Atomic scale dynamic process of oxide growth during copper oxidation*

Understanding oxide growth mechanism during metal oxidation is essential for rational design and control of oxides for applications in catalysts, sensors, as well as corrosion protection. Despite ample research on bulk oxidation, little is known on the initial oxide growth process. In this work, we use correlated in situ Environmental Transmission Electron Microscope, DFT simulation, quantitative data extraction and statistical analysis to investigate the dynamic atomic process of initial oxide growth. An unusual layer-by-layer growth of Cu₂O island along Cu₂O(110) plane is observed, instead of along the previously assumed Cu₂O(100) plane that is parallel to the Cu surface. Statistical analysis of growth dynamics indicates a diffusion limited monolayer growth process. DFT results showed Cu₂O(110) has lower surface energy, favorable Cu and O diffusion barriers and adsorption energies during oxidation, leading to easier Cu₂O monolayer formation along Cu₂O(110). These results shed new light on surface oxidation process.