Atlanta
(May 17, 2005) — Smaller, faster computers, bullet
proof t-shirts and itty-bitty robots, such are the
promises of nanotechnology and the cylinder-shaped
collection of carbon molecules known as nanotubes.
But in order for these exciting technologies to hit
the marketplace (who wouldn't want an itty-bitty
robot), scientists must understand how these miracle-molecules
perform under all sorts of conditions. For, without
nanoscience, there would be no nanotechnology.
In
a recent study, researchers at the Georgia Institute
of Technology, along with colleagues from the IBM
Watson Research Center and the Ecole Polytechnique
Federale de Lausanne in Switzerland, found that while
nanotubes are extremely stiff when pulled from the
ends, they give when poked in the middle. The larger
the radius, the softer they become. The finding,
which is important for the development of nanoelectronics,
is published in the May 6, 2005 edition of the
journal Physical Review Letters.
“We know from previous studies that nanotubes are very stiff in the axial direction
(end to end) but very little is known about their radial elasticity, mainly because
when you're working with tubes that small it's very difficult to poke them without
pushing them beyond the point where they will be irremediably damaged,” said
Elisa Riedo, assistant professor of physics at Georgia Tech.
Using an atomic force microscope (AFM) and testing it with a tip of 35
nanometers in radius, researchers lightly prodded the nanotubes to measure
the elasticity.
“By making a very small indentation in the tubes, we were able to measure the
radial elasticity of a number of single and multiwalled carbon nanotubes of different
radii. What we found was that as we tested this technique with wider and wider
nanotubes, the bigger tubes were much less stiff than the smaller tubes,” said
Riedo.
Riedo and colleagues began with a single-walled nanotube with a radius of only 0.2
nanometers and slowly inched, or rather nanometered, their way up to multiwalled
nanotubes measuring 12 nanometers in radius. They tested 39 nanotubes
in all.
“We started with single-walled nanotubes and then measured tubes with an increasing
number of layers, keeping the external radius twice as large as internal radius,” said
Riedo. “Our experiments show that for nanotubes with small internal radii, increasing
the radii makes them softer. This means that for these tubes, the radial rigidity
is controlled by the magnitude of the internal radius, whereas the number of
layers plays a minor role.”
But, for the nanotubes with larger radii, the elasticity of the nanotubes is
almost constant. This could mean that the softening that occurs as the internal
radius of a nanotube is increased, is counterbalanced by the stiffening effect
that occurs as the number of layers increases, up to the point at which the nanotube's
properties reach those of graphite, she said.
Understanding just how much these nanotubes of various sizes and layers can bend
is an important step in the development of nanoelectronics and the nanowires
that carry electrical current through them. Recently, a team of scientists at
the University of California, Irvine, demonstrated that transistors made of single-walled
nanotubes can operate at much faster speeds than traditional transistors. Knowing
just how far these tubes can bend may lead to even more efficient nanowires.
Since the team kept the external radius twice the distance as the tubes' internal
radius in this round of tests, Riedo said the next step is to change this ratio
and vary the number of layers, while keeping the internal radius constant and
vice-versa to see how these changes affect the tubes' elastic properties.
Related Link
Elisa
Riedo
http://www.physics.gatech.edu/people/faculty/eriedo.html
The
Georgia Institute of Technology is one of the nation's
premiere research universities. Ranked among U.S.
News & World Report 's top 10 public universities,
Georgia Tech educates more than 16,000 students every
year through its Colleges of Architecture, Computing,
Engineering, Liberal Arts, Management and Sciences.
Tech maintains a diverse campus and is among the
nation's top producers of women and African-American
engineers. The Institute offers research opportunities
to both undergraduate and graduate students and is
home to more than 100 interdisciplinary units plus
the Georgia Tech Research Institute. During the 2003-2004
academic year, Georgia Tech reached $341.9 million
in new research award funding.
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