October 30, 2003

Monumental Nanotubes

Source:  Z.F. Ren et. al.

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Single freestanding multi-wall carbon nanotubes on a nickel substrate. Physicists at Boston College have grown these structures for the first time on a grid pattern, which might permit the tubes to be used in field emission flat panel displays. It is not known why the tubes taper at the top, making them look like nanoscopic versions of the Washington Monument.

Patterned growth of freestanding carbon nanotubes on submicron nickel dots on silicon has been achieved by plasma-enhanced-hot-filament-chemical-vapor deposition PE-HF-CVD. A thin film nickel grid was fabricated on a silicon wafer by standard microlithographic techniques, and the PE-HF-CVD was done using acetylene (C2H2) gas as the carbon source and ammonia (NH3) 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 mm, 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 nanotubes such as scanning probe microscopy, field emission flat panel displays, etc. can be fabricated without difficulty.