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Atomistic simulations contain the position and type of all atoms, therefore, an analysis of density, size, and composition applied directly to simulated results cannot be directly compared with APT results. The data (atomic positions and types) should at least be treated similarly to what has been done in this work (Methodology section) in terms of lateral resolu- tion and detection efficiency, so as to mimic the effect of APT. Indications about the best way to do so, depending on the APT technique, should be given by experimentalists. Moreover, the limitations of the analysis methods (e.g., the overestimation of the size of small clusters using MSM, or its underestimation using IPM) should be used as a criterion to judge the comparison between simulation and experiments. Ideally, precise protocols should be deduced on how to treat simulation data, in order for the comparison with APT experiments to be performed on equal footing.
CONCLUSIONS
The aim of this work was to provide insight into the limita- tions and uncertainties associated with reported APT data, which would be useful both to the atom probe community and also to modelers. Simulations of microstructural data, which take into account estimates of common experimental artifacts associated with APT (reduced detection efficiency, positioning uncertainty, and local magnification effects), were performed. A simple method for modeling local magnification effects was proposed and it was shown to be effective in accounting for the observed increased density of atoms in solute clusters in experimental data. The resulting simulated microstructures have been
analyzed using two algorithms, the MSM and the IPM. The results show that for the identification of clusters ≳1 nm, both MSM and IPM work extremely well, provided that the parameters are carefully chosen. Detection of clusters with a radius of ~0.5nm is possible, but care is needed interpreting quoted compositions. Further work on core shell structured clusters is underway and will provide additional insight on the capability of methodologies used to characterize clusters observed in atom probe data. Recommendations will be developed which, if adopted,
will enable inter-comparison of results between different labs, enabling trends in microstructural development to be more readily observed, and provide information that can be directly used to support calibration of models from the modeling community.
ACKNOWLEDGMENTS
This work was part-funded under the EU FP7 NUGENIA+ project. Grant number 604965.
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