1. Department of Electronic Engineering, Ming Chuan University, Taoyuan 333, Taiwan
2. Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan
3. Department of Traffic Science, Central Police University, Taoyuan 333, Taiwan
4. Green Energy and Environment Research Labs, Industrial Technology Research Institute, Hsinchu 310, Taiwan
5. Department of Physics and Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung 804, Taiwan