In a recent issue of Nanotechnology, researchers have shown that the deposition of an ultra thin Au layer has a drastic influence on the subsequent growth of Fe-Si nanostructures on the Si(111) surface. Depending on the coverage and deposition temperature, the Au layer induces a different surface superstructure: Si(111) – 5x2, α-√3x√3, β-√3x√3 and 6x6 – Au. The subsequent deposition of a submonolayer amount of Fe at an elevated temperature results in the formation of Fe-Si nanostructures. Their morphological properties critically depend on the underlying surface as presented in figure 1.
Compared with the Si(111)-7x7 reconstruction, the growth on the Au-induced reconstructions results in less, but distinct, well-defined and larger islands due to the passivation of the dangling bonds which increases the diffusion length of the deposited Fe atoms. As such, the presence of the Au layer causes a decoupling of surface diffusion and substrate temperature and hence, the growth of nanodots becomes possible at considerably lower temperatures compared with the bare Si surface. This is of course an important issue in industrial process flows. Nevertheless, despite the passivation with a thin Au layer, the reaction of Fe with the substrate is preserved and Fe-silicide nanostructures are formed directly on the Si(111) surface.
Ultimately, with an ideal suitable choice of substrate, passivation layer, coverage, deposition temperature and deposition rate, nanostructures can be grown in a controlled way and with the desired morphological and physical properties.