1. Institute of Physics and Applied Physics, Yonsei University, Seoul, 120-749 Korea
2. School of Integrated Technology, Yonsei University, Incheon, 406-840 Korea
3. Department of Materials
Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea
4. Korea Research Institute of Standards and Science, Daejeon 305-340, Republic of Korea