Potential Dependence of Competitive Adsorption of PEG, Cl[sup −], and SPS/MPS on Cu

Potential-dependent adsorption of bis-(3-sulfopropyl) disulfide (SPS), 3-mercaptopropyl sulfonate (MPS), chloride ( ), and polyethylene glycol (PEG) on evaporated Cu thin films was examined using in situ spectroscopic ellipsometry at , , and under quiescent conditions. The adsorption for the thiol compound was similar at all potentials examined, but the adsorption of the disulfide increased at more negative potentials. The influence of on the substrate was greatly diminished and PEG concurrently less strongly adsorbed at more negative potentials, as measured by ellipsometric responses. Both adsorbed MPS and SPS inhibited the specific adsorption of PEG in the presence of . Likewise MPS and SPS added to the electrolyte displaced preadsorbed PEG/ layers, with the displacement by the disulfide compound strongly potential dependent. At all potentials studied, the disulfide was less effective than MPS at displacement of preadsorbed PEG/ .