1. Department of Energy Systems Research, Ajou University, Suwon 443-739, South Korea
2. Samsung Electronics, 1-1, Samsungeonja-ro, Hwasung-si, Gyeonggi-do 445-701, South Korea
3. Division of Materials Science and Engineering, Hanyang University, Seoul 133-791, South Korea
4. Department of Materials Science and Engineering, Ajou University, Suwon 443-739, South Korea