Thermomechanical In Situ Monitoring of Bi 2 Te 3 Thin Film and Its Relationship with Microstructure and Thermoelectric Performances

Performance enhancement has been studied for thin-film thermoelectric materials for small-scale energy applications. The microstructural evolution of bismuth telluride (Bi 2 Te 3 ) was investigated with respect to performance enhancement via in situ thermomechanical analysis due to the post-annealing process. The thermomechanical behavior of Bi 2 Te 3 changes gradually at approximately 200 °C with the formation of a quintuple-layer structure, which was confirmed by X-ray diffraction, transmission electron microscopy and Raman spectroscopy. It was found that highly oriented (006), (0015) was formed with a quintuple-layer structure parallel to the substrate, and the E g 2 Raman vibration mode of Bi 2 Te 3 significantly increased after forming the layer structure with decreased defects. Therefore, the slope of the stress curve was affected by the longer atomic distance of the van der Waals bonds with the formation of (00 l ) oriented layered-structure grain. The decreased number of defects in the layer structure affects the electrical and thermal properties of the Bi 2 Te 3 thin film. Due to the microstructural evolution, the power factor of Bi 2 Te 3 was enhanced by approximately 14.8 times by the quintuple-layer structure of Bi 2 Te 3 formed during the annealing process, which contributed to a better understanding of the performance enhancement via post-annealing and to research on other highly oriented layer structure materials. Graphical Abstract