November 13, 2006

More nanotube progress

Hongjie Dai and his colleagues take a new approach for getting 100% semiconducting nanotubes. They grow a mixed bunch of semiconducting and metallic nanotubes on a silicon wafer and have them bridge the source and drain of a transistor. Then they expose the devices to methane plasma at 400 °C. The hot, ionized methane particles eat away the carbon atoms, but only in the metallic nanotubes, converting the tubes into a hydrocarbon gas. (The plasma also etches out nanotubes with diameters smaller than about 1.4 nanometers.) Next, the researchers treat the wafer in a vacuum at a temperature of 600 °C; this treatment gets rid of carbon-hydrogen groups that latch on to the semiconducting nanotubes during the plasma treatment. This leaves behind purely semiconducting nanotubes with a consistent range of diameters stretching across the source and drain. With this heat based approach, one can treat an entire wafer, which may contain several devices, at once.

From space, NASA's Goddard Space Flight Center in Greenbelt, Maryland licensed its patented technique for manufacturing high-quality single-walled carbon nanotubes (CNTs) to Idaho Space Materials (ISM) in Boise. Having successfully commercialized NASA's manufacturing process to increase production capacity while maintaining quality, ISM can produce single-walled CNTs at a rate of 50 grams per hour. The key to the innovation developed by Dr. Benavides was the ability to produce bundles of CNTs without using a metal catalyst, dramatically reducing pre- and post-production costs while generating higher yields of better quality product.