bluuebunny/crossref_metadata_2025_split huggingface dataset:
Direct Kinetic Studies of Silicon Hydride Radicals
Authors: Jasinski Joseph M. 
Published: March 2011

AbstractLaser-based techniques have been developed to directly study the kinetics of the reactions of the mono-silicon hydride radicals SiH, SiH2 and SiH3. A summary of rate constants obtained from these studies is presented along with a discussion of the implications of these results for present mechanistic models of the PECVD of amorphous hydrogenated silicon from silane.
Interdiffusion of Cadmium Arachidate in Langmuir-Blodgett Films
Authors: Stroeve Pieter , Rabolt John F. , Hilleke Russ O. , Felcher Gian P. , Chen Sow-Hsin 
Published: March 2011

ABSTRACTThe interdiffusion of Cadmium Arachidate (CdA) in Langmuir-Blodgett films has been studied by neutron reflection at the Intense Pulsed Neutron Source of Argonne National Laboratory. One of the samples consisted of a few layers of perhydro H-CdA deposited on a silicon support, overlayered with a few layers of deuterated D-CdA, for a total thickness of ∼300 Angstroms. In a second sample the layers of perhydro-and deuterated- CdA were separated by two monolayers of Hn-octadecene/co-maleic acid copolymer. When heated for 15 minutes at 70°C, well below the disorder temperature [1], approximately 25% of the D-CdA molecules were replaced by H-CdA molecules, although the overall Langmuir-Blodgett film structure is known to remain unchanged [1]. The presence of copolymer layers limited the interdiffusion process to about 5%.
Neutron Diffraction Studies of Cd1−xMnxSe Epilayers and ZnSe/MnSe Multilayers
Authors: Giebultowicz T. M. , Klosowski P. , Rhyne J. J. , Samarth N. , Luo H. , Furdyna J.K. 
Published: March 2011

ABSTRACTNeutron diffraction patterns of MBE-grown single crystal zinc-blende epilayers of Cd1−xMnxSe with x=0.70 and 0.75 reveal the onset of long-range Type-III AF ordering at low T, in sharp contrast with earlier studies of bulk II-VI diluted magnetic semiconductors, where only short-range Type III correlations are observed. Results of first neutron diffraction studies of magnetic ordering in MBE-grown ZnSe/MnSe superlattices are also reported.
Local Environmental Effects in Magnetic Alloys and Multilayers: Calculations of the Static Response Functions
Authors: Johnson D. D. , Staunton J. B. , Györffy B. L. , Pinski F. J. , Stocks G. M. 
Published: March 2011

ABSTRACTWe have developed an ab-initio method for calculating the static response functions in substitutional alloys. For magnetic alloys, in addition to the nuclear diffuse scattering, a contribution to the alloy diffuse scattering intensities results from the response of the local moments to changes in the ‘local’ chemical environment (i.e. ∂μi/∂cj). We present results of firstprinciples calculations of these ‘local’ response functions in magnetic alloys. These response functions, which may be directly compared to neutron-scattering and Mößbauer experiments, are derived via a mean-field statistical mechanical description of compositional fluctuations in alloys. The statistical averages are performed via the Korringa-Kohn-Rostoker coherent potential approximation, which incorporates the electronic structure of the high-temperature, chemically disordered state. As a first application of the theory, we have investigated the environmental dependence of the moments in NiFe alloys and FeV alloys and multilayers. We compare our results with experiments on bulk alloys and multilayers. Also, a comparison is made to a set of first-principle ‘supercell’ calculations. Although preliminary, the results demonstrate the utility of these response functions for investigating the effects of changes in the chemical environment on the alloy moments and for aiding experimental interpretation in other multilayer systems that are less experimentally amenable than FeV.
Determination of Hydrogen(Deuterium) Density Profiles in Thin Metal Films and Multilayers by Neutron Reflection
Authors: Majkrzak C. F. , Satija S. , Neumann O. A. , Rush J. J. , Lashmore D. , Johnson C. , Bradshaw J. , Passell L. , Dinardo R. 
Published: March 2011

ABSTRACTThe density of hydrogen in thin films or multilayers of metal hydrides can be inferred from an expansion of the host lattice as measured by conventional x-ray diffraction techniques. However, because hydrogen and deuterium have scattering lengths for neutrons that are comparable to those of most metal nuclei, unlike the corresponding case for x-ray atomic scattering amplitudes, the hydrogen density profile normal to the surface of a flat, thin film can be determined directly from neutron reflectivity measurements. The hydrogen (deuterium) density modulation in an artificial superlattice along the growth direction can also be determined in this manner. The thin film or multilayer host metal material need not even be crystalline. Furthermore, because relatively large, flat single crystal substrates such as Si or quartz are nearly transparent to neutrons, the substrate can serve as the incident medium and the reflectivities of films or multilayers in contact with liquid solutions can be obtained. Thus, in situ studies employing active electrochemical cells, for example, can be performed. In addition to discussing the sensitivity of the method, the results of some neutron reflectivity experiments on metal multilayers and films, electrolytically loaded in situ with deuterium, are reported in this paper.
Diffuse Neutron Scattering Study of Short-Range Order in Fe0.8Al0.2Alloy
Authors: Sciiweika Werner 
Published: March 2011

ABSTRACTDiffuse neutron scattering experiments have been performed on a single crystal Fe0.8Al0.2at T-1013K. The data are analysed in terms of short-range order and lattice displacements. Effective pair-interactions have been determined by the inverse Monte Carlo method.Further measurements of the temperature dependence of the diffuse scattering reveal a long-range ordered phase with the B32 structure belowT∼ 650K.This new phase is related to the influence of the magnetism on the chemical ordering in the, iron-aluminum alloys.
Residual Stress Analysis with Neutrons
Authors: Krawitz Aaron D. 
Published: March 2011

ABSTRACTThe use of neutrons for the measurement of stress is complementary to and extends traditional x-ray diffraction methods to new types of problems. This is due to the lower absorption of neutrons compared to x-rays by most engineering materials, which increases the sampling depth from microns to millimeters. It is particularly suitable for triaxial macrostress gradients through the depth of engineering components and volumetric microstresses in composites. In addition, applied stress studies may also be performed. This paper briefly describes the nature of residual stresses, the use of diffraction for stress measurements, experimental aspects of the use of neutrons, and illustrative applications.
Neutron Measurement of Residual Stresses in a Used Railway Rail
Authors: Webster P.J. , Low K.S. , Mills G. , Webster G.A. 
Published: March 2011

ABSTRACTThe high resolution neutron diffraction technique has been applied to determine, non-destructively, the residual stress distribution developed in the head of a railway rail after normal service.Measurements were made, using the neutron strain scanner at the Institut Laue Langevin, Grenoble, on a transverse slice of rail 12mm thick taken from a section of straight track. The rail head was scanned in the three principal orientations in a series of parallel traverses sufficiently close to enable a two- dimensional matrix of data to be accumulated and vertical, transverse and longitudinal residual stress contours to be drawn.Substantial residual compressive and tensile stresses and steep stress gradients were observed related to the depth below the top surface, distance from the running line and shape of the rail head. The highest stresses and stress gradients were observed in transverse and vertical directions but significant stresses were also retained in the longitudinal (12mm thick) direction of the rail.The results demonstrate the effectiveness and unique characteristics of the neutron technique to determine non- destructively and continuously the residual stresses inside engineering components.
TOF Measurements of Pulsed Neutrons for Texture Analysis of Low Symmetry Materials
Authors: Larson Allen C. , Vergamini Phillip J. , Wenk Hans-Rudolf 
Published: March 2011

ABSTRACTThe single crystal diffractometer at LANSCE, SCD, provides an ideal ca- pability for the study of preferred orientation in geological samples by time-of flight(TOF) measurement of pulsed neutrons. The 2-d position sensitive neutron detector with the large wave length range allows one to measure the complete dis- tribution of intensities for several poles very quickly. Each histogram covers about πt2/16 radians of reciprocal space and contains information from all possible poles visible with the wave length range used, usually about 0.5 to 5.OÅ. With this method complete pole figures of many lattice planes can be constructed from only 12 to 20 sample orientations as compared to over 1000 sample settings per lattice plane using conventional diffractometers.Pole figures from measurements of experimentally deformed standard samples of calcite and quartzite with a known history of deformation provide in- formation about deformation mechanisms and their temperature/strain history. This information can be applied to interpret preferred orientation of naturally de- formed rocks.
Characterization of Sol-Clay Composites by Small-Angle Neutron Scattering
Authors: Moini Ahmad , Pinnavaia Thomas J. , Thiyagarajan P. 
Published: March 2011

ABSTRACTSilica-clay composites were prepared by reacting a 40 Å silica sol with aqueous clay suspensions. The clays which were studied included Na+-montmorillonite, fluorohectorite, and the synthetic clay Laponite. The aggregation mechanism of the sol particles and the degree of dispersion of the clay layers were monitored by small-angle neutron scattering. The data for powdered silica-montmorillonite products showed the presence of highly dispersed clay platelets and spherical sol particles. The results suggest that the interaction between these two components inhibits the sol aggregation process. Studies on the products prepared from other types of clays, however, showed that this interaction is highly dependent on the morphology and charge density of the clay platelets.
A Sans Study of Capillary Condensation in Porous Media
Authors: Lin M.Y. , Sinha S.K. , Huang J.S. , Abeles B. , Johnson J.W. , Drake J.M. , Glinka C.J. 
Published: March 2011

ABSTRACTWe use small angle neutron scattering (SANS) to study the microstructure of porous Vycor glass and the capillary condensation of fluids in the medium. Using a chord distribution model, we can predict the structure factor measured by SANS. Excellent agreement with the data is obtained. The fitted parameters characterize quantitatively the porous structure before and during the process of condensation, and are in good agreement with isotherm measurements. However, at the latest stages of the process, when all the pores are nearly filled, the model can no longer describe the system.
Real Space Method of Powder Diffraction for Non-Periodic and Nearly Periodic Materials
Authors: Egami T. , Toby B. H. , Dmowski W. , Janot Chr. , Jorgensen J. D. 
Published: March 2011

ABSTRACTThe use of high-energy neutrons from pulsed or hot sources allows the method of atomic pair distribution analysis to be applied to the structural determination of crystalline as well as amorphous solids. This method complements the standard crystallographic methods in studying non-periodic aspects of solids with or without long range order.
Neutron Rietveld Analysis of Anion and Cation Disorder in the Fast-Ion Conducting Pyrochlore System Y2(ZrxTi1−x)2O7
Authors: Haile Sossina M. , Wuensch B. J. , Prince E. 
Published: March 2011

ABSTRACTAll information on the site occupancies and atomic displacements which relate a pyrochlore superstructure to the parent fluorite-type subcell is contained in the normally-weak superstructure diffraction intensities. As Ti has a negative scattering length, the supercell maxima in the present phases are up to three times as intense as the fluorite-like reflections, and neutron diffraction provides an especially sensitive probe of the state of disorder. Y2Ti2O7 is found to have a fullyordered anion array and slight disorder, Y0.984Ti0.015, among the cations. In Y2(Zro.6TiO.4)2O7 the oxygen site normally vacant in pyrochlore is half filled and on the order of 15% exchange between cation sites has occurred.
Gas Phase Characterization in LP CVD Processes by a Performant Raman Equipment: Gas Temperature in the Vicinity of the Substrate
Authors: Gaufres R. , Huguet P. , Boya D. , Lafforet J. 
Published: March 2011

AbstractUsing a performant spontaneous Raman equipment, with intracavity laser excitation, the temperatures of tungsten hexafluoride and hydrogen have been measured in a cell reproducing the industrial conditions of C.V.D. tungsten deposition, in the vicinity of a heated graphite substrate. For tungsten hexafluoride, a vibrational temperature, much lower than that of the substrate, is determined. For hydrogen, rotational temperatures much higher than that of the substrate are found. After a discussion of the sources of experimental errors, possible interpretations of the results are given.
Characterization of Silicide Formation of LPCVD-W By Means of Rutherford Backscatrering Spectrometry and X-Ray Diffractometry
Authors: Zhang S.-L. , Buchta R. , Östling M. 
Published: March 2011

AbstractTungsten disilicide (WSi2 ) was formed by annealing 185 nm and 750 nm thick LPCVD-W films deposited on <100>-Si substrates. The thickness of the formed WSi2 was observed by Rutherford backscattering measurements (RBS) to increase parabolically with the annealing time. This agrees with the behavior reported in the literature for sputter deposited or evaporated W films. However, a higher stlicide growth rate was found in this work. An activation energy of 2.6 eV/atom was measured, which is smaller than those for sputter deposited or evaporated W films. The crystal structures of the formed WSi2 and the unreacted W films were analyzed using X-ray diffraction (XRD) technique. The thermal history of the samples was found to play an important role for the crystal structure of the unreacted W and formed WSi2. The as-deposited W films became more oriented to the <100> direction with increasing film thickness, while the unreacted W films on top of the formed WSi2, from the samples annealed at temperatures from 700 to 800°C, became more <100> direction dominated with decreasing W film thickness. The preferred orientation of the grown WSi2 films also varied with the silicidation conditions. These observations indicate that the simple method of determining W film thickness by comparing the W diffraction peak heights of the remaining W films after heat treatment to a reference sample will unavoidably introduce large errors. A compensation technique was suggested where both the W and WSi2 diffraction signals were used. A parameter x, a function of reacted W thickness, was introduced to fit the compensation procedure. The conclusion of this study is that attention should be paid to the orientation change of W and WSi2 films during heat treatment if XRD is employed to study the kinetics of WSi2 formation.
Influence of Impurities and Microstructure on the Resistivity of LPCVD Titanium Nitride Films
Authors: Buiting M. J. , Reader A. H. 
Published: March 2011

AbstractThe electrical resistivity of LPCVD TiN films deposited at temperatures between 450 and 700°C has been found to vary from about 900 to 150 μ Ωcm. The elemental composition (Ti:N), impurity content and the microstructure of the films have been investigated in order to explain the resistivity variation. It appears that this variation is directly related to the chlorine (impurity) content of the films. Films deposited at 700°C have both the lowest chlorine content and the lowest value of resistivity. Additionally the difference between the resistivity of this latter film and the (lower) value for bulk TiN is discussed.
Influence of Substrate and Process Parameters on The Properties of CVD-SiC
Authors: Parretta A. , Giunta G. , Cappelli E. , Adoncecchi V. , Vittori V. 
Published: March 2011

AbstractThe microstructure and mechanical properties (adhesion, hardness) of beta-SiC coatings, prepared in a cold wall reactor, were studied by examining different substrates and deposition process conditions. Hard (3500 HK), fine grained beta-SiC coatings were deposited onto graphite at relatively high deposition terperatures (1473–1673 K) using SiC14,C3H8,H2 gas mixtures. The thermal decomposition of methyltrichlorosilane (MTS) in hydrogen and argon allowed the production of beta-SiC coatings onto a variety of substrate materials in the temperature range 1173–1373 K. The growth mechanisms of SiC deposited from MTS/H2/Ar system onto graphite and polycrystalline alfa-SiC substrates were studied. At low (40 kPa) and atmospheric pressure, the growth kinetics is limited by surface reactions. Also, a strong dependence of the microstructure and crystallographic orientation on the deposition parameters was observed. Hard metals (WC/Co) were succesfully coated with beta-SiC using the MTS/H2/Ar system. Problems of chemical compatibility between the substrate and the beta-SiC coating were minimized by deposition of an intermediate layer of TiN.
Oxidation Resistant Coatings Produced by Chemical Vapor Deposition :Iridium and Aluminum Oxynitride Coatings
Authors: Netter P. , Campros Ph. 
Published: March 2011

AbstractOxidation resistant coatings of iridium on graphite, carbon/ carbon or molybdenum and of aluminum oxynitride on graphite and carbon/carbon have been produced by low pressure CVD from halide starting compounds (IrF6 and AlCl3). The resulting deposits are adherent, non porous and have proved to be impervious to oxygen in subsequent heating to 2000° C in air for more than 30 minutes (no evidence of deterioration).These coatings materials are promising for effective protection against oxidation in rocket engines, gas turbines and thermal protection tiles space shuttles or against corrosion in the glass industry (iridium).
Reactive Chemical Vapor Deposition (R.C.V.D.) as a Method for Coating Carbon Fibre with Carbides
Authors: Bouix J. , Vincent C. , Vincent H. , Favre R. 
Published: March 2011

AbstractCarbon fibre is an ideal material for reinforcing inorganic matrix composites, especially for high temperatures. Its main drawback is its susceptibility to oxidation and to reaction with metals.Our challenge was to perfect a method of producing a carbon fibre in which each elementary filament is covered and protected by a very thin and adherent layer of a refractory carbide such as SiC, B4C, etc…For this purpose, we use reactive chemical vapor deposition (R.C.V.D.) in which only the M element of the M C carbide is carried by the gas phase, carbon being supplied by the fibre itself. The growth rate is self regulated by the solid state diffusion.This method has been developed in a continuous reactor with ex-PAN (6K) or ex-PITCH (2K) fibres.The mechanical behaviour of the coated fibres is very near that of the initial ones, but their oxidation rate at 600°C is 100 times lower.
Low Temperature Mocvd of Silicon-Based Ceramic Films
Authors: Du Honghua , Bae Yongwoong , Gallois Bernard , Gonsalves Kenneth E. 
Published: March 2011

AbstractA liquid methylsilazane compound, [CH3SiHNH]n, was used, with H2, NH3, and a 60%/40% mixture of NH3/H2, to deposit silicon-based ceramic films in a CVD reactor at 873–1073 K. Characterization of the films by ellipsometry, Fourier transform infrared spectrometry (FTIR) and Auger electron spectrometry (AES) showed that the methylsilazane was pyrolyzed to form silicon carbonitride in H2, and silicon nitride in both NH3and NH3/H2, with the incorporation of appreciable amounts of oxygen. The deposition rate increases and the activation energy decreases in order from NH3-, NH3/H2-, and H2-[CH3SiHNH]ngas mixtures. The temperature dependence of the structural density of the films increases in the same order.
Preparation, Structure and Properties of VOx and TiO2 Thin Films By Mocvd
Authors: Chang H. L. M. , Parker J. C. , You H. , xu J. J. , Lam D. J. 
Published: March 2011

AbstractTitanium and vanadium oxide thin films have been prepared in a cold wall low pressure MOCVD system for the study of MOCVD processing of epitaxial oxide films. Films were deposited on Si(111) and sapphire (0001) and (1120) at temperatures from 400 to 800°C. Processing parameter-structureproperty relationship was examined in detail and the result is presented.
Low-temperature Chemical Vapor Deposition of Rhodium and Iridium thin Films
Authors: Smith David C. , Pattillo Steve G. , Elliott Norman E. , Zocco Thomas G. , Burns Carol J. , Laia Joseph R. , Sattelberger Alfred P. 
Published: March 2011

AbstractLow-temperature chemical vapor deposition of M(allyl)3 (M = Rh, Ir; allyl = η3 -C3H5) in the presence of H• yields thin, crystalline metal films of greater than 97% metal composition. Depositions using H2 result in the formation of materials which are amorphous and contain a significant amount of residual carbon (14%). The composition of these materials does not differ significantly from that obtained from the vacuum thermal deposition of M(allyl)3.
Analytical Simulation of an Improved Cvi Process for Forming Highly Densified Ceramic Composites
Authors: Tai Nyan-Hwa , Chou Tsu-Wei 
Published: March 2011

AbstractA model for chemical vapor infiltration (CVI) under pressure and temperature gradients is applied to the study of deposition of SiC from the pyrolysis of CH3SiCl3 within a 3-D woven fibrous preform. The model considers the infiltration of reactants into a preform with temperature gradients by applying a pressure gradient between the vapor inlet and outlet; it also takes into account the variation in concentration of the vapor precursor. A quasi-steady state approach has been adopted to simulate the matrix deposition in a 3-D unit cell. The density distribution, consolidation profile, and total fabrication period have been theoretically predicted.
Modelling Transport, Reaction, and Pore Structure Evolution During Densification of Cellular or Fibrous Structures
Authors: Sotirchos Stratis V. , Tomadakis Manolis M. 
Published: March 2011

AbstractA mathematical model is developed to describe mass transport, reaction., and structure evolution during densification of porous media of initially fibrous or cellular structure. The use of Monte Carlo simulation procedures for determining the variation of the local (average) structural properties of the porous structure and of the effective diffusion coefficients in the porous medium with the porosity is also discussed, and results are presented for Knudsen diffusion in cellular or fibrous media. The model is used to theoretically study the transient behavior of the densification process during preparation of SiC/SiC ceramic matrix composites by chemical vapor infiltration (CVI) of porous preforms. Particular emphasis is placed on the investigation of the effects of pressure pulsing on the density gradients in the densifying structure.
Borazine Adsorption and Reaction on a Re(0001) Surface
Authors: He J.-W. , Goodman D. W. 
Published: March 2011

AbstractThe interaction of borazine (N3B3H6) with a Re(0001) surface has been studied by low energy electron diffraction (LEED), thermal desorption spectroscopy (TDS), Auger electron spectroscopy (AES) and electron energy loss spectroscopy (ELS). It is shown that chemisorbed borazine dissociates into atomic N, B and H on Re(0001) at sample temperatures > 450K. However, borazine is found to decompose to a boron-nitrogen compound when irradiated with a 2 KeY e–beam.