LAUSR

The functionality of nuclear structural materials, sensors, and microelectronics in harsh environments such as radiation relies on understanding defect generation and evolution processes in oxide layers. The initial radiation response of epitaxial thin films of Fe3O4(111), Cr2O3(0001), and Fe3O4(111)/Cr2O3(0001) heterostructures deposited on Al2O3(0001) by oxygen‐assisted molecular beam epitaxy and irradiated with 200 keV He+ is characterized. X‐ray diffraction and X‐ray absorption near edge spectroscopy showed that the Cr2O3 layers underwent significant lattice expansion and disordering under irradiation, whereas the Fe3O4 layers do not exhibit noticeable changes. In contrast, positron annihilation spectroscopy revealed an evolution of cation vacancy point defects in the Fe3O4 layers into larger vacancy clusters with increasing irradiation, while the cation vacancies in Cr2O3 remained primarily as single vacancies and small clusters. The results suggest that the Fe3O4 lattice can utilize the free volume of the larger vacancy clusters to relax but the small vacancies in the Cr2O3 lattice do not facilitate relaxation. Comparing defect concentrations in the single layer films versus the heterostructure suggests that point defects may cross the interface from Fe3O4 into Cr2O3. Together, these results enhance the understanding of the initial defect evolution mechanisms in oxide layers in harsh irradiation environments.