1. Department
of Materials Science and Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan
2. National Synchrotron Radiation Research Center, Hsinchu, Taiwan
3. Laboratoire de Physique des Solides, Université Paris Sud, CNRS UMR 8502, F-91405
Orsay, France
4. Department
of Physics, National Tsing Hua University, Hsinchu, Taiwan
5. Green
Energy and Environment Research Laboratories, Industrial Technology Research Institute, Chutung, Hsinchu, Taiwan
6. Institute of Physics, Academia Sinica, Taipei, Taiwan