Specimen preparation for correlating transmission electron microscopy and atom probe tomography of mesoscale features

Atom-probe tomography (APT) provides atomic-scale spatial and compositional resolution that is ideally suited for the analysis of grain boundaries. The small sample volume analyzed in APT presents, however, a challenge for capturing mesoscale features, such as grain boundaries. A new site-specific method utilizing transmission electron microscopy (TEM) for the precise selection and isolation of mesoscale microstructural features in a focused-ion-beam (FIB) microscope lift-out sample, from below the original surface of the bulk sample, for targeted preparation of an APT microtip by FIB–SEM microscopy is presented. This methodology is demonstrated for the targeted extraction of a prior austenite grain boundary in a martensitic steel alloy; it can, however, be easily applied to other mesoscale features, such as heterophase interfaces, precipitates, and the tips of cracks.