Effects of metal coating on self-assembled monolayers on gold. 1. copper on dodecanethiol and octadecanethiol

We report studies on the perturbations induced by the evaporation of copper metal overlayers on dodecanethiol and octadecanethiol self-assembled monolayers (SAMs). Monolayers were characterized after deposition on a gold substrate from an ethanolic solution, after heat treatment alone, after acid treatment alone, after physical evaporation of a submonolayer copper layer alone, and after deposition of an optically thick copper layer followed by stripping with a nitric acid solution. The monolayers were studied using cyclic voltammetry, grazing-angle IR spectroscopy and X-ray photoelectron spectroscopy. Cyclic voltammetry revealed that the gold electrodes are passivated by the formation of the monolayers. The degree of passivation does not decrease with exposure to < 6 N nitric acid solutions or after copper deposition and removal with nitric acid. The IR studies indicate that the deposition of metal induced a reorganization, interpreted as increased disordering, of the monolayer, that is similar to heat treatment alone. X-ray photoelectron spectroscopy experiments showed no evidence of bond formation between carbon and copper upon deposition of the copper layer on the SAM.