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Self-Assembled Film for Aligning Carbon Nanotubes

Scanning electron microscope (SEM) images of aligned carbon nanotubes.
Scanning electron microscope (SEM) images of aligned carbon nanotubes. (a) Nanotubes grow outwards perpendicularly from all surfaces of a thin-film-like mesoporous silica substrate. (b) This high magnification SEM image shows aligned and separated nanotubes. (c) This carbon nanotube pattern was formed by using a transmission electron microscope grid with a square opening as a shadow mask. (d) A network of aligned carbon nanotubes is formed.

Carbon nanotubes—lined up and sticking up like brush bristles—have been grown in the laboratory of Sheng Dai and postdoctoral scientist Zhengwei Pan, both in ORNL’s Chemical Sciences Division. Dai and Pan have produced a self-assembled sol-gel silica film doped with iron nanoparticles. This “self-assembled ordered mesoporous film” grows in such a way that it has evenly distributed pores into which iron nanoparticles settle. “These iron particles nestled in the film are the seeds that allow carbon nanotubes to grow,” Dai says.

The film is then heated in a furnace along with acetylene gas in a process called chemical vapor deposition. This carbon-bearing gas then decomposes, causing the carbon to deposit on the film. The nanotubes sprout up from the iron nanoparticles, which are catalysts that spur the growth of aligned carbon nanotubes.

“We also have made nickel nanowires using self-assembled ordered mesoporous films formed from silica,” Dai says, adding that this research was done in collaboration with ORNL postdoctoral scientist Zongtao Zhang. “These mesoporous films have parallel channels, so they are good templates for making wires. We dope the film with nickel and tiny wires form along the channels.”

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