1. Center for Nanochemistry; Beijing Science and Engineering Center for Nanocarbons; Beijing National Laboratory for Molecular Sciences; College of Chemistry and Molecular Engineering; Academy for Advanced Interdisciplinary Studies; Peking University; Beijing 100871 P. R. China
2. National Center for Nanoscience and Technology; Chinese Academy of Sciences; Beijing 100190 P. R. China
3. Department of Materials Science and Engineering; College of Engineering; Peking University; Beijing 100871 P. R. China