We have prepared and characterized self-assembled monolayers (SAMs) of rigid p-methylterphenyl thiol (MTPT) on Au(111). According to ellipsometry and reflection−absorption infrared spectroscopy (RAIRS), MTPT forms densely packed monolayers on gold with the molecular axes slightly tilted away from the surface normal (∼17°). At room temperature, monatomically high islands are observed by scanning tunneling microscopy (STM) instead of the typical monatomically deep holes characteristic of alkanethiol films. Molecular resolution images of the MTPT monolayer reveal a (√3×√3)R30°-like packing with slightly larger lattice vectors (a = 5.3 ± 0.3 Å, b = 5.3 ± 0.4 Å, γ = 60° ± 2°) than those of typical alkanethiol monolayers. This is probably due to the mismatch between the lowest energy packing configuration of the terphenyl monolayer (similar to that of crystalline terphenyl solid) and that of the underlying (√3×√3)R30° structure of the sulfur headgroups. As a result, small domains of order and a high density of defects are observed in the film.

Self-assembled monolayers (SAMs) of 6-phenyl-n-hexanethiol (PHT) and 6-(p-vinylphenyl)-n-hexanethiol (VHT) on Au(111) have been investigated by reflection-absorption infrared spectroscopy (RAIRS), ellipsometry, and scanning tunneling microscopy (STM). Both molecules chemisorbed as thiolates. The packing order and structural changes of the PHT monolayer were investigated at room temperature and following annealing in ultrahigh vacuum. Three different stripe phases (δ, ′, and ), characterized by molecular axes oriented almost parallel to the surface plane, were observed by STM. In contrast, the VHT monolayer had a structure in which the average molecular tilt angle was close to the surface normal. Polymerization of the VHT SAM, as followed by RAIRS, was achieved by either UV-light irradiation or thermal treatment. Ultraviolet irradiation produced longer chain polymers with a maximum of ∼70% conversion, whereas annealing produced shorter chain polymers with CH3 as the end group. The UV-light polymerized film was more robust than the thermally polymerized film.