Electrochimica Acta 50 (2005) 5465–5472 The underpotential deposition of bismuth and tellurium on cold rolled silver substrate by ECALE W. Zhu,J.Y. Yang ∗ , X.H. Gao, J. Hou, S.Q. Bao, X.A. Fan State Key Laboratory of Die and Mould Technology, College of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, PR China Received 9 January 2005; received in revised form 3 March 2005; accepted 5 March 2005 Available online 31 May 2005 Abstract Thin-layer electrochemical studies of the underpotential deposition (UPD) of Bi and Te on cold rolled silver substrate have been performed. Different approaches have been employed to investigate the influence of silver oxide film on Bi UPD. As a result, the precedent deposition of a little bismuth can effectively prevent silver from surface oxidation. The voltammetric analysis of underpotential shift demonstrates that the first Te UPD on Bi-covered Ag and Bi UPD on Te-covered Ag fit UPD dynamics mechanism. Thin film of bismuth telluride was formed using an automated flow deposition system, by alternately depositing Te and Bi. The electrochemical conditions necessary to form Bi 2 Te 3 deposits of 50 cycles on cold rolled silver by ECALE are described here. X-ray diffraction indicated the deposits were Bi 2 Te 3 . EDX quantitative analysis gave the 2:3 stoichiometric ratio of Bi to Te, which is consistent with XRD result. Electron probe microanalysis of the deposits showed a worm-like network structure. The map of Te and Bi element indicated the distribution of both Te and Bi is homogeneous and locates the same sites, which is favorable to Te–Bi binary system. The composition analysis of structural expanded image also showed the approximately constant composition of Te:Bi ≈ 3:2 has taken place. © 2005 Elsevier Ltd. All rights reserved. Keywords: ECALE; UPD; Bismuth telluride; Thermoelectric material; Thin film 1. Introduction Bismuth telluride belong to the class of VA–VIA bi- nary chalcogenide compound semiconductor with a nar- row optical energy band gap of 0.13 eV and a very high figure of merit [1–3]. These materials are widely used for thermoelectric and optoelectronic devices, for example in solid-state refrigeration, heat pumps, subminiature elec- tronic devices, infrared sensors and high efficiency photo- voltaic solar cells. Thin films of bismuth telluride and related compounds have already been elaborated by flash evapo- ration [4], co-evaporation [5], molecular beam epitaxy [6] and metal–organic chemical vapor deposition [7,8]. These methods are thermal and generally performed in vacuum. ∗ Corresponding author. Tel.: +86 27 87540944; fax: +86 27 87543776. E-mail addresses: wennar@sina.com (W. Zhu), jyyang@public.wh.hb.cn (J.Y. Yang). Atomic layer epitaxy (ALE) can form thin film by using surface limited reactions. Electrochemical atomic layer epi- taxy (ECALE) [9–17] is the electrochemical analog of ALE. ECALE involves the alternated electrochemical deposition of elements to form a compound. Epitaxial deposition is achieved by using underpotential deposition (UPD) as the means to achieve surface chemistry-limited growth [18–22]. The phenomenon of UPD involves the deposition of an atomic layer of one element on a second, at a potential prior to (under) that needed to form deposits of the element on itself. The driving force is generally thermodynamic, involving the Gibbs energy of formation of a surface compound. IIB–VIA compounds such as CdTe [9,10], CdS [11,12], and ZnSe [13] have been successfully formed by using EC- ALE, as well as IIIA–VA compound InAs [14], IIIA–VIA compound In 2 Se 3 [15], IVA–VIA compound PbSe [16], VA–VIA compound Bi 2 S 3 [17]. In our previous work, a first trial and preliminary result were reported on forming a Bi 2 Te 3 0013-4686/$ – see front matter © 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2005.03.028