Direct nanoscale imaging of ballistic and diffusive thermal transport in graphene nanostructures

The list of graphene properties showing potential for nano-electronics applications includes high carrier mobility, superior mechanical strength, and high thermal conductivity [1]. With the mean-free-path (MFP) of thermal phonons at room temperature in graphene on the order of 700 nm and modern semiconductor devices having features on the order of few tens of nm, it is apparent that the ballistic regime must play a significant role in the thermal transport in such nanodevices. Whereas extraordinary thermal properties of graphene suggest it use for heat management, graphene behaviour in such structures is to a great degree unexplored due to lack of suitable methods. Experimentally, so far these phenomena were studied using micro-Raman spectroscopy with lateral resolution inevitably restricted by the optical wavelength to the range of 0.5-1 μm [2,3]. In our study we addressed the challenge of exploration of thermal phenomena in graphene nanostructures by using nanoscale scanning thermal probe [4] in high vacuum (HV) environment (Fig. 1) that allowed us to directly map thermal transport in suspended and supported graphene layers with nanoscale resolution, and to explore both ballistic and diffusive regimes of heat transfer.