1. Institute of Atomic and Molecular Sciences, 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 Sciences, 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. Advanced Research Centre for Green Materials Science and Technology, National Taiwan University, Taipei 10617, Taiwan