Cyclic Voltammetry and in situ Infrared Reflection Absorption Spectroscopy on Kinetic Effect of Physisorbed Dioctadecylsulfide on a Cu-UPD Process on Au(111) Electrode Surface

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The presence of a self-assembled monolayer (SAM) of dioctadecyl sulfide (DOS) on a Au(111) electrode affects the underpotential deposition (UPD) of copper in sulfuric acid solution. The first stage of the UPD, i.e., formation of the √3 × √3 R30° lattice comprising the honeycomb structure of copper, is delayed by the DOS SAM of the lower-density phase, in which the chain axis is parallel to the surface. Neutral molecules are preferentially adsorbed on the Au(111) electrode surface at around the potential of zero charge (pzc), which is approximately −0.1 V (vs. Hg|Hg₂SO₄) in sulfuric acid solution. The adsorption of copper ions at this potential is inhibited by the DOS SAM, which delays the successive Cu-UPD process in the first stage. In contrast, the DOS SAM of the higher-density phase, in which the chain axis is standing upright, inhibits the entire UPD process. [DOI: 10.1380/ejssnt.2018.60]