Miniature Motor: Nanotubes central to new rotating device

Motors, pumps, and other electromechanical devices are tinier than ever–and getting even smaller. Now, for the first time, researchers have used miniature, nested cylinders, called multiwalled carbon nanotubes, to make a motor that’s only 300 nanometers long.

A variety of molecular-scale motors and other actuators are under development around the world, but many rely on biological parts, such as enzymes (SN: 11/9/02, p. 291: Available to subscribers at Nanotech Switch: Strategy controls minuscule motor). In comparison, the new system–built by Alex Zettl’s research team at the University of California, Berkeley and the Lawrence Berkeley National Laboratory–is synthetic and might operate under conditions that biological components find unfriendly, such as extreme heat and harsh solvents.

Zettl’s graduate students Adam Fennimore and Tom Yuzvinsky fabricated the new actuator on a silicon wafer. The rotor consists of a gold plate centered on a nanotube shaft whose ends are anchored to electrically conductive pads. The plate rotates when a voltage is applied to three stationary gold electrodes positioned on the wafer a short distance from the shaft. The nanomachinists report their results in the July 24 Nature.

In the team’s first experiments, large voltages induced the entire shaft to twist only 20 degrees. That could prove useful, Zettl notes, but his team was aiming for a nanomotor capable of full rotations.

A route toward this goal emerged from previous studies. Three years ago, Zettl and graduate student John Cumings found that the interior tubes of a multiwalled carbon nanotube could move freely within the more exterior tubes (SN: 7/29/00, p. 71: Available to subscribers at A new carbon nanotool springs to life).

To take advantage of this property, Zettl’s team severed the outermost shell–or several of them–on either side of the rotor plate. This step decouples the rotor-bearing segment of the shaft from the rest of the multiwalled nanotube.

With a judicious combination of small voltages applied to the stationary electrodes, the researchers could make the rotor move any amount between 0 and 360. They also made it flip back and forth quickly between two positions thousands of times and found that it showed no wear.

“This first demonstration of a rotational actuator using a nanotube axle and bearing is a truly exciting advance that could have important technological applications,” comments Ray Baughman of the University of Texas at Dallas.

Zettl predicts that uses for nanoscale motors are “going to be huge and very diverse.” Potential examples include switches in optical communication devices and pumps that move solutions though minuscule channels for mixing and analysis.

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