1. Department of Materials Science and Engineering, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon 999077, Hong Kong SAR, People’s Republic of China
2. Department of Applied Physics, The Hong Kong Polytechnic University, 11 Yuk Choi Road, Hung Hom 999077, Hong Kong SAR, People’s Republic of China
3. College of Optoelectronics and Key Lab of Advanced Transducers and Intelligent Control System of Ministry of Education, Taiyuan University of Technology, Taiyuan 030024, People’s Republic of China