Significant Progress Toward Molecular Computers
A team of UCLA chemists reports significant progress toward the
creation of molecular computers with the first demonstration of a
reconfigurable molecular switch that works in a solid state at
room temperature - a breakthrough that solves one of the
obstacles toward the creation of molecular computers that could
be much cheaper, smaller and more efficient than today's
silicon-based computers.
In the Aug. 18 issue of the journal Science, the UCLA chemists
resolve the challenge of a reconfigurable molecular switch that
they presented last year in a paper on molecular computers. The
earlier paper, published in the July 16, 1999, issue of Science,
received worldwide attention.
"Last year's paper was the first experimental step toward
molecular computers," said James R. Heath, professor of
chemistry at UCLA. "This is the second experimental step, and
the steps are no longer a slow walk, but a fast jog."
The team is led by Heath; J. Fraser Stoddart, who is UCLA's Saul
Winstein Professor of Organic Chemistry; and Pat Collier, a
postdoctoral scholar in Heath's laboratory.
"This molecular approach could have failed early on in many
places, and it's not failing," Heath said. "These are still early days,
but right now, it seems that everything is beginning to work
together well and that many avenues are opening up. That means
that if our next set of experiments doesn't work, we will have a
number of other options to pursue. We're getting there. Overall,
the progress is faster than any of us expected."
Stoddart agreed, saying, "When I joined UCLA's faculty three
years ago, if someone had asked me how far off molecular
computing was, I would have said on a scale of a
quarter-of-a-century. Things I was only dreaming of are suddenly
becoming a reality in Jim's lab."
In last year's Science paper, the researchers could switch the
molecules only once; now they have done so hundreds of times.
"Last year, we published an architectural demonstration with
molecules and demonstrated that it is possible to do simple
mathematical operations," Heath said. "However, the switches
used in that work switched only once, and this limited their
relevance to any serious technology. Now we have taken another
class of Fraser's molecules and demonstrated that they may be
repeatedly switched on and off over reasonably long periods of
time in a solid-state device under normal laboratory conditions.
For the first time, we are able to turn the molecular switches on
and off repeatedly."
Closing in on molecular RAM Developing molecular RAM
(random access memory) was one of the major challenges the
researchers cited last year, and now they are close to reaching it.
"With this paper, we have achieved a critical step on the way to
molecular RAM at room temperature - which is required if this is
to be a viable technology," Heath said. "From here, molecular
RAM may well be just a matter of time. While there are many
pitfalls between the demonstration of a technology and the actual
invention, at the moment, we can't see how any of those pitfalls
could prove fatal."
The research team gives much of the credit to the unique
molecules that Stoddart and his team develop. Stoddart has been
working for more than a decade on interlocking molecules with
recognition sites.
"Not only do the molecular components in these interlocked
molecules communicate efficiently with one another but the
molecules also interrelate to one another in the solid-state
device," Stoddart said. "It's significant that we have moved from
the incoherence we had in the solution state, and have progressed
from molecules that behaved like pedestrians walking in a
shopping mall to molecules that march like a united, well-trained
army. Where molecules were previously swimming around
incoherently in solution, now we see coherent molecular motion
in a solid-state device. The molecules have the ability to
recognize one another and line up in an efficient manner."
Stoddart's molecules, called catenanes, consist of two tiny
mechanically interlocked rings made up of atoms linked in a
circle. To interlock the ring components, Stoddart and his
research team build chemical groups that recognize one another
into the components' precursors so that, when the appropriate
pieces are brought together in solution, they self-assemble to form
a pair of interlocked rings. In catenanes containing the right two
rings, one ring can be stimulated to move between two different
states with respect to the other reference ring, giving the catenane
molecule its bistability. It is the switching motion, which can be
induced by taking away and giving back an electron that is the
molecular basis for the present device. In last year's Science paper,
the chemists used another kind of interlocked molecule
synthesized in the Stoddart labs. Called a rotaxane, it has a
dumbbell-shaped component that is encircled by a ring
component after the style of an abacus. Rotaxanes can also be
made to switch their molecular states.
The catenanes reported in the new Science paper work much
better than last year's rotaxanes, said the chemists, who added that
they are already working with a new class of molecules that lead
to significantly better switching performance than the catenanes.
In fact, the chemists are working with more than a half-dozen
different kinds of molecular switches, each with its own unique
characteristics.
Molecular computers hold the promise of being far less
expensive, much smaller, and much more energy-efficient than
today's silicon-based computers. The UCLA groups, in
collaboration with Hewlett-Packard researchers, are working on
making molecular computers that may "learn and improve the
more they are used," Heath said.
While the research could dramatically influence the computer
industry, it may also have a significant impact on very different
uses of information technologies, Heath and Stoddart said.
"Molecular machines will lead to other new technologies beyond
molecular electronic computers," Stoddart said. "Other fields
besides computers may be revolutionized by this molecular
approach, although it is too soon to say precisely which ones will
be the first to benefit."
The unimaginable may be possible Heath believes eventually
there may be a new molecular manufacturing technology. "What
once seemed like science fiction is now looking more and more
like actual science," Heath said. "A molecular computer will
enable us to do things we cannot even imagine now."
In addition to Heath, Stoddart and Collier, the research team
includes Francisco Raymo and Gunter Mattersteig, former
postdoctoral scholars in Stoddart's laboratory; Eric Wong, a
postdoctoral scholar in Heath's laboratory; graduate student Chris
Beverly; and Jose Sampaio, a visiting professor on sabbatical at
UCLA.
"We're trying to learn to make a computer from the bottom up,
and learning how to do such manufacturing is really what this
research is all about," Heath said. "The power of Fraser's
chemistry is that it's like a Tinkertoy set, and various desirable
physical and chemical properties can be generated by piecing
together the appropriate molecular components. Until very
recently, it wasn't clear whether these unique molecular properties
would translate into exploitable solid-state device characteristics.
In fact, this research provides compelling evidence that this does
happen. As we rearrange the Tinkertoys, we find that we can
modify and improve the properties of these devices in ways that
make complete chemical sense. This opens up a lot of possibilities
for new devices and technologies."
Within a few years, Heath thinks the research team will develop
circuits that have molecular logic, molecular memory and
nano-size wires. A hybrid computer that interfaces with molecular
memory with silicon logic is only a few years away, and a
scientific demonstration of a nano-scale computer that is largely
molecular - with molecular logic and molecular memory - will
likely happen within the decade," Heath estimated.
Stoddart came to UCLA from England's University of
Birmingham, where he was head of the school of chemistry and
professor of organic chemistry.
"I tried to get collaborators to work on a molecular computer in
Europe, but I drew a blank," Stoddart said. "It was all a dream
until I came to UCLA."
"I liken Southern California today to Paris in 1900, which was
the place to go if you were an artist," Stoddart said. "When I was
working in England in the '90s, I felt that the place to make
things happen as a scientist was Southern California, and I have
been proved right."
In the July 1999 paper in Science, Heath, Stoddart and their
colleagues, including researchers at Hewlett-Packard
Laboratories, demonstrated highly effective molecular-based
logic gates for the first time, and showed that, for certain tasks,
molecules can effectively achieve results the same as, or better
results than, silicon. For example, they showed that molecular
circuitry, when assembled into the appropriate configuration, can
tolerate manufacturing defects. That paper was widely considered
the first real step toward making a molecular computer.
In addition to conducting this research, Heath is a leader of a joint
proposal by UCLA and UC Santa Barbara to create a
wide-ranging California Nanosystems Institute that could help
revolutionize many fields of science. The project has been chosen
as a finalist in the competition for one of the California Institutes
for Science and Innovation proposed by Gov. Gray Davis.
Nanosystems involve the science, engineering and manufacturing
of molecular-based structures. The UCLA-UCSB collaboration
focuses primarily on molecular medicine and information
technology.
The research reported in Science was funded by the Defense
Advanced Research Projects Agency.
Editor's Note: The original news release can be found at
http://www.uclanews.ucla.edu/Docs/LSSW358.html
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