Dynamics of potential-dependent transformations in sulfur adlayers on Au(111) electrodes

The potential (E)-dependent transformations of adsorbed sulfur on Au(111) in 0.1 M NaOH + 3 x 10(-3) M Na2S have been followed by in situ STM imaging. When E is changed from -0.6 to -0.8 V, the transformation from rectangular S-8 surface structures to a root 3 x root 3 R30 degrees S lattice takes place. This process involves sulfur atom desorption, the formation of rectangular tetramerical surface structures, and the displacement of sulfur atoms to nearest hollow sites, When E moves from -0.8 to -1.0 V fast desorption of the root 3 x root 3 R 30 degrees lattice from Au (111)terraces is observed while sulfur atoms become progressively bonded to step edges. Sulfur atom readsorption to form the root 3 x root 3 R 30 degrees lattice takes place by returning to E = -0.8 V. Experimental data provide an estimation of the excess of binding energy close to step edges.