1. School of Materials Science and Engineering, University of New South Wales, Sydney 2052, Australia
2. Department of Physics, National Cheng Kung University, No.1, University Road, Tainan City 701, Taiwan R.O.C.
3. The Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
4. Department of Materials Science and Engineering, Penn State University, University Park, Pennsylvania 16802, United States
5. Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu 30010, Taiwan
6. Department of Physics, Tamkang University, Tamsui 251, Taiwan