The Role of Laser Pulse Energy on Data Quality and Reconstruction of Olivine Atom Probe Tomography Data

The study of the structure and geochemistry of olivine crystal defects is important but difficult because of their nanometer size and the analytical limitations of most techniques. Laser-assisted atom probe tomography (APT) is capable of sub-nanometer resolution, quantitative geochemical analysis and 3D reconstruction of olivine defects, but optimal analytical conditions and data reconstruction strategies have not been sufficiently studied. Here, we investigate the effect of different laser pulse energy (LPE) and crystal orientations on the quality and reconstruction parameters of APT data using specimens from two San Carlos olivine grains. Our findings show that increased LPE reduces the background noise, percentage of multiple hit events, and applied electric field, as shown by the Mg2+/Mg+ ratio, but increases the peak tails. The major element compositions show inaccuracies under all LPEs but exhibit higher consistency for higher LPEs. We determine that a LPE of 150pJ is the best compromise for optimal data quality in olivine. Using scanning electron microscopy imaging before and after APT analyses, we suggest that the Mg2+/Mg+ ratio can be used as a guide to estimate the electric field parameter and results in more accurate reconstructions.