[1] Yonsei Univ, Atom Scale Surface Sci Res Ctr, Seoul 120749, South Korea
[2] Yonsei Univ, Dept Met Engn, Seoul 120749, South Korea
[3] Yonsei Univ, Dept Phys, Seoul 120749, South Korea
[4] Korea Inst Sci & Technol, Adv Anal Ctr, Seoul 130650, South Korea