By JOHN MARKOFF
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 today 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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