Adsorption Processes of Self-Assembled Monolayers Made from Terphenyl Thiols

We investigated the adsorption processes of terphenyl (TP) derivatized thiols, [1,1‘:4‘,1‘ ‘-terphenyl]-4-thiol (TP0), which form self-assembled monolayers (SAMs) on Au(111). Scanning tunneling microscopy observation revealed that the adsorption process is dependent on the solvent in which the TP0 molecules can dissolve. When methylene chloride was used as a solvent, the TP0 molecules nucleate anisotropically along 〈112〉 directions with a 3-fold symmetry at the initial stage. At 1 min of immersion, a phase-separated image was taken. In the topographically lower region, molecular lattices ( a = 0.65 ± 0.05 nm, b = 1.3 ± 0.05 nm) appeared, where the TP0 molecules were arranged parallel to the Au surface. After more than 5 min of immersion, the molecular lattices disappeared and larger striped patterns with a spacing of ca. 8 nm were observed. On the other hand, when ethanol was used as a solvent, the adsorption process of the TP0 molecules completely changed, and such larger striped patterns were not observed after 1 day of immersion. Our data demonstrate that ethanol facilitated the formation of the more densely packed TP0 SAMs than methylene chloride solvent.