Epitaxial growth of maghemite (001) and (111) on platinum: An ab-initio study

Abstract

In this study, maghemite, the second most stable iron oxide, has been investigated using a DFT+U approach. The relative stability of the different surface terminations from the (001) and (111) planes are discussed, allowing the discrimination of preferred terminations among oxygen vs. iron, with octahedral or tetrahedral cations sites, etc. To move towards epitaxial growth of maghemite on a Pt substrate, the strain effect induced by lattice mismatch is then considered, first for isolated maghemite, then when grown on the substrate. Among bare surfaces, (001) terminations are more stable than (111) ones, strain effect significantly destabilizes (001) in contrast with (111), resulting in a change in stability. Moreover, the lower formation energy indicates that the growth of the (111) surface will be favored over the one of the (001) on the Pt substrate due to numerous Pt-O interactions. Finally, various electronic properties such as bond-lengths, bonding, charges, and density of states are analyzed to understand the nature and stability of the surfaces. For surfaces, bandgaps are smaller than bulk, with a higher deviation for (001) than for (111) surfaces.