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Unexpected nanotube heat transfer suggests new way to cool processors

Spooky action at a (small) distance

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A strange phenomenon observed at the University of Maryland could pave the way to new techniques for cooling electronics: when researchers passed a current through carbon nanotubes, they didn’t heat up – but other nearby objects did.

While still studying exactly what mechanism produces the phenomenon, the researchers report that when they passed a current through the carbon nanotubes, the tubes remained relatively cool, apparently transferring the heat directly to the silicon nitride substrate that hosted the tubes.

In what they’ve dubbed “remote Joule heating”, the scientists, led by then-student Kamal Baloch, found that the heating of the substrate was enough to melt metal particles on its surface.

The normal heating of metals carrying a current, Joule heating, happens when energy is transferred from the travelling electrons to the atoms in the wire, causing them to vibrate.

In the University of Maryland experiment, the researchers believe the transfer of heat from the carbon nanotubes to the substrate is being caused not by the direct contact of electrons colliding with atoms, but rather by electrical fields.

“We believe that the nanotube's electrons are creating electrical fields due to the current, and the substrate's atoms are directly responding to those fields,” says assistant professor John Cumings.

“The transfer of energy is taking place through these intermediaries, and not because the nanotube's electrons are bouncing off of the substrate's atoms. While there is some analogy to a microwave oven, the physics behind the two phenomena is actually very different.”

The observations were made using a technique called electron thermal microscopy, developed in Cumings’ laboratory, which maps where heat is generated in nanoscale devices.

Baloch says the phenomenon would be useful in semiconductor design, because it provides a way to design thermal properties independently of the electrical properties of a device. “This new mechanism of thermal transport would allow you to engineer your thermal conductor and electrical conductor separately, choosing the best properties for each without requiring the two to be the same material occupying the same region of space,” he said.

The next step in the research is to see what other materials might exhibit similar behavior. The research is published in Nature Nanotechnology, abstract here. ®

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