Electrochemical atom-by-atom growth of highly uniform thin sheets of thermoelectric bismuth telluride via the route of ECALE Wen Zhu a, * , Junyou Yang a, * , Dongxiang Zhou b , Chenjin Xiao a , Xinkai Duan a a State Key Lab of Material Processing and Die and Mould Technology, Huazhong University of Science and Technology, Wuhan 430074, PR China b Department of Electronic Science and Technology, Huazhong University of Science and Technology, Wuhan 430074, PR China Received 16 August 2007; received in revised form 3 November 2007; accepted 6 November 2007 Abstract Thermoelectric films of Bi 2 Te 3 with highly uniform thin sheets structure were grown on Au substrate via the route of electrochemical atomic layer epitaxy (ECALE) in this work. Electrochemical aspects of Te and Bi on Au, Te on Bi-covered Au, and Bi on Te-covered Au were characterized by means of cyclic voltammetry and coulometry. A steady ECALE deposition for Bi 2 Te 3 compound could be attained after positively adjusting the underpotential deposition (UPD) potentials of Bi and Te on Au in steps over the initial 40 cycles, and the potentials could be kept constant for the following deposition. A 400-cycle deposit, which was grown with the steady deposition poten- tials, was proved to be a single phase Bi 2 Te 3 compound by X-ray diffraction (XRD) analysis. The 2:3 stoichiometric ratio of the deposit was further verified by energy dispersive X-ray (EDX) quantitative analysis. The band gap of the Bi 2 Te 3 film was determined as 0.33 eV by Fourier transform infrared spectroscopy (FTIR) and blueshifted in comparison with that of the bulk Bi 2 Te 3 single crystal. The field emission scanning electron microscope (FE-SEM) observation shows the deposit consisted of numberless interlaced thin sheets, which grown perpendicularly with the substrate. The formation mechanism of the morphology is investigated and it should be related to the property of the substrate and the lattice structure of Bi 2 Te 3 compound. It is believed that the interlaced thin sheets structure may be profitable for the improvement of the thermoelectric properties. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Electrochemical atomic layer epitaxy; Underpotential deposition; Bi 2 Te 3 ; Thermoelectric materials; Thin film 1. Introduction As an important thermoelectric material, bismuth telluride (Bi 2 Te 3 ) and its solid solutions are widely utilized as electric-generators or coolers in micro- and optoelec- tronic and biomedical fields, such as in situ powering or mini-cooling IC chips, optoelectronic sensors, MEMS devices, biochips, infrared detectors, and so on. However, they have been suffering from their low thermoelectric efficiency for several decades. Thermoelectric efficiency is determined by the figure of merit (ZT) of materials, which is expressed as ZT ¼ S 2 T r=j, where S , r, T and j are the Seebeck coefficient, electrical conductivity, absolute tem- perature and total thermal conductivity, respectively. Thus, the enhancement of the figure of merit can be achieved by increasing S as well as r or by decreasing j. Nanothermo- electric materials have been thought to improve thermo- electric efficiency greatly due to the quantum confinement and interface effect [1]. Nanothermoelectric materials have a large density of states near the Fermi surface and there- fore they may have a large Seebeck coefficient. In the nanomaterials, phonon scattering could be strengthened greatly by the high-density interface; meanwhile, electrons could be limited in the quantum well, thereby reducing the thermal conductivity without producing a deterioration of electronic transport [2,3]. Thus, nanothermoelectric materials have received considerable attention in recent years [4,5]. 0022-0728/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jelechem.2007.11.014 * Corresponding authors. Tel.: +86 27 8754 0944; fax: +86 27 8754 3776. E-mail addresses: wennarhust@yahoo.com.cn (W. Zhu), jyyang@pu- blic.wh.hb.cn (J. Yang). www.elsevier.com/locate/jelechem Available online at www.sciencedirect.com Journal of Electroanalytical Chemistry 614 (2008) 41–48 Journal of Electroanalytical Chemistry