1. Department of Materials Science and Engineering, Nanchang University, 999 Xue Fu Da Dao, Nanchang 330031, P. R. China
2. Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Gustav WiedsVej 14, 8000 Aarhus C, Denmark
3. Department of Physics, Nanchang University, 999 Xue FuDa Dao, Nanchang 330031, P. R. China