Mapping energetics of atom probe evaporation events through first principles calculations

The purpose of this work is to use atomistic modeling to determine accurate inputs into the atom probe tomography (APT) reconstruction process. One of these inputs is evaporation held; however, a challenge occurs because single ions and dimers have different evaporation fields. We have calculated the evaporation held of Al and Sc ions and Al-Al and Al-Sc dimers from an L1(2)-Al3Sc surface using ab initio calculations and with a high electric held applied to the surface. The evaporation held is defined as the electric held at which the energy barrier size is calculated as zero, corresponding to the minimum held that atoms horn the surface can break their bonds and evaporate from the surface. The evaporation field of the surface atoms are ranked from least to greatest as: Al-Al dimer, Al ion, Sc ion, and Al-Sc dimer. The first principles results were compared with experimental data in the form of an ion evaporation map, which maps multi-ion evaporations. From the ion evaporation map of L12-Al3Sc, we extract relative evaporation fields and identify that an Al-Al dimer has a lower evaporation held than an Al-Sc (timer. Additionally, comparatively an Al-Al surface dimer is more likely to evaporate as a dimer, while an Al-Sc surface (timer is more likely to evaporate as single ions. These conclusions from the experiment agree with the ab initio calculations, validating the use of this approach for modeling APT energetics. (C) 2013 Elsevier B.V. All rights reserved.