1. Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing 100871, People’s Republic of China
2. Center for Nanochemistry (CNC), Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, People’s Republic of China
3. Research Center for Wide Gap Semiconductor, Peking University, Beijing 100871, People’s Republic of China
4. CAS Key Laboratory of Standardization and Measurement for Nanotechnology, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing 100190, People’s Republic of China