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

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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 preferential 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 near-surface layers. Based on these results, a route for the synthesis of bidimensional arrays of Co nanoparticles within the rutile TiO₂ matrix is proposed.