Digital Heat Flow

The first observation of digital heat flow in a nanostructure at ambient conditions has been made using carbon nanotubes suspended between two electrodes. A new experiment carried out at Caltech, and reported at the AVS Science & Technology meeting in Boston, furthers the effort to employ nanotubes as a means for removing unwanted heat from microcircuits.

Carbon nanotubes, nanometer-wide cylinders made from rolled up graphitic sheets have a versatile array of mechanical, electrical, and magnetic properties. Their thermal properties should be just as valuable. Because phonons (the particle manifestations of heat flow) can move so freely in nanotubes, even ballistically (meaning that they refrain from scattering and travel in straight lines), the flow of heat in nanotubes should have quantum properties.

Indeed, Caltech scientist Marc Bockrath (mwb@caltech.edu) and his colleagues have observed that heat conductivity in nanotubes can readily reach quantum-mechanical limits; heat conduction occurs in multiples of a quantum unit of heat flow. Phonons seem to move nearly as far as a micron (a long distance for nanoscopically sized objects) even at temperatures of 900 degrees Celsius. The mean free path between scattering for the phonons should be even larger at room temperature. This, says Bockrath, underscores the fantastic potential of nanotubes as thermal conduits.

Meeting paper NS-ThM4