1. Department of Applied Materials and Optoelectronic Engineering, National Chi Nan University, Nantou 54561, Taiwan
2. Institute of Optoelectronic Sciences, National Taiwan Ocean University, Keelung 202, Taiwan
3. Undergraduate Program in Optoelectronic and Materials Technology, National Taiwan Ocean University, Keelung 202, Taiwan
4. Department of Physics and Center for Nanotechnology, Chung Yuan Christian University, ChungLi 32023, Taiwan