Studies on the adsorption behavior of 2,5-dimercapto-1,3,4-thiadiazole and2-mercapto-5-methyl-1,3,4-thiadiazole at gold and copper electrode surfaces

The adsorption behavior of 2,5-dimercapto-1,3,4-thiadiazole (DMcT) and 2-me rcapto-5-methyl-1,3,4-thiadiazole (McMT) on Au and Cu electrode surfaces wa s studied using a 5 MHz quartz crystal microbalance (QCM), cyclic voltammet ry, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and phase m easurement interferometric microscopy (PMIM). Different behaviors were obse rved for the adsorption of DMcT and McMT on Au and Cu electrodes. Exposing the Au electrode to a McMT solution resulted in the formation of a stable, self-assembled monolayer on the electrode surface. A sharp peak resulting f rom the reductive desorption (RD) of McMT was observed for McMT chemisorbed on the Au electrode. It was also found that dimer-DMcT (di-DMcT) should be used in order to construct a stable DMcT layer on an Au electrode. Detaile d comparisons of charge consumption and mass change during reductive desorp tion suggest that chemisorbed di-DMcT is monomeric and desorbs completely f rom the Au electrode in the RD process. However, on a Cu elect-rode surface , a stable McMT layer could not be constructed. It was also confirmed from PMIM experiments and Raman spectroscopy that DMcT etched copper electrodes, along with concurrent formation of a dimer form of DMcT (di-DMcT). The app arent reason for the different adsorption behaviors between DMcT and McMT i s that DMcT is a stronger proton donor and oxidant.