bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural and Magnetic Studies of Amorphous and Icosahedral Al65Cr10Fe10Ge15 Synthesized through Mechanical Alloying
Authors: Bahadur D. , Singh K. , Srivastava C. M. , Ivanov E. 
Published: July 2007

AbstractThe mechanical alloying is used to synthesize the amorphous powder of the nominal composition Al65Cr10Fe10Ge15. On the basis of DTA studies, the compound is heat treated at 530 K. The X‐ray diffraction of the heat treated phase can be indexed to icosahedral indices. The magnetic susceptibility measurement particularly exhibits some interesting features. A qualitative explanation based on the competition between on‐site Coulomb repulsion, which favours local moment formation and the s‐d interaction that leads to itinerancy, is attempted which is found to be well correlated with the structural disorder in the system.
Could the Oxygen Vacancy in Oxides of the Perovskite Family Be a Dipole Center?
Authors: Prosandeyev S. A. , Osipenko I. A. 
Published: July 2007

AbstractThe lattice polarization in oxides of the perovskite family is demonstrated to give rise to symmetry breaking of one‐electron orbitals at F centers. This can provide an explanation of recent experiments on paraelectric KTaO3 where, by the second harmonic generation method, approximately 1018 cm−3 dipole centers were found, the concentration of which depends on reduction and oxidation processes.
Temperature Dependent Elastic and Lattice Dynamical Behaviour of Solids. An Effective Approach
Authors: Saxena S. K. , Agrawal R. M. , Rathore R. P. S. 
Published: July 2007

AbstractAn effective approach in terms of core and ionic radii is developed to study the form factor, energy wave number characteristics, phonon frequencies, and elastic constants of some scarcely studied transition metals, i.e. b.c.c. zirconium and b.c.c. titanium. The radial and tangential force constants extending up to 15th neighbours are computed for these metals. A reasonably good agreement between the computed and experimental findings on phonon dispersion and elastic constants is obtained.
The Ionicity Character Seen by the Charge Density in Copper Halides
Authors: Zaoui A. , Ferhat M. , Certier M. , Soltani M. , Khelifa B. 
Published: July 2007

AbstractThe electronic charge densities of copper halides CuX (X = Cl, Br, I) are calculated using the nonlocal empirical pseudopotential method in order to obtain their ionicities. The resulting ionicity values are compared with those of the Phillips scale. A favorable agreement is found.
Influence of Temperature on Magnetophonon Resonances in Four‐Component Solid Solution of ZnxCdyHg1−x−yTe
Authors: Sheregii E. M. , Polit J. , Cebulski J. , Andrukhiv A. M. 
Published: July 2007

AbstractThe influence of temperature on oscillations of the transverse magnetoresistance of ZnxCdyHg1−x−yTe (x = 0.08, y = 0.11) in the range 77 to 200 K and under magnetic fields of up to 2.5 T is studied. It is shown that the structure of the observed oscillations cannot be interpreted by participation of one kind of phonons only in magnetophonon resonance. The interpretation of experimental peaks with the help of magnetophonon resonances at different phonon frequencies describing the different sublattices of the solid solution (HgTe‐like, CdTe‐like, ZnTe‐like) is given.
Magnetic Excitation in Peierls‐Hubbard Model
Authors: Chen Bin , Yu Chaofan , Fang Hui , Jiao Zhengkuan , Zhang Qirui 
Published: July 2007

AbstractBased on the Peierls‐Hubbard Hamiltonian, the influence of electron‐phonon interaction on the spin excitation of itinerant systems has been analyzed. It is shown that the interaction not only changes the dynamic response properties, but also decreases the gap between two spin subbands, which makes the electron‐hole pairs easy to be excited singly. It should be emphasized that the spin excitation spectrum has an energy gap due to the presence of the electron‐phonon interaction mentioned above.
Optical Properties of Interband Transitions in the Oxygen‐Plasma‐Anodised Film on Gallium Arsenide 〈100〉
Authors: Xu Xiao‐Liang , Zhu Li‐Xin , Chen T. P. , Fung S. 
Published: July 2007

AbstractA first study of optical emission and excitation properties from interband transitions in an oxygen‐plasma‐anodised (OPA) film on GaAs 〈100〉 is reported. Six optical emission (EM) structures ranging from 2.83 to 4.60 eV are observed using cathodoluminescence (CL) and photoluminescence (PL) methods. The PL excitation spectra (EX) obtained have also demonstrated that the nine absorption transitions are related to the EM bands.
Nanostructures and Semiconductor Electronics
Authors: Lüth H. 
Published: July 2007

AbstractIn a short introduction limitations of present semiconductor microelectronics are discussed. At the beginning of the next century both technological and physical limits will severely affect further miniaturisation of integrated circuits (IC) into the deep submicron, i.e. below 100nm feature size range. Several novel device concepts being based on the use of quantum effects in nanostructures are discussed which might open new pathways to faster, lower consumption, and more compact semiconductor ICs: Resonant tunneling structures might play an important role as multifunctional devices which allow the integration of more complex logical functions in one and the same device under more relaxed lithography conditions. A further approach in quantum electronics is focussed on electron interference in high mobility two‐dimensional electron gases (2DEG) at semiconductor heterointerfaces. Novel processor concepts might be possible by use of quantum dot arrangements and single electron tunneling. The underlying physics is explained and several experimental approaches for the realisation of quantum dots and wires are presented.
Scattering of Small Molecules at Surfaces
Authors: Heiland W. , Schlathölter T. , Vicanek M. 
Published: July 2007

AbstractThe interaction of energetic molecules with surfaces is of interest for nuclear fusion experiments, for the erosion of space vehicles, and for the understanding of basic charge exchange phenomena between metal surfaces and molecules. For the latter reason experiments with hyperthermal molecules are also of interest for catalytic processes and for the functioning of solid state sensors. In many cases the interaction of molecules with surfaces is governed by charge exchange processes. An obvious case is the catalytic oxidation of CO at surfaces where a negative carbon dioxide species is identified as an intermediate of the reaction. Negative carbon dioxide species are also found in beam experiments. Their yield and the correlated dissociation probabilities show the expected dependencies on e.g. the coverage of the metal with alkali metal layers. In the case of hydrogen molecules the influence of alkali layers is quite different. In chemisorption experiments alkalis cause a decrease of the dissociative chemisorption of hydrogen. In our beam experiments an increase of the molecular survival with alkali coverage is found accordingly. The interpretation of the findings gives more detailed insight into the dissociation mechanisms of small molecules.
Building Nanostructures by Controlled Manipulation of Single Atoms and Molecules with the Scanning Tunneling Microscope
Authors: Meyer G. , Neu B. , Rieder K.‐H. 
Published: July 2007

AbstractOur present experiences in manipulating single atoms and molecules on solid surfaces by using the tip of a scanning tunneling microscope (STM) are reviewed. The construction and performance characteristics of our temperature variable STM is shortly described, which allows investigations in the temperature range between 15 and 300 K. As example for horizontal manipulation, in which the adatoms or admolecules are pulled along the surface by the STM tip, and the formation of man‐made surface structures, the formation of the letters ‘F’ and ‘U’, which form the logo of our university is presented. The adspecies used in these experiments are CO molecules and the substrate a Cu(211) surface. An example of vertical manipulation, in which an adparticle is picked up by the tip, carried to another place and released back to the surface, concerns Xe on the same substrate. The latter technique allows also to vary the chemical composition of the tip apex in a well‐defined manner. Consequences in imaging the surface with tips of different compositions are presented and discussed. Finally, STM observations of ordered high density phases of CO on the Cu(211) substrate are discussed.
Ultrathin Films of F.C.C. (001) Co and Cu: Electronic Structure, Photoemission, and Magnetic Dichroism
Authors: Henk J. , Scheunemann T. , Halilov S. V. , Feder R. 
Published: July 2007

AbstractA relativistic Green function theory of the layer‐KKR type has been applied to calculate the electronic structure and its manifestation in valence‐band photoemission of ferromagnetic layer systems of the form Co/Cu/Co(001) and Cu/Co/Cu(001). The spin‐ and layer‐resolved density of states in Co films of one to ten monolayers on Cu(001) is almost mirror symmetric with respect to the central Co plane. For Cu films on Co(001), minority spin “quantum well states” have constant weights in the Cu monolayers and a stronger weight in the first Co monolayer. For all systems, spin‐resolved photoemission spectra mostly reflect the spin character of the initial states with modifications by spin‐orbit coupling. As a consequence, the spin‐averaged photocurrent by p‐polarized light from films with in‐plane magnetization shows a pronounced dependence on the magnetization direction, i.e. magnetic linear dichroism. For perpendicular magnetization, circularly polarized light produces sizeable magnetic circular dichroism in photoemission.
Characterization of Metal Alloy Systems by Scanning Tunneling Microscopy and Low‐Energy Ion Backscattering
Authors: Niehus H. 
Published: July 2007

AbstractLow‐energy ion backscattering and scanning tunneling microscopy (STM) can be used in combination to study the surface crystallography of single crystals, in particular also for alloy and ordered intermetallic compound systems. The elemental composition as well as the location of the atoms is determined by low‐energy noble gas impact collision ion scattering spectroscopy with neutral detection (NICISS). Microscopic information on an atomic scale is obtained with the help of STM. The influence of adsorption‐induced surface modifications is investigated at Cu3Au and compared with Cu surfaces. From the NICISS investigation the AuCu termination is inferred for clean Cu3Au(100) and (110). After careful preparation of the clean Cu3Au(110) surface the prominent (2 × 1) LEED superstructure changes into a pronounced (4 × 1) LEED pattern. The (4 × 1) structure can be explaining by row pairing of CuCu and AuAu rows in the topmost layer. Upon oxygen exposure of the Cu3Au compounds, Cu tends to segregate to the surface. In case of Cu3Au(110) a (2 × 1)O superstructure appears which is in part similar to the known added row structure obtained for Cu(110)(2 × 1)O. Comparison with the Cu(110)O surface shows, however, that the known periodically ordered structure of CuO stripes at undersaturation with oxygen does not show up at Cu3Au(110)‐O.
Characterization of Supported Catalyst Systems with Surface Spectroscopies
Authors: Taglauer E. , Knözinger H. 
Published: July 2007

AbstractSupported catalysts of transition metals and their oxides are widely used for a variety of reactions. They typically consist of a high surface area oxide as support material (e.g. Al2O3, TiO2, SiO2) and finely dispersed metal or metal oxide particles (e.g. Rh, MoO3, V2O5) as active components (or their precursor) and promoters. The catalytic properties are determined by these components, their structural arrangement, and their interactions. Studies of real and model catalyst systems are reported for which low‐energy ion scattering (LEIS) is used in combination with other spectroscopies, such as RBS, AES, TDS, XPS, and Raman spectroscopy. The applicability of these techniques to real systems and the relevance of model catalysts is discussed. The results shown demonstrate the usefulness of these spectroscopies for the characterization of supported catalysts, in particular for the analysis of the composition and the arrangement of the topmost atomic layers. Among the examples given are special aspects of catalyst impregnation, the investigation of solid‐solid wetting which may be relevant to catalyst preparation and strong metal‐support interactions (SMSI effect) in supported Rh metal catalysts.Übergangsmetalle und ihre Oxide werden in Trägerkatalysatoren für eine große Zahl von Reaktionen verwendet. Sie bestehen typisch aus einem Oxid mit großer spezifischer Oberfläche als Trägermaterial (z. B. Al2O3, TiO2, SiO2) und fein verteiltem Metall oder Metalloxid als aktiver Komponente (z. B. Rh, MoO3, V2O5) oder deren Vorläufer und als Promotoren. Die Eigenschaften des Katalysators (Aktivität, Selektivität) werden von diesen Komponenten. ihrer strukturellen Anordnung und ihrer chemischen Wechselwirkung bestimmt. Es werden Untersuchungen an Real‐ und Modellkatalysatoren dargestellt, für die die Niederenergie‐Ionenstreuung in Kombination mit anderen Spektroskopien wie RBS, AES, TDS, XPS und Ramanspektroskopie verwendet werden. Die Ergebnisse demonstrieren die Nützlichkeit dieser Methoden für die Charakterisierung von Trägerkatalysatoren, insbesondere für die Analyse der Zusammensetzung und geometrischen Anordnung der obersten Atomlagen. Die angeführten Beispiele betreffen spezielle Aspekte der Imprägnierung, die Untersuchung von Festkörper‐Fest‐körper‐Benetzung als einer Möglichkeit der Präparation von Katalysatoren und die sogenannte starke Metall‐Träger‐Wechselwirkung am Beispiel von getragenen Rh‐Modellkatalysatoren.
High‐Resolution Auger Spectroscopy Applied to Metals and Alloys
Authors: Kleiman G. G. 
Published: July 2007

AbstractAuger electron spectroscopy (AES) is fundamentally a spectroscopy of excited states, so that the resulting information is complementary to that from X‐ray photoelectron spectroscopy (XPS). Consequently, high‐resolution AES has received a great deal of theoretical and experimental attention in recent years. In metals and their alloys, much of the interest has involved valence band spectra, which are explained in terms of the quasi‐atomic model of final‐state screening, especially in closed d‐shell metals, such as Cu and Ag. In open shell metals, such as Ni and Pd, however, the shapes of the valence band spectra are often ambiguous. Core level spectra, which might reduce uncertainties, are often complex and not readily interpretable. It is shown that the high‐energy LMM spectra of the 4d metals and their alloys are sufficiently simple in form and narrow to permit unambiguous comparisons with quasi‐atomic theories. The exploitation of the experimental systematics of the LMM Auger parameter elucidates screening mechanisms as well as the nature of d‐band holes and the extension of the analysis to the 3d and 5d metals indicates similar results. Application to metallic alloys clarifies the electronic structure changes; examples of Pd‐based alloys are presented. Consideration of the lineshapes of these spectra reveals a satellite structure which can, with considerable certainty, be identified with shake‐up processes associated with 4d‐band spectator vacancies.
Two‐Dimensional Growth of Si Grains inside Au Thin Films
Authors: Pasa Pasa A. A. , Losch W. , Bauer G. H. 
Published: July 2007

AbstractThe growth of Si grains inside Au thin films is studied in the Au/aSi: H bilayer system. The crystallization process is promoted at low temperatures and the samples are characterized by scanning electron microscopy (SEM) and in‐situ electrical measurements. SEM micrographs obtained on samples submitted to isothermal treatment show the appearance of Si grains on the Au thin film surface. The number of nuclei did not change during the reaction and the crystallized area shows a quadratic dependence on the treatment time, a typical behavior of an interface‐limited crystallization process. The electrical measurements allowed monitoring the crystallization process and the determination of the growth parameter n varying between 1.9 and 2.6. Comparison between the two techniques permits us to conclude that the Si grains grow two‐dimensionally inside the Au thin film.
Anharmonicity, weak localization, and reciprocal length of ultrasound attenuation
Authors: Zhernov A. P. , Chulkin E. P. 
Published: July 2007

AbstractProceeding from the concepts of localization processes in anharmonic lattices with impurity quasi‐local excitations (resonance localized scattering centers) universal anomalies in the temperature dependences of the reciprocal length of ultrasound attenuation in amorphous systems are described within the temperature range where a plateau in thermal conductivity is observable. A probability of the manifestation of the localization process in quantum crystals is also discussed.
Effect of Quantum confinement on impurity hopping in quantum wells
Authors: Keiper R. , Wang W. , Zvyagin I. P. 
Published: July 2007

AbstractThe problem of evaluation of the impurity hopping conductance in quantum wells is discussed, taking account of the impurity position‐dependent shifts of the binding energies and the variation of the localization radii. It is demonstrated that these effects give rise to a temperature dependence of the conductance of the form σ = σ0exp {−(T0/T)1/3}, where the parameter T0depends on the well width L. Numerical calculations using the variational principle show that this dependence is strong for strongly compensated samples in the region of L/a* ≦ 1, where a* is the effective Bohr radius.
Alternative analytical descriptions of the temperature dependence of the energy gap in cadmium sulfide
Authors: Pässler R. 
Published: July 2007

AbstractExperimental data available from published literature for the temperature dependence of the energy gap in CdS (A‐gap) are fitted numerically on the basis of four different analytical models. In analogy to earlier applications to many other semiconductor materials, the conventional models due to Varshni (1967) and Viña et al. (1984) are found here also for CdS to provide some rough fits of experimental data. A high‐precision fit is shown to be given by a novel analytical expression of the form \documentclass{article}\pagestyle{empty}\begin{document}$ E_{\rm g} (T) = E_g (0) - (a/2)(\sqrt {(2)^p + \theta ^p - \theta),} $\end{document} where α is the familiar (limiting) gap shrinkage coefficient and θ tbond; ħω/k represents the effective phonon energy on temperature scale. The corresponding low‐temperature Tp‐power exponent p is found for CdS to be nearly equal to 2.5. Thus we are concerned with a fractional exponent whose magnitude is markedly larger than its conventional value of 2. The associated θ value of about 150 K suggests that the main contribution to the gap shrinkage effect in CdS should be due to acoustic phonons ranging energetically slightly below the middle of the total phonon energy spectrum.
Finite‐temperature ferromagnetism of f.c.c. cobalt
Authors: Vega A. , Nolting W. 
Published: July 2007

AbstractThe influence of electron correlations on the temperature dependent electronic structure of ferromagnetic f.c.c. cobalt is investigated by a many‐body evaluation of a generalized model of magnetism. The single‐particle part of the model‐Hamiltonian is taken from an LDA band structure calculation. The interaction part contains two parameters, an intraband Coulomb interaction U and an interband exchange J. With U = 3.5 eV and J = 0.3 eV the self‐consistent model solution yields a magnetic T = 0 moment of about 1.75μB and a Curie temperature of 1375 K. The magnetic behaviour finds a conclusive microscopic explanation by the temperature and density dependent quasiparticle density of states. Typical differences as well as common features in the electronic structures of Fe, Co, and Ni are worked out. Contrary to Ni, no satellite appears in Fe and Co.
Linear optical properties of the dopyballs C60−nXn (X = B or N; n = 1, 2)
Authors: Xu Qiang , Jiang Jie , Dong Jinming , Xing D. Y. 
Published: July 2007

AbstractThe linear optical absorption of dopyballs C60−nXn (X = B or N; n = 1, 2) is studied using the extended Su‐Schrieffer‐Heeger model and the sum‐over‐states approach. Comparing the calculated results C60−nXn with those of C60, it is shown that the substitutional doping of impurity atoms (B or N) can greatly change the optical properties of the c60 system. Many absorption peaks due to substitutional doping appear in the low frequency region. In particular, a remarkable peak is found at the low frequency end in C58X2 (1,60) isomers.
Dielectric function and plasmon excitations in silver
Authors: Fehrenbach G. M. , Bross H. 
Published: July 2007

AbstractThe microscopic dielectric function of silver is investigated in the framework of the time‐dependent density‐functional theory underlying a spline augmented plane‐wave band calculation. A reasonable overall agreement is found when comparing our results with experimental data. Small systematic errors in the position of the peaks can be ascribed to the local density approximation. It is shown that in the long‐wave limit a zero of the diagonal element corresponds to a plasmon excitation. The frequency of the q = 0 plasmon excitation agrees quite well with its experimental value. No plasmon excitation can be found even for small values of the propagation vector.
Structure of YBaSiON glasses by neutron diffraction
Authors: Jin J. S. , Kozuka H. , Yoko T. , Fukunaga T. 
Published: July 2007

AbstractThe structure of YBaSiON glasses is investigated by neutron diffraction, and their physical and chemical properties are measured. It is found from the analysis of the radial distribution functions that nitrogen atoms exist as a mixture of two‐coordinated and three‐coordinated states in the glass, and the ratio of the three‐ to the two‐coordinated nitrogens decreases as the nitrogen content increases. The relationship between structure and properties is also discussed.
Cu2(1−z)MnzGa2Se4 alloys: Phase diagram and effects of Mn ordering on magnetic behaviour
Authors: Quintero M. , Lopez M. , Morocoima M. , Rivero A. , Bocaranda P. , Woolley J. C. , Lamarche G. , Re R. Brundel 
Published: July 2007

AbstractX‐ray powder diffraction, differential thermal analysis, and magnetic susceptibility measurements on polycrystalline samples are used to determine the details of the T(z) phase diagram of the alloy system Cu2(1−z)MnzGa2Se4. At high temperatures, there is a single phase solid solution across the complete diagram in a disordered zincblende phase. However, at lower temperatures, the singlephase range is limited to relatively wide terminal fields, which are ordered structures based on a zincblende subcell. Several different ordered phases are found to occur and the values of the Curie‐Weiss constant θ are used to investigate the changes in ordering with composition. It is shown that these ordering changes cause discontinuous changes in the slope of the graphs against composition of the lattice parameters, optical energy gap, and Néel temperature values.
Surface thermal stability of nickel clusters
Authors: Chen Xiaoshuang , Zhao Jijun , Sun Qiang , Liu Fengqi , Wang Guanghou , Shen Xue Chu 
Published: July 2007

AbstractOverall and surface melting of NiN clusters have been studied using Monte Carlo simulation and effective interaction model potential. Physical quantities such as internal energy per atom, specific heat, and bond length fluctuations are calculated as a function of temperature to illustrate overall and surface thermal softening of these clusters. It is found that the surface melting temperature is lower than the overall melting temperature for a Ni cluster of certain size. The results show that the surface and core atoms play different roles in the melting process. The recent experimental observations about metal cluster melting might be explained by using surface melting arising from the surface atom disorder first appearing due to an increase of temperature.