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. State Key Laboratory for Mesoscopic Physics; Collaborative Innovation Center of Quantum Matter; School of Physics; Peking University; Beijing 100871 P. R. China
3. Academy for Advanced Interdisciplinary Studies; Peking University; Beijing 100871 China
4. Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics; Peking University; Beijing 100871 P. R. China
5. Department of Physics and Clarendon Laboratory; University of Oxford; Parks Road Oxford OX1 3PU UK
6. Stanford Nano Shared Facilities; Stanford University; Stanford, California 94305 USA
7. Institute of Textile and Clothing; Hong Kong Polytechnic University; Kowloon, Hong Kong China