Irradiation effects in an HfO2/MgO/HfO2 tri-layer structure induced by 10 MeV Au ions

In this report, we present radiation damage effects in a thin film, tri-layer structure, HfO2/MgO/HfO2. Irradiations were performed with 10 MeV Au ions in a recently developed medium energy ion irradiation facility at Los Alamos National Laboratory, which is described in this paper. Energy deposition by 10 MeV Au ions corresponds to a mixed regime, wherein electronic and nuclear stopping contribute to radiation damage. In this study, we investigated modifications of both surface and bulk properties in order to assess the structural stability of our oxide tri-layers under the severe irradiation conditions employed here. The most dramatic structural changes were observed to occur on the surfaces of the tri-layer samples. Surface features consisted of large craters and spires. The dimensions of these craters and spires exceed those of the individual ion tracks by almost three orders of magnitude. As for the bulk tri-layer structure, our conclusions are that this structure is stable in terms of: (i) resistance to amorphization; (ii) resistance to compositional mixing and (iii) resistance to pronounced nucleation and growth of extended defects. The main effect observed in the tri-layer structure was the transformation of the first HfO2 layer from a monoclinic to either a tetragonal or cubic form of HfO2.