1. School of Advanced Materials Science and Engineering; Sungkyunkwan University (SKKU); Suwon 440-746 Republic of Korea
2. School of Department of Physics; Ewha Womens University; Seoul 120-750 Republic of Korea
3. SKKU Advanced Institute of Nanotechnology (SAINT); Center for Human Interface Nanotechnology (HINT); SKKU-Samsung Graphene Center; Sungkyunkwan University (SKKU); Suwon 440-746 Republic of Korea
4. Samsung Advanced Institute of Technology; Yongin 446-712 Republic of Korea