1. Department of Material Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Korea
2. Department of Applied
Organic Materials Engineering, Inha University, Incheon 402-751, Korea
3. National Nanofab Center, KAIST, Daejeon 305-701, Korea
4. Department of Chemistry
Education, Seoul National University, Seoul 151-742, Korea
5. KAIST Institute for the Nanocentury, Graphene
Research Center, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea