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 change s 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 hydroxi de 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 la yer propagated across terraces starting from edges. An ordered oxidize d surface structure was not resolved and the surface roughness is appr oximately 0.08 +/- 0.02 nm. This is ascribed tentatively to the format ion of a monolayer of oxide by place exchange. During a slow cathodic sweep, the oxidized surface restructured into wormlike islands of mona tomic height at the peak potential for oxide reduction at 1.15 V vs. R HE. These islands coalesced to form flat terraces with monatomic pits in the surface at potentials within the double-layer region. Pits even tually fused with terrace ledges to restore the original terrace morph ology.