The influence of interfacial structure and strain energy on phonon transport*

Phonon transport across interfaces is an inherently complex topic of great scientific and technological importance. Several experimental and theoretical results which aim to establish a fundamental understanding of heat transfer across interfaces will be presented. First, I will demonstrate how phonon diffraction and dimensionality crossover effects arise when the nanoscale structure and strain field of interfaces and grain boundaries (GBs) are considered. Next, an experimental study is presented where the thermal boundary resistance is measured on individual Si-Si twist GBs at different twist angles. The thermal boundary resistance at GBs, again, seems to be dominated by the interfacial strain field. Finally, it is shown how the thermal boundary resistance can be controlled by modifying the GB with 2D materials. Several layers of graphene were introduced into the GBs of skutterudite materials which dramatically increases the materials thermal boundary resistance, negligibly effecting electronic transport, resulting in a 24% improvement in measured thermoelectric device efficiency.