Tilting column and 3D pattern formation during ion beam assisted growth of carbon:nickel nanocomposite films

Ion assistance provides unique opportunities to influence the microstructure of growing films due to energy and momentum transfer. Here, ion effects on the microstructure of C:Ni nanocomposite thin films grown at RT to 500°C by ion-beam sputtering with assisting oblique incidence angle Ar+ ion beam irradiation (50 – 130 eV) are studied by SEM, (c)AFM, TEM, GISAXS, and TRI3DYN simulations. Two types of ordered metallic nanostructures in an amorphous carbon matrix are identified and characterized: i) tilted parallel columns [1] and ii) rippled, periodic three-dimensional nanoparticle arrays [2]. For the former one, the tilt angle and diameter of the nanocolumns are controlled by the deposition parameters. Ion-enhanced diffusivity and ion-induced surface drift are responsible for the tilted column microstructure. 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 3D pattern is attributed to the transfer of compositionally modulated surface ripples into the bulk of the C:Ni thin film. The essential experimental features are reproduced by three-dimensional binary collision computer simulations. This agreement points to ion-induced preferential displacements as the driving force for the 3D pattern formation.