1. College of Information Science & Electronic Engineering, Zhejiang University, Hangzhou 310027, P. R. China
2. International Joint Innovation Center, Zhejiang University, Haining 314400, P. R. China
3. Shanghai Precision Metrology & Test Research Institute, Shanghai 201109, P. R. China
4. College of Electronics & Information, Hangzhou Dianzi University, Hangzhou 310018, P. R. China
5. Cambridge Graphene Centre, University of Cambridge, Cambridge CB3 0FA, United Kingdom
6. Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 100083, P. R. China