emerging field of molecular electronics using nanoscale
molecules as key components in computers and other electronic
devices is in excellent health and has a bright future,
conclude UCLA, Caltech and University of California,
Santa Barbara, chemists who assess the field in the
Dec. 17 issue of the journal Science.
electronics is in its infancy, and its adolescence
and adulthood will be very exciting as we push toward
the promise of molecular electronics: smaller, more
versatile and more efficient," said Amar Flood,
a UCLA researcher in Fraser Stoddart's supramolecular
chemistry group, and lead author of the Science paper.
combination of active molecules with electronic circuitry
is opening up exciting new areas of science,"
Flood said. "It is too early to predict precisely
what will come from this marriage, but we expect that
the unique properties of molecules, including sight,
taste and smell, may be put to very good effect by
marrying them with silicon."
first applications are likely to involve hybrid devices
that combine molecular electronics with existing technologies,
such as silicon, said Stoddart, director of the California
NanoSystems Institute (CNSI), who holds UCLA's Fred
Kavli Chair in NanoSystems Sciences.
electronic components are already working, say Stoddart,
Flood and co-authors James R. Heath, who is Elizabeth
W. Gilloon Professor of Chemistry at Caltech and a
member of CNSI's scientific board; and David Steuerman,
a CNSI postdoctoral fellow in physics at University
of California, Santa Barbara. For example, logic gates,
memory circuits, rectifiers, sensors and many other
fundamental components have been demonstrated to work.
toward incorporating molecules as the active components
in electronic circuitry has advanced rapidly over
the past five years. Heath describes the progress
as "real and rapid."
have published 64-bit random access memory circuits
using bistable rotaxane molecules as the memory elements,
and we are in the process of fabricating a 16-kilobit
memory circuit at a density of devices that far exceeds
current technology," Heath said. "On a Moore's
Law graph, our memory circuit is at a density of Intel-like
circuits that will be manufactured decades from now."
I was having less than a decade ago are becoming a
reality in our labs," said Stoddart, whose areas
of expertise include nanoelectronics, mechanically
interlocked molecules, molecular machines, molecular
nanotechnology, molecular self-assembly processes
and molecular recognition, among many other fields
many classes of molecules can be used for molecular
electronics, only a small percentage of these have
been assessed so far," Flood said.
the past decade, scientists around the world have
taken a few model molecular systems, including bistable
catenanes and rotaxanes, and have addressed many of
the fundamental scientific principles related to harnessing
their potential in electronic circuits.
research summarized in the Science paper describes
experiments in which the UCLA/Caltech team has used
its bistable catenanes and rotaxanes in many different
environments. For example, they use the bistable molecules
in environments where chemists are comfortable, such
as the solution phase, and in environments where engineers
are comfortable: electronic circuits.
said, "We can now correlate quantitatively the
properties of bistable catenanes and rotaxanes from
the solution phase, where they are easy to interrogate,
to a device, where they are much more difficult to
interrogate. Ultimately, we would like to have control
over device properties through molecular synthesis.
This paper in Science highlights the fact that we
are beginning to achieve this goal."
UCLA/Caltech team has verified that bistable catenanes
and rotaxanes work as molecular switches that can
be turned on and off when they are attached to surfaces
and when they are buried in polymer blends with the
consistency of a rubber tire.
we apply a positive voltage, they turn on, and when
we apply a negative voltage pulse, they switch off
instantly," Stoddart said. "We have verified
that the same mechanism works in a device, in solution
and in two other environments. In addition, we have
measured how fast the bistable molecules switch in
different environments. We can slow down the switching
on the order of 10,000 times on going from solution
to device. What takes 10 minutes in a device takes
one-tenth of a second in solution. This type of control
allows us to store bits of memory using these molecules."
role of environments on the molecules' switching speeds
is elaborated on in the final issue in 2004 of Chemistry
A European Journal (volume 10, page 6,558).
UCLA/Caltech team also can produce the colors red,
green and blue within a single molecule. The red-to-green
color changes are highlighted in pictures published
in Angewandte Chemie International Edition earlier
this month (volume 43, page 6,486). If Stoddart's
molecular switches are incorporated into a future
generation of computers, there is also the prospect
of using the same molecular switches as the basis
for the displays in these and in other new technologies.
The UCLA/Caltech team is working with multiple kinds
of molecular switches, each with unique characteristics.
this research could affect the computer industry dramatically,
it also may have a significant impact on very different
uses of information technologies, Heath and Stoddart
said. These potential outcomes are recognized by the
fact that their research is funded by the Defense
Advanced Research Projects Agency.
CNSI, a joint enterprise between UCLA and the University
of California, Santa Barbara, is exploring the power
and potential of organizing and manipulating matter
atom-by-atom, molecule-by-molecule, to engineer "new
devices and systems that will extend the scope of
many existing technologies and foster commercial development
far beyond anything we might have contemplated up
until now," Stoddart said.
Stuart Wolpert ( firstname.lastname@example.org )