  We report on atom probe tomography analyses of Pd and Pd@Au nanoparticles
embedded in a Ni matrix and the effects of local evaporation field variations
on the atom probe data. In order to assess the integrity of the reconstructed
atom maps, we performed numerical simulations of the field evaporation
processes and compared the simulated datasets with experimentally acquired
data. The distortions seen in the atom maps for both Pd and Pd@Au nanoparticles
could be mostly ascribed to local variations in chemical composition and
elemental evaporation fields. The evaporation field values for Pd and Ni, taken
from the image hump model and assumed in the simulations, yielded a good
agreement between experimental and simulation results. In contrast, the
evaporation field for Au, as predicted from the image hump model, appeared to
be substantially overestimated and resulted in a large discrepancy between
experiments and simulations.
