Characterization of the first layer and second layer adsorbates on Au electrodes using ATR-IR spectroscopy

The first and second layer adsorbates on Au thin film electrodes were elucidated with respect to deproptonation of organic monolayers or Cu-upd (under potential deposition) on Au(1 1 1) using attenuated total reflection-infrared spectroscopy. The v(ClO) band from ClO4− ions at the second layer, located outside the uracil monolayer, shows invariant frequency, while the ClO4− band at the bare Au surface increases with the potential. The Cl− ions coadsorb with sulfate species during the Cu-upd process. In contrast to the XPS data, the surface coverage of the halide ions does not change significantly at the second upd peak. In addition, we found a robust method to improve the adhesion properties of the Au thin films onto a Si prism base, which enables in situ monitoring of 11-mercaptoundecanoic acid-self-assembled monolayer formation and the following deprotonation process with varying electrode potential or pH in electrolyte solutions. Simultaneously, the electrolyte ions and water species in the vicinity of the first layer adsorbates were feasibly characterized without disturbance by bulk solution species.