Electrochemical fabrication of a heterogeneous binary SAM on polycrystalline Au

An electrochemical method for generating a phase-segregated mixed monolayer of 2-aminoethanethiol (AET) and 11-mercaptoundecanoic acid (MUA) on a polycrystalline gold bead electrode is presented. Electric potential was used to disrupt a monolayer of AET on Au through numerous cycles of reductive desorption followed by incomplete readsorption. Cyclic voltammetry and differential capacitance were used to monitor the successive removal of AET from the metal with potential cycling; however, capacitance was determined to be a more sensitive measure of fractional coverage. Using differential capacitance as a probe, we determined the most efficient method to make the Au surface completely void of AET involved a potential step to a significantly negative potential for a holding time of 15 min. Using this optimal condition, the negative potential was restricted to limit desorption of AET from only the (1 1 1) sites of the polycrystalline metal. The exposed Au(1 1 1) regions were backfilled with MUA through a separate incubation resulting in the formation of the heterogeneous mixed monolayer with limited thiol exchange of the residual AET for the incoming MUA.