1. School of Material Science and Engineering
2. Tianjin Polytechnic University
3. Tianjin 300387
4. China
5. Beijing National Laboratory for Condensed Matter Physics
6. Institute of Physics
7. Chinese Academy of Sciences
8. Beijing 100190
9. P. R. China
10. School of Physics Science
11. University of Chinese Academy of Sciences
12. Department of Chemistry
13. University of Illinois at Chicago
14. Chicago
15. USA