1. Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hum, Kowloon, Hong Kong 999077, China
2. Institute of Textiles and Clothing, The Hong Kong Polytechnic University, Hung Hum, Kowloon, Hong Kong 999077, China
3. The Hong Kong Polytechnic University Shenzhen Research Institute, Shenzhen 518057, China