Although atom probe tomography (APT) reconstructions do not directly influence the local elemental analysis, any structural inferences from APT volumes demand an accurate reconstruction of the point cloud. Current reconstruction methods are based on simplistic geometrical assumptions that are actually never fulfilled in reality. These algorithms are developed to take into account the evolution of the specimen’s tip radius of curvature during the analysis, either by making use of the applied voltage and / or directly from the specimen geometry derived from ex-situ observations. The conventional reconstruction algorithms makes use of parameters such as the initial tip radius (R0), the cone angle (α), the image compression factor (ξ), the field reduction factor (kf), the evaporation ﬁeld (Fe) and the detection efficiency (η). To obtain an accurate reconstruction it is necessary to precisely calibrate these reconstruction parameters.
The aim of this work is to achieve automated calibration of reconstruction parameters from electron microscopy (EM) images of the APT specimens. The key principle being a 2D cross-correlation of microstructural features observed both in APT reconstructions and in the corresponding electron microscopy image. As the electron microscopy gives a projected image of the inner part of the specimen, we propose to compare these images with 2D projection images created from the APT volume. A large number of 2D projection images are obtained for a range of reconstructed APT volumes at different rotation angles about the main specimen axis. The best APT reconstruction parameters are selected based on a maximization of the correlation between the EM and the APT. We also used this automated calibration method to compare reconstructions employing voltage and cone angle algorithms.