1. Nano System Functionality Center, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044
2. ICORP, Japan Science and Technology Agency (JST), Kawaguchi, Saitama 332-0023
3. Department of Materials Science and Engineering, Iwate University, Morioka 020-8551
4. Institute for Materials Research, Tohoku University, Sendai 980-8577
5. Department of Physics Education, Seoul National University, Seoul 151-742, Korea