1. Department of Physics, National Taiwan University, 10617 Taipei, Taiwan
2. Department of Physics, Tamkang University, 25137 New Taipei City, Taiwan
3. National Synchrotron Radiation Research Center, 30076 Hsinchu, Taiwan
4. Department of Optoelectric Physics, Chinese Culture University, 11114 Taipei, Taiwan
5. Institute of Atomic and Molecular Sciences, Academia Sinica, 10617 Taipei, Taiwan