Scanning thermal microscopy studies of 2D materials

Measurement of thermal properties at the nanoscale presents a number if unique challenges. Here we report the exploration of the thermal properties of a range of 2D materials using scanning thermal microscopy (SThM) on the length scale of ca. 0.3nm (monolayer) incrementally to bulk. Materials include graphene, MoS2, Bi2Se3, GaTe, GaS and GaSe. SThM is a modification of the more well-known Atomic Force Microscope (AFM) employing a self-heated probe which is bought into contact with the sample correspondingly causing a drop in the probe temperature which can be electronically monitored and interpreted to understand the samples thermal properties. We have investigated how these properties change as a function of sample thickness for the range of 2D materials listed above on substrates of both high and low thermal conductivity. We observe well defined values of thermal conductance for monolayer and near monolayer thicknesses, however some materials show increased conductance at increasing multilayers whilst others show a decrease – in most cases the conductance does not scale simply with thickness. We will discuss experimental considerations and possible thermal conductance models to explain these interesting results and describe a new approach for thermal quantification – Force Spectroscopy SThM