Adsorption processes of self-assembled monolayers made from terphenyl thiols

We investigated the adsorption processes of terphenyl (TP) derivatized thio ls, [1,1':4',1 " -terphenyl]4-thiol (TP0), which form self-assembled monola yers (SAMs) on Au(111). Scanning tunneling microscopy observation revealed that the adsorption process is dependent on the solvent in which the TPO mo lecules can dissolve. When methylene chloride was used as a solvent, the TP O molecules nucleate anisotropically along (112) directions with a 3-fold s ymmetry at the initial stage. At 1 min of immersion, a phase-separated imag e was taken. In the topographically lower region, molecular lattices (a = 0 .65 +/- 0.05 nm, b = 1.3 +/- 0.05 nm) appeared, where the TPO molecules wer e arranged parallel to the Au surface. After more than 5 min of immersion t he molecular lattices disappeared and larger striped patterns with a spacin g of ca. 8 nn were observed. On the other hand, when ethanol was used. as a solvent, the adsorption process of the TPO molecules completely changed, a nd such larger striped patterns were not observed after 1 day of immersion. Our data demonstrate that ethanol facilitated the formation of the more de nsely packed TPO SAMs than methylene chloride solvent.