Origin of enhanced zone lines in field evaporation maps

JYW Qi and C Oberdorfer and EA Marquis and W Windl, SCRIPTA MATERIALIA, 230, 115406 (2023).

DOI: 10.1016/j.scriptamat.2023.115406

In atom probe tomography (APT), individual atoms are evaporated in high field from a needle shaped specimen. Their impact sequence and positions on a detector along with mass analysis allow 3D reconstruction through a simple projection law. Artifacts in the evaporation map of the detector hits, including enhanced "zone lines" with high atomic impact intensity, impede a truthful reconstruction. Since APT is destructive, simulation is the only approach to explaining the origin of these zone lines, but previous work could not reproduce them. Here, we use a new ab-initio simulation technique adding electrostatic forces to interatomic forces in a molecular-dynamics simulation, and evaporation happens when the electrostatic force overpowers the interatomic force. We show for the canonical example of tungsten that the misalignment of the two forces deviates the launch direction of certain atoms away from the radial direction, giving rise to an accumulation of hit events around zone lines.

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