We have studied ion beam surface modifications on titanium dioxide (TiO₂) single crystals and polycrystalline thin films following implantation with 30 keV Ga⁺ ions using a focused ion beam (FIB). AFM and SEM analyses were used to investigate the evolution of surface morphology and surface recession as a function of ion fluence in the range of 10¹⁴-10¹⁷ ions/cm².

For ion fluences higher than 10¹⁵ ions/cm², the surface recession behaviour is influenced by the surface structure. For the smooth single crystals the initial recession rate is slightly lower than the steady state value, which is reached for fluences above 6x10¹⁶ ions/cm². However, for the thin films, having a surface with grooves and ridges, the initial recession rate is much faster than the steady state value, reached at approximately the same fluence as for the smooth single crystals.  In the thin film case the surface also undergoes pronounced morphological changes with ion fluence. It loses its grainy appearance and becomes smooth on the nanometre scale. The steady state recession rate is not reached until after this smoothening process. The experimental data on surface recession rates are compared with TRIDYN-based numerical simulations. Various effects which might be a cause of the observed differences will be discussed

For ion fluences lower than 10¹⁵ ions/cm², swelling of the irradiated areas occurs on the single crystal. SEM and AFM show that these areas become W-shaped at 4x10¹⁴ ions/cm². We interpret this as the fluence at which ion-induced removal of material becomes dominant over swelling.