Evolution of CuO thin films through thermal oxidation of Cu films prepared by physical vapour deposition techniques

Understanding the conversion process of Cu thin films into copper oxide via thermal oxidation reaction is critical to determine their environmental stability as well as to prepare copper oxide thin films and nanostructures. This study reports the evolution of copper oxides through the thermal oxidation of Cu metal thin films deposited using two different processes i.e., DC sputtering and vacuum evaporation. The sputtered Cu films contain a fine-granular morphology with some porosity while the evaporated Cu films have a compact, coarse-granular sur -face. The oxidation of deposited Cu films was performed in ambient air at different temperatures ranging from 200 to 400 degrees C for 2-5 h. The polycrystalline cubic phase of Cu completely converts into a polycrystalline, cubic phase of Cu2O at 300 degrees C and the complete conversion of Cu2O phase into thermally stable, single-phase monoclinic CuO is achieved at 400 degrees C. The Cu2O and CuO films having a crystallite size of-15 nm exhibit an optical band gap of-2.3 and-1.8 eV, respectively. It is found that the CuO phase evolves through Cu2O intermediate phase via solid-state-reaction between Cu and oxygen. It is further noticed that the sputtered Cu films with smaller grains oxidize faster than the evaporated films having large-sized grains.

Automated summary

Understanding the conversion process of Cu thin films into copper oxide is important for environmental stability and preparation of copper oxide thin films. This study investigates the evolution of copper oxides through thermal oxidation of Cu films deposited using different processes. The oxidation of deposited films results in the complete conversion of Cu to Cu2O at 300°C and Cu2O to CuO at 400°C. The CuO films exhibit an optical band gap of approximately 1.8 eV. It is observed that sputtered Cu films oxidize faster than evaporated films.