1. School of Physics and Technology, and MOE Key Laboratory of Artificial Micro- and Nano-structures, Wuhan University, Wuhan 430072, China
2. Institute of Microscale Optoelectronics, Shenzhen Key Laboratory of Flexible Memory Materials and Devices, Shenzhen University, Shenzhen 518000, China
3. Center for Electron Microscopy, Wuhan University, Wuhan 430072, China