1. School of Physics and Microelectronics, and Key Laboratory of Material Physics, Ministry of Education, Zhengzhou University, Zhengzhou, Henan 450052, China
2. Department of Electrical and Computer Engineering, University of California San Diego, La Jolla, California 92093, United States
3. Key Laboratory of Multifunctional Nanomaterials and Smart Systems, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou, Jiangsu 215123, China