bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ensemble averaged coherent state path integral for disordered bosons with a repulsive interaction (Derivation of mean field equations)
Authors: Mieck B. 
Published: July 2007

AbstractWe consider bosonic atoms with a repulsive contact interaction in a trap potential for a Bose‐Einstein condensation (BEC) and additionally include a random potential. The ensemble averages for two models of static (I) and dynamic (II) disorder are performed and investigated in parallel. The bosonic many body systems of the two disorder models are represented by coherent state path integralson the Keldysh time contour which allow exact ensemble averages for zero and finite temperatures. These ensemble averages of coherent state path integrals therefore present alternatives to replica field theories or super‐symmetric averaging techniques. Hubbard‐Stratonovich transformations (HST) lead to two corresponding self‐energies for the hermitian repulsive interaction and for the non‐hermitian disorder‐interaction. The self‐energy of the repulsive interaction is absorbed by a shift into the disorder‐self‐energy which comprises as an element of a larger symplectic Lie algebrasp(4M) the self‐energy of the repulsive interaction as a subalgebra (which is equivalent to the direct product ofM×sp(2); ‘M’ is the number of discrete time intervals of the disorder‐self‐energy in the generating function). After removal of the remaining Gaussian integral for the self‐energy of the repulsive interaction, the first order variations of the coherent state path integralsmagnified imageresult in the exact mean field or saddle point equations, solely depending on the disorder‐self‐energy matrix. These equations can be solved by continued fractions and are reminiscent to the `Nambu‐Gorkov' Green function formalism in superconductivity because anomalous terms or pair condensates of the bosonic atoms are also included into the selfenergies. The derived mean field equations of the models with static (I) and dynamic (II) disorder are particularly applicable for BEC ind= 3 spatial dimensions because of the singularity of the density of states at vanishing wavevector. However, one usually starts out from restricted applicability of the mean field approach ford= 2; therefore, it is also pointed out that one should consider different HST's ind= 2 spatial dimensions with the block diagonal densities as ‘hinge’ functions and that one has to introduce a coset decompositionSp(4M)\U(2M) into densities and anomalous terms of the total disorder‐self‐energysp(4M) for deriving a nonlinear sigma model.
Misfit dislocations in highly mismatched oxide interfaces, an X‐ray diffraction study
Authors: Conchon F. , Boulle A. , Guinebretière R. 
Published: July 2007

AbstractWe present here a detailed study describing the strain relaxation mechanisms occurring in the highly mismatched ZrO2/MgO system. Especially, we show using reciprocal space mapping that the ZrO2islands epitaxially grown on the MgO substrate are fully relaxed implying the formation of misfit dislocations at the interface. Furthermore, an analysis of transverse scans performed through symmetrical ZrO2reflections for several azimuthal positions of the sample lets us conclude that dislocations form a square network parallel to ZrO2cell axes. Finally, an accurate analysis of the diffraction data evidences the existence of two subsets of misfit dislocations. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High‐temperature induced nano‐crystal formation in ion beam‐induced amorphous silicon ripples
Authors: Grenzer J. , Mücklich A. , Grigorian S. , Pietsch U. , Datta D. P. , Chini T. K. , Hazra S. , Sanyal M. K. 
Published: July 2007

AbstractWe report on in‐situ investigations of a recrystallization process of amorphous and damaged crystalline parts generated during ion‐beam induced rippling on a Si(100) surface. The ripple structure was created by 60 keV 40Ar+ irradiation with a dose of ∼5 × 1017 ions/cm2 at ion incident angle of 60° with respect to the surface normal. At this dose the ripples have an average spatial periodicity of about 715 nm and surface undulations with an amplitude of about 40 nm. Structure and morphology of ripples were studied by two types of X‐ray scattering (grazing incidence diffraction and amorphous scattering) methods, transmission electron microscopy and atomic force microscopy. X‐ray grazing‐incidence amorphous scattering pattern were recorded in‐situ for a temperature range from 250 to 750 °C. Up to about 500 °C mainly we found a single broad scattering maximum corresponding to the Si(111) inter‐planar distances. At higher temperature these peaks become sharp and intense indicating the onset of a re‐crystallization process in the amorphous top layer.Two processes were found, a formation of crystalline islands on top of the former amorphous surface ripples and a growth of polycrystalline twins close to the former amorphous‐crystalline interface. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
First order phase transition in MnAs nanodisks
Authors: Jenichen B. , Kaganer V. M. , Takagaki Y. , Herrmann C. , Ploog K. H. , Dudzik E. , Feyerherm R. 
Published: July 2007

AbstractThe first order phase transition between ferromagnetic α‐MnAs and paramagnetic β‐MnAs in nanoscale disks etched out of an epitaxial MnAs film on GaAs(001) is studied by means of X‐ray diffraction and magnetic force microscopy. The temperature hysteresis loop is observed to be expanded with decreasing disk size. The hysteresis is absent in the original continuous epitaxial film from which the disks are fabricated. The hysteresis is explained as a competition between the energy gain due to the phase transition and the energy loss due to the elastic strain. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phase contrast X‐ray imaging of large samples using an incoherent laboratory source
Authors: Kottler C. , Pfeiffer F. , Bunk O. , Grünzweig C. , Bruder J. , Kaufmann R. , Tlustos L. , Walt H. , Briod I. , Weitkamp T. , David C. 
Published: July 2007

AbstractAn interferometric method to record quantitative X‐ray phase contrast images has been developed that can be used at polychromatic and incoherent X‐ray sources such as laboratory tubes. With respect to previously presented results, in this work we report on recent developments and results that have been achieved in view of potential future applications such as in medicine or biology. In particular, due to improvements in the fabrication process large area diffraction gratings with high aspect ratio were achieved. Thereby, the field of view of the interferometer has been drastically increased to 64 × 64 mm2 and the design value of the photon energy for the gratings could be increased up to 28 keV. Moreover, the use of a Medipix2 single photon‐counting pixel detector shows a considerable improvement in image quality and sensitivity over the integrating detector used so far. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High‐resolution X‐ray diffraction study of CZ‐grown GaAsP crystals
Authors: Kowalski G. , Gronkowski J. , Czyżak A. , Słupiński T. , Borowski J. 
Published: July 2007

AbstractWe report results of X‐ray investigations of tellurium‐doped GaAs1–x Px (with 0.07 ≤ x ≤ 0.20) single crystals, conducted in order to support finding proper growth parameters which would yield a material of sufficient homogeneity of the lattice parameter for prospective applications. Our samples were studied using high‐resolution diffractometry which allowed to obtain both rocking curves and reciprocal space maps of the diffracted intensity, as well as using plane‐wave topography in the reflection mode. Weak reflections were also used to study the influence of Te atoms on the compound lattice. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
In‐plane lattice parameter determination of Zn:LiNbO3 thin films epitaxially grown on x‐cut LiNbO3 substrates using X‐ray diffraction methods
Authors: Kräußlich J. , Dubs C. , Lorenz A. , Tünnermann A. 
Published: July 2007

AbstractAs a precursor material for electrooptical applications in the integrated optics, nominal pure as well as Zn‐doped stoichiometric LiNbO3 thin films of a few µm thickness were grown by liquid phase epitaxy on congruent LiNbO3 substrates. The crystalline perfection and lattice parameters of the epitaxially grown films were investigated by means of high‐resolution X‐ray diffraction methods. The symmetric θ /2θ ‐diffractograms show a lattice parameter increase perpendicular to the sample surface (Δd /d)⊥ up to 10–3 with increasing Zn content. X‐ray diffraction reciprocal space measurements taken up with asymmetric reflections are well suited to determine the in‐plane lattice parameters of the grown films. Despite different Zn contents, the Zn:LiNbO3 thin films reveal a distinctly pseudomorphous growth. Using the generalized Hooke's law in matrix way of writing and taking the measured values into account, the relaxed lattice parameters of the grown films as well as the in‐plane strain and tension components have been numerically calculated. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Observation of interference fringes due to lattice distortion by resonant scattering X‐ray topography
Authors: Negishi Riichirou , Fukamachi Tomoe , Yoshizawa Masami , Hirano Keiichi , Kawamura Takaaki 
Published: July 2007

AbstractThe interference fringe caused by lattice distortion around a defect is observed in the resonant scattering X‐ray topography for the GaAs 200 reflection in the Laue case. The amplitude of the fringe can be maximized when the Fourier transform of the imaginary part of X‐ray polarizability χhi is zero. The fringe position relative to the defect shifts when the incident angle is varied, and the fringe spacing changes as a function of the distance from the defect. A kinematical image can be distinguished from a dynamical one by observing the image position when the incident angle is varied in the case of χhi = 0. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of SR thermal load studied by FEA
Authors: Áč V. , Korytár D. 
Published: July 2007

AbstractThis work deals with analysis of the thermal effects and inherent mechanical deformations under absorption of the X‐ray beam heat. The work is motivated by recent research concentrated on the development of optics for high‐flux synchrotron radiation sources. We present the analyses of the static thermal load effects on the surface deformation field for a monocrystalline silicon target, which is the basic material for crystal X‐ray optics. The surface and bulk thermal load induces the gradient of temperature and mechanical deformations of the target that are affecting the reflection and diffraction properties of the target. The paper presents the finite‐element analyses (FEA) and simulation results of mechanical deformation of flat and slotted silicon targets. The hints for improved target geometry and physical limits for an actual cooling system can be obtained from the presented analyses. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Gerhard Borrmann (1908–2006) and Gerhard Hildebrandt (1922–2005): their life stories and their contribution to the revival of dynamical theory in the 1950's
Authors: Authier A. , Klapper H. 
Published: July 2007

AbstractG. Borrmann and his former student and co‐worker G. Hildebrandt passed way a few months ago. Both have given major contributions to the development of the dynamical theory of diffraction and to X‐ray imaging topography. Their career and their scientific achievements are reviewed briefly, with emphasis on Borrmann's very early work (Kossel lines, the discovery of anomalous absorption and of the Borrmann fan). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Determination of stress distribution in III–V single crystal layers for heterogeneous integration applications
Authors: Jackson M. , Goorsky M. S. , Noori A. , Hayashi S. , Sandhu R. , Poust B. , Chang‐Chien P. , Gutierrez‐Aitken A. , Tsai R. 
Published: July 2007

AbstractDouble crystal X‐ray diffraction imaging and a variable temperature stage are employed to determine the stress distribution in heterogeneous wafer bonded layers though the superposition of images produced at different rocking curve angles. The stress distribution in InP layers transferred to a silicon substrate at room temperature exhibits an anticlastic deformation, with different regions of the wafer experiencing different signs of curvature. Measurements at elevated temperatures (≤125 °C) reveals that differences in thermal expansion coefficients dominate the stress and that interfacial particulates introduce very high local stress gradients that increase with increased temperature. For thinned GaAs substrates (100 μm) bonded using patterned metal interlayers to a separate GaAs substrate at ≈200 °C, residual stresses are produced at room temperature due to local stress points from metallization contacts and vias and the complex stress patterns can be observed using the diffraction imaging technique. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Features of dislocation images reconstructed from step‐scanned white X‐ray section topographs
Authors: Kajiwara Kentaro , Kawado Seiji , Iida Satoshi , Suzuki Yoshifumi , Chikaura Yoshinori 
Published: July 2007

AbstractWe have observed dislocations in a CZ‐silicon crystal using step‐scanning white X‐ray section topography and examined the feature of the dislocation images reconstructed by stacking 200 shots of sec‐ tion topographs. These topographs were obtained from symmetric 004‐reflection in the Laue case using 20, 30, and 60 keV X‐rays. Direct images, intermediary images, and dynamical images of dislocations were observed in a tomogram, i.e., a sliced image obtained from the stacked section topographs, and the contrast of the dynamical images was reduced with increasing X‐ray energy. The stacked section topographs provided three‐dimensional images of the dislocations based on the direct images, and the sliced image enabled us to observe the dislocations separately in a highly dislocated region of the CZ‐silicon crystal. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamical theory of X‐ray diffraction by multilayered structures with microdefects
Authors: Molodkin V. B. , Olikhovskii S. I. , Kislovskii E. N. , Fodchuk I. M. , Skakunova E. S. , Pervak E. V. , Molodkin V. V. 
Published: July 2007

AbstractThe dynamical recurrence relation for amplitudes of coherent waves in the multilayered structure with Coulomb‐type defects (2D and 3D defects or microdefects) has been derived and the expression for the diffuse component of reflection coefficient of this structure has been obtained with account for the dynamical redistribution of intensities of transmitted and diffracted coherent waves in each layer. The derived formulas, which self‐consistently take into account both the diffuse scattering contribution to the diffracted intensity and its extinction due to diffuse scattering, have been applied to analyze the rocking curve of InGaAs/GaAs multilayered structure with quantum well. Layer thicknesses and chemical compositions as well as strains and concentration profiles of chemical elements in layers have been found. Additionally, characteristics of dislocation loops in the substrate of the multilayered structure have been determined. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of phase contrast hard X‐ray microscopy using planar sets of refractive crossed linear parabolic lenses made from SU‐8 polymer
Authors: Reznikova E. , Weitkamp T. , Nazmov V. , Last A. , Simon M. , Saile V. 
Published: July 2007

AbstractPlanar X‐ray refractive lenses with parabolic surface profile, and in crossed geometry to provide 2D focusing, are fabricated from SU‐8 polymer using the LIGA process and deep X‐ray lithography technology. A transmission X‐ray microscope (TXM) using a condenser and an objective lens based on this type of X‐ray optics was set up at the ESRF beamline BM 5, for photon energies of 17.1 and 18 keV. Test structures made of gold and SU‐8, with different thicknesses, were imaged with this TXM using in‐line phase‐contrast, with X‐ray magnification factors of 13–20, spatial resolution between 0.2 and 0.3 µm and exposure times around 1 s. The advantages of a TXM based on refractive SU‐8 planar crossed condenser and objective and the optimisation of the optical scheme and of the condenser focusing profile are discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A magnetron sputter deposition chamber for in‐situ investigation of multilayer film growth using a state of the art Laboratory Diffractometer
Authors: Ringpfeil Clemens , Lützenkirchen‐Hecht Dirk , Frahm Ronald 
Published: July 2007

AbstractAn Fe2O3–Al2O3 bilayer film was prepared on a Si(111)‐wafer by sputter deposition in a vacuum chamber with two integrated small magnetron sources and in‐situ investigated using grazing incidence X‐ray reflectivity, X‐ray scattering and X‐ray diffraction experiments. We will present details of the new cell and present first results of the prepared Fe2O3–Al2O3 thin films, which exhibit an amorphous film structure with a reduced density and a roughness increasing with film thickness. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Defect structure of silicon crystals implanted with H2+ ions
Authors: Shalimov Artem , Shcherbachev Kirill D. , Bak‐Misiuk Jadwiga , Misiuk Andrzej 
Published: July 2007

AbstractSi(001) single crystal was implanted with hydrogen ions with energy 135 keV and dose 5 × 1016 cm–2. After implantation, Si:H samples were annealed at 450 and 650 °C under atmospheric and enhanced hydrostatic pressure (1.1 GPa). Defect structure of as‐implanted and processed Si:H was determined by X‐ray scattering methods. Two types of defect clusters contributing to diffuse scattering were revealed: (i) the defects produced by hydrogen diffusion, characterized by small dimensions, with concentration dependent on annealing temperature; (ii) rather large bubbles and platelets produced due to hydrogen agglomeration at defects with negative dilatation. The samples annealed under high pressure contain large defects with the double force tensor equivalent to the dislocation loops one. It is found that the high pressure heat treatment retards the hydrogen diffusion. Distribution of diffuse scattering around the 004 reciprocal lattice point for each type of defects is simulated and compared with the experimental data. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Oxidation as an assistant tool for structural analysis of inhomogeneous nanoscale InAs/AlAs(001) island system
Authors: Zolotaryov A. , Bolz A. , Schramm A. , Hansen W. , Johnson R. L. 
Published: July 2007

AbstractIn the paper we present the structural and morphological investigation of an InAs/AlAs(001) island system under growth conditions where partial island coalescence takes place. To provide the structural analysis of elastically strained islands, new experimental X‐ray diffraction technique based on effect of islands oxidation is proposed and verified. It is found that both elastically strained and plastically relaxed islands coexist and have distinctly different sizes and chemical composition what can be explained by differences in their formation mechanisms. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transport and mobility properties of wurtzite InN and GaN
Authors: Yarar Zeki 
Published: July 2007

AbstractThe results of an ensemble Monte Carlo model of the electron transport in wurtzite gallium nitride (GaN) and indium nitride (InN) are presented. There is a controversy over the material parameters of InN, therefore the recently reported and the traditionally accepted parameter values for InN are used in simulations and the results are compared. The steady‐state and transient electron transport characteristics are analyzed and the valley populations of electrons are determined as a function of electric field. The low‐field mobility of electrons is also obtained as a function of temperature and over a wide range of carrier concentrations. It is seen that with the recently published material parameters the peak velocity of carriers in InN increases significantly, while the field at which it is attained decreases. The calculated maximum low field mobility at 300 K in InN with the recent material parameters is about 10000 cm2/V s for low carrier concentrations. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High‐pressure behavior of Ni‐filled and Fe‐filled multiwalled carbon nanotubes
Authors: Poswal H. K. , Karmakar S. , Tyagi Pawan K. , Misra D. S. , Busetto E. , Sharma Surinder M. , Sood A. K. 
Published: July 2007

AbstractThe high‐pressure behavior of Ni‐filled and Fe‐filled multiwalled carbon nanotubes has been investigated up to 27 GPa and 19 GPa, respectively, with the help of synchrotron‐based angle‐dispersive X‐ray diffraction. These nanotubes do not show any structural transformation up to the highest pressures studied. These results are similar to that of Co‐filled nanotubes [1], but are in sharp contrast to the earlier results on Fe‐filled tubes [2], where the tubes were found to undergo a sudden collapse of intertube separation. Our present observations suggest that the occurrence of an isostructural phase transition in Fe3C, observed in our earlier study, may be responsible for the structural transition in nanotubes in that case. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The effect of interstitial hydrogen on the electronic structure of the B2 FeAl alloy
Authors: González Estela A. , Jasen Paula V. , Brizuela Graciela , Juan Alfredo , Nieminen Risto 
Published: July 2007

AbstractThe electronic structure and bonding in a B2 Fe–Al alloy with and without hydrogen as an interstitial atom were studied within the framework of the density functional theory and the findings compared with previous results in Fe an Al. The hydrogen absorption turns out to be a favorable process. The hydrogen was found near an Al octahedral site, the Al–H distance being shorter than that of Fe–H. The density of states (DOS) curves show several peaks below the d metal band which is made up mostly of hydrogen based states (>50% H1s) while the metal contribution includes mainly s‐ and p‐orbitals. An electron transfer of nearby 0.14 e– comes from the metal to the H. The overlap population values reveal metal–metal bond breaking, the intermetallic bond being the most affected. The H bond mainly with the Al atoms and the reported Fe–H overlap population is much lower than that corresponding to FePd alloys and BCC Fe. The changes in the overlap population show the Fe–Al bond is weakening nearly 53% after H absorption, while the Fe–Fe bond is only weakened 23%. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)