1. Center of Super-Diamond and Advanced Films (COSDAF), City University of Hong Kong, Kowloon, Hong Kong SAR 000000, P. R. China
2. Department of Chemistry, City University of Hong Kong, Kowloon, Hong Kong SAR 000000, P. R. China
3. Department of Material Science and Engineering, City University of Hong Kong, Kowloon, Hong Kong SAR 000000, P. R. China