Like a dimmer switch, turning a nanotube can control electrical flow

November 30, 2000

Scientists at the University of North Carolina at Chapel Hill and North Carolina State University have found that by rotating a carbon nanotube, they can control its ability to conduct electrical current to another material, just as you can control the flow of electricity to lights by turning a dimmer switch.

The discovery marks the first time scientists have been able to show that by rotating a nanostructure they can control its electrical resistance.

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.
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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."

Editor's note: A color digital representation of a carbon nanotube is available by contacting Tim Lucas, NC State News Services, at (919) 515-3470 or tim_lucas@ncsu.edu, or by contacting Dr. Buongiorno Nardelli at (919) 515-7228 or nardelli@nemo.physics.ncsu.edu. The abstract from the research team's Science paper follows. For a copy of the full text, contact Lucas or Buongiorno Nardelli.

"Tunable Resistance of a Carbon Nanotube-Graphite Interface.'

Published: Dec. 1, 2000 in Science
Authors: S. Paulson, A. Helser, M. Buongiorno Nardelli, R.M. Taylor II, M. Falvo, R. Superfine, S. Washburn.

Abstract: The transfer of electrons from one material to another is usually described in terms of energy conservation, with no attention being paid to momentum conservation. Here we present results on the junction resistance between a carbon nanotube and a graphite substrate and show that details of momentum conservation also can change the contact resistance. By changing the angular alignment of the atomic lattices, we found that contact resistance varied by more than an order of magnitude in a controlled and reproducible fashion, indicating that momentum conservation, in addition to energy conservation, can dictate the junction resistance in graphene systems such as carbon nanotube junctions and devices.

North Carolina State University

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