[1] Fudan Univ, Dept Phys, Shanghai 200433, Peoples R China
[2] Fudan Univ, State Key Lab Surface Phys, Shanghai 200433, Peoples R China
[3] Univ Calif Davis, Dept Phys, Davis, CA 95616 USA
[4] Lawrence Berkeley Natl Lab, NCEM, Mol Foundry, Berkeley, CA 94720 USA
[5] Collaborat Innovat Ctr Adv Microstruct, Nanjing 210093, Jiangsu, Peoples R China