Electrochemical characterization of copper surface modified by n-alkanethiols in chloride-containing solutions

The self-assembled monolayers (SAMs) of three n-alkanethiols, 1-octadecanethiol (C18SH), 1-dodecanethiol (C12SH), and 1-hexanethiol (C6SH), were formed on the fresh copper surface pretreated by nitric acid etch. The surface properties of the alkanethiol modified copper electrode in chloride-containing solutions were electrochemically characterized. The polarization measurements have shown that alkanethiol SAMs onto copper were able to protect effectively the underlying copper against corrosion. The cyclic voltammetric results, together with FT-IR measurements, showed that alkanethiol SAMs had quite good anodic inhibition at the lower anodic potentials, but this inhibition action gradually lost because of removal of SAMs from the copper substrate with the increase of anodic potentials. Alkanethiol SAMs were proved to be defective by scanning Kelvin probe (SKP) measurements. Electrochemical noise (EN) experiments have shown that SAMs-covered copper electrode suffered pitting attack in HCl solutions. The formation mechanism of pits was explained in this paper.