COSMOSAT: An Optimized Atom Probe Tomography Instrument for Geochemistry and Cosmochemistry

The study of geological materials relies on the analysis of intrinsically complex samples, in which mineral phases, inclusions, and chemical zonations reflect formation and evolution processes across a wide range of spatial and temporal scales. Whether dealing with terrestrial rocks or extraterrestrial materials, these objects preserve part of the history of their environment within their fine structure. Extracting this information requires analytical tools capable of probing matter at increasingly fine resolutions, down to the atomic scale. Over the past ten years, the study of geological materials using Atom Probe Tomography (APT) has expanded significantly and now represents a major advance in the nanometer-scale characterization of these materials [1–3]. APT provides simultaneous access to elemental composition, through identification and quantification of chemical elements, as well as isotopic composition, enabling distinction between isotopes of a given element and measurement of their relative abundances, which is essential for geochronology and for tracing the processes experienced by rocks. However, Atom Probe Tomography was initially developed for the analysis of metals, for which it proved particularly well suited [1,2]. With the later introduction of pulsed lasers, the technique was extended to dielectric materials. Nevertheless, the analysis of poorly electrically conducting materials remains variable depending on the specimen and is difficult to standardize. In particular, compounds such as oxides, nitrides, and phosphates—and therefore many geological materials—exhibit complex evaporation behaviour, leading to biases in both composition measurements and data reconstruction [4]. This paper presents the first results obtained with COSMO-SAT, a new generation of APT instrument dedicated to the analysis of terrestrial and extraterrestrial samples, with the specific goal of significantly improving elemental and isotopic measurements at the nanometer scale. The instrument pursues several ambitious objectives for the analysis of cosmochemical samples, as presented in Fig. 1: • The ultra-high-vacuum chamber is optimized for geological samples through the integration of a fast cryo-transfer hub compatible with LEAP sample holders. This development is intended to improve the measurement of light atoms (H, He, C, etc.) that are volatile at room temperature. • A new reflectron design and advanced laser pulsing capabilities: the redesigned reflectron, combined with a versatile multi-wavelength achromatic laser pulsing system, increases the mass spectrometry performance of the instrument. The versatile optical system has recently been used in two applications operating with light pulses at opposite ends of the optical spectrum: in the deep UV (λ = 260 nm) and in the far infrared (λ = 300 μm), in the terahertz (THz) range [5,6]. • The core of an APT instrument is its position- and time-sensitive ion detector. For geological materials, evaporation processes are often complex, with frequent multiple-hit events. In such cases, there is a significant probability of selective loss (“pile-up”). A new DLD detector with improved multihit capability has been developed using a new acquisition system based on a faster digitization card [7,8]. The COSMO-SAT prototype [8]. This instrument features: a) a full compatibility with LEAPTM sample holder b) An optimized and ultrafast transfer hub for cryotransfer c) A new reflectron/detector design d) A new achromatic focusing design for ultrafast laser pulsing e) a new generation of MCP DLD detector with high repetition rate capability