bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effective Pair Interactions between Localised Defects Inside a CuO2 Plane in the Superconducting Copper Oxides
Authors: Germain Ph. , Labbé J. 
Published: July 2007

AbstractThe effective pair interaction potentials between localised defects inside a CuO2 plane are deduced from our calculated susceptibility of the clectron gas. The very peculiar shape of the Fermi line, which is perfectly square for a half‐filled band, leads to a strongly anisotropic interaction, changing from the expected two‐dimensional behaviour along the [1, 0] or [0, 1,] direction to a purely one‐dimensional one along the [1,1] or [1, 1] direction. Thus, the impurities in the CuO2 planes of the new superconductors are not independent since the range of their interactions can be much larger than in a usual two‐dimensional system. This could lead to superstructure effects. These results, applied to magnetic impurities, highly complicate the discussion of the frustration in a possible spin‐glass phase, since the interaction between two localised spins strongly depends on the considered direction.
Study of Molecular Motions in 2‐Adamantanone by Nuclear Magnetic Resonance
Authors: Decressain R. , Amoureux J. P. , Cochon E. 
Published: July 2007

AbstractThe temperature dependence of proton and carbon spin‐lattice relaxation rates in 2‐adamantanone is measured. The present experiments are analyzed in terms of relaxation resulting from intramolecular reorientation modulation of the spin‐spin interaction. In the plastic phase the molecular reorientations involve a superposition of uniaxial rotation and tumbling reorientation of the dipolar axis. The calculation of the corresponding autocorrelation function is made by using a Frenkel model. The resulting expression for T1 leads to a determination of the plastic phase residence times in good agreement with values previously deduced from quasi‐elastic neutron scattering and dielectric relaxation. In the low‐temperature phase the motions are completely frozen and T1 is rather constant.
Cluster Expansion for a Sublattice System with Unequal Coordination Numbers
Authors: Mohri T. , Oates W. A. 
Published: July 2007

AbstractA cluster expansion of the internal energy is carried out for a phase comprised of sublattices which have different coordination numbers, and the equation for the mixing energy is derived. The resultant expression of the mixing energy is equivalent to that derived using the higher‐order approximation of the Bond Energy Model. It is shown that the effective pair interaction energy of the cluster expansion is exactly the site exchangc energy of the Bond Energy Model. The cluster expansion method is suitable for use in higher‐order approximation calculations of the free energy.
Study of the Electronic Polarizability of Metal Clusters
Authors: Utreras‐Díaz C. A. , García E. Martín , Troncoso M. A. Rojas 
Published: July 2007

AbstractA study of alkaline metal clusters, both neutral and ionized is presented as a function of the number of atoms in the cluster N in the Thomas‐Fermi‐Dirac‐Weizsäcker approximation for the spherical jellium model. Numerical solutions are found for the electronic density using the program COLSYS and the surface energy and the ionization energy of the clusters are studied as functions of N for N up to 10000 atoms. To calculate the polarizability of the cluster, a one‐parameter trial density is proposed, based upon the numerical solution for neutral clusters, to approximate the distorted electronic density under a constant electric field. An alternative approach is also considered and described, but it is not implemented numerically in this work.
Polaronic Hamiltonian and Polar Optical Vibrations in Multilayer Structures
Authors: Klimin S. N. , Pokatilov E. P. , Fomin V. M. 
Published: July 2007

AbstractA theory of polar optical vibrations in multilayer semiconductor structures is developed taking into account phonon dispersion. A method of diagonalization of the equations of motion for inertial polarization vectors in the finite basis is used, that is founded on a finite number of degrees of freedom of the system. The Hamiltonian of the electron‐phonon interaction is deduced. The dispersion law and the spatial dependence of the obtained eigenmodes are in good agreement with experimental data and microscopic models. It is shown that the electron scattering rate in a magnetic field depends on the chosen model of polar optical vibrations.
A Study of XANES Associated with the L Absorption Discontinuities of Some Rare Earths in Their Oxides and Cuprates
Authors: Moghe N. V. , Sapre V. B. , Nigam A. N. , Mande C. 
Published: July 2007

AbstractThe XANES region of the LII and LIII absorption discontinuities of some rare earths in their oxides and cuprates is studied. The main absorption peak and the peak adjacent to it are attributed to the transitions of electrons from the inner L levels to the outer levels t2g and eg, which are formed due to the crystalline field in the materials. It is observed that the energy difference between these two peaks varies linearly with the atomic number Z for the oxides as well as the cuprates.
Photoreflectance Study of a Fibonacci Superlattice
Authors: Pánek P. , Munzar D. , Humlíček J. , Lukeš F. , Ploog K. 
Published: July 2007

AbstractPhotoreflectance spectra of a GaAs/GaAlAs Fibonacci superlattice in the temperature range from 20 to 300 K are reported. A new method for the modulation beam shift in sweeping photoreflectance is presented. The experimental results are compared with the theoretical spectra calculated with the help of the envelope function approximation, using the first‐derivative model for the photoreflectance lineshapes. The model predictions are in good agreement with spectra measured at low temperatures. The temperature evolution of the spectra is also discussed.
Rigidity Percolation and Chemical Ordering in Ge‐In‐Se Glasses
Authors: Saffarini G. , Schlieper A. 
Published: July 2007

AbstractThe dependence of the mean atomic volume Va of chalcogenide glasses belonging to the GexIn6Se94−x and GexIn12Se88−x families of the Ge‐In‐Se system, on the average coordination number Z is investigated. The Va‐Z plots for both families display maxima at Z = 2.75 and 2.83 corresponding to the tie‐line composition in In6 and In12 families, respectively. The Va‐Z dependence for the In6 family exhibits a minimum at Z = 2.54 and a broad local maximum at Z = 2.67, and that of the In12 family shows a marked change in slope at Z = 2.50. These results are discussed in the framework of the chemically ordered covalent network model, Tanaka's model of topological transition, and the Phillips‐Thorpe model of rigidity percolation.
Langevin‐Type Charge Carrier Recombination in a Disordered Hopping System
Authors: Albrecht U. , Bässler H. 
Published: July 2007

AbstractA Monte Carlo simulation study is performed to determine the ratio γ/μ of the rate coefficient for bimolecular charge recombination and the charge carrier mobility in a hopping system with built‐in energetic disorder. The result indicates that γ/μ is independent of disorder but increases at large electric fields at which the charge carrier velocity saturates.
Electronic Pairing Mechanism Due to Band Modification with Increasing Pair Number
Authors: Mizia J. 
Published: July 2007

AbstractIt is shown that a shift of an electron band with electron occupation number n, which is changing during the transition to the superconducting state, can lower the total energy of the system. In fact it will bring a negative contribution to the pairing potential, which is proportional to the product of the electron band shift with occupation number and the charge transfer during the transition to the superconducting state. The shift of the electron band comes from the change of stresses and the change of correlation effects in the CuO2 plane with n, that in turn is caused by the changing oxygen concentration. This model explains the phenomenological success of Hirsch's model, which gives no explanation how the band shift in energy can give rise to superconductivity.
Spin‐Wave Theory on Quasi‐One‐Dimensional Heisenberg Antiferromagnets
Authors: Du A. , Wei G. Z. 
Published: July 2007

AbstractThe low‐temperature of quasi‐one‐dimensional Heisenberg antiferromagnets with ferromagnetic coupling between nerest‐neighbor spins within a chain and antiferromagnetic couplng between nearest‐neighbor spins withina chain and antiferromagnetic coupling between chains are studied by the spin‐wave theory. The effects of interchain coupoling on the ground state energy, sublattice magnetization, and perpendicular susceptibility at zero temperture are calculated numerically. At low temperatures, asympototic expressions of sublattice magnetization, internal energy, magnetic specific heat, parallel and perpendicular susceptibilities are given as functions of temperature and interchain coupling strength within tow sub‐temerature regions. It is found that if interchain coupling is weak, with increasing temperature the properties of the system change from threedimensional behavior (Δm ∝ T2, ΔE ∝T4, Cm ∝ T3, X∥ ∝ T5/2, ΔX⊥ ∝ T2) To quasi‐one‐dimensional bahavior (Δm ∝ T, ΔE ∝ T3/2, Cm ∝ T1/2, X∥ ∝ T3/2, ΔX⊥ ∝ T).
Spectroscopic Study of Cr3+ Impurities Embedded into Crystallites of Mullite Glass Ceramics
Authors: Männik J. , Sildos I. 
Published: July 2007

AbstractFluorescence spectra of Cr3+ impurities in a mullite glass ceramic are investigated by using time‐resolved fluorescence‐line‐narrowing spectroscopy. The dependence of fluorescence spectra on the excitation wavelength inside the inhomogeneously broadened R‐like line of Cr3+ ions embedded in mullite crystallites is studied. In these spectra a large inhomogeneous broadening, strong non‐correlation between different electron transitions, and non‐exponential decay patterns of fluorescence in spite of resonant narrow‐band laser excitation are revealed. The influence of the compositional and mesoscopic structure of the mullite glass ceramic on the spectra of the impurities is analyzed and an attempt is made to separate the contributions of these two factors.
Shift of Optical Resonant Reflectance Extrema Due to Damping and Spatial Dispersion
Authors: Grigorchuk N. I. 
Published: July 2007

AbstractThe energy shifts of light reflectance extrema in the region of exciton resonances are studied taking into account the transitional layers, spatial dispersion (SD), and damping. The values and directions of the shifts of the extrema are determined depending on the round‐trip phase delay in the transitional layer. It is found that in the phase interval nπ ≦ θ < nπ + π/4 (n = 0, 1, …) the long‐wave shift of the maximum is dominant while in the interval nπ + π/4 < θ ≦ nπ + π/2 mainly a short‐wave shift of the minimum occurs. The comparative roles of SD and damping are discussed. The equivalence of the mechanisms of SD and of damping effects on the frequency shift is established; the first one playing a more important role. Theoretical results agree with the available experimental data. Corresponding estimates for CdS, GaAs, and LiH crystals are made.
XPS Studies on Ce/Al2O3 and on CoRh/Nb2O5 Catalysts
Authors: Appel L. G. , Frydman A. , Perez C. A. C. , Eon J. G. , Castner D. G. , Campbell Ch. T. , Schmal Schmal M. 
Published: July 2007

AbstractThe surface properties of supported catalysts are studied. XPS data are used to identify the different surface species but, alone, it is not sufficient to provide enough information to describe the correct form and distribution of these species and phases on the surface. However, XPS supported by an accurate mathematical formalism to model catalysts surface structure, may become a powerful tool to help understanding surface properties. First, a new mathematical model for supported bimetallic Co‐Rh/Nb2O5 catalysts is proposed based on quantitative analysis of XPS intensities assisted only by TPR data. XPS peak intensities are compared to the values predicted from different structural models of the oxide particles. Secondly, the Ce/Al2O3 system generated from different precursors of cerium salts and contents is examined using different techniques. XPS results show the effect of the precursor on the Ce/Al ratio while TEM the morphology. In addition, the EPR data show the Ce3+ species distributed in regions underneath the topmost surface layer. Then, an improved model is proposed based on quantitative analysis of XPS intensities, XRD, and TEM results.
Analysis of hydrogen and paramagnetic defects in aSi: H aerosol particles. Resulting from thermal decomposition of silane
Authors: Onischuk A. A. , Strunin V. P. , Ushakova M. A. , Samoilova R. I. , Panfilov V. N. 
Published: July 2007

AbstractHydrogen and paramagnetic centers contained in aSi:H aerosol particles, formed during thermal decomposition of silane are studied. The methods of IR spectroscopy, effusion of hydrogen, and ESR spectroscopy are used. For low temperatures of aerosol formation (T ≦ 833 K) paramagnetic centers with g ∼ 2.0051 are recorded in aerosol particles. For high temperatures (T > 880 K) paramagnetic centers with g ∼ 2.0055 are recorded. The obtained experimental results testify that the existence of paramagnetic centers with g ∼ 2.0051 is related to the presence of polysilane chains. The existence of paramagnetic centers with g ∼ 2.0055 is related to the presence of monohydride groups with the frequency of stretching vibrations near 2100cm−1 located on the surface of interconnected microvoids and microchannels. The quantitative relations between the fractions of hydrogen present in various structural groups and IR absorptions in the corresponding regions of the IR spectra are obtained.
Screening effect on polarizabilities of shallow donors and acceptors in finite‐barrier quantum wells
Authors: Ilaiwi K. F. 
Published: July 2007

AbstractPolarizabilities of shallow donors and acceptors in finite‐barrier GaAs/Ga1−xAlxAs quantum wells are calculated using Hasse's variational method within the effective mass approximation. The effect of spatially dependent screening on polarizabilities is taken into account with an r‐dependent dielectric response. It is shown that spatially dependent screening effects can be more important for acceptors than for donors in GaAs/Ga1−xAlxAs quantum wells. The effects of electric and magnetic fields on binding energy are also studied.
Studies of the CuO Bond in (Pb, Cd)‐1212 and (Pb, Cd)‐1201 cuprates by X‐ray photoelectron spectroscopy
Authors: Yu W. J. , Mao Z. Q. , Tian M. L. , Wang Y. , Zhou G. E. , Zhang Y. H. 
Published: July 2007

AbstractIt is shown that in (Pb0.5Cd0.5)Sr2(Y0.5Ca0.5)Cu2O7 and (Pb0.5Cd0.5)SrLaCuO5 cuprates, where Cu2+ ions are in pyramidal and octahedral geometry with five and six neighboring oxygens, respectively, the Cu2p3/2(2p53d10L) XPS core line is broader than that in Nd2CuO4 where Cu2+ ions are in a square planar geometry with four coordination oxygen ions, and that for (Pb0.5Cd0.5)SrLaCuO5 is the broadest. To explain these changes in the XPS Cu2p3/2 main line, two different charge transfer mechanisms from the O2p to the Cu3d orbitals are considered. For the square planar geometry (CuO4) only the O2px,y → Cu3d charge transfer is allowed, whereas for pyramidal and octahedral geometries an additional apical O2pz → Cu3d transition could take place, and in octahedral geometry the latter transition is more significant. The valence band spectra of the cuprates also confirm this proposition.
Spin waves of anisotropic ferrimagnets with nearest neighbor and next‐nearest neighbor interactions
Authors: Xue D. S. , Gao M. Z. , Yang J. B. , Kong Y. , Li F. S. 
Published: July 2007

AbstractAn anisotropic Heisenberg model with nearest neighbor and next‐nearest neighbor interactions is introduced to study the spin wave spectra of two‐sublattice ferrimagnets. The matrix Green function is applied to deal with the NaCl‐ and CsCl‐type ferrimagnets. The results show that the spin wave spectra separate into two branches, and the numerical calculation at finite temperature indicates that the absolute value of the spin wave energy increases with increasing extension and strength of the exchange interactions. It is found that the influences of the next‐nearest neighbor and anisotropic interactions are quite different. Simultaneously, the influences of the structure and the temperature are discussed.
The effect of anisotropy on magneto‐optics of type‐II semiconductor superlattices
Authors: Lau W. , Singh M. 
Published: July 2007

AbstractA theory of cyclotron resonance (CR) for type‐II (InAs/GaSb) superlattices based on the 8 × 8 k · p matrix Hamiltonian (Bodnar model), which includes the effect of electron‐hole interactions is developed. In this model, the effect of nonparabolicity and anisotropy is included. Using linear response theory, an expression for the cyclotron absorption coefficient is obtained. It is predicted for the first time that due to the anisotropy of the band structure, the CR transitions are sensitive to the orientation of the sample relative to the growth direction. This prediction agrees with the experiments on a qualitative basis. In addition it is predicted that as the strength of the magnetic field increases the square of the matrix elements of the CR transitions also increases. The present theory can also be applied to study the interband magneto‐optical transitions along with the intraband transitions.
On the pressure dependence of the Grüneisen parameter and debye temperature for CsI crystals
Authors: Kulkarni R. G. , Abd‐Elmeguid M. , Bukshpan S. , Milants K. , Verheyden J. , Pattyn H. 
Published: July 2007

AbstractAn analysis of the pressure dependence of the Grüneisen parameter γ and the Debye temperature θ for CsI based on the model developed by Kumari and Dass is presented. From the pressure dependence of the recoilless fraction behaviour γ is deduced which shows that γ varies linearly with pressure as γ(p,T) = γ0 − ηp, where η is found to be pressure independent. θ(p) also displays a linear variation with p, which is consistent with the recoilless fraction behaviour of γ‐ray emission or absorption in the Mössbauer effect for low pressures. Various thermodynamic approximations implied in the analysis are tested and found to be true.
The formation of germanium nanocrystals by thermal annealing of a‐SiOx: H/a‐GeOx: H multilayers
Authors: Freistedt H. , Stolze F. , Zacharias M. , Bläsing J. , Drüsedau Tilo P. 
Published: July 2007

AbstractMultilayer films consisting of alternating sublayers of hydrogenated amorphous silicon oxide and germanium oxide were prepared by dual magnetron sputtering of silicon and germanium targets in an argon/water vapor atmosphere. The number and thickness of the a‐GeOx: H sublayers ranged from one to eight and from 80 to 7 nm, respectively. The structure of the multilayers and their components were investigated by means of optical transmission and reflection, infrared spectroscopy, wide‐angle X‐ray scattering, and X‐ray reflectometry. Upon annealing, first an ordering of the amorphous germanium oxide network connected with an outdiffusion of oxygen and an increase of the surface roughness are observed. Depending on sublayer thickness, the onset of the formation of Ge nanocrystals is observed around 700 K. Crystallization of the germanium oxide sublayers is nearly completed at 870 K, and the crystallite diameter ranges from 4 to 13 nm depending on sublayer thickness. With crystallization the surface roughness decreased and the structure of the silicon oxide was improved.
Electron structure near abrupt edges in 2DEG under strong magnetic field
Authors: Bartos I. , Rosenstein B. 
Published: July 2007

AbstractEnergies and wave functions of edge states in a two‐dimensional electron gas are evaluated for a finite step potential barrier model. The spectrum, instead of smooth bending of Landau branches in the vicinity of the barrier acquires a step‐like form; unexpected edge plateaus and significant energy gap reduction take place between the neighbouring Landau branches above the barrier tops. The origin of these phenomena is traced. Stability with respect to modifications is established. Manifestation of the qualitatively new features of electron densities of states in abrupt confinements through magnetooptical and nuclear magnetic spin relaxation effects is proposed.
Dynamics of an inhomogeneous anisotropic antiferromagnetic spin chain
Authors: Daniel M. , Amuda R. 
Published: July 2007

AbstractNonlinear spin excitations in the two‐sublattice model of a one‐dimensional classical continuum Heisenberg inhomogeneous antiferromagnetic spin chain are investigated. The dynamics of the inhomogeneous chain reduces to that of its homogeneous counterpart when the inhomogeneity assumes a particular form. Apart from the twists, some planar configurations representing the nonlinear dynamics of spins are obtained.
Refined RBS and AES techniques for the analysis of thin films used in photovoltaic devices
Authors: Bohne W. , Fenske F. , Kelling S. , Schöpke A. , Selle B. 
Published: July 2007

AbstractThe analytical potential of refined RBS and AES techniques is demonstrated by two examples: (i) thin FeSi2 absorber layers on Si and (ii) TiNiAg multilayer contact structures. Both systems have prospects as components in photovoltaic cell devices. In the case of RBS, the refinement concerns an improved mass resolution achieved by applying projectile ions of higher masses (15N, 22Ne) at higher energies (up to 25 MeV). For AES the principal component analysis (PCA) formalism is adopted starting with a peak‐to‐peak height normalization of the relevant Auger peaks in the measured spectra. This evaluation procedure, which takes advantage of the chemical information inherent in the Auger line shape, gives depth profiles of the elements with respect to their chemical bonding state.
Vegard's rule and Sb2Te3−xSex crystals
Authors: Karamazov S. , Nesládek P. , Horák J. , Matyas M. 
Published: July 2007

AbstractSb2Te3−xSex crystals were prepared from 5N purity elements and their crystal parameters a, c and Hall coefficients RH were measured as functions of the Se concentration up to x = 1. Well defined deviations of both crystal parameters from the linear Vegard's law are observed up to x = 0.4. At higher Se concentrations the linear Vegard's law is fulfilled. The main idea explaining this behaviour is the decrease of antisite defects of the type SbTe with increasing Se concentration. This process is complicated and its details are given in the paper.
Heat capacity of niobium and tantalum carbides NbCy and TaCy in disordered and ordered states below 300 K
Authors: Gusev A. I. , Rempel A. A. , Lipatnikov V. N. 
Published: July 2007

AbstractThe low‐temperature heat capacity of nonstoichiometric niobium and tantalum carbides in disordered and ordered states is measured by an adiabatic calorimetry method. It is found that in the temperature interval from 4 to 300 K the investigated ordered carbides have a higher heat capacity than the disordered carbides of the same composition. The effect of ordering on the heat capacity of nonstoichiometric carbides is interpreted in terms of the order parameter functional (OPF) method. Changes in heat capacity due to ordering in niobium and tantalum carbides are calculated. The degree of long‐range order in ordered carbides is estimated by comparing of the calculated and experimental results.
Presurface exciton spectrum at finite temperatures
Authors: Tkach M. V. , Paziuk V. V. 
Published: July 2007

AbstractThe Hamiltonian of the presurface excitons interacting with the bulk and interface phonons in a heterosystem with a plane interface is obtained in the representation of second quantization in all variables. The spectrum parameters (shift and half‐width) of the shape function of the basic band at arbitrary temperatures are calculated with the help of the Green function method. The temperature dependence of the spectrum parameters is studied and the physical mechanism of their formation is established on the example of particular heterosystems.