Correlative Approach for Atom Probe Sample Preparation of Interfaces Using Plasma Focused Ion Beam Without Lift-Out.

Plasma focused ion beam microscopy (PFIB) is a recent nanofabrication technique that is suitable for site-specific atom probe sample preparation. Higher milling rates and fewer artifacts make it superior to Ga+ FIBs for the preparation of samples where large volumes of material must be removed, for example, when trying to avoid lift-out techniques. Transmission Kikuchi diffraction (TKD) is a method that has facilitated phase identification and crystallographic measurements in such electron transparent samples. We propose a procedure for preparing atom probe tomography (APT) tips from mechanically prepared ribbons by using PFIB. This is highly suitable for the preparation of atom probe tips of interfaces such as interphase boundaries from challenging materials where lift-out tips easily fracture. Our method, in combination with TKD, allows the positioning of regions of interest such as interfaces close to the apex of the tip. We showcase the efficacy of the proposed method in a case study on Alloy 718, where the interface between γ-matrix and δ-phase has not been yet extensively explored through APT due to preparation challenges. Results show depletion of γ″-precipitates near the γ/δ interface. A quantitative evaluation of the composition of phases in the bulk versus near the interface is achieved.