1. Carbon Convergence Materials Research Center, Institute of Advanced Composites Materials, Korea Institute of Science and Technology, Eunha-ri san 101, Bongdong-eup, Wanju-gun, Jeollabuk-do 565-905, Korea
2. Department of Chemical Engineering, Dong-A University, Nakdong-Daero 550, Saha-gu, Busan 604-714, Korea
3. Department of Materials Science and Engineering, Hongik University 72-1, Sangsu-dong, Mapo-gu, Seoul 121-791, Korea