1. Center of Super-Diamond and Advanced Films (COSDAF) and Department of Physics and Materials Science, City University of Hong Kong, Hong Kong SAR, People’s Republic of China
2. School of Electronic Science and Applied Physics, Hefei University of Technology, Hefei, Anhui, 230009, People’s Republic of China
3. Department of Physics, South China University of Technology, Guangzhou, 510641, Guangdong Province, People’s Republic of China