1. Photo-Electronic Hybrids Research Center, Korea Institute of Science and Technology (KIST), Seoul 136-791, Korea
2. Department of Chemical and Biological Engineering, Korea University, Anam-dong, Seongbuk-gu, Seoul 136-713, Korea
3. Green School, Korea University, 145,
Anam-ro, Seongbuk-gu, Seoul 136-701, Korea