Surface reconstruction of the polar spinel MgAl₂O₄(001) surface

Abstract

The atomic-scale surface structure governs the surface chemistry of materials. Magnesium aluminate (MgAl2O4) spinel, a wide-gap insulator, poses considerable challenges for experimental surface characterization. Using noncontact atomic force microscopy (nc-AFM), we resolve the atomic structure of the MgAl2O4(001) surface. The surface adopts a c(2×4) reconstruction accompanied by altered surface stoichiometry. The reconstructed surface is enriched in aluminum and contains ordered pairs of octahedrally coordinated Mg atoms that, in bulk, occupy tetrahedral sites. This cation redistribution stabilizes the otherwise polar MgAl2O4(001) termination. The resulting structure closely resembles reconstructions observed on other spinel oxides, suggesting a common mechanism for polarity compensation across the spinel group.