Spectroscopic, Voltammetric, and Electrochemical Scanning Tunneling Microscopic Study of Underpotentially Deposited Cu Corrosion and Passivation with Self-Assembled Organomercaptan Monolayers

Abstract

FTIR−external reflectance spectroscopy (FTIR-ERS), X-ray photoelectron spectroscopy (XPS), electrochemistry, and electrochemical scanning tunneling microscopy (ECSTM) were used to study the effect of aromatic and linear-chain thiol adsorbates on the oxidation of underpotentially deposited Cu on Au (Au/Cu-UPD) in HClO4-containing electrolyte solutions. The morphology of the corroding Cu layer and its stripping potential are influenced by the presence of the organomercaptan self-assembled monolayers (SAMs). For n-alkanethiol SAMs, the Cu-UPD stripping potential shifts positive as the SAM thickness increases. Aromatic SAMs were found to passivate the Cu−UPD surface more effectively than linear-chain SAMs of equal thickness. Furthermore, a methyl-terminated aromatic SAM shifts the potential for Cu−UPD oxidation more positive than a hydroxy-terminated aromatic SAM. For longer chain n-alkanethiol SAMs, the presence of the Cu−UPD layer markedly improves the stability of the SAM compared to when it is adsorbed di...