Morphological Change in FePt Nanogranular Thin Films Induced by Irradiation with 2.4 MeV Cu²⁺ Ions: Electron Tomography Observation

Abstract

Nanogranular thin films, in which FePt nannoparticles are dispersed in an amorphous 20 nm thick Al₂O₃ layer, were irradiated with 2.4 MeV Cu²⁺ ions up to 5×10¹⁹ ions/m² at room temperature. Electron tomography with a tilt series of bright-field transmission electron microscope images was employed to identify 3-dimensional structural changes due to irradiation. Electron tomography images have clearly revealed that the irradiation with 2.4 MeV Cu²⁺ ions causes anisotropic deformation of FePt nanoparticles with elongation along the direction of ions trajectory and slight shrinkage in the perpendicular directions. Ion-irradiation results in disordering in FePt, but post-irradiation annealing at 923 K for 1 h (3.6 ks) leads to re-ordering without significant coarsening and shape change of FePt particles. It has been demonstrated that electron tomography is a quite useful technique for characterization of shape and dispersion of metallic nanoparticles embedded in an amorphous oxide film.