Grain size-dependent thermal conductivity of polycrystalline twisted bilayer graphene

We report the room temperature thermal conductivity of polycrystalline twisted bilayer graphene (tBLG) as a function of grain size measured by employing a noncontact optical technique based on micro-Raman spectroscopy. Polycrystalline tBLG sheets of different grain sizes were synthesized on copper by hot filament chemical vapor deposition. The thermal conductivity values are 1305 +/- 122, 971 +/- 73, and 657 +/- 42 Wm(-1)K(-1) for polycrystalline tBLG with average grain sizes of 54, 21, and 8 nm, respectively. Based on these thermal conductivity values, we also estimated the grain boundary conductance, 14.43 +/- 1.21 x 10(10) Wm(-2)K(-1), and the thermal conductivity for single crystal tBLG, 1510 +/- 103 Wm(-1)K(-1). Our results show that the relative degradation of thermal conductivity due to grain boundaries is smaller in bilayer than in monolayer graphene. Molecular dynamics simulations indicate that interlayer interactions play an important role in the heat conductivity of polycrystalline bilayer graphene. The quantitative study of the grain size dependent thermal conductivity of polycrystalline bilayer graphene is valuable in technological applications as well as for fundamental scientific understanding. (C) 2017 The Authors. Published by Elsevier Ltd.