Phonon transport at interfaces: Determining the correct modes of vibration

Abstract

For many decades, phonon transport at interfaces has been interpreted in terms of phonons impinging on an interface and subsequently transmitting a certain fraction of their energy into the other material. It has also been largely assumed that when one joins two bulk materials, interfacial phonon transport can be described in terms of the modes that exist in each material separately. However, a new formalism for calculating the modal contributions to thermal interface conductance with full inclusion of anharmonicity has been recently developed, which now offers a means for checking the validity of this assumption. Here, we examine the assumption of using the bulk materials' modes to describe the interfacial transport. The results indicate that when two materials are joined, a new set of vibrational modes are required to correctly describe the transport. As the modes are analyzed, certain classifications emerge and some of the most important modes are localized at the interface and can exhibit large conductance contributions that cannot be explained by the current physical picture based on transmission probability.