1. Institute of Physics, National Chiao Tung University, Hsinchu 30010, Taiwan
2. Department of Physics, School of Education, Can Tho University, 3/2 Street, Can Tho, Vietnam
3. Key Laboratory of Polar Materials and Devices, Ministry of Education, East China Normal University, Shanghai 200062, China
4. Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya 456-8587, Japan
5. Department of Physics, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan
6. Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
7. Department of Electrophysics, National Chiao Tung University, Hshinchu 30010, Taiwan
8. National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
9. Department of Physics, National Tsing Hua University, Hsinchu 30043, Taiwan
10. Institute of Physics, Academia Sinica, Taipei 11529, Taiwan
11. Department of Physics, Durham University, Durham DH1 3LE, United Kingdom
12. Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu 30010, Taiwan