Direct Measurement of the Crystallographically Sensitive Atomic Termination of Nanophase Cerium Dioxide

Aberration-corrected high-resolution transmission electron microscopy (HRTEM) was used to study the surface termination of nanophase cerium dioxide particles. Application of computational exit-wave restoration and comparison with simulations confirmed the {111} surfaces to have an oxygen termination, and while structurally unstable at room temperature the {100} facets exhibited a metal terminating plane. This crystallographically sensitive atomic termination was found to be maintained under the reducing conditions of the electron beam. During electron beam irradiation, Electron Energy Loss Spectroscopy (EELS) analysis revealed that a change from Ce4+ to Ce3+ originates at the particle surface, and gradually extends into the particle as reduction continues. The results aid understanding of the oxygen buffering mechanism in cerium dioxide, and provide valuable insight into the use of CeO2 nanoparticles in catalysis.