1. Department of Physics Hong Kong Baptist University Kowloon Hong Kong SAR P. R. China
2. Institute of Mechanics Chinese Academy of Sciences Beijing 100190 P. R. China
3. Department of Physics Southeast University Nanjing Jiangsu 211189 P. R. China
4. Department of Chemistry Yale University New Haven CT 06520 USA
5. Department of Chemical and Environmental Engineering Yale University New Haven CT 06520 USA