Regensburg 2025 – scientific programme
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O: Fachverband Oberflächenphysik
O 6: Oxides and Insulator Surfaces: Structure, Epitaxy and Growth
O 6.7: Talk
Monday, March 17, 2025, 12:00–12:15, H8
The polar spinel MgAl2O4 (001) surface is stabilized by an aluminum-rich reconstruction — •David Kugler1, Andrea Conti1, Johanna I. Hütner1, Soumyajit Rajak2, Matthias Meier1, Nan Jiang2, Florian Mittendorfer1, Michael Schmid1, Ulrike Diebold1, Gareth S. Parkinson1, and Jan Balajka1 — 1Institute of Applied Physics, TU Wien, Vienna, Austria — 2Department of Chemistry, University of Illinois Chicago, USA
The atomic-scale surface structure of spinel oxides is key to understanding their catalytic properties. Magnesium aluminate (MgAl2O4, spinel), which gave this class of materials its name, is a wide-gap insulator and poses considerable challenges for experimental surface structure determination. Noncontact atomic force microscopy (nc-AFM) with a qPlus sensor and a well-defined tip apex allowed us to directly resolve the surface structure with atomic resolution and chemical sensitivity. The MgAl2O4(001) surface adopts a c(2 × 4) reconstruction accompanied by an increase of the Al/Mg ratio, as detected by x-ray photoelectron spectroscopy (XPS). The reconstructed surface is enriched in aluminum and contains ordered pairs of octahedrally coordinated magnesium atoms replacing their tetrahedral bulk sites. This charge redistribution within the reconstructed surface layer stabilizes the otherwise polar MgAl2O4(001) termination. The proposed surface reconstruction is similar to those observed on other spinel oxides, such as Fe3O4(001) and Mn3O4(001), suggesting a universal mechanism for compensating the polarity of spinel (001) surfaces.
Keywords: spinel; oxide; surface; reconstruction; afm