Fabrication and mechanism study of CuO layers on double surfaces of polyimide substrate using surface modification

Formation process and mechanism of continuous CuO layers on double surfaces of polyimide films were studied. The composite films were prepared using the facile surface modification and ion exchange technique. By alkaline-induced chemical modification and ion-exchange reaction, Cu²⁺ ions were incorporated into the surface of polyimide substrate. Thermal treatment in ambient atmosphere resulted in the formation of CuO particles that further agglomerated on the film surface and produced well-defined CuO thin layers on the double surfaces of polyimide films. The changes in the chemical structure, surface morphology, crystalline state and the surface roughness with the increase of ambient temperature were investigated. It was interesting to find that the conversion of metallic copper and low valence sub-oxide Cu₂O to high valence oxide CuO was observed in the thermal treatment process. The agglomeration mechanism for the CuO particles was proposed and proved by three steps, which illustrated that copper-catalyzed and oxygen-assisted decomposition of the polyimide overlayer resulted in the agglomeration of CuO particles. The final composite films retained the thermal stability of the pure polyimide.