bluuebunny/crossref_metadata_2025_split huggingface dataset:
Surface Investigation by Neutron Reflection
Authors: Farnoux B. 
Published: March 2011

ABSTRACTSeveral phenomena analogous to those observed in classical optics, such as reflection, refraction and interference, are also observed with slow neutrons. Information on surface properties, described by a refractive index profile, can be extracted from reflection experiments. This information is similar to that obtained by X-ray reflection. However, there are some instances where the new neutron method provides a distinct advantage. The refractive index is related to the scattering length density, a parameter which describes the neutron-matter interaction. Owing to the magnetic interaction, magnetic materials have a neutron spin dependent refractive index, and a critical reflection of polarized neutrons is a particularly sensitive probe of surface magnetism. On the other hand, in contrast to X-rays, neutron scattering length values vary randomly from element to element. Isotopic substitution can then produce a contrast in the scattering length density. Of particular importance is the large difference between hydrogen and deuterium. This is a distinct advantage for studiyng many problems in surface chemistry, particularly in the polymer field.
Initial Stages in the Growth of Oxide Thin Films by CVD
Authors: Tietz Lisa A. , Summerfelt Scott R. , English Gerald R. , Carter C. Barry 
Published: March 2011

AbstractA technique has been developed for studying the early stages of heteroepitactic nucleation and growth of oxide thin films by TEM using direct deposition onto electron-transparent ceramic substrates. Observations of α-Fe2O3 island growth on four orientations of α-Al2O3 – (0001), {1102}, {1010}, and {1120} – are reported. Moir6 fringes and selected-area diffraction are used to show heteroepitactic growth. Island morphology is compared to known growth habits of hematite crystals. Preferential nucleation of islands at low-energy sites (e.g. surface steps) is also demonstrated.
Predicting The Chemistry In Cvd Systems
Authors: Spear Karl E. , Dirkx Ryan R. 
Published: March 2011

AbstractTailoring the chemical and physical nature of CVD deposits for specific applications requires understanding and controlling the chemical processes occurring in a deposition reactor. This implies understanding the combined equilibrium, kinetic, and transport processes. The occurring processes produce composition gradients in the reactor which can cause variations in the deposition chemistry. Derived physical and mathematical models of possible mechanisms provide critical tools for manipulating and controlling the chemical and physical nature of CVD deposits. Examples of silicon boride deposition from SiH4, BC13, and H2 mixtures are used to illustrate thermochemical modeling techniques which utilize the concept of partial equilibrium. Predictions of limits on the chemical behavior, and comparison of these limits with experimental observations are used to hypotheses deposition mechanisms.
Internal Stresses In Amorphous Mocvd SiO2 Films
Authors: Desu Seshu B. 
Published: March 2011

AbstractAmorphous SiO2 films were deposited by the low pressure pyrolysis of organometallic precursors at temperatures of 350 to 500°C. Films were deposited on both single crystal silicon and fused quartz substrates. Intrinsic stresses in the films were measured by a curvature method as a function of deposition conditions and thermal processing conditions. As–deposited films showed significant tensile stress of the order of 400 MPa. The intrinsic stresses in the films increased as the deposition temperature decreased and deposition pressure increased. Small concentrations of dopants like B2O3 and P2O5 significantly decreased the intrinsic stress of as–deposited films. Stress reduction was also achieved by post deposition annealing. SiO2 film stress is correlated to the Si-O-Si bond angle distribution in the structure of the resultant film.
Morphological Evolution Of Titanium Carbide Whiskers
Authors: Mathur R. , Gallois B. M. 
Published: March 2011

AbstractThe early growth of titanium carbide whiskers from mixtures of TiCl4-CH4-H2 was investigated. Fine nickel particles were the catalytic agent in a hot-wall CVD reactor. It was confirmed that whisker growth is initiated by the vapor-liquid-solid mechanism at the growth temperature of 1423 K. The initial growth proceeds by the diffusion of the constituent species through a Ni-Ti liquid droplet and is characterized by a rapid increase in whisker length, the diameter remaining essentially constant. In the later stage, the whiskers grow primarily in the axial direction at a reduced rate with a gradual increase in the diameter. The whisker diameter (D) and its rate of increase are independent of the nickel particle sizes, but increased proportionately to the reactant supersaturations. The whisker length (L) also increased with increasing nickel particle size and reactant supersaturation, resulting in large aspect ratios (L/D = 12.5). The whiskers exhibited extensive branching and kinking and a <100> primary growth direction.
Characterization Of Ceramic Matrix Composites Fabricated By Chemical Vapor Infiltration
Authors: Stinton D. P. , Hembree D. M. , More K. L. , Sheldon B. W. , Besmann T. M. 
Published: March 2011

AbstractA process for the preparation of fiber-reinforced SiC composites by chemical vapor deposition has been developed at Oak Ridge National Laboratory. Composites are prepared by infiltrating fibrous preforms with reactant gases that decompose at elevated temperatures to deposit silicon carbide between and around the fibers. Because the infiltration process utilizes both temperature and pressure gradients, SiC is deposited under conditions that vary considerably from the hot face to the cool face of the composite. Matrix characterization of composite samples by transmission electron microscopy and Raman spectroscopy are described.
Benefits and limits of the thermodynamic approach to C.V.D. Processes
Authors: Bernard C. , Madar R. 
Published: March 2011

AbstractThis paper intends to develop and illustrate by a few examples the principles of thermodynamic analysis which can be applied at an early stage to assist in selecting the following:• the material to be deposited for a well-defined application,• the nature of reactants• the range of experimental parameters.Specific emphasis will be given to the main problems relating to data selection: assessments, availability of coherent data, sensitivity of results to data accuracy, etc.Finally, the validity of a thermodynamic approach at equilibrium will be discussed with a view to optimizing a dynamic non-equilibrium process.
Gas Phase Reactions Relevant to Chemical Vapor Deposition: Numerical Modeling
Authors: Burgess D. , Zachariah M. R. 
Published: March 2011

AbstractNumerical modeling of gas phase chemical kinetics was used to investigate reactions following silane decomposition to suggest experimental conditions and to interpret concentrations measurements. The effects of concentration and temperature gradients on kinetic pathways and reactive intermediates were studied. These processes are relevant to silicon-based chemical vapor deposition (CVD), to flame-driven gas phase particle nucleation, and to laser-induced processes for materials fabrication.
Structure, Composition, and Properties of Mocvd ZrO2 Thin Films
Authors: Desu Seshu B. , Shi Tian , Kwok Chi K. 
Published: March 2011

AbstractZrO2 films were deposited on silicon substrates at temperatures from 350 to 550 °C by metallorganic chemical vapor deposition (MOCVD) using zirconium acetylacetonates. Depositions were carried out at both atmospheric and low pressures. The optical properties, structure, microstructure, and composition of these films were characterized by Ellipsometer, X-ray diffraction, scanning electron microscopy (SEM), and electron spectroscopy for chemical analysis (ESCA), respectively. The deposition was kinetically controlled at low temperatures and mass transfer controlled at high temperatures. Use of zirconium (IV) acetylacetonate resulted in cubic ZrO2 with some carbon contamination whereas, tetragonal pure ZrO2 were obtained with the precursor zirconium (IV) trifluroacetylacetonate. The tetragonal ZrO2 films are fine grained and showed preferential orientation. The measured values of dielectric constant, refractive index, and electrical resistivity of ZrO2 films are 18, 2.0, and 5E13 Ohm.cm, respectively.
Chemical Vapor Deposition of Niobium Carbide using a Novel Organometallic Precursor.
Authors: Stupik Paul D. , Cheatham Linda K. , Graham John J. , Barron Andrew R. 
Published: March 2011

AbstractChemical vapor deposition from (MeCp)2Nb(allyl) at atmospheric pressure yields niobium carbide films at temperatures as low as 300°C. X-ray photoelectron spectroscopy (XPS) studies indicate that the bulk films contain a carbide phase and a nearly stoichiometric ratio of niobium to carbon. The morphology of the films has been examined by scanning electron microscopy (SEM).
Transport Properties of CVI Preforms and Composites
Authors: Freeman G. B. , Starr T. L. , Elston T. C. 
Published: March 2011

AbstractA simple model, based on physical microstructure, that predicts the anisotropic transport properties of cloth lay-up composites is discussed. This anisotropic material is modeled as a layer structure consisting of two, or more, isotropic components. Composite transport coefficients perpendicular and parallel to the layers are given by “series” and “parallel” combining laws involving the isotropic coefficients of these component materials and their volume fractions. These component material properties are determined using microstructural information and fundamental material properties. Model calculations are compared to experimental measurements for gas permeability.
3-D Modeling of Forced-Flow Thermal-Gradient CVI for Ceramic Composite Fabrication
Authors: Starr Thomas L. , Smith Arlynn W. 
Published: March 2011

AbstractForced-flow thermal-gradient chemical vapor infiltration (FCVI) has demonstrated excellent potential for fabrication of high strength, high toughness ceramic composites. Extension of this process to large and complex shapes is facilitated by use of a computer model to optimize process conditions and hardware for rapid, uniform infiltration.A 3-D model has been developed using a “finite volume” formulation. A steady-state solution for heat conduction and Darcy's law permeation produces temperature and gas flow distributions within the fiber preform. These are used to generated matrix deposition rates within each volume element. By “marching” through time, a complete simulation of the densification process can be obtained.The model is demonstrated for a FCVI system with cylindrical symmetry and compared to experimental results obtained at the Oak Ridge National Laboratory. The model results suggest a self-optimizing feature of the force flow/thermal gradient CVI process that produces uniform density in the final composite over a range of infiltration conditions. This matches experimental observation where good uniformity has been achieved over a wide range of gas flows, pressure and temperature.
Infrared and Raman Spectroscopy of Phonons in n-Type High Tc Superconductors
Authors: Crawford M. K. , Burns G. , Chandrashekhar G. V. , Dacol F. H. , Farneth W. E. , Carrón, III E. M. Mc , Smalley R. J. 
Published: March 2011

AbstractWe have measured the infrared (IR) reflectance and Raman spectra of electron doped and undoped Nd2CuO4 and Pr2CuO4. Utilizing the results from doped ceramics and undoped ab plane oriented single crystals, we observe and assign all the IR active phonons (3A2u + 4Eu) predicted by group theory. We have also observed the Raman active modes involving atom motion along the c axis. We compare our results to those found in the related hole superconductors based upon La2CuO4.
The Upper Critical Magnetic Field of Superconducting YBa2(Cu1-xNix)3O7
Authors: Xu Youwen , Moodenbaugh A. R. , Suenaga M. 
Published: March 2011

AbstractThe upper critical magnetic field of a series samples of YBa2(Cu1-xNix)3O7 is measured. Other related parameters, such as the lower critical magnetic field Hc1, the Ginsberg-Landau parameter k, the jump in the specific heat ∆C/Tc, the superconducting coherence length ξ, and the penetration depth λ, are calculated from Tc, dHc2/dT and dM/dH. The results show that Hc2(0), and consequently ξ(0), are essentially constant, but Hc and ∆C/Tc decrease with increasing Ni content.
Magnetic Phase Diagram of YBa2(Cu1–xFex)30y and YBa2 (Cu1–xCox)30y
Authors: Doyama Masao , Matsui Masaaki , Matsuoka Hiroshi , Ishikawa Kazuhito , Hayashi Eiji , Nishiyama K. , Nagamine K. 
Published: March 2011

AbstractMagnetic phase diagrams of YBa2 (Cu1–xFex)30y and YBa2 (Cu1–xCox)30y were determined by measuring positive muon spin relaxation and magnetic susceptibility (SQUID).
Fe Doping Effects in Aerosol Processed YBa2 (Cu1-xFex)307–δ Submicrocrystalline Grains
Authors: Boolchand P. , Biswas P. , Zhou D. , McDaniel D. , Huff W. , Oostens J. , Farrell D. 
Published: March 2011

AbstractMagnetization and Mössbauer spectroscopy results on aerosol processed YBa2 (Cu1-xFex)307–δ samples are presented. Systematics of Tc(x), x(x) and Fe dopant site occupancies In/I(x) as a function of dopant concentration ‘x’ are deduced and compared to those established on analogous solid-state- reacted samples. The absence of twinning in the aerosol processed grains leads to a random replacement of Cu for Fe in chains and planes of the host structure.
The Effects of Transition Metal Substitutions for Copper in the Bi-Sr-Ca-Cu-O Superconducting System
Authors: Bennett J.C. , Boswell F.W. , Corbett J.M. , Kohara S. , Razavi F.S. 
Published: March 2011

AbstractThe effects of transition metal dopants on superconductivity in samples of nominal composition Bi2CaSr2(Cu1-xMx)208+δ with M = Co, Fe, Ni and Zn have been investigated for 0 ≤ x ≤ 1. Co and Fe additions progressively suppress the ? of the doped material and result in semiconducting behaviour for x ≤ 0.2. In the ranges 0 ≤ x ≤ .07 and near x = 1.0, x-ray diffraction reveals the samples are essentially single phase but are multiphase otherwise. Ni and Zn dopants have only a very slight effect on Tc; however, EDX analysis reveals these elements are not significantly Incorporated into the superconducting phase.
Magnetically-Related Properties of Bismuth-Based High Tc Superconductors
Authors: Vezzoli G.C. , Chen M.F. , Craver F. , Burke T. , Moon B.M. , Safari A. , Lalevic B. , Stanley W. 
Published: March 2011

AbstractThe effect of magnetic fields to 15T on the electrical resistance (R) of Bi-Sr-Ca-Cu-O superconductors has been measured at precise temperatures during the transition to the superconducting state. The results show that the temperature at which the externally-applied magnetic field causes a divergence of resistance (R) as a function of inverse temperature is approximately at the same temperature where the positive Hall coefficient begins its steep descent to zero. At slightly higher temperature the Hall coefficient shows a singularity peak akin to a delta function. Internal electric field calculations show that the structure of the superconducting oxides, having more than a single building block polyhedron, gives rise to strong electrostatic fields in the unit cell which in turn causes charge separation or polarization. The charge separation is in accord with the importance of high oxidation states of the multivalence cations and suggests the use of high oxygen overpressure during processing. The magnitude of Tc scales closely with the number of bound holes (associated with the charge transfer excitations) per unit cell. Extensive computer calculations using this model indicate attractive pairing of electrons at inter-electron separations of about 10–15A.
Structural and Physical Properties in the Bi‐Sr‐Cu‐O System
Authors: Sunshine S. A. , Schneemeyer L. F. , Fleming R. M. , Fiory A. T. , Martin S. , Glarum S. H. 
Published: March 2011

AbstractThe structure/property relationships in the Bi‐Sr‐Cu‐O system near Bi2Sr2CuOx have been investigated. The properties and phase limits of the solid solution Bi2+xSr2_yCuO6±δ have been determined and a structural model for Bi2Sr2CuO6 is proposed.
Superconductivity of Bi1.6Pb0.4Sr2Ca2(Cu1-xAgx30y and Bi1.6Pb0.4Sr2Ca2Cu30y + wt% Ag
Authors: Vei Chongde , Lin Chin , Peng Qingrong , Liu Zunxiao , Lan JIAN , Sun YUNXI , Li Guozhong , Vu Ke , Xue Lixin , Gan Zizhao 
Published: March 2011

AbstractBoth interstitially Ag-doped Bi1.6Pb0.4Sr2Ca2Cu30y + x(wt%) Ag with x = 0.5, 1.0, 5.0, 10.0, 15.0, and substitutionally doped Bi1.6Pb0.4Sr2Ca2(Cu1-xAgx)0y with x = 0.025, 0.05, 0.10, 0.20, 0.40 systems were studied. Magnetic susceptibility Measurements indicate that both the interstitial and substitutional Ag-doping yield auch higher diaiagnetic signal for ZFC in a field of 60 0e at 5 K. At 80 K, -4πH/H was also enhanced by Ag-doping for H<200 Oe. Substitutionally Ag-doping also enhances the Magnetic critical current for x ≤ 0.2. Possible explanation was discussed.
Partial Superconductivity in YBa2Cu3O7 at 90 K < T < 300 K
Authors: Munger R. , Smith H.J.T. 
Published: March 2011

AbstractPartial superconductivity has been observed in bulk polycrystalline samples of YBa2Cu3O7 at temperatures as high as room temperature. The technique used was to measure the current-voltage characteristics of bulk samples in the presence of microwaves and magnetic fields. The measurements have been repeated on three samples that had been prepared separately.
Investigation of Possible Superconductivity in Titanium Borides
Authors: Ahern Brian S. , Bachowski Stephen , Horrigan Jane 
Published: March 2011

AbstractInterest in the titanium boride system stems from a patent disclosure by Vahldiek in 1982. In that disclosure TiBx(x=1.6) crystals were subjected to pressures of 300,000 psi and found to have vanishingly low resistivities at room temperature. In this study we processed TiBx crystals by a variety of techniques and pressurized the samples up to 350,000 psi. No high temperature superconductivity was observed.
The Electrochemical Response of YBa2Cu3O7-x in Aqueous Solutions
Authors: Chin T.S. , Shih H.C. , Lin C.A. , Huang T.W. , Tsai W.T. , Hung M.P. 
Published: March 2011

AbstractElectrochemical behavior of a YBa2Cu3O7 (YBCO for short) superconductor was studied by potentiodynamic scanning in different aqueous solutions with 0.1 M concentration. The electrochemical stability of the YBC0 compound was found to be superior in sulfurous acid, NaC1, or KC1 solutions. The dissolution potential in the above solutions ranges from 36 – 92 mV, polarization wasn't possible. However, E raised up to 360 – 960 mV in acids corr solutions with oxidizing potential including suluric, phosphoric and nitric acids indicating a passive behavior. Polarization was observed in sulfuric, sulfurous, and phosphoric acids depicting their potential to be used as etching solutions in lithography of this oxide superconductor. Its electrochemical behavior in HC1 solution is peculiar and informative. It shows three transitions in the polarization curve, corresponding to 272, 756, and 1013 mV, respectively. This is probably related to the transition in the valence states of copper ions during dissolution which is suppressed in the oxidizing acids. In comparison with metallic copper, the YBCO is more stable in the above solutions. The Galvanic current decreases at the order of A1 > Cu > Ag, when the YBC0 is coupled with each of them in 1 M phosphoric acid solution.
High-Tc Superconductor Multilevel Structures formed with Ta205 Spacer Layers
Authors: Bhattacharya Rabi S. , Kosel P.B. , Peterson T. 
Published: March 2011

AbstractAn important class of electronic devices could be realized with current state-of-the-art high-Tc superconductor (HTSC) thin films if a method were found for the formation of multilevel structures separated by thin dielectric layers. It has been found that such structures can be formed with tantalum oxide as the spacer layer because of its high melting point (1870°C) and good chemical stability at the high temperatures commonly used to anneal thin films of YBaCuO superconductor. Good results have been achieved with thin films prepared by electron beam (EB) sequential deposition from Y, BaF2 and Cu targets onto oriented (100) strontium titanate substrates and oxygen furnace annealing at 850°C to promote the epitaxial alignment and growth of the superconducting crystalline phase. Two-layer structures have been formed by interposing a tantalum oxide barrier deposited by EB evaporation between two successive layers of HTSC films. The transition temperatures of both layers were checked by resistance measurements and found to display superconductivity after annealing. However, the top (second) layer was found to always show a reduced abruptness of the transition characteristic thereby indicating, perhaps, a lesser degree of epitaxial alignment since it makes no direct contact with the substrate surface.
Oxide Films for the Protection of Cuprate Superconductors
Authors: Baney Ronald H. , Bergstrom Debora F. , Carpenter Leslie E. , Petersen Donald R. , Elwell Dennis F. , Shapiro Andrew A. , Fleishner Paul S. 
Published: March 2011

AbstractThe cuprate superconductors rapidly degrade in moisture and in the presence of organic compounds. A protection method has been developed with a coating process using sol/gel routes to the low temperature formation of oxide films. In contrast to traditional protective films, amorphous silica films formed from a solution precursors gave excellent protection and caused little degradation of the superconductors.The protective abilities of the films were assessed by monitoring the degradation of Y1Ba2Cu307-d in the presence of 85% relative humidity at 85 C. Volume magnetic susceptibility, four-point probe resistivity, current density measurements and x-ray diffraction were performed. Without protection, degradation was almost complete within 30 minutes of exposure. With protection, superconducting properties were maintained even after 48 hours of exposure.
Investigation of Potential Diffusion Barriers Between YBa2Cu3O7-x and Silicon
Authors: Lubig A. , Buchal Ch. , Zander W. , Stritzker B. 
Published: March 2011

AbstractThin films of ZrO2, BaF2, and noble metals on TiN have been examined by RBS as potential diffusion barriers between Si(100) substrates and high-temperature superconductors. As best result so far, a buffer layer of 260 nm ZrO2 enabled the growth of a 230 nm film of YBa2Cu3O7-x, which had been deposited by laser ablation. The relatively low zero resistance temperature of about 60 K may result from some interdiffusion between YBaCuO components and the ZrO2 layer or from holes in the film. A 520 nm BaF2 layer was able to prevent Si outdiffusion towards the surface, when exposed to an oxidizing ambient at typical YBa2Cu3O7-x deposition temperatures between 750 and 800°C. A strong reaction between YBaCuO components and BaF2, however, resulted in non-superconducting films. At high temperatures in oxidizing ambient the noble metal/TiN/Si samples suffered severely from oxidation and surface roughening.
On the Stability of YBa2Cu3O7-y with Refractory Ceramics
Authors: Del Angel P. , Dominguez J. M. , Falcony C. , Guzman O. , Montoya A. , Vicente L. 
Published: March 2011

AbstractA series of ceramic oxides were prepared by adding alumina to the superconductor YBaCuO. The solids were characterized by X-ray diffraction, transmission (TEM) and scanning electron microscopy (SEM) with EDS and electrical measurements. Partial drops in electrical resistance (R ≠ 0) indicate the presence of superconducting phases trapped in ceramic masses. Additionally, the systematic diminution of Tc could indicate a partial substitution of Cu by Al.