1. Department of Materials Science
and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan, ROC
2. Department of Electrophysics, National Chiao Tung University, Hsinchu 30010, Taiwan,
ROC
3. Department of Physics,
Tamkang
University, Tamsui 251, Taiwan, ROC
4. Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam
603 102, India
5. Scientific Research
Division, National Synchrotron Radiation Research Center, Hsinchu
30076, Taiwan, ROC