1. Department of Materials Science and Engineering, Yonsei University, Seoul 120-749, Republic of Korea
2. Department of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749, Republic of Korea
3. Department of Materials Science and Engineering, Inha University, Inchon 790-784, Republic of Korea
4. Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Republic of Korea