Comparative behavior of aromatic disulfide and diselenide monolayers on polycrystalline gold films using cyclic voltammetry, STM, and quartz crystal microbalance

A comparative investigation of the self-assembled monolayers of diphenyl di sulfide (DDS), diphenyl diselenide (DDSe), and naphthalene disulfide (NDS) on polycrystalline gold films using STM, QCM, and electrochemical technique s is presented. The geometric constraint imposed by the rigid naphthalene r ing for NDS inhibits the cleavage of the SS bond, thus adversely affecting the monolayer organization and stability relative to the monolayers formed with DDS and DDSe. A comparative analysis using techniques like cyclic volt ammetry and quartz-crystal microbalance indicates that, for DDS, the facile cleavage of the S-S bond leads to strong binding of the adsorbate molecule s at the preferred surface sites, resulting in a rather well-organized self -assembled structure. The STM pattern of NDS reveals a periodic domain (i.e ., less than 10 nm in size) while no such small domains are seen in the cas e of DDS and DDSe due to the orientational flexibility of the rings. (C) 20 01 Academic Press.