1. Department
of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, People’s Republic of China
2. The Hong Kong Polytechnic University Shenzhen Research Institute, Shenzhen, People’s Republic of China
3. Department
of Electronic and Information Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, People’s Republic of China
4. Department
of Physics and Materials Science, City University of Hong Kong 83 Tai Chee
Road, Kowloon, Hong Kong, People’s Republic of China