1. Department of Physics/QTC/Hi-GEM, National Cheng Kung University, Tainan, Taiwan
2. Center for Micro/Nano Science and Technology, National Cheng Kung University, Tainan, Taiwan
3. Department of Physics, National Chung Cheng University, Chiayi, Taiwan
4. Center of General Studies, National Kaohsiung University of Science and Technology, Kaohsiung, Taiwan