Control of surface ripple amplitude in ion beam sputtered polycrystalline cobalt films

We have grown both polycrystalline and partially textured cobalt films by magnetron sputter deposition in the range of thickness (50–200 nm). Kinetic roughening of the growing film leads to a controlled rms surface roughness values (1–6 nm) increasing with the as-grown film thickness. Ion erosion of a low energy 1 keV Ar+ beam at glancing incidence (80°) on the cobalt film changes the surface morphology to a ripple pattern of nanometric wavelength. The wavelength evolution at relatively low fluency is strongly dependent on the initial surface topography (a wavelength selection mechanism hereby confirmed in polycrystalline rough surfaces and based on the shadowing instability). At sufficiently large fluency, the ripple wavelength steadily increases on a coarsening regime and does not recall the virgin surface morphology. Remarkably, the use of a rough virgin surface makes the ripple amplitude in the final pattern can be controllably increased without affecting the ripple wavelength.