1. Department of Materials Science and Engineering; Seoul National University; Seoul 151-742 South Korea
2. Department of Polymer Science and Engineering; Inha University; Incheon 402-751 South Korea
3. Department of Physics and Astronomy; Seoul National University; Seoul 151-747 South Korea
4. Department of Physics; Incheon National University; Incheon 406-772 South Korea
5. Carbon Convergence Materials Research Center; Korea Institute of Science and Technology; Wanju-gun 565-905 South Korea