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. Academy
for Advanced Interdisciplinary Studies, Peking University, Beijing 100871, P. R. China
3. Clarendon
Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
4. State
Key Laboratory of Functional Materials for Informatics, Shanghai Institute
of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences, 865 Changning Road, Shanghai 200050, P. R. China