Understanding atom probe's analytical performance for iron oxides using correlation histograms and ab initio calculations

TL;DR

This study investigates how molecular ion dissociation affects atom probe tomography (APT) analysis of iron oxides, combining experimental correlation histograms with ab initio calculations to understand and improve analytical accuracy.

Contribution

It introduces a combined approach using correlation histograms and DFT calculations to analyze molecular ion dissociation in APT of iron oxides, enhancing understanding of its impact on analysis.

Findings

Dissociation reactions are identified and confirmed in experiments.

Neutral species from dissociation can lead to detection loss or misinterpretation.

The approach improves understanding of APT performance for iron oxides.

Abstract

Field evaporation from ionic or covalently bonded materials often leads to the emission of molecular ions. The metastability of these molecular ions, particularly under the influence of the intense electrostatic field (1010 Vm-1), makes them prone to dissociation with or without an exchange of energy amongst them. These processes can affect the analytical performance of atom probe tomography (APT). For instance, neutral species formed through dissociation may not be detected at all or with a time of flight no longer related to their mass, causing their loss from the analysis. Here, we evaluated the changes in the measured composition of FeO, Fe2O3 and Fe3O4 across a wide range of analysis conditions. Possible dissociation reactions are predicted by density-functional theory (DFT) calculations considering the spin states of the molecules. The energetically favoured reactions are traced on to the multi-hit ion correlation histograms, to confirm their existence within experiments, using an automated Python-based routine. The detected reactions are carefully analysed to reflect upon the influence of these neutrals from dissociation reactions on the performance of APT for analysing iron oxides.