1. Center
of Super-Diamond and Advanced Films (COSDAF) and Department of Physics
and Materials Science, City University of Hong Kong, Hong Kong SAR, China
2. National
Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, China
3. Institute of Functional Nano & Soft Materials (FUNSOM) and Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215123, China