Thermal conductivity near armchair and zigzag edges of supported graphene

While graphene is known for its high thermal conductivity at room temperature, the thermal conductivity near its edges (armchair and zigzag)---where phonon-boundary scattering becomes significant---remains less explored. Microscopic roughness at the boundaries of exfoliated graphene flakes often leads to dominant diffuse reflections. Recent theoretical studies have suggested that such diffuse reflections can significantly reduce thermal conductivity in low-dimensional crystals. In this work, we experimentally investigate the thermal conductivity and interface thermal conductance near the armchair and zigzag edges of supported monolayer graphene using optothermal Raman spectroscopy. Additionally,we perform simulations based on a two-dimensional finite difference model to understand the temperature distribution and the heat flow near the edges, comparing the results with the interior region. Our results show a significant change in the temperature distribution near the edges, leading to a substantial reduction ($\ensuremath{\sim}50%$) in in-plane thermal conductivity. This reduction is attributed to a shorter phonon mean free path due to increased phonon-boundary scattering. Notably, despite the localized electronic states at the zigzag edge, we observe no significant differences in the thermal transport properties between the armchair and zigzag edges. Furthermore, in most samples, the interface thermal conductance per unit area decreases at the edges, indicating reduced adhesion to the substrate.