Thermal diffusivity microscope: Zooming in on anisotropic heat transport

Anisotropic heat-conducting materials play crucial roles in designing electronic, optoelectronic, and thermoelectric devices, where temperature and thermal stress are important. Despite substantial research efforts, a major obstacle to determining the anisotropic thermal diffusivity tensor in polycrystalline systems is the need for a robust, direct, and nondestructive technique to distinguish between distinct thermal diffusivities. Here, we demonstrate a conceptually unique thermal diffusivity microscope capable of performing high-resolution local measurements of anisotropic thermal diffusivity. The microscope features a unique micro four-point probe for fast, nondestructive scanning without calibration or extra sample preparation. It measures anisotropic thermal diffusivity based on thermal delay from a single heater. Through a series of experiments, we demonstrate that the anisotropy of the measured thermal diffusivity correlates excellently with the crystallographic direction of prototypical Bi₂Te₃. The anisotropic heat transport shows that the lattice contribution dominates the heat transport for both in- and out-of-plane directions.