1. Engineering Laboratory of Advanced Energy Materials, Ningbo Institute of Materials Engineering and Technology, Chinese Academy of Sciences, Ningbo, Zhejiang 315201, China
2. Thin Film Physics Division, Linköping University, IFM, 581 83 Linköping, Sweden
3. State Key Laboratory of Nuclear Physics and Technology, Center for Applied Physics and Technology, Peking University, Beijing 100871, China
4. Optical and Electronic Materials Unit, National Institute for Materials Science (NIMS), Tsukuba, Ibaraki 305-0044, Japan