1. Department of Engineering Science, University of Oxford, OX1 3PJ Oxford, United Kingdom
2. SKKU Advanced Institute of Nanotechnology, Sungkyunkwan University, Suwon 440-746, South Korea
3. Holland Computing Centre, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA
4. Department of Chemistry, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA
5. Division of Physics and Semiconductor Science, Dongguk University-Seoul, Seoul 100-715, South Korea
6. Samsung Advanced Institute of Technology, D&S Research Centre, Samsung Electronics, Youngtong-gu, Suwon-si, Gyeonggi-do 443-803, South Korea
7. School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon 440-746, South Korea
8. Department of Physics, Sungkyunkwan University, Suwon 16419, South Korea
9. Department of Engineering, University of Cambridge, CB3 0FA, Cambridge, United Kingdom