Sulfidation of a Cu submonolayer at the Au(111)/electrolyte interface - An in situ STM study

We describe the electrochemical preparation of an ultrathin copper sulfide film on Au(111) and its structural characterization by in situ STM. The first step, underpotential deposition of a Cu submonolayer from CuSO4/H2SO4 solution, is followed by two electrolyte exchanges for (i) Cu-free (blank) H2SO4 solution and (ii) NaOH/Na2S solution. The well-known (root 3 x root 3)R30 degrees structure of the upd Cu layer is stable in the blank electrolyte for at least 2 h. After exposure to bisulfide, the Cu layer contracts and forms two-dimensional islands of two distinct ordered surface phases, i.e. a rectangular and, at higher potentials, a hexagonal phase, with Cu-free Au(111) regions between them, the latter exhibiting the characteristic (root 3 x root 3)R30 degrees-S adlayer structure. Potential changes lead to a complex phase behaviour including HS- reversible arrow S-x oxidation/reduction and, at strongly anodic potentials, dissolution of the Cu adlayer. (c) 2006 Elsevier B.V. All rights reserved.