1. Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk 790-784, Korea
2. Samsung Display Co., Ltd., Giheung-Gu, Yongin, Gyeonggi-do 446-711, Korea
3. Department of Materials Science and Engineering, Chungnam National University (CNU), Daejeon 34134, Korea