Propagation of nanoscale ripples on ion-irradiated surfaces

The irradiation of glass surfaces by 30 keV Ga+ ions under oblique incidence angles results in the development of “ripple”-like nanostructures. The evolution of these ripples was monitored in situ in the ion fluence range from 3 × 1016 to 1 × 1018 Ga+ ions/cm2 using a focused ion beam system which incorporates a scanning electron microscope. With increasing fluence, the ripples were found to propagate across the surface in a direction which coincides with the projection of the ion beam’s incident direction onto the surface. The propagation velocity was determined to be constant over the investigated fluence regime and to amount to 77 ± 1.8 nm/1017 ions cm−2. Ex situ atomic force microscopy was employed to derive the post-mortem wavelength and amplitude of the ripple structures and their values were 450 ± 43 and 127 ± 23 nm, respectively.