1. The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan
2. Bionanotechnology Research Center, Korea Research Institute of Bioscience & Biotechnology, 111 Gwahangno, Yuseong-gu, Daejeon 305-806, Korea
3. Department of Fine Chemical Engineering and Chemistry, 220 Kung-dong, Yusung-gu, Daejeon 305-764, Korea
4. Division of Quantum Phases & Devices, School of Physics, Konkuk University, Seoul 143-701, Korea