Transmission electron microscopy study of ion-beaminduced amorphization of Ca2La8(SiO4)6O2

In-situ transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) were used to study ion-beam-induced amorphization of Ca2La8(SiO4)6O2, a silicate ceramic with the apatite structure. In-situ TEM was performed during irradiation with 1 MeV Ar+, 1.5 MeV Kr+ and 1.5 MeV Xe+ ions over the temperature range from 20 to 773 K to determine the ion dose required for complete amorphization of the crystal (critical amorphization dose D c). D c increased with increasing irradiation temperature and decreased with increasing ion mass. Samples irradiated with Ar+, Kr+ and Xe+ ions to various doses were used in a detailed HRTEM study of the amorphization process. The residual irradiation damage after low ion doses appeared as nanometre scale amorphous domains. The images of these domains are extremely sensitive to the sample thickness. Small domains of subcascade size were found only at the very thin edge of the sample at lower doses. In thicker regions, amorphous domains appear after higher doses as the result of the subcascade overlap in projection. At higher temperatures, the observed amorphous domains are smaller indicating thermally activated epitaxial recovery at the amorphous-crystalline interface. The amorphous domains are larger in size after irradiation with ions of higher mass. The results are consistent with the D c-temperature curves determined by in-situ TEM and suggest an amorphization mechanism through direct subcascade impact or subcascade overlapping. Growth of the surface amorphous layer with increasing ion dose and the effects of electron beam on damage recovery were also noted. In addition, cross-sectional TEM, computer simulation of damage production and digital image processing have also been performed to understand better the plan-view HRTEM observations.