1. School of Electronic and Information Engineering, State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, China
2. School of Physics Science and Technology, Lanzhou University, Lanzhou 730000, China
3. School of Material Science and Engineering, Xi’an University of Technology, Xi’an 710048, China
4. State Key Discipline Laboratory of Wide Band Gap Semiconductor Technology, School of Microelectronics, Xidian University, Xi’an 710071, China
5. School of Material Science and Engineering and State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, China
6. Ernst Ruska Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich, D-52425 Jülich, Germany