1. Key Laboratory for the Physics and Chemistry of Nanodevices
2. Department of Electronics
3. Peking University
4. Beijing 100871
5. China
6. Leiden Institute of Physics
7. Universiteit Leiden
8. 2333 CA Leiden
9. Netherlands
10. Walter Schottky Institut and Physik-Department
11. Technische Universtität München
12. 85748 Garching
13. Germany
14. Nanosystems Initiative Munich (NIM)
15. Department of Physics
16. Universität Basel
17. 4056 Basel
18. Switzerland
19. Swiss Nanoscience Institute