Electronic Design

Results Of Nanotube Study Hold Promise For Ultra-Small Circuits

Researchers at the University of North Carolina at Chapel Hill have announced practical results in their ongoing research on nanotubes. The team has discovered that the electrical resistance between nanotubes and graphite surfaces varies according to the orientation of the tubes. This discovery may prove fruitful for the future of telecommunications as well as other electronic applications.

Nanotubes are carbon tubes so incredibly thin that several million lying side by side cover only an inch. The material was first discovered in 1992 by scientist Sumio Iijima of Japan's NEC Corporation. A form of soot, nanotubes are created by arcing electricity between two sticks of carbon. Measuring about 10 to 30 nm in diameter, the tubes are approximately one millionth to five millionths of a meter long.

Scientists found that electrical resistance between a nanotube and a graphite surface peaks six times as the end of the nanotube is rotated 360°. This nature of electrical resistance occurs because the atoms in the nanotube and the graphite are arranged in hexagons (see the figure). The results of this study indicate that the resistance of a nanotube may be altered merely by changing the tube's position on a flat surface.

The UNC researchers believe this discovery heightens the usefulness of nanotubes as ultra-small circuits. The preferred directions of the nanotubes would necessarily be aligned when the devices are assembled to manipulate electrical resistance. Moreover, this nature of resistance may be used to measure the rotation of nanometer-scale objects. The tunable resistance of nanotubes may also be useful in molecular-scale machinery with moving, sliding, or rotating parts.

UNC's ongoing nanotube research uses a proprietary device known as the nanoManipulator. It com-bines a commercially available atomic-force microscope, complete with a small, gold-tipped probe capable of manipulating molecule-sized particles, and a force-feedback virtual-reality system. The virtual-reality component lets the re-searchers explore a representation of the nanotube surface enlarged up to 1 million times.

These latest findings compound other useful results derived by the nanotube project. Previously, it was discovered that the nanotubes have an incredible capacity to bend and rebend. University researchers also used carbon-13 nuclear magnetic resonance (NMR) to measure the number of electrons in single-walled nanotubes as well as the tubes' electrical properties.

Much of the research at UNChas been dedicated to distinguishing the properties of metallic and semiconducting nanotubes. The results reveal the potential to fabricate either all-metallic or all-semiconducting carbon nanotubes with tunable structures. Additionally, UNC researchers have found that the nanotubes require significantly more energy to roll across some surfaces than to slide over these same surfaces. Electrical interactions are believed to be responsible for this behavior.

The UNC researchers project future use of the carbon nanotubes in flat-panel displays, telecommunications devices, fuel cells, Li-ion batteries, high-strength composites, and novel molecular electronics.

For more information about the University of North Carolina's nanotube research project, point your browser to www.unc.edu.

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