[1] Hanyang Univ, Dept Nanotechnol, Seoul 133791, South Korea
[2] Sungkyunkwan Univ, Ctr Nanotubes & Nanostruct Composites, Suwon 440746, South Korea
[3] Sungkyunkwan Univ, Dept Phys, Suwon 440746, South Korea
[4] Sungkyunkwan Univ, Dept Adv Mat Engn, Suwon 440746, South Korea