1. Polymer Science and Engineering Program, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea
2. School of Electrical Engineering and Computer Science, Inter-university Semiconductor Research Center, Seoul National University, Seoul 151-742, Korea
3. Department of Chemistry, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea
4. Department of Applied Chemistry, Kumoh National Institute of Technology, Gumi 730-701, Korea