Metrology of small particles and solute clusters by atom probe tomography

Abstract

Atom probe tomography (APT) is routinely used for analyzing property-enhancing particles in the nanometer-size range and below, and plays a prominent role in the analysis of solute clusters. However, the question of how well these small particles are measured has never been addressed because of a lack of a reliable benchmark. Here, to address this critical gap, we use an approach that allows direct comparison of APT and small-angle (X-Ray) scattering (SA(X)S) performed on the same material. We introduce the notion of an effective spatial resolution for the analysis of particles, which, importantly in this context, is very different than the technique's inherent spatial resolution. This effective resolution is highly specific to the system being considered, as well as the analysis conditions. There is no hard limit below which the technique will fail, but for particles with a radius of order of 2σ = 1 nm, i.e. 250 atoms, cannot be accurately measured, even though the particles are detected. This thorough metrological assessment of APT in the analysis of particles allows us to discuss the pulse spread function of the technique and the physics underpinning its limits. We conclude that great care should be taken when analysing solute clusters by APT, in particular when reporting particle size and composition.

Enabling near-atomic–scale analysis of frozen water

“…The preanalysis scanning electron micrographs only provide an indication of the total analyzed depth. Yet, one can assume that the relative topology of the data on a local scale would map to the structure in the original specimen, although the effective spatial resolution in such a case is not precisely known ( 7 ). The length of the ice layer on top of the NPG was used as an upper bound to assess that, although arbitrary, the reconstruction would be a reasonable representation of the analyzed volume.…”

“…Atom probe tomography (APT) is a burgeoning technique that enables three-dimensional (3D) elemental mapping ( 6 ) with subnanometer resolution ( 7 ) and a chemical sensitivity potentially down to only tens of parts per million (ppm) ( 8 ). The usefulness of APT in studying wet chemical systems has been limited by the challenges inherent to the analysis of liquid media.…”

Reflections on the Analysis of Interfaces and Grain Boundaries by Atom Probe Tomography

“…Yet, APT is primarily a mass spectrometry technique (Müller et al, 1968), albeit with a very high spatial resolution (Vurpillot et al, 2000b(Vurpillot et al, , 2001Gault et al, 2009Gault et al, , 2010. The spatial resolution in APT results from a complex interplay between the field evaporation process that dictates the order in which ions are removed from the surface (Vurpillot et al, 2000b;Marquis & Vurpillot, 2008;Gault et al, 2010;De Geuser & Gault, 2020) and the shape of the specimen up to the level of the atomic arrangements at the specimen's surface. Combined, these factors determine the nature of the projection of the ions from the apex of the specimen onto the position-sensitive ion detector (Rolland et al, 2015;De Geuser & Gault, 2017).…”

Exploring the hidden world of solute atoms, clusters and vacancies in aluminium alloys

“…The size of clusters hardly seems to evolve during NA [28] and the evolution of their composition has been presented differently. One issue might be the way cluster search algorithms are applied but there might also be a fundamental limitation linked to the trajectories of atoms that prevent very small clusters to be analysed properly [29].…”