1. Department
of Materials Science and Engineering, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong 999077, People’s Republic of China
2. School
of Materials Science and Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen 518055, People’s Republic of China
3. Center
for Nanoscale Characterization and Devices, Wuhan National Laboratory
for Optoelectronics, School of Physics, School of Optical and Electronic
Information, Huazhong University of Science and Technology, Wuhan 430074, People’s Republic of China
4. Shenzhen Research Institute, City University of Hong Kong, Nanshan District, Shenzhen 518057, People’s Republic of China