In-Plane Thermal Conductivity of Polycrystalline Chemical Vapor Deposition Graphene with Controlled Grain Sizes

Abstract

Manipulation of the chemical vapor deposition graphene synthesis conditions, such as operating P, T, heating/cooling time intervals, and precursor gas concentration ratios (CH 4 /H 2 ), allowed for synthesis of polycrystalline single-layered graphene with controlled grain sizes. The graphene samples were then suspended on 8 μm diameter patterned holes on a silicon-nitride (Si 3 N 4 ) substrate, and the in-plane thermal conductivities k ( T ) for 320 K < T < 510 K were measured to be 2660–1230, 1890–1020, and 680–340 W/m·K for average grain sizes of 4.1, 2.2, and 0.5 μm, respectively, using an opto-thermal Raman technique. Fitting of these data by a simple linear chain model of polycrystalline thermal transport determined k = 5500–1980 W/m·K for single-crystal graphene for the same temperature range above; thus, significant reduction of k was achieved when the grain size was decreased from infinite down to 0.5 μm. Furthermore, detailed elaborations were performed to assess the measurement reliability of k by addressing the hole-edge boundary condition, and the air-convection/radiation losses from the graphene surface.