APT User Meeting

19 Nov 2024, 12:00 → 21 Nov 2024, 17:55 Europe/Berlin

Room 203 (large seminar room) (Max-Planck-Institut für Eisenforschung GmbH)

Aparna Saksena (MPI SusMat), Baptiste Gault (MPIE), Tim Schwarz (MPI SusMat)

 

We’re pleased to announce the 10^th edition of our world-famous NRW-APT user meeting, hosted at the Max-Planck-Institut für Eisenforschung. And on its 10th anniversary, we aim to bring APT users together from not only NRW but from all across Europe!

We expect an emphasis on:

 

- cryo-developments for specimens preparation 

- machine-learning for APT data processing

- bio-minerals and bio-materials

- APT for energy materials

- Nanostructure in metals and semiconductors

- ...

 

The meeting is planned in person from 19^th to 21^st November 2024. 

 

The idea was always to have discussions, so you may want to prioritize topics that are not yet fully understood but on which you want feedback and raise discussions and maybe gain from the experience of other colleagues who’ve faced similar problems.

10th APT User Meeting 2024_Schedule_final.pdf

Tuesday 19 November

12:00 Arrival and Light Lunch

Advancement in Instrumentation

1 Advancements in 3D Field Ion Microscopy for Atomic-Scale Material Characterization

Starting in the 1950s and continuing over the next two decades, field ion microscopy (FIM) became the first true atomic-scale microscopy technique [1], allowing for the direct imaging of individual atom positions on a material's surface with sub-angstrom precision [2]. By controlling the field evaporation of atoms from the surface, a three-dimensional (3D) reconstruction can be achieved through digital processing of a sequence of micrographs [3]. Spatial resolutions, both lateral and in-depth, can reach fractions of an angstrom. Detection efficiency is also improved compared to atom probe tomography (APT), with a global efficiency reaching 85% and a local efficiency nearing 100%. Additionally, contrast differences in the spots observed in FIM images, which reveal the presence of different chemical species, can be used to create a qualitative map of atomic distribution within the sample.

These capabilities allow for the 3D reconstruction of defects such as dislocations, nano-voids, and even vacancies [3][4]. Recent advances in 3D FIM have been applied to characterize various samples, including the orientation of the superlattice of ordered phases in meteorites, the evolution of amorphous glasses after annealing, and small defects created by irradiation damage. Despite these capabilities which allow the analysis of the finest crystalline defects, 3D FIM remains limited in its ability to identify chemical elements. It is generally necessary to complement these analyses with other instruments, such as APT.

Future developments involving time-resolved cameras could lead to the creation of an instrument that combines the mass resolution of APT with the spatial resolution of 3D FIM, thereby merging the best features of both instruments into one.

[1] E.W. Müller et al. 1956 Phys. Rev. 102 624–31
[2] E.W. Muller 1965 Science 149 591–601
[3] B. Klaes et al., 2021. Microsc Microanal. 27 365-384
[4] S. Katnagallu et al. 2019 New J. Phys. 21 123020

Speaker: Benjamin Klaes (GPM-Université de Rouen)

2 Project SATMET: Combining Atom Probe Tomography and Transmission Electron Microscopy in a single tool

During the last few decades, Atom Probe Tomography (APT) has proven itself as one of the best material characterization tools due to the combination of atomic resolution and 3D reconstruction capabilities. Still, there are some limitations, as the crystallographic information obtained from APT data is limited. To tackle that issue, a correlative approach of combined Transmission Electron Microscopy (TEM) and APT is often utilized. The limitation of the correlative approach is an increased probability of a sample fracture during transfer and a specimen deterioration due to air exposure. Additionally, the sample is being repeatedly cooled down to cryogenic temperatures and re-heated, resulting in additional contamination. Although, this issue can be addressed by the utilization of cryo-transfer setups [L.Stephenson]. Naturally, the idea to combine APT and TEM in one instrument was stirring the minds of scientist for some time [T.Kelly][T.Kelly]. The work on the project of combining TEM and APT setups in a single instrument began in Groupe de Physique des Matériaux as early as 2014, bearing the name SATMET [W.Lefebvre, ER-C Jülich 2016].

The current generation of SATMET instrument is based on a commercial JEOL F2 TEM equipped with a custom-made straight path APT detection system. To provoke field evaporation a custom-made cryo-specimen holder capable of applying voltage pulses was designed. It allows to perform experiments with the temperature of 78K at the tip position. In addition, the SATMET instrument is equipped with the software to perform 4D-STEM acquisitions. 4D-STEM mapping can be extremely useful to gauge the electric field on the APT tip surface to improve our understand of the field evaporation processes. This talk will illustrate some of the preliminary results obtained on this new tool, merging APT and TEM in a single instrument [G.Da Costa, submitted to Nature Communications 2024].

Speaker: Aidar Zakirov (GPM Rouen)

3 Technology and Applications of the LEAP 6000XR and Invizo 6000 atom probes

Rene Chemnitzer (Cameca)
“Technology and Applications of the LEAP 6000XR and Invizo 6000 atom probes”

Speaker: Rene Chemnitzer (Cameca Instruments)

4 AdAPTS: An Adaptive Atom Probe Tomography Simulation Library

AdAPTS: An Adaptive Atom Probe Tomography Simulation Library

Speaker: Julian Lüken (University of Antwerp)

14:40 Coffee Break

Advancement FIB Preparation

5 How Cold is Cold Enough? Exploring the effects of cryogenic temperature on FIB sample preparation for APT samples

Cryogenic sample preparation for atom probe tomography is becoming more widespread and has allowed the analysis of many new material systems including frozen liquids, solid/liquid interfaces and soft matter. Much of the work has been adapted from the life sciences where temperature control is very stringent and restrict the user to temperatures below the vitrification point of water, effectively requiring the use of liquid nitrogen. Using liquid nitrogen in this manner requires extensive modifications to instrumentation and restriction in location and times of operation due to health and safety regulations. Many systems of interest to material science requiring cryogenic sample preparation do not require liquid nitrogen temperature and so in these cases, it is possible to avoid the use of liquid nitrogen and instead use an alternative solid state cooling system such as a Peltier cooled stage. There are a number of commercial systems that provide cooling down to -100°C and can be installed on instrument stages with minimal feedthrough requirements, making this an option for non cryogenic specialist facilities to engaged in cryogenic sample preparation. In order to determine whether this approach is appropriate for a given material system, the effect of sample preparation at various temperatures needs to be carried out. Commercially pure titanium is known to form hydrides during room temperature Ga FIB sample preparation for APT and TEM and so typically Ga FIB sample preparation is carried out using liquid nitrogen temperatures. In this presentation we discuss the effects of Ga FIB preparation of APT samples from commercially pure titanium at a variety of cryogenic temperatures within the reach of a Peltier stage (between room temperature and -100°C) by using a nitrogen gas cooled stage combined with a stage heater.

Speaker: James Douglas (Imperial College London)

6 The advance analysis of liquid containing materials using cryogenic FIB

The current materials science research and industrial development needs bring new challenges of analyzing unconventional samples inside a FIB-SEM, such as liquid form samples, solid liquid inter-face samples, and other soft and beam sensitive samples. Often, such materials tend to be air sen-sitive as well. Hence, an inert gas filled glove box is also needed in sample handling. Prior to the invention of cryogenic FIB, it was unimaginable to analyze such challenging samples in a FIB-SEM. The key components of a cryogenic workflow for 3D analysis and TEM sample fabrication include a cryo stage, a cryo nanomanipulator, a cryo transfer system and most importantly a cryo sample preparation station.
In this abstract we share the instrumental set up of a unique inert gas and cryogenic sample prepa-ration workflow. We will also present a variety of application usecases, for instance beam sensitive materials such as perovskite samples, liquid containing materials such as oil and water containing samples. The challenges in the cryo workflow development will be discussed. Various cryo and inert gas transfer workflow determined by sample types will also be illustrated. In addition, we will pro-vide an overview of the cryo instrumentation in the current market.

Speaker: Min Wu (THERMO FISHER SCIENTIFIC)

7 Workflows and Capabilities enabled with Zeiss crossbeam laser

The new technological improvement of all type of materials, including functional, semiconductors, micro-electro-mechanical, medical, needs a proper microstructure investigation from mm- up to nmscale. One of the most used techniques is the focused ion beam (FIB), with a Ga+ beam for materials removal and specimen preparation for much high resolution techniques such as (TEM, APT ,..etc ). However, the material removal rate of FIB is very limited and time consuming for most applications.
Hence, attaching a laser to cut faster into the FIB system is becoming a good strategy for rapid sitespecific samples preparation at large scale [1].

Zeiss Crossbeam new generation combines a femtosecond laser source in a FIB/SEM for higher accuracy and resolution imaging to enables the fastest workflows. In addition, to this, contamination issues of the SEM/FIB chamber are considered, for this an isolated laser chamber is designed to prevent the contamination of electron column and detectors. At the meantime, the crossbeam system is well integrated by guaranteeing an easy and accurate sample transfer between the SEM and laser chamber under vacuum.

In this talk we will explore the capabilities and workflows enabled with the Zeiss crossbeam laser using a short, pulsed femtosecond laser <300 fs to cut > 1 mm 3 of Si piece as an example in only 5 mins. The short pulses regime offers minimal to no artifacts from laser heat affected zone which reduces the thermal damaged happened with the laser and grant a better process control with less edges or curtaining. Thus, a direct visibility of the region of interest after laser preparation. Several examples will be shown providing the fastest time to results for cross-sectional analysis of deeply buried features at nanoscale resolutions.
References:
[1] Manuel Pfeifenberger Desertation “ Implementation of femtosecond laser processing for materials testing and research “

Speaker: Dr Martina Heller (Carl Zeiss Microscopy GmbH)

16:00 Coffee Break

Application of Cryogenic Preparation

8 Look What You Made Me Glue - Cryogenic liftout for APT using electron curing liquid adhesives

A major challenge with cryogenic atom probe sample preparation is that Gas Injection System based deposition is generally unsuitable to liftout and mount samples to support structures due to a lack of control of deposition. Developments in localized in-situ sputtering of metals have avoided this issue and have facilitated mounting of samples for many material systems requiring cryogenic conditions, including free standing liquids. This approach requires an initial amount of redeposition from the sample to the support structure itself prior to any in-situ redeposition from the sputter source and so relies on a significant amount of contact between the sample and support structure. In the case of sample liftouts with non typical geometries such as those involving free standing thin films or materials that mill very easily compared to the support structure, this can prove extremely difficult as no firm contact can be made and the sample is frequently lost. This is especially an issue when using plasma based species for milling due to the decreased resolution of the beam. In these situations, a a more reliable method to carry that initial attachment is required.
In this presentation, we demonstrate a method of lifting out and mounting atom probe samples at cryogenic conditions using a commercially available vacuum safe and electron curing liquid adhesive called “Sem-Glu” (Kleindiek). This adhesive remains viscous to -90°C and so can be applied in-situ via the micromanipulator down to this temperature if the material system is stable at these temperatures but will promote still adhesion to a surface and can be used down to -180°C if applied in advance at room temperature to manipulators and supports structures.

Speaker: James Douglas (Imperial College London)

9 A correlative love story: Cryo APT and Operando liquid cell TEM

The energy transition relies on materials with complex and dynamic interfaces involving low atomic weight and mobile liquid, solid, and gaseous species. Understanding the chemistry, phase, and morphology of these interfaces at high-resolution length scales is crucial for optimising their behaviour and performance. However, existing high-resolution imaging and characterisation techniques struggle to capture dynamic solid-liquid interfaces at atomic resolutions, leading to poor understandings of key electrochemical phenomena like solid-electrolyte interphase (SEI) formation.
While various techniques have been applied to study such interfaces, none alone can provide the necessary dynamic and atomic level resolution to fully understand and characterise these types of complex systems at high resolutions. Liquid-cell transmission electron microscopy (LCTEM) offers real-time imaging of dynamic electrochemical processes at high temporal and spatial resolution but is limited by sample thickness and beam-induced effects. On the other hand, cryogenic microscopy, such as cryogenic Atom Probe Tomography (Cryo APT), enables 3D compositional reconstructions of frozen nanoscale volumes with sub-nanometre spatial resolution and ppm-level chemical sensitivity for all elements. Cryogenic microscopy techniques are however only capable of offering a snapshot of a particular system when a full dynamic understanding is required. This makes dynamic liquid microscopy techniques and high-resolution cryogenic microscopy techniques extremely complimentary.
This work successfully combines operando LCTEM with Cryo APT through the use of an inert glovebox, cryogenic PFIB/SEM, and vacuum cryo transfer module (VCTM) technology. This integrated approach enables dynamic sub-nanometre compositional analysis of electrochemical phenomena in lithium-based battery systems. By combining the strengths of liquid microscopy for real-time observation and cryogenic techniques for high-resolution compositional analysis, this method provides unprecedented insights into early-stage Li plating, intercalation, dendrite growth, and SEI formation. This approach marks a significant advancement in understanding and optimising dynamic electrochemical systems critical to energy technologies.

Speaker: Neil Mulcahy (Imperial College London)

10 APT analysis of Li-containing materials: We Are Never Ever Getting Back Together

APT analysis of Li-containing materials: We Are Never Ever Getting Back Together

Speaker: Baptiste Gault (Max-Planck-Institut für Nachhaltige Materialien GmbH)

Wednesday 20 November

Advancement in Theory of Field Evaporation

11 Theoretical Insights into Electric Field Effects on Metal Surfaces: Implications for Atomic-Scale Characterization

Understanding how high electric fields influence metal surfaces is essential for advancing atomic-scale characterization techniques. In this talk, I will present our theoretical investigations into electric field effects on metals, using density functional theory (DFT) calculations to provide insights relevant to experimental observations.
Firstly, we investigate vacancy formation in Ni and Pt under high electric fields. While 3D field ion microscopy (FIM) allows imaging of vacancies and their interactions with other atoms, there is debate over whether the high electric fields used might introduce artificial vacancies. Our DFT simulations show that, contrary to conventional expectations, the reaction barrier for vacancy formation increases in the presence of an electric field compared to the field-free case. Furthermore, electric fields introduce kinetic barriers that inhibit mechanisms which would normally eliminate vacancies.
Secondly, we explore the challenges faced in atom probe tomography (APT) of Li. While APT can offer valuable atomic-scale insights into Li-containing materials, it often encounters evaporation artifacts that compromise data reliability. Our DFT studies reveal that at certain electric field strengths below the threshold for Li evaporation, the preferred adsorption sites for Li atoms shift. This shift leads to barrier-less diffusion of Li atoms across the surface, resulting in the “spotty” evaporation patterns observed experimentally.
Lastly, we address the computational challenges in modelling field evaporation and ionization. Traditional ab initio simulations are computationally intensive due to the shallow potential energy surfaces involved. To overcome this, we explore machine learning interatomic potentials with a charge equilibration scheme. We validate this approach using DFT reference data for Pt slabs under electric fields ranging from 1 to 4.5 V/Å.
By elucidating the mechanisms behind surface diffusion, field evaporation, and vacancy formation under electric fields, we aim to improve the interpretation of experimental data and the development of advanced materials characterization techniques.

Speaker: Shyam Katnagallu (Max Planck Institute for Sustainable Materials)

12 Local contrast in FIM - opportunities and limits of interpretation by comparison to theory

Local contrast in FIM - opportunities and limits of interpretation by comparison to theory

Speaker: Christoph Freysoldt (Max Planck Institute for Sustainable Materials)

13 Comparing and integrating alternative theories of field ion imaging, and assessing what more needs to be done

Recent treatments of field-ion (FI) imaging theory (e.g., [1]) differ from older treatments (e.g., [2]). Modern theories consider the availability of in-specimen final electron states. Particularly with alloy specimens, this is long overdue and welcome. However, aspects of modern theories seem incompatible with older theories firmly backed by experiment, or incompatible with scientific thinking outside atom-probe.
This presentation points out the separate limitations of both old and modern imaging theories, attempts to combine their separate strong points into a qualitative-level integrated theory, and explores possible future developments.
Topics covered (as time permits) are:
– Using the "7-dimensional" (or "amount-based") imaging equation r_FI=CQ_e. The "amount of operating-gas ionized per unit volume per unit time" (r_FI) at some point R in space is given by the product of the "effective" gas concentration (C) at R and the electron transfer rate-constant (Q_e) at R. Q_e is given by the product of the electron transition rate-constant (P_e) (rate-constant in free space) at R and a factor representing availability of specimen "final states".
– Gas atom history, "best image field", the "Assumption of corresponding potential structures", and the roles of C and Q_e in image formation.
– Charged-surfaces theory (charge and dipole charge distributions, electrical surface, critical surface).
– The choice between tunnelling-integral-based and overlap-integral-based theories of rate-constants, and evidence that prefers tunnelling integrals.
– The desirability of validating imaging theories using He-on-W imaging of the (111) plane near 80 K; Ruska blurring.
– Field adsorption and its possible effects on C and Q_e.
– The possible role of charge-transfer between surface atoms of different species.
– What theoretically needs doing next? Better field ionization tunnelling theory, certainly, but what else ?
[1] S. Bhatt et al., Phys. Rev. B 107 (2023) 235413.
[2] R.G. Forbes, Appl. Surf. Sci. 94/95 (1996) 1–16.
emphasized text

Speaker: Richard G. Forbes (University of Surrey)

10:20 Coffee Break

Advancement in Data Processing

14 Machine Learning and Data Science Applications for Atom Probe Tomography Data Analysis

This presentation will cover ongoing work that integrates machine learning (ML) and data science methods with Atom Probe Tomography (APT) data analysis. The primary objective is to develop a tool (APyT) that automates APT data processing and analysis routines. Additionally, the project aims to create an interface between APyT and existing commercial software like AP Suite to streamline workflows. A key example will demonstrate how ML techniques such as Gaussian Mixture Models and DBSCAN clustering can enhance APT data processing, particularly in composition clustering.

Speaker: Dr Navyanth Kusampudi (Max-Planck-Institut für Nachhaltige Materialien GmbH)

15 Quantifying Vacancy Supersaturation via Diffusivity Measurements by APT

Detecting and quantifying excess vacancies in materials remains a significant challenge in materials science, as these vacancies are critical in accelerating phase transitions but have been difficult to measure accurately. Traditional methods, such as Positron Annihilation Spectroscopy (PAS), are limited by detection thresholds around 10^-7. To overcome these limitations, we have developed a novel approach utilizing Atom Probe Tomography (APT) to measure diffusivity enhancements, thereby enabling the detection and quantification of vacancy supersaturation. By incorporating a cryogenic microstructure freezing and sample preparation technique, we characterized the evolution of spinodal decomposition to more effectively capture the impact of vacancy oversaturation on diffusion-driven phase transitions. This advancement holds substantial promise for industrial applications, where harnessing vacancy-enhanced phase transitions could lead to significant breakthroughs in material design and optimization.

Speaker: Xinren Chen (MPI-SM)

16 Artificial intelligence-enhanced atom probe microscopy: Local chemical ordering analysis

In solids, chemical short-range order (CSRO) refers to the self-organisation of atoms of certain species occupying specific crystal sites. CSRO is increasingly being envisaged as a lever to tailor the mechanical and functional properties of materials. CSRO is typically characterized indirectly, using volume-averaged (e.g. X-ray/neutron scattering) or through projection microscopy techniques that fail to capture the complex, 3D atomistic architectures. Quantitative assessment of CSRO and concrete structure-property relationships have remained so far unachievable. Herein, we showcase how machine learning-enhanced atom probe tomography (APT) can mine the near-atomically resolved APT data and jointly exploit the technique’s high elemental sensitivity to provide a 3D quantitative analysis of CSRO in a series of metallic materials, including Fe-Al, Fe-Ga, and CoCrNi medium-entropy alloys. We reveal multiple CSRO configurations, with their formation supported by state-of-the-art Monte-Carlo simulations. Quantitative analysis of these CSROs allows us to establish relationships between processing parameters and physical properties. The proposed strategy can be generally employed to investigate short/medium/long-range ordering phenomena in a vast array of materials and help design future high-performance materials.

Speaker: Yue Li (Max-Planck-Institut für Nachhaltige Materialien GmbH)

17 Atom probe tomography:a local probe for chemical bonds in solids

Atom probe tomography is frequently employed to characterize the elemental distributionin solids with atomic resolution. Here we review and discuss the potential of this techniqueto locally probe chemical bonds. Two processes characterize the bond rupture in laser-assisted field emission, the probability of molecular ions, i.e. the probability that molecularions (PMI) are evaporated instead of single (atomic) ions, and the probability of multipleevents, i.e. the correlated field-evaporation of more than a single fragment (PME) uponlaser- or voltage pulse excitation. Here we demonstrate that one can clearly distinguishsolids with metallic, covalent, and metavalent bonds based on their bond rupture, i.e. theirPME and PMI values. Differences in the field penetration depth can largely explain thesedifferences in bond breaking. These findings open new avenues in understanding anddesigning advanced materials, since they allow a quantification of bonds in solids on ananometer scale, as will be shown for several examples. These possibilities would evenjustify calling the present approach bonding probe tomography (BPT).

Speaker: Yuan Yu (RWTH Aachen University)

12:00 Lunch Break

Applied Materials: Oxides: Applied Material: Oxides

18 Switching preferential evaporation for core/shell field emitters

When measuring heterogeneous samples with atom probe tomography (APT), the different evaporation behaviour of the materials can lead to non-hemispherical apex topographies [1]. Because the local curvature is one of the main factors determining the ion trajectories, any deviation from a hemispherical shape can lead to locally varying magnifications and therefore, spatial inaccuracies [2]. In our work, we investigate the dependence of the local magnification on the applied voltage and laser power in APT.

Pre-sharpened silicon microtip coupons were coated with vanadium oxide by atomic layer deposition [3], yielding silicon/vanadium oxide core/shell tips. Identical behaviour was observed for coupons coated with vanadium dioxide (VO2) and vanadium pentoxide (V2O5). We will show that the applied voltage (electric field) is driving a change of the (local) magnification of the silicon core. Furthermore, atomic force microscopy on APT tips [4] reveals a clear link to the apex topography, where a protruding centre corresponds to a high magnification of the core and a concaving centre to a low magnification. Together with 2D evaporation simulations, where the experimental ion maps were reproduced qualitatively by varying the ratio of the evaporation fields of the materials, we conclude that silicon and vanadium oxide exhibit a field driven switch in preferential evaporation. We suggest a evaporation barrier reduction dependent on the hole density in each material as underlying reason. A redistribution of holes dependent on the electric field leads to a change in the relative evaporation barriers und thus the switch in preferential evaporation of silicon and vanadium oxide.

[1] Miller, M.K., and Hetherington, M.G., Surface Science 246.1-3 (1991): 442-449.
[2] Grenier, A., et al. Ultramicroscopy 136 (2014): 185-192.
[3] Mattelaer, F., et al. RSC advances 6.115 (2016): 114658-114665.
[4] Op de Beeck, J., et al. J. Phys. Chem. C 124.11 (2019): 6371-6378.

Speaker: Nadya Spettel (KU Leuven)

19 Advancing Atom Probe Tomography of SrTiO₃: Measurement Methodology, Impurity Detection Limits and Grain Boundary Analysis

Strontium titanate (STO) is a material with promising properties for applications in thermoelectricity, catalysis, fuel cells and other fields but its properties are highly sensitive to stoichiometry and the presence of impurities and other defects, particularly grain boundaries. Transmission electron microscopy (TEM) has been instrumental in studying the atomic-scale structure of STO; however, it provides limited chemical and three-dimensional information. These gaps can normally be filled by using atom probe tomography (APT) but this has faced challenges in analyzing STO, particularly the early fracture of specimens. In this study, we demonstrate that metal-coated STO specimens can be successfully analyzed, with nearly 100% yield. We apply this method to both undoped and 1 at% Nb-doped STO, achieving a sensitivity capable of detecting as little as 0.7 at% Nb. Additionally, we report on successful APT analysis of a bicrystal STO grain boundary. Direct comparison with scanning transmission electron microscopy (STEM) of the facetted grain boundary reveals a Sr depletion of 30% within a 2 nm wide region. This work presents a robust APT methodology for reliable, high-resolution chemical analysis of STO at the nanometer scale.

Speaker: Jan Erik Rybak (Institut für Materialphysik, Georg-August-Universität Göttingen)

20 Atomic-Scale Analysis of Bismuth-Based Layered Oxy-chalcogenides Using Atom Probe Tomography

The beauty of Bismuth-based layered oxy-chalcogenide is their two distinct alternatively stacked layered structure having completely different chemical bonds in each layer i.e., oxide layer and chalcogen layer. This interesting layered structure allows the tuning of properties and can make a potential candidate in different fields such as thermoelectrics. For a thermoelectric device, Bi2O2Se is considered a perfect n-type candidate to pair with p-type BiCuSeO. The thermoelectric performance is related to their microstructure, chemical composition, and bonding mechanism. However, the studies show that a small variation in chemical composition leads to a great change in properties. However, atom probe tomography has a unique ability to explain the bonding mechanism of materials. In the literature, the Bismuth-based layered oxy-chalcogenides analysis on an atomic scale has not been reported until now. In this study, the atom probe data on three compositions, Bi2O2Se, Bi2O2Se0.5Te0.5, and Bi2O2Te, will be discussed to understand the chemical bonding mechanism in these layered structures.

Speaker: Sumayya Sumayya (RWTH, Aachen)

14:30 Coffee Break

Applied Functional Materials

21 Atom probe analysis of hexagonal Ge grown on GaAs nanowires

M. Krämer$^a$, I. Dudko$^{b,c}$, A.D. Lamirand$^b$, C. Botella$^b$, P. Regreny$^b$, A. Danescu$^b$, M. Bugnet$^d$, S. Walia$^c$, J. Penuelas$^b$, N. Chauvin$^b$ and B. Gault$^{a,e}$

(a) Max Planck Institute for Sustainable Materials, Max-Planck-Straße 1, 40237 Düsseldorf, Germany
(b) Ecole Centrale de Lyon, CNRS, INSA Lyon, Université Claude Bernard Lyon 1, CPE Lyon, INL, UMR 5270, 69130 Ecully, France
(c) School of Engineering, RMIT University, Melbourne 3001, Victoria, Australia
(d) Univ Lyon, CNRS, INSA Lyon, UCBL, MATEIS, UMR 5510, 69621 Villeurbanne, France
(e) Department of Materials, Royal School of Mines, Imperial College London, London, SW7 2AZ UK

Semiconductors with strong light emission and absorption are required for optoelectronic applications, where an electronic signal is converted to an optical signal and vice versa. Hexagonal Ge is a promising candidate for group IV photonics because, unlike its natural cubic phase, it has a direct band gap and therefore stronger light emission. Hexagonal Ge can be synthesized by the crystal transfer method, in which the small lattice mismatch allows Ge to be grown, for example, on the facets of wurtzite GaAs nanowires by molecular beam epitaxy, thereby adopting the hexagonal structure.

Atom probe tomography and high-resolution transmission electron microscopy of such grown hexagonal Ge on GaAs nanowires reveal the formation of quantum dots, that coalesce into radial quantum wells with increasing growth time. Photoluminescence spectroscopy on heterostructures reveals strong quantum confinement in the quantum dots, resulting in strong light emission in the telecom bands, which disappears with the onset of coalescence.

Speaker: Mathias Krämer (Max Planck Institute for Sustainable Materials)

22 Effect of Ag nanoadditivation on microstructure formation in Nd-Fe-B magnets built by laser powder bed fusion

Additive manufacturing of Nd-Fe-B permanent magnets through laser powder bed fusion of metals (PBF-LB/M) provides opportunities for microstructural manipulation leading to novel combination of properties. Additivation of the feedstock powder with Ag nanoparticles (NPs) improves the coercivity of PBF-LB/M-produced Nd-Fe-B magnets by 17 ± 6% in as-built conditions (935 kA/m) compared to the unadditivated counterpart. To advance the understanding of the associated mechanisms, we use atom probe tomography (APT) and show that Ag-nanoadditivation leads to a fine dispersion of Ag-rich nanophase regions, on which the main 2:14:1 magnetic phase nucleates heterogeneously. This refines the magnetic particle size distribution, which, along with a change in phase composition in comparison to the unmodified feedstock, explains the improved properties.

Speaker: Varatharaja Nallathambi (Max Planck Institute for Sustainable Materials)

23 Correlative STEM/APT analysis of antiferromagnetic thin films

Multiferroic antiperovskite materials have shown considerable promise in recent years due to functionalities enabled by the coupling between their magnetic, mechanical, or electronic properties, leading to potential applications in sensors, transduers, spintronics, and novel memory devices. Understanding this coupling, and most importantly reliably controlling it with the application of various stimuli is crucial if these materials were to be used as the next generation of functional devices.

The thin film material Mn₃Cu₀.₅Sn₀.₅N (MCSN) is a non-collinear antiferromagnet with unique magnetostructural coupling properties, such as negative thermal expansion and the magnetocaloric effect. These properties are highly sensitive to local strain variations, which can significantly influence the magnetic behavior of the material. Given the strong link between magnetic properties and structure, techniques such as 4D-STEM provide an ideal resolution and length scale to analyze strain effects and the presence of structurally distinct phases. Additionally, relating compositional variations with structural features is another important aspect we wanted to explore. For this, we used APT to correlate chemistry in 3 dimensions with electron diffraction data, allowing a better understanding on how the two relate to the magnetic properties at the nanoscale, providing insight into bulk magnetic measurements previously performed on these thin films.

Speaker: Geri Topore (Imperial College London)

15:50 Coffee Break

Applied Functional Materials

24 Catalytic Efficiency of RuTi Thin Films and its Dependence on Microstructure and Chemistry

Increasing environmental concerns have emphasized the significance of hydrogen and its production through sustainable routes. Hydrogen generation by water electrolysis has been considered an effective and environmentally friendly approach in which catalysis or electrocatalysis plays a vital role. Up to now, catalysts based on platinum group materials have dominated the market, with platinum and iridium being considered the most efficient catalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). However, there is a need to develop active, long-lasting and cost-effective electrocatalysts made from abundant materials for a feasible hydrogen economy.
Ruthenium is considered to be a promising alternative to platinum due to its similar catalytic activity and significantly lower cost. Previous studies have demonstrated that adding titanium to ruthenium-iridium catalysts increases stability without compromising catalytic activity. Defects and local chemistry at defects have been also investigated and identified as a prominent influence on the catalytic activity.
Our study focuses on a systematic investigation of microstructure and composition and their role on the catalytic activity of ruthenium-titanium thin film. We investigated different compositions and varied the grain size to deconvolute their significance on the catalytic activity. Atom probe tomography revealed the presence of local compositional differences in the microstructure and subsequent electrochemical characterization showed promising findings.

Speaker: Beste Payam (Max-Planck-Institut für Eisenforschung GmbH)

25 Advancing Grain Boundary Research with Atom Probe Tomography: Unveiling Atomic-Scale Mechanisms in Ultrafine Nanomaterials

Grain boundaries (GBs) critically impact the mechanical, electrical, and catalytic properties of polycrystalline materials, making their investigation essential for material science progress. Atom probe tomography (APT) offers an advanced technique for atomic-scale analysis of GBs, generating three-dimensional compositional maps with sub-nanometer resolution. Using APT, we can directly observe elemental segregation at GBs and its influence on the behavior of ultrafine nanomaterials (approximately 2 nm in size), particularly in mitigating the degradation of functional properties. APT also provides precise measurements of solute distribution, revealing the mechanisms that govern GB interactions. Combined with complementary methods such as electron microscopy, APT enhances our understanding of GB chemistry and structure, driving innovations in material design. Our study highlights the critical role of APT in advancing GB research and its contribution to the development of high-performance functional materials.

Speaker: Xin Geng (Max Planck Institute for Sustainable Materials)

26 Probing Dealloying Mechanisms in Thin-Film Nanoporous Metals Using Atom Probe Tomography

Dealloying corrosion has become a popular method for obtaining highly functional nanoporous gold (NPG) substrates1. The selective dissolution of Ag from AgAu solid solutions in acidic environments leads to the formation of an open-pore, bicontinuous 3D, nanoporous structure. Using thin film precursors, as opposed to solid-solution alloys, facilitates easier integration of NPG into energy stor-age and catalytic devices owing to the inherent substrate-support feature2,3. High-resolution studies of dealloyed thin films could guide optimization efforts by revealing the effect of as-deposited struc-ture and dealloying conditions on the morphology and chemical structure of dealloyed substrates.

In this investigation, we focus on studying NPG made by dealloying AgAu thin films deposited via magnetron sputtering. Using scanning electron microcopy (SEM) and electron backscatter diffrac-tion (EBSD), we uncovered the different morphologies attained due to non-equilibrium AgAu com-positions created by the sputtering process. Atom probe tomography (APT) was used to study the influence of dealloying conditions on nanoligament compositions, at the atomic-scale4. We correlate our findings to subtleties in the dealloying mechanism of AgAu, that are introduced by the thin-film properties of AgAu. Significant findings include the different electrochemical regimes of dealloying and the formation of Au-rich segregates at grain boundaries.

Speaker: Ezgi Hatipoglu (Max-Planck-Institut für Nachhaltige Materialien GmbH)

Thursday 21 November

Applied Structural Materials

27 High-precision elemental analysis in atom probe tomography: The benefits of short laser wavelengths

This study focuses on the influence of laser wavelength and pulse energy on the elemental accuracy of atom probe tomography (APT) analysis of stoichiometric TiN coatings. By utilizing three different commercial atom probe systems — LEAP 3000X HR, LEAP 5000 XR, and LEAP 6000 XR — it is illuminated how short laser wavelengths, especially those in the deep ultraviolet (DUV) range, impact the evaporation behavior and the precision of the measurements. The findings demonstrate that shorter wavelengths result in enhanced elemental accuracy by minimizing the laser pulse energy while maintaining consistent electric field strengths, thus reducing thermal effects that typically degrade the mass resolving power. These improvements are critical to achieve accurate and reliable compositional data, particularly in materials where maintaining structural integrity during analysis is essential.
In addition, an analysis of the energy density ratios across the three atom probe systems is presented, highlighting that shorter wavelengths correlate with smaller laser spot sizes and consequently higher energy densities. These increased energy densities, while potentially resulting in higher heat input, are confined to a smaller region at the apex of the specimen. This allows for faster cooling rates, minimizing thermal diffusion and surface migration, both of which are detrimental to the elemental accuracy of APT measurements.
Furthermore, advancements in detector technology were evaluated to assess their role in improving measurement accuracy. Detector dead-times and dead-zones were thoroughly analyzed to understand their effect on ion pile-up behavior, which can compromise the accuracy of APT measurements. The results showed that while the improvements in detector technology enhance the overall system performance, the reduction in laser wavelength plays a more significant role in improving the elemental accuracy.

Speaker: Maximilian Schiester (Department of Materials Science, Montanuniversität Leoben)

28 Understanding the role of impurities in recycled Cu from EV batteries

Electric vehicles (EVs) are on the rise and with it, the expected number of scrap or end-of-life batteries. Since battery production from raw materials is energy-intensive and environmentally burdensome, it is economically beneficial to recycle batteries than to dispose them. However, the diverse range of cathode materials makes the recycling process complex, as the purity standards are typically not met. In this work, we have performed a detailed microstructural analysis near-atomic scale of recycled Cu from EV battery current collectors. We observe oxygen segregation at the grain boundaries and the presence of nano-sized BCT precipitates enriched in Fe, Co and Ni distributed in a Cu matrix. The presence of these precipitates decrease the conductivity of Cu, nevertheless, the dirty Cu reveals a similar cyclic performance as a standard current collector. Our findings provide insights on the influence of impurities during recycling and informs the optimization of the current battery recycling practices towards a circular economy.

Speaker: Raymond Kwesi Nutor (Max-Planck-Institut für Nachhaltige Materialien GmbH)

29 Difficulties in the detection of interstitial atom segregation on dislocations in steels using atom probe tomography

Atom Probe Tomography (APT) can be used to analyze the structure of matter at the smallest scales, such as grain boundaries, dislocations or even atomic planes in certain special cases. As such, APT can be used to study dynamic strain-ageing in steels, which relies on the segregation of free interstitials (C and N) on dislocations. Surprisingly, very few studies regarding the segregation on dislocations using APT are available in the literature and there are no reviews concerning carbon segregation to dislocations in steel using APT.

In this study, we present APT results from industrial welds of low-alloy or carbon-manganese steels. The materials were studied in the heat-affected zone (HAZ) or in the weld metal, with or without post weld heat treatment (PWHT). The dislocation density of the studied steels was rather high, about 1014 m-2, as determined by multiple experimental techniques. In some cases, the decoration of dislocations by segregation of solute atoms is easily observed and the dislocation density determined by APT is in agreement with that obtained by the other techniques. However, segregation on dislocations was not observed in some steels, in a total of 200 APT volumes, even though one dislocation is expected every 2 to 3 APT volumes.

Other experiments have been carried out to try and understand the origin of this problem, but none have been able to solve it. A number of hypotheses have been put forward to understand our observations, including the possibility of dislocations escaping from the tip during the APT analysis or the absence of segregation on the dislocations, but none is fully satisfactory to explain the problem encountered.

Keywords: Atom Probe Tomography, Segregation, Dislocations, Steel

Speaker: William MOTTAY (IM2NP - Framatome)

30 Unveiling nanometric phase formation and oxidation achieved by spark plasma sintering of Zn-Mg-(Ag) alloys for bioresorbable implants

Zn-based alloys have considerable potential as bioresorbable scaffolds for implants. Alloying with Mg or Ag enhances both biocompatibility and mechanical properties through precipitation strengthening and grain refinement during material production. Here we seek to advance the understanding of the precipitation mechanisms in Zn-Mg-(Ag) alloys prepared by a combination of mechanical alloying (MA), spark plasma sintering (SPS), and rapid hot extrusion for subsequent consolidation. Nanometric precipitates enriched in Mg, which have a high reactivity with oxygen, form during processing, as revealed by atom probe tomography (APT), a spatially-resolved three-dimensional mass spectroscopy technique. We provide a range of novel insights into the structure and composition of the intermetallic precipitates. The effects of microalloying additions to Zn-Mg alloys and the deformation processes on the microstructure formed and degradation behavior are often poorly characterized in the literature, leaving several knowledge gaps that our present study addresses in an effort to help guide improvements in Zn-based alloy design for bioresorbable materials.

Speaker: Selase Torkornoo (Max-Planck-Institut für Nachhaltige Materialien GmbH)

10:20 Coffee Break

Applied Structural Materials

31 Vacuum Dealloyed Brass: A Tale of Materials Development with an Electrifying Second Act

Dealloyed yellow brass (CuZn37) has demonstrated promise as a porous support medium for various applications. This study focuses on vacuum dealloying of yellow brass prepared at varying temperatures. Dealloying allows more complete zinc removal compared to chemical methods enabling the evaluation of the microstructural evolution1,2. The resultant microstructure and porosity were analyzed using nano-computed tomography (nano-CT), revealing detailed morphological changes. It was found that increasing the dealloying temperature led to progressively coarsened pores, characteristic of Kirkendall void formation.

Characterization of the chemical changes occurring at different dealloying temperatures, employed atom probe tomography (APT), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDX). These methods provided insights into elemental redistribution, surface composition, and porosity, offering a comprehensive understanding of the dealloying process and its effects on the material's properties, such as concentration of zinc around pores. The performance of these materials, including metrics such as charge capacity and cycling stability, is presented alongside chemical analysis of the electrodes post-cycling. This study elucidates the impact of dealloying temperature on microstructure and chemistry and also highlights the potential of vacuum dealloyed brass as an advanced material for energy storage applications.

Heading

Speaker: Eric Woods (MDES)

32 Nano-scale investigation of fractal abnormal grains and grain boundaries in Pd-Au

Nanocrystalline (NC) Pd-Au prepared by inert gas condensation exhibits
fractal abnormal grain growth during heat treatment. The resulting
microstructure is characterized by a bimodal grain size distribution
with micrometer-sized grains (FG) embedded in a matrix of NC
grains (NG). To elucidate this unusual manifestation of grain growth,
we analyzed FG and NG bulk regions, as well
as the FG-FG and FG-NG interface regions with APT. The NG region exhibited an O
content that was multiple times higher in comparison with the FG region.
Cluster analysis confirmed the presence of a multitude of O-rich
clusters in the NG, but not in the FG region. Furthermore, the reconstructions
of the boundary regions revealed an unexpected diversity
of host and contamination element distributions at the FG-FG and
FG-NG interfaces.

Speaker: Johannes Wild (Institute for Applied Materials (IAM-WK), Karlsruhe Institute of Technology)

33 Microscopy of atom probe needles and how this might inform data reconstruction protocols

Microscopy of atom probe needles and how this might inform data reconstruction protocols

Speaker: Claudia Fleischmann (KU Leuven, imec)

12:00 Lunch and Departure