The adsorption behavior of 2,5-dimercapto-1,3,4-thiadiazole (DMcT) and 2-mercapto-5-methyl-1,3,4-thiadiazole (McMT) on Au and Cu electrode surfaces was studied using a 5 MHz quartz crystal microbalance
(QCM), cyclic voltammetry, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and phase
measurement interferometric microscopy (PMIM). Different behaviors were observed 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 from
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. Detailed comparisons of charge consumption and mass change during reductive desorption
suggest that chemisorbed di-DMcT is monomeric and desorbs completely from the Au electrode in the RD
process. However, on a Cu electrode 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 apparent reason for the different
adsorption behaviors between DMcT and McMT is that DMcT is a stronger proton donor and oxidant.
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