1. Graduate School of EEWS (WCU), Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong Gu, Daejeon 305-701, Republic of Korea
2. Frontier Research Laboratory, Samsung Advanced Institute of Technology, Samsung Electronics, Yongin, Kyunggi-do 446-712, Republic of Korea
3. KAIST Institute Nano Century, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong Gu, Daejeon, 305-701, Republic of Korea