Scientists Advance on Path to Make Electronics Tinier
By JOHN MARKOFF
hemists 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.
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A molecule becomes
an electronic switch
that flicks uon and off.
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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.
