1. Department of Applied Physics
2. The Hong Kong Polytechnic University
3. Hung Hom
4. Hong Kong
5. Research Center for Functional Materials and Nanomolecular Science
6. Jacobs University Bremen
7. 28759 Bremen
8. Germany
9. Geballe Laboratory for Advanced Materials
10. Department of Materials Science and Engineering
11. Stanford University
12. Stanford
13. USA