THE SURFACE-STRUCTURE OF AU(111) IN THE PRESENCE OF ORGANIC ADLAYERS - A COMBINED ELECTROCHEMICAL AND SURFACE X-RAY-SCATTERING STUDY

In situ X-ray scattering studies of the Au(111) electrode surface have been carried out in KClO4 solutions containing uracil, pyridine or 2, 2'-bipyridine using grazing incident-angle diffraction. At sufficientl y negative potentials, the (p x root 3) surface reconstruction forms w ith a stripe separation p = 23. The formation of a two-dimensional con densed 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 th e base electrolyte, the presence of the organic compounds blocks this process considerably. Only a small, step-like increase in p is observe d, where the adlayer is disordered. There exists a 0.7 V hysteresis be tween the lifting and the subsequent formation of the reconstruction. The(p x root 3) phase reappears at potentials where a 'gas-like' adlay er is formed once again. Cyclic diffractograms and potential step meas urements have been employed to study the time dependence of these subs trate transitions for the system uracil/Au(111).