Pattern transitions on Ge surfaces during low-energy ion beam erosion

During sputtering of Ge surfaces with Xe + ions at 2 keV ion energy at room temperature, self-organized ripple and dot nanostructures with a mean wavelength below 60 nm emerge as the ion incidence angle is varied. Dots evolving at normal ion incidence pass into ripple patterns with increasing ion incidence angle. Furthermore, for ion incidence angles above 10 deg to the surface normal a gradual transition from ripples to dots is observed. Guided by the previous existence of ripples these evolving dot patterns show a long range hexagonal ordering extending across the whole sample surface.