S.J. Zhao, Y.C. Wang, J.Q. You, Q.B. Yang, L.G. Zhou and H.Q. Ye (Department of Physics, Xiangtan University, Xiangtan 411105, China)(Laboratory of Atomic Imaging of Solids, Institute of Metal Research, The Chinese Academy of Sciences,Shenyang 110015, China)(Department of Materials Science, Northeastern University, Shenyang 110006, China)