Scalable substrate development for aqueous sample preparation for atom probe tomography

Abstract

AbstractReliable and consistent preparation of atom probe tomography (APT) specimens from aqueous and hydrated biological specimens remains a significant challenge. One particularly difficult process step is the use of a focused ion beam (FIB) instrument for preparing the required needle‐shaped specimen, typically involving a ‘lift‐out’ procedure of a small sample of material. Here, two alternative substrate designs are introduced that enable using FIB only for sharpening, along with example APT datasets. The first design is a laser‐cut FIB‐style half‐grid close to those used for transmission electron microscopy (TEM) that can be used in a grid holder compatible with APT pucks. The second design is a larger, standalone self‐supporting substrate called a ‘crown’, with several specimen positions, which self‐aligns in APT pucks, prepared by electrical discharge machining (EDM). Both designs are made nanoporous, to provide strength to the liquid–substrate interface, using chemical and vacuum dealloying. Alpha brass, a simple, widely available, lower‐cost alternative to previously proposed substrates, was selected for this work. The resulting designs and APT data are presented and suggestions are provided to help drive wider community adoption.