1. Department of Chemistry City University of Hong Kong Tat Chee Avenue Kowloon 999077 Hong Kong
2. Siyuan Laboratory Guangdong Provincial Engineering Technology Research Center of Vacuum Coating Technologies and New Energy Materials Department of Physics Jinan University Guangzhou 510632 P. R. China
3. Department of Materials Science and Engineering University of Washington Seattle WA 98195 USA
4. Department of Material Science and Engineering City University of Hong Kong Tat Chee Avenue Kowloon 999077 Hong Kong