1. Department of Physics, The Chinese University of Hong Kong, Shatin 999077, Hong Kong
2. Department of Electronic and Information Engineering, The Hong Kong Polytechnic University, Kowloon 999077, Hong Kong
3. Department of Electronic Engineering, The Chinese University of Hong Kong, Shatin 999077, Hong Kong
4. National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan