1. Institute of Physics and Applied Physics; Yonsei University; Seoul 120-749 Korea
2. Division of Materials Science; Korea Basic Science Institute; Daejeon 305-333 Korea
3. Korea Research Institute of Standards and Science; Daejeon 305-540; Korea
4. Department of Material Science and Engineering; Yonsei University; Seoul 120-749 Korea
5. School of Advanced Materials Science and Engineering; Sungkyunkwan University; Suwon 440-746 Korea