Journal of Electroanalytical Chemistry 500 (2001) 453 – 460 www.elsevier.nl/locate/jelechem Preparation and characterization of octadecylsilane monolayers on indium – tin oxide (ITO) surfaces Inna Markovich, Daniel Mandler * Department of Inorganic and Analytical Chemistry, The Hebrew Uniersity of Jerusalem, Jerusalem 91904, Israel Received 9 August 2000; received in revised form 11 October 2000; accepted 11 October 2000 Dedicated to Professor Roger Parsons on the occasion of his retirement from the position of Editor-in-Chief of the Journal of Electroanalytical Chemistry and in recognition of his contribution to electrochemistry Abstract The preparation and characterization of octadecylsilane, C 18 , monolayers on indium–tin oxide (ITO) have been studied carefully. A reproducible procedure was developed for the formation of C 18 /ITO employing octadecyltrimethoxysilane (OTMS) as a monomer. The films were studied by means of electrochemistry, wettability, infrared and atomic force microscopy. All these measurements provide evidence for the formation of a disorganized, ‘brush-type’ monolayer with a maximum surface fractional coverage of 0.90 0.04. The surface coverage can be controlled through the silanization time. The applications and implications of such disorganized monolayers in electroanalytical chemistry are discussed. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Indium – tin oxide electrode; Octadecylsilane; Self-assembled monolayers 1. Introduction Self-assembled monolayers (SAMs) have been used extensively as a means of structuring and controlling the chemical and physical properties of the solid  liquid interface [1–4]. Wetting [5–12], adhesion [13–16], elec- tron transfer [17–21], catalysis [22] and adsorption [23 – 25] are among the variety of interfacial properties that can be tuned by monolayers. With respect to electrochemistry, self-assembly has become one of the major approaches for designing selective electrodes and sensors for electroanalytical applications [26 – 29]. The requirements of SAMs for such applications include chemical and electrochemical inertness, and at the same time a strong attachment onto inert conducting sur- faces, e.g. gold and platinum, while maintaining the ability to functionalize the monolayer  electrolyte inter- face. These have made monolayers of alkanethiols on gold the most popular among electrochemists. An addi- tional benefit which alkanethiols on gold offer is their ease of characterization by a large number of surface techniques, due to the smoothness of the underlying gold surface. Their predecessors, i.e. alkylsilanes attached cova- lently onto hydroxylated surfaces, are more difficult to prepare reproducibly, and the formation of dense monolayers is usually limited to non-conducting sur- faces such as Si/SiO 2 [30–35] and glass [36–38]. In this respect, it is worth mentioning recent work that aims at attaching alkyl chains directly to silicon surfaces [39,40]. At the same time, the significant advantage of silane monolayers originates from their thermal [41 – 44], mechanical [45] and chemical stability [30]. Some efforts have been made to attach alkylsilane monolay- ers onto conducting substrates, such as SnO 2 [46–52], glassy carbon [48,53 – 55] and Pt/PtO 2 [54]. Conse- quently, the number of reports where these monolayers have been characterized by electrochemical methods, and on the other hand used in electroanalytical applica- tions, has increased constantly [50 – 52,55]. Although transparent and conducting indium – tin oxide (ITO) is an attractive substrate for silane attach- ment, only a relatively small number of studies have been reported which aim at attaching alkyl chains onto * Corresponding author. Tel.: +972-2-6585831; fax: +972-2- 6585319. E-mail address: mandler@vms.huji.ac.il (D. Mandler). 0022-0728/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0022-0728(00)00458-7