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 p O 2 = 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 p O 2 = 1 × 10 –7 Torr, which then transforms to the missing-row reconstruction with a higher oxygen coverage and upon increasing p O 2 from 1 × 10 –6 to 1 × 10 –3 Torr. After reaching p O 2 = 1 × 10 –2 Torr, nucleation and growth of Cu 2 O islands occurs by consuming the regions. Increasing p O 2 to 0.1 Torr results in the continued Cu 2 O growth with increased surface roughness. The surface is quickly covered with a CuO layer upon increasing p O 2 to 1 Torr, at which the surface oxidation occurs via the CuO/Cu 2 O bilayer growth. The measurements delineate the range of p O 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.