Au-Induced Nanostructuring of Vicinal Si Surfaces

We have investigated the Au-induced nanofaceting of vicinal silicon surfaces tilted from [111] towards [112-bar]. Using samples miscut 3.80, and 80, from [111] respectively we have used scanning tunnelling microscopy (STM) to measure the surface morphology as a function of Au coverage (0.04 to 0.44 ML). As expected, Au adsorption produces dramatic changes in surface morphology on both samples. On the 3.80 sample we find that as little as 0.04 ML of Au is sufficient to remove the faceting present on the clean surface. As more Au is deposited 1-dimensional chain structures nucleate at step edges. These chain structures eventually grow to form (775)-Au facets. At 0.17 ML we observe a surface with Si(111)7 x 7 terraces and (775)-Au nanofacets. With more Au (111) terraces transform from a 7 x 7 to a 5 x 2 reconstruction and at 0.4 ML the sample consists of Si(111)5 x 2-Au terraces separated by (775)-Au facets. The morphology of the 80 sample also depends critically on Au coverage. Below 0.32 ML all 80 surfaces include (775)-Au nanofacets. Above 0.32 ML (775)-Au facet is no longer stable and Au is accommodated on the surface via the formation of higher angle facets with smaller chain spacing. In both samples, the persistence of the (775)-Au facet reinforces the idea that it represents a low energy facet on these Au modified vicinal surfaces