Atomistic structure of oxide nanoparticles supported on an oxide substrate

The atomistic structures of SrO (15x15x2.2 nm), CaO (14x14x2 nm), and MgO (12x12x2 nm) nanoparticles, supported on BaO(001) and synthesized using a simulated amorphization and recrystallization strategy, are presented. The SrO and CaO exhibit cubic slab morphologies in contrast to the MgO nanoparticle, which comprises various misaligned interconnecting crystallites. The lattice misfit was found to have a profound influence on the structure of the nanoparticles. The SrO nanoparticle (-7% misfit) was found to lie coherent with respect to the substrate across the entire area covered by the SrO. Conversely, only small regions of the CaO were found to be coherent with the BaO substrate (-15% misfit), with screw-edge dislocations located at regions where the ions became misaligned. The MgO nanoparticle (-31% misfit) exhibited no regions of coherence with respect to the underlying BaO substrate. Defects (vacancies and substitutionals) and defect clusters including voids were also identified for each system and act to help reduce locally the lattice misfit thereby enhancing the stability. Specifically, the results indicate that as the lattice misfit associated with the system increases, so the interfacial layer of the substrate becomes more defective. Arguments, based on the results of the study, are presented, which suggest that the area of the nanoparticle in contact with the substrate is linked with the critical thickness to dislocation evolution for a particular system. That the limitations of periodic boundary conditions can be eliminated when simulating nanoparticles compared with thin films, which cover completely the substrate material, is discussed.