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.

Patterned growth of freestanding carbon nanotube͑s͒ on submicron nickel dot͑s͒ on silicon has been achieved by plasma-enhanced-hot-filament-chemical-vapor deposition ͑PE-HF-CVD͒. A thin film nickel grid was fabricated on a silicon wafer by standard microlithographic techniques, and the PE-HF-CVD was done using acetylene (C 2 H 2 ) gas as the carbon source and ammonia (NH 3 ) as a catalyst and dilution gas. Well separated, single carbon nanotubes were observed to grow on the grid. The structures had rounded base diameters of approximately 150 nm, heights ranging from 0.1 to 5 m, and sharp pointed tips. Transmission electron microscopy cross-sectional image clearly showed that the structures are indeed hollow nanotubes. The diameter and height depend on the nickel dot size and growth time, respectively. This nanotube growth process is compatible with silicon integrated circuit processing. Using this method, devices requiring freestanding vertical carbon nanotube͑s͒ such as scanning probe microscopy, field emission flat panel displays, etc. can be fabricated without difficulty.

A high-resolution scanning superconducting quantum interference device microscopy study of tetragonal single-layer Tl 2 Ba 2 CuO 6+δ films, deposited on tricrystal SrTiO 3 substrates, demonstrates the effect of spontaneously generated half flux quanta. This observation shows that in addition to YBa 2 Cu 3 O 7 , the order parameter symmetry in Tl 2 Ba 2 CuO 6+δ is consistent with that of a d x 2 - y 2 pair state. This result also rules out any bilayer or twinning effects and any pairing that is incompatible with the fourfold rotational symmetry as in the Tl 2 Ba 2 CuO 6+δ superconducting system.

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