1. Department of Materials Science, Chiba University, Chiba 263-8522, Japan
2. Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
3. Graduate Institute of Applied Physics, National Taiwan University, Taipei 10617, Taiwan
4. School of Electronic and Electrical Engineering, Sungkyunkwan University, Suwon 16419, Republic of Korea
5. Department of Electrophysics, National Chiayi University, Chiayi 600, Taiwan
6. Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan