1. Center for Nanochemistry; Beijing National Laboratory for Molecular Sciences; State Key Laboratory for Structural; Chemistry of Unstable and Stable Species; College of Chemistry and Molecular Engineering; Peking University; Beijing 100871 PR China
2. Key Laboratory for the Physics and Chemistry of Nanodevices; Department of Electronics; Peking University; Beijing 100871 PR China
3. National Center for Nanoscience and Technology; Beijing 100190 PR China
4. Institute of Physics; Chinese Academy of Sciences; Beijing 100190 PR China
5. Shanghai Institute of Applied Physics; Chinese Academy of Sciences; Shanghai 201204 PR China