Transmission electron microscopy study of ion-beam-induced amorphization of Ca2La8(SiO4)(6)O-2

In-situ transmission electron microscopy (TEM) and high-resolution transmis sion electron microscopy (HRTEM) were used to study ion-beam-induced amorph ization of Ca2La8(SiO4)(6)O-2, a silicate ceramic with the apatite structur e. In-situ TEM was performed during irradiation with 1 MeVAr+, 1.5 MeV Krand 1.5MeV Xe+ ions over the temperature range from 20 to 773 K to determin e the ion dose required for complete amorphization of the crystal (critical amorphization dose D-c). D-c increased with increasing irradiation tempera ture and decreased with increasing ion mass. Samples irradiated with Ar+, K r+ 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 subcasca de 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 res ult of the subcascade overlap in projection. At higher temperatures. the ob served amorphous domains are smaller indicating thermally activated epitaxi al recovery at the amorphous-crystalline interface. The amorphous domains a re larger in size after irradiation with ions of higher mass. The results a re consistent with the D-c-temperature curves determined by in-sills TEM an d suggest an amorphization mechanism through direct subcascade impact or su bcascade overlapping. Growth of the surface amorphous layer with increasing ion dose and the effects of electron beam on damage recovery were also not ed. In addition; cross-sectional TEM, computer simulation of damage product ion and digital image processing have also been performed to understand bet ter the plan-view HRTEM observations.