Use of a Soluble Anode in Electrodeposition of Thick Bismuth Telluride Layers M. MAAS, 1,3 S. DILIBERTO, 1 C. de VAULX, 2 K. AZZOUZ, 2 and C. BOULANGER 1,4 1.—Institut Jean Lamour UMR CNRS 7198, Universite ´ de Lorraine, 1 bd Arago, 57078 Metz, France. 2.—Valeo Syste `mes Thermiques, 8 rue Louis Lormand, BP 517 La Verrie `re, 78321 Le Mesnil Saint Denis, France. 3.—French Environment and Energy Management Agency 20, ave- nue du Gre ´sille ´, BP 90406, 49004 Angers Cedex 01, France. 4.—e-mail: clotilde.boulanger@ univ-lorraine.fr Integration of thermoelectric devices within an automotive heat exchanger could enable conversion of lost heat into electrical energy, contributing to improved total output from the engine. For this purpose, synthesis of thick bismuth telluride (Bi 2 Te 3 ) films is required. Bismuth telluride has been pro- duced by an electrochemical method in nitric acid with a sacrificial bismuth telluride anode as the source of cations. The binary layer grows on the working electrode while the counter-electrode, a Bi 2 Te 3 disk obtained by high fre- quency melting, is oxidized to Bi III and Te IV . This process leads to auto- regeneration of the solution without modification of its composition. The thickness of films deposited by use of the Bi 2 Te 3 anode was approximately 10 times that without. To demonstrate the utility of a soluble anode in electro- chemical deposition, we report characterization of the composition and mor- phology of the films obtained under different experimental conditions. Perfectly dense and regular Bi 2 Te 3 films (400 lm) with low internal stress and uniform composition across the cross-section were prepared. Their ther- moelectric properties were assessed. Key words: Bismuth telluride, thick films, soluble anode, thermoelectric INTRODUCTION With current increasing demands for energy, thermoelectric materials have attracted interest because of their high potential. Electroplating has been recognized by the thermoelectric community as an attractive approach for preparation of ther- moelectric compounds, especially binary and ter- nary V 2 VI 3 compounds, 1–6 materials which have high thermoelectric coefficients at room tempera- ture. Electrodeposition has advantages over physi- cal processes because of its cost-effective operation (large area, low temperature, and mild processing of materials) and its adaptability (for instance the possibility of coating substrates with complex shapes, precise control of film thickness via electrolysis charge and of composition via chemical/ electrolysis conditions). Nevertheless the ionic pre- cursors (Bi III and tellurite Te +IV or selenite Se +IV ions) are poorly soluble in aqueous media, even in an acidic medium or with a chelating agent for Sb III , which limits the rate of growth and the thickness, and results in thick deposited layers with poor morphology. The recent literature reports optimized methods enabling regulation of growth rate and thus preparation of layers with better morphology and compactness. The benefit of pulse plating, combining voltage-controlled deposition pulses with current-controlled resting pulses was demonstrated by Glatz et al. 7 in 2008. This method enables depo- sition of thick, stable, and stress-free layers 800 lm thick at a rate of 50 lmh 1 . The stoichiometry constant over the thickness may be changed by adjustment of the potential of the deposition pulse. Another option is use or addition of non-aqueous (Received October 24, 2013; accepted June 17, 2014; published online July 12, 2014) Journal of ELECTRONIC MATERIALS, Vol. 43, No. 10, 2014 DOI: 10.1007/s11664-014-3292-1 Ó 2014 TMS 3857