bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modèle cristallochimique des semiconducteurs magnétiques
Authors: Suchet J. P. 
Published: July 2007

AbstractLa position des bandes de valence et de conduction d'un cristal, résultant de l'élargissement des niveaux liant et antiliant d'une molécule, est comparée à celle des sous‐niveaux t2g et eg résultant de la levée de la dégénérescence du niveau d par le champ cristallin de charges effectives atomiques ponctuelles. L'hybridation des orbitales dx2–y2 et dz2 avec les orbitales p est envisagée lorsque leurs énergies sont voisines et permet d'expliquer le grand nombre de composés équiatomiques métalliques. L'auteur donne de la conduction électrique dans les composés d'élements de transition une interprétation générale qui rend bien compte des résultats expérimentaux obtenus jusqu'ici sans contredire les principales idées antérieurement avancées. Le terme de pseudométal est proposé pour un groupe de cristaux de propriétés intermédiaires entre celles des métaux et des semiconducteurs. Quelques remarques permettent enfin de prévoir les classes de semiconducteurs susceptibles d'associer une mobilité des porteurs élevée à un ordre magnétique.
Minoritätsträger in CdS. II. Konzentration und Lebensdauer von Majoritäts‐ und Minoritätsträgern
Authors: Palz W. , Ruppel W. 
Published: July 2007

AbstractDie quantitative Erklärung der stationären Photospannung an einem Metall‐CdS Kontakt der durch Minoritätsträgererzeugung in Teil I gestattet es, die Konzentration und Lebensdauer der Minoritätsträger in CdS zu bestimmen und sie mit entsprechenden Daten für die Majoritätsträger zu vergleichen. Da die Berechnung der Lebensdauern aus optisch erzeugten Konzentrationsänderungen die Kenntnis der optischen Erzeugungsrate der Majoritäts‐ und Minoritätsträger erfordert, werden die Erzeugungsraten bei Belichtung mit verschiedenen Wellenlängen diskutiert. Für die untersuchten Proben liegt die Löcherlebensdauer im Bereich zwischen 10−8 und 10−14 s. In Cu‐dotiertem CdS entspricht eine große Elektronenlebensdauer einer kurzen Löcherlebensdauer, und es ergibt sich ein Produkt aus beiden Lebensdauern, das näherungsweise unabhängig vom Cu‐Gehalt ist. Für In‐dotiertes CdS wird keine so einfache Beziehung zwischen Elektronen‐ und Löcherlebensdauer gefunden.
Zur Aufladung belichteter CdS‐Kristalle bei verschiedenen Kontakten
Authors: Ruppel W. , Schlaile H. G. 
Published: July 2007

AbstractDie Aufladung von CdS‐Kristallen im Kontakt mit In, Te, Se, n‐Ge, p‐Ge, n‐Si und p‐Si wird im Dunkeln und bei Belichtung gemessen. Im Dunkeln wird eine negative Aufladung, die einer Elektronenanreicherungsrandschicht entspricht, für In, n‐Ge und n‐Si beobachtet, während eine positive Aufladung, entsprechend einer Elektronenverarmung, für Te, Se, p‐Ge und p‐Si gefunden wird. Bei Belichtung wird die Aufladung im allgemeinen positiver und kann sich sogar von negativ zu positiv ändern, womit der Umschlag von Elektronenanreicherung zu Elektronenverarmung angezeigt wird. Messungen der Photoleitung unterstützen die Vorstellung, daß der Wechsel der Raumladungsschicht bei Belichtung durch ein stärkeres Ansteigen der Konzentration freier Elektronen im Volumen gegenüber der Oberfläche hervorgerufen wird, entsprechend einer größeren Rekombinationslebensdauer im Volumen als an der Oberfläche.
Electromagnetic Properties of Superconductors in the Fröhlich Hamiltonian Model
Authors: Kresin V. Z. , Litovchenko V. A. 
Published: July 2007

AbstractA general gauge invariant expression for the superconductive current density is derived. The treatment is based on the Fröhlich Hamiltonian taking into account the electron‐phonon interaction. The results are used to describe the electromagnetic properties of the anomalous superconductors (Pb and Hg), in which the electron‐phonon interaction is strong. For this case, the usual treatment based on the Bardeen Hamiltonian cannot be employed. The results are in satisfactory agreement with the experimental data.
Distribution Function of Hot Carriers
Authors: Kamieniecki E. 
Published: July 2007

AbstractFrom the general, time‐dependent, Boltzmann equation for a non‐degenerate electron (or hole) gas, the integral form of the distribution function of hot carriers is obtained. Assuming that the scattering of carriers is due mainly to optical modes, the distribution function in the “zero‐order approximation” is derived and numerical calculations performed. The distribution function of hot electrons is found to be strongly anisotropic with a plateau and small local minimum in the direction opposite to that of the electric field.
Etch Pits at Dislocations in High‐Purity Iron Single Crystals
Authors: Šesták B. , Kadečková S. 
Published: July 2007

AbstractA description is given of the etching (in a solution of 2% nital) of both fresh and grown‐in dislocations on polished (100) surfaces of iron single crystals. The single crystals contain 25 to 50 ppm of carbon, 40 ppm of oxygen, 2 ppm of nitrogen, and other impurities totalling 15 ppm, and are prepared by the strain annealing method from Johnson and Matthey spectrographic iron.
Effect of Neutron and γ‐Ray Irradiation on the Carrier Lifetime and Detectivity of InSb
Authors: Euthymiou P. C. , Tanenbaum A. L. 
Published: July 2007

AbstractSingle crystals of p‐type InSb were irradiated by 4.5 MeV neutrons or γ‐rays at liquid nitrogen temperature. The damage produced by neutron irradiation resulted in a small decrease of the carrier lifetime and a large decrease of the detectivity of the crystal. The damage produced by γ‐rays resulted in an increase or decrease of lifetime, the change depending on how strongly p‐type the crystal was. The detectivity was decreased upon γ‐irradiation. Annealing experiments show that neutron damage is permanent while γ‐ray defects can be completely annihilated near or above room temperature, giving a similar result as electron irradiation. Analysis of the effects on lifetime and detectivity shows that neutron damage effects, although severe and permanent, produce no important decrease of lifetime.
Development of Glide Bands During Plastic Deformation of LiF Crystals
Authors: Smirnov B. I. , Efimov B. A. 
Published: July 2007

AbstractThe development of the dislocation structure and shear strain in glide bands of LiF crystals under an applied stress is studied. The following parameters are determined: the rate of lateral band growth ω, the change of shear strain γ in bands during this growth, and the average slip distance of screw dislocations λ during band formation. It is found that the widening of the bands occurs asymmetrically, an increase in the band width resulting in a decrease in ω and in an increase in γ (γ eventually reaches a certain limiting value). On the average, the rate of lateral band growth is about an order of magnitude less than the velocity of the individual dislocations. It is found that λ has a value of 1.5 mm at 20°C which decreases with an increase of the magnesium content of the crystal and also decreases with a decrease of the deformation temperature.
Electrical Conductivity of p‐GaSe Single Crystals in Strong Electric Fields
Authors: Abdullaev G. B. , Guseinova E. S. , Tagiev B. G. 
Published: July 2007

AbstractThe electrical conductivity of p‐GaSe single crystals is measured in strong electric fields up to 3 × 104 V/cm. Pulse duration is used with 4 μs and a repetition rate of 50 Hz. The critical field for p‐GaSe is about 1600 V/cm, above which Ohm's law fails and the conductivity increases with field according to Frenkel's law: σ = σ0 eβ \documentclass{article}\pagestyle{empty}\begin{document}$\sqrt E $\end{document}. From the deduced temperature dependence of β \documentclass{article}\pagestyle{empty}\begin{document}$\\({\beta = \sqrt {e^3 /} k{\rm}T\sqrt \varepsilon}$\end{document} the dielectric constant ϵ of p‐GaSe single crystals is found to be approximately five. The hole activation energy determined from the temperature dependence of the conductivity, decreases with increasing field, which agrees with Frenkel's theory. By extrapolating the lg σ = f(1/T) straight lines a thermal breakdown temperature of about 25000 °K is found, which can be referred to as the metallization temperature (Tm). It is found that k Tm ≈︁ 2 eV is the thermal energy gap at absolute zero. By extrapolating the lg σ = f (\documentclass{article}\pagestyle{empty}\begin{document}$\sqrt E $\end{document}) straight lines a breakdown intensity, Eb, of about 107 V/cm is found, which characterizes the electrical strength. The width of the energy gap ΔE0, obtained from the expression: ΔE0 = 2 e \documentclass{article}\pagestyle{empty}\begin{document}$\sqrt {eE_b /\varepsilon} $\end{document} appears to be about 1.9 eV.
Zur Berechnung der Wechselwirkung einer Ansammlung von ausgerichteten magnetischen Einbereichsteilchen
Authors: Straubel R. , Robaschik D. 
Published: July 2007

AbstractEs wird ein Verfahren zur Berechnung der magnetischen Kennwerte, insbesondere des Verlaufs der Magnetisierung einer großen Ansammlung von länglichen Einbereichsteilchen bei frei wählbaren Magnetisierungszyklen angegeben. Bei beliebiger Anordnung der Teilchen sollen jedoch deren Längsachsen vollständig parallel ausgerichtet sein, so daß jedem Teilchen eine exakt rechteckige individuelle Magnetisierungskurve zugeordnet werden kann. Dabei wirkt jedes Teilchen mit seinem äußeren Streufeld magnetisierungsabhängig auf jedes andere Teilchen. Das Verfahren wird zunächst an dem Néel‐Wohlfartschen Pärchenmodell demonstriert.
Ramp Field Switching in Thin Magnetic Films
Authors: Lachowicz H. 
Published: July 2007

AbstractA model of magnetization reversal by the domain wall movement is proposed. This model is formulated in general for polycrystalline square loop ferromagnets which are magnetized by a linearly increasing magnetic field. The switching time and dynamic coercivity of the material are expressed as a function of the rate of increase of the field. These calculation are based on the expression for the velocity of a domain wall obtained from the well‐known Landau‐Lifshits equation. Experimental results, for thin permalloy films are in good agreement with theoretical predictions. A practical aspect of the present work is a new method of determining the static coercivity of the material.
Zur Zeitabhängigkeit raumladungsbegrenzter Injektionsströme in Halbleitern
Authors: Lemke H. 
Published: July 2007

AbstractEs wird die Zeitabhängigkeit von Raumladungsströmen unter Berücksichtigung eines Haftterms untersucht. Für die Füllung und Entleerung der Haftstellen werden Näherungslösungen angegeben, aus denen die Einfangszeit τc und Emissionszeit τe bestimmt werden können. Bei hinreichend kleiner Spannung ändert sich der Injektionsstrom exponentiell mit der Zeitkonstanten τc. Nach Abschalten der Injektionsspannung werden die freien Ladungsträger von dem durch haftende Raumladung verursachten Feld aus dem Kristall herausgeschwemmt, wodurch die thermische Ladungsträgerkonzentration p0 auf den Minimalwert p = (τR/τe) p0 (τR dielektrische Relaxationszeit) absinken kann. Bei starker Füllung des Haftterms gegenüber dem thermischen Gleichgewicht ändert sich dabei die haftende Raumladungskonzentration exponentiell mit der Zeitkonstanten τe. Bei schwacher zusätzlicher Haftstellenfüllung ist die zeitliche Änderung der haftenden Raumladung konstant und hängt von der im thermischen Gleichgewicht vorhandenen Besetzung ab.
Ferromagnetic Curie Temperatures of Some Iron‐Zinc Solid Solutions
Authors: Wriedt H. A. , Arajs S. 
Published: July 2007

AbstractThe preparation of homogeneous iron‐zinc alloys by zinc‐vapor impregnation of iron is described. Ferromagnetic Curie temperatures of the b.c.c. solid solutions containing 11.2, 14.4, and 20.1 at% zinc were determined to be 981.3, 957.0, and 925.0°K, respectively. These measurements are in good agreement with the results obtained by Fallot but not with those of other investigators. Zinc lowers the Curie temperature of iron linearly by about 5.8 deg/at% zinc. This lowering is inconsistent with the simple molecular field predictions.
Interrupted Vapour Deposition of Epitaxial Gold Films Grown Inside an Electron Microscope
Authors: Stowell M. J. , Law T. J. 
Published: July 2007

AbstractDuring the growth of epitaxial gold films inside an electron microscope, the gold vapour stream was interrupted in order to study changes in the deposit structure which occur in the absence of incident vapour. It is shown that rapid shape changes of the deposit islands characteristic of ‘liquid‐like’ coalescence continue when deposition is stopped and that further coalescences do occur. The results of these experiments give added confirmation to the thesis of Pashley et al. [1] that the ‘liquid‐like’ shape changes of coalescing deposit islands are brought about by surface self‐diffusion motivated by capillarity forces.
Energy Band Structures of Selenium and Tellurium (Kohn‐Rostoker Method)
Authors: Treusch J. , Sandrock R. 
Published: July 2007

AbstractThe band structures of hexagonal Se and Te are calculated using a group theoretical treatment based on the Kohn‐Rostoker method. With certain assumptions the method yields continuous wave functions with continuous derivatives. The energy gaps agree qualitatively with experiment. The polarization dependence of optical transitions can be explained by the present band models. Hole effective masses are estimated, and it is found that m∥ is about four times as large as m∥ in both substances. The variation of the Se energy gap with pressure is investigated and found to fit experiments.
Lattice Vibrations of Aluminium on the Basis of Krebs's Model
Authors: Shukla M. M. , Dayal B. 
Published: July 2007

AbstractThe vibration spectrum of aluminium is studied using Krebs's model. The phonon dispersion curves for the three symmetry directions [100], [110] and [111] are presented and are found to be in very good agreement with neutron scattering measurements. The (θ ‐ T)‐curves calculated from Krebs's model agree very well with experiment using a screening parameter deduced from the Bohm‐Pines theory.
Émission photoluminescente visible du gadolinium inclus dans le réseau cristallin du sulfure de zinc
Authors: Bancie‐Grillot M. , Bourtayre P. 
Published: July 2007

AbstractNous précisons ici certains caractères de l'émission de raies visibles du sulfure de zinc activé par du gadolinium, que nous avons récemment découverte [1]. Elle est constituée de 46 raies fines, s'étendant entre 4664 et 7057 Å; six d'entre elles, formant un systéme secondaire, disparaissent par adjonction de minimes traces de cobalt et sont atténuées dans les cristaux mixtes de zinc et de cadmium. Cette émission ne peut être attribuée à l'ion trivalent Gd3+, seule forme considérée chimiquement stable de ce lanthanide. Il est en effet connu que le premier état excité de cet ion est, énergétiquement, à prè de 4 eV au‐dessus de son état fondamental correspondant à la configuration électronique 4f7. Dans le réseaucristallin assez fortement covalent du sulfure de zinc, le gadolinium capterait solidement un électron, son état stable non excité étant probablement 4f7 5d1.
Mesures du temps de retournement ferroélectrique de KH2PO4
Authors: Guyon P. , Lajzerowicz J. 
Published: July 2007

AbstractDes mesures du temps de retournement en régime impulsionnel ont été faites et mettent en évidence, à faibles champs, un retournement en deux temps. D'autre part, de nouvelles mesures du champ coercitif sont également présentées.
Electron Microscopy of Irradiation‐Induced Defect Clusters in Magnesium Fluoride
Authors: Barber D. J. 
Published: July 2007

AbstractThe passage of electrons through thin crystals of magnesium fluoride produces point defects. These defects are mobile at temperatures normally attained under the electron beam, and they can give rise both to dislocation loops and to precipitate platelets. The aggregation of these radiation‐induced defects can be controlled by using a cooled specimen stage in the electron microscope. This allows the growth and characteristics of the defect clusters to be studied. Dislocation loops lie on {011} planes and they sometimes show stacking fault contrast; their Burgers vectors are 1/2 〈011〉 and 〈011〉. Prolonged irradiation can produce precipitates on and within the loops. Higher beam intensities produce precipitates directly. The nature of the loops and precipitates is discussed in relation to the production of point defects by ionization mechanisms and irradiation‐stimulated migration.
On the Electrical and Magnetic Properties of Coloured and Uncoloured Calcium Fluoride Crystals
Authors: Ratnam V. V. 
Published: July 2007

AbstractThe electrical and magnetic properties of uncoloured calcium fluoride crystals and of specimens of these crystals coloured by X‐rays and electrolysis, are reported. The dc conductivity and dielectric loss measurements of uncoloured and X‐ray coloured CaF2 crystals show that in a freshly prepared crystal 1. the number of free negative ion vacancies is very small and 2. the anti‐Frenkel defects which are initially present are in the associated form. These points explain why, for irradiation at room temperature, the α‐band (the F‐band of this system) is not observed in optical absorption. The nature of the traps is also discussed in the context of the observed changes in the dc conductivity accompanying the thermal bleaching of the colour centres in an X‐irradiated crystal. The temperature variation of the magnetic susceptibility indicates that X‐irradiation produces both paramagnetic and diamagnetic colour centres. From the results of measurements on electrolytically coloured crystals, the oscillator strength of the F‐band is estimated as about 10−2; this also explains why the formation of the α‐band is not detected for room temperature X‐irradiation.
Interactions between Domain Walls in Coupled Films
Authors: Biragnet F. , Devenyi J. , Clerc G. , Massenet O. , Montmory R. , Yelon A. 
Published: July 2007

AbstractA study is made of the domain‐wall structure of coupled uniaxial ferromagnetic films separated by a thin non‐magnetic layer. It is found that the walls in the two films are not always superimposed. After demagnetization in the hard direction they are separated but tend to cross frequently. After demagnetization in the easy direction, they may be separated and parallel or they may be superimposed. An explanation of this behaviour in terms of wall‐hyphen;quasi‐wall interactions is considered.
Nonradiative Destruction of F‐Centres in X‐Irradiated KCl Doped with Anionic Impurities
Authors: Mukherjee M. Ludwig , Bose H. N. 
Published: July 2007

AbstractA study is made of the thermoluminescent behaviour and room temperature stability of F‐centres produced by X‐rays in KCl doped with some anionic impurities. A low percentage of KNO3, KOH, and K2CO3 enhances the formation of F‐centres but a high percentage inhibits this formation. F‐centres in lightly doped samples which are stored in the dark and at room temperature are found to decay with time, in two stages, by some nonradiative processes. The thermoluminescence intensities of these samples are poor. In the case of KNO3 doping, infrared absorption at 7.1 and 7.7 μm due to (NO3)− and (NO2)− ions decreases after irradiation by X‐rays suggesting decomposition of these complexes. It is suggested that the diffusion of decomposition products with trapped holes is responsible for the decay of F‐centres with time at room temperature. The activation energies for the diffusion processes are of the order of 0.98 and 1.05 eV in all the samples. With 1 mol% of KNO3 doping, the F‐centres are almost undetectable. It is estimated that in this case the average distance between one nitrate or nitrite ion and an F‐centre is of the order of 12 atomic units.
Distribution électronique anisotrope dans les semiconducteurs purs au voisinage de l'avalanche
Authors: Granger R. 
Published: July 2007

AbstractNous présentons une étude de la distribution électronique dans les semiconducteurs purs soumis à des champs électriques E intenses, permettant de rendre compte du phénomène d'ionisation par choc à travers la largeur de bande interdite ϵi. Dès que la concentration électronique est inférieure à 1015 cm−3, les collisions interélectroniques ne suffisent plus pour maintenir la distribution isotrope et la notion de température électronique n'est alors plus valable. D'autres mécanismes de relaxation sont cependant efficaces et nous considérons particulièrement les cas de diffusion par phonons acoustiques ou optiques. Nous montrons que dans le dernier cas, une partie de la distribution (pour des énergies ϵ > ϵ0(E)), est constituée essentiellement d'électrons dont le moment est dans la direction du champ électrique; ces électrons appelés „balistiques”︁ sont ceux qui, accélérés dans le champ électrique, atteignent une énergie supérieure à ϵi, et causent l'ionisation par choc. Nous séparons la distribution à l'état stationnaire en trois classes: ϵ < ϵ0, ϵ0 < ϵ < ϵi, ϵ < ϵi et calculons les probabilités de transition d'une classe à l'autre. Nous obtenons alors les populations des trois classes en fonction du champ électrique et déduisons enfin la caractéristique courant‐tension. Les résultats numériques sont donnés pour plusieurs semiconducteurs, et en particulier le champ de claquage à différentes températures. Si la distribution reste relativement isotrope, la contribution de la partie anisotrope n'en est pas moins efficace, le temps de relaxation des porteurs étant de cinq ordres de grandeur plus faible que leur durée de vie. Nous comparons cette théorie avec les résultats expérimentaux sur InSb.
Comparison of Magnetic Measurements and Theoretical Predictions for Nickel‐Iron Films Over a Wide Composition Range
Authors: Cundall J. A. , King A. P. 
Published: July 2007

AbstractA comparison is made of the theoretical predictions of several recent models of polycrystalline magnetic films with the experimental results obtained for nickel‐iron films in a wide composition range. The models considered are the micro‐magnetic and the random anisotropy models. Magnetic measurements were made of the remanence distribution and the easy direction domain wall coercive force. The results suggest that no single theory adequately describes the properties of the films over the whole composition range although all have a limited success for different parts of the range.
The Theory of the Stability of the Solid‐Liquid Interface under Constitutional Supercooling (I)
Authors: Delves R. T. 
Published: July 2007

AbstractThis paper discusses the stability of the solid‐liquid interface when a crystal is grown from a melt which contains a segregating component. The transient motion of the interface in response to a thermodynamic fluctuation in concentration is calculated using the time dependent diffusion equations. An expansion is made in powers of the amplitude of the fluctuation, the first order terms are found exactly, and some important higher order terms are included. The interface is either stable and returns to its original flat shape or else distorts exponentially with time into the cellular shape. The stability condition is exactly the original constitutional supercooling criterion of Tiller et al. Physical and mathematical arguments show that the interface is either stable or unstable and that no steady state slightly perturbed interface can exist. This paper is restricted to the special case of infinite thermal diffusivity, and does not include effects on an atomic scale.