1. College of Physics
2. Qingdao University
3. Qingdao 266071
4. China
5. School of Materials Science and Engineering
6. Department of Materials Science and Engineering & Department of Energy and Resources Engineering
7. College of Engineering
8. Peking University
9. Beijing 100871
10. P. R. China
11. Institut für Chemie
12. Humboldt-Universität zu Berlin
13. 12489 Berlin
14. Germany