Full-Dynamics Field Evaporation Simulation: Overcoming Limitations of Transition State Theory for Atom Probe Tomography

In atom probe tomography (APT), individual atoms or molecules are field-evaporated by an intense electric field from the surface of a needle-shape specimen. Via reconstruction of a three-dimensional distribution of atoms, both positions and chemical identities of the atoms in the specimen can be resolved. However, due to the destructive nature of the field evaporation process, the verification of reconstruction results and quantification of their uncertainty are difficult and necessitate atomic-scale forward modeling, where each atom can be traced.

Previous atomic-scale modeling of field evaporation in APT has implicitly relied on harmonic transition state theory (TST). However, TST is limited to predicting the rate of transition between states and fails to describe the underlying dynamics. Consequently, these models introduce ad-hoc assumptions and many distinct features observed in experiments, arising from the full dynamics of the atoms, cannot be reproduced or explained truthfully.

In this talk, I will introduce the full dynamics field evaporation simulation approach "TAPSim-MD", which employs molecular dynamics (MD) with appropriate acceleration algorithms to overcome the limitations of TST in describing field evaporation. I will demonstrate the importance of involving full dynamics for the example of simulating enhanced zone lines in field evaporation maps, which are dynamic features beyond the capabilities of TST-based models. I will also talk about simulations of GP-zones in Al-Cu alloys as an example to show the inherent inaccuracies of APT in resolving atomic positions and discuss the effect of interatomic potentials on such simulations.