[1] Tsinghua Univ, Dept Mat Sci & Engn, Adv Mat Lab, Beijing 100084, Peoples R China
[2] Yonsei Univ, Inst Phys & Appl Phys, Seoul 120749, South Korea
[3] Yonsei Univ, Atom Scale Surface Sci Res Ctr, Seoul 120749, South Korea
[4] Gen Hosp Guangzhou Mil Command PLA, Dept Orthoped, Guangzhou 510010, Guangdong, Peoples R China