Figure 3

a Top view of the relaxed (3 × 3)/(4 × 4) Pb/Cu(111) structure, and the green parallelogram indicates one super cell. b The relative positions of Pb and Cu atoms in Cu(111) 1 × 1 surface cell for the same structure as (a). The black dot, blue triangle and red square are for the atoms of Cu substrate, first Pb layer and second Pb layer, respectively. The distances (Å) between some Pb atoms are also shown