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O: Fachverband Oberflächenphysik
O 6: Oxides and Insulator Surfaces: Structure, Epitaxy and Growth
O 6.2: Vortrag
Montag, 17. März 2025, 10:45–11:00, H8
Chromium Oxide Thin Films on Pt(111): An STM and DFT Excursion through the Phase Diagram — •Ghada Missaoui1, Piotr Igor Wemhoff1, 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
Formation of chromium oxide thin films on Pt(111) was investigated by electron diffraction and low-temperature scanning tunneling microscopy. Depending on the nominal Cr coverage and the oxygen-chemical potential used for preparation, two oxide phases were identified. A (√3×√3)R30∘ phase emerges at sub-monolayer Cr exposure and O-rich oxidation conditions, while a (2x2) phase develops at higher coverage and after a vacuum-annealing step. For both phases, the atomic nature of cationic and anionic sub-lattices and the chemical composition were determined in detail. Guided by this experimental input, a global structure optimization was performed by genetic algorithms and key configurations were refined by density functional theory calculations afterwards. For the (√3×√3)R30∘ phase, good agreement was revealed for a Cr3O6 trilayer, comprising a mixture of Cr3+ and Cr4+ ions in the central cationic plane. The (2x2) phase matches well a Cr6O11 film, in which an O-Cr-O trilayer is capped by a Cr2O3 honeycomb plane. The identified configurations not only reproduce structure and symmetry deduced from experiment but also have the most favorable energetics at the employed oxygen chemical potential.
Keywords: Chromium oxide; Thin film; Surface structure; Scanning tunneling microscopy; Density functional theory