Introducing a Crystallography-Mediated Reconstruction (CMR) Approach to Atom Probe Tomography

Abstract

Current approaches to reconstruction in atom probe tomography produce results that exhibit substantial distortions throughout the analysis depth. This is largely because of the need to apply a multitude of assumptions when estimating the evolution of the tip shape, and other pseudo-empirical reconstruction factors, which vary both across the face of the tip and throughout the analysis depth. We introduce a new crystallography-mediated reconstruction to improve the spatial accuracy and dramatically reduce these in-depth variations. To achieve this, we developed a barycentric transform to directly relate atomic positions in detector space to real space. This is mediated by novel crystallographic analysis techniques, including: (1) calculating the orientation of a crystal directly from the field evaporation map, (2) tracking pole locations throughout the evaporation sequence, and (3) accounting for the evolving tip radius in a manner that removes the dependence on the geometric field factor. By improving the in-depth spatial accuracy of the atom probe reconstruction, a greater accuracy of the atomic neighborhood relationships is available. This is critical in modern materials science and engineering, where an understanding of the solid solution architecture, precipitate dispersions, and descriptions of the interfaces between phases or grains are key inputs to microstructure–property relationships.

Recent Developments in APT Analysis Automation and Support for User-Defined Custom Analysis Procedures in IVAS 4

“…IVAS also serves a critical purpose in the conversion of raw experimental file-types (RHIT and HITS), to user-readable file-types containing reconstructed APT data (POS and EPOS). It is this data that underpins and informs a very active area of research in the development of novel computational analysis procedures to extend the capabilities of APT [1][2][3][4] and enable new understandings in materials science [5].…”

“…Requiring a reconstruction protocol [1] and spatial distribution map analysis [4] performed with user-defined scripts executed within the custom analysis environment. 2.…”

“…A systematic analysis of the effect of acquisition conditions in both straight flight-path and reflectron LEAP ® instruments on the resolution of crystallographic planes in Al-based samples. Requiring a reconstruction protocol [1] and spatial distribution map analysis [4] performed with user-defined scripts executed within the custom analysis environment. 2.…”

Expanding the Limits of Atom Probe Crystallographic Analysis

“…The crystallographic information contained within atom probe tomography (APT) datasets of crystalline specimens is useful for a variety of reasons. It can facilitate calibration of the tomographic reconstruction [1] as well as enable direct crystallographic measurements of microstructural features such as grain boundaries [2] or site occupancy behavior in ordered phases at the atomic scale. The results of these types of crystallographic analysis methods are often of particular interest to better understand structure-property-processing relationships in engineering materials.…”

Improving Spatial Accuracy in Atom Probe Tomography through a Crystallography-Mediated Reconstruction (CMR)

“…Furthermore, the calibration procedure is often performed at a discrete interval in the evaporation history, thus assuming the reconstruction parameters remain static throughout the entire evaporation. As this process fails to account for the dynamic changes of the reconstruction parameters throughout both the analysis depth, and across the specimen surface [5], it is common to produce results that exhibit substantial distortions throughout the analysis depth, as measured by observed planar-spacing and angles between poles [6] In this work, we present a crystallography-mediated reconstruction (CMR) [7] protocol to improve the spatial accuracy and dramatically improve measured in-depth distortions. To achieve this, we developed a geometric transform framework to translate atomic positions from 'detector space' to 'reconstructed space' through a barycentric transform, without necessary input of pseudo-empirical reconstruction factors ICF or kf.…”