We investigate the dissociation of ${\text{O}}_2$ on Pb(111) surface using first-principles calculations. It is found that in a practical high-vacuum environment, the adsorption of molecular ${\text{O}}_2$ takes place on clean Pb surfaces only at low temperatures such as 100 K, but the ${\text{O}}_2$ easily desorbs at (elevated) room temperatures. It is further found that the Pb adatoms enhance the molecular adsorption and activate the adsorbed ${\text{O}}_2$ to dissociate during subsequent room-temperature annealing. Our theory explains the observation of a two-step oxidation process on the Pb surfaces by the unique role of Pb adatoms.

• Received 16 July 2009

DOI:https://doi.org/10.1103/PhysRevB.80.073406