SCIENCE & ENGINEERING NEWS

San Diego, CA — Chemists at the University of California at Los Angeles are reporting a further advance in the effort to produce electronic circuitry on a molecular scale.

In an article being published in the journal Science, the U.C.L.A. team says it has succeeded in using a molecule to create an electronic switch that can be reconfigured – that is, it can be turned on and off, and on again – like a transistor.

Previous research had produced molecular switches that could change their state only once – on to off, or vice versa – or could operate only for a limited time or at very low temperatures.

The latest achievement is a significant step toward building a new generation of memory devices and computers that are far more powerful and consume less power than today’s microelectronic systems.

The advance is part of a quest for electronic circuits that are perhaps one-thousandth the size of today’s transistors, which are made lithographically by etching circuits on silicon with light.

In the future, arrays of billions of circuits would self-assemble by means of chemical reactions, which would make individual circuits far less costly.

“I am extremely excited about this,” said James Ellenbogen, a scientist for the Mitre Corporation, a government-financed research organization, and an expert in the developing field of molecular electronics. “It takes your breath away.”

Dozens of molecular-electronics efforts are going on around the country, including projects at major manufacturers like I.B.M., Hewlett-Packard and Motorola. And earlier this year the Clinton administration undertook an ambitious program to spend almost $500 million a year on research in the area, known as nanotechnology.

Last summer, the U.C.L.A. group, working with computer architects and chemists at Hewlett-Packard, reported that it had developed a nonreversible switch based on a molecule known as rotaxane.

The university chemists, led by James Heath and J. Fraser Stoddart, then began searching for a new class of molecule that could switch back and forth or on and off – from one state to another when a small voltage was applied.

They found what they were looking for in catenanes, a type of organic molecule composed of two interlocking rings, Mr. Heath said. The group has benefited from the work of Mr. Stoddart, who over several decades has developed an international reputation for creating unique molecules with unusual properties.

“Last fall we began looking at what Fraser had on his shelf,” Mr. Heath said.

The catenanes consist of two tiny mechanically interlocked rings created from atoms linked in a circle. The group discovered that one ring can be stimulated to move between two different states – for instance, from one angle to another – with respect to the other ring, he said.

The group was particularly intrigued by the molecules because they can be stimulated by either electricity or light, suggesting the possibility of optical computing machines as well as electronic ones, he said. Moreover, the resulting switches can operate at room temperature.

A major challenge is to figure out how to address the individual molecular switches, Mr. Ellenbogen said. So far, the research of the U.C.L.A. scientists and of a similar group of researchers at Yale University and Rice University has created molecules that can be switched on and off only in unison.

The Yale-Rice team and a group at Harvard also reported creating reversible molecular switches within the last year, but they operated under more limited conditions.

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