Study of the electrodeposition of rhenium thin films by electrochemical quartz microbalance and X-ray photoelectron spectroscopy R. Schrebler a, T , P. Cury a , C. Sua ´rez a , E. Mun ˜oz a , F. Vera a , R. Co ´ rdova a , H. Go ´mez a , J.R. Ramos-Barrado b , D. Leinen b , E.A. Dalchiele c a Instituto de Quı ´mica, Facultad de Ciencias, Universidad Cato ´lica de Valparaı ´so, Casilla 4059, Valparaı ´so, Chile b Laboratorio de Materiales y Superficie, Unidad asociada al CSIC, Departamento de Fı ´sica Aplicada and Departamento de Ingenierı ´a Quı ´mica, Facultad de Ciencias, Universidad de Ma ´laga, 29071 Ma ´laga, Espan ˜a c Instituto de Fı ´sica, Facultad de Ingenierı ´a, Herrera y Reissig 565, C.C. 30, 11000 Montevideo, Uruguay Received 10 December 2003; accepted in revised form 9 December 2004 Available online 10 March 2005 Abstract Rhenium thin films were prepared by electrodeposition from an aqueous solution containing 0.1 M Na 2 SO 4 +H 2 SO 4 , pH 2 in presence of y mM HReO 4 . As substrates polycrystalline gold ( y =0.75 mM HReO 4 ) and monocrystalline n-Si(100) ( y =40 mM HReO 4 ) were used. The electrochemical growth of rhenium was studied by cyclic voltammetry and electrochemical quartz microbalance on gold electrodes. The results found in the potential region before the hydrogen evolution reaction (her) showed that ReO 3 , ReO 2 and Re 2 O 3 with different hydration grades can be formed. In the potential region where the her is occurring, either on gold or n-Si(100) the electrodeposition of metallic rhenium takes place. On both substrates, rhenium films were formed by electrolysis at constant potential and X-ray photoelectron spectroscopy technique was used to characterise these deposits. It was concluded that the electrodeposited films were of metallic rhenium and only the uppermost atomic layer contained rhenium oxide species. D 2005 Elsevier B.V. All rights reserved. Keywords: Rhenium; Electrodeposition; X-ray photoelectron spectroscopy; Electrochemical quartz microbalance 1. Introduction In the last time, the electrodeposition of rhenium species from acid solutions of perrhenate on different electrodic substrates is being studied with relative interest because both oxides or metallic rhenium present an important catalytic activity in bimetallic catalyst systems [1,2]. Also, electrocatalytic activities for reduction reactions such as hydrogen evolution [3,4], carbon dioxide [5,6], perchlorate [7] and nitrate [8] ions have been observed. The effect of rhenium species in the electrooxidation of methanol [9,10] and formic acid [11] on platinum has also been reported. Besides the rhenium applications mentioned above, there is a great interest on rhenium–semiconductor interfaces to be used in the silicon microelectronics: in field emitters, barriers, high resistant layers, stabilisation of porous silicon and in thermoelectric applications [12–14]. Electrochemical metal deposition on semiconductors is a single and promising technique for the production of high quality ohmic contacts, Schottky barriers, and gas sensors. Fur- thermore, in the case of rhenium, in spite of its high melting point (3190 8C), rhenium deposits can be obtained by electrochemical methods at room temperature. In relation to the electrode processes of rhenium species, in a previous communication [11], it was found that when the electroreduction of ReO 4  ion takes place onto a platinum electrode in sulphuric acid media, the species being deposited was ReO 2 . These results have been confirmed by Szabo et al. [15]. They suggested that in 0.5 MH 2 SO 4 media in the potential range prior to the hydrogen 0040-6090/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2004.12.061 T Corresponding author. Fax: +56 32 273422. E-mail address: rschrebl@ucv.cl (R. Schrebler). Thin Solid Films 483 (2005) 50 – 59 www.elsevier.com/locate/tsf