The surface structure of Au(111) in the presence of organic adlayers: a combined electrochemical and surface X-ray scattering study

Abstract

In situ X-ray scattering studies of the Au(111) electrode surface have been carried out in KClO 4 solutions containing uracil, pyridine or 2,2′-bipyridine using grazing-incident-angle diffraction. At sufficiently negative potentials, the ( p × √3) surface reconstruction forms with a stripe separation p = 23. The formation of a two-dimensional condensed uracil film or a complete monolayer of planar oriented pyridine or 2,2′-bipyridine hinders the lifting of the reconstruction. Whereas the stripe separation increases continuously over a 0.6 V range in the base electrolyte, the presence of the organic compounds blocks this process considerably. Only a small, step-like increase in p is observed, where the adlayer is disordered. There exists a 0.7 V hysteresis between the lifting and the subsequent formation of the reconstruction. The ( p × √3) phase reappears at potentials where a ‘gas-like’ adlayer is formed once again. Cyclic diffractograms and potential step measurements have been employed to study the time dependence of these substrate transitions for the system uracil | Au(111).