Sulfide anion interaction with Cu(1 0 0) and Cu modified Au(1 0 0): An electrochemical STM study

We describe the formation of thin copper sulfide semiconductor films under electrochemical conditions. In a first step we investigated the fundamental interaction of the Cu(1 0 0) surface with a sulfide anions containing electrolyte. Beside the classical p (2 × 2)‐S and c (2 × 6)‐S adlayer phases we found the formation of a closer packed “pseudo‐ c (2 × 2)”‐S phase accompanied by an expansion of the topmost copper layer. For a further investigation of this “pseudo‐ c (2 × 2)”‐S phase, we switched from the bulk Cu(1 0 0) electrode to a copper monolayer on a Au(1 0 0) electrode, which can be easily prepard using copper underpotential deposition. Since such a copper monolayer is pseudomorphic to the Au(1 0 0) surface and therefore expanded by 12.5% with respect to the bulk Cu(1 0 0)‐plane, exclusively a commensurate c (2 × 2)‐S structure is instantaneously formed and remains stable over a wide potential range.