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 BiTe. The anisotropic heat transport shows that the lattice contribution dominates the heat transport for both in- and out-of-plane directions.