Initial steps toward Au_ad island nucleation on a c(2 × 2)-Cl Au(001) surface investigated by DFT

Density functional theory calculations are reported that elucidate the initial steps toward Au ad-island nucleation on c(2 × 2)-Cl covered Au(001) surfaces, which is relevant for Au electrodeposition in Cl^- containing electrolytes. The atomic geometry of (Au_ad)_n adatom structures for n ≤ 4, as well as their stability as a function of Cl chemical potential, has been determined. The electrolyte, however, has not been accounted for in the computation. We find a weakly bonded (Au_adCl₂)-chain as the most stable structure in the case of Cl chemical potentials such that Cl vacancies are suppressed. In the range of Cl chemical potential, where Cl vacancies occur in equilibrium and bind to an (modified) Au_ad induced ad-structure, the formation of a dimer from two monomers is accompanied by an energy gain between 0.06 and 0.23 eV. For Au_ad trimer and tetramer formation, the calculations suggest a similar tendency. This suggests that on c(2 × 2)-Cl covered Au(001) surfaces, the Au ad-island nucleation is supported by the presence of vacancies in the Cl adlayer.