The Fabrication of Atom Probe Tomography Specimens From Mineral Nanoplates by Focused Ion Beam Redeposition

Many materials, including those containing platinum group elements and noble metals, form nanometer-thick plates (nanoplates) in a range of natural environments, including ore deposits and serpentinites. Materials research uses metallic nanoplates, such as 2D metal oxide/sulfide in applications ranging from superconductors to biomedical engineering, because of their unique properties. A few techniques with sufficient spatial resolution can analyze these nanomaterials, such as nano-secondary ion mass spectroscopy. An alternative is atom probe tomography (APT), which provides in situ major and trace element data with nanometer-scale resolution and can analyze nanoplates. This research describes a novel method to produce APT samples from geological nanoplates using focused ion beam (FIB) lift-out. The redeposited material is used to fill voids at the interface between the plate and the substrate, consolidating the wedge that is lifted out for analysis. A case study of APT specimen preparation from a ∼500-nm-thick FeS plate, separated from an olivine substrate, by voids, ≤20 µm3 in volume, is described. The method produces robust specimens that yield millions of atoms during APT analysis. This method can be applied to nanoplates of different compositions and thicknesses from a broad range of materials, and to free-standing films supported by window structures.