[1] Sogang Univ, Dept Phys, Seoul 121742, South Korea
[2] Inha Univ, Dept Phys, Inchon 402751, South Korea
[3] Korea Basic Sci Inst, Div Mat Sci, Taejon 305333, South Korea
[4] Natl Inst Adv Ind Sci & Tech, Nanoelect Res Ctr, Tsukuba, Ibaraki 3058568, Japan