1. School of Materials Science, Japan Advanced Institute of Science & Technology, 1-1 Asahidai, Nomi City, Ishikawa 923-1292, Japan, Department of Mechano-Micro Engineering, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8502, Japan, and Department of Electrical Engineering, Dong-A University, 840 Hadan-2dong, Saha-gu, Busan 604-714, Korea