Energetics and kinetics of the c(2 x 2) to (2√2 x √2)R45° transition during the early stages of Cu(100) oxidation

The energetics and kinetics of the c(2 x 2) to (2 root 2 x root 2)R45 degrees missing-row reconstruction transition on the Cu(100) surface are investigated using density functional theory calculations. First, oxygen-molecule-induced surface restructuring on the unreconstructed Cu(100) surface is compared to that on the missing-row reconstructed surface. We find that the surface-oxide energy decrease on the missing-row reconstruction (-0.149 eV/angstrom(2)) is larger than that on the unreconstructed surface (-0.080 eV/angstrom(2)). Cu2O-like structures, which are found on the reconstructed surface, are not found on the unreconstructed surface. These results indicate that the missing-row reconstruction is necessary for the formation of Cu2O on the Cu(100) surface. Then, we investigate copper ejection from the c(2 x 2) phase using the nudged elastic band method. A series of ejections onto the nearest-neighbor copper atom is found to be the most probable mechanism for the formation of the missing row. The barriers for the subsequent copper diffusion events are comparable to those on the perfect c(2 x 2) phase and the clean copper surface, suggesting that the c(2 x 2) phase acts as a copper diffusion channel during surface oxidation.