COADSORPTION OF SULFATE ANIONS AND SILVER ADATOMS ON THE AU(111) SINGLE-CRYSTAL ELECTRODE - EX-SITU AND IN-SITU COMPARISON

Interactions of sulfate anions in diluted sulfuric acid solutions with the Ag/Au(111) surface were studied using Auger Electron Spectroscopy (AES), Low Energy Electron Diffraction (LEED), Atomic Force Microscop y (AFM), Core Electron Energy Loss Spectroscopy (CEELS) and electroche mistry. At electrode potentials more positive than these within the si lver deposition range sulfate adsorbate forms an ordered Au(111)(root 3 x root 3)R30 degrees adlattice, and gives rise to a corresponding, b ut diffuse, LEED pattern. Following extensive rinsing procedure, silve r forms two well-ordered structures, Au(111)p(3 x 3) and Au(111)p(5 x 5). However, AFM images reveal a clear p(3 x 3)-4Ag structure, which c ondenses to a close packed p(1 x 1)-Ag overlayer at more negative pote ntials. Distinctive S(LMM) Anger electron transitions and the S(L(2,3) ) core electron energy loss of the sulfate adsorbate show a characteri stic S6+ sulfur valency, giving evidence that the sulfur oxidation sta te is not altered in the ultra-high vacuum environment following solut ion/vacuum transfer.