1. Graphene Research Center of KI for the NanoCentury; Korea Advanced Institute of Science and Technology; Daejeon 305-338 Republic of Korea
2. Department of Materials Science and Engineering; Korea Advanced Institute of Science and Technology; Daejeon 305-338 Republic of Korea
3. Center for Nanoparticle Research; Institute for Basic Science (IBS); Department of Materials Science and Engineering; Research Institute of Advanced Materials (RIAM); Seoul National University; Seoul 151-742 Republic of Korea