1. School of Electrical and Computer Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907
2. Samsung Advanced Institute of Technology, San #14-1 Nongseo-do, Giheung-gu, Yongin-si, Gyeonggi-do, Korea 446-712
3. School of Electrical and Computer Engineering, Korea University, Anam-dong, Seongbuk-Gu, Seoul 131-701, Republic of Korea
4. Department of Physics, Kyonggi University, Suwon, Kyonggi-Do 443-760, Republic of Korea