Role of Graphene in Oxidation of Underlying Cu Substrates Elucidated through Angle-Resolved X‑ray Photoelectron Spectroscopy: Implications for Corrosion Protection of Graphene/Cu

The role of single-layer graphene in the oxidation process of Cu substrates underlying graphene remains controversial, and the evolution of interfacial oxide layers of graphene/Cu (Gr/Cu) over time has not been reported. Qualitative and quantitative studies of the interfacial oxide layer of Gr/Cu samples upon exposure to ambient conditions for long periods are crucial for revealing the role of graphene in the oxidation process of underlying Cu substrates, so as to further promote the research on corrosion protection of copper surfaces. Angle-resolved X-ray photoelectron spectroscopy (ARXPS) is a practical characterization technology for studying the structure, composition, and thickness of interfacial oxide layers. In this work, we propose an extended model to elucidate the role of graphene in oxidation of underlying Cu substrates through ARXPS study of evolution of interfacial oxide layers. The thickness of an interfacial oxide layer is positively correlated with air exposure time, and it is thinner than that of an oxide layer on a Cu surface; the fractional coverage of the island-like interfacial oxide layer is within the range of 0.4–0.6. For Gr/Cu samples exposed to ambient conditions for less than 6 months, graphene can inhibit the formation of Cu₂O, whereas it promotes the formation of CuO in the interfacial oxide layer for long-term oxidized Gr/Cu samples (≥12 months), leading to the embedded structure of the interfacial oxide layer. The results of this study can serve as a guide for the corrosion protection of copper-based devices.