1. CAS
Key Laboratory of Standardization and Measurement for Nanotechnology, National Center for Nanoscience and Technology, Beijing 100190, P. R. China
2. Department
of Applied Physics, Chongqing University, Chongqing 401331, P. R. China
3. 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