Structural effects in UO₂ thin films irradiated with U ions

Highlights: • Quantitative characterisation of radiation damage by kernel average misorientation. • UO₂ (1 1 1) plane showed higher irradiation tolerance than (1 1 0) plane. • UO₂ film-YSZ substrate interface is stable under low fluence irradiation. • (0 0 1), (1 1 0), (1 1 1) single crystal UO₂ thin films on YSZ substrates are expected. - Abstract: This work presents the results of a detailed structural characterisation of irradiated and unirradiated single crystal thin films of UO₂. Thin films of UO₂ were produced by reactive magnetron sputtering onto (0 0 1), (1 1 0) and (1 1 1) single crystal yttria-stabilised zirconia (YSZ) substrates. Half of the samples were irradiated with 110 MeV ²³⁸U³¹⁺ ions to fluences of 5 × 10¹⁰, 5 × 10¹¹ and 5 × 10¹² ions/cm² to induce radiation damage, with the remainder kept for reference measurements. It was observed that as-produced UO₂ films adopted the crystallographic orientation of their YSZ substrates. The irradiation fluences used in this study however, were not sufficient to cause any permanent change in the crystalline nature of UO₂. It has been demonstrated that the effect of epitaxial re-crystallisation of the induced radiation damage can be quantified in terms of kernel average misorientation (KAM) and different crystallographic orientations of UO₂ respond differently to ion irradiation.