Free-standing Bi–Sb–Te films derived from thermal annealing of sputter-deposited Sb2Te3/Bi2Te3 multilayer films for thermoelectric applications

We introduce an easily acceptable method to produce free-standing Bi-Sb-Te films from Sb2Te3/Bi2Te3 multilayer films based on solid-state reactions. When sputter-deposited Sb2Te3/Bi2Te3 multilayer films were annealed at 400 degrees C under a N-2 gas atmosphere, they were transformed into single layers composed of Bi-Sb-Te films. At the same time, they were spontaneously stripped on a large scale from the substrates (1 cm x 1 cm) without chemical etching. The as-fabricated free-standing Bi-Sb-Te films were very flexible, with a thickness of about 400 nm. The findings confirmed that the formation of voids and the strong flow rate of ambient gas play important roles in fabricating free-standing Bi-Sb-Te films during the thermal annealing process. The temperature-dependent crystallization behaviors of each of the Sb2Te3 and Bi2Te3 films were also investigated to understand the mechanism. Moreover, the thermoelectric properties of the freestanding Bi-Sb-Te films were examined with different thicknesses of the films. We believe that this method can contribute to the development of low-dimensional nanostructures that can be useful in various applications such as energy conversion, energy storage and wearable electronics.