Abstract: An automated thin-layer flow cell electrodeposition system was developed for growing Bi₂Te₃ thin film by ECALE. The dependence of the Bi and Te deposition potentials on Pt electrode was studied. In the first attempt, this reductive Te underpotential deposition(UPD)/reductive Bi UPD cycle was performed to 100 layers. A better linearity of the stripping charge with the number of cycles has been shown and confirmed a layer-by-layer growth mode, which is consistent with an epitaxial growth. The 4∶3 stoichiometric ratio of Bi to Te suggests that the incomplete charge transfer in HTeO⁺₂ reduction excludes the possibility of Bi₂Te₃ formation. X-ray photoelectron spectroscopy (XPS) analysis also reveals that the incomplete charge transfer in HTeO⁺₂ occurs in Te direct deposition. The effective way of depositing Bi₂Te₃ on Pt consists in oxidative Te UPD and reductive Bi UPD. The thin film deposited by this procedure was characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM) and X-ray photoelectron spectroscopy(XPS).  A polycrystalline characteristic was confirmed by XRD. The 2∶3 stoichiometric ratio was confirmed by XPS. The SEM image indicates that the deposit looks like a series of buttons about 0.3-0.4μm in diameter, which is corresponding with calculated thickness of the epitaxial film. This suggests that the particle growth appears to be linear with the number of cycles, as it is consistent with a layer by layer growth mode.

Key words: thermoelectric material; ECALE; UPD; bismuth telluride; thin film