1. Department of Electrical Engineering, Chungnam National University, Yuseong-Gu, Daejeon 305-764, Korea
2. Department of Applied Chemistry, Kyung Hee University, Yongin, Gyeonggi 446-701, Korea
3. Department of Nano Manufacturing Technology, Korea Institute of Machinery and Materials, Yuseong-Gu, Daejeon 305-343, Korea
4. School of Mechatronics, Gwangju Institute of Science and Technology (GIST), Buk-gu, Gwangju 500-712, Korea