Self-assembled monolayers (SAMs) of 6-phenyl-n-hexanethiol (PHT) and 6-(p-vinylphenyl)-n-hexanethiol (VHT) on Au(lll) 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 (delta, chi ', and beta), 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 similar to 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.