Pit formation and segregation effects during Cu thin-film growth on Ag(1 1 1)

The growth of 2–40 ML Cu on Ag(1 1 1) is investigated using scanning tunnelling microscopy (STM). The surface morphology of this bimetallic system appears to be dominated by Ag segregation. At large Cu coverages, a very moderate annealing favours the segregation process and the formation of characteristic pits penetrating through the Cu film. The segregation effect is evidenced by the (9 × 9) superstructure reported for one Ag monolayer deposited onto Cu(1 1 1). Some holes that penetrate well into the Ag substrate are interpreted as efficient diffusion paths for Ag atoms segregating towards the surface.