Depth-dependent and surface damages in MgAl2O4 and MgO irradiated with energetic iodine ions

Samples of polycrystalline ceramics of MgAl2O4 irradiated at the ambient temperature with 85 MeV I7+ iodine ions to doses up to 1×1019 m−2 is observed to be amorphized up to depths around 6 μm from the ion-incident surface for a dose of 1.2×1019 m−2, through a cross-sectional transmission electron microscopy. A step height of 1 μm is formed across the border between the masked and irradiated regions of the surface. The height of the step is observed to increase sharply from the irradiated area towards the edge at the border, forming a peak as tall as 1.5 μm. A glossy, silver-gray film with a thickness less than 0.1 μm is unexpectedly observed to have formed on the surface of samples of MgAl2O4 and MgO, in about 3.5 years aging after the irradiation to 1.2×1019 m−2, being left untouched in the air. The film is easily peeled off along grain boundaries and found to be amorphous from the electron diffraction pattern. The film from MgAl2O4 sample contains Al, Mg and Si. Silicon, which is one of impurities, is found to be enriched noticeably at the surface.