nanotubes make clean crystals
Technology Research News
Carbon nanotubes have often been compared
to cooked spaghetti; the tiny tubes, whether self-assembled or manufactured
chemically, tend to be tangled messes with variable properties. Separating
the two basic types of nanotubes - semiconductors and metals - is usually
an arduous task.
Researchers at IBM have come up with an efficient method to make uniform
metallic nanotubes. Instead of a congealing imbroglio of pasta pieces,
the resulting array lines up like ten thousand neatly stacked, matching
strands of dry spaghetti arranged in a hexagonal bundle.
Each nanotube is the same size as its neighbors and also shares the same
electronic and chemical properties. Since the tubes are perfectly crystalline,
they are also stronger, smoother, lighter and more flexible than regular
carbon nanotubes, said James Gimzewski, who was on the IBM research team
and is currently a chemistry professor at the University of California
at Los Angeles.
Nanotubes have a wide range of potential applications from environmental
sensors to components of nanoelectronic circuits. Uniform properties will
make it easier for researchers to apply nanotubes practically. Nanotubes
could eventually be used as hydrogen energy storage devices, gas detectors,
biochemical markers, nanoscale tweezers, or as a building material for
car and plane bodies, according to the researchers.
To make the uniform nanotubes, the researchers evaporated alternate layers
of buckyballs and molecules of a nickel catalyst through a shadow mask,
or screen, containing holes 300 nanometers in diameter. The catalyst causes
the buckyballs, soccer-ball shaped molecules made of 60 carbon atoms,
to unzip and form nanotubes. The researchers used heat and magnetic force
to control the process, making the nanotubes uniformly aligned and structurally
identical. Other chemical vapor deposition processes produce larger, discrete
Each tube in the array is about 1 nanometer wide, which is about 75,000
times narrower than a human hair. Each hexagonal crystal-like array contains
about 10,000 nanotubes spaced about 1.5 nanometers apart. “The crystals
can be up to 2 microns wide at the moment,” said Gimzewski. A micron is
one thousandth of a millimeter, or roughly one seventy-fifth the width
of a human hair.
The entire process takes about “twenty five minutes with a coffee break
in between,” said Gimzewski. In that time, the researchers produced 30,000
bundles of 10,000 nanotubes, or a million billion nanotubes. The area
these tubes occupy is about half an inch square.
The tubes produced are about a hundred times stronger and ten times lighter
than steel, and are defect-free, according to Gimzewski. They are also
incredibly flexible. When you bend a plastic pipe, for example, and then
unbend it, a kink always remains. These tubes, when they unbend, “just
go back to being perfect again,” Gimzewski said.
Another property of the tubes is that they conduct heat along their lengths
but not across their widths. This could allow them to efficiently dissipate
heat in a computer chip.
“The results are impressive,” said Phillipe Poulin of the National Center
for Scientific Research, (CNRS) at the University of Bordeaux, in France.
“For the first time, single wall carbon nanotubes are produced as a perfect
bulk material,” he said. Although the method might be difficult to scale
up for large production, “it definitely opens new and very promising routes
to the use of carbon nanotubes in electronics,” he said.
“I think that this work will motivate extensive research in different
laboratories to try to improve the yield and to explore the commercial
interest of the obtained materials,” Poulin said.
“If this synthetic method can produce [a] large yield of nanotube single
crystals…these nanotube single crystals will have tremendous potential
for fundamental research,” said Peidong Yang, assistant professor of chemistry
at the University of California at Berkeley. “Immediate things to do would
be…intercalation” of chemicals such as potassium or sodium into the spaces
between the nanotubes, in order to induce superconductivity in the crystals,
“The challenge is how long could you make them?” said Gimzewski. His ultimate
goal is to be able to spin the tubes “like a nanospider,” he said. The
nanotube thread would be so fine, that it would be invisible. This might
be “a bit sci fi, however I am pretty sure that a filament would have
applications as a cutting tool superior to lasers in medicine,” he said.
“We have the evidence that you can make such things.”
The researchers are aiming to increase the scale of nanotube manufacturing
and make the process less expensive. One possibility is to use a less
expensive carbon source than buckyballs, said Gimzewski.
Single-walled carbon nanotube crystal-like arrays could be in practical
use within the next 10 years, Gimzewski said.
Gimzewski’s colleagues were R. R. Schlitter and J. W. Seo at IBM’s Zurich
Research Laboratory, C. Durkan, Maria S. M. Saifullah, and Mark Wellund
of the University of Cambridge. They published their research in the 5
April 2001issue of Sciencexpress. The research was funded by the European
Union under the Information Society Technologies’ Future and Emerging
Technologies program (IST FET).
Timeline: < 10 years
TRN Categories: Nanotechnology & Materials Science and
Story Type: News
Related Elements: Technical paper, "Single Crystals of Single-Walled
Carbon Nanotubes Formed by Self-Assembly" in Sciencexpress, April 5, 2001.
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