1. CAS Center for Excellence in Nanoscience; National Center for Nanoscience and Technology; Beijing 100190 China
2. CAS Key Laboratory for Standardization and Measurement for Nanotechnology; National Center for Nanoscience and Technology; Beijing 100190 China
3. University of Chinese Academy of Sciences; Beijing 100049 China
4. Department of Electrical and Computer Engineering; National University of Singapore; Singapore 117576 Singapore
5. CAS Key Laboratory of Nanosystem and Hierarchical Fabrication; National Center for Nanoscience and Technology; Beijing 100190 China
6. Key Laboratory of Microelectronic Devices and Integrated Technology; Institute of Microelectronics; Chinese Academy of Sciences; Beijing 100029 China
7. State Key Laboratory of Electronic Thin Film and Integrated Devices; University of Electronic Science and Technology of China; Chengdu 610054 China