Step-mediated size selection and ordering of heteroepitaxial nanocrystals

It is necessary to control the size, shape, and uniformity of self-assembled and self-organized nanocrystals in order to use them in real devices. The way to achieve this in epitaxial nanocrystal arrays is by manipulating the bulk stress and/or the surface stress. In this work, an additional and fundamentally different mechanism of CoSi₂ nanocrystal size selection is reported, based on a preferential reaction of Co adatoms with Si ledge atoms at the step bunches on a vicinal Si(111) surface, where the mean silicide nanocrystal size and nanocrystal-nanocrystal separation distance along the ledge are determined by the step-bunch height. These results may have important implications for the lithography-free fabrication of ordered functional nanostructure ensembles.