1. Photo-Electronic Hybrids Research Center, Korea Institute of Science and Technology, Hwarang-ro 14-gil 5, Sungbuk-gu, Seoul 136-791, Republic of Korea
2. School of Applied Chemical Engineering, College of Engineering, Chonnam National University, 77 Yongbong-ro, Buk-gu, GwangJu 500-757, Republic of Korea