1. Department of Physics and Materials Science, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong 999077, China
2. Institute of Textiles and Clothing, The Hong Kong Polytechnic University, 11 Hong Chong Road, Hung Hom, Hong Kong 999077, China
3. Shenzhen Research Institute, City University of Hong Kong, 8 Yuexing Yi Road, Nanshan, Shenzhen 518000, China