1. Collaborative Innovation Center for Nanomaterials & Devices, College of Physics, Qingdao University, Qingdao 266071, China
2. Center for Nanofibers & Nanotechnology, Faculty of Engineering, National University of Singapore, Singapore 119077, Singapore
3. State Key Laboratory of Bio-Fibers & Eco-Textiles (Qingdao University), Qingdao 266071, China