1. School of Information Science and Technology
2. Fudan University
3. Shanghai 200433
4. P. R. China
5. College of Science
6. Zhejiang University of Technology
7. Hangzhou 310023
8. China
9. Physikalisches Institut and Center for Nanotechnology
10. Universität Münster
11. 48149 Münster
12. Germany
13. Key Laboratory of Polar Materials and Devices (MOE)
14. Department of Electronics
15. East China Normal University
16. Shanghai 200241