Reduction of phonon mean free path: from low temperature physics to room temperature applications in thermoelectricity

TL;DR

This paper reviews methods to reduce phonon mean free path in nanostructures to enhance thermoelectric efficiency, demonstrating how geometry and nanostructuring can significantly alter phonon transport from low to room temperatures.

Contribution

It presents experimental evidence on how nanostructuring and geometry modifications can effectively reduce phonon mean free path across a wide temperature range.

Findings

Nanostructuring significantly reduces phonon mean free path.

Geometry modifications can transition phonon transport from ballistic to diffusive.

Altered phonon transport impacts thermoelectric performance.

Abstract

It has been proposed for a long time now that the reduction of the thermal conductivity by reducing the phonon mean free path is one of the best way to improve the current performance of thermoelectrics. By measuring the thermal conductance and thermal conductivity of nanowires and thin films, we show different ways of increasing the phonon scattering from low temperature up to room temperature experiments. It is shown that playing with the geometry (constriction, periodic structures, nano-inclusions), from the ballistic to the diffusive limit, the phonon thermal transport can be severely altered in single crystalline semiconducting structures; the phonon mean free path being in consequence reduced. The diverse implications on thermoelectric properties will be eventually discussed.