1. Research Institute of Advanced Materials (RIAM), Department of Materials Science and Engineering, Seoul National University, Daehak-Dong, Gwanak-Gu, Seoul 151-744, Korea
2. Department of Fiber System Engineering, Dankook University, 126 Jukjeon-dong, Suji-gu, Yongin-si, Gyeonggi-do 448-701, Korea