bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical Properties of Titanium‐Doped Sb2Te3Single Crystals
Authors: Drašar Č. , Lošťák P. , Navrátil J. , Černohorský T. , Mach V. 
Published: July 2007

AbstractThe reflectance and the transmittance spectra in the IR region are measured on Ti‐doped Sb2Te3single crystal samples grown by a modified Bridgman technique. The plasma resonance frequency, the optical relaxation time, and the high‐frequency dielectric constant are determined by fitting the Drude‐Zener formulas to the reflectance spectra. It is found that Ti impurities in Sb2Te3behave as donors. The transmittance spectra are used for the determination of the dependence of the absorption coefficientKon the energy of incident photons. The optical width of the energy gap is found to decrease with increasing Ti content. The values of the exponent α from the relation ofK∼ λαfor the long‐wavelength absorption edge range within the interval of 1.8 to 2.2, i.e. the dominant scattering mechanism of free current carriers in Sb2Te3crystals doped with Ti atoms is the scattering by acoustic phonons.
Mechanical Relaxation of Linear Viscoelastic Materials Described by the Modified Anelastic Element
Authors: Povolo F. , Hermida Élida B. 
Published: July 2007

AbstractThe stress relaxation and creep in amorphous materials, the dielectric relaxation in conducting polymers, the spin relaxation in spin‐glasses, are examples of processes described by the mathematical formalism of the theory of linear viscoelasticity. This description, given by a spectrum or distribution function, allows to express the temporal evolution of the relaxation through integral transformations. In many cases, however, this evolution is given directly using the empirical expression exp [—;(t/τ)γ], known as fractional exponential behaviour, where τ is a characteristic relaxation time and γ is a constant (0 < γ ≦ 1). It is shown that this empirical expression can be derived from the modified anelastic element (MAE) whose relaxation time depends on the time of the quasistatic test. From this dependence the spectrum for the MAE is calculated and correlated with the log—normal distribution. A novel procedure to calculate the parameters of the MAE is presented and applied to stress relaxation curves.
Polarized XANES Studies of Cu L3 Edges of Bi‐2212 Superconducting Single Crystals Using Total and Fluorescence Yield Techniques
Authors: Venkatesh S. , Srivastava P. , Saini N. L. , Garg K. B. , Studer F. , Ruyter A. , Menovsky A. , Ohkubo H. , Akinaga M. 
Published: July 2007

AbstractXANES with polarized synchrotron light is now established to be one of the important techniques for the study of the electronic structure of high‐Tc superconductors in order to find out the symmetry of holes and their implication to the theoretical models proposed to explain superconductivity in these cuprates. The XANES spectra are measured by two methods in the soft X‐ray region, namely, total yield (TY) and fluorescence yield (FY) methods, which give different results with respect to out‐of‐plane Cu 3d(z2) symmetric holes. The reason of this discrepancy is not quite clear. Polarized XANES measurements on Bi‐2212 single crystals at the Cu L3 edge by the TY and FY methods are reported and the results are discussed in detail.
Exchange Integrals and Magnetic Properties of Mixed Chromium Spinel Systems: Zn1−xAxCr2X4 (A = Cd, Hg and X  S, Se)
Authors: Hamedoun M. , Zerhouni A. , Rachadi A. , Slimani M. , Benyoussef A. 
Published: July 2007

AbstractA lot of magnetic measurements are accomplished in order to improve the phase diagrams of the systems Zn1‐xCdxCr2S4 and Zn1‐xCdxCr2Se4 particularly in the region of intermediate concentrations with mixed structure. The exchange integrals for the first and second coordination spheres (J and K) are calculated in terms of dilution for the three systems Zn1‐xCdxCr2Se4, Zn1‐xCdxCr2Se4, and Zn1‐xHgxCr2Se4. The evolution of the structure and the magnetic properties with the substitution of diamagnetic ions at tetrahedral sites is the result of the competition between the ferromagnetic and antiferromagnetic interactions. Besides, the magnetic properties are compared with the phase diagrams (T, x) of these systems. Because of its complicated antiferromagnetic structure, the sulfur compound seems to have particular characteristics among the mixed spinel systems.
Nanostructure of the Surface and Interface and Mechanisms of Thermal Growth of Ultrathin Films of Si3N4 on Si(001)
Authors: Baumvol I. J. R. , Stedile F. C. 
Published: July 2007

AbstractThe chemical situation of the Si atoms at the surface of Si3N4 ultrathin films thermally grown onto Si(001) substrates 2 × 1 reconstructed in a NH3 atmosphere has been recently studied in detail by core‐level spectroscopy using synchrotron radiation, as well as the chemical situation of the Si atoms at the film/substrate interface. The Si atoms at the surface are assigned to be either bonded to N atoms that are located in the layer just below the surface and having one dangling bond, or terminated by NH2. The Si atoms at the interface present intermediate oxidation states. Also recently high resolution isotopic tracing studies of N and H showed that nitrogeneous species (most probably NHx radicals, x < 3) are mobile during thermal growth of silicon nitride films, while isotopic tracing of Si showed that this species appears to be immobile during growth. This newly built experimental scenario for the nanostructure of the surface and interface, and for the atomic transport processes taking place during nitride growth, led us to develop a model for the mechanism of thermal growth of Si3N4 ultra‐thin films on Si(100), that is capable to explain the self‐limited character which makes them extremely attractive for applications in the VLSI and ULSI technologies for microfabrication of silicon devices.
Metal Oxide Surfaces: Electronic Structure and Molecular Adsorption
Authors: Freund H.‐J. 
Published: July 2007

AbstractThe surface science of oxides has received considerably less attention than the study of metal surfaces. We review some of our work on structural characterization and electronic structure investigations on oxide surfaces which we prepare as thin oxide films on metallic substrates. This preparation method leads to certain experimental advantages concerning the application of electron spectroscopies on such systems. We discuss molecular adsorption on non‐polar and polar surfaces of clean oxides. The influence of metal deposition onto the oxide surfaces and on their properties with respect to adsorption is described. Light induced processes with full quantum state detection of desorbing molecules are addressed. The possibility of studying dynamic processes in adsorbates on oxides via electron spin resonance spectroscopy is evaluated.
Surface Modification by Metal Deposition
Authors: Oster K. , Schmidt M. , Nohlen M. , Radnik J. , Wandelt K. 
Published: July 2007

AbstractThe adsorption of metal films is a promising way to modify the physical and chemical properties of substrate surfaces. In the present work several aspects such as growth structure, electronic properties, surface alloy formation and adsorption behavior of such films is discussed on the basis of LEED, ARUPS, PAX, ΔΦ, and TDS results for the deposition of Cu on different Pt surfaces. In a first part results on the growth of multilayer films of Cu on Pt(111) obtained by dynamical work function measurements are presented. Intermediate coadsorption of oxygen on a previously deposited Cu film of 2 ML leads to oscillatory work function changes during further Cu deposition. This behavior is discussed in terms of a growth model which considers the influence of surface morphology via the Smoluchowski effect. On the reconstructed Pt(100) surface the deposition of Cu at 300 K leads to a lifting of the reconstruction in the Cu‐covered areas, while the Cu‐free part of the surface stays reconstructed. This is in agreement with results of Au/Pt(100) and Ag/Pt(100), but in the case of Cu/Pt(100) strain minimization cannot be the only reason for this restructuring so that additional electronic effects must be taken into account. For multilayer Cu deposited on Pt(100) the segregation of Pt leads to alloying and chemical ordering in the temperature range between 500 and 1000 K. Several phase transitions between disordered and ordered surface alloys can be found. Both, a Cu3Pt(100) and a “Cu5Pt3(100)” surface alloy are Cu terminated as detected by PAX, while after annealing to 1000 K the surface again consists only of Pt atoms in the reconstructed arrangement. As an example for modified chemical properties of metal films with respect to the bulk material adsorption experiments of molecular hydrogen on Cu/Pt(100) at 100 and 300 K are presented. In contrast to bulk Cu they show the capability to dissociate H2 for coverages of up to 10 ML Cu.
Study of Metal Coverage on Alumina from Group‐6 Metal Carbonyl Precursors
Authors: Baibich I. M. , Stedile F. C. , Baumvol I. J. R. , Dos Santos J. H. Z. , Santarosa V. E. 
Published: July 2007

AbstractThe metal loading on alumina surfaces from group‐6 metal (Cr, Mo, W) carbonyls and their derivatives is determined by Rutherford backscattering spectroscopy. The subcarbonyl species are generated by photochemical activation and monitored by Fourier transform‐infrared spectroscopy. No chemical adsorption takes place for the three systems studied. Nevertheless, in the presence of the ligand triphenylphosphine (PPh3) and the assistance of UV radiation, surface species chemically bonded to γ‐Al2O3 can be observed, achieving a maximum metal loading of 0.3% in the case of Cr and 0.4% in the case of W.Die metallische Sättigung von Alumina‐Oberflächen mit Metall‐(Cr, Mo, W)‐Carbonylen der Gruppe 6 wird mit RBS bestimmt. Die subcarbonylen Arten werden mit UV‐Strahlung erzeugt. Für die drei Systeme findet keine chemische Adsorption statt. Mit Triphenylphosphin als Ligand werden an der Oberfläche jedoch chemisch gebundene Carbonylarten beobachtet. Die maximale Sättigung beträgt 0.3% für Cr und 0.4% für W.
Study of RF Sputtered aSi: H and aGe: H by Photothermal Deflection Spectroscopy
Authors: Rovira P. I. , Alvarez F. 
Published: July 2007

AbstractThe effect of hydrogenation in radio‐frequency (rf) sputtered aSi: H and aGe: H films is studied. Photothermal deflection spectroscopy is used to study the evolution of the sample quality on hydrogen incorporation. The influence of the substrate temperature, target bias, and hydrogen partial pressure on the sub‐gap absorption coefficient and on the hydrogen incorporated in the films is reported.
Influence of the Deposition Conditions on the Properties of Amorphous Germanium Nitrogen Alloys
Authors: Vilcarromero J. , Marques F. C. 
Published: July 2007

AbstractA study of the band‐gap tailoring of amorphous germanium nitrogen alloys is presented. They have been prepared by the rf reactive sputtering technique, using a c‐Ge target in an Ar + NH3 atmosphere. The alloy composition is found to be strongly dependent on the deposition conditions. The optical gap of the material could be tailored from approximately 1.0 to about 3.0 eV by varying the rf power, substrate temperature, nitrogen and hydrogen partial pressures. The rf power, and not the gas composition, is found to be the most important parameter in determining the nitrogen concentration. The hydrogen concentration, on the other hand, has a small influence on the band gap, while the temperature plays an important role on the determination of the alloy structure.
Stress and Elastic Constants of Amorphous Germanium Nitrogen Alloys
Authors: Marques F. C. , Lacerda R. G. , Lima M. M. , Vilcarromero J. 
Published: July 2007

AbstractThermomechanical properties (stress, thermal expansion coefficient, and elastic modulus) of a‐GeNx: H thin films prepared by the rf sputtering technique are reported. Stress measurements are made using a Dektak profilometer to determine the radius of curvature of the film/substrate structure. The majority of the films prepared in this work have compressive stress. A second apparatus based on the deflection of a HeNe laser beam is used to determine the thermal expansion coefficient and the Young's modulus/(1‐Poisson's ratio) by the thermally induced bending method. They depend strongly on the nitrogen concentration.
Transport and optical properties of PbTe1−xSx (x = 0.02 and x = 0.05) mixed crystals
Authors: Miljković J. M. , Romčević N. , Popovic Z. V. , Köunig W. , Nikiforov V. N. 
Published: July 2007

AbstractFar‐infrared and Raman scattering spectra as well as galvanomagnetic measurements of PbTe1−xSx (x = 0.02 and 0.05) mixed crystals in the temperature range from 10 to 300 K are presented. The far‐infrared reflectivity spectra are analysed using a fitting procedure based on the plasmon‐phonon interaction model. Galvanomagnetic and far‐infrared measurements indicate the existence of a phase transition at about Tc = 60 K for x = 0.05, whereas for samples with x = 0.02 the phase transition is not observed. Also, it is found that the long‐wavelength optical phonon modes of these mixed crystals show a “two‐mode” behaviour.
Surface states in finite CdMnTe/CdTe superlattices
Authors: Diouri J. , Afif K. 
Published: July 2007

AbstractAnalytic equations are derived, giving both the envelope functions and the energies of electronic states for finite CdMnTe/CdTe superlattices with different boundary conditions and variable number of CdTe wells and periods of the superlattice. Calculations are performed in the effective mass approximation and transfer‐matrix formalism. The effects of superlattice dimensions and boundary conditions on the surface states as well as the conditions for their existence are presented and discussed.Des équations analytiques sont établies, donnant à la fois les fonctions enveloppes et les énergies des états électroniques dans les superréseaux finis CdMnTe/CdTe avec differentes conditions aux limites et pour un nombre variable des puits CdTe et de périodes du superréseau. Les calculs sont menés dans le cadre de I'approximation de la masse effective et du formalisme de matrice de transfert. Les effets des dimensions du superréseau et des conditions aux limites sur les états de surface aussi bien que leurs conditions d'existence sont présentés et discutés.
Inter‐Landau level tunneling in an InGaAs/AlAs/GaAs structure under tilted magnetic field
Authors: Gobato Y. Galvão , Berroir J. M. , Guldner Y. , Vinter B. , Nagle J. , Rivera P. H. 
Published: July 2007

AbstractMagneto‐tunneling studies in a high‐quality InGaAs/AlAs/GaAs triple well structure in a tilted magnetic field are reported. Well‐defined structures in the 1(V) characteristic in the resonance regime are observed which correspond to tunneling from Landau levels in the prewell into the midwell with non‐conservation of the Landau‐level index tunneling transitions. These tunneling transitions with Δn both positive and negative are observed for the first time in the resonant regime under tilted magnetic field. Finally, the results are shown to be in fair agreement with a coherent magneto‐tunneling model where the effect of the transverse component of the magnetic field is treated as a perturbation.
Exchange disorder band bending of the Cd1−xFexS diluted magnetic semiconductor
Authors: Chou W. C. , Kuo S. S. , Chen F. R. , Twardowski A. , Tworzydlo J. , Chen Y. F. 
Published: July 2007

AbstractThe energy of excitons A, B, and C of Cd1−xFexS (x < 0.02) is studied as a function of Fe concentration at T = 10 K in the absence of a magnetic field. The observed band bending effect (largest for exciton A) is attributed to the s, p‐d exchange interaction correction resulting from the exchange disorder.
Oxygen behavior in NiO
Authors: Kamal M. , Debza Y. , Hugel J. 
Published: July 2007

AbstractThe behavior of the 2p functions is studied in NiO within the local spin density approximation (LSDA) based on an LCAO representation. The ionicity is related to the spatial extension of the 2p orbitals and increases when the oxygen orbitals spread out. The corrected LSDA + U version enhances both the ionicity and the spin moment. As a result the intrasite Coulomb interaction U shrinks the d orbitals and extends the 2p functions.
Ordering in GaInP2 studied by optical spectroscopy
Authors: Ernst P. , Geng C. , Scholz F. , Schweizer H. 
Published: July 2007

AbstractThe optical properties of spontaneously ordered GaInP2 grown by MOVPE are studied by means of photoluminescence, time‐resolved photoluminescence, and polarization dependent photoluminescence excitation spectroscopy. Ordered samples grown on a substrate which is misoriented 6° toward [111]B show clear excitonic features both in luminescence and absorption. In excitation spectra both valence band edges are clearly resolved and are shown to be polarization dependent as predicted by band structure calculations. In these samples an additional non‐excitonic low‐energy photoluminescence emission is observed the peak energy of which depends strongly on excitation density and temperature and which shows extremely long luminescence lifetimes. A density of states model for ordered GaInP2 is proposed which allows to explain the results obtained in the last few years. The density of states model is discussed with respect to the microstructure of the ordered alloy as known from TEM investigations.
Deep UV emissions of ionic Cs2+F− states in Ne and Ar matrices
Authors: Sliwinski G. , Bressler Ch. , Schwentner N. 
Published: July 2007

AbstractPulsed electron beam excitation of 0.45 to 0.7% CsF doped in rare gas matrices at 5 K leads to emission bands at 196.5 nm (FWHM 9.6 nm) and 227 nm (FWHM 15 nm) in Ne and at 211.2 nm in Ar. The short‐wavelength bands are assigned to B2 → X2− transitions in the ionic Cs2+F− excimer on the basis of transition energies, lineshapes, and the efficiency of Cs2+F− ionization by energy transfer from the host. The long‐wavelength band in Ne corresponds to a C2II‐A2II transition. The 196.5 nm band provides a large cross section for stimulated emission of 2.5 × 10−16 cm2. The red shifts of 0.4 and 0.8 eV of the B → X emission in Ne and Ar, respectively, are discussed in terms of solvation of the Cs2+F− ion and of its dipole moment. Optimal concentrations are similar to those obtained for the gas phase.
Temperature and excitation dependent photoluminescence of undoped and nitrogen‐doped ZnSe epilayers
Authors: Gurskii A. L. , Gavrilenko A. N. , Lutsenko E. V. , Yablonskii G. P. , Taudt W. , Hamadeh H. , Wachtendorf B. , Söllner J. , Schmoranzer J. , Heuken M. 
Published: July 2007

AbstractThe photoluminescence (PL) properties of ZnSe epitaxial layers grown by metal‐organic vapor phase epitaxy are investigated. A correlation between the electron‐hole plasma (EHP) band position and the PL intensity is found and on this basis the nonequilibrium carrier lifetime τ and the PL efficiency η are estimated in the ZnSe layers: τ = 10−9 to 10−11 s, η = 0.1 to 0.001%. It is shown that these parameters decrease with decreasing layer thickness and with increasing concentration of contaminations and native defects. The influence of the excitation level and temperature on the intensity and peak position of the band at 472 nm in ZnSe: N and the band at 620 nm in undoped ZnSe epilayers at 78 K grown at temperatures of TD > 500 °C are studied. It is supposed that these bands are due to recombinations described in the configurational coordinate model.
Ag‐substituted AlCuFe icosahedral phases
Authors: Manaila R. , Macovei D. , Jianu A. , Popescu R. , Nicula R. , Zavaliche F. , Devenyi A. , Xie Y. , Hu T. 
Published: July 2007

AbstractThe gradual substitution of Cu by Ag in the Al62Cu25.5−xAgxFe12.5 icosahedral phase (x ≤ 10) is investigated by X‐ray diffraction from the viewpoint of the induced structural changes. The phonon and random phason disorders, estimated from diffraction linewidths, increase with x, the latter showing, however, an induction range of Ag concentrations. EXAFS results at the CuK and FeK edges show, for low Ag contents, and enhanced disorder in the first coordination sphere, partly relaxed for higher x values. The 6D hypercubic lattice parameter is found to be independent of the Ag content, despite the large diameter of monovalent Ag. The latter facts suggest a d‐sp hybridization of the Ag bonds to the surrounding Al, taking place above a certain x value.
Molecular motions and phase transitions in solid tris(n‐propylammonium) hexabromobismuthate (III)
Authors: Pislewski N. , Tritt‐Goc J. , Jakubas R. 
Published: July 2007

AbstractThe proton NMR second moment and spin‐lattice relaxation time for polycrystalline tris(n‐propylammonium) hexabromobismuthate (n‐C3H7NH3)3BiBr6 (nPBB) are measured from 70 to 290 K. The results are interpreted in terms of the methyl and ammonium group reorientations for which the activation parameters are determined. In addition linear thermal expansion measurements are carried out in the temperature range 270 to 295K. A distinct anomaly in the thermal dilation occurs at 281 K indicating a first‐order phase transition.
Lattice dynamics of bromotrifluoromethane
Authors: Zeng W. Y. , Anderson A. 
Published: July 2007

AbstractThe vibrations of crystalline bromotrifluoromethane at low temperatures are represented by a simple force constant model. Sixteen adjustable parameters (ten intermolecular and six intramolecular) are used to calculate the frequencies of twenty‐one lattice modes and thirty‐six components of internal modes, and good agreement with recent spectroscopic results is obtained. Principal intermolecular interactions, primarily between various pairs of halogen atoms, are identified and appear to be of the standard van der Waals type. As a result, intramolecular force constants are only slightly changed from their gas phase values.
The amorphous transverse spin‐3/2 ising model
Authors: El‐Atri A. , Ainane A. , Saber M. 
Published: July 2007

AbstractThe amorphization of the spin‐3/2 transverse Ising model on a cubic lattice (N = 6) is studied within the effective field theory. The total longitudinal and transverse moments are obtained. A number of interesting phenomena is found in these quantities, due to the fluctuation of exchange interactions and the applied transverse field.
MBE growth of cubic GaN on GaAs substrates
Authors: Yang H. , Brandt O. , Ploog K. 
Published: July 2007

AbstractWe review our recent results on plasma‐assisted molecular beam epitaxy of cubic GaN films on GaAs(001). The crucial role of the nucleation stage for obtaining epitaxial growth is highlighted by reflection high‐energy electron diffraction and transmission electron microscopy. For the subsequent growth, it is found that the surface stoichiometry determines the phase composition of the epilayers as determined by X‐ray reciprocal space mapping, Raman and cathodoluminescence spectroscopy. For an in situ control of the surface stoichiometry, we develop a method based on the transitions of the surface reconstructions of cubic (001)GaN. Films grown under conditions optimized by this method are single‐phase cubic and exhibit intense excitonic luminescence up to room temperature.
XRD investigations of WSiN and LaB6 layers on GaAs
Authors: Nebauer E. 
Published: July 2007

AbstractThe microstructures of WSiN and LaB6 thin layers (amorphous or crystalline) on GaAs substrates are studied in dependence on the deposition and annealing treatments by means of the TFXRD parallel‐beam technique. From the I(2θ) diffractograms the recrystallization behaviour of the sputtered a‐WSiN and a‐LaB6 layers can be especially investigated. These results are of relevance for the choice of suitable materials for diffusion barriers in contact systems.