1. Department of PhysicsZhejiang University Hangzhou 310027 China
2. Collaborative Innovation Center of Advanced Microstructures Nanjing 210093 China
3. Center of Electron MicroscopeState Key Laboratory of Silicon MaterialSchool of Material Science & EngineeringZhejiang University Hangzhou 310027 China
4. State Key Laboratory of Functional Materials for InformaticsShanghai Institute of Microsystem and Information TechnologyChinese Academy of Sciences Shanghai 200050 China
5. School of Physical Science and TechnologyShanghaiTech University Shanghai 200031 China