[1] Sungkyunkwan Univ SKKU, Sch Adv Mat Sci & Engn, Suwon 440746, South Korea
[2] Ewha Womans Univ, Sch Dept Phys, Seoul 120750, South Korea
[3] Sungkyunkwan Univ SKKU, SKKU Adv Inst Nanotechnol SAINT, Ctr Human Interface Nanotechnol HINT, SKKU Samsung Graphene Ctr, Suwon 440746, South Korea
[4] Samsung Adv Inst Technol, Yongin 446712, South Korea