[1] Gwangju Inst Sci & Technol, Heeger Ctr Adv Mat, Kwangju 500712, South Korea
[2] Gwangju Inst Sci & Technol, Dept Mat Sci & Engn, Kwangju 500712, South Korea
[3] Elect & Telecommun Res Inst, Natl Creat Res Initiat, Ctr Smart Mol Memory, IT Convergence Components Lab, Taejon 305350, South Korea