Innovative Aspects of Sample Preparation Overcome the Challenges of Poorly Conductive, Fragile Materials, and the Analysis of Liquid/Solid Interfaces in Atom Probe Tomography

Atom probe tomography (APT) combines the capability of high spatial resolution (<1 nm) with high chemical sensitivity in the range of tens of ppms to map the composition and microstructure of materials [1]. The development of laser-pulsed APT unlocked the analysis of a wide range of poorly conducting materials including insulators, semiconductors, organic materials and even frozen liquid [2-3]. In recent years, enormous efforts have been made to develop new cryo-workflows and cryo-FIB preparation methods [4-6], enabling the analysis of liquids and liquid-solid interfaces towards hydrated organic molecules [6-8]. We will present two different innovative sample preparation approach from cryo for liquid-solid interface towards metallic coating of APT specimens We present a new cryo-FIB preparation approach that has made it possible to possible to quasi-"in-situ" analyse the reactive solid-liquid interface by cryo-APT and investigate the early corrosion mechanisms of a Mg0.1Ca alloy [9]. These metastable defect phases at the reactive interface could only be observed by quasi- “in-situ” cryo-APT analyses of the corrosion process, yet these early reaction products are highly reactive and must play a critical role in accelerating the corrosion. This new approach will enable the characterization of liquid-solid interfaces at a near-atomic scale, providing new insight into their chemical composition and structure – and improve our understanding of how materials such as metals, battery catalysts and biomaterials degrade. However, besides the challenges in analyzing liquids und liquid/solid interfaces several material classes (geomaterials, biomaterials, porous samples, battery materials etc.) poses major challenges for APT due to their poor thermal and electrical conductivity, electron/ion beam sensitivity during preparation and mechanical instability during APT measurement, which affect yield and data quality. To overcome these challenges, we introduced a controlled in-situ deposition of a thin metal layer on specimens directly inside the focused ion beam (FIB) as the last step of the preparation [10]. The metallic coating increases the field-of-view, sample yield of very fragile specimens and improves the data quality for materials with a poor thermal conductivity, especially biomaterials [11]. This new approach paves the way for exploring the possibilities and advantages of metallic coatings for analyzing different material system from metals [10] to battery materials [12]. For biomaterials [11], we showcased data accuracy enabling to overcome previous analytical limits. We present two innovative sample preparation approaches that have opened new possibilities, overcome previous hurdles, and demonstrated the potential for APT to be used in other research areas [13]. Two innovative sample preparation methods are introduced: (A) a cryo-workflow for preparing APT specimens from liquid-solid interfaces, and (B) a Cr-coating technique for overcoming the challenges of poorly conductive and fragile materials.