Like A Dimmer Switch, Turning A Nanotube Can Control Electrical Flow

That knowledge could be especially useful to researchers working in fields like wireless communications or micro-robotics by making it easier for them to design electronic devices and actuating systems -- on/off power switches and the like -- at the nanoscale level.

The UNC and NC State scientists published their finding in a peer-reviewed paper in the Dec. 1 issue of Science.

First discovered in 1991, carbon nanotubes are structures so small that thousands could fit on the tip of a pen. Their molecular size and mechanical and electronic properties make them prime candidates for use as components in nanometer-sized electronic and actuating devices that many scientists feel are the wave of the future.

"We found that we can change the electrical resistance between the carbon nanotube and a graphite substrate up to a factor of 50 by simply rotating the nanotube," said Dr. Marco Buongiorno Nardelli, a research associate in physics at NC State. Being able to do this, he says, gives nanoscale-device designers a controllable, continuous means of converting mechanical signals into electrical signals -- something they have long sought.

"Being able to adjust the electrical resistance in this way could, one day, lead to much faster, more energy - efficient electronic devices," he said.

In addition to Buongiorno Nardelli, the seven-person research team includes Drs. S. Paulson, A. Helser, R.M. Taylor II, M. Falvo, R. Superfine and S. Washburn, all of UNC-Chapel Hill. (Paulson is now at Duke University.) The experiments were carried out at Chapel Hill.

Buongiorno Nardelli, a native of Rome, Italy, served as team’s sole theoretical physicist.

He says even without its long-term practical applications, the team's discovery is significant, because it represents another building block in modern science's understanding of nanotechnology fundamentals. The transfer of electrons from one material to another has almost always been thought of in terms of energy conservation, with no attention being paid to momentum conservation, he says. "These experiments show us that momentum conservation plays a role, too."