1. Department of Physics, University of South Florida, Tampa, Florida 33620, USA
2. School of Materials Science and Engineering, Inner Mongolia University of Technology, Hohhot 010051, China
3. School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China
4. 1D Nanomaterials Group, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan