1. Department of Materials Science and Engineering; Graphene Research Center of KI for the NanoCentury; Korea Advanced Institute of Science and Technology; Daejeon 305-701 Republic of Korea
2. Department of Physics, Graphene Research Center of KI for the NanoCentury; Korea Advanced Institute of Science and Technology; Daejeon 305-701 Republic of Korea
3. Department of Electrical Engineering; Graphene Research Center of KI for the NanoCentury; Korea Advanced Institute of Science and Technology; Daejeon 305-701 Republic of Korea
4. School of Chemical Engineering and Bioengineering; University of Ulsan; Namgu, Daehakro 93 Ulsan 680-749 Republic of Korea