1. Beijing Science and Engineering Center for Nanocarbons School of Materials Science and Engineering College of Chemistry and Molecular Engineering Peking University Beijing 100871 P. R. China
2. State Key Laboratory of Applied Organic Chemistry Key Laboratory of Special Function Materials and Structure Design College of Chemistry and Chemical Engineering Lanzhou University Lanzhou 730000 P. R. China
3. State Key Laboratory for Mesoscopic Physics Academy for Advanced Interdisciplinary Studies School of Physics Peking University Beijing 100871 P. R. China
4. School of Materials Science and Engineering Peking University Beijing 100871 P. R. China