1. Department of Chemistry, College of Sciences, Nanjing Agricultural University, Nanjing 210095, Jiangsu, P. R. China
2. Department of Materials Science and Engineering, City University of Hong Kong, 83 Tat Chee Avenue, Hong Kong, SAR 999077, P. R. China
3. Center of Super-Diamond and Advanced Films (COSDAF), City University of Hong Kong, Hong Kong, SAR 999077, P. R. China