1. Electronic Materials Laboratory, Samsung Advanced Institute of Technology, P.O. Box 111, Suwon, 440-600, Korea, Department of Applied Chemistry, Ajou University, Suwon, 442-749, Korea, Department of Advanced Materials, Sungkyunkwan University, Suwon, 440-746, Korea, School of Chemical Engineering, Seoul National University, Seoul, 151-744, Korea, and Department of Chemistry, University of California, Santa Barbara, California 93106