1. Department of Applied Science, ROC Naval Academy, Kaohsiung 813, Taiwan
2. Center for Nanoscience and Nanotechnology, National Sun Yat-sen University, Kaohsiung 80424, Taiwan
3. Department of Photonics, National Cheng Kung University, Tainan 701, Taiwan, ROC
4. Department of Materials and Optoelectronic Science, National Sun Yat-sen University, Kaohsiung 80424, Taiwan
5. Department of Physics, National Sun Yat-sen University, Kaohsiung 80424, Taiwan