The adsorption of Cu electrodeposition accelerating agents bis-(3-sodiumsulfopropyl disulfide) (SPS) and (3-mercaptopropyl) sulfonate (MPS) on evaporated Cu thin films was examined in situ using spectroscopic ellipsometry under quiescent conditions. Both the thiol MPS and disulfide SPS resulted in definitive changes in the optical response of the interface, indicative of irreversible chemisorption. The optical responses of the films formed from the two additives were different, however, suggesting a difference in the adsorbed states. Cl-can reversibly coadsorb with either MPS or SPS. Preadsorption of either MPS or SPS inhibits the specific adsorption of polyethylene glycol (PEG) in the presence of Cl-. Both SPS and MPS adsorption displace preadsorbed PEG layers. The kinetics of the PEG displacement reaction differ significantly between the thiol and disulfide, consistent with observations of their respective effect on metal deposition kinetics. (c) 2006 The Electrochemical Society.