1. Department of Materials Science and Engineering; National Cheng Kung University; Tainan 70101 Taiwan
2. Department of Physics; National Sun Yat-Sen University; Kaohsiung 80424 Taiwan
3. Department of Materials Science and Engineering; Center for Micro/Nano Science and Technology; Research Center for Energy Technology and Strategy; Advanced Optoelectronic Technology Center; National Cheng Kung University; Tainan 70101 Taiwan