Chemisorption of alkyl thiols and S-alkyl thiosulfates on Pt(1Â 1Â 1) and polycrystalline platinum surfaces

The self-assembled monolayers prepared from 1-dodecanethiol (C12SH) or S-dodecylthiosulfate (Bunte salt, C12SSO3Na) have been characterised on polycrystalline gold and platinum surfaces and on Pt(1 1 1). Contact angle and impedance measurements show that the film quality decreases in the order Au/C12SH > Pt/C12SH ∼ Au/C12SSO3Na > Pt/C12S SO3Na. XPS measurements show that the S-SO3 bond of organic thiosulfates is broken on platinum surfaces and the state of the surface-bound sulfur is indistinguishable from that of thiolate. On platinum three sulfur species are formed upon SAM formation and we suggest that the catalytic activity of platinum is responsible for their existence in pristine monolayers.