By Sean Henahan, Access Excellence

ITHACA, NY (Sept. 6, 1996) Researchers at Cornell University have created the world's smallest wires, only six angstroms in diameter. The next objective will be to find uses for the molecular-sized wires.

Caption: Molecular wire of molybdenum selenide embedded in a polymeric matrix. The thickness of a single wire is approximately three atoms in diameter, with the length about 110 atoms. Scanning tunneling electron micrograph; mag.=1x 1million.

The wires, only 6 angstroms in diameter, or just several atoms wide, could be kept separate or bunched together to make cables inside a polymer matrix, depending on the intended purpose, the researchers say. The wires can be up to at least 10,000 angstroms in length.

"No one has ever made wires this small before, so we're not sure what all the uses are going to be," said Francis J. DiSalvo, Cornell professor of chemistry who led the work with his Cornell colleague, Jean M.J. Frechet, the Peter J. Debye Professor of Chemistry.

The research team took atoms of the metallic substances molybdenum and selenium separated by lithium. By putting them in a solvent of ethylene carbonate -- which polymerizes into polyvinylene carbonate -- the lithium was separated out, leaving long strings of the metals. Then they added an agent to make the polymer. By doing so quickly, the organic polymers gelled before the wires had a chance to clump together.

"It's like trapping a small, skinny sausage in a big bowl of spaghetti," DiSalvo said. "We trapped the wires in the solution. The trick is to do it very fast, before they have a chance to clump."

The end result is a plastic block laced with subnanometer-sized wires. To make cables of more than one wire held together, the researchers just increased the amount of metallic grains.

"We polymerize it very quickly using light. It freezes the wires in whatever orientation they are in," said Frechet, a polymer chemist. "What is remarkable is that this is so tiny -- the size of a molecule -- and we can do that. We can't do anything very useful with them yet, but this is the way science progresses. In time, we will. For now we can study their interaction with light."

The researchers did not know for sure that they had succeeded until their experiments were subjected to scanning transmission electron microscopy (STEM). The images confirmed that the wires were in place. The microscopists used an imaging technique in which the atomic number of the metallic ions are distinguished from the polymer's organic materials, which have lower atomic numbers.

The images showed single wires from 6 angstroms diameter, and double wires of about twice that size, and groups of wires, or cables, up to 40 angstroms diameter, all of which can act as electrical conductors.

Now that they have shown it is possible to make such materials, the researchers are turning their attention to what they can do with them. The chemists are trying to use the new structures as membranes, in which the wires act as a solid-state catalyst. Other possibilities, they say, include, anti-static polymeric materials for microelectronics, such as in the packaging of chips or for computer housings, and anti-static agents for film. In many cases, static discharges can destroy sensitive electronic equipment or leave a blotch on film.

"Part of the problem is in the basic science," DiSalvo said. "We can make these perfect wires 6 angstroms in diameter. How do you make electrical contacts for wire that thick? We have more basic science to think about. What happens to the properties when you go from bulk to a single thin wire? Maybe now we can test some theories that propose unusual behavior of such narrow wires."

For more details on this research see the article in the journal Science (Aug. 9, 1996).