1. Collaborative Innovation Center for Nanomaterials & Devices, College of Physics, Qingdao University, Qingdao 266071, China
2. Department of Electronic & Computer Engineering, The Hong Kong University of Science & Technology, Kowloon, Hong Kong, China
3. Center for Nanofibers & Nanotechnology, Department of Mechanical Engineering, National University of Singapore, Singapore 117574
4. Collaborative Innovation Center for Eco-Textiles of Shandong Province, and State Key Laboratory of Bio-Fibers & Eco-Textiles, Qingdao University, Qingdao 266071, China