Atom probe tomography (APT) is often quoted to provide "atomic-scale" analysis of materials in three-dimensions. Despite efforts to quantify APT's spatial resolution, misunderstandings remain regarding its true spatial performance. If the depth resolution was once reported to be 20 pm, quoting this value outside of its specific context is misleading and should be avoided. The resolution achievable in pure metals, at one specific location, within one reconstructed dataset, does not generally apply across materials or analysis conditions, or even throughout a single tomographic reconstruction. Here, we review various efforts at defining and measuring the spatial resolution in the study of single phase and single element materials-i.e., pure metals-in field-ion microscopy (FIM) and APT. We also report on the degradation of the resolution arising from ion optical devices used to improve the mass-resolution. We aim to offer some perspective as to how reported resolutions may be or may not be of any relevance to most of the materials characterization efforts by APT, including cases of precipitates in a matrix that emphasize the need to consider an effective resolution. Finally, we discuss concepts to improve the spatial accuracy of the technique in a relatively distant future.

Monazite (CePO4) is widely used in U-Th-Pb geochronology due to its reliable age determinations, although isotopic disturbances often require investigation at the nanoscale to better understand the mechanisms at play. Atom probe tomography (APT) offers unique capabilities for nanoscale chemical analysis and 3D atomic reconstruction but presents challenges for insulating materials such as CePO4, particularly due to oxygen loss during field evaporation. This study investigates the effects of laser wavelength, energy, metallic coatings, and detection device on mass spectrum optimization and compositional accuracy in synthetic CePO4 samples. Results show that shorter laser wavelengths (260 nm) enhance peak resolution, particularly when combined with advanced reflectron configurations, as demonstrated with the LEAP 6000 XR. Chromium coatings further improve thermal dissipation and reduce noise levels. However, compositional measurements reveal systematic underestimation of oxygen and overestimation of P and Ce, likely influenced by preferential low-field evaporation of certain elements. These findings highlight the need to carefully tune experimental parameters to mitigate quantification biases and enhance the reliability of APT analyses for geological materials.

Atom probe tomography (APT) is now routinely used to study solute atom segregation at crystalline defects in different materials. The present study reports unexpected observations concerning carbon (C) segregation at dislocations in APT volumes analyzed from two different industrial steel grades. APT analyses reveal that C segregation at dislocations could only be observed with Mo co-segregation. Indeed, transmission electron microscopy (TEM) observations on APT tips and correlative TEM-APT analysis show that despite dislocations being present in the samples prior to APT analyses, C segregation was not observed in the absence of Mo segregation. Statistics on the distribution of C composition in the different APT volumes from Mo-free steels show important discrepancies, with 35% of the volumes exhibiting C content in solid solution five times higher than expected. It is concluded that APT measurements of both C segregation at dislocations and C content in solution in iron may be incorrect due to the possibility of dislocations leaving the APT samples when subjected to a high electric field before or during field evaporation.

Atom probe tomography data are composed of a list of coordinates of the reconstructed atoms in the probed volume. The elemental identity of each atom is derived from time-of-flight mass spectrometry, with no local chemical information readily available. In this study, we use a data processing technique referred to as field evaporation energy loss spectroscopy (FEELS), which analyzes the tails of mass peaks. FEELS was used to extract critical energetic parameters that are related to the activation energy for atoms to escape from the surface under intense electrostatic field and dependent of the path followed by the departing atoms. We focused our study on pure face-centered cubic metals. We demonstrate that the energetic parameters can be mapped in two-dimensional with nanometric resolution. A dependence on the considered crystallographic planes is observed, with sets of planes of low Miller indices showing a lower sensitivity to the field. The temperature is also an important parameter in particular for aluminum, which we attribute to an energetic transition between two paths of field evaporation between 25 and 60 K close to (002) pole. This paper shows that the information that can be retrieved from the measured energy loss of surface atoms is important both experimentally and theoretically.

The investigation of hydrogen in atom probe tomography appears as a relevant challenge due to its low mass, high diffusion coefficient, and presence as a residual gas in vacuum chambers, resulting in multiple complications for atom probe studies. Different solutions were proposed in the literature like ex situ charging coupled with cryotransfer or H charging at high temperature in a separate chamber. Nevertheless, these solutions often faced challenges due to the complex control of specimen temperature during hydrogen charging and subsequent analysis. In this paper, we propose an alternative route for in situ H charging in atom probe derived from a method developed in field ion microscopy. By applying negative voltage nanosecond pulse on the specimen in an atom probe chamber under a low pressure of H2, it is demonstrated that a high dose of H can be implanted in the range 2-20 nm beneath the specimen surface. An atom probe chamber was modified to enable direct negative pulse application with controlled gas pressure, pulse repetition rate, and pulse amplitude. Through electrodynamical simulations, we show that the implantation energy falls within the range 100-1,000 eV and a theoretical depth of implantation was predicted and compared to experiments.

Reconstructions in atom probe tomography (APT) are biased by image distortions arising from dynamic changes of the specimen geometry that controls image projection. Despite the strong efforts to build realistic models for understanding and reproducing image artifacts, the current models are too slow or not adapted to be routinely used in image correction approaches. To understand the APT imaging process for real size samples submitted to realistic experimental conditions of electric field and temperature, we propose an alternative simulation tool based on a coarse-grained model of the sample surface. The surface electric field on a meshed surface is calculated by using continuous models describing field evaporation. The dynamic evolution of the sample surface and the image projection are predicted using materials properties. We show that the interplay between temperature and electric field is an important ingredient in predicting the ion projection, in pure metals and in more complex materials. This fast approach accurately reproduces the well-known local magnification and trajectory overlaps effects in the evaporation of small particles. By combining prior knowledge about the sample structure and properties, the model could be used to improve the reconstruction approaches for complex sample geometries.

Silicon carbide (SiC) may be considered as a model system for the study of field ion evaporation of carbides, which must be understood to perform accurate analyses of these systems by atom probe tomography (APT). As for other wide-bandgap semiconductors, the measurement of the composition of SiC by APT presents biases depending on the experimental parameters. Unlike silicon, carbon is characterized by a complex surface behavior, including the formation of molecules and the tendency to produce correlated evaporation. Furthermore, the spatial precision of three-dimensional (3D) reconstructions is strongly degraded in the direction parallel to the specimen surface, which points out to a strong roughening or dynamic degradation of the surface. This is confirmed by field ion microscopy (FIM) analysis, which reveals that atoms may move on the specimen surface under the influence of the high electric field. This complex surface behavior eventually translates into hidden detection events and, therefore, to errors in the measurement of composition.

Titanium dioxide (TiO2) nanoparticles (NPs) are the subject of numerous studies and controversies on the risks they could pose to the environment and human health. When in contact with biological tissues, NPs can sometimes be challenging to precisely localize within subcellular structures (typically around 0.1 µm) when they exist as isolated NPs, particularly when using the SIMS approach. Indeed, the chemical signals produced by isolated NPs are very low, so they can be confused with background signals. This was the motivation behind our development of a new strategy for correlating TEM/SIMS to detect TiO2 NPs in close proximity to cutaneous corneocytes. For this purpose, we initially developed a new tool for TEM and SIMS image registration based on a non-rigid image-deformation-enabling image overlay. Combining SIMS and TEM data through this overlay enhances NP localization’s precision. Secondly, we developed an algorithm based on the statistical analysis of multiplane SIMS images to denoise them. As a result, background noise was reduced, illuminating the low yet specific signals from isolated NPs. Finally, this new correlative approach enables the precise 3D localization of isolated NPs within the analyzed volume. We consider this method a breakthrough for subcellular-scale NP localization.

This article presents a numerical model dedicated to the simulation of field ion microscopy (FIM). FIM was the first technique to image individual atoms on the surface of a material. By a careful control of the field evaporation of the atoms from the surface, the bulk of the material exposed, and, through a digitally processing a sequence of micrographs, a three-dimensional reconstruction can be achieved. 3DFIM is particularly suited to the direct observation of crystalline defects such as vacancies, interstitials, vacancy clusters, dislocations, and any combinations of theses defects that underpin the physical properties of materials. This makes 3DFIM extremely valuable for many material science and engineering applications, and further developing this technique is becoming crucial. The proposed model enables the simulation of imaging artefacts that are induced by non-regular field evaporation and by the impact of the perturbation of the electric field distribution of the distorted distribution of atoms close to defects. The model combines the meshless algorithm for field evaporation proposed by Rolland et al. (Robin-Rolland Model, or RRM) with fundamental aspects of the field ionization process of the gas image involved in FIM.

It is widely accepted that the different types of crystalline imperfections, such as vacancies or dislocations, greatly influence a material’s physical and mechanical properties. However, imaging individual vacancies in solids and revealing their atomic neighborhood remains one of the frontiers of microscopy and microanalysis. Here, we study a creep-deformed binary Ni-2 at.% Ta alloy. Atom probe tomography reveals a random distribution of Ta. Field ion microscopy, with contrast interpretation supported by density-functional theory and time-of-flight mass spectrometry, evidences a positive correlation of Ta with vacancies, supporting positive solute-vacancy interactions previously predicted by atomistic simula-

This article presents a fast and highly efficient algorithm developed to reconstruct a three-dimensional (3D) volume with a high spatial precision from a set of field ion microscopy (FIM) images, and specific tools developed to characterize crystallographic lattice and defects. A set of FIM digital images and image processing algorithms allow the construction of a 3D reconstruction of the sample at the atomic scale. The capability of the 3D FIM to resolve the crystallographic lattice and the finest defects in metals opens a new way to analyze materials. This spatial precision was quantified on tungsten, analyzed at different analyzing conditions. A specific data mining tool, based on Fourier transforms, was also developed to characterize lattice distortions in the reconstructed volumes. This tool has been used in simulated and experimental volumes to successfully locate and characterize defects such as dislocations and grain boundaries.

Three-dimensional field ion microscopy is a powerful technique to analyze material at a truly atomic scale. Most previous studies have been made on pure, crystalline materials such as tungsten or iron. In this article, we study more complex materials, and we present the first images of an amorphous sample, showing the capability to visualize the compositional fluctuations compatible with theoretical medium order in a metallic glass (FeBSi), which is extremely challenging to observe directly using other microscopy techniques. The intensity of the spots of the atoms at the moment of field evaporation in a field ion micrograph can be used as a proxy for identifying the elemental identity of the imaged atoms. By exploiting the elemental identification and positioning information from field ion images, we show the capability of this technique to provide imaging of recrystallized phases in the annealed sample with a superior spatial resolution compared with atom probe tomography.

Atom probe tomography is often introduced as providing "atomic-scale" mapping of the composition of materials and as such is often exploited to analyse atomic neighbourhoods within a material. Yet quantifying the actual spatial performance of the technique in a general case remains challenging, as they depend on the material system being investigated as well as on the specimen's geometry. Here, by using comparisons with field-ion microscopy experiments and field-ion imaging and field evaporation simulations, we provide the basis for a critical reflection on the spatial performance of atom probe tomography in the analysis of pure metals, low alloyed systems and concentrated solid solutions (i.e. akin to high-entropy alloys). The spatial resolution imposes strong limitations on the possible interpretation of measured atomic neighbourhoods, and directional neighbourhood analyses restricted to the depth are expected to be more robust. We hope this work gets the community to reflect on its practices, in the same way, it got us to reflect on our work.