Temperature-induced segregation of Co- and Ni-rich nanoparticles on rutile TiO₂(001)

Cobalt- and nickel-rich nanoparticles were produced by direct segregation from a single crystal rutile TiO₂ in ultra-high vacuum conditions. It was shown that, similarly to the previous findings for Fe, also in the case of Co and Ni, the segregation of a noticeable amount of material is possible on the (001) surface. Segregation of these metals results in formation of nanoparticles and their distribution on the surface partially reflects the substrate symmetry in the case of Co and reveals some signs of self-organization for Ni. Cyclic appearance and disappearance of Co- and Ni-rich nanoparticles can be fully controlled by the temperature of annealing. The explanation of the mechanism of repeatable segregation is proposed basing on interaction of Co and Ni cations with Ti interstitials. These new findings can be especially important for catalysis and spintronic applications where the controlled nanoparticles size and concentration are crucial. (paper)