The World's Tiniest Bearings

Multiwalled nanotubes, sliding almost without friction, could be a part of future molecular motors.

Researchers have developed yet another component of what could one day become a futuristic set of machines hardly bigger than a few molecules. In the 28 July issue of Science, they report that carbon nanotubes can slide into and out of each other with almost no friction. Experts say this could make them ideal bearings for motors and other nanotechnological devices.

Nanotubes--chickenwire-like lattices of carbon atoms rolled up in tubes--have been bent and stretched by researchers. But nobody had looked at the friction that occurs when so-called multiwalled carbon nanotubes, in which several lattices are embedded in each other, act like a bearing. John Cumings and Alex Zettl from the University of California, Berkeley, did just that with a nanomanipulator, a minuscule tip whose movements can be precisely controlled.

First the researchers attached one end of a multiwalled carbon nanotube to a stationary gold electrode. At the other end, they spot-welded the tip of the manipulator to the inner tubes by sending a current through it, and pulled the inner tubes out. "We grabbed on to the tip and telescoped it out--and then we let it go," Cumings says.

Using a scanning electron microscope, the team could watch how the inner core was pulled back inside by intermolecular forces. These so-called Van der Waals forces are very weak, but because they moved the tubes, the friction must be extraordinarily small, the team concludes. The researchers are now investigating ways to attach this tiny bearing to other nanoparts. "We are taking baby steps in that direction," Cumings says.

The new bearing may indeed be "a very efficient part of future molecular motors," says physicist Laszlo Forró of the Ecole Polytechnique Federale de Lausanne in Switzerland in a Perspective in the same issue. And "another extremely interesting application" of the bearing is a so-called nanoswitch. By applying a voltage to the bearing, researchers can very rapidly force the central tube to stick out, says Forró. He adds that the work will "play a major role in our ability to manufacture nanomachines and nanomotors in the near future."

Related sites
A carbon nanotube page, by Peter Harris of Cambridge University
The nanotube site

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