February 27, 2001–Upton, New York–Scientists at the U.S. Department of Energy’s Brookhaven National Laboratory (BNL) and Stanford University have developed molecular wires millions of times smaller in diameter than a human hair. These nanowires have high rates of electron transfer with very low resistance.
In their quest for tiny wires, chemist John Smalley and his colleagues were interested in an organic molecule called oligophenylenevinylene (OPV), synthesized at Stanford. “These molecules are essentially ‘chains’ of repeating links made up of carbon and hydrogen atoms arranged to promote strong, long-range electronic interactions through these molecules,” Smalley explains.
The technique uses a laser to heat up the gold electrode and change its electrical potential. A very sensitive voltmeter then measures the change in electrical potential over time as electrons move back and forth across the connection formed by the molecular wires. The faster the change, the faster the rate of electron transfer, and the lower the resistance in the wire.
The scientists found a very high rate of electron transfer. “We think the electrons are actually popping across through a process called electron tunneling in less than 20 picoseconds (trillionths of a second),” says Smalley. “That means OPV should make pretty good low-resistance molecular wires.”
Furthermore, while the scientists expected the rate of electron transfer to decrease as more links were added to the molecular wire chain, making it longer, this didn’t happen. The rate remained fast, and the resistance low, up to lengths of nearly 3nm–relatively long on a nanometer scale. “That means wiring circuits will be easier because you don’t have to worry so much about the distances,” Smalley says.
The wires aren’t perfect, however, because the resistance is not as low as it should be according to certain theoretical expectations. “Something else seems to be increasing the resistance,” says Smalley. But this drawback could even turn into a benefit if the scientists can figure out what that factor is and how to control it. That might enable them to make electronic components such as tiny transistors and diodes, which work on the basis of varying the electrical resistance.
This research was funded by the U.S. Department of Energy, the National Science Foundation, the National Institute of General Medical Science, and the Stanford University Office of Technology Licensing.