CHAMPAIGN, Ill. – Metallic carbon nanotubes have been proposed as interconnects in future electronic devices packed with high-density nanoscale circuits.
But can they stand up to the heat?
Recent experiments have shown the absence of the thermoelectric effect in metallic carbon nanotubes. Building upon earlier theoretical work, researchers at the University of Illinois say they can explain this peculiar behavior, and put it to good use.
“Our work shows that carbon nanotubes that come in metallic form have different thermal and electrical properties than normal conductors,” said Jean-Pierre Leburton, the Gregory Stillman Professor of Electrical and Computer Engineering at Illinois and co-author of a paper published in the Dec. 19 issue of the journal Physical Review Letters, and in the Jan. 5 issue of the Virtual Journal of Nanoscale Science and Technology.
“Specifically, metallic carbon nanotubes don’t exhibit the thermoelectric effect, which is a fundamental property of conductors by which a current flows because of a temperature difference between two points of contact,” said Leburton, who is also affiliated with the Beckman Institute, the Micro and Nanotechnology Laboratory, and the Frederick Seitz Materials Research Laboratory. “This is a metal, which doesn’t behave like an ordinary metal.”
In a normal conductor, a current can be induced by applying a potential difference (voltage) or by creating a temperature difference between two contacts. Electrons will flow from the higher voltage to the lower, and from the higher temperature to the lower. There is a similarity between temperature imbalance and electric field.
In metallic carbon nanotubes, however, the lack of the thermoelectric effect means no current will flow because of temperature change between two contacts. The similarity between temperature imbalance and voltage disappears.
This is a fundamental property of metallic carbon nanotubes, Leburton said, peculiar to their particular structure. Semiconductor nanotubes, which possess a different chirality, behave differently.
Also, in normal conductors, electrons can acquire a range of velocities, with some traveling much faster than others. In metallic carbon nanotubes, however, all electrons travel at the same velocity, similar to the behavior of photons. Heating the nanotube does not change the electron velocity.
“This means metallic carbon nanotubes offer less resistance than other metal conductors,” Leburton said. “And, in high-density circuits, metallic carbon nanotube interconnects would reduce heat losses and require far less cooling than copper nanowires.”
With Leburton, physics graduate student Marcelo Kuroda is co-author of the paper. The current work is an extension of theoretical work Leburton, Kuroda and electrical and computer engineering professor Andreas Cangellaris first published in the Dec. 21, 2005, issue of Physical Review Letters.