In situ STM Imaging of Two-Component Self-Assembled Monolayers of 1-Decanethiol and 3-Mercaptopropionic Acid on Au(111)

Abstract

Two-component self-assembled monolayers composed of 1-decanethiol (CH₃(HC₂)₉SH : C₁₀SH) and 3-mercaptopropionic acid (MPA) on Au(111) were studied with in situ scanning tunneling microscopy (STM). STM images with molecular resolution revealed that the monolayer consisted of phase-separated domains with molecularly ordered structures, each of which was dominantly formed by one of the constituent molecules. The C₁₀SH domains in the monolayer exhibited ordered phases with a (p × √3) structure, well-established for alkanethiols. On the other hand, a molecular arrangement of MPA defined as a (3 × 3) structure was observed for the MPA domains. It was demonstrated that individual molecules of the monolayer constituents were successfully visualized in the two-component, phase-separated monolayer in solution.