bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reflection of femtosecond pulses from soft X‐ray free‐electron laser by periodical multilayers
Authors: Ksenzov D. , Grigorian S. , Hendel S. , Bienert F. , Sacher M. D. , Heinzmann U. , Pietsch U. 
Published: June 2009

AbstractRecent experiments on a soft X‐ray free‐electron laser (FEL) source (FLASH in Hamburg) have shown that multilayers (MLs) can be used as optical elements for highly intense X‐ray irradiation. An effort to find most appropriate MLs has to consider the femtosecond time structure and the particular photon energy of the FEL. In this paper we have analysed the time response of ‘low absorbing’ MLs (e.g. such as La/B4C) as a function of the number of periods. Interaction of a pulse train of Gaussian shaped sub‐pulses using a realistic ML grown by electron‐beam evaporation technique has been analysed in the soft‐X‐ray range. The structural parameters of the MLs were obtained by reflectivity measurements at BESSY II and subsequent profile fittings.
A furnace for coherent beam transmission topography applied to ferroelectric crystals
Authors: Pernot Petra , Gorges Bernard , Vitoux Hugo , Kluender Rafael , Masiello Fabio , Baruchel José 
Published: June 2009

AbstractWe describe a small furnace for transmission diffraction imaging studies, designed to (i) go up to 800 °C while having a temperature gradient as reduced as possible on a platelet‐shaped insulating sample, (ii) allow a large and homogeneous beam to be transmitted/diffracted and (iii) preserve the coherence properties of these transmitted and diffracted beams, which are recorded at variable crystal‐to‐detector distances (typically 2–200 cm). We report experiments, to test the temperature gradient, on the ferroelectric to paraelectric transition of BaTiO3, and to check the preservation of the coherence properties of the beam, which include the observation of ferroelectric domains in a poled LiNbO3 crystal.
X‐ray diffuse scattering effects from Coulomb‐type defects in multilayered structures
Authors: Olikhovskii S. I. , Molodkin V. B. , Skakunova E. S. , Kislovskii E. N. , Fodchuk I. M. 
Published: June 2009

AbstractThe theoretical X‐ray diffraction model starting from Takagi–Taupin equation has been developed for the description of coherent and diffuse components of the rocking curve (RC) measured from the multilayered crystal structure with randomly distributed Coulomb‐type defects in all the layers and substrate. The model describes both diffuse scattering (DS) intensity distribution and influence of DS on attenuation and angular redistribution of the coherent X‐ray scattering intensity. By analyzing the total measured RC with using the proposed diffraction model, the chemical compositions, strains, and characteristics of dislocation loops in layers and substrate of the multilayered structure with InGaAsN/GaAs single quantum well have been determined.
Interdiffusion in Ge rich SiGe/Ge multilayers studied by in situ diffraction
Authors: Meduňa M. , Caha O. , Keplinger M. , Stangl J. , Bauer G. , Mussler G. , Grützmacher D. 
Published: June 2009

AbstractWe report on the investigation of diffusion properties of SiGe/Ge multiple quantum well (MQW) structures with period of 24 nm grown strain symmetrized on relaxed SiGe buffers on Si (001) substrates by molecular beam epitaxy. During in situ annealing, X‐ray diffraction experiments were performed on series of MQW structures with average Ge contents of about 70 and 90% using reciprocal space mapping around the (224) reciprocal lattice point. The reciprocal space maps were obtained at elevated temperatures at the ESRF for temperatures from about 600 to 800 °C. The temperatures, where interdiffusion becomes observable, is in the range from 680 to 780 °C for xGe = 0.7 and from 650 to 720 °C for xGe = 0.9. The diffusion parameters were obtained from the analysis of the decay of the periodic satellites in the recorded intensity maps.
Observation of dislocations in hen egg‐white lysozyme crystals by synchrotron monochromatic‐beam X‐ray topography
Authors: Mukobayashi Yu. , Kitajima Natsuko , Yamamoto Yu. , Kajiwara Kentaro , Sugiyama Hiroshi , Hirano Keiichi , Kojima Kenichi , Tachibana Masaru 
Published: June 2009

AbstractDislocations in large hen egg‐white lysozyme (HEWL) crystals with tetragonal and orthorhombic forms were investigated by means of synchrotron monochromatic‐beam X‐ray topography. For the tetragonal form, not only screw dislocations but also edge ones are found to be included in predominant ones parallel to 〈110〉 directions. In addition, curved dislocations that can be related to (001)〈110〉 slip system are observed at the crystal edges. For the orthorhombic form, predominant edge dislocations with [001] Burgers vector are stereoscopically observed. It is clarified that they are generated at or around the nucleus centre or sector boundary.
Characterization of phases in an Al casting alloy by synchrotron tomography
Authors: Tolnai Domonkos , Degischer Hans Peter , Lendvai János 
Published: June 2009

AbstractThe microstructure of a gravity cast aluminium alloy is investigated, containing 8 wt% Si, 5 wt% Mg as alloying elements, and 0.6 wt% Fe as main impurity. The solidification starts with the formation of α‐Al dendrites, which are presented after subtraction of the interdendritic eutectic regions. There, α‐Al/Mg2Si eutectic solidifies from the remaining Mg‐ and Si‐rich liquid forming coral‐like so‐called ‘Chinese script’ Mg2Si. Simultaneously, an AlFeSi phase solidifies in 2D shapes. At last, the remaining liquid freezes as fine structured α‐Al/Mg2Si/Si ternary eutectic. Synchrotron tomographic measurements were carried out at ESRF ID19, to reveal the 3D microstructure with a spatial resolution of <1 µm. The phases of the eutectics, the AlFeSi phase and the α‐Al dendrites could be segmented, and quantitatively analysed by 3D image processing and analysis.
A dynamical theory for the X‐ray diffraction from the partially relaxed layers
Authors: Benediktovich Andrey , Feranchuk Ilya 
Published: June 2009

AbstractThe dynamical theory for X‐ray diffraction from the bilayer crystal structure with different lateral periods of the crystal unit cells (lateral mismatch) is considered in the present paper. The amplitudes of the principal diffraction waves and all harmonics conditioned by the lateral mismatch are calculated. The formation of the Bragg peaks is analysed taking into account the sphericity of the incident beam wave front set. The connection between the parameters of the coherent diffraction potential in the partially relaxed (epitaxial) crystals and the microscopic characteristics of the dislocations is also discussed.
In‐phase and anti‐phase interference fringes in Laue case
Authors: Negishi Riichirou , Fukamachi Tomoe , Yoshizawa Masami , Hirano Kenji , Hirano Keiichi , Kawamura Takaaki 
Published: June 2009

AbstractBy using X‐rays from synchrotron radiation, we measured the rocking curves due to only the imaginary part of the atomic scattering factor in Laue case. The interference fringes are observed which are totally different from the Pendellösung fringe. The fringes of the diffracted and transmitted rocking curves are in‐phase with each other. We studied the origin of the in‐phase fringes by using the complex dispersion surface and the electric field in the crystal, and also the relation with a coupled pendulum.
From nanoislands to nanowires: Growth of germanium on gallium‐terminated silicon surfaces
Authors: Schmidt Th. , Flege J. I. , Speckmann M. , Clausen T. , Gangopadhyay S. , Locatelli A. , Mentes T. O. , Heun S. , Guo F. Z. , Sutter P. , Falta J. 
Published: June 2009

AbstractThe influence of Ga pre‐adsorption on Si(111), Si(113) and Si(112) surfaces on Ge growth has been investigated by low‐energy electron diffraction and microscopy as well as X‐ray photoemission spectroscopy. On Si(111), step edges and substrate domain boundaries are decorated with Ga at high deposition temperatures, enabling selective growth and alignment of three‐dimensional Ge islands on a chemically modulated surface. On Si(113), a morphological modulation is achieved by Ga saturation, as the Si substrate decomposes into an ordered array of (112) and (115) facets. This results in the growth of Ge islands aligned at the facets. These islands exhibit an anisotropy, as they are elongated along [$1\bar 10$]. Ga pre‐adsorption on Si(112) smoothens the initially faceted bare surface, and subsequent Ge growth leads to the formation of nanoscale Ge wires. The results are discussed in terms of surface chemistry, as well as diffusion and strain relaxation anisotropy.
Anomalous X‐ray scattering study of the local structure in Ge‐Se glasses
Authors: Hosokawa S. , Oh I. , Sakurai M. , Pilgrim W.‐C. , Boudet N. , Bérar J.‐F. 
Published: June 2009

AbstractAnomalous X‐ray scattering experiments on glassy GexSe1−x semiconductors have been carried out at energies close to the Ge and Se K edges in a wide concentration range from x = 0.15 to 0.333 across the rigidity percolation threshold composition of x = 0.20. The total structure factors, S(Q), show considerable variation with x in both the position and intensity of the prepeak at about 10 nm−1, while in the remaining Q range, it stays almost unchanged. The differential structure factors, ΔiS(Q), comprise characteristic features, depending on the absorption edges. Comparing them suggests that the prepeak indicating the existence of intermediate‐range order (IRO) purely originates from the Ge‐Ge partial correlations. In contrast to the S(Q), the prepeak in ΔGeS(Q) changes very slightly with varying x down to x ∼ 0.20, suggesting that the prepeak height in SGeGe(Q) largely enhances with decrease in the Ge concentration, in particular at the the rigidity percolation threshold composition. However, a sudden decrease and a shift of the Q position are seen at the Ge concentration less than the stiffness transition composition, which may relate to the sudden decrease of the GeSe4–GeSe4 connections in the floppy region of this glassy system.
Integrated intensities in Laue–Bragg cases for non‐absorbing crystals in X‐ray dynamical diffraction
Authors: Saka Takashi 
Published: June 2009

AbstractIntegrated power ratios in Laue–Bragg cases are obtained for non‐absorbing crystals. The reciprocity theorem is used to show that wave fields on exit surfaces in Laue–Bragg cases are identical to crystal wave fields of the Bragg case. The formulae are expressed analytically by a combination of modified Bessel and Struve functions of the first order.
High‐resolution three‐dimensional reciprocal space mapping of semiconductor nanostructures
Authors: Mariager Simon O. , Schlepütz Christian M. , Aagesen Martin , Sørensen Claus B. , Johnson Erik , Willmott Philip R. , Feidenhans'l Robert 
Published: June 2009

AbstractBy combining a 2D PILATUS 100 K detector and a surface diffractometer, high‐resolution 3D reciprocal space maps with a resolution up to 2 × 10−3 A−1 have been obtained, at an acquisition speed of 20 min per Bragg point. To illustrate the possibilities, the shape and facets of molecular beam epitaxy grown GaAs nanowires are identified by studying the diffuse scattering around Bragg points from the different crystal structures in the wires. The wires are bound by {111} facets from alternating domains with zincblende structure and its twin, creating a microfaceted wire with a hexagonal cross‐section.magnified imageIsosurface of a [$11\bar 1$] Bragg point from a GaAs nanowire with crystal truncation rods originating from the wires' microfacets.
A combined X‐ray, ellipsometry and atomic force microscopy study on thin parylene‐C films
Authors: Flesch Heinz‐Georg , Werzer Oliver , Weis Martin , Jakabovič Ján , Kováč Jaroslav , Haško Daniel , Jakopič Georg , Wondergem Harry J. , Resel Roland 
Published: June 2009

AbstractParylene‐C thin films in a thickness range from 7 to 35 nm are deposited on silicon oxide and investigated for their structural and morphological properties by different methods. It is shown that spectroscopic ellipsometry (SE) is a powerful tool to obtain spatially resolved information on the homogeneity of thin films revealing relative changes in layer thickness and in the refractive index. However, the results can be considerably improved in combination with X‐ray reflectivity (XRR) which provides highly accurate results on layer thickness. The layer thickness from XRR is used as a fixed input value for the evaluation of the ellipsometry data which reveals a layer thickness dependence of the refractive index in the thin film regime. The interface roughness is determined from XRR as well as the surface rms roughness which can be compared to the roughness found by atomic force microscopy (AFM) which varies between 0.5 and 2.0 nm. Both results for the roughness show excellent agreement. Additionally a correlation of the roughness and the deposition rate is found.
Lattice parameter determination by coincidental multi‐beam X‐ray diffraction
Authors: Borcha Mariana , Fodchuk Igor , Krytsun Igor 
Published: June 2009

AbstractHigh‐precision determination of the absolute value of lattice parameter for cubic single crystals is demonstrated by the example of silicon using coincidental multi‐beam X‐ray diffraction realized by superposition of two three‐beam reflections at fixed sample temperature. Based on a semi‐kinematical approximation of X‐ray scattering theory, the algorithm for calculation of multi‐beam diffractograms is developed enabling a more thorough quantitative analysis of experimental results.
Nano‐lightsticks: polymer nanotubes with embedded chemiluminescent dopants
Authors: Lovera Pierre , Reynolds Kenneth , Redmond Gareth 
Published: June 2009

AbstractAligned arrays of perylene doped poly(methyl methacrylate) nanotubes are synthesized by solution assisted template wetting. Optical studies yield well resolved absorption and photoluminescence spectra consistent with good dopant dispersion throughout the host material. True color photoluminescence images of tubes also reveal uniform, characteristic bright blue, perylene emission. Blue perylene chemiluminescence is observed from nanotubes on exposure to a mixture of aqueous hydrogen peroxide and oxalyl chloride in hexane with a rapid emission decay being consistent with a fast reaction between reagents and dopants. Finally, by monitoring the behavior of individual nanotubes, it is shown that single tubes may act as nanoscale chemiluminescent light sources.
Charge transport property of one‐dimensional gold–polyaniline composite networks
Authors: Mallick Kaushik , Witcomb Michael J. , Strydom Andre M. 
Published: June 2009

AbstractA facile synthesis route is described for the preparation of a gold–polyaniline nanocomposite material. The gold nanoparticles were highly dispersed and stabilized throughout the polyaniline fibers that formed a metal–polymer composite material. We measured the temperature‐dependent electrical conductivity of the metal–polymer composite material. The conductivity data are commensurate with the one‐dimensional geometry of the resultant material. The temperature dependence of the Hall coefficient on the composite is in evidence of a possible contribution of a charge carrier deficit and a temperature‐dependent mobility in this material.
Preparation of tin nanocomposite as anode material by molten salts method and its application in lithium ion batteries
Authors: Hassan Mohd Faiz , Guo ZaiPing , Du GuoDong , Wexler David , Liu HuaKun 
Published: June 2009

AbstractA nanocomposite material (SnO2Co3O4) has been synthesized as an anode material for lithium‐ion batteries by the molten salt method. Characterization by X‐ray diffraction (XRD) and transmission electron microscopy (TEM) showed that the composite has a small particle size. The electrochemical performance was examined, including the charge–discharge and cycling properties. The experimental results showed that the sample containing the highest amount of Co3O4 compound exhibited a specific capacity of 355 mAh g−1 after 40 cycles, with cycling at 70 mA g−1 (35.2% higher than for the sample containing a lower amount of Co3O4). It seems that increasing the amount of Co3O4 can give good capacity retention and high specific capacity.
Investigation on internal electric field distribution of organic light‐emitting diodes (OLEDs) with Eu2O3 buffer layer
Authors: Shi Shengwei , Ma Dongge 
Published: June 2009

AbstractWe have found that organic light‐emitting diode (OLED) performance was highly improved by using europium oxide (Eu2O3) as a buffer layer on indium tin oxide (ITO) in OLEDs based on tris‐(8‐hydroxyquinoline) aluminium (Alq3), which showed low turn‐on voltage, high luminance, and high electroluminescent (EL) efficiency. The thickness of Eu2O3 generally was 0.5–1.5 nm. We investigated the effects of Eu2O3 on internal electric field distributions in the device through the analysis of current–voltage characteristics, and found that the introduction of the buffer layer balanced the internal electric field distributions in hole transport layer (HTL) and electron transport layer (ETL), which should fully explain the role of the buffer layer in improving device performance. Our investigation demonstrates that the hole injection is Fowler–Nordheim (FN) tunnelling and the electron injection is Richardson–Schottky (RS) thermionic emission, which are very significant in understanding the operational mechanism and improving the performance of OLEDs.
Theoretical analysis of optical gain in PbSe/Pb1–xSrxSe quantum well lasers
Authors: Sun Y. H. , Xu L. J. , Zhang B. , Xu Q. F. , Wang R. , Dai N. , Wu H. Z. 
Published: June 2009

AbstractIn this article, theoretical calculation of optical gain has been performed for IV–VI lead salt PbSe/Pb1–xSrxSe quantum well lasers emitting at about 4–6 µm by using an analytic gain expression. The reduced density of states and interband transition matrix elements used in the calculation were derived in the framework of the k·p model. Peak optical gain as a function of carrier concentration and radiative current density was calculated. The material parameters and laser structures that affect device performance were analyzed in details.
Effect of rapid thermal annealing on the electrical and structural properties of Ru/n‐InP (100) Schottky rectifiers
Authors: Janardhanam V. , Kumar A. Ashok , Reddy M. Bhaskar , Reddy V. Rajagopal , Reddy P. Narasimha , Balamurugan A. K. , Tyagi A. K. 
Published: June 2009

AbstractThe effects of rapid thermal annealing on the electrical and structural properties of Ru/n‐InP Schottky diode have been investigated by current–voltage (I–V), capacitance–voltage (C–V), X‐ray diffraction (XRD) and secondary ion‐mass spectroscopy (SIMS) techniques. Results showed that the Schottky barrier height of the as‐deposited Ru/n‐InP has been found to be 0.53 eV (I–V) and 0.69 eV (C–V). The Schottky barrier height increased to 0.54 eV (I–V) 0.73 eV (C–V), 0.56 eV (I–V) and 0.78 eV (C–V) after annealing at 300 and 400 °C for 1 min in nitrogen ambient. Further increase in the annealing temperature up to 500 °C resulted in the increase of barrier height to 0.57 eV (I–V) and 0.80 eV (C–V). However, after annealing at temperature 600 °C, the barrier height decreases to 0.51 eV (I–V) and 0.67 eV (C–V). Based on the results of XRD and SIMS studies, the formation of indium phases at Ru/n‐InP interface could be the reason for the increase of barrier height upon annealing at 500 °C. The atomic force microscopy results showed that the surface morphology of the contact annealed at 600 °C is fairly smooth with a root mean square roughness of 1.8 nm.
Phase transitions and electrical conductivity of Bi‐doped La2Mo2O9 oxide ion conductors
Authors: Voronkova Valentina , Kharitonova Elena , Krasilnikova Alexandra 
Published: June 2009

AbstractLa2−xBixMo2Oy (x = 0, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08, 0.1, 0.16, 0.24, 0.3) ceramic samples have been characterized by X‐ray diffraction, differential scanning calorimetry (DSC) and conductivity measurements in order to assess the dynamics of the transitions between the low‐temperature (α), high‐temperature (β) and metastable (βms) phases. Bi doping to x ≥ 0.05 fully stabilizes the cubic phase, suppressing the β → α phase transition. In addition, DSC results demonstrate that considerable doping levels give rise to a small thermal event between 450 and 500 °C, which has been identified as the βms → β phase transition between cubic phases with static and dynamic oxygen disorder. In this temperature range, the conductivity of the doped materials experiences a transition from Arrhenius to Vogel–Tammann–Fulcher behaviour. Low bismuth concentrations have a significant effect on the conductivity of La2Mo2O9.
Green photoluminescence of SrGa2S4:Sn phosphors
Authors: Nagata Mutsumi , Okamoto Shinji , Tanaka Katsu , Sakai Toshikatsu , Tamaki Akira 
Published: June 2009

AbstractThe phosphor SrGa2S4:Sn exhibits a new green photoluminescence (PL) whose spectrum peaks at 534 nm. The phosphor also exhibits yellow and orange PL with very broad spectral bands when the excitation wavelength of the UV light is changed. These emissions are caused by the 5p–5s transition in the 5s2 configuration of Sn2+ ions occupying Sr2+ sites. The origin of the green emission was investigated by analyzing the PL excitation spectra and the electronic states of Sn2+ substituting at three different Sr2+ sites. The electronic states were analyzed in a first‐principles calculation of the density of states.
Use of nanoparticles for preparation of rare‐earth doped silica fibers
Authors: Podrazky Ondrej , Kasik Ivan , Pospisilova Marie , Matejec Vlastimil 
Published: June 2009

AbstractA new approach to preparation of rare‐earth and aluminium doped silica fibers is presented in this paper. Common Modified Chemical Vapor Deposition (MCVD) technique and solution‐doping method were employed while nanoparticle dispersions were used instead of solutions for erbium and aluminium co‐doping. Prepared preforms were analyzed by refraction index profiler, EPMA and confocal microscopy. Attenuation refractive index profile and emission of erbium fluorescence were measured in fibers prepared from preforms. Resulting fibers show better homogeneity of dopants concentration distributions and significant increase in erbium emission at 1550 nm. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of stack number on the threshold current density and emission wavelength in quantum dash/dot lasers
Authors: Zhou D. , Piron R. , Dontabactouny M. , Homeyer E. , Dehaese O. , Batte T. , Gicquel M. , Grillot F. , Tavernier K. , Even J. , Loualiche S. 
Published: June 2009

AbstractInAs quantum dash and dot (QDH and QD) lasers grown by molecular beam epitaxy on InP substrate are studied. The grown lasers with active zone containing multiple stacked layers exhibit lasing wavelength at 1.55 μm. On these devices, the experimental threshold current density reaches its minimum value for a double stacked QDH/QD structure. Other basic laser properties like gain and quantum efficiency are compared. QD lasers exhibit better threshold current densities but equivalent modal gain per layer than QDH. Finally, the analysis of the modal gain on QD laser structures shows a promising potential for improvement of the laser properties. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)