1. Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan
2. Colleage of Semiconductor Research, National Tsing-Hua University, Hsinchu 30013, Taiwan
3. Department of Physics, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan
4. Department of Materials Science and Engineering, Korea University, Seoul 02841, Republic of Korea
5. National Synchrotron Radiation Research Center, Hsinchu 300092, Taiwan
6. Center for Nanotechnology, Materials Science, and Microsystem, National Tsing-Hua University, Hsinchu 30013, Taiwan