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, 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 directly on the Au surface. These findings raise the possibility for new strategies to prevent corrosion using very thin, Easily prepared composite films.