1. Division of Nanophotonics; CAS Key Laboratory of Standardization and Measurement for Nanotechnology; CAS Center for Excellence in Nanoscience; National Center for Nanoscience and Technology; Beijing 100190 P. R. China
2. University of Chinese Academy of Sciences; 19 A Yuquan Rd Shijingshan District Beijing 100049 P. R. China
3. School of Physical and Mathematical Sciences; Nanyang Technological University; Singapore 637371 Singapore
4. State Key Laboratory of Chemical Resource Engineering; Beijing University of Chemical Technology; Beijing 100029 P. R. China
5. Center for Nanochemistry (CNC); Beijing National Laboratory for Molecular Sciences; College of Chemistry and Molecular Engineering; Academy for Advanced Interdisciplinary Studies; Peking University; Beijing 100871 P. R. China
6. Department of Materials Science and Engineering; College of Engineering; Peking University; Beijing 100871 P. R. China
7. Division of Physics and Applied Physics; School of Physical and Mathematical Sciences; Nanyang Technological University; Singapore 637371 Singapore