OBSERVING SURFACE CHEMICAL-TRANSFORMATIONS BY ATOMIC-RESOLUTION SCANNING TUNNELING MICROSCOPY - SULFIDE ELECTROOXIDATION ON AU(111)

The prospects of utilizing atomic-resolution scanning tunneling microscopy (STM) as a real-space in-situ probe of molecular transformations on electrochemical surfaces are illustrated for the specific case of sulfide electrooxidation on Au(111) in aqueous solution. At relatively low electrode potentials, sulfide adsorption yields ordered (square-root 3 x square-root 3)R30-degrees layers. The onset of sulfide electrooxidation produces marked changes in the adsorbate structure, arrays of rectangular close-packed structures being formed which consist predominantly of S8 rings. The ring dimensions, including the S-S bond distances, differ significantly from bulk-phase polysulfur, being affected apparently by the gold substrate structure. Further reaction yields multilayer S(x) structures exhibiting greater disorder. The likely scope of reactive surface electrochemistry amenable to STM is noted.