1. State
Key Discipline Laboratory of Wide Band Gap Semiconductor Technology,
School of Microelectronics, Xidian University, Xi’an 710071, China
2. School
of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048, China
3. Center
for Integrated Nanotechnologies (CINT), Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
4. Shenzhen
Key Laboratory of Special Functional Materials, College of Materials
Science and Engineering, Shenzhen University, Nanshan District, Shenzhen 518060, China
5. Department
of Physics, South University of Science and Technology, Nanshan District, Shenzhen 518055, China
6. Department
of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
7. Ernst
Ruska Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich, D-52425 Jülich, Germany