1Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan
2Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan
3Department of Chemistry, National Taiwan Normal University, Taipei 116, Taiwan
4Present address: Graduate Institute of Electro-Optical Engineering Tatung University, Taipei 104 (Taiwan)
5Kuei-Hsien Chen, Institute of Atomic and Molecular Sciences Academia Sinica, Taipei 10617 (Taiwan).
6Li-Chyong Chen, Center for Condensed Matter Sciences National Taiwan University, Taipei 10617 (Taiwan).
7Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan