1. Department of Electrical Engineering and Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
2. Department of Polymer Science and Engineering and Key Laboratory of High Performance Polymer Materials and Technology of MOE, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China
3. Department of Materials Science and Engineering, Inha University, Incheon 402-751, South Korea