Impact of Extreme Electrical Fields on Charge Density Distributions in Alloys

The purpose of this work is to identify the field evaporation mechanism associated with charge density distribution under extreme fields, linking atom probe tomography (APT) experiments with density functional theory (DFT) modeling. DFT is used to model a materials surface bonding, which affects the evaporation field of the surface atoms under high electric fields. We show how the evaporation field of atoms is related to the charge density by comparing the directionality and localization of the electrons with the evaporation of single ions versus dimers. This evaporation mechanism is important for the reconstruction of APT data, which is partially dependent on the input evaporation fields of the atoms. In $L1_{2}-Al_{3}Sc$, $Al-Al$ surface atoms are more likely to evaporate as dimers than $Al-Sc$ surface atoms. We find that this is due to $Al-Al$ having a shared charge density, while $Al-Sc$ has an increased density localized around the $Sc$ atom. Further, the role of subsurface layers on the evaporation physics of the surface atoms as a function of charge density is considered. Beyond the practical considerations of improving reconstruction of APT data, this work provides an approach for design of surface chemistry for extreme environments.

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