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 pO(2) = 10(-7) to 1 Torr at T = 350 degrees C, we show that the oxidation of Cu(100) takes place by dissociative chemisorption of oxygen to first form the p(2 X 2) phase at pO(2) = 1 x 10(-7) Torr, which then transforms to the (2 root 2 x root 2)R45 degrees missing-row reconstruction with a higher oxygen coverage and upon increasing pO(2) from 1 x 10(-6) to 1 x 10(-3) Torr. After reaching pO(2) = 1 X 10(-2) Torr, nucleation and growth of Cu2O islands occurs by consuming the (2 root 2 x root 2 )R45 degrees regions. Increasing pO(2) 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 pO(2) to 1 Torr, at which the surface oxidation occurs via the CuO/Cu2O bilayer growth. The measurements delineate the range of pO(2) 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.