Preparation and Characterization of Self-Assembled Monolayers on Indium Tin Oxide

• Published in: Langmuir 2000-07, Vol.16 (15), p.6208-6215
• Main Authors: Yan, C, Zharnikov, M, Gölzhäuser, A, Grunze, M
• Format: Article
• Language: English
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la000128u

Self-assembly of amphiphilic molecules, alkanethiols CH3(CH2) n SH (n = 15, 17), carboxylic acids CH3(CH2) n COOH (n = 16, 18) and bifunctional SH(CH2)15COOH on indium tin oxide (ITO) surfaces was investigated by X-ray photoelectron and near edge X-ray absorption fine structure spectroscopies, contact angle measurements, and atomic force microscopy. These molecules were found to form homogeneous, well-oriented monolayers on ITO. XPS indicates that at low coverages, thiol molecules adsorb as thiolates, whereas at saturation coverage ∼30% of the molecules adsorb as unbound thiols. From NEXAFS, we determined average alkyl chain tilts of 33° for thiol from the neat liquid, 44° for thiols prepared via CVD, 38° for carboxylic acids from hexadecane, and 43° for COOH(CH2)15SH from ethanol. Adsorption from a mixed hexadecane solution results in a preferred adsorption of carboxylic acids over thiol. Thus, COOH(CH2)15SH is found to bind to ITO via the carboxylic acids, forming a thiol-terminated SAM.