A scanning tunnelling microscopy view of the surfactant-assisted growth of iron on Cu(111)

We report a scanning tunnelling microscopy study of the growth of iron on Cu(111) using lead as a surfactant. In the absence of surfactant, the growth of iron on Cu(111) proceeds in the form of three-dimensional islands, giving rise to an irregular granular film, with the presence of both face-centred cubic (fcc) and body-centred cubic crystallites whose relative population depends on the film thickness. The deposition of iron is accompanied by an active etching process, which results in chemical heterogeneity of the islands and the appearance of vacancy islands in the substrate surface. On the contrary, during the growth of iron on Pb/Cu(111): (1) the reaction at the interface is considerably limited, producing initially an almost perfect two-dimensional bilayer; (2) the subsequent growth results in a multi-level rough film due to limited interlayer mass transport; and (3) the iron film, continuous and monocrystalline, has the fcc structure as suggested by the persistence of a (4 ×4) lead superstructure present on the top surface layer up to at least six monolayers.