Electrochemical polymerization of an aniline-terminated self-assembled monolayer on indium tin oxide electrodes and its effect on polyaniline electrodeposition Rodolfo Cruz-Silva a, ⁎ , María E. Nicho a , Mary C. Reséndiz a , Vivechana Agarwal a , Felipe F. Castillón b , Mario H. Farías b a Centro de Investigación en Ingeniería y Ciencias Aplicadas, UAEM. Av. Universidad # 1001Col. Chamilpa, CP 62210, Cuernavaca, Mor., Mexico b Centro de Ciencias de la Materia Condensada de la UNAM, Apdo. Postal 2681 C.P. 22800 Ensenada, B.C., Mexico Received 7 July 2006; received in revised form 17 July 2007; accepted 24 August 2007 Available online 1 September 2007 Abstract Indium tin oxide (ITO) transparent electrodes were surface modified by a self-assembled monolayer of N-phenyl-γ-aminopropyl-trimethoxysilane (PAPTS). Cyclic voltammetry of the PAPTS monolayer in aniline-free aqueous electrolyte showed the typical shape of a surface-confined monomer, due to the oxidation of the aniline moieties. This process resulted in a two-dimensional polyaniline film with uniform thickness of 1.3 nm, as measured by atomic force microscopy. X-ray photoelectron and UV–visible spectroscopic techniques confirm the formation of a conjugated polymer film. The influence of the surface modification of ITO electrodes on polyaniline electrochemical deposition was also studied. The initial oxidation rate of aniline increased in the PAPTS-modified ITO electrodes, although the overall film formation rate was lower than that of unmodified ITO electrodes. The morphology of the electrodeposited polyaniline films on PAPTS-modified and unmodified ITO electrodes was studied by atomic force microscopy. Films of smaller grain were grown in the PAPTS-modified ITO as compared to films grown on unmodified ITO. A blocking effect due to the propyl spacer is proposed to explain the reduced electron transfer in PAPTS-modified electrodes. © 2007 Elsevier B.V. All rights reserved. Keywords: Surface-confined monomer; Self-assembled monolayer; Electrochemistry; Indium tin oxide electrodes; Atomic force microscopy; Polymerization; X-ray photoelectron spectroscopy 1. Introduction Electrochemical polymerization of self-assembled mono- layers has received great attention due to potential applications in emerging technologies, such as organic electronics, sensors and nanotechnology. The formation of monolayers bearing elec- troactive monomers provides an efficient method to control the dimensionality and order of monomers confined to the surface of electrodes. Once assembled, these monolayer can be electro- chemically oxidized and transformed into a two-dimensional polymer film. It is common to use a surface-confined monomer to alter the electrochemical deposition of an analogous polymer, either to improve the mechanical and electrochemical stability of the film [1,2] or conversely, to avoid the adhesion or deposition of the film in order to pattern its deposition [3,4]. The formation of self-assembled monolayer is commonly done by using thiol- based compounds, which are known to form high quality monolayers on gold electrodes [5]. Aniline is probably the most studied monomer in surface-confined systems, and mainly two methods have been used to generate monolayers bearing ani- line moieties. The first method is a one-step approach and involves the adsorption of an aniline-terminated thiol in solution [6–10]. The second method requires the use of non-electroactive monolayers, in combination with further electrostatic or cova- lent assembly of the aniline moieties [11–16]. Regardless of the chosen method, the electrochemical behaviour of aniline- terminated monolayers is quite similar. Schomburg and McCarley [6] studied in detail the electrochemical behaviour of aniline-terminated monolayers in aqueous media. Hayes and Available online at www.sciencedirect.com Thin Solid Films 516 (2008) 4793 – 4802 www.elsevier.com/locate/tsf ⁎ Corresponding author. Tel.: +52 777 329 7084x6241; fax: +52 777 329 7084. E-mail address: rcruzsilva@uaem.mx (R. Cruz-Silva). 0040-6090/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2007.08.128