1. School of Physics and Materials Science
2. Anhui University
3. Hefei 230601
4. P. R. China
5. Key Laboratory of Materials Physics
6. Centre for Environmental and Energy Nanomaterials
7. Anhui Key Laboratory of Nanomaterials and Nanostructures
8. CAS Center for Excellence in Nanoscience
9. Institute of Solid State Physics
10. Department of Physics
11. The Chinese University of Hong Kong
12. New Territory
13. Hong Kong