1. Institute of Atomic and Molecular Sciences, Academia Sinica, P.O. Box 23-166, Taipei, Taiwan 106, Republic of China, National Creative Research Initiative Center for Functional Nanomaterials, Department of Chemistry, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea, and Department of Chemical and Materials Engineering, National Central University, Chung-Li, Taiwan 320, Republic of China