OBSERVATION OF AN ORDERED BROMIDE MONOLAYER AT THE PT(111)-SOLUTION INTERFACE BY IN-SITU SURFACE X-RAY-SCATTERING

We present an in-situ surface X-ray scattering study of the formation of an ordered bromide monolayer at the Pt(111)-solution interface. Over a wide potential range, we observe a hexagonal, close-packed, bromide monolayer that is incommensurate, but aligned with the underlying platinum lattice, and undergoes compression as the potential is increased. The in-plane diffraction measurements are correlated with X-ray specular reflectivity results, to confirm the surface coverages and give information about the surface normal structure. The bromide results are also compared to the adsorption of chloride anions, where the substrate-adatom interaction is known to be significantly weaker. In this case, despite the inability to detect any in-plane ordered structure, interpretation of the specular reflectivity is also consistent with the presence of a close-packed chloride monolayer.