Unusual Thermal Conductivity of Carbon Nanosheets with Self-Emerged Graphitic Carbon Dots

Abstract

The thermal conductivity (kappa) of two-dimensional conducting and transparent carbon nanosheets (CNSs) prepared by a catalyst- and transfer-free process is calculated for the first time by the optothermal Raman technique. A systematic structural analysis of CNSs reveals that the thickness of polymer films affects the interaction between molecules and a Si wafer significantly, thus helping to determine the ratio of sp(2) and sp(3) bonding configurations of carbon (C) atoms in the CNS. Notably, the holding time of carbonization can realize a hierarchical structure with graphitic carbon dots emerging from the CNS through the rearrangement of carbon atoms, leading to the excellent kappa value of 540 W/(m.K) at 310 K. It is demonstrated that an appropriate increase in carbonization time can be an effective approach for improving the ratio of sp(2)- to sp(3)-bonded C atoms in the CNS. The thermal conductivity of the CNS with the highest ratio of sp(2)- to sp(3)-bonded C atoms exhibits superior behavior and is comparable to that of reduced graphene oxide and supported graphene, respectively. Finally, when the CNS with the highest kappa value of 540 W/(m.K) was applied to a heater as the heat-dissipating material, the heater showed the temperature decrease by 14 degrees C compared to the case without the CNS. The catalyst- and transfer-free approach for the synthesis of CNSs is highly desirable for use as heat sink materials or substrates with heat dissipation functions for extensively integrated electronic devices.