Self-assembled monolayer formation on copper: A real time electrochemical impedance study

Even though electrochemical impedance spectroscopy (EIS) has already been used for the in situ electrochemical study of organothiol self-assembled monolayer (SAM) formation on gold, such studies are not available on oxidizable metals. A scrupulous study of SAM formation on oxidizable metals is a challenge, even by ex situ techniques, because of their highly oxidizable nature and their high interaction with the solvent which are irrelevant with the noble metals. In this report, the self-assembling of n-dodecanethiol, n-dodecaneselenol, didodecyl disulfide, and didodecyl diselenide on copper substrate is studied in real time by in situ electrochemical impedance spectroscopy. The interfacial capacitance variation with time was used to study the adsorption process as a function of time. The self-assembling of n-dodecanethiol and n-dodecaneselenol results in the formation of a layer with coverage of around 90% within 10 s. This fast step happens with an effective removal of the surface copper oxide layer. The second stage involves a long-term additional adsorption and consolidation of the SAM. Didodecyl disulfide is incapable for the effective removal of copper oxide layer, and its adsorption is slow and ineffective. Monolayer formation with didodecyl diselenide takes longer time due to slow copper oxide removal. The in situ EIS results were supported by the polarization modulation infrared reflection absorption spectroscopic (PM-IRRAS) studies.