1. Key Laboratory of Materials Physics and Anhui Key Laboratory of Nanomaterials and Nanotechnology; Institute of Solid State Physics; Chinese Academy of Sciences; Hefei Anhui 230031 P. R. China
2. Department of Materials Science & Engineering; University of Science and Technology of China; Hefei Anhui 230026 P. R. China
3. Institute of Technical Biology and Agriculture Engineering; Hefei Institutes of Physical Sciences; Chinese Academy of Sciences; Hefei Anhui 230031 P. R. China
4. Institute of Chemical Materials; China Academy of Engineering Physics; Mianyang Sichuan 621900 P. R. China