1. Department
of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Avenue SE, Minneapolis, Minnesota 55455, United States
2. National Center for Nanoprocess and Equipment, Korea Institute of Industrial Technology, 208-6, Cheomdangwagi-ro, Buk-gu, Gwang-ju 500-480, Republic of Korea
3. Department of Physics, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwang-ju 500-757, Republic of Korea
4. Optoelectronic Convergence Research center, Department
of Materials Science and Engineering Chonnam National University, 300 Yongbong-Dong, Puk-Gu, Gwangju 500-757, South Korea