Focused ion beam induced swelling in MgO(0 0 1)

The interplay between swelling and milling phenomena in determining the morphology of Focused Ion Beam (FIB) -processed MgO(0 0 1) was investigated by atomic force microscopy. At the early stages of ion irradiation, before milling erosion is observed, MgO shows a relevant swelling behaviour with protrusion of the bombarded areas up to 6 nm for a dose of 5 × 1016 ions cm−2. The effect is mainly ascribed to subsurface defect accumulation, while the low Ga ions concentration, as measured by in-depth Auger analysis, seems to exclude a contribution from ion implantation. In order to explain and control the morphology of Fe/NiO FIB patterned sub-micron structures on MgO substrates, we have also investigated FIB effects on Fe(0 0 1) and NiO(0 0 1) single crystals. Absent or negligible swelling has been observed on these materials.