Article Dans Une Revue Journal of Physical Chemistry C Année : 2024

Chromium Oxide Thin Films on Pt(111): An STM and DFT Excursion through the Phase Diagram

Résumé

The formation of chromium oxide thin films on Pt(111) was investigated by electron diffraction, X-ray photoelectron spectroscopy, and low-temperature scanning tunneling microscopy. Depending on the nominal Cr coverage and the oxygen chemical potential during preparation, two distinct oxide phases were identified. A (√3 × √3)R30° phase emerges at submonolayer Cr exposure and O-rich oxidation conditions, while a (2 × 2) phase develops at higher coverage and after a vacuum-annealing step. For both phases, the atomic nature of cationic and anionic sublattices and the chemical composition were determined in detail. Guided by this experimental input, a comprehensive global structure optimization was performed by genetic algorithms, and key configurations were refined by density functional theory calculations in a second step. 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 (2 × 2) phase matches well with a Cr6O11 film, in which an O–Cr–O trilayer is capped by a Cr2O3 honeycomb plane. The identified configurations not only reproduce the structure and symmetry deduced from experiments but also have the most favorable energetics at the employed oxygen chemical potential. Our work delivers reliable insights into the atomic nature of the two main CrOx phases on Pt(111) and clears up the conflicting models found in the literature.

Dates et versions

hal-04727500 , version 1 (09-10-2024)

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Ghada Missaoui, Piotr Igor Wemhoff, Claudine Noguera, Jacek Goniakowski, Niklas Nilius. Chromium Oxide Thin Films on Pt(111): An STM and DFT Excursion through the Phase Diagram. Journal of Physical Chemistry C, 2024, 128 (30), pp.12726-12734. ⟨10.1021/acs.jpcc.4c03483⟩. ⟨hal-04727500⟩
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