Pulickel M. Ajayan, Ganapathiraman Ramanath, and coworkers achieve this by first using photolithography to pattern a silicon surface with silica (SiO₂) features. The substrate is then exposed to a mixture of ferrocene and xylene vapors at around 800 °C. Iron clusters believed to form under these conditions serve as the catalyst for the growth of multiwalled nanotubes from carbon fragments derived from the xylene.

Adapted from Nature copyright 2002

The nanotubes, 20 to 30 nm in diameter, grow only on the SiO₂ surfaces and perpendicular to them. Thus, if the pattern consists of thin-film dots of SiO₂ in a square array, the nanotubes all grow vertically, forming blocks of micrometer-long pillars of densely packed nanotubes, as seen in the micrograph at right.

If, however, the SiO₂ films are at least 2 or 3µm thick, nanotubes can grow horizontally from the sides as well as vertically from the top face of the film. If this thick film is circular or polygonal, the nanotubes will grow out in several directions at once, as is the case in the daisy-shaped nanotube assemblies seen at left.

This technique could find use in the manufacture of microelectromechanical devices or membranes consisting of interwoven nanotube fibers.

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Copyright © 2002 American Chemical Society