Phonon Scattering by Externded Defects in Polycrystalline Graphene

Phonon scattering by static stress fields created by grain boundaries (GBs) in graphene was studied with the deformation potential method. This method provides exact analytical expressions for phonon mean free paths as a result of scattering by GBs with arbitrary geometries in the Born approximation. Two regimes, k–1 and k–3, of the mean free path behavior are discovered in the limit of small momenta. The first (dislocation) regime is realized for open configurations in polycrystalline graphene, while the second regime is realized for closed configurations and Stone-Wales defects in pure graphene. The mean free path does not depend on k for any GB in the short-wave limit (large k). Thermal conductivity in graphene with GBs was calculated using the Callaway model which considers both normal phonon processes and umklapp processes. The contribution from these defects to the thermal conductivity is shown to exceed substantially the contribution from point defects and vacancies in a wide range of temperatures.