bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Fast Neutron Irradiation and of Impurities on the X‐Ray Intensities Diffracted by Germanium and Silicon Crystals
Authors: Colella R. , Merlini A.
Published: July 2007

An investigation is made of the effects of fast neutron irradiation and of impurities on the X‐ray diffraction intensities of Ge and Si crystals having low dislocation densities. Monochromatic CuKα and MoKα radiations are used in both the transmission and reflection geometries. Appreciable increases of the integrated intensities are found for Si crystals irradiated with a dose of 3 × 1020 nvt. These increases are greatest if transmission geometry and MoKα radiation (thin crystal case) are used. There is, however, no variation in the diffraction intensities in anomalous transmission. The irradiation is found to have no effect on the diffraction intensities in Ge crystals irradiated up to 3 × 1020 nvt. With Si crystals doped with boron up to a maximum atomic fraction of 1.3 × 10−3 the intensities increase with increasing concentration of the doping element in the transmission geometry, when MoKα radiation is used. In anomalous transmission the intensities vary greatly in different regions of the most heavily doped Si crystal.
A New Manifestation of Magnetic After‐Effect
Authors: Knowles J. E. , van Groenou A. Broese
Published: July 2007

Minor hysteresis loops of magnetite were observed at room temperature. Immediately after demagnetization the loop was of the Rayleigh type, but changed with time, while a small alternating field was present into a very rectangular loop which disappeared abruptly after one hour. It is shown that if the amplitude of the wall displacement is large compared to the wall thickness, then instead of the wall forming a single potential well as described by the existing theory of magnetic after‐effect, it will form two adjacent wells, which give rise to the above phenomenon.
Transverse Gain in GaAs Laser Structures
Authors: Burrell G. J. , Moss T. S. , Hetherington A.
Published: July 2007

Gain measurements are reported for radiation of wavelength 8466 Å propagating in a direction perpendicular to the junction of a GaAs injection laser operated at 80 °K. These results, used in conjunction with measurements of spontaneous emission, show that a gain of 2.3% is achieved at 7000 A/cm2. In thermal equilibrium 0.78% of the transmitted radiation is absorbed in traversing the active region, 135 A/cm2 being required to off‐set this loss before net gain is obtained.
Influence de la structure locale de l'anisotropie magnétique induite sur la dispersion de l'aimantation dans les couches minces de permalloy
Authors: Roth M.
Published: July 2007

On calcule la dispersion de l'aimantation d'un film mince polycristallin de permalloy en tenant compte du fait que, par traitement dans un champ magnétique uniforme, l'anisotropie uniaxiale induite due à l'ordre directionnel et à la déformation imposée par le support est différente dans chaque cristallite car elle dépend de l'orientation cristallographique de celui‐ci. On trouve qu'en général la dispersion résultante est supérieure à celle que l'on obtient en ne considérant que l'effet de l'anisotropie magnétocristalline, et que contrairement à ce qu'il est admis couramment, la dispersion ne décroit pas de façon monotone quand l'énergie Ku d'anisotropie uniaxiale augmente mais commence par décroître (pour des valeurs de Ku plus petites que l'énergie d'anisotropie magnétocristalline) jusqu'à un minimum puis augmente avec Ku.
The Ferromagnetic Domain Structure of Thin Single‐Crystal Fe Platelets in an External Field
Authors: Gemperle R.
Published: July 2007

The domain structure of small iron single‐crystals in the shape of thin rectangular platelets is studied by means of a colloid technique during magnetization. The observations indicate that the demagnetizing field of the sample is formed by charges on the domain walls. Changes in the domain structure are compared with a magnetization curve obtained by measuring the areas of individual domains.
Origin of the Condenser Photo‐E.M.F. in Semiconductors and of the Photoinduced Change in the Contact Potential
Authors: Akimov I. A. , Meshkov A. M. , Terenin A. N.
Published: July 2007

The sign of the surface charge and its effect on the magnitude of the magnitude of the photo‐response are investigated for high‐ohmic inorganic and organic semiconductors by using Bergmann und Kelvin condensers. An explanation is given of the origin and polarity of the photo‐response, and the changes in its spectral distribution. The results indicate the reliability of condenser methods for determining the sign of photo‐excited carriers in the absorption band of a semiconductor. The spectral phenomena occurring at the band edge can successfully be used to study the surface states of the semiconductor.
Heliconwellenausbreitung in InSb und InAs
Authors: Flietner H. , Kliefoth K.
Published: July 2007

Die Heliconausbreitung wird bei 24,8 GHz und Zimmertemperatur für InSb und InAs nach einer Resonanzmethode und einer Phasenvergleichsmethode untersucht. Die für isotrope effektive Masse und energieunabhängige Relaxationszeit sich ergebene Dispersionsrelation wird bestätigt.
Magnetic Properties of Eu3O4
Authors: Wang F. F. Y.
Published: July 2007

A new Eu3O4 preparation method is described. Eu3O4 is produced by the solid state reaction between Eu and Eu2O3. Static magnetic susceptibility measurements were made by the Faraday method from 6 to 300°K. Eu3O4 was found to be ferrimagnetic with a Curie point of 77 °K.
Optical Absorption Band Grown in Thermally Bleached Neutron‐Irradiated Lithium Fluoride
Authors: Kamikawa T. , Kazumata Y. , Ozawa K.
Published: July 2007

An absorption band having a maximum at 630 nm is observed in neutron irradiated “pure” LiF crystals which have been thermally bleached and aged. The properties of this band are studied, and its origin is discussed.
Two‐Particle Green's Function Method in the Theory of Light Absorption by Impurity Centres in Solids
Authors: Lubchenko A. F. , Dudkin S. I.
Published: July 2007

A two‐particle Green's function method is used to calculate the dispersion and absorption of light by impurity centres in solids, assuming the electron‐level separation to be of the same order of magnitude as the maximum phonon energy and assuming a weak electronphonon interaction. The absorption spectrum and corresponding dispersion curve are shown to contain phonon and non‐phonon contributions. The forms of these contributions are calculated and their variation with temperature and the electronic structure of the impurity centre is investigated.
Investigation of Gold Doped Germanium in High Electric Fields
Authors: Sondaevskii V. P. , Karakushan E. I. , Stafeev V. I.
Published: July 2007

Current voltage characteristics of n‐type Ge diodes with an incompletely filled Au level at 0.2 eV are investigated at liquid nitrogen temperature. The current voltage dependence exhibits three stable regions, denoted by “a”, “b”, and the high current region. Region “a” is only stable at low voltages where the capture cross section is independent on electric field strength. Transition from region “a” to “b” is due to a field induced electron capture by the 0.2 eV level at higher voltages. At sufficiently high currents hole injection begins to play the predominant role, and the characteristic becomes S‐type. The intermediate regions between the stable ones are characterized by large current and voltage oscillations.
Two‐Stage Excitation of the Phosphorescence of Ruby
Authors: Morgenshtern Z. L. , Neustruev V. B.
Published: July 2007

A long‐time phosphorescence of ruby is found under intense optical excitation in the spectral region of the R‐lines. From the initial brightness decay, as a function of the intensity and wavelength of the exciting light, it is suggested that the phosphorescence has a recombination character. The long‐wavelength limit of excitation corresponds to about 2 eV. These results indicate a complex character for the phosphorescence excitation (two‐photon or two‐step). To differentiate between these two possibilities experiments are performed using two excitation pulses with various time delays between them. These experiments show that two‐step excitation of electrons into the conduction band of ruby takes place over 2E levels of the Cr ions. From the results, and absorption data of ruby and corundum, a band scheme is proposed which explains the long‐wavelength limit of phosphorescence excitation in terms of indirect transitions.
On the Use of Thiele's Semi‐Invariants in Ferromagnetism
Authors: Ferris‐Prabhu A. V. M.
Published: July 2007

The semi‐invariants of Thiele are used to calculate the effect of the kinematical interactions on the temperature dependence of the magnetization on the spinwave model of ferromagnetism. It is first assumed that the only effect is to restrict the spinwave eigenvalue spectrum to 2 S. The semi‐invariants are calculated exactly and an expression is obtained for the magnetization which contains only half odd integer powers of T. The coefficients contain the factor 1–(1 + 2 S)−n/2 and as S → ∞ reduce to Dyson's coefficients. Next the interaction of the spinwaves is specifically included. The first three semi‐invariants are calculated exactly. A conjecture is made as to the form of the first order term of the n‐th semi‐invariant from which the magnetization is calculated. The expression bears an interesting resemblance to Watson's generalized integral.
E. P. R.‐Studies of V2O5 Single Crystals. I. Defect Centres in Pure, Non‐stoichiometric Vanadium Pentoxide
Authors: Gillis E. , Boesman E.
Published: July 2007

The E.P.R.‐spectra of zone‐refined V2O5 are interpreted in terms of a defect centre consisting of an unpaired electron interacting with two equivalent vanadium nuclei separated by an oxygen vacancy. This conception leads to the establishment of a defect formula for V2O5, involving V4+ and V3+ ions. A self‐consistent mechanism is proposed for the formation of the low‐temperature form of non‐stoichiometry in V2O5. Principal values of the approximately axially‐symmetric spin‐Hamiltonian are
E. P. R.‐Studies of V2O5 Single Crystals. II. Defect Centres in Molybdenum‐Doped Vanadium Pentoxide
Authors: Boesman E. , Gillis E.
Published: July 2007

In Mo‐doped V2O5 a paramagnetic defect is formed, in which the unpaired spin interacts with only one vanadium nucleus. Two non‐equivalent centres are present per unit cell. Both have the c‐axis as the principal axis of the g‐and hyperfine tensor, whereas one of the other axes forms an angle of ±7° with b‐axis. The results are summarized by an orthorhombic spin‐Hamiltonian with

Some possible models are discussed.
Temperaturabhängigkeit des Photoeffekts von anodisch hergestellten ZrO2‐Schichten
Authors: Hartl M. , Achtziger K.
Published: July 2007

Das photoelektrische Verhalten ohne angelegte Spannung bei Bestrahlung mit UV‐Licht wurde an anodisch oxydierten und metallkontaktierten Zr‐Blechen als Funktion der Temperatur im Bereich von +25°C bis −150°C bei Oxyddicken zwischen 75 und 1500 Å gemessen. Der Photokurzschlußstrom zeigt mit fallender Temperatur eine starke Abnahme, welche mit zunehmender Oxyddicke ausgeprägter wird und sich einer e‐Funktion nähert. Als Erklärung wird eine gleichlaufende Temperaturabhängigkeit der Diffusionslänge der vom Licht angeregten und durch einen Potentialgradienten im Oxyd getrennten Ladungsträger angenommen. Die Photospannung dagegen ist bei dünnen Schichten (≦ 500 Å) nahezu temperaturunabhängig, während sie bei dickeren Schichten mit abnehmender Temperatur geringer wird, im direkten Gegensatz zu den anderweitig berichteten hohen Werten bei tiefen Temperaturen [12]. Ergänzend wird noch von Abweichungen berichtet, welche bei Verwendung von aufgedampftem Zr auftraten.
Domain Wall Creep Rate in Thin Permalloy Films
Authors: Telesnin R. V. , Ilicheva E. N. , Kanavina N. G. , Shishkov A. G.
Published: July 2007

An analysis of the experimental dependence of the domain wall creep rate, V, on the intensity of magnetic fields in the “easy” (HL) and “hard” (HT) directions gives a characteristic exponential dependence of V on HL with HT = const. The parameters of the exponential V (HL) for films of different thickness are presented, and it is shown that one of the parameters should be the critical start field of the wall, Hw. st., rather than the coercivity, Hc. It is shown how the creep parameters vary when the sinusoidal bipolar alternating field along the “hard” axis is replaced by a unipolar magnetic field.
Theory of the Optical Spectrum of Ion Pairs of 3d3 Iron‐Group Impurities in Crystals
Authors: Nikiforov A. E. , Cherepanov V. I.
Published: July 2007

A calculation is made of the energy spectrum of impurity ion pairs with 3d3 configuration in crystals. The optical spectrum of these crystals is interpreted by assuming that a large part of the low‐symmetry crystalline field acts on the impurity ion; the electric‐dipole interaction being taken into account. The case of ruby (Cr3+:Al2O3) is treated in detail as an example. The results are compared with experimental data.
Photo‐Field‐Emission from High‐Resistance Silicon and Germanium
Authors: Borzyak P. G. , Yatsenko A. F. , Miroshnichenko L. S.
Published: July 2007

The characteristics of field and photo‐field‐emission from high‐resistance Si and Ge at low temperature are presented. On the basis of a dielectric field cathode model, the nature of the dark current and the conditions of voltage redistribution across the emitter and vacuum gap are discussed. The photofield emission characteristics are also discussed.
Structured Luminescence Emission in Cadmium Sulphide at 2.0 to 2.8 μm
Authors: Bryant F. J. , Cox A. F. J.
Published: July 2007

For cadmium sulphide a new structured luminescence emission in the wavelength region 2.0 to 2.8 μm and the corresponding excitation spectra are reported. The luminescence is believed to occur at an acceptor centre analogous to that responsible for the 1.5 to 2.2 μm banded emission. Cadmium sulphide phosphors which exhibit luminescence between 2.0 and 2.8 μm also show an apparent shift of the well‐known 1.06 μm emission band to shorter wavelengths, the shift is caused by the existence of a new luminescence emission band with an intensity maximum at 0.90 μm. By considering the new acceptor centre and a common donor level the 0.90 μm luminescence emission band may be explained on the same donor‐acceptor pair model previously proposed to explain the origin of the 1.06 μm luminescence emission band. Comparision of absorption and emission transitions for the two luminescence centres on the model proposed to explain the 1.06 μm and 1.5 to 2.2 μm emission bands leads to a consistent value of approximately 0.2 eV for the energy separation of the two acceptor levels.
Electrical Properties of Single Crystals of Hexagonal Ferrites with the W Structure
Authors: Šimša Z. , Zalesskij A. V. , Závêta K.
Published: July 2007

Single crystals of a hexagonal ferrite of composition BaFe18O27 with the W‐structure are found to have an anisotropic electrical conductivity, which is believed to be an intrinsic property of the material. From the temperature dependence of the electrical resistivity, and from thermoelectric measurements, it is concluded that electron hopping between Fe2+ and Fe3+ ions plays a prominent role in the conduction process. The possible origin of the anisotropy in the conductivity is discussed in relation to specific features of the W‐structure.
Investigation of Current Carrier Drift in Organic Substances (Tetracene)
Authors: Frankevich E. L. , Balabanov E. I.
Published: July 2007

The pulses of hole conduction current induced by pulse electron bombardment in a thin sublimed film of tetracene are studied. It is shown that electrons produced by ionization cannot be extracted into the bulk of the sample by an external electric field. The hole mobility is estimated as μ ≧ 0.5 cm2/Vs. The integral of hole current per pulse is shown to rise with the applied voltage U, though special experiments demonstrate that no trapping occurs in the sample. The linear increase of the hole current integral is explained by competition between extraction of holes from the electrode‐adjacent layer and recombination of holes with electrons injected into the tetracene from the Al electrode. This conclusion is confirmed by the rectifying properties of the Al‐tetracene contact and by photovoltage. The hole current integral in the admixture containing samples is shown to be proportional to U2. This is due to a combination of two processes: the hole extraction probability increases linearly with U and also the hole displacement before trapping in the sample increases linearly with U.
The Effect of Exposure to Air on Dislocations in Zinc and Cadmium Crystals
Authors: Michell D. , Ogilvie G. J.
Published: July 2007

X‐ray topographs of initially perfect and unstrained crystals of zinc and cadmium show that loops and line defects nucleate and grow in them as a result of their exposure to air. This phenomenon is attributed to the growth of an oxide film causing vacancies to be injected into the crystal which aggregate to produce the visible defects. Observations on cadmium crystals in an electron microscope show nucleation and growth of similar defects and these results can be explained using the same model.
Bestimmung der Diffusionskoeffizienten des Nickels und der Leerstellenkonzentration in der β‐Phase des Systems Nickel‐Antimon
Authors: Heumann Th. , Stüer H.
Published: July 2007

In der β‐Phase des Systems Nickel—Antimon zeigt das Nickel eine ungewöhnlich hohe Beweglichkeit. Messungen mit dem radioaktiven Nickelisotop Ni63 ergaben Frequenzfaktoren von etwa 5 × 10−4 cm2/s und Aktivierungsenergien von ungefähr 15 kcal/Mol. Durch Bestimmung der makroskopischen Dichte sowie der Gitterkonstanten der β‐Phase in Abhängigkeit von der Konzentration konnte nachgewiesen werden, daß die große Beweglichkeit des Nickels durch strukturelle Leerstellen bewirkt wird, die dadurch auftreten, daß mit wachsender Antimonkonzentration Plätze im Nickelteilgitter unbesetzt bleiben. Dabei ergab sich, daß die der vollbesetzten Struktur entsprechende stöchiometrische Zusammensetzung Ni3Sb außerhalb des Homogenitätsbereiches der β‐Phase liegt.
Negative Knight‐Shift und Suszeptibilität in Übergangsmetall‐Hydriden: Chromhydrid
Authors: Albrecht G. , Schnabel B.
Published: July 2007

Es wurden eigene Messungen der Größe, des Vorzeichens und der Temperaturabhängigkeit der H1‐Knight‐Shift und der Suszeptibilität im CrH benutzt, um die Einflüsse und Beiträge des Spin‐Paramagnetismus der s‐ und d‐Bänder sowie des Bahn‐Paramagnetismus zu ermitteln. Die Möglichkeit von “exchange‐enhancement” der d‐Spin‐Suszeptibilität wurde diskutiert. Kovalente Bindungsanteile zwischen Cr und H wurden angenommen und die Spin‐Bahn‐Kopplung benutzt, um das negative Vorzeichen des Bahnbeitrages zur H1‐Knight‐Shift zu erklären.
Nachweis großer Schmelzpunktserniedrigungen bei dünnen Metallschichten
Authors: Gladkich N. T. , Niedermayer R. , Spiegel K.
Published: July 2007

Die Struktur dünner Silberschichten wurde während des Wachstums bei erhöhten Temperaturen mit Elektronenbeugung in einem Vakuum von 10−9 Torr untersucht. Bei einer Temperatur über 550 °C wuchsen die Schichten zunächst im flüssigen Zustand und gingen erst bei einer bestimmten temperaturabhängigen Schichtdicke in den festen Zustand über. Unter denselben Bedingungen wurde auch der Schmelzpunkt dünner Schichten von Ag, Cu, Al und Ge bestimmt. Für dünnste Schichten konnte eine minimale Schmelztemperatur gefunden werden, und zwar für Ag 550 °C und für Cu 670 °C.
The Mössbauer Effect for 57Fe Impurity Atoms
Authors: Bara J. , Hrynkiewicz A. Z.
Published: July 2007

The Debye‐Waller factors for the 14.4 keV γ‐rays of 57Fe atoms as a dilute impurity in 16 crystal lattices are measured at room temperature. The force constants for the hostimpurity atoms are found to be almost the same as for the host‐host atoms. A correlation between the isomer shifts and the standard electrode potentials is observed.
The Influence of External Electric Fields on the Absorption of Ag+‐Centres in KCl (II)
Authors: Gebhardt W. , Mohler E.
Published: July 2007

A group theoretical analysis of Stark effect measurements in KCl:Ag+ is reported. The irreducible representations of the excited states are determined assuming that the electronic transitions associated with the four measured absorption bands arise from the same ground state singlet, and that the Ag+‐centre has Oh‐symmetry. The results can be understood qualitatively by considering the Ag+Cl6−‐complex in terms of MO theory.
Susceptibility Measurements and the Magnetocrystalline Anisotropy of Polycrystalline Ferromagnetic Films
Authors: Leaver K. D. , Prutton M. , West F. G.
Published: July 2007

This paper reports a comparison of observations of the transverse susceptibility with some ripple theories due to a number of authors. A very wide range of films was investigated. It is demonstrated that these theories are qualitatively successful in relating macroscopic magnetic observables to single crystal magneto‐crystalline and magneto‐elastic effects. However, quantitative comparisons require unreasonably large values of magneto‐crystalline anisotropy K1 to fit the observations in cases where magneto‐elastic effects should be negligible. Better fits to the observations and more reasonable values of K1 are obtained for a ripple field theory of the type described by Feldtkeller, but in which the power of the field dependence of the susceptibility is allowed to vary for different films. Such behaviour is consistent with a two‐component model of the magnetization ripple, the properties of which are briefly outlined.
Effects of Liquid Metalls on the Fracture Strength of Germanium
Authors: Pugh E. N. , Westwood A. R. C. , Hitch T. T.
Published: July 2007

A study has been made of the effects of certain liquid metals from Groups II to Von the fracture strength of germanium monocrystals tested in three‐point bending over the temperature range 30 to 680 °C. At low temperatures, when the behavior of the solid is purely brittle, the presence of liquid metals causes marked reductions in fracture stress. These are attributed to the notch effect of etch pits produced by the liquid metals. At higher temperatures, when the significant increase in ductility reduces the effect of such notches, true liquid‐metal embrittlement phenomena are observed. Possible correlations between the degree of liquid‐metal embrittlement and the properties of the individual liquid metals are discussed.
The Interaction of Microwave Phonons with Irradiation Centres in Quartz
Authors: Lewis M. F. , Rosenberg H. M. , Wigmore J. K.
Published: July 2007

The electron spin resonance spectrum of the paramagnetic centres produced by the X‐irradiation of quartz has been investigated at 1.8 °K at 10 GHz from well below to above the microwave saturation region. Hypersonics at 10 GHz were then introduced and this reduced the resonance signal. The effect has been studied as a function of hypersonic power and frequency, microwave monitoring power and magnetic field orientation. The experimental results suggest that the spin‐lattice relaxation time is of the order of 6 s at 1.8 °K and is determined by cross relaxation processes.
Simultaneous Diffusion of Argon and Krypton in Single Crystals of KCl‐RbCl
Authors: Schmeling P. , Schroerschwarz R.
Published: July 2007

The simultaneous diffusion of Ar41 and Kr85m into single crystals containing 30 mole percent of KCl and 70 mole percent of RbCl is studied. The rare‐gases are created by irradiation with fast neutrons. The diffusion kinetics are similar to those of the systems KCl/Ar and RbCl/Kr. The interesting high temperature region is characterized by activation energies of (0.28 ± 0.035) eV and (0.56 ± 0.035) eV for KCl—RbCl/Ar and KCl—RbCl/Kr, respectively. The diffusion coefficients of argon are about one order of magnitude higher than those of krypton. Comparison with experiments performed after irradiation to high neutron doses shows that these values are not affected by radiation damage.
Plasma‐Type Oscillations of Kinked Dislocations
Authors: Alefeld G.
Published: July 2007

The oscillation frequencies of interacting kinks of both signs have been determined taking into account long range interaction between kinks. The frequencies are proportional to the square root of the sum of positive and negative kink densities and are consequently temperature dependent, in contrast to the frequencies of the dislocation string model. The temperature dependence of the relaxation time for the phonon scattering peak is therefore determined not only by the temperature dependence of the damping constant B but also by that of the kink densities.
Injektionsbestimmte Defektelektronenströme in Anthracenkristallen
Authors: Riehl N. , Becker G. , Bässler H.
Published: July 2007

In Anthracenkristallen (Harshaw) wurden Dunkelströme parallel zur ab‐Ebene gemessen. Die Kontaktierung erfolgte mit Leitsilber. Eine spezielle Anordnung gestattete die Variierung der Elektrodentemperatur unabhängig von der Temperatur des Kristallvolumens. Es zeigte sich, daß der stationäre Kristallstrom nur von der Temperatur der Anode abhängt. Die zugehörige Aktivierungsenergie beträgt 0,7 eV. Die Injektion von Defektelektronen muß daher geschwindigkeitsbestimmend für den Leitungsmechanismus sein. Sättigungsverhalten wurde nicht beobachtet, da die Injektionsrate angenähert proportional der Feldstärke anwächst. Der Strom ist unabhängig von der Driftgeschwindigkeit der Ladungsträger, so daß Einfang‐ und Ausheizeffekte, die von der Lage des Fermi‐Niveaus für Löcher abhängen, keine Rolle spielen. Schließlich wird gezeigt, daß wahrscheinlich alle früher gemessenen Dunkelströme in Anthracen injektionsbestimmt waren.
Kristallbaufehler beim epitaxialen Wachstum von Silizium auf Magnesium–Aluminium‐Spinell
Authors: Schlötterer H. , Zaminer Ch.
Published: July 2007

Bis zu 30 μm dicke Siliziumschichten, die durch thermische Zersetzung von SiCl4 bei ca. 1200 °C in Wasserstoffatmosphäre auf synthetischen Spinelleinkristallen epitaxial abgeschieden worden waren, konnten mit Hilfe der Methode der Ionenätzung bis auf eine Dicke von 0,1 bis 0,5 μm abgetragen werden. Diese gedünnten Schichten ließen sich im Elektronenmikroskop durchstrahlen und untersuchen. Dabei zeigte sich, daß im auf solche Weise hergestellten Silizium verschiedene Arten von Kristallbaufehlern enthalten sind, nämlich viele primäre Wachstumszwillinge und Versetzungen, gelegentlich auch sekundäre Wachstumszwillinge und Tripyramiden. Der kristallographische Nachweis der Zwillingsnatur geschah durch Kombination von Elektronen‐Feinbereichsbeugung und elektronenmikroskopischer Dunkelfeldabbildung. Der Einfluß der Kristallstörungen auf die elektrischen Eigenschaften der Siliziumschichten wird diskutiert.
Antiferromagnetic Structure of Uranium Diphosphide
Authors: Troć R. , Leciejewicz J. , Ciszewski R.
Published: July 2007

The antiferromagnetic structure of tetragonal UP2 below the Néel temperature (203 °K) is determined by neutron diffraction with polycrystalline samples. The magnetic unit cell is twice the size of the chemical one along the c‐axis. The magnetic structure consists of ferromagnetic sheets of uranium stacked along the c‐axis in the order + − − +. The magnetic moments of the uranium are parallel to the c‐axis; their magnitude is (1.0 ± 0.1) BM.
Zur Analyse des Ummagnetisierungsprozesses von Strontiumferritmagneten
Authors: Heinecke U. , Müller H.‐G.
Published: July 2007

Ein Vergleich der drei von Wohlfarth angegebenen Remanenzarten, gemessen an anisotropen Strontiumferritmagneten mit Magnetisierungskoerzitivfeldstärkewerten von 2800 Oe zeigt, daß die umgerechneten Kurven große Abweichungen voneinander aufweisen. Es wird ein sukzessives Verfahren zur Analyse der inneren Schleifen angegeben, mit dem diese Abweichungen einmal im Prinzip auf die von Kooy und Enz bekannten Magnetisierungsschleifen von Bariumferriteinkristallen und zum anderen auf eine positive Wechselwirkung zwischen den einzelnen Kristalliten zurückgeführt werden können. Bei der Deutung der Ergebnisse werden die reversiblen Magnetisierungsänderungen mit berücksichtigt.
Electromechanical Effect in Semi‐Metals
Authors: Upit G. P. , Varchenya S. A. , Spalvin I. P.
Published: July 2007

The electromechanical effect representing a decrease of microhardness of the surface layer due to an electric field applied between the sample and the indenter is observed in the semimetals antimony and bismuth. The dependence of the magnitude of this effect upon load, electric field intensity and indenter orientation is investigated. The inconsistencies of the concepts regarding the mechanism of the photomechanical and electromechanical effects are discussed. An attempt is made to explain the effects on a common basis. It is suggested that an increase in the mobility of dislocations which appear on the surface is caused by a change of surface energy or bond metallization in a surface layer.
Modèle cristallochimique des semiconducteurs magnétiques
Authors: Suchet J. P.
Published: July 2007

La 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

Die 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

Die 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

A 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

From 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

A 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

Single 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

The 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

The 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

Es 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

A 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

Es 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

The 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

During 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

The 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

The 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

Nous 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

Des 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

The 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

The 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

A 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

A 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.