Ni/Si(111) system: Formation and evolution of two- and three-dimensional phases studied by spectromicroscopy

The spatial variations in the composition and electronic structure of Ni/Si interfaces formed via reactive epitaxy at 830 K and successively annealed to 950 K have been studied by synchrotron-radiation scanning photoelectron microscopy, a method that combines chemical mapping with photoelectron spectroscopy from selected spots of the surface. The combination of submicron spatial resolution ({}0.15 {μ}m) with high energy resolution allowed us to characterize the coexisting phases including micron-sized silicide islands and two-dimensional structures. Deposition of 0.7 ML Ni at 830 K produced domains of the √19 phase with different Ni concentration, coexisting with NiSi and NiSi₂ islands. Annealing this interface to 950 K led to conversion of the √19 to a (1×{}1)-RC structure (where RC is ring cluster), which appears to be more uniform than the √19 surface. From the chemical maps and the Si 2p, Ni 3p, and valence-band spectra corresponding to the coexisting phases the nature of the phases was determined and the mechanism of the Ni mass transport on the √19 and (1×{}1)-RC surfaces was examined.