Showing papers by "Zhifeng Ren published in 1998"

Synthesis of Large Arrays of Well-Aligned Carbon Nanotubes on Glass

Abstract: Free-standing aligned carbon nanotubes have previously been grown above 700°C on mesoporous silica embedded with iron nanoparticles. Here, carbon nanotubes aligned over areas up to several square centimeters were grown on nickel-coated glass below 666°C by plasma-enhanced hot filament chemical vapor deposition. Acetylene gas was used as the carbon source and ammonia gas was used as a catalyst and dilution gas. Nanotubes with controllable diameters from 20 to 400 nanometers and lengths from 0.1 to 50 micrometers were obtained. Using this method, large panels of aligned carbon nanotubes can be made under conditions that are suitable for device fabrication.

Growth of Highly-Oriented Carbon Nanotubes by Plasma-Enhanced Hot Filament Chemical Vapor Deposition

Abstract: Highly-oriented, multi-walled carbon nanotubes were grown on polished polycrystalline and single crystal nickel substrates by plasma enhanced hot filament chemical vapor deposition at temperatures below 666"C. The carbon nanotubes range from 10 to 500 nm in diameter and 0.1 to 50 pm in length depending on growth conditions. Acetylene is used as the carbon source for the growth of the carbon nanotubes and ammonia is used for dilution gas and catalysis. The plasma intensity, acetylene to ammonia gas ratio and their flow rates, etc. affect the diameters and uniformity of the carbon nanotubes. In summary, we synthesized large-area highly-oriented carbon nanotubes at temperatures below 666C by plasma-enhanced hot filament chemical vapor deposition. Acetylene gas is used to provide carbon for nanotube growth and ammonia gas is used for dilution and catalysis. Plasma intensity is critical in determining the nanotube aspect ratios (diameter and length), and range of both site and height distributions within a given film.

Superconducting thallium oxide films by the electrodeposition method

Abstract: A low cost electrodeposition method is tested for the fabricating high-temperature superconducting wire or tape. Recent studies on the development of biaxially textured electrodeposited (ED) films on Ag-coated, single-crystal substrates are reported. Pole-figure measurements of electrodeposited (Tl)–Ba–Ca–Cu–O and (Tl, Bi)–(Sr, Ba)–Ca–Cu–Ag–O films on 300 A Ag/LaAlO3, with thickness between 1 and 5 μm, clearly show strong biaxial texturing. The omega scan and phi scan of (TlBi)0.9Sr1.6Ba0.4Ca2Cu3Ag0.2Ox indicate the full width half maximum (FWHM) of only 0.9° and 1.2°, respectively, which indicate a very high-quality film prepared by electrodeposition process. Transport measurements for the ED films show values of 3×105 A/cm2 at 77 K in zero field. Single-layer thallium-oxide films, with Pb, Bi, and Sr substitution, offer the potential for operation at 77 K in practical magnetic fields of 3–5 T.

Epitaxial Film Growth of Tl0.78Bi0.22Sr1.6Ba0.4Ca2Cu3O9 on Rolling Assisted Biaxially Textured Nickel Substrates with YSZ And CeO2 Buffer Layers

Abstract: Epitaxial film growth of Tl0.78Bi0.22Sr1.6Ba0.4Ca2Cu3O9 ((Tl,Bi)-1223) on rolling assisted biaxially textured substrates with YSZ and CeO2 buffer layers (RABiTS) has been successfully demonstrated by laser ablation and post-deposition annealing in flowing argon. X-ray diffraction (XRD) θ-2θ spectra showed that the films consisted mainly of c-axis aligned 1223 phase with some intergrown 1212 phase, while XRD Φ-scans of (102) pole figure revealed that the films are also a- and b-axes aligned, with an epitaxy of the «100» of (Tl,Bi)-1223 film on the «110» of the top YSZ buffer layer. Four-terminal electrical transport measurements showed that the zero-resistance transition temperature (Tc) was in the range of 106 - 110 K, and the critical current density (Jc) at 77 K and zero field was about 105 A/cm2 for the entire film width (3 mm) of a longer film (14 mm) which was processed differently from the shorter films (7 mm). For a shorter film (7 mm) that showed better ab-in-plane alignment, the magnetization Jc, at 77 K and extrapolated to zero field, calculated from Bean's model using the full film width (3.5 mm) as the appropriate lateral dimension, was 2 × 105 A/cm2.