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.

文献中广泛假设边界处声子传输（前向散射）和反射（后向散射）的镜面反射参数是相同的，即，入射声子和传出声子模式范围之间的跃迁概率的统计分布对于传输和反射都是相同的。然而，Li 和 McGaughey 假设需要单独的镜面反射参数来正确描述超晶格和多晶材料中透射和反射声子的行为。我们通过分析为石墨烯晶界处的透射和反射过程分别计算的模式分辨镜面反射参数来测试这一假设。我们的结果表明，在大多数频率和极化下，后向散射比前向散射更加漫射，为 Li 和 McGaughey 的假设提供了强有力的证据，