IN-SITU SCANNING-TUNNELING-MICROSCOPY STUDIES OF THE FORMATION AND REDUCTION OF A GOLD OXIDE MONOLAYER ON AU(111)

An in situ scanning tunneling microscopy study of morphological changes during formation and reduction of an oxide monolayer on Au(111) in 0.1M HClO4 is presented. During oxidation of a freshly prepared surface, the (1 x 1) arrangement of metal atoms persisted through the hydroxide peak at 1.35 V vs. reversible hydrogen electrode (RHE). At the peak potential for AuO formation (1.55 V vs. RHE), a slightly roughened layer propagated across terraces starting from edges. An ordered oxidized surface structure was not resolved and the surface roughness is approximately 0.08 +/- 0.02 nm. This is ascribed tentatively to the formation of a monolayer of oxide by place exchange. During a slow cathodic sweep, the oxidized surface restructured into wormlike islands of monatomic height at the peak potential for oxide reduction at 1.15 V vs. RHE. These islands coalesced to form flat terraces with monatomic pits in the surface at potentials within the double-layer region. Pits eventually fused with terrace ledges to restore the original terrace morphology.