1. National Creative Research Initiative Center for Oxide Nanocrystalline Materials and School of Chemical and Biological Engineering, Seoul National University, Seoul 151‐744, Korea, Fax: +82‐2‐886‐8457
2. School of Chemical and Biological Engineering, Seoul National University, Seoul 151‐744, Korea
3. Hanwha Chemical, Nano Technology Research Division, Research and Development Center, Daejeon 305‐804, Korea