May 2005

10 Emerging Technologies

Continued from page 1

By Technology Review

Quantum Wires
POWER TRANSMISSION Wires spun from carbon nanotubes could carry electricity farther and more efficiently. By Erika Jonietz

Richard Smalley toys with a clear plastic tube that holds a thin, dark gray fiber. About 15 centimeters long, the fiber comprises billions of carbon nanotubes, and according to the Rice University chemist, it represents the first step toward a new type of wire that could transform the electrical power grid.

Smalley's lab has embarked on a four-year project to create a prototype of a nanotube-based "quantum wire." Cables made from quantum wires should conduct much better than copper. The wires' lighter weight and greater strength would also allow existing towers to carry fatter cables with a capacity ten times that of the heavy and inefficient steel-reinforced aluminum cables used in today's aging power grid.

The goal is to make a wire with so little electrical resistance that it does not dissipate electricity as heat. Smalley says quantum wires could perform at least as well as existing superconductors -- without the need for expensive cooling equipment. The reason: on the nanometer scale, the weird properties of quantum physics take over, and a wire can carry current without resistance. But until a couple of years ago, no one knew whether this amazing property would hold up when nanotubes were assembled into a macroscopic system. Then Jianping Lu, a physicist at the University of North Carolina at Chapel Hill, calculated that electrons could travel down a wire of perfectly aligned, overlapping carbon nanotubes with almost no loss of energy.

Smalley's group has already produced 100-meter-long fibers consisting of well-aligned nanotubes. But the fibers are mixtures of 150 different types of nanotubes, which limits their conductivity. The best wire would consist of just one kind of nanotube -- ideally the so-called 5,5-armchair nanotube, named for the arrangement of its carbon atoms. Existing production techniques generate multiple types of nanotubes, indiscriminately. But Smalley believes that adding tiny bits of a single carbon nanotube at the beginning of the process could catalyze the production of huge numbers of identical nanotubes -- in essence, "cloning" the original tube.