1. Center for Nanoscale Characterization & Devices (CNCD), Wuhan National Laboratory for Optoelectronics (WNLO) and School of Physics, Huazhong University of Science and Technology (HUST), LuoyuRoad 1037, Wuhan 430074, P.R. China
2. School of Material Science & Engineering, Guangxi Nonferrous Metals Mineral and Materials, Collaborative Innovation Center, Guilin University of Technology, Jian’ganRoad 12, Guilin 541004, Guangxi P.R. China