Two-Step Oxidation of Pb(111) Surfaces

We report on a two-step method for oxidation of Pb(111) surfaces, which consists of low temperature (90K) adsorption of O2 and subsequent annealing to room temperature. In situ scanning tunnelling microscopy observation reveals that oxidation of Pb(111) can occur effectively by this method, while direct room temperature adsorption results in no oxidation. Temperature-dependent adsorption behaviour suggests the existence of a precursor state for O2 adsorption on Pb(111) surfaces and can explain the oxidation-resistance of clean Pb(111) surface at room temperature.