Surface Structure, Thermal Behavior, and Electrochemical Stability of Oligo(ethylene glycol)-Terminated Alkanethiolate Self-Assembled Monolayers on Au(111)

To investigate the effects of oligo(ethylene glycol) (OEG) chain length and thermal factors on the formation of self-assembled monolayers (SAMs), the surface structure, adsorption state, and electrochemical stability of SAMs of 2-[2-(2-methoxyethoxy)ethoxy]ethanethiol (EG3 SAMs) on Au(111) at an elevated temperature were examined using scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV). To gain a clearer understanding, the results for EG3 SAMs were directly compared with those observed for decanethiolate (DT) SAMs. STM observations revealed that DT SAMs formed after deposition at 323 K for 2 and 24 h exhibited a well-ordered c(4 × 2) phase regardless of the deposition time, whereas EG3 SAMs at 323 K for 2 h displayed a mixed morphology of ordered and disordered phases containing brightly aggregated rows. After deposition at 323 K for 24 h, the brightly aggregated rows almost disappeared and more uniformly ordered SAMs were formed on the entire Au (111) surface. Moreover, CV measurements showed that EG3 SAMs are reductively desorbed from the Au surface much more easily than DT SAMs. In this study, we clearly demonstrated that the OEG backbone significantly affects the formation, surface structure, thermal behavior, and electrochemical stability of SAMs.