1. Key Laboratory of Microelectronic Devices and Circuits (MOE); Institute of Microelectronics; Peking University; Beijing 100871 China
2. National Synchrotron Radiation Laboratory; CAS Center for Excellence in Nanoscience; University of Science and Technology of China; Hefei Anhui 230029 China
3. CAS Key Laboratory of Standardization and Measurement for Nanotechnology CAS Center for Excellence in Nanoscience; National Center for Nanoscience and Technology; Beijing 100190 China