Credit: © 2007 ACS

Carbon nanotubes have been proposed as components for numerous tiny devices, owing to their unique electronic properties. Now Hidemi Shigekawa at the University of Tsukuba and co-workers have achieved precise control over these properties, by deliberately distorting nanotube surfaces with a scanning tunnelling microscope (STM)1.

Single-walled nanotubes were deposited onto a gold substrate by spin-coating, and observed using an STM. The STM tip was positioned above a defect-free area of the nanotube and the voltage used to image the nanotube was ramped up. At a certain threshold voltage, the researchers observed a spike in current, caused by the appearance of a defect. Two types of protruding defect were created — adsorption defects in which a foreign molecule became stuck to the surface, and defects caused by distortion of the nanotube lattice. The researchers believe the lattice defects are probably caused by rotating carbon–carbon bonds, and that these modify the electronic energy levels in the nanotube.

The protrusions remain stable for several days. More importantly, the defect can be made to disappear by applying a second voltage ramp. This represents the first reversible manipulation of a nanotube wall, and could be used to create confined areas in nanotubes.