Effect of graphene-substrate conformity on the in-plane thermal conductivity of supported graphene

Abstract

Measuring the thermal conductivity k(g) of supported graphene is inherently complicated due to uncertainties associated with the heat dissipation into the substrate. We innovate the use of an ultra-thin 8-nm SiO2 substrate to alleviate these uncertainties and thus improve the accuracy of optothermal Raman technique to measure k(g) of supported graphene. As a result, we present an extensive k(g) database for a wide temperature range from 325 K to 575 K. Furthermore, we have found that the thermal conductivity of supported graphene before annealing is close to that of suspended graphene at 3000 W m(-1) K-1, which is attributable to graphene "suspension" lightly on the substrate roughness, and then progressively decreases over repeated thermal annealing. We elaborate on this annealing-induced kg to occur mainly because of the thermally enhanced graphene-substrate conformity and interfacial scattering by probing the Raman spectroscopic characterization of charge carrier density in graphene and the thermal expansion mismatching strain between graphene and substrate. Repeated thermal annealing also expedites the depletion of intercalated impurities to reduce the graphene-substrate separation distance, which acts to further reduces k(g), ultimately to its lower bound under vacuum-annealing. Therefore, manipulating the thermo-mechanical affiliation can offer an alternative route to control the in-plane thermal conductivity of supported graphene. (C) 2017 Elsevier Ltd. All rights reserved.