Credit: © 2008 APS

Molecular motors have been built that are driven electrically, chemically and optically. On the macroscale, electrically driven motors are the most efficient, whereas on the nanoscale, there is the intriguing possibility of having electrical motors powered by tunnelling electrons. Previously, tunnelling electrons have been used to provoke periodic vibrational and translation motion. Now, Boyang Wang, Lela Vuković and Petr Král of the University of Illinois at Chicago1 have carried out simulations to assess whether electron tunnelling could be used to drive rotary nanoscale machines.

The researchers designed a device composed of a carbon nanotube shaft with covalently attached 'isolating' molecular arms that end with 'conducting' blades. The molecular arms, equally spaced around the shaft, are made up of polymerized iceane molecules (C12H18), and the blades are made of either fullerene or planar aromatic molecules with triangular shapes.

Using semiclassical molecular dynamics simulations, Petr Král and colleagues found that an external electric field (E) could be used to periodically charge and discharge the blades by electron tunnelling from two metallic electrodes. This tunnelling maintains an electric dipole (p) on the blades of the rotor, which can be unidirectionally rotated by the electric field. Furthermore, the team found that these molecular motors could be effective under external loads and in the presence of noise and defects.