1. Technical Institute of Physics and Chemistry; Chinese Academy of Sciences; Beijing 100190 China
2. Institute of Physics and Beijing National Laboratory for Condensed Matter Physics; Chinese Academy of Sciences; Beijing 100190 China
3. University of Chinese Academy of Sciences; Beijing 100049 China
4. Laboratory for Nanosystem and Hierarchy Fabrication; National Center for Nanoscience and Technology; Beijing 100190 P. R. China
5. Beijing National Laboratory for Molecular Sciences; College of Chemistry and Molecular Engineering; Peking University; Beijing 100871 China
6. School of Materials Science and Engineering; Tianjin University; Tianjin 300072 China