1. Center of Super-Diamond and Advanced Films (COSDAF); Department of Physics and Materials Science; City University of Hong Kong; Tat Chee Avenue Kowloon Hong Kong China
2. Technical Institute of Physics and Chemistry; Chinese Academy of Sciences; Beijing 100190 China
3. Department of Chemistry; Institute for Advanced Study, Institute of Molecular Functional Materials and Division of Biomedical Engineering; The Hong Kong University of Science and Technology; Clear Water Bay Kowloon Hong Kong China