Nanoscale Localization of an Atom Probe Tip through Electric Field Mapping

Abstract

This work concerns one of the main challenges in atom probe tomography (APT) of heterogeneous systems, that is, the reliable placement of evaporated atoms in the reconstructed volume with subnanometer precision. The accurate determination of the nanoscale needle specimen shape constitutes an essential requirement to overcome this challenge as it enables one to include the details of the tip shape in the reconstruction algorithms distortions. Recently, scanning probe microscopy (SPM) has been pioneered as a promising approach to capture the topography of the APT specimen in three dimensions. However, reaching the unusual tip-on-tip measurement configuration requires approaching the specimen with the SPM probe in a highly controlled manner to avoid any damage to probe or specimen. Here, we propose a new method to align the SPM probe with an APT tip through a measurement of the electrostatic interaction between both. The method is free of any mechanical interaction between both tips prior to surface imaging and is applicable for all possible probe geometries. Additional insights into the resolution through a simulation of the electrostatic interaction between the SPM probe and a biased APT tip are provided. In prospect, this study opens doors to probe the electric field around an APT tip in three dimensions.

The Prospect of Spatially Accurate Reconstructed Atom Probe Data Using Experimental Emitter Shapes

“…Nevertheless, we speculate that the overall analysis time in an integrated SPM-APT tool is not expected to increase significantly in comparison to a regular APT analysis. Indeed, the SPM topography characterization can be performed in 10 min when applying the potentially automated, rapid tip-on-tip alignment procedure previously developed (Op de Beeck et al, 2020). Furthermore, the prediction of the emitter topography dynamics (Haley et al, 2018; Fletcher et al, 2019; Hatzoglou & Vurpillot, 2019) constrained or guided by the experimental data is an additional promising avenue to decrease the frequency at which emitter shapes need to be acquired.…”

“…Measurements were performed using super sharp silicon probes (Nanosensors, tip radius ≈ 2 nm) or custom carbon nanotube probes (CDI, tip radius ≈ 1 nm). Tip-on-tip alignment was performed as outlined by Op de Beeck et al (2020). The experiment alternating between APT and SPM was performed on a sample mounted on a flat top coupon (Thompson et al, 2005) which allowed us to track and maintain the orientation of the specimen for the subsequent round of APT.…”

“…Hence, a more refined reconstruction approach can be considered following a three-step process. First, the geometry of the APT specimen is determined using either experimental methods, such as scanning probe microscopy (SPM; Fleischmann et al, 2018;Op de Beeck et al, 2020), electron microscopy (Sha et al, 2008;Shariq et al, 2009;Marquis et al, 2010;Haley et al, 2011;Koelling et al, 2011), soft X-ray ptychography (van der Heide et al, 2019), or simulation-based methods (Vurpillot et al, 1999(Vurpillot et al, , 2004Marquis et al, 2010;Larson et al, 2011Larson et al, , 2012Rolland et al, 2015a), or a combination of both (Fletcher et al, 2019). Independent of the chosen method, it is vital to obtain an accurate threedimensional emitter shape to realistically calculate the electric field distribution.…”

A System for Electrostatic Reconstructions

“…They employ various computational techniques and embody different pieces of the relevant physics to predict the specimen endform evolution. In addition, recent development in complementary techniques such as atomic force microscopy promise to provide direct 3D measurements of specimen shapes, possibly at multiple times during an atom probe analysis [9,10]. Incorporating the inhomogeneous magnification imposed by a non-spherical apex will allow us to improve reconstruction accuracy in a more physically correct way than the various techniques currently used.…”