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 Microscopy (AFM), Core Electron Energy Loss Spectroscopy (CEELS) and electrochemistry. At electrode potentials more positive than these within the silver deposition range sulfate adsorbate forms an ordered Au(111)(root 3 x root 3)R30 degrees adlattice, and gives rise to a corresponding, but diffuse, LEED pattern. Following extensive rinsing procedure, silver 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 condenses to a close packed p(1 x 1)-Ag overlayer at more negative potentials. Distinctive S(LMM) Anger electron transitions and the S(L(2,3)) core electron energy loss of the sulfate adsorbate show a characteristic S6+ sulfur valency, giving evidence that the sulfur oxidation state is not altered in the ultra-high vacuum environment following solution/vacuum transfer.