Regensburg 2025 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 37: Functional and Complex Materials

MM 37.2: Talk

Friday, March 21, 2025, 12:15–12:30, H22

Decoding Molecular Ion Dissociation Effects in Atom Probe Tomography of Iron Oxides — •Shyam Katnagallu¹, SeHo Kim¹, Shalini Bhatt¹, Daniel K Schreiber², Jörg Neugebauer¹, Baptiste Gault¹, and Christoph Freysoldt¹ — ¹Max Planck Institute for Sustainable Materials, Düsseldorf, Germany — ²Energy and Environment Directorate, PNNL, Richland, USA.

To mitigate CO2 emissions, we require efficient carbon-free reduction processes for iron ores. Atom probe tomography (APT) can elucidate the gradual reduction of FexO at the nanometer length scale, but it is hindered by compositional bias. We investigated the changes in the measured composition of FeO, Fe2O3, and Fe3O4 across a range of analysis conditions. However, APT of ionic or covalently bonded materials often results in molecular ions. The metastability of these molecular ions, under an intense electrostatic field, makes them vulnerable to dissociation. These processes can significantly impact the analytical performance of APT. For instance, neutral molecules formed through dissociation may not be detected or may have a time-of-flight no longer associated with their actual mass, leading to their loss from the analysis. To predict possible dissociation reactions of molecular ions, we employed density-functional theory that considered the spin states of the molecules. The energetically favoured reactions were traced onto multi-hit correlation histograms to validate their existence within APT data. These detected reactions were carefully analysed to assess the impact of neutrals resulting from dissociation reactions on the performance of APT for analysing iron oxides.

Keywords: Atom probe tomography; Iron Oxides; Molecular dissosiation; Density functional theory; Correlations