Probing phonon-surface interaction by wave-packet simulation: Effect of roughness and morphology

One way to reduce the lattice thermal conductivity of solids is to induce additional phonon-surface scattering through nanostructures. However, the way in which phonons interact with surfaces, especially at the atomic level, is not well understood at present. In this work, we perform two-dimensional atomistic wave-packet simulations to investigate angular-resolved phonon reflection at a surface. Different surface morphologies, including smooth surfaces, periodically rough surfaces, and surfaces with amorphous coatings, are considered. For a smooth surface, mode conversion can occur after reflection, with the resulting wave-packet energy distribution depending on the surface condition and the polarization of the incident phonon. At a periodically rough surface, the reflected wave-packet distribution does not follow the well-known Ziman model but shows a nonmonotonic dependence on the depth of the surface roughness. When an amorphous layer is attached to a smooth surface, the incident wave packet is absorbed by the amorphous region and is then reflected diffusively at the surface. Our results show that the commonly adopted specular-diffusive model is insufficient to describe phonon reflection at a periodically rough surface and that an amorphous layer can induce strong diffusive reflection. This work provides a comprehensive analysis of phonon reflection at different types of surfaces, which is important for better understanding of thermal transport in various nanostructures. Published by AIP Publishing.