XPS study of irradiation damage and different metal–sulfur bonds in dodecanethiol monolayers on gold and platinum surfaces

The X-ray induced irradiation damage is studied in the CH3(CH2)11SH monolayers on gold and platinum surfaces to get information on the metal–sulfur bonds. This is important because the sulfur–substrate bond is one of the crucial factors in thiol SAMs. The X-ray photoelectron spectra (XPS) of the S 2p and C 1s emission were analyzed. During the modification of the surface the thiol/platinum system behaves differently than the thiol/gold system. In the latter case the S 2p spectrum changes as a function of time during the measurement and two chemically different sulfur species, associated with Au-thiolates and irradiation induced sulfur species, can be identified in the spectra. On platinum, there are two chemically different sulfur species in pristine monolayers and their ratio remains unchanged as a function of measurement time. This trend is obviously surface induced and is related to the nature of the metal–sulfur bonds in the self-assembled thiol layers.