1. Department of Materials
Science, Graduate School of Engineering, Tohoku University, 6-6-11
Aoba-yama, Sendai 980-8579, Japan
2. Nanoelectronics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 5, 1-1-1 Higashi, Tsukuba 305-8565, Japan
3. Department
of Electronic Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791, Korea