Three-Dimensional Tomographic Analyses of CeO₂ Nanoparticles

A detailed morphological and structural analysis of CeO₂ nanoparticles has been performed using electron tomography in scanning transmission mode in high angle annular dark field. The nanoparticles have been prepared through a solvothermal synthesis assisted by microwave heating. An adequate choice of the synthesis parameters leads to particles with various well-defined morphologies: cubes, octahedrons, and nanorods. In the case of cubic CeO₂ nanoparticles, the three-dimensional analysis allowed us to precisely calculate the type and the proportion of the minor facets exposed at the nanoparticle surface. For the CeO₂ nanoparticles with an octahedron shape, it has been demonstrated that the ambiguous interpretation of the objects giving triangular views in classical transmission electron microscopy can be prevented; furthermore, precise assignments of their external shape, surface crystallography, and type of minor facets were realized. In the case of nanorods, it was shown that the external shape and the transversal symmetry are strongly dependent on the nanorod sizes. The presence of a well-defined porosity inside the rods was also evidenced thanks to the ability of the electron tomography to solve the internal structure of a nano-object.