Initial Stages of Oxide Formation on Copper Surfaces during Oxygen Bombardment at Room Temperature

We have studied the oxidation kinetics of initial stages of oxide formation on clean metallic copper surfaces during low-energy O2+ bombardment at room temperature using X-ray photoelectron spectroscopy around Cu 2p and O 1s core-levels and Auger Cu LMM peaks. Two stages in the oxidation process of Cu were observed. For the lower oxygen doses, a single, Cu2O, phase was formed, while the growth of the second, CuO, phase preferentially forms at higher doses. The relative contributions of Cu2O and CuO phases were determined from the deconvolution of Auger Cu LMM spectra, while the thickness of the oxides was estimated from the intensity of the underlying metallic Cu LMM signal and in-depth profiles obtained by secondary ion mass spectrometry. While the growth of the Cu2O layer follows the linear oxidation kinetics, characteristic of the fast chemical reactions of oxygen with the host atoms around the penetration depth of impinging oxygen atoms, the logarithmic law was found for the CuO growth, consistent with the formation of CuO nuclei within the Cu2O matrix.