1. Research Institution for Biomimetics and Soft Matter, Fujian Key Provincial Laboratory for Soft Functional Materials Research, College of Materials, Xiamen University, 422 Siming South Road, Xiamen 361005, China
2. State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
3. Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore