1. Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing 100871, China
2. State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
3. CAS Key Laboratory of Standardization and Measurement for Nanotechnology, CAS Center of Excellence for Nanoscience, National Center for Nanoscience and Technology, Beijing 100190, China
4. School of Physics, Peking University, Beijing 100871, China
5. Electron Microscopy Laboratory, International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China
6. Key Laboratory of Eco-Chemical Engineering, Ministry of Education, College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042, China
7. Joint Key Laboratory of the Ministry of Education, Institute of Applied Physics and Materials Engineering, University of Macau, Avenida da Universidade Taipa, Macao 999078, China
8. Research Center for Wide Gap Semiconductor, Peking University, Beijing 100871, China