Phase-formation diagram for precursors to epitaxial growth ofNiSi2on Si(111)

Using reflection high-energy electron diffraction and Auger microanalysis in a custom-built ultrahigh vacuum scanning electron microscope we have identified six ordered structures that precede epitaxial ${\mathrm{NiSi}}_2$ during the annealing of nickel overlayers on Si(111). A novel technique of depositing through holes in a mask positioned near the sample allows us to obtain the complete coverage dependence of these structures in a single annealing cycle. The role of these structures in relation to the ${\mathrm{NiSi}}_2$ (B) (twinned) and ${\mathrm{NiSi}}_2$ (A) (nontwinned) structures is described.