Enhancing bonding strength between Cu and Cu2O through crystallographic orientation variation

Copper is a widely used material but is susceptible to oxidation under atmospheric conditions, resulting in the formation of oxide layers that are prone to cracking and peeling even under minimal mechanical stress. To address this issue, the development of a dense and solid copper oxide layer with strong oxide–copper interfacial bonding is crucial; however, achieving such strong bonding is challenging owing to the substantial lattice misfit of approximately 18 %. This study presents a novel approach to create an adhesive and robust Cu2O layer on copper through a simple and reproducible heat treatment procedure conducted under extremely low air pressures in vacuum conditions. Remarkably, an unexpected reduction in lattice misfit at the interface is achieved by promoting the growth of a large-grain oxide layer that fully covers the copper surface. Despite the presence of arbitrary crystallographic relationships between copper and Cu2O, the crystallographic orientation of copper is intentionally altered by introducing geometrically necessary dislocations and atomic array tilting, which results in the formation of a stable oxide layer that exhibits exceptional resistance against cracking, peeling, plastic deformation, and mechanical scratching. The effectiveness of this approach is demonstrated by the enhanced robustness and stability it imparts to copper oxides.