1. Chinese Academy of Sciences (CAS) Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing 100190, China.
2. Department of Electrical and Computer Engineering, National University of Singapore, 117576 Singapore, Singapore.
3. CAS Key Laboratory for Standardization and Measurement for Nanotechnology, National Center for Nanoscience and Technology, Beijing 100190, China.
4. University of Chinese Academy of Sciences, Beijing 100049, China.
5. CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, National Center for Nanoscience and Technology, Beijing 100190, China.