1. Center for Integrated Nanostructure Physics, Institute for Basic Science, Sungkyunkwan University, Suwon 440-746, Republic of Korea
2. Laboratoire de Nanotechnologie et d’Instrumentation Optique, Institut Charles Delaunay, CNRS-UMR 6281, Université de Technologie de Troyes, BP 2060, 10010 Troyes, France
3. Department of Energy Science, Sungkyunkwan University, Suwon 440-746, Republic of Korea
4. Department of Energy and Materials Engineering, Dongguk University, Seoul 100-715, Republic of Korea