Towards High Fidelity in Atom Probe Tomography (APT): Through Instrument Design, Crystallography and Reconstruction

Abstract

The primary aim of this thesis was to improve the utility of atom probe tomography (APT) through instrument development, applied crystallographic procedures, and reconstruction. This work represents a unified approach through instrument development, enhanced crystallographic analysis capabilities and improved reconstruction to move toward high-fidelity in APT.

A modern instrument is modified to enable specimen temperatures < 10 K. This new parameter space is explored to develop relationships between temperature and metrics such as spatial and mass resolution, stoichiometry, and evaporated charge-state ratios. Here, the spatial resolution of APT was extended beyond current limitations – enabling the characterisation of crystallography in datasets that typically do not produce crystallographic signals in APT.

Novel methods were developed to elucidate latent crystallographic information in APT datasets. This enhanced visibility of crystallographic information enhances both crystallographic reconstruction methodologies and applied crystallographic analysis techniques. Next, the application of crystallography as a method to characterise grain boundary misorientation was explored. Here, the validity of APT as a crystallographic tool was verified through a correlative study through transmission Kikuchi diffraction (TKD). A metric was developed to define the spatial accuracy of a tomographic reconstruction in APT, with reference to observed crystallography. A new reconstruction technique termed crystallography-mediated reconstruction (CMR) was then developed and compared to current standard reconstruction procedures. Finally, CMR is extended to operate on datasets with limited crystallography. This enabled precise reconstruction procedures to be applied to a greater number of datasets, enabling more precise reconstructions across a wide application space.