1. Department of Materials Science and Engineering University of Pennsylvania Philadelphia PA 19104 USA
2. School of Electrical Engineering Seoul National University Kwanak P.O. Box 34 Seoul 08826 Republic of Korea
3. Department of Convergence System Engineering Chungnam National University Daejeon 34134 Republic of Korea
4. Department of Electrical Electronics and Communication Engineering Education Chungnam National University Daejeon 34134 Republic of Korea