Self-Assembled Monolayers of Alkanethioacetates on Au(111) in Ammonium Hydroxide Solution

To shed light on the effects of NH4OH deprotection reagent on the formation of self-assembled monolayers (SAMs) from alkanethioacetates on Au(111), we examined the surface structure and adsorption conditions of SAMs on Au(111) prepared in a 1 mM octanethioacetate (C8SAc) methanol solution and in a 1 mM methanol solution formed after in situ deprotection of C8SAc by NH4OH. Scanning tunneling microscopy (STM) imaging revealed that direct adsorption of C8SAc on Au(111) created only disordered SAMs regardless of the polarity of solvent (methanol, DMF, and hexane). In contrast, highly ordered SAMs with a well-ordered c(4 x 2) phase were formed via in situ deprotection of C8SAc by NH4OH (deprotection condition: 30.7 mM NH4OH, 323 K, and 3 h). X-ray photoelectron spectroscopy measurements also showed that the SAMs formed via in situ deprotection show uniform adsorption, whereas those prepared by direct adsorption show very complicated adsorption, which agrees well with STM results.