Oxidation of copper during physical sputtering deposition: mechanism,   avoidance and utilization
  In this paper, oxidation of Cu during physical sputtering deposition in a high purity and low pressure Ar atmosphere without introducing O2 gas flow was studied systemically. It was found that various flexible Cu-based films could be obtained by simply adjusting deposition parameters. Electrical and optical testing results showed that the achieved pure Cu films and Cu+Cu2O composite films both presented an intriguing combination of metal and semiconductor characteristics. It is expected that such Cu-based films with a superior conductivity and a solar-window bandgap may have fascinating potential applications such as in high electron mobility transistors, electrodes and solar cells. Further, the oxidation mechanisms of Cu under different deposition parameters and the main O2 source during physical sputtering deposition were also explored. 
Jiangbin Su, Yang Liu, Meiping Jiang, Xianfang Zhu
cond-mat.mtrl-sci