Corrosion Passivation of Gold by n-Alkanethiol Self-Assembled Monolayers: Effect of Chain Length and End Group

Abstract

Electrochemistry, FTIR-external reflection spectroscopy (FTIR-ERS), and scanning tunneling microscopy (STM) were used to study the ability of n-alkanethiol self-assembled monolayers (SAMs) to protect Au from corrosion in aqueous Br- solutions. The thickness and terminal functional group of the SAMs were varied to determine which factors lead to the greatest corrosion passivation. SAMs prepared on Au from the following molecules were studied: HS(CH2)15CH3, HS(CH2)11CH3, HS(CH2)10COOH, and HS(CH2)11OH. The data reveal that, prior to corrosion, the SAMs are crystalline and highly ordered but that afterward they are disordered and oriented parallel to the surface plane. The results show that, for SAMs containing the same terminal functional group, corrosion resistance increases as the SAM thickness increases. For SAMs that are equal in thickness but contain different terminal functional groups, the end groups resulting in the most corrosion resistance follow the order OH > COOH > CH3. The hydrophilic SAM-mod...