1. Department
of Materials Science and Engineering, National Chiao Tung University, Hsinchu 300, Taiwan
2. Department
of Physics, Durham University, Durham DH1 3LE, United Kingdom
3. School
of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China
4. Institute
of Physics, Academia Sinica, Taipei 155, Taiwan
5. National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
6. Advanced
Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
7. Department
of Electrophysics, National Chiao Tung University, Hsinchu 300, Taiwan