Self-assembled monolayers of 3-MPT and its mixed-monolayers with alkanethiol on silver: studies by XPS and electrochemical methods

Abstract

A self-assembled monolayer (SAM) of (3-mercaptopropyl) trimethoxysilane (3-MPT) chemisorbed on a silver surface was chemically modified by 1-octadecanethiol (C18H37SH) to form the dense packed self-assembled mixed-monolayers (SAMM). The self-assembled mixed-monolayers were characterized by X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and contact-angle measurements (CAM). The contact-angle with the silver surface, either uncovered or covered with 3-MPT monolayers increased when chemically modified with 1-octadecanethiol. CV measurements indicated that mixed-monolayers have higher packed densities than 3-MPT SAM. XPS analysis indicated several different excited Si states in mixed-monolayers depending on the preparation sequence of mixed-monolayers; these excited states can be assigned to HOSiO2, Si(OH)3 and their intermediates.