SILVER DEPOSITION ON THE AU(111) ELECTRODE WITHOUT INTERFERENCE BY SPECIFICALLY ADSORBED ANIONS

We have studied underpotential deposition of silver on the Au(111) ele ctrode in dilute fluoric acid solution using ultra-high vacuum (UHV) t echniques combined with electrochemistry. The main silver adlattice st ructure is p(3 x 3), in agreement with an earlier study in sulfate med ia using scanning probe microscopies (STM/AFM) and low energy electron diffraction (LEED). As the potential is made more negative, a series of phase transformations occurs to the adlattice, from p(3 x 3) and p( 5 x 5) to compressed (5 x 5) and (6 x 6), and to (1 x 1). These are no n-rotated (n x n) structures on an unreconstructed (1 x 1)Au(111) surf ace. We correlate our structural data to surface coverages and show th at they are quantitatively consistent. Our study shows that the silver growth in HF occurs through a monolayer-simultaneous-multilayer (MSM) mechanism, and underscores the significance of anion coadsorption in the underpotential deposition. The role of coadsorbed water molecules in the process is discussed.