flashes fire up nanotubes
Technology Research News
An undergraduate at Rensselaer Polytechnic
Institute has made a startling discovery that resulted not from a flash
of inspiration but from the flash of a camera.
He found that a clump of single-walled carbon nanotubes will burst into
flame if exposed to a flash of light. Carbon nanotubes are one-atom-thick
sheets of graphite rolled into tubes as narrow as a few atoms across.
Many researchers are exploring ways of using the light-emitting and electricity-conducting
properties of carbon nanotubes to make electronic devices. But they needn't
fear that a stray flash of light will vaporize the results of their labors.
The effect seems to be limited to raw clumps of nanotubes rather than
individual tubes or artificial arrays, said Pulickel Ajayan, an associate
professor of materials science and engineering at RPI.
The researchers' work describing the interaction of carbon nanotubes and
light could improve nanotubes-based devices that integrate light and electricity,
said Ajayan. The controlled ignition of nanotubes could be used in optoelectronic
devices, nanosensors or even remotely triggered combustion experiments,
Carbon nanotubes are made by blasting carbon with an electric arc or a
laser, or by condensing a vapor of carbon atoms under the right conditions.
Raw nanotubes form in tangled mats of small bundles of nanotubes.
In examining the fiery phenomenon of flash ignition, the researchers found
that the light overloads some of the nanotubes. "Exposure to a light flash
results in large absorption of energy and large local increases in temperature
[within] the sample," said Ajayan. "This, if done in air or oxygen, results
in ignition of the sample," he said.
The sample has to be "fluffy and porous" for ignition to occur, said Ajayan.
This is the case for most raw clumps of nanotubes because there is space
between the nanotube bundles that make up the clumps, he said.
"The local increase in temperatures can only happen if there are heat
traps, as in the porous sample with a random tangle of nanotubes," he
said. If a raw clump of nanotubes is compacted, ignition can't occur because
there is less oxygen in the sample and because more of the bundles come
into contact with each other, causing the heat from the absorbed light
to rapidly dissipate, according to Ajayan.
Flash ignition "is just one of many unusual effects related to nanotubes,"
said Jianping Lu, an associate professor of physics at the University
of North Carolina. That the nanotubes actually ignite is surprising, he
said. "It is difficult to understand how the temperature can be increased
so dramatically to induce the ignition," he said.
Most practical applications of the effect like light-triggered ignition
sources would take 10 to 20 to develop, said Ajayan.
Ajayan's research colleagues were Andres de la Guardia and Bingqing Wei
of RPI, Mauricio Terrones of the Potosino Institute Of Scientific and
Technological Investigation in Mexico and the University of Sussex in
England, Nicole Grobert of the University of Sussex, and Henri Lezec and
Thomas W. Ebbesen of Louis Pasteur University in France. They published
the research in the April 26, 2002 issue of the journal Science. The research
was funded in part by Philip Morris.
Timeline: 10-20 years
TRN Categories: Materials Science and Engineering
Story Type: News
Related Elements: Technical paper, "Nanotubes in a Flash--
Ignition and Reconstruction," Science, April 26, 2002
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