1. Graduate School of EEWS (WCU), Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea
2. Materials and Process Simulation Center, California Institute of Technology, Pasadena, California 91125, United States
3. School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245, United States
4. Department of Electrical and Computer Engineering, University of California, Davis, California 95616, United States