Theoretical STM images of Cu atoms on a Si(1 1 1) surface

We calculated scanning tunneling microscope images (STM) of Cu atoms adsorbed on a Si(1 1 1)-1 × 1 structure within the Tersoff–Hamann approximation. The following configurations were considered: CuSi substitutional, CuSi2 interstitial and Cu2Si with Cu atoms residing both in H3 sites and substituting Si in the top layer of the Si(1 1 1) double layer. Our images of the CuSi and Cu2Si show hexagonal arrays of deep crater-like features, surrounded by bright protrusions. Their shape depends on the bias voltage, in accordance with experimental findings. Additionally, we found shallow dark spots, whose contrast also changes with applied bias voltage. The interstitial CuSi2 resembles a pure Si(1 1 1)-1 × 1 structure. Our calculations suggest that the origin of craters observed in the experiments cannot unambiguously be connected solely to the topographic features, but that the local density of states plays an important role in the image formation.