1. Department of Physics, Tamkang University, Tamsui, New Taipei City 251, Taiwan
2. Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720
3. Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064
4. The Institute for Solid State Physics, The University of Tokyo, Kashiwanoha, Kashiwa, Chiba 277-8526, Japan
5. National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan