[1] Univ Washington, Dept Elect Engn, Seattle, WA 98195 USA
[2] Univ Washington, Dept Chem, Seattle, WA 98195 USA
[3] Univ Washington, Dept Mat Sci & Engn, Seattle, WA 98195 USA
[4] Natl Chi Nan Univ, Dept Appl Mat & Optoelect Engn, Nantou 54561, Taiwan
[5] Natl Taiwan Normal Univ, Inst Electroopt Sci & Technol, Taipei 116, Taiwan