1. Department of Applied Physics, The Hong Kong Polytechnic University, Kowloon, Hong Kong, China
2. The Hong Kong Polytechnic University Shenzhen Research Institute, Shenzhen 518057, China
3. Department of Chemistry and Center of Super-Diamond & Advanced Films (COSDAF), City University of Hong Kong, Kowloon, Hong Kong, China
4. City University of Hong Kong Shenzhen Research Institute, Shenzhen 518057, China