1. Collaborative Innovation Center for Nanomaterials & Devices, Innovation Institute for Advanced Nanofibers, College of Physics, Qingdao University, Qingdao 266071, China
2. Department of Electrical and Computer Engineering, Herbert Wertheim College of Engineering, University of Florida, Gainesville, FL 32608, USA
3. Center for Nanotechnology & Sustainability, Department of Mechanical Engineering, College of Design and Engineering, National University of Singapore, Singapore 117574, Singapore