1. Department of Applied Chemistry; National Chiao Tung University; 1001 University Road Hsinchu 300 Taiwan
2. Present address: Research Institute for Electronic Science; Hokkaido University; N20W10, Kita-Ward Sapporo 001-0020 Japan
3. Graduate School of Materials Science; Nara Institute of Science and Technology; 8916-5 Takayama-cho, Ikoma Nara 630-0192 Japan