Scientists hike carbon nanotube capacity

Feb. 10, 2009 at 4:04 PM

CHAMPAIGN, Ill., Feb. 10 (UPI) -- U.S. scientists say they've been able to increase the current-carrying capacity of carbon nanotubes to a level previously thought impossible to achieve.

University of Illinois researchers said they used an avalanche process that carries more electrons down more paths, similar to the way a multilane highway carries more traffic than a one-lane road.

"Single-wall carbon nanotubes are already known to carry current densities up to 100 times higher than the best metals like copper," said Professor Eric Pop. "We now show that semiconducting nanotubes can carry nearly twice as much current as previously thought."

The scientists said they discovered high electric fields of 10 volts per micron energetic electrons and holes can create additional electron-hole pairs, leading to the avalanche effect in which free carriers multiply and the current rapidly increases until the nanotube breaks down.

The sharp increase in current, Pop said, is due to the onset of avalanche impact ionization -- a phenomenon observed in certain semiconductor diodes and transistors at high electric fields, but not previously seen in nanotubes.

The research that included students Albert Liao and Yang Zhao is reported in the journal Physical Review Letters.

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