Simultaneous measurement of anisotropic thermal conductivity and thermal boundary conductance of 2-dimensional materials
The rapidly increasing number of 2-dimensional (2D) materials that have been isolated or synthesized provides an enormous opportunity to realize new device functionalities. Whereas their optical and electrical characterizations have been more readily reported, quantitative thermal characterization is more challenging due to the difficulties with localizing heat flow. Optical pump-probe techniques that are well established for the study of bulk materials or thin films have limited sensitivity to in-plane heat transport, and the characterization of the thermal anisotropy that is common in 2D materials is, therefore, challenging. Here, we present a new approach to quantify the thermal properties based on the magneto-optical Kerr effect that yields quantitative insight into cross-plane and in-plane heat transport. The use of a very thin magnetic material as heater/thermometer increases in-plane thermal gradients without complicating the data analysis in spite of the layer being optically semitransparent. The approach has the added benefit that it does not require the sample to be suspended, providing insight into thermal transport in supported, devicelike environments. We apply this approach to measure the thermal properties of a range of 2D materials, which are of interest for device applications, including single-layer graphene, few-layer hexagonal boron nitride, single- and few-layer MoS2, and bulk MoSe2 crystal. The measured thermal properties will have important implications for thermal management in device applications.