A new method of sorting single-walled carbon nanotubes (SWNTs) according to their chirality, could help solve a long standing problem in the fabrication of nanotube-based electronics.

A SWNT can behave as either a metal or a semiconductor, depending on the spatial arrangement of its carbon atoms, or chirality. SWNTs are produced as a mixture of both types, however, these do not work well together and need to be separated before use.

While number of methods have been devised to separate the two types of SWNTs, none have proven practical for large scale applications.

Working on the theory that metallic and semiconducting SWNTs should interact differently with certain functional groups, researchers from Stanford University reasoned they could simultaneously sort nanotubes by chiralty and make thin film transistors by adding functional group coatings to the surface of silicon substrates and then applying the SWNTs via spin coating. They found that semiconducting nanotubes preferentially cling to substrates with a coating of primary amines, while metallic SWNTs are attracted to substrates coated with phenyl groups. The spin coating process repels the non-sticking type of nanotube.

From a typical SWNT blend, the team at Stanford University was able to produce transistors with between 90 and 95 per cent of nanotubes with the desired chirality.