Structural Phase Transitions in an Adsorbed Chlorine Layer on a Pre-Oxidized Ag(111) Surface

The structural transformations occurring in a chlorine monolayer on a previously oxidized Ag(111) surface, containing Ag₆O₆ oxide rings centered at vacancies in the upper silver layer, were investigated using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. It is found that, at a temperature of 80 K in the initial stage, chlorine atoms form chain structures in the gaps between oxide rings. As the coverage increases, chlorine forms domains having a uniaxially compressed structure, with boundaries determined by the local oxide. Continued Cl₂ adsorption leads to condensation of molecular chlorine. Annealing of the resulting system to 300 K causes significant structural transformations on the surface, resulting in the formation of islands of (20–30) Å in size with the reconstruction Ag(111)-(3 × 3)-Cl, as well as chains of objects with a height of ≈1 Å. Based on the DFT calculations these objects were found to be O–Cl quasi-molecules, formed by surface oxygen atoms and adsorbed chlorine atoms.