January 23, 2007

Turning an axel mounted molecular wheel

Researchers at the Centre for Material Development and Structural Studies in Toulouse (CEMES-CNRS) and their colleagues at the Free University of Berlin have, for the first time, managed to control the rotation of a wheel in a molecule. This nano-mechanical experiment concerned an 0.7 nm diameter wheel attached to a 0.6 nm-long axle. This success opens the way to creating the first molecular machines. The study was published on-line on January 21, 2007, in the journal Nature Nanotechnology.

To prepare this nano-mechanical experiment, the CEMES-CNRS chemists designed and synthesised simple molecular machinery made up of an 0.6 nm-long axle-molecule, bound chemically with two triptycene wheels with a diameter of around 0.7 nm (Figure 1). The type of wheel and surface were very carefully chosen. Two notched, "tyre-less" wheels were used because of their maximum adherence to the running surface, an ultraclean copper plate. Its natural roughness presented rows of copper atoms separated by a distance of about 0.3 nm, and about one atom high.

The experiment consisted in delicately placing wheel-axle-wheel molecules on the copper surface and then using scanning tunnelling microscopy (STM) imaging at very low temperature to detect molecules lying in the correct orientation with respect to the rows of atoms on the surface. The STM tip positioned on a wheel made the latter rotate.

By advancing the STM tip, the microscope behaved like a finger to trigger the rotation.