1. Yunnan Key Laboratory for Micro/Nano Materials & Technology, National Center for International Research on Photoelectric and Energy Materials, School of Materials and Energy, Yunnan University, Kunming 650091, China
2. Electron Microscopy Center, Yunnan University, Kunming 650091, China
3. Department of Physics, Key Laboratory of Yunnan Provincial Higher Education Institutions for Optoelectronics Device Engineering, Yunnan University, Kunming 650091, People’s Republic of China