1. Center of Super-Diamond and Advanced Films (COSDAF) & Department of Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong SAR, P. R. China
2. Nano-organic Photoelectronic Laboratory (NOPEL), TIPC, CAS-CityU Joint Laboratory, Dongguan, Guangdong 523000, P. R. China
3. School of Life Science, Beijing Institute of Technology, Beijing 100081, P. R. China
4. Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China