Insight into the Phase Transformation Pathways of Copper Oxidation: From Oxygen Chemisorption on the Clean Surface to Multilayer Bulk Oxide Growth

We have employed ambient-pressure X-ray photoelectron spectroscopy to monitor the full pathway of copper oxidation from the initial stages of oxygen chemisorption on the clean surface to oxide nucleation and growth and then to growing continuous oxide layer. By increasing oxygen pressure in a stepwise way from pO₂ = 10^-7 to 1 Torr at T = 350 °C, we show that the oxidation of Cu(100) takes place by dissociative chemisorption of oxygen to first form the p(2 × 2) phase at pO₂ = 1 × 10^-7 Torr, which then transforms to the (22×2)R45° missing-row reconstruction with a higher oxygen coverage and upon increasing pO₂ from 1 × 10^-6 to 1 × 10^-3 Torr. After reaching pO₂ = 1 × 10^-2 Torr, nucleation and growth of Cu₂O islands occurs by consuming the (22×2)R45° regions. Increasing pO₂ to 0.1 Torr results in the continued Cu₂O growth with increased surface roughness. The surface is quickly covered with a CuO layer upon increasing pO₂ to 1 Torr, at which the surface oxidation occurs via the CuO/Cu₂O bilayer growth. The measurements delineate the range of pO₂ required for the crossover between the different stages of the surface oxidation and may have practical importance by tuning the oxidation conditions that allow for controlling the oxide phase and atomic structure of the surface.