How to grow nanotubes as metallic or semiconducting
October 2, 2009 | Source: KurzweilAI
The nanotubes are grown in a vacuum chamber by exposing iron particles to methane gas. The gas contains carbon and hydrogen, and the iron particles act as a catalyst to liberate carbon from the gas. The particles are heated to about 800 degrees Celsius. With increasing exposure, the iron eventually contains too much carbon and becomes supersaturated, and the carbon precipitates as a solid, causing the nanotube to begin forming.
The researchers found they could control whether the carbon nanotubes become metal or semiconductor by using either argon or helium as “carrier gases” to aid in flowing the methane into the chamber in the presence of water. The technique was used to produce large quantities of nanotubes.
The findings will be detailed in “Preferential Growth of Single-Walled Carbon Nanotubes with Metallic Conductivity,” appearing Friday (Oct. 2) in the journal Science.