1. School
of Electrical Engineering (EE), Korea Advanced Institution of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
2. NASA Ames Research Center, Moffett Field, California 94035, United States
3. College of Engineering, Korea University, Seoul 136-713, Republic of Korea
4. Department of Material
Science and Engineering, KAIST, Daejeon 34141, Republic of Korea