experimental data are obtained for the antiferromagnetic compound α‐Fe2O3 by the Mössbauer technique. α‐Fe2O3 exhibits interesting properties, viz. the quantization axis of the spins of the iron ions changes direction by 90° at Tt = 260 °K, and the between 260 °K and the Néel temperature of 956 °K it shows weak ferromagnetism. The changes of the internal fields at the transition temperature are studied in detail. The effective magnetic field Heff drops abruptly by 8 kOe on heating α‐Fe2O3 through the transition temperature. Furthermore, the curve of Heff against T shows temperature hysteresis around Tt. An explanation for the discontinuity in Heff at Tt can be given on the basis of a small asymmetry of the charge distribution of the 3d‐electrons of the Fe3+ ions; this produces a contribution on the effective magnetic field of the orbital and spin magnetic moments of these electrons which is in addition to the contact field. The temperature dependence of Heff is also determined and cannot be described in terms of a Brillouin curve for S = 5/2.
Studies on the Electrical Properties of Uranium Oxides II. Non‐stoichiometric U3O8
Authors: Singh N. , Karkhanavala M. D.
Published: July 2007

The electrical conductivity σ and Hall coefficient RH are measured over the range 250 to 400 °K on pellets of U3O8 sintered for different periods up to 120 h at 900 °C. The sintering results in a progressive decrease of the O/U ratio from 2.666 to 2.63 accompanied by an increase in the density from 5.62 (“green” density) to 8.08 g/cm3. The values of the electrical conductivity are corrected for porosity. With decreasing O/U ratio, the conductivity and Hall mobility increase, while the conductivity activation energy decreases. The results for the highly sintered (96.5% of theoretical density) material of composition UO2.63 are interpreted on the basis of the hopping of small polarons.
Screw Dislocations in and near Lamellar Inclusions
Authors: Chou Y. T.
Published: July 2007

Using the method of images, the stress field of a screw dislocation in and near a lamellar inclusion is determined. The general solution holds for many simple cases involving straight boundaries, such as metals with surface film, thin plates, or composite materials of laminated structure. The image force on the dislocation is derived and discussed in terms of the thickness and rigidity of the inclusion.
Crystal Growth Measurements on Potassium Aluminium Alum and Sodium Chlorate from Slightly Supersaturated Solutions
Authors: Bennema P.
Published: July 2007

Measurements of the rate of growth R of a potassium aluminium alum crystal and a sodium chlorate crystal are presented. For alum, when the relative supersaturation σ lies between 3 × 10−5 and 10−2, R is found to be proportional to σ but for σ greater than 10−2 when spontaneous nucleation occurs, some points (showing considerable scatter) are obtained which lie above the linear curve. For sodium chlorate in the range 3 × 10−5 ⪅ σ ⪅ 5 × 10−4 a distinctly non‐linear (nearly parabolic) (R, σ) law is observed and for the range 5 × 10−4 ⪅ σ ⪅ 1.5 × 10−3 a linear curve is found which upon extrapolation to low values of σ does not pass through the origin. The theoretical (R, σ) curve resulting from the surface diffusion model of Burton, Cabrera, and Frank [1, 2] fits the measured (R, σ) points of sodium chlorate in a satisfactory way. It follows from the experiments that R does not depend on the velocity of flow of the solution.
Crystal Field Calculation in the CdWO4 Lattice
Authors: Kubec F.
Published: July 2007

The components of the crystal field potential at a cadmium site in CdWO4 are evaluated using the point charge model and taking into account the effect of induced dipoles. The calculation is carried out in the direction of the magnetic z axis of Cu2+ in CdWO4 and Fe3+ in ZnWO4 by summing the monopoles up to 25000 and dipoles up to 1000. It is found that the dipolar contribution is substantial and alters the sign of the crystalline field component obtained from point‐charges only. As the value of this contribution is rather large, it is neccessary to take into account the covalency effect of the crystal and to reduce the charges of the diamagnetic ions. The ground state wave function of Cu2+ and the zero field splitting of Fe3+, determined from experiments, are in reasonable agreement with those obtained by this calculation.
Zum Epitaxieverhalten dünner Silberaufdampfschichten
Authors: Jahrreiss H. , Isken H. ‐J.
Published: July 2007

Auf Steinsalzspaltflächen wurden Silberschichten verschiedener Dicke unter genauer Temperaturkontrolle aufgedampft und nach Ablösung von der Unterlage mittels Elektronenbeugung in Durchstrahlung untersucht. Die Aufdampfraten wurden dabei in sehr kleinen Schritten variiert, und es ergab sich für jede Temperatur T eine kritische Aufdampfrate Rk, bei der ein nahezu sprunghafter Übergang von rein monokristalliner Orientierung zu nur noch teilweiser Ausrichtung erfolgt. Der Funktionszusammenhang Rk(T) ermöglicht eine Bestimmung der Platzweschselenergie der Ag‐Atome auf der Oberfläche und stimmt überein mit der Modellvorstellung, daß mit der Ausbildung von Ag‐Atompaaren auf der NaCl‐Oberfläche ohne Möglichkeit vorherigen Platzwechsels in energetisch günstige Positionen eine vollständige Monokristallausrichtung nicht mehr zustandekommt.
AC Measurements on Hard Superconductors
Authors: Ullmaier H. A.
Published: July 2007

Cylindrical samples of PbIn, NbZr, and NbTa were exposed to a longitudinal, static magnetic field with a collinear alternating field, and the voltages produced in pick up coils wound around the samples were observed on an oscilloscope. The shape of the voltage‐time curves can be adequately explained by considering a surface sheath which is able to carry a certain critical surface current and a bulk region where the pinning forces dominate the magnetic behavior. It is shown that an analysis of the voltage‐time curves obtained yields values for the critical surface current and the bulk critical current density which are in good agreement with static measurements. While the bulk critical current density goes to zero when the external field reaches the upper critical field Hc2, the surface currents can be seen up to a field Hc3 > Hc2. Values of the bulk critical current density obtained were then used to determine the pinning force per unit volume and the pinning force on a single vortex line, as a function of the vortex line density.