1. Material and Chemical Research Laboratories, Industrial Technology Research Institute, Hsinchu 300, Taiwan, R. O. C.
2. Department of Chemistry, National Taiwan University, Taipei 106, Taiwan, R. O. C.
3. Department of Physics, National Tsing Hua University, Hsinchu 300, Taiwan, R. O. C.
4. Department of Chemistry, National Tsing Hua University, Hsinchu 300, Taiwan, R. O. C.