[1] Stanford Univ, Dept Elect Engn, Stanford, CA 94305 USA
[2] ITRI, Elect & Optoelect Res Labs, Nanoelect Technol Div, Hsinchu 31040, Taiwan
[3] Natl Tsing Hua Univ, Inst Elect Engn, Hsinchu 30013, Taiwan
[4] Ming Hsin Univ Sci & Technol, Dept Chem & Mat Engn, Hsinchu 30401, Taiwan