[1] Natl Chiao Tung Univ, Inst Phys, Hsinchu 300, Taiwan
[2] Natl Chiao Tung Univ, Dept Elect Engn, Hsinchu 300, Taiwan
[3] Natl Taipei Univ Technol, Inst Organ & Polymer Mat, Taipei 106, Taiwan
[4] Natl Chiao Tung Univ, Dept Appl Chem, Hsinchu 300, Taiwan
[5] Natl Tsing Hua Univ, Dept Phys, Hsinchu 300, Taiwan