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O: Fachverband Oberflächenphysik
O 55: Oxide and insulator surfaces: Structure, epitaxy and growth II
O 55.2: Vortrag
Mittwoch, 11. März 2026, 10:45–11:00, HSZ/0204
How coordination preferences dictate the mixing behavior of 2D oxide films: Fe/Cr spinel-type oxides on Pt(111) — Ghada Missaoui1, Claudine Noguera2, Jacek Goniakowski2, and •Niklas Nilius1 — 1Carl von Ossietzky University, Institute of Physics, D-26111 Oldenburg, Germany — 2CNRS-Sorbonne University, UMR 7588, INSP, F-75005 Paris, France
Fe/Cr mixed oxide films, prepared by reactive co-deposition of both elements on Pt(111), are analyzed by STM and DFT calculations. The mixed oxide grows into bi- (h=0.5 nm) and tri-stack films (h=0.7 nm) terminated either by open (2x2) (bi-stacks) or dense (1x1) atomic patterns (bi- and tri-stacks). The former is identified as Cr6O11 phase composed of an interfacial O-Cr-O trilayer and a Cr2O3 honeycomb plane. The latter develops upon substituting Fe into the surface plane, where it forms a hexagonally dense-packed Fe-O bi-layer. Two polymorphs with different mixing enthalpy occur as a function of mixing ratio. At high Fe content, X6O9-type bi-stacks prevail (X = Fe,Cr) with Cr preferentially accumulating in octahedral sites at the interface and Fe filling tetrahedral sites at the surface. At low Fe content, the Cr interface stack reconstructs to stabilize more oxygen, while the surface stack remains Fe-dominated. The resulting film has X6O11 stoichiometry and deviates from the X6O9 structure not only by the oxygen content but also by its workfunction and surface buckling, in agreement with STM data. The observed cationic stacking, with alternating Fe and Cr planes resembles the bulk ilmenite structure (FeCrO3).
Keywords: Oxide; mixing; Cr; Fe; coordination