Thermal transport into graphene through nanoscopic contacts.

Superior thermal conductivity of graphene is frequently reported and used to justify its technical relevance for ultimately scaled devices. However, this extraordinary property is size dependent, and understanding of graphene's thermal properties in the quasiballistic thermal transport regime is lacking. To overcome this limitation, we directly probe local heat transfer into graphene by high-resolution scanning thermal microscopy on amorphous silicon oxide (SiO2) and crystalline silicon carbide (SiC). We quantify thickness-dependent thermal resistance modulations at sub-10-nm lateral resolution and thermal sensitivity for the individual atomic layers. On SiO2, we observe a decrease of thermal resistance with increasing number of graphene layers. We attribute this trend to the spreading of heat using the thickness dependence of graphene's thermal conductivity. On SiC, the heated tip-sample contact is scaled below the phonon mean free path of both the graphene and its supporting substrate. Consistently, we find the thermal interface resistances of the graphene top and bottom contacts dominating thermal transport.