Bethany Halford
January 28, 2008
 Volume 86, Number 04    p. 15

TYING TOGETHER materials science and chemistry, scientists have
developed a chemical method for making carbon ribbons less than 10 nm
wide and just one atom thick (Science, DOI: 10.1126/science.1150878).
The semiconducting properties of these so-called graphene nanoribbons
make them promising materials for electronics applications.

To create the graphene ribbons, Hongjie Dai and colleagues at Stanford
University first chemically exfoliate graphite, loosening individual
layers of graphene by giving the graphite a 60-second bath in 3%
hydrogen in argon gas at 1,000 °C. They then "tear" the graphene into
strips by sonicating the material in solution. Previously, scientists
used lithographic patterning to cut graphene into ribbons. But Dai's
chemical method yields narrower ribbons with far smoother edges.

Rodney S. Ruoff, a nanoengineering professor at the University of
Texas, Austin, says the work is exciting. "It is surprising that such
fine ribbons could result from processing through use of ultrasound,"
he notes, "so there is some underlying mechanics of a fairly selective
propagation of 'cracks' or 'tears'" in the exfoliated graphene.

Dai's effort represents a "significant leap" in graphene research,
according to Andre Geim, a physics professor at England's University
of Manchester. The new work, he says, shows "one needs to make ribbons
only a couple of times narrower than were previously reported to make
a qualitative change in characteristics and reach a good transistor
action required for integrated circuit applications."

To that end, Dai says the slim nanoribbons have useful properties at
room temperature that make them promising electronic components for
field-effect transistors and sensors. Furthermore, all the nanoribbons
that were less than 10 nm wide were semiconducting, unlike their
carbon nanotube cousins, which exist as a mix of semiconducting and
metallic materials.

Dai says that the electronic performance of nanoribbon-based devices
still needs further investigation. In the meantime, he says, the
nanoribbons "will provide an experimental test bed for studies of many
fundamental electrical, spectroscopic, and spin properties predicted
for these materials."

http://pubs.acs.org/cen/news/86/i04/8604notw7.html