Carbon nanotubes are rolled up sheets of graphite that display novel electronic properties as a result of their one-dimensional structure. Nanotubes also display mechanical strength along their length, but can be easily deformed in the radial direction.

Hugh Romero and Peter Eklund of Pennsylvania State University, and Kim Bolton and Arne Rosen of Göteborg University and Chalmers University of Technology have now shown that the tiny deformations or dents caused by collisions with various gas species can change the electronic properties of the nanotubes.

The team measured how the thermoelectric power and electrical resistance of thin films containing bundles of single-walled nanotubes (SWNT) changed when they were exposed to the various gases at a pressure of around one atmosphere. The nanotubes in the sample were between 1 and 1.6 nanometres in diameter and several microns long.

Romero and co-workers studied the effects of collisions of inert gas atoms (helium, neon, argon, krypton and xenon) and small molecules (methane and nitrogen), and found that changes in both the thermopower and the resistance increased with the cube root of the mass of the atom or molecule.

"Our work shows that carbon nanotubes can be used to detect gases that are very difficult to observe with current measurement techniques," says Bolton. "When the walls are deformed by collisions with a gas, the flow of electricity is hindered and this allows us to measure the presence - and pressure - of the gas."