In situ Visualization of Cluster-mediated Oxidation Dynamics and Kinetics on Cu(111)

The structural evolution of Cu(111) surfaces in O₂ was studied using in situ scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The spontaneous formation of Cu₃O clusters was observed on Cu(111) and resolved at an atomic scale. These Cu₃O clusters formed preferentially at step edges, serve as building blocks, which diffuse across neighboring terraces, coalesce into larger clusters, and eventually transform into "5-7" Cu₂O overlayers at room temperature and above. DFT calculations elucidated the selective formation of Cu₃O clusters, originating from Cu detachment near steps and facilitating oxide growth front expansion. A comparison between cluster diffusion and attachment demonstrated the growth dynamics of compact Cu₂O morphologies on terraces. Simulations predicted preferential oxide growth from {100}-oriented steps and favored O diffusion along adjacent {111} facets, explaining the observed triangular fractal morphologies of Cu2O at steps. Our combined STM and DFT approach provides insights into cluster-mediated oxidation dynamics on Cu(111) and could be adapted to understand larger-scale oxidation processes.