Thermal diffusivity microscope – zooming-in on anisotropic heat transport

Abstract Anisotropic heat conducting materials, where heat flows faster in one direction than another, play crucial roles in designing electronic, optoelectronic, and thermoelectric devices, where temperature and thermal stress are important. Despite significant research efforts, a major obstacle to determining the anisotropic thermal diffusivity tensor in polycrystalline systems is the need for a robust, direct, and non-destructive technique to distinguish between distinct thermal diffusivities. Here, we demonstrate a conceptually new thermal diffusivity microscope capable of performing high-resolution local measurements of anisotropic thermal diffusivity. The microscope is based on a unique micro four-point probe, providing fast, nondestructive scanning and calibration-free measurements. Through a series of experiments, we demonstrate that the anisotropy of the thermal diffusivity correlates excellently with the crystallographic direction of prototypical Bi2Te3. Our results provide insights into the complex anisotropic heat transport and show that the lattice contribution dominates the heat transport for both in- and out-of-plane directions.