Substrate Effects on the Morphology of Carbon Encapsulated Nickel Nanoparticles Grown by Surface Diffusion Assisted Phase Separation

Encapsulated nanoparticles formed by surface diffusion assisted phase separation during thin film growth are promising candidates for the multifunctional devices or as large scale templates for nanowire fabrication. In this study, substrate type influence on the morphology of encapsulated metal nanoparticles in C:Ni films grown by ion beam cosputtering is investigated. C:Ni (similar to 15 atom %) nanocomposite thin films (similar to 50-70 nm thick) were grown at 400 degrees C on amorphous SiO2 and Nb2O5, polycrystalline TiN, and single crystalline MgO (001) substrates. Combined diagnostics using transmission electron microscopy, grazing incidence small-angle X-ray scattering, and superconducting quantum interference device magnetometry demonstrate that all the films exhibit metallic nanoparticles elongated along the film growth direction, while the substrate material strongly influences their morphology even far away from the film/substrate interface despite the fact that repeated nucleation occurs in all the films. The mean nanoparticle diameter is strongly substrate dependent and ranges from similar to 2 to similar to 18 nm in the sequence SiO2 < MgO < Nb2O5 < TiN. In addition, the substrate type influences strongly the vertical film constituent distribution, resulting in a homogeneous metal constituent distribution for the films grown on the SiO2 and MgO substrates while causing the metal segregation at the film surface for the films grown on the Nb2O5 and TiN substrates. The results strongly suggest that the metal diffusivity, not that of carbon, is the limiting factor determining the film structure. The results are consistent with the nucleation and growth mechanism, with the repeated nucleation events being correlated with the preceding film morphology, rather than that of spinodal decomposition. Furthermore, the findings suggest that a controlled growth of encapsulated nanoparticles may be achieved with an ordinary cosputtering technique by changing the substrate type or state or by applying a variety of prepatterning recipes.