Ion-guided microstructure evolution of carbon-nickel nanocomposite films during ion beam assisted deposition: 3D sculpting at the nanoscale

Ion assistance during film growth provides unique opportunities to influence the microstructure due to energy transfer and imposed directionality. For this study, the carbon:nickel system was chosen as model system. The growth of C:Ni nanocomposites without ion assistance is controlled by the phase separation under kinetic constraints of surface and volume diffusion and by the film growth rate. A systematic study of ion irradiation as a pure energy and momentum transfer agent in the context of surface diffusion assisted phase separations is, however, lacking. Here the influence of low energy (50-140 eV) assisting Ar+ ion irradiation on the morphology of C:Ni (~ 5 at.% Ni to ~ 50 at.% Ni) thin films will be reported. Two types of ordered nanostructures are identified and characterized: i) tilted columns and ii) compositionally modulated ripples, which are transferred into a periodic three-dimensional nanoparticle array. For i), the tilt angle and diameter of the nanocolumns are controlled by the deposition parameters. Complex secondary structures like chevrons with partially epitaxial junctions are grown by sequential deposition. For a given composition of the depositing flux, the transition from the columnar growth to the 3D pattern formation regime as a function of the assisting ion energy is demonstrated. The effects of the metal content and the assisting ion current on the self-organized 3D patterns and surface periodicity are studied. The observed microstructures evolution is explained by ion-induced effects.