1. Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506, USA
2. Institute of Physics, National Chiao Tung University, 30010 Hsinchu, Taiwan
3. Department of Physics, Southeast University, 211189 Nanjing, China
4. Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
5. National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
6. Department of Chemical Engineering and Material Science, University of Minnesota, Minneapolis, Minnesota 55455, USA
7. Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA
8. Department of Materials Science and Engineering, National Chiao Tung University, 30010 Hsinchu, Taiwan
9. Institute of Physics, Academia Sinica, 105 Taipei, Taiwan