Physicists Make the Smallest Electric Rotor

By Ed Gerstner, July 24, 2003

This story describes the latest discovery made by Physics Professor Alex Zettl and his lab in the field of nanotechnology. © Nature News Service. Reproduced by kind permission.

Scientists have built an electric rotor 2,000 times smaller than the width of a human hair.

A small rotor twists the blade © Alex Zettl, et al.

Its gold blade is 300 millionths of a millimetre long. This sits atop an axle made from a multiwalled carbon nanotube — a molecule structured much like a leek. Gold electrodes at either end of the axle lash the device to a silicon chip.

Applying a small voltage between the nanotube and one of three more electrodes around it twists the rotor blade. A large voltage shears the blade and the nanotube's outer shell free of the rest of the structure, enabling the blade to rotate freely. A constant or oscillating voltage hold the blade in place or drive it at a constant speed, respectively.

"When I first saw electron-microscope images of multiwalled carbon nanotubes, I immediately thought of sliding those shells with respect to one another to form unusual electromechanical devices," says Alex Zettl, who designed and built the rotor with colleagues at the University of California, Berkeley.

Microchip rotors have been made before, but were either much larger or more unwieldy to drive, requiring lasers or magnets. Natural molecular motors operate on a similar, cellular scale, but only under highly specialized conditions.

Zettl's nanotube rotor is easy to drive and can operate at great speed, over a wide range of temperature and chemical conditions — even in a vacuum. This lends it to a wide range of applications.

Using the gold rotor blade as a mirror to direct and switch light signals rapidly is one possibility. Detecting the presence of certain chemicals attached to its blade by monitoring its resonant rotational speed is another.

The most exciting developments may not have even been thought of, says Zettl. "Like projections in the early days of lasers and integrated circuits, no matter how visionary we try to be, we will no doubt misjudge where the most successful applications will arise," he says.

Reference

Zettl, A. et al. Title Nature, 424, 408-410 , (2003)

© Nature News Service. Reproduced by kind permission. For more free
daily science news like this visit www.nature.com/nsu.

See also, Physicists build world's smallest motor using nanotubes and etched silicon, UC Berkeley July 23, 2003.