1. Department of Electrical Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan
2. National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8565, Japan
3. Center for Micro/Nano Science and Technology, National Cheng Kung University, Tainan 70101, Taiwan
4. Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan