1. College of Mechanical Engineering and Automation
2. Fuzhou University
3. Fuzhou 350108
4. P. R. China
5. Department of Physics
6. State Key Laboratory of Low-Dimensional Quantum Physics
7. Tsinghua University
8. Beijing 100084
9. School of Materials Science and Engineering
10. National Institute for Advanced Materials
11. Nankai University
12. Tianjin 300350