Researchers
at Columbia University's Nanoscience Center are on
the verge of solving one of the most vexing barriers
facing advances in molecular electronics: incorporating
individual molecules into functional nanoscale devices
and exploiting their electrical and chemical properties.
Scientists have long been intrigued by carbon nanotubes,
tiny straws of pure carbon measuring less than a
hair's width across. Successfully linking them in
stable arrangements would allow for an impressive
increase in both the speed and power of a variety
of electronics. This new research at Columbia sets
the stage for advances in real-time diagnosis and
disease treatment, surgical robotics, and information
storage and retrieval, potentially rendering room-sized
supercomputers obsolete.
In the Jan. 20, 2006, issue of Science ,
Columbia scientists explain how they have developed
a unique way to connect the ends of carbon nanotubes
by forming robust molecular bridges between them.
The Columbia team was able to combine the best qualities
of carbon nanotubes and organic molecules in a single
electronic switch, the journal reported.
Previously, researchers working in this area of
nanotechnology have made transistors out of carbon
nanotubes with switches connecting molecules to metal
wire leads. This Columbia research illustrates a
more elegant way of making molecular transistors,
since the nanotube leads are already the same size
as the molecules, and they are made of carbon, making
it easier to connect them chemically.
This new method of wiring molecules into the gaps
of single-walled carbon nanotubes employs oxidative
cutting -- a lithographic technique that makes each
cut-end of the nanotube more prone to molecular bonding.
These new methods of constructing molecular bridges
could one day revolutionize the size and scale of
computer hardware by allowing engineers to design
circuits at the nanoscale limits. The Columbia research,
involving the ability to link nanotubes with an incredibly
small diameter, brings scientists closer to creating
miniature devices that also process information with
molecules.
"Molecular electronics has real-world relevance," says
Colin Nuckolls, an associate professor of chemistry,
and a co-author of the Science paper. "It
opens the door to new types of ultrasmall switches
and sensors. We are able to form a bridge, both literally
and figuratively, by combining reaction chemistry
with ultrafine lithography."
The nanotubes themselves are long, thin cylinders
of carbon unique for their size, shape and physical
structure. They can be thought of as a sheet of graphite
forming a hexagonal lattice of carbon, (see image)
rolled into a tube, explains Columbia senior research
scientist Shalom Wind, another co-author of the paper.
They have been shown to possess remarkable mechanical
and electronic properties, he added.
Attaching molecular wires to single-walled nanotubes
involves cutting a tube using nanolithography combined
with a localized oxidation process that leaves a
nanotube with two ends that are capped with carbon-based
acid groups and separated by a molecule-sized gap.
In that tiny space, a molecule can be chemically
joined with each end to form a robust nanotube/molecule
complex, which operates as a nanoscale transistor.
The nature of this work is also expected to keep
alive "Moore's Law," the prediction made in 1965
by Intel co-founder Gordon Moore who predicted the
number of transistors per square inch on integrated
circuits would double every year. Moore said the
trend would continue for the foreseeable future;
but without an order-of-magnitude shift in the scale
of computer circuitry -- a promise represented in
Columbia's latest work–that prediction could hit
a wall in the next decade, experts say.
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