1. Electronics and Telecommunications Research Institute, P.O. Box 106, Yuseong, Daejeon 305-350, Korea, Korea Research Institute of Standards and Science, P.O. Box 102, Yuseong, Daejon 305-600, Korea, School of Materials Science and Engineering, University of Ulsan, Ulsan 609-735, Korea, and Department of Chemistry, Chungnam National University, Daejeon 305-764, Korea