Credit: © 2008 ACS

Carbon nanotubes are considered key components in future nanoscale electronic devices such as field-effect transistors. In order to create practical devices, however, control over the electrical conductivity of the nanotubes will be crucial. Now, Christoph Marquardt and colleagues1 from Forschungszentrum Karlsruhe and Universitat Karlsruhe have produced reversible metal-to-insulator changes in single-walled carbon nanotubes through electron-beam irradiation.

Individual nanotubes — with diameters of around 1 nm and lengths of about 1 µm — were positioned between palladium electrodes, formed on doped silicon with an oxide layer. The device was then loaded into a scanning electron microscope. Irradiation of a section of the nanotube by an electron beam with a diameter of 2–3 nm induced a decrease of three orders of magnitude in the electrical conduction. Notably, a large voltage applied to the nanotube returned it to its original metallic state.

The researchers suggest that the observed changes are due to charges that get trapped in the substrate during irradiation, and they expect that the results will have significant implications for the characterization of carbon nanotubes using scanning electron microscopy, as well as device fabrication.