Roll your sleeves

The ability to control the movement of a tiny carbon nanotube 'sleeve' with electric currents could prove useful for powering nanoscale mechanical devices

Credit: © 2008 AAAS

Carbon nanotubes hold great potential as moving parts for nanoscale devices. Adrian Bachtold of the Universitat Autònoma de Barcelona and co-workers¹ in Spain, Austria and Switzerland have managed to move and rotate one carbon nanotube around another by using electrical currents to introduce a temperature gradient. The technique could be used to pump fluids inside nanotubes or even to deliver drugs via tiny syringes.

Bachtold and co-workers started by adding a small amount of gold to a multiwalled carbon nanotube. Electrical heating was then used to break down some of the outer shells. The region of the outermost shell covered by the gold did not break down because the metal coating absorbed the heat, leaving a 'sleeve' that could move along the tubes inside it. By suspending the nanotube between two electrodes and applying an electrical current, the researchers could move the sleeve along the tube, and cause it to rotate.

The process works because the centre of the nanotube gets hotter than the ends. Heat therefore moves outwards from the centre, transferring kinetic energy to the sleeve — effectively the opposite of the heat dissipation caused by friction. However the current has to be large enough to rid the surface of contaminants and loose bonds that would otherwise get in the way of the motion.