Specular transmission and diffuse reflection in phonon scattering at grain boundary

TL;DR

This study investigates whether separate specularity parameters are necessary for phonon transmission and reflection at grain boundaries, revealing that backward scattering is more diffuse than forward scattering, which challenges previous assumptions.

Contribution

The paper provides the first detailed analysis of mode-resolved specularity parameters for transmission and reflection, confirming the need for separate parameters in phonon boundary modeling.

Findings

Backward scattering is more diffuse than forward scattering at most frequencies.

Separate specularity parameters are required for accurate phonon transport modeling.

Results support the hypothesis that transmission and reflection should be described with different parameters.

Abstract

It is widely assumed in the literature that the specularity parameters for phonon transmission (forward scattering) and reflection (backward scattering) at a boundary are identical, i.e., the statistical distributions of the transition probabilities between an incident phonon and the range of outgoing phonon modes are the same for both transmission and reflection. However, it is hypothesized by Li and McGaughey that separate specularity parameters are needed to describe the behavior of transmitted and reflected phonons in superlattices and polycrystalline materials correctly. We test this hypothesis by analyzing the mode-resolved specularity parameters computed separately for transmission and reflection processes at a graphene grain boundary. Our results show that backward scattering is considerably more diffuse than forward scattering at most frequencies and polarizations, providing strong evidence for Li and McGaughey's hypothesis, and shed new light on how surfaces and interfaces modify phonon transport within and between domains in nanostructured materials.