Growth, structure and oxidation of ordered silicon layers on nickel (001)

Thin silicon films deposited in ultra-high vacuum on Ni(001) have been studied, as a function of annealing and/or O₂ exposure, using Auger spectroscopy and low energy electron diffraction. Annealing at temperatures as low as 200 ° C causes rapid intermixing, with only about one monolayer of Si (θ ≈ 1) remaining in a disordered surface layer. Annealing at successively higher temperatures causes further intermixing and the appearance of a c(2 × 2) ordered overlayer (θ = 0.5). The rate of O chemisorption and the structure of the oxide are found to depend on the structure of the adsorbed Si layer. For the c(2 × 2) layer, O₂ exposure leads to the rapid formation of multiple Si---O bonds at all surface Si sites, as in the case of bulk Ni₃Si. This effect is less pronounced (and the saturation O coverage lower) for a surface having a somewhat higher Si coverage but in the form of a disordered layer. The results are interpreted in terms of the involvement of underlayer Ni atoms in promoting O₂ dissociation.