1. Key Laboratory of Materials Physics, Anhui Key Laboratory of Nanomaterials and Nanotechnology, CAS Center for Excellence in Nanoscience, Institute of Solid State Physics, HFIPS Chinese Academy of Sciences Hefei 230031 China
2. Key Laboratory of Precision and Intelligent Chemistry, University of Science and Technology of China Hefei 230026 P. R. China
3. Institute of Physical Science and Information Technology Anhui University Hefei 230601 P.R. China
4. State Key Laboratory of Multiphase Complex Systems Institute of Process Engineering Chinese Academy of Sciences Beijing 100190 P. R. China
5. Instruments' Center for Physical Science University of Science and Technology of China Hefei 230026 P. R. China
6. Shenzhen Engineering Center for the Fabrication of Two-Dimensional Atomic Crystals, Shenzhen Institutes of Advanced Technology Chinese Academy of Sciences Shenzhen 518055 P. R. China
7. Tsinghua University-Peking University Joint Center for Life Sciences, School of Life Sciences Tsinghua University Beijing 100084 P.R.China
8. MOE Key Laboratory of Bioinformatics, School of Life Sciences Tsinghua University Beijing 100084 P.R.China