1. Department of Energy Engineering; School of Energy and Chemical Engineering; Low Dimensional Carbon Materials Center; Ulsan National Institute of Science and Technology (UNIST); Ulsan 689-798 South Korea
2. Pohang Accelerator Laboratory; Pohang University of Science and Technology; Pohang Kyungbuk 790-784 South Korea
3. Department of Materials Physics; Dong-A University; Busan 604-714 Republic of Korea