1. Center for Nanochemistry Beijing Science and Engineering Center for Nanocarbons Beijing National Laboratory for Molecular Sciences College of Chemistry and Molecular Engineering Peking University Beijing 100871 P. R. China
2. Beijing Graphene Institute Beijing 100095 P. R. China
3. Department of Engineering University of Cambridge Cambridge CB3 0FA UK
4. Academy for Advanced Interdisciplinary Studies Peking University Beijing 100871 P. R. China
5. Songshan Lake Materials Laboratory Dongguan Guangdong 523808 P. R. China
6. Beijing National Laboratory for Condensed Matter Physics and Institute of Physics Chinese Academy of Sciences Beijing 100190 P. R. China
7. School of Physical Sciences University of Chinese Academy of Sciences Beijing 100049 P. R. China
8. Department of Physics and Astronomy University of Manchester Manchester M13 9PL UK
9. Electron Microscopy Laboratory and International Center for Quantum Materials School of Physics Peking University Beijing 100871 P. R. China
10. Collaborative Innovation Center of Quantum Matter Beijing 100871 P. R. China
11. Materials Science and Engineering National University of Singapore Singapore 119077 Singapore