SAN
DIEGO -- North Carolina scientists have found that
"thinnest" is not necessarily "best"
in rating structure and function of carbon nanotubes,
the molecule-sized cylinders that show promise for
futuristic technology scaled at a billionths of a
meter
.
During an American Chemical Society national meeting,
researchers at Duke University and Xintek, Inc. of
Research Triangle Park, N.C., will report on the synthesis
and testing of a new class of nanotubes made up of
two to five layers of carbon atoms. The scientists
find these "few-walled" carbon nanotubes
are structurally nearly as perfect as one carbon atom
thick "single-walled" carbon nanotubes,
while being cheaper to make than their single-walled
cousins, said Duke assistant chemistry professor Jie
Liu Liu and his colleagues discovered how to create
the tubes within heated streams of alcohol and hydrogen.
Moreover, tests by Liu's collaborators
at Xintek found that few-walled nanotubes can be made
to spew out electrons with better performance than
current commercial carbon nanotubes, Liu added.
Xintek is already commercializing
varieties of carbon nanotubes as "field emitters"
that generate electrons to empower portable and miniaturized
X-ray sources. Other possible uses for electron field
emitters would include-flat panel displays and new
kinds of light sources.
Liu will report on the synthesis
and evaluation of few-walled nanotubes during a scientific
session on polymer nanocomposites (the prefix "nano"
referring to billionths of a meter dimensions) beginning
at 8 a.m. Pacific Standard Time on Wednesday, March
16, 2005, at the Torrey Room 1 and 2 of the San Diego
Marriott Hotel.
The work is being funded by
NASA.
Since carbon nanotubes were
first discovered in 1991, chemists such as Liu and
material scientists such as Xintek co-founder Otto
Zhou have been attracted by the potential of these
graphite-like nanocylinders to become 21st century
wonder materials.
Carbon nanotubes of both single-walled
and multi-walled varieties combine ultra miniaturization
with exceptionally high structural strength. Their
electronic properties can range between metal-like
and semiconductor-like, depending on their structural
alignments.
Liu's own laboratory, which
is also linked to the University of North Carolina
at Chapel Hill-based North Carolina Center for Nanoscale
Materials directed by Zhou, who is a UNC-Chapel Hill
professor, has evaluated various methods for making
nanotubes.
Liu's teams of researchers
have also developed techniques to make exceptionally
long single-walled carbon nanotubes for potential
use in nanoscale electronic circuitry.
The fact that single-walled
carbon nanotubes are composed of just one layer makes
them more predictable and reliable for use as precision
electronic components. However, Liu said, "The
problem is that single-walled nanotubes are very hard
to make, and very hard to make in large quantities."
By contrast, "multi-walled
nanotubes can be made very easily and in very large
quantities, although in most cases they have a lot
of structural defects," he added. Because of
their ease of manufacture, multi-walled carbon nanotubes
are becoming commercially available for uses that
can accommodate structural flaws, Liu said.
As an example, he described
how using small portions of multi-walled nanotubes
in manufacturing plastic auto parts alters the plastic's
electrical charges in a way that makes automotive
paint stick more uniformly.
Multi-walled nanotubes are
normally encased by 10 to 30 consecutive layers of
carbon atoms. But few-walled carbon nanotubes are
different, Liu said. "The fact that they are
smaller in diameter makes them uniquely suitable for
certain applications. They are also more rigid than
single-walled nanotubes. And they can be made much,
much cheaper than single walled nanotubes."
His Duke laboratory stumbled
onto few-walled nanotubes during a failed attempt
to make single-walled carbon nanotubes. When the researchers
tried growing the single-walled variety in a heated
glass tube within a stream of alcohol and hydrogen
under the influence of metal catalysts, they grew
few-walled nanotubes instead.
Duke and Xintek have applied
for a patent on the application of few-walled carbon
nanotubes for electron field emission.
Contact: Monte Basgall
monte.basgall@duke.edu
919-681-8057
Duke University
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