Potential dependent adlayer structures of a sulfur-covered Au(1Â 1Â 1) electrode in alkaline solution: An in situ STM study

A sulfur-covered Au(1 1 1) electrode (ΘS=0.33 ML) subjected to potential increases in an S-free NaOH solution, i.e., at a fixed S coverage, leads to the reversible formation of a rhombic phase at anodic potentials. The local S coverage increase which is required for the formation of the rhombic phase results from a coverage decrease within the (3×3)R30° regions, where single-S-atom-defects and, in later stages, S vacancy islands are formed. Due to the high potential induced S-Au bond strength, it was possible for the first time to retain islands of this incomplete (3×3)R30° S layer in the 2D solid state. Furthermore, a Au mass transport was observed during the growth of the rhombic phase. This clearly calls for a reinterpretation of its chemical nature.