[1] Sungkyunkwan Univ, Ctr Nanotubes & Nanostruct Composites, Inst Basic Sci, BK21 Phys Div, Suwon 440746, South Korea
[2] Seoul Natl Univ, Dept Phys, Seoul 130743, South Korea
[3] Gwangju Inst Sci & Technol, Adv Photon Res Inst, Kwangju 500712, South Korea