Electroreductive Desorption of Alkanethiols on Gold and UPD Copper/Gold Surfaces Using In Situ Second Harmonic Generation

The reductive desorption of three alkanethiols: 1-decanethiol (DT), 1-dodecanethiol (DDT), and 1-octadecanethiol (ODT) was studied. Real-time second harmonic generation (SHG) was used to monitor changes at the surface as the self-assembled monolayer was electrodesorbed from a gold and UPD Cu/Au electrode through cyclic voltammetry (CV). Before and after reductive desorption, samples are examined ex situ with sum frequency generation (SFG) spectroscopy, X-ray photoelectron spectroscopy (XPS), and contact angle (CA). These techniques confirmed the electrodesorption of short-chain alkanethiols, while long-chain alkanethiols were proven to remain near the surface of the electrode. However, a difference was observed for a DDT monolayer on the UPD Cu/Au electrode. While DDT was easily desorbed from a gold substrate, DDT on the UPD Cu/Au electrode behaved similarly to a long-chain alkanethiol on gold. Significantly, SHG was able to determine the relative alkanethiol coverage even while the desorption-features in the CV were obscured by the hydrogen evolution current.