1. Collaborative Innovation Center for Nanomaterials & Devices, College of Physics, Qingdao University Qingdao 266071, P. R. China
2. Collaborative Innovation Center for Eco-Textiles of Shandong Province and State Key Laboratory of Bio-Fibers and Eco-Textiles, Qingdao University, Qingdao 266071, P. R. China