Unique hierarchical structure and high thermoelectric properties of antimony telluride pillar arrays

The p-type antimony telluride (Sb₂Te₃) pillar arrays with unique hierarchical architecture have been self-assembled in large scale by a simple vacuum thermal evaporation technique. The composition and the microstructure of the films are studied by X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy, and high-resolution transmission electron microscopy. The results show that the hierarchical film with multi-scale and multi-dimensional structure is well-oriented pillar arrays perpendicular to the substrate. A large number of nanowires (NWs) are assembled into a submicro/micro-scaled pillar, while antisite defects and dislocations as well as other defects are found in the one-dimensional NWs. The growth mechanism of such nanostructure is proposed and investigated. The thermoelectric (TE) properties, i.e., electrical conductivity (σ), Seebeck coefficient (S), and thermal conductivity (κ) of the films are measured. The properties of the hierarchical Sb₂Te₃ film have been greatly enhanced in comparison with those of the ordinary Sb₂Te₃ films. A TE dimensionless figure-of-merit ZT = 0.88 in the novel hierarchical Sb₂Te₃ film is obtained at room temperature.