An atomistic S-Matrix method for computing boundary scattering amplitudes and predicting the mode-resolved phonon specularity parameter

A critical element in the reduced thermal conductivity of semiconducting nanowires and thin films is phonon momentum dissipation from boundary scattering, which varies with the specularity parameter and depends on the boundary structure and the incident phonon mode.
However, current theories of phonon scattering cannot fully predict the boundary structure and mode dependence of the specularity parameter. In this talk, I describe how the the scattering amplitudes for phonon reflection/transmission and mode-resolved specularity parameter can be determined using the atomistic S-matrix method [2] developed from the Atomistic Green’s Function method [3].
I show the edge chirality dependence of phonon-boundary scattering and explain why the armchair edge is more effective in momentum dissipation than the zigzag edge. To characterize boundary roughness, I also describe how the mode-resolved specularity and coherence parameters can be estimated from the statistics of the scattering amplitudes, using phonon scattering at graphene grain boundaries as an example [3].
References
1. Ong, Phys. Rev. B 98, 195301 (2018).
2. Ong and Zhang, Phys. Rev. B 91, 174302 (2015); Ong, J. Appl. Phys. 124, 151101 (2018).
3. Ong, Schusteritsch, and Pickard, Phy. Rev. B 101, 195410 (2020).