Identification of the Surface Phases Formed on the Ag(111) Face during Molecular Oxygen Adsorption at Room Temperature

Adsorption of molecular oxygen on the Ag(111) surface at room temperature has been studied using scanning tunneling microscopy (STM), Auger-electron spectroscopy (AES), temperature programmed desorption (TPD), and density functional theory (DFT). In the early stage of adsorption, the STM images show formation of a disordered phase in the form of dark spots (local oxide (Ag6O6) rings. Further O2 dosing leads to the formation of a set of bright objects 5–8 Å in size, which were associated with CO2 molecules stabilized on the surface due to the presence of H2O molecules. Heating of the system to temperatures above 423 K led to partial desorption of silver dioxide molecules and formation of ordered striped ( $$8 \times 2\sqrt 3 $$ ) and hexagonal (3 × 3) phases. According to the DFT calculations, the (3 × 3) phase can be interpreted as surface high-temperature silver carbonate (Ag2CO3), adsorbed on Ag(111). Small areas with the (3 × 3) phase can be seen in STM images even after heating to 540 K, which indicates higher temperature stability of surface carbonates on Ag(111) than it was believed previously.