Epitaxial films of rare-earth (RE = La, Ce, Eu, and Gd) tantalates, RE3TaO7 with pyrochlore structures were grown on biaxially textured nickel-3 at.% tungsten (Ni-W) substrates using chemical solution deposition (CSD) process. Precursor solution of 0.3∼0.4 M concentration of total cations were spin coated on to short samples of Ni-W substrates and the films were crystallized at 1050∼1100 °C in a gas mixture of Ar- 4% H2 for 15 to 60 min. X-ray studies show that the films of pyrochlore RE tantalate films are highly textured with cube-on-cube epitaxy. Improved texture was observed in case of lanthanum tantalate (La3TaO7) film grown on Ni-W substrates. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) investigations of RE3TaO7 films reveal a fairly dense and smooth microstructure without cracks and porosity. The rare-earth tantalate layers may be potentially used as buffer layers for YBa2Cu3O7-δ (YBCO) coated conductors.

Adhesion of thin films of epitaxial oxides to nickel-based metallic substrates is important for the successful development of high-temperature superconductor coated conductors. Detachment of epitaxial oxide buffer layers at the oxide/metal interface during either oxide growth or subsequent processing renders the conductor useless. In this study, thermal desorption spectroscopy (TDS) has been used to identify and understand one of the causes of buffer layer detachment, oxidation of carbon at the oxide–metal interface to form carbon monoxide. Results of TDS indicate that on the surface of a bare nickel-based alloy substrate, the rate of carbon oxidation depends on both the supply of carbon from the substrate and the supply of oxygen from the vapor. Sulfur at the surface of the alloy substrate reduces the rate of carbon oxidation. The effectiveness of various treatments of the bare substrate to eliminate CO formation and epitaxial oxide detachment has been demonstrated. TDS provides both a means to evaluate the kinetics of the oxidation reaction and a tool to assess the need and effectiveness of a substrate oxidation treatment.

The effects of conversion parameters on transport properties of YBa2Cu3O7-δ (YBCO) films on rolling assisted biaxially textured substrates (RABiTS) in the BaF2 ex situ process were investigated for total pressures Ptotal between 0.1 and 1.3 atm, water vapor pressures PH2O between approximately 7 and 70 Torr and processing temperatures TS between 700 and 790 °C. For this study, a 0.3-μm-thick Y–BaF2–Cu–O precursor film was deposited on a 1-cm-wide Ni=3 at.% W RABiTS with a buffer layer architecture of CeO2/YSZ/Y2O3/Ni deposited in single passes in various reel-to-reel systems for each layer. Under the conditions of Ptotal = 0.1 atm, TS = 740 °C and PO2 approximately 150 mTorr, JC > 2 MA/cm2 was obtained at 77 K and self field for PH2O ≤ 20 Torr. At higher PH2O (=70 Torr), however, the maximum attainable JC decreased. In addition, the JC at these higher PH2O dropped rapidly with increased dwell time. The highest JC, 2.5 MA/cm2, was achieved at 730 °C with Ptotal = 0.1 atm and PH2O approximately 7 Torr. Finally, the variation of IC with wet conversion time was performed at each processing temperature.

We investigated the influence of a chemisorbed S template with c(2 × 2) structure on the epitaxial growth of different oxide buffer layers on {100}〈100〉 Ni. The sulfur superstructure spontaneously forms on the Ni surface during the texturing anneal as a consequence of segregation. However, depending on the initial S bulk concentration and/or specific annealing conditions, the S layer can cover less than the entire substrate's surface. We show that an incomplete c(2 × 2) coverage causes degradation of the seed buffer layer texture as compared to the substrate texture. A simple step consisting of an H2S predeposition anneal can be used to control the superstructure coverage and optimize the seed layer texture.

We present a study of the {100}<100> biaxially textured Ni (001) surface and oxide seed layer nucleation by in situ reflection high-energy electron diffraction and Auger electron spectroscopy. Our observations revealed the existence of a c(2×2) superstructure on the textured Ni surface due to segregation of sulfur contained in the bulk metal. The sulfur superstructure promotes the epitaxial (002) nucleation of seed layers such as Y2O3-stabilized ZrO2 (YSZ) and CeO2 on the metal and optimizes the biaxial texture necessary for high Jc superconductors on RABiTS.

The Mo-Si phase diagram exhibits a Mo5Si3-MoSi2 eutectic at the 54% Si composition. Since the terminal phases have comparable melting points and are equidistant from the eutectic composition, there is the possibility of obtaining lamellar microstructures in this system. In addition, if the alloys are directionally solidified, there is the further possibility of obtaining aligned lamellae. In this study, a high temperature (xenon-arc-lamp) optical floating zone furnace is utilized to directionally solidify Mo-Si alloys of the eutectic composition. Growth conditions are systematically varied to investigate their effects on the solidification microstructure. Growth rates and rotation speeds are identified that result in lamellar microstructures.

Multiphase Mo silicide alloys containing T2 (Mo5SiB2), Mo3Si and Mo phases were prepared by both melting & casting (M&C) and powder metallurgical (PM) processes. Glassy phases are observed in PM materials but not in M&C materials. Microstructural studies indicate that the primary phase is Mo-rich solid solution in alloys containing ≤(9.4Si+13.8B, at. %) and T2 in alloys with ≥(9.8Si+14.6B). An eutectic composition is estimated to be close to Mo–9.6Si–14.2B. The mechanical properties of multiphase silicide alloys were determined by hardness, tensile and bending tests at room temperature. The multiphase alloy MSB-18 (Mo–9.4Si–13.8B) possesses a flexure strength distinctly higher than that of MoSi2 and other Mo5Si3 silicide alloys containing no Mo particles. Also, MSB-18 is tougher than MoSi2 by a factor of 4.

Addition of a small amount of oxygen to the CH4 and H2 feed gas permits hot filament assisted chemical vapor deposition (HFCVD) of diamond at significantly lower filament and substrate temperatures. The former can be reduced to as low as 1400 °C and the latter to 450 °C. The amount of oxygen required is much lower than what has been used in most studies of the oxygen effect. For each CH4%, there is a narrow window in the O/C ratio, where diamond can be deposited at low temperature. This window shifts to higher O/C ratios as the CH4% increases and expands with increases in filament temperature. The effect of changing substrate and filament temperatures on growth rate and film quality are often not consistent with previous experiences with HFCVD of diamond. Increasing the filament temperature does not always improve the growth rate and film quality, and the non-diamond carbon content in the film is dramatically reduced at lower substrate temperatures. Optimum conditions were found that gave reasonable growth rates (∼0.5 μm/h) with high film quality at filament temperatures below 1750 °C and substrate temperatures below 600 °C. With these reductions in operating temperatures, power consumption can be significantly reduced and the filament lifetime extended indefinitely.

The utility of polysynthetically-twinned (PST) TiAI, which contains a high density of parallel, atomically-flat interfaces within a set of identical crystallographic orientations, as a potential model system for a detailed investigation of interface diffusion is explored. Macroscopic PST crystals were grown in an optical float zone furnace. Thin films were cut from oriented crystals and polished with <112> directions normal to the film. After sputter cleaning, Ag was deposited on one side of the TiAI thin films. Auger spectra were obtained from these films over a wide range of sputter/anneal conditions. The Al and Ti concentrations were analyzed as well as the important impurity elements, S, Ar, C, N and O. Using the present data and existing knowledge of the microstructure and crystallography of PST TiAI, the potential of this material for providing a detailed understanding of the atomistic mechanisms of interface diffusion is analyzed.

A thick as-grown diamond film was examined directly by conventional transmission electron microscopy (TEM) without thinning, and the important microstructures near the growth surface were characterized. Specimen preparation for TEM involved simply fracturing the film; some of the diamond grains located on the specimen edge were thin enough to be directly examined by TEM. The 3-D topography of the diamond grains located at the intersection of the growth and the fracture surfaces was obtained using secondary electron images, so that the 2-D projected grain geometry could be derived easily to help interpret the TEM images. A diamond film grown with a 〈001〉 texture and having grains 2–3 μm diameter with {001} facets parallel to the substrate and four inclined {111} facets was examined. Grains with fracture surfaces that intersected the top (001) facet, grains with fractures that intersected only {111} facets, and unfractured grains were studied. It was found that the core volume bounded by the (001) top facet and its projected column defined by orthogonal internal {110} were free from microtwins, but contained a few dislocations. The remaining volume around this core, bounded by {111} facets (or grain boundaries) and the internal {110}, was filled with microtwins. The microtwins were not merely at the {111} surfaces. Our results reveal a growth mechanism in which microtwins are formed as material is added to {111} but not {001}. The formation of microtwins in CVD diamond is thus clearly associated with growth on {111} surface facets.

Single crystal, type IIa natural diamond substrates have been implanted with 4 MeV carbon ions to doses ranging from 0.5–130×1016 cm-2. The accumulation of implantation damage is studied by Raman and RBS/channeling. Similar effects are observed for crystals of [100], [110], and [111] orientation but with different rates of damage accumulation. With increasing implantation damage, the triply degenerate Raman mode at 1332 cm-1 broadens and shifts down to around 1300 cm-1. This corresponds to a peak in the one-phonon density of states as predicted for Raman from an amorphous sp3 network. There is no evidence for the existence of sp2 carbon in the implanted area. Additional non-graphite Raman peaks appear at 1451, 1494, and 1635 cm-1. At the higher doses, the 1332 cm-1 Raman mode is no longer observed; however, RBS/channeling still shows the surface region to be crystalline and it is possible to grow high quality homoepitaxial diamond films on these substrates.

We have used x-ray diffraction to characterize diamond films grown in three characteristic morphologies by chemical vapor deposition. Each morphology has a fiber texture about the growth direction; we report the crystal axis aligned in this direction for each morphology. In all cases the average lattice constant agrees with that of bulk diamond; we report the range of strain in each sample.