Light
flashes fire up nanotubes
By
Eric Smalley,
Technology Research NewsAn 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, he said.
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
Funding: Corporate
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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May 1/8, 2002
Page One
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