1. Hitachi High-Tech Science Corporation, 36-1 Takenoshita, Oyama-cho 410-1393, Japan and School of Materials Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi 923-1292, Japan
2. School of Materials Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi 923-1292, Japan; Nano Research Group, University of Southampton, Highfield, Southampton SO17 1BJ, United Kingdom; and Institute of Microengineering and Nanoelectronics, Universiti Kebangsaan Malaysia, UKM, 43600 Bangi, Selangor, Malaysia