1. Institute of Atomic and Molecular Science, Academia Sinica, Taipei 115, Taiwan
2. Department of Physics, National Central University, Chung-Li 320, Taiwan
3. Molecular Science and Technology Program, Taiwan International Graduate Program, Institute of Atomic and Molecular Science, Academia Sinica, Taipei 115, Taiwan
4. Department of Physics, National Taiwan University, Taipei 106, Taiwan
5. Nanoscience and Nanotechnology Program, Taiwan International Graduate Program, Institute of Physics, Academia Sinica, Taipei 106, Taiwan
6. Department of Chemistry, National Taiwan University, Taipei 106, Taiwan
7. Department of Engineering and System Science, National Tsing Hua University, Hsinchu 300, Taiwan
8. Institute of Chemistry, Academia Sinica, Taipei 115, Taiwan