  In atom probe tomography (APT), accurate reconstruction of the spatial
positions of field evaporated ions from measured detector patterns depends upon
a correct understanding of the dynamic tip shape evolution and evaporation laws
of component atoms. Artifacts in APT reconstructions of heterogeneous materials
can be attributed to the assumption of homogeneous evaporation of all the
elements in the material in addition to the assumption of a steady state
hemispherical dynamic tip shape evolution. A level set method based specimen
shape evolution model is developed in this study to simulate the evaporation of
synthetic layered-structured APT tips. The simulation results of the shape
evolution by the level set model qualitatively agree with the finite element
method and the literature data using the finite difference method. The
asymmetric evolving shape predicted by the level set model demonstrates the
complex evaporation behavior of heterogeneous tip and the interface curvature
can potentially lead to the artifacts in the APT reconstruction of such
materials. Compared with other APT simulation methods, the new method provides
smoother interface representation with the aid of the intrinsic sub-grid
accuracy. Two evaporation models (linear and exponential evaporation laws) are
implemented in the level set simulations and the effect of evaporation laws on
the tip shape evolution is also presented.
