bluuebunny/crossref_metadata_2025_split huggingface dataset:
Novel Langmuir-Blodgett Films of Electrically Conducting Polyion Complexes and Diblock Copolymers
Authors: Timothy Royappa A. , Saunders Randall S. , Cohen Robert E. , Rubner Michael F. 
Published: March 2011

ABSTRACTThe Langmuir-Blodgett (LB) technique has been used to form two different types of multilayer films with novel molecular organizations. In the first case, a new method of fabricating superlattices of conducting polymers has been devised and studied. This method involves forming polyion complexes of acid derivatized conducting polymers with stearylamine (StNH2) and subsequently manipulating them into AB type superlattices by the LB technique. To date, superlattices consisting of isolated alternating monolayers of poly(thiophene acetic acid) (PTAA) and sulfonated polyaniline (PAn) have been studied. The layered structure of these films was found to be very similar to that of their respective homopolymer LB films, as evidenced by X-ray diffraction patterns. The conductivity of these superlattices was in the range of 10−1 S/cm, which is approximately one order of magnitude higher than that obtained with the homopolymer LB films (about 10−2 S/cm). In the second case, LB films of a novel diblock copolymer have been made, where one of the blocks is a water-insoluble polyacetylene precursor and the other block a non-conjugated, water-soluble poly(norbornene) derivative. The precursor block of the LB films could be converted to trans-polyacetylene by heating, and doped to a conductivity of 10−3 S/cm, which was significantly higher than that of cast (10−7 S/cm) or spin-coated (10−5 S/cm) films of the same material. Thus, in both cases, the unique molecular organization created by the LB technique has resulted in films with higher conductivities than those obtained by traditional casting techniques.
Application of Positron Annihilation Methods for Investigation and Testing of Polymer
Authors: Tishin S. A. , Tishin V. A. , Kestelman V. N. 
Published: March 2011

ABSTRACTThe principal directions of application of positron annihilation methods (MAP) for investigation of polymer and polymer composition with attraction the original dates are analyzed. The results obtained allow to make the conclusion about efficiency of MAP at analyses microvoids and microdefects in disordered polymer (5…20 Å) which are inaccessible or difficult for the other analytical methods. The correlation of the probability of positronium formation and its annihilation characteristics with microstructure properties is discussed.
Intermolecular Effects on Third Order Nonlinear Optical Properties
Authors: Dudis D. S. , Yeates A. T. , Kurtz H. A. 
Published: March 2011

ABSTRACTHartree-Fock ab initio calculations have been used to examine the magnitude of non-polar intermolecular interactions on polarizabilities and second hyperpolarizabilities. In the present case two ethylene molecules were examined in a cofacial interaction. Basis set requirements and correlation effects were considered in deriving the intermolecular potential. Two basis sets were considered for the intermolecular interactions at the Hartree-Fock level, while one set of calculations was performed with corrections for correlation. It is found that intermolecular contacts at the van der Waals distance has little effect on the molecular second hyperpolarizability, but it is not clear what the effect would be for longer oligomers.
Large Nonlinear Refractive Indices of Nickel Dithiolene Doped Polymethylmethacrylate
Authors: Winter Christopher S. , Oliver S. N. , Hill C A. S. 
Published: March 2011

ABSTRACTThe nonlinear refractive index, linear and nonlinear absorption coefficients of a number of nickel dithiolene-doped PMMA polymers have been measured. Nonlinear refractive indices up to about 10−8 cm−2/KW were observed, with figures of merit defined by δnsat/αλ and Reχ(3) / Im χ(3) within acceptable device limits.
Interactive use of Electron Microscopy and Light Scattering as Diagnostics for Pyrogenic Aggregates
Authors: Dobbins Richard A. 
Published: March 2011

AbstractBoth electron microscopy and light scattering have played an important role in elucidating the processes of inception, growth, and oxidation of carbonaceous particles in flames. The techniques developed have application to the various pyrogenic materials including the metallic oxides, carbides, etc. Thermophoretic sampling has been developed to afford efficient extraction of particle samples from hot reaction zones. The sampling procedure preserves the particle morphology for subsequent analysis by transmission electron microscopy (TEM). Studies using this technique have shown aggregate structures with fractal dimensions of 1.6 to 1.8, a result that is consistent with the computer simulations of the cluster-cluster aggregation process. Diverse morphologies, including microparticles found in the particle inception zone, reveal the evolution of these aggregates. The optical cross sections for polydisperse aggregates which are used to interpret the laser scattering/extinction tests (LSE) are described. Population averaged properties - volume fraction, volume mean diameter, monomer and aggregate number concentrations, mean-square radius of gyration - are derived. The interactive use TEM and LSE data leads to a global description of the aggregate dynamic processes which are found to be regionally partitioned within the laminar hydrocarbon diffusion flame.
Axial Concentration Profile of H2 Produced in the CVD of Si3N4.
Authors: Hay Stephen O. , Roman Ward C. 
Published: March 2011

AbstractSilicon nitride (Si3N4) has been demonstrated to be an effective high temperature anti-oxidant when deposited in its α-crystalline form. The Materials Technology Laboratory at UTRC has developed a pilot-scale chemical vapor deposition (CVD) reactor capable of depositing α-Si3N4 from ammonia (NH3) and silicon tetrafluoride (SiF4) at 1.8 torr and 1440 C. Coherent anti-Stokes Raman spectroscopy (CARS) has been applied to measure H2 produced in this reactor. Axial concentration measurements have been performed both in the presence and absence of SiF4. Previous CARS measurements demonstrated the importance of surface (Si3N4) catalyzed decomposition of NH3: as a competing reaction to: in the CVD reactor under deposition conditions. The observed hydrogen concentration profiles confirm these measurements and allow quantitative comparison between the competing reactions. NH3 decomposition is suppressed 20% by the addition of SiF 4 in a 6:1 (NH3:SiF4) molar ratio. No decomposition is observed in the absence of Si3N4.
CVD of Silicon Nitride Plate from HsiCl3-NH3-H2 Mixtures
Authors: Lennartz J. W. , Dowell M. B. 
Published: March 2011

AbstractPreferred conditions for deposition of thick α-Si3 N4 plate from HSiCl3 -NH3-H2 on the vertical surfaces of a lowpressure, hot-wall CVD reactor were identified by means of a designed experiment. The design included the range of temperatures 1300°C-1500°C, pressures 0.5–2.0 Torr, and residence times 0.01–1.0 sec. The vertical deposition surfaces received a viscous, laminar flow of well mixed, thermally equilibrated reactants. Plates 0.05–0.5 mm thick were produced on multiple vertical substrates 350 cm2 in area at deposition rates 5–70 μm/hr. Plates 0.5–4.0 mm thick were produced on horizontal substrates at deposition rates of 60–120 μm/hr. When NH3 flows in stoichiometric excess, deposition rates on vertical surfaces increase approximately linearly with the flow rate of HSiCl3 but depend little on temperature, as would be expected if the reaction proceeds under mass transport control with product depletion. Multiple correlation analyses show that thickness variations in the deposit are reduced by increasing the temperature and decreasing the gas residence time. CVD silicon nitride plate produced under the optimized conditions exhibits theoretical density and is free of pores and cracks. It exhibits a columnar morphology in which the <222> and <101> crystallographic directions are oriented preferentially normal to a surface, which consists of well-defined trigonal facets 10–50 μm across. Crystallite sizes determined by Xray line broadening range from 0.06–1.0 μm. This CVD plate is gray and contains approximately 0.5 w/o C and 0.5 w/o 0 as principal impurities.
Chemical Vapor Deposition of Multiphase Boron-Carbon-Silicon Ceramics
Authors: Golda E. Michael , Gallois B. 
Published: March 2011

AbstractSpecific compositions of boron-carbon-silicon ceramics exhibit improved abrasive wear and good thermal shock resistance, but require bulk sintering at temperatures in excess of 2100K. The formation of such phases by chemical vapor deposition was investigated in the temperature range of 1073K–1573K. Methyltrichlorosilane (CH3SiCl3), boron trichloride, and methane were chosen as reactant gases, with hydrogen as a carrier gas and diluent. The coatings were deposited in a computer-controlled, hot-wall reactor at a pressure of 33 MPa (200 Torr).Below 1473K the coatings were amorphous. At higher temperatures non-equilibrium reactions controlled the deposition process. The most common coating consisted of a silicon carbide matrix and a silicon boride, SiB6, dispersed phase. Multiphase coatings of B+B4C+SiB6 and SiC+SiB6+SiB14 were also deposited by controlling the partial pressure of methane and boron trichloride. Non-equilibrium thermodynamic analysis qualitatively predicted the experimentally deposited multiphase coatings.
SiC Thin Films by Chemical Conversion of Single Crystal Si
Authors: Chiu Chien C. , Kwok Chi Kong , Desu Seshu B. 
Published: March 2011

AbstractThe reaction of (100)Si with C2H2 in a hot wall CVD reactor has been studied using a X-ray photolectron spectroscopy, and a scanning electron microscopy. The growth of the SiC films was observed through the behavior of Si2p peaks and their plasmons. Smooth surface morphology with a monolayer of SiC was obtained at 950°C for 7 minutes and defects were observed for longer reaction times at this temperature. For higher reaction temperatures (e.g. 1000°C), defects were observed for reaction times as short as 10 seconds. The formation of defects was correlated to the out-diffusion of Si in the carborization process.
Low-Temperature PACVD Silicon Carbide Coatings
Authors: Halverson W. , Vakerlis G. D. , Garg D. , Dyer P. N. 
Published: March 2011

AbstractPlasma-assisted chemical vapor deposition (PACVD) is used extensively to coat planar (2-dimensional) substrates. In principle, the technique can be used to deposit coatings on 3-dinensional objects. However, extending PACVD to coat 3-dimensional objects uniformly requires careful control of the plasma, substrate temperature, and reactant concentrations over a large volume. A novel low-temperature radio frequency PACVD reactor design was developed to deposit coatings uniformly and reproducibly on 3-dimensional metallic substrates. The design features a temperature-controlled reaction chamber fitted with one or more rf-driven electrodes to generate uniform, large-volume plasma. The reactor was used to develop a series of silicon carbide coatings, which were deposited at or below 500°C. The coatings contain SiC and varying amounts of free silicon and/or amorphous carbon (diamond-like carbon), depending on reagent gas composition and reactor operating parameters. The coatings significantly reduced wear on stainless steel samples in ball-on-disk and abrasive wear tests and provided oxidation protection to molybdenum and titanium alloy.
X-Ray Tomographic Microscopy of Nicalon Preforms and Chemical Vapor Infiltrated Nicalon/Silicon Carbide Composites
Authors: Butts M. D. , Stock S. R. , Kinney J. H. , Starr T. L. , Nichols M. C. , Lundgren C. A. , Breunig T. M. , Guvenilir A. 
Published: March 2011

AbstractFollowing the evolving microstructure of composites through all stages of chemical vapor infiltration (CVI) is a key to improved understanding and control of the process. X-ray Tomographic Microscopy (XTM), i.e., very high resolution computed tomography, allows the microstructure of macroscopic volumes of a composite to be imaged nondestructively with resolution approaching one micrometer. Results obtained with XTM on dense SiC/SiC composites and on woven SiC fiber preforms illustrate how details of the densification process can be followed using this technique during interruptions in processing. Ways in which the three-dimensional microstructural information may be used to improve modeling are also indicated.
Effect of Bn Interfacial Coating on the Strength of a Silicon Carbide/Silicon Nitride Composite
Authors: Norton Kirk P. , Streckert Holger H. 
Published: March 2011

AbstractBoron nitride has been identified as a good fiber/matrix interface coating for SiC fibers in a Si3N4 matrix. Boron nitride thin films prepared from BCl3 and NH3 at 1000°C and from B2 H6 and NH3 at 550°C were deposited on SiC (Nicalon®) cloth in a low pressure chemical vapor deposition reactor. The coating thickness was varied from 0.1 μm up to 4 μm. Six layers of cloth for each coating thickness were incorporated into a chemical vapor infiltrated matrix of amorphous Si3N4.Flexural strength data and composite toughness were obtained from three-point bend tests. Scanning electron microscopy and metallographic analysis of fracture surface morphology were used to determine the failure mode.
Microwave Assisted Chemical Vapor Infiltration
Authors: Devlin D. J. , Currier R. P. , Barbero R. S. , Espinoza B. F. , Elliott N. 
Published: March 2011

AbstractA microwave assisted process for production of continuous fiber reinforced ceramic matrix composites is described. A simple apparatus combining a chemical vapor infiltration reactor with a conventional 700 W multimode oven is described. Microwave induced inverted thermal gradients are exploited with the ultimate goal of reducing processing times on complex shapes. Thermal gradients in stacks of SiC (Nicalon) cloths have been measured using optical thermometry. Initial results on the “inside out” deposition of SiC via decomposition of methyltrichlorosilane in hydrogen are presented. Several key processing issues are identified and discussed.
CVD Coating of Ceramic Monofilaments
Authors: Guth Jason R. 
Published: March 2011

AbstractIn many composite systems it has become apparent that coatings on the reinforcements are necessary to achieve high toughness materials. In order to examine materials which may be used as coatings on ceramic monofilaments and remain stable in high temperature, oxidizing environments, the deposition of a number of refractory metals has been attempted. The results of coating experiments using silicon carbide fibers as substrates as well as general observations concerning the prospects of continuously coating long lengths of fibers will be discussed. The materials studied include carbon, cobalt, zirconium, molybdenum, tantalum, tungsten, and iridium. Carbon has been deposited from methane and propylene onto both SiC and sapphire fibers. Deposition of the metals has been achieved by direct chlorination of the metals followed by hydrogen reduction at the fiber. Iridium(III)2,4-pentanedionate has been used to deposit iridium metal. All metals were deposited at low pressure in a hot wall reactor with fibers continuously spooled through the reactor.
CVD of SiC and AlN Using Cyclic Organometallic Precursors
Authors: Interrante L. V. , Larkin D. J. , Amato C. 
Published: March 2011

AbstractThe use of cyclic organometallic molecules as single-source MOCVD precursors is illustrated by means of examples taken from our recent work on SiC and AlN deposition, with particular focus on SiC. Molecules containing (SiC)2 and (AlN)3 rings as the “core structure” were employed as the source materials for these studies. The organoaluminum amide, [Me2AlNH2]3, was used as the AlN source and has been studied in a molecular beam sampling apparatus in order to determine the gas phase species present in a hot-wall CVD reactor environment. In the case of SiC CVD, a series of disilacyclobutanes, [Si(XX′)CH2]2 (with X and X′ - H, CH3 , and CH2 SiH2CH3), were examined in a cold-wall, hot-stage CVD reactor in order to compare their relative reactivities and prospective utility as single-source CVD precursors. The parent compound, disilacyclobutane, [SiH2 CH2]2, was found to exhibit the lowest deposition temperature (ca. 670 °C) and to yield the highest purity SiC films. This precursor gave a highly textured, polycrystalline film on the Si(100) substrates (70% with a SiC<lll> orientation).
The Chemical Vapor Deposoitin of Pure Nickel and Nickel Boride Thin Films from Borane Cluster Compounds
Authors: Kher Shreyas , Spencer James T. 
Published: March 2011

AbstractSeveral borane cluster compounds, such as pentaborane(9) and their corresponding metal complexes have been investigated in our laboratory for their utility as unique source materials for synthesizing metal/metal boride thin films by MOCVD. In this paper we report the preparation of thin films of nickel boride from the thermal decomposition of nido- pentaborane( 9) in the presence of anhydrous nickel chloride [NiCl2] in the vapor phase. Crystalline nickel boride thin films of controlled composition ranging from 0.1 to several microns have been readily prepared by controlling the temperature and the flow rate of the pentaborane(9) into the reaction chamber. The nickel boride films on GaAs were thermally annealed to form the Ni7B3 phase as hexagonal crystals in a Ni3B matrix. These films have been characterized by AA, AES, EDXA, SEM, XRD and electron diffraction. The phases were determined primarily by X-ray and electron diffraction experiments.
Routes to Diamond Heteroepiitaxy
Authors: Badzian Andrzej , Badzian Teresa 
Published: March 2011

AbstractThis paper reviews the status of diamond heteroepitaxy approached by chemical vapor deposition and by physical methods. Reported are experiments with cubic boron nitride and nickel conducted with the help of microwave plasma chemical vapor deposition. X-ray diffraction data confirm diamond heteroepitaxy on the (111) faces of cubic boron nitride crystals. Heteroepitaxy on nickel was not demonstrated yet nevertheless suppression of graphite nucleation was achieved by formation of nickel hydride.
Kinetic Modelling of the Deposition of SiC from Methyltrichlorosilane
Authors: Sotirchos Stratis V. , Papasouliotis George D. 
Published: March 2011

AbstractA kinetic model is presented for the deposition of silicon carbide through decomposition of methyltrichlorosilane (MTS). The developed model includes gas phase (homogeneous) reactions that lead to formation of deposition precursors and surface (heterogeneous) reactions that lead or can lead to deposition of silicon carbide, silicon, and carbon. The kinetic model is incorporated in a transport and reaction model for a tubular hot-wall reactor, and the overall reactor model is used to obtain some preliminary results on the effects of pressure and distance in the reactor on the rate of deposition and the composition of the deposit. The results show that the model can reproduce most of the experimental observations of the literature.
Growth and Characterization of PECVD Diamond Films
Authors: Mucha J. A. , Seibles L. 
Published: March 2011

AbstractPolycrystalline diamond films have been deposited on (100) silicon wafers by plasma enhanced chemical vapor deposition (PECVD) using a 1.5 kW microwave source to dissociate dilute gas mixtures of CH4 and O2 in H2. Films as thick as 20μm covering a 2″ diameter area were deposited at 925 °C, 40 Torr total pressure, and 500 sccm total flow. These have been characterized as a function of CH4 [0.2–4%] and Os [0–3%] concentrations by measurements of deposition rate, stress, surface roughness, morphology, and impurity levels (C-H and amorphous-graphitic carbon). Addition of oxygen to the discharge tends to reduce impurity levels in the diamond films; however, this is accompanied by a reduction in deposition rate. When an effective CH4 concentration [= %CH4 - %O2] is used as a metric for O2 -containing feed compositions, deposition rates as well as film properties are found to agree well with those obtained in the absence of O2. Thus, 1% CH4 in hydrogen is nearly equivalent to 4% CH4, 3% O2 in hydrogen as feed compositions for depositing diamond.
Correlation of Raman Spectra and Bonding in DLC Films Deposited by Laser Ablation and Laser-Plasma Ablation Techniques
Authors: Rengan A. , Narayan J. , Park J. L. 
Published: March 2011

AbstractWe have deposited diamondlike carbon (DLC) films on a variety of substrates from 250° C and higher. The effects of deposition temperature on the properties of DLC films deposited by a conventional laser ablation technique are compared with that of a unique laser-plasma deposition scheme. The calculated values of neff, the effective number of valence electrons, suggest that, with the increase in the deposition temperature, the diamondlike component (sp3 bonds) remains invariant for the laser deposited samples, and increases for the laser-plasma deposited films. Raman measurements show that the Raman allowed ‘G’ band upshifts to ˜1600 cm−1 for both deposition schemes. However, the disorder induced 'D' band remains invariant at ˜1370 cm−2 for the laser ablated samples, and downshifts to ˜1350 cm−1 for the laser-plasma deposited samples. These results suggest a correlation between the diamondlike content (sp3 bonds) and the Raman shift of the ‘D’ band.
Kinetics of Chemical Vapor Deposition of Sic Between 750 and 850°C at 1 Bar Total Pressure
Authors: Neuschütz Dieter , Salehomoum Farzin 
Published: March 2011

AbstractThe deposition rate from mixtures of methyltrichlorosilane (MTS), hydrogen and methane was measured thermogravimetrically using a hot wall vertical reactor and planar SiC substrates. Below 850 °C and at sufficiently high gas velocities, the rate of the phase boundary reaction could be determined. In the absence of CH4 and at H2 :MTS=55, Si was deposited together with SiC. Addition of CH4 lowered the Si content, pure SiC being deposited at CH4 :MTS above 10. The deposition rate j in the range 750 to 850 °C follows the equation with E(Si) = 160 and E(SiC) = 300 kJ/mol. Reaction mechanisms are presented to account for the observed reaction orders with respect to MTS. Between 900 and 970 °C, the reaction rate decreased with temperature indicating a change in the deposition mechanism.
Rapid Growth of Ceramic Films by Particle-Vapor Codeposition
Authors: Hurt Robert H. , Allendorf Mark D. 
Published: March 2011

AbstractParticle-enhanced chemical vapor deposition (PECVD) is capable of producing ceramic films at high deposition rates. A mathematical model of the particle-vapor codeposition process has been developed and has been applied to PECVD processes to predict deposition rate enhancements and deposit properties.
Determination of the Roughness of CVD Surfaces by Laser Scattering
Authors: Klein Max , Gallois Bernard 
Published: March 2011

AbstractA laser scattering apparatus was developed for the determination of surface roughness and other surface statistical parameters of chemically vapor-deposited coatings. Visual examination of HeNe laser scattering patterns reflected from polished sapphire and CVD titanium nitride surfaces showed a sensitivity to roughness differences of tens of nanometers. The scattering apparatus was integrated with a cold-wall CVD reactor. The root mean square roughness of silicon carbide deposits on silicon in the early stages of growth was determined from the intensity of the specularly reflected beam. Changes in roughness and the spatial arrangement of depositing crystallites were monitored in situ by angular resolution of the scattered light spectra. Both ex situ and in situ results were in good agreement with profilometric examinations of the rough surfaces.