1. Shaanxi Joint Key Laboratory of Graphene, School of Advanced Materials and Nanotechnology Xidian University Xi'an 710126 P. R. China
2. Guangzhou Institute of Technology Xidian University Guangzhou 710068 P. R. China
3. State Key Laboratory of Materials Processing and Die & Mould Technology, School of Materials Science and Engineering Huazhong University of Science and Technology Wuhan 430074 P. R. China
4. Institute of Information Sensing Xidian University Xi'an 710126 P. R. China
5. Key Laboratory of Materials Physics, Anhui Key Laboratory of Nanomaterials and Nanotechnology, Institute of Solid State Physics, Hefei Institutes of Physical Science Chinese Academy of Sciences Hefei 230031 P. R. China
6. Optics Valley Laboratory Hubei 430074 P. R. China