1. Contribution from the School of Advanced Materials Engineering, Kookmin University, Jeongneung-dong, Seongbuk-gu, Seoul 136-702, Korea, School of Chemical and Biological Engineering & NANO Systems Institute-National Core Research Center, Seoul National University, San 56-1, Shilim-dong, Kwanak-gu, Seoul 151-744, Korea, and Centre for Nanoscience and Nanotechnology, Department of Chemical and Biomolecular Engineering, The University of Melbourne, Victoria 3010, Australia