Credit: © 2006 AAAS

A major obstacle to the use of semiconducting single-walled carbon nanotubes (SWNTs) in electronic devices is the presence of metallic SWNTs. In addition to this ‘electrical short’ problem, devices often have poor electronic properties due to chemically modified nanotube surfaces and lack of nanotube size control.

Now, Hongjie Dai and co-workers1 at Stanford University in the USA have made devices containing only semiconducting SWNTs. Built on Si/SiO2 substrates, each device has a pair of ‘source–drain’ Ti/Au electrodes bridged by up to three SWNTs. Initially, 45% of devices were shorted as they contained at least one metallic nanotube. The failure rate was reduced to 7% following reaction with a methane plasma at 400 °C, which selectively destroyed medium-sized metallic SWNTs as well as small nanotubes of both types. Annealing at 600 °C removed unwanted chemical groups from the nanotube surfaces. Following these processing steps, the remaining nanotubes have a narrow size range and are not chemically altered. This results in consistent electronic properties such as a large bandgap and a high on/off conductance ratio.

Moreover, a 100% yield of working devices was achieved when they were scaled up to include 20 SWNTs. Because this process is compatible with current microfabrication technology, it may have a significant impact on the field of nanotube devices.