1. Institute of Microelectronics and Nanoelectronics, Key Laboratory of Micro-Nano Electronics and Smart System of Zhejiang Province, College of Information Science & Electronic Engineering, Zhejiang University, Hangzhou 310027, China
2. State Key Laboratory for Artificial Microstructure and Microscopic Physics, School of Physics, Peking University, Beijing 100871, China
3. Department of Materials Science and Engineering, University of California Los Angeles, Los Angeles, California 90095, USA