1. Department of Physics; Yonsei University; Seoul 120-749 South Korea
2. Department of Physics; Sungkyunkwan University; Suwon 440-746 South Korea
3. Material Research Centre; Samsung Advanced Institute of Technology; Suwon 16678 South Korea
4. Display Materials & Components Research Center; Korea Electronics Technology Institute; Seongnam 463-816 South Korea
5. Materials Science and Engineering Division of Physical Sciences and Engineering; King Abdullah University of Science and Technology; Thuwal 23955-6900 Saudi Arabia