In situ study of the process of formation of hexagonal NiSi2 nanoplates and spherical Ni nanoparticles embedded in a Si(001) wafer covered by a Ni-doped SiO2 thin film

Abstract

We have studied for the first time the relevant features of the thermally activated nanostructural transformations occurring in a material initially consisting of a flat Si(001) wafer in which a nanoporous Ni-doped silica film is deposited. Two simultaneous transformation processes occur, and both were investigated by in situ grazing-incidence small-angle X-ray scattering during isothermal annealing at 405 °C, namely the kinetics of formation of (i) oriented NiSi2 hexagonal nanoplates endotaxially buried in a Si(001) wafer, and (ii) a set of randomly oriented spherical Ni nanocrystals with a two-mode radius distribution embedded in a Ni-doped silica thin film deposited on the Si wafer and in an intermediate layer between SiO2 film and the layer in which NiSi2 nanoplates are embedded. The analyses of the successive 2D scattering patterns measured in situ during isothermal annealing led us to establish the time invariances of the average radii of the spherical Ni nanocrystals and the time dependence of their number, together with the time dependences of the maximum diameter, thickness, number and total volume of the hexagonal NiSi2 nanoplates buried in the Si wafer.