University of Maryland researchers fabricated semiconducting carbon nanotubes claimed to have the highest mobility of any known material at room temperature. Mobility is the conductivity of a material divided by the number of current-carrying charges. It is the number used to compare conduction properties of one semiconductor to another. The mobility of these nanotubes exceeds 100,000 cm3/Vsec at room temperature. For comparison, the silicon used in today's computer chips has a mobility of only about 1,500 cm3/Vsec.
Carbon nanotubes are single-atom-thick sheets of graphite, rolled into a seamless cylinder. The semiconducting carbon nanotubes may replace conventional semiconductor materials in applications from computer chips to biochemical sensors. "Many challenges remain before nanotubes can replace silicon in computer chips," says Michael Fuhrer, assistant professor of physics. "The contact resistance between nanotube and metal electrodes must be controlled. Nanotube batches must be prepared that contain only semiconducting nanotubes. And nanotubes must be placed with precision on substrates," he adds.