Study of Fe deposition onto 3×3-Al/Si(1 1 1) template by scanning tunneling microscopy

The surface dynamics of Fe deposited onto the template surface of 3×3-Al adatom-layer on Si(1 1 1) has been studied using scanning tunneling microscopy (STM). By imaging at both positive and negative sample bias, we identify the locations of Fe, Al and Si atoms by the susceptibility differences of these sites in receiving electrons and holes from the STM tip. When 0.1 ML of Fe atoms are deposited at room temperature, some Fe atoms incorporate themselves into the adlayer as dispersed atoms or small Fe clusters with 2-10 atoms. A smaller amount of Fe atoms choose to sit on the adlayer, once again as dispersed atoms or small Fe clusters. As the Fe coverage increases beyond 0.1 ML, both Fe clusters in and on the adlayer grow into 3-dimensional islands. Raising the growth temperature to 100 °C is enough to enhance the diffusivity of Fe atoms and initiate a small degree of cluster coalescence. However, these clusters still do not show any crystallinity by STM observation until they are annealed. Deposition of Fe atoms at 400 °C or post-deposition annealing above this temperature leads to the formation of iron silicide islands with a 2 × 2 surface lattice and a CsCl-type iron silicide structure, which are surrounded by 3×3-Al/Si(1 1 1) adlayer domains with a depletion of Si atoms near the silicide islands. Most of these islands have a triangular shape, and grow preferentially along the step edges of the Si(1 1 1) surface. The 3×3-Al adlayer appears to passivate the Si surface and enhances the diffusivity of Fe atoms but the passivation is not thermally stable.