Interpreting nanovoids in atom probe tomography data for accurate local compositional measurements

Abstract

Quantifying chemical compositions around nanovoids is a fundamental task for research and development of various materials. Atom probe tomography (APT) and scanning transmission electron microscopy (STEM) are currently the most suitable tools because of their ability to probe materials at the nanoscale. Both techniques have limitations, particularly APT, because of insufficient understanding of void imaging. Here, we employ a correlative APT and STEM approach to investigate the APT imaging process and reveal that voids can lead to either an increase or a decrease in local atomic densities in the APT reconstruction. Simulated APT experiments demonstrate the local density variations near voids are controlled by the unique ring structures as voids open and the different evaporation fields of the surrounding atoms. We provide a general approach for quantifying chemical segregations near voids within an APT dataset, in which the composition can be directly determined with a higher accuracy than STEM-based techniques.

Enabling near-atomic–scale analysis of frozen water

“…The composition in Ag at the ligament core is higher than might be expected (77 at %), as the surface diffusion–based model of the dealloying process supports a composition at the ligament core that is close to the bulk composition of the parent alloy. Trajectory aberrations arising from the high-evaporation field of the nanoligaments, compared to the hydrous matrix, will lead to trajectory overlaps that will affect the compositional estimates—this might explain the relatively low composition of water around the ligaments, as atoms originating from the ligaments are subject to strong aberrations and are imaged as part of the pores, typical of the aberrations caused by differences in the electric field necessary for field evaporation ( 61 ).…”

Investigating radiation-induced segregation on intragranular defects in a 316L(N)

“…Nevertheless, the feature #4 is not believed to be a precipitate, at least sole. The presence of a cavity associated with RIS at its interface with the matrix could explain such low value of reduced core density [44], but the shape of the reduced density profile does not match with the one obtained. However, from the observed contrasts in the close-up view of the cluster imaged by STEM, the presence of a precipitate associated with the cavity exhibiting RIS is suspected as it seems to be the case from S/TEM imaging associated with analytical STEM-EDS.…”

“…One of them is spherical, it could possibly be a cavity, the other one is ellipsoidal, and is assumed to be a precipitate associated with the cavity. Presence of a cavity within the cluster could explain such a low value for reduced core density [44]. RIS on the cavity and the precipitate could correspond to the cluster shell while the precipitate having an evaporation field close to the matrix has an ellipsoidal shape, then may have not suffer from any distortion.…”

First principles model for voids decorated by transmutation solutes: Short-range order effects and application to neutron irradiated tungsten

“…High density artefacts are introduced into APT reconstructions due to local curvature induced trajectory aberrations at the periphery of the void, as outlined by Wang et. al [129]. In all of these analyses using maximum separation methods, there was no indication that either σ or χ phase formation had occurred.…”