Nanoscale Thermal Transport in Bi ₂ (Te, Se) ₃ Thermoelectric Material Using Pulsed STEM

Understanding thermal transport properties at the nanoscale can provide strategies for efficiently managing heat or improving energy conversion efficiency in various applications. Furthermore, when thermal paths can be traced and imaged at the nanoscale, materials or electronic devices can be designed to minimize heat loss. The demand for these technologies continues to grow rapidly. Here, we demonstrate imaging of thermal propagation in thermoelectric material (Bi 2 (Te, Se) 3 ) using a spatially resolved technique that uses thermal waves induced by a pulsed convergent electron beam in a scanning transmission electron microscopy (STEM) mode at room temperature. The measurements with nanoscale clearly reveal the anisotropy inherent in Bi 2 (Te, Se) 3 by quantifying the relative values of phase delay at each irradiated position. Also, the thermal wave propagation is significantly sensitive to the directions of the media, as if the heat carriers lose their memory of the vibration mode in each direction and switch to a new mode. Capturing various thermal properties, such as directional thermal pathways, from nanoscale imaging can provide a deeper understanding of how materials affect heat transport. This insight plays a vital role in designing materials for thermal management and energy conversion devices.