Substrate-Driven Formation of Bidimensional Arrays of Co Nanocrystals in TiO2 Thin Films

Ferromagnetic metal nanocrystals in semiconducting hosts are currently investigated for their potential applications in nanotechnology. Still, the controlled growth of the nanocrystals along particular directions or planes is not yet achievable in most nanocomposites like Co/TiO2, where referential localizations are generally accompanied by a distribution of nanoclusters over the whole overlayer. Here we present planar arrays of cobalt nanoparticles embedded in TiO2 layers prepared by pulsed laser deposition on amorphous Si3N4 membranes. High resolution transmission electron microscopy reveals the presence of Co nanocrystals arranged in bidimensional arrays at the film-substrate interface within the rutile TiO2 matrix. X-ray absorption spectra at the Ti L-, O K-, and Co L-edges carried out in surface sensitive and bulk sensitive modalities confirm the rutile phase of the titania matrix and the metallic state of Co atoms and indicate only negligible concentration of Co in the nearsurface layers. Based on these results, a route for the synthesis of bidimensional arrays of Co nanoparticles within the rutile TiO2 matrix is proposed.