Simulation tools for atom probe tomography: A path for diagnosis and treatment of image degradation

Abstract

The ideal picture of a near-perfect 3D microscope often presented regarding Atom Probe Tomography faces several issues. These issues degrade the metrological performance of the instrument and find their roots in the phenomena acting at the atomic to the mesoscopic level in the vicinity of the surface of a field emitter. From the field evaporation process at the atomic scale, to the macroscopic scale of the instrument, the path to model the imaging process and to develop more accurate and reliable reconstruction algorithms is not a single lane road. This paper focused on the numerical methods used to understand, treat, and potentially heal imaging issues commonly affecting the data in atom probe experiments. A lot of room for improvement exists in solving accuracy problems observed in complex materials by means of purely electrostatic models describing the image formation in a classical approach. Looking at the sample at the atomic scale, the phenomena perturbing the imaging process are subtle. An examination of atomic scale modifications of the sample surface in the presence of a high surface electric field is therefore mandatory.Atomic scale molecular dynamic models integrating the influence of the high surface electric are being developed with this aim. It is also demonstrated that the complex behavior of atoms and molecules in high fields, and consequences on collected data, can be understood through the use of accurate ab-initio models modified to include the impact of the extreme surface electric field.The capability to correlate the physical properties of materials to the local three dimensional distribution of atoms is nowadays crucial in designing new and improved materials and devices. When designing nanostructured materials, the dream is to be able to catch with the highest metrological performance a snapshot of the region of interest. Being able to identify structural and elemental information with 3D details on the single-atom level could transform the understanding of the relationship between structure (e.g. composition, defects, crystallography) and properties (e.g. magnetic, electric, photonic, or mechanical properties for instance) at the most fundamental level. This approach is explored using the atom probe tomography instrument (APT). This instrument is indeed unique in the world of nano-analysis tools, for its ability to provide, after analysis of a volume of interest in the material, a 3D map of atom positions, with atoms labelled by their elemental identities [1,2,3,4].By wandering between the static positions of atoms present in an APT dataset, the instrument's user often feels that the three dimensional image is a snapshot of the specimen that was left unharmed by the analysis process. This feeling is obviously an illusion. At the APT specimen level, i.e. a sharply pointed needle (called the tip), the imaging process utilizes extremely intense physical mechanisms on the surface and sub-surface of the materials. A strong electric voltage generates locally a huge surface electric field (sever...

Interpreting nanovoids in atom probe tomography data for accurate local compositional measurements

“…It is counterintuitive that a void, which is essentially empty space, can exhibit an increased local atomic density region at the void position in the APT reconstruction. Simulated APT experiments provide a unique approach to gain insight on how the field-evaporation process is affected by the void's structure and surrounding composition 33 . Such simulations reproduce the gradual evolution of a virtual APT specimen by evaporating the tip atom-by-atom with an evaporation field assigned to each element comprising the material.…”

Combining Experiments and Atom Probe Tomography‐Informed Simulations on γ′ Precipitation Strengthening in the Polycrystalline Ni‐Base Superalloy A718Plus

“…At this point, no algorithm is published that would allow for the knowledge about the field evaporation artifacts to be included into the reconstruction at the scale of the datasets presented here. However, correlative 3D microscopy, combined with recently published field evaporation simulations based on full‐scale models may allow for the implementation of already published approaches for smaller scale corrections in a self‐consistent manner in the near future. We therefore directly used the 3D data from the atom probe for the atomistic simulations as a first approach, accounting for the discrepancies (see Section ).…”

Nanoscale Perspectives of Metal Degradation via In Situ Atom Probe Tomography

“…A direct application of this method can be reasonably considered in the case of "real" nanoparticles such as enriched Co nanoparticles, Co/MnO x [47], and nanoalloys, CoCu [51]. Finally, it is important to notice that even if the oxygen exposure is performed in absence of electric field, the precise mechanism of field evaporation remains widely unknown and is still a matter of discussion within the APM community [52]. For the Co oxidation case, an additional investigation will be necessary to determine the influence of the electric field and the laser energy on the nature of the ions detected [53].…”