On the instrument-dependent appearance of ion dissociation events in atom probe tomography mass spectra.

The successful application of atom probe tomography (APT) relies on the accurate interpretation of the mass spectrum (i.e.m/z histogram) from a sample. Some materials yield mass spectra that are amenable to a straightforward peak assignment/ranging, however, there are many materials that produce mass spectra with features that defy simple interpretation. One such example is GaO which yields mass spectra containing several broad and difficult to interpret features. Herein, we study the GaO→ O+ Ga dissociation and we explain how this dissociation process gives rise to broad and previously unassigned features in the mass spectrum. Trajectory simulations are performed for the dissociation reaction utilizing realistic electrostatic models and compared to experiments using commercially available straight flight and reflectron based local electrode (LE) APT instruments. It is shown that the appearance of these features is strongly dependent on the specific design of the time-of-flight (ToF) mass analyzer. We explore how various experimental parameters can affect the appearance of the dissociation process in the one-dimensional (1D) mass spectrum and in the two-dimensional (2D) correlation histogram. While the focus of this work is on a particular dissociation process related to GaO, the understanding gained in the course of these simulations and experiments should be applicable to the interpretation of dissociation processes in other materials.