1. Department of Physics, Institute of Low-dimensional Carbons and Device Physics, Shanghai University, Shanghai 200444, People’s Republic of China
2. Key Lab of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences (CAS), Suzhou 215123, People’s Republic of China
3. College of Materials Sciences and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China