[1] Chungbuk Natl Univ, Dept Phys, Cheongju 28644, Chungbuk, South Korea
[2] Chungbuk Natl Univ, Res Inst Nanoscale Sci & Technol, Cheongju 28644, Chungbuk, South Korea
[3] Chungnam Natl Univ, Dept Mat Sci, Daejeon 34134, South Korea
[4] Chungnam Natl Univ, Grad Sch Energy Sci & Technol, Daejeon 34134, South Korea
[5] Pohang Accelerator Lab, Pohang 37673, South Korea
[6] Korea Res Inst Stand & Sci, Ctr Nanometrol, Daejeon 34113, South Korea