Air stability of alkanethiol self-assembled monolayers on silver and gold surfaces

Surface Raman spectroscopy, electrochemistry, and X-ray photoelectron spectroscopy have been used to study the effects of air exposure on the stability of self-assembled monolayers (SAMs) formed from alkanethiols on mechanically polished, smooth Ag and Au surfaces. Ramancspectra exhibit oxidized sulfur modes after only hours of air exposure. X-ray photoelectron spectroscopy of the S 2p region porvides additional evidence for sulfur oxidaton. Cyclic voltammetry of Ru(NH₃)(3+) indicates that oxidized alkanethiol SAMs retain blocking characteristics toward electron transfer, even after exposure of the oxidized SAM-surface to a solubilizing solvent. Control experiments suggest ozone as the primary oxidant in ambient laboratory air which causes rapid oxidation of the thiolate moiety. These results have important ramification for the general use of SAms in many proposed application.