Examining Heat Flow at the Nanoscale
Just as in many other disciplines, examining assumptions can yield interesting and important results. Such was the case with the recent work of researchers at MIT, Boston University, Boston College, and the California Institute of Technology. The assumption they targeted concerned how heat moves through a superlattice made of layers the thickness of a strand of DNA.
The quantum of heat is a quasi-particle representing a unit of vibrational energy called the phonon. Like other quanta, it exists with both wave and particle properties, but depending on the situation may favor one form other another. The assumption is that when the interface between two materials is rough enough, the scattering of the phonons would cause them to act as particles and not waves, but when actually tested, the results were not so simple. For high frequency phonons, the scattering was enough to make them act as particles, but lower frequency phonons acted like waves.
By controlling the roughness of the interface between the layers of material in a superlattice, it should be possible to also control the heat flow. Such manipulation would be very useful for thermoelectrics, which require a heat differential and computer chips, which want to stay cool.