1. Research Center for Applied Sciences, Academia Sinica, Taipei 115, Taiwan
2. Institute of Physics, Academia Sinica, Taipei 115, Taiwan
3. Department of Applied Chemistry, National Yang Ming Chiao Tung University, Hsinchu 300, Taiwan
4. Department of Chemistry, National Taiwan University, Taipei 106, Taiwan
5. Department of Materials Science and Engineering, National Dong Hwa University, Hualien 974, Taiwan