  Atom probe tomography (APT) is a 3D analysis technique that offers unique
chemical accuracy and sensitivity with sub-nanometer spatial resolution.
Recently, there is an increasing interest in the application of APT to complex
oxides materials, giving new insight into the relation between local variations
in chemical composition and emergent physical properties. However, in contrast
to the field of metallurgy, where APT is routinely applied to study materials
at the atomic level, complex oxides and their specific field evaporation
mechanisms are much less explored. Here, we perform APT measurements on the
hexagonal manganite ErMnO3 and systematically study the effect of different
experimental parameters on the measured composition and atomic structure. We
demonstrate that both the mass resolving power (MRP) and compositional accuracy
can be improved by increasing the charge-state ratio (CSR) working at low laser
energy (< 5 pJ). Furthermore, we observe a substantial preferential retention
of Er atoms, which is suppressed at higher CSRs. We explain our findings based
on fundamental field evaporation concepts, expanding the knowledge about the
impact of key experimental parameters and the field evaporation process in
complex oxides in general.
