[1] Catholic Univ Daegu, Dept Elect Engn, Hayang 712702, South Korea
[2] Hanyang Univ, Dept Appl Phys, Ansan 426791, Kyunggi Do, South Korea
[3] Hanyang Univ, Dept Bionanotechnol, Ansan 426791, Kyunggi Do, South Korea
[4] Rensselaer Polytech Inst, Dept Phys Appl Phys & Astron, Troy, NY 12180 USA