Sliding and spinning

One carbon nanotube inside another can act as a molecular motor providing both linear and rotary motion

Credit: © 2008 ACS

Biological systems contain tiny motors with linear and rotary motion; for example, the contracting proteins in muscles or the spinning flagella of bacteria. Scientists want to mimic these natural molecular motors for nanotechnology devices. Kaori Hirahara and co-workers at Osaka University and Osaka Prefecture University have come one step closer¹ to this goal, by observing carbon nanotubes (CNTs) both rotating and moving linearly one inside another.

The researchers made a capsule-like CNT just 3.2 nanometres long by heating C₆₀ buckyball molecules inside a larger host CNT until the buckyballs coalesced. This capsule was trapped in a cavity in the host, between the ends of two other CNTs. It was seen to jump spontaneously between the ends of the cavity, spinning at the same time.

The capsule is probably held in place by van der Waals forces at the end of the cavity, but these are overcome by thermal energy to produce the random jumping action. This means that in future the movement could be controlled and triggered by heat, light or electron beams. More importantly, the system developed by Hirahara and co-workers operates at room temperature, promising great practical potential for tiny oscillators or switches for memory devices.