1. Electronic Materials Research Center; Korea Institute of Science and Technology; Seoul 136-791 Korea
2. School of Advanced Materials Engineering; Yonsei University; Seoul 120-749 Korea
3. Institute for Research in Electronics and Applied Physics; University of Maryland; College Park 20742 MD
4. Department of Chemistry & Nano Sciences; Ewha Womans University; Seoul 120-750 Korea
5. Department of Materials Science and Engineering; Korea University; Seoul 136-701 Korea