1. Department of Electrical Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan
2. Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
3. Inorganic Functional Materials Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Nagoya 463-8560, Japan
4. Department of Mechanical Engineering, The University of Tokyo, Tokyo 113-8656, Japan