1. Department of Chemistry, KAIST, Daejeon 305-701, Korea, R&D Center, Dongkuk Steel Mill Company, Ltd., Pohang 790-729, Korea, Department of Materials Science and Engineering, Yonsei University, Seoul 120-749, Korea, Corporate R&D Center, Samsung SDI Company, Ltd., Yong-in 449-577, Korea, and Nano Materials Research Team, KBSI, Daejeon 305-333, Korea