Superfluid helium nanodroplets act as ultracold, nanoscale “cryostats” that enable the synthesis of exceptionally pure metallic, bimetallic, and hybrid nanoparticles with precise control over size and architecture. This review highlights how advanced electron microscopy—particularly aberration‐corrected scanning transmission electron microscopy combined with spectroscopy—reveals the structure, composition, and three‐dimensional morphology of these particles at near‐atomic resolution. In situ heating and cooling experiments uncover unique thermodynamic behaviors, such as nanowire breakup, alloying, and structural inversion, while studies on beam‐induced effects expose atomic displacements and radiolysis‐driven chemistry. The soft‐landing deposition of the helium droplet method preserves metastable configurations and facilitates the creation of nanoparticle architectures that are unattainable by conventional routes. Looking ahead, emerging low‐dose imaging techniques, phase‐sensitive methods, and machine learning‐driven analyses promise to further expand our ability to design and study functional nanomaterials for use in catalysis, plasmonics, and quantum technologies.

Spectroscopic electron tomography using EDX and EELS signals presents significant challenges in both data acquisition and processing, particularly when aiming for high-fidelity 3D reconstructions. In this work, we present complete workflows that address these challenges through scripting-based solutions for automated parallel acquisition of EDX and EELS tilt series on the same microscope, as well as post-processing methods for correlating datasets acquired on different instruments. We demonstrate the advantages of a multimodal joint reconstruction, especially for undersampled or noisy data, where the combination of signals improves the reconstruction quality and enables lower-dose acquisition strategies. The developed workflows are applied to a spinodal CuNiFe alloy sample with inherently low HAADF contrast, successfully resolving ambiguities in the structure of nanoscale precipitates.

Single atom detection in nanoporous materials is a significant challenge, particularly due to their sensitivity to electron irradiation. Here, natural beryl (Be 3 Al 2 Si 6 O 18 ) is used as a model system to quantitatively analyse the occupancy of its atomic channels. High-angle annular dark-field imaging in a scanning transmission electron microscope is employed, revealing the presence of Cs atoms within the channels. Through statistical analysis of atomic column intensities and comparison with a series of multislice simulations, we successfully pinpoint the three-dimensional positions of individual Cs atoms. Our findings indicate a non-uniform distribution of Cs atoms in the crystal. Importantly, by extracting both the crystal thickness and atomic positions from a single high-resolution micrograph, we effectively minimize the adverse effects of beam damage. This approach offers a promising pathway for accurately determining the three-dimensional distribution of dopant atoms in various porous materials, opening new possibilities for the study and application of these technologically important materials.

Exploring the chemical micro- and nanostructure of metal alloys is essential to understand their physical properties, such as magnetism or hardness. Additively manufactured (AM) materials, e.g. via laser powder bed fusion (LPBF) followed by various heat treatments, can raise further questions concerning the printed material. For the in-situ alloyed, spinodal Fe 54 Cr 31 Co 15 system, the macroscopic magnetic behaviour is greatly influenced by subsequent homogenisation and heat treatment steps. Here we show that the decomposition takes place on the nanometre scale, resulting in ferromagnetic FeCo-rich particles embedded in a Cr-rich matrix. By studying phenomena like chemical homogeneity, grain structure, and texture of the in-situ alloyed material at different scales, we reveal correlations between the heat treatment and the resulting nanostructure and its ferromagnetic properties. We found that the isothermal heating conditions determine the degree of phase segregation and that a homogenization step can be omitted for additively manufactured, in-situ alloyed FeCrCo alloys. The approach thereby offers insight and a path for also tailoring specific manufacturing parameters to provide the right quality printed materials with desired functionalities. For example, magnetic FeCrCo alloys are often used in electric motors or magnetic sensors, and the flexibility of the presented approach can lead to optimal use of the material.

Ball-milling and harsh manufacturing processes often generate crystal disorder which have practical implications on the physical and chemical stabilities of solid drugs during subsequent storage, transport, and handling. The impact of the physical state of solid drugs, containing different degrees/levels of crystal disorder, on their autoxidative stability under storage has not been widely investigated. This study investigates the impact of differing degrees of crystal disorder on the autoxidation of Mifepristone (MFP) to develop a predictive (semi-empirical) stability model. Crystalline MFP was subjected to different durations of ambient ball milling, and the resulting disorder/ amorphous content was quantified using a partial least square (PLS) regression model based on Raman spectroscopy data. Samples of MFP milled to generate varying levels of disorder were subjected to a range of (accelerated) stability conditions, and periodically sampled to examine their recrystallization and degradation extents. Crystallinity was monitored by Raman spectroscopy, and the degradation was evaluated by liquid chromatography. The analyses of milled samples demonstrated a competition between recrystallization and degradation via autoxidation of MFP, to different extents depending on stability conditions/exposure time. The degradation kinetics were analyzed by accounting for the preceding amorphous content, and fitted with a diffusion model. An extended Arrhenius equation was used to predict the degradation of stored samples under long-term (25°C/60% RH) and accelerated (40°C/75% RH, 50°C/75% RH) stability conditions. This study highlights the utility of such a predictive stability model for identifying the autoxidative instability in non-crystalline/partially crystalline MFP, owing to the degradation of the amorphous phases. This study is particularly useful for identifying drug-product instability by leveraging the concept of material sciences.

Nanoparticles with diameters in the range of a few nanometers, consisting of gold and vanadium oxide, are synthesized by sequential doping of cold helium droplets in a molecular beam apparatus and deposited on solid carbon substrates. After surface deposition, the samples are removed and various measurement techniques are applied to characterize the created particles: scanning transmission electron microscopy (STEM) at atomic resolution, temperature dependent STEM and TEM up to 650 °C, energy-dispersive X-ray spectroscopy (EDXS) and electron energy loss spectroscopy (EELS). In previous experiments we have shown that pure V2O5 nanoparticles can be generated by sublimation from the bulk and deposited without affecting their original stoichiometry. Interestingly, our follow-up attempts to create Au@V2O5 core@shell particles do not yield the expected encapsulated structure. Instead, Janus particles of Au and V2O5 with diameters between 10 and 20 nm are identified after deposition. At the interface of the Au and the V2O5 parts we observe an epitaxial-like growth of the vanadium oxide next to the Au structure. To test the temperature stability of these Janus-type particles, the samples are heated in situ during the STEM measurements from room temperature up to 650 °C, where a reduction from V2O5 to V2O3 is followed by a restructuring of the gold atoms to form a Wulff-shaped cluster layer. The temperature dependent dynamic interplay between gold and vanadium oxide in structures of only a few nanometer size is the central topic of this contribution to the Faraday Discussion.

Abstract The detection of single atoms with atomic resolution is a major challenge, in particular for technologically highly relevant nanoporous materials. Their nano-sized pores provide a large surface area and can also confine individual atoms and molecules, enabling the fine-tuning of catalytic performance or molecular transport properties. Previous studies employing aberration-corrected scanning transmission electron microscopy (STEM) have been limited to visualizing guest components within the pores without providing quantitative information. In this study, utilizing natural beryl (Be3Al2Si6O18) as a model system, we present a quantitative analysis of atomic occupancy within its channels. Through high-angle annular dark-field (HAADF) imaging, we clearly demonstrate the presence of Cs atoms within the channels. Furthermore, employing statistical analysis of atomic column intensities and comparison with a series of multislice simulations, we successfully determine the three-dimensional positions of individual Cs atoms within the channels. Thereby, we also reveal that the Cs atoms are non-uniformly distributed within the channels. By extracting the necessary information from a single high-resolution micrograph, we minimize the adverse effects of beam damage, making this methodology a promising approach for the analysis of diverse porous materials.

Magnetic spinodal alloys are ideal materials for studying the relationship between the microstructure of an alloy and its magnetic properties. To unravel this relation, a profound knowledge of the chemical as well as the magnetic microstructure, i.e. the magnetic domain structure, is necessary. However, mapping the magnetic domain structure is rarely accomplished even though it is of major interest for both, fundamental research as well as applications using such alloys. In this study, the magnetic domain structure as well as the evolution of the microstructure of spinodally decomposed Cu52Ni34Fe14 alloys is investigated with various modern (scanning) transmission electron microscopy ((S)TEM) methods. The magnetic domain structure was mapped using differential phase contrast imaging (STEM DPC) and magnetic-force microscopy (MFM). The chemical microstructure was determined using high-angle annular dark field imaging (HAADF) and energy-dispersive X-ray spectroscopy (EDXS) elemental mapping.

High-resolution STEM-EELS provides information about the composition of crystalline materials at the atomic scale, though a reliable quantitative chemical analysis is often hampered by zone axis conditions, where neighbouring atomic column intensities contribute to the signal at the probe position. In this work, we present a procedure to determine the concentration of two elements within equivalent atomic columns from EELS elemental maps - in our case barium and lanthanum within the A-sites of Ba1.1La1.9Fe2O7, a second order Ruddlesden-Popper phase. We took advantage of the large changes in the elemental distribution from column to column and introduced a technique, which substitutes inelastic scattering cross sections during the quantification step by using parameters obtained from the actual experiment. We considered channelling / de-channelling effects via inelastic multislice simulations and were thereby able to count occupancies in each atomic column. The EELS quantification results were then used as prior information during the Rietveld refinement in XRD measurements in order to differentiate between barium and lanthanum.

Precipitation hardened and tempered martensitic-ferritic steels (TMFSs) are used in many areas of our daily lives as tools, components in power generation industries, or in the oil and gas (O&G) industry for creep and corrosion resistance. In addition to the metallurgical and forging processes, the unique properties of the materials in service are determined by the quality heat treatment (HT). By performing a quenching and partitioning HT during an in situ high energy synchrotron radiation experiment in a dilatometer, the evolution of retained austenite, martensite laths, dislocations, and carbides was characterized in detail. Atomic-scale studies on a specimen with the same HT subjected to a laser scanning confocal microscope show how dislocations facilitate cloud formation around carbides. These clouds have a discrete build-up, and thermodynamic calculations and density functional theory explain their stability.

Intrinsically magnetic layered materials – especially monolayers – suffer from the lack of ambient stability and mostly exhibit magnetic ordering only at cryogenic temperatures. These restrains impose a great challenge for the integration of two-dimensional magnetic materials into future technologies. We propose to overcome this by exploiting phyllosilicates, such as iron-rich talc. Via combined magnetic force microscopy in applied external magnetic fields, superconducting quantum interference device magnetometry, first-principle calculations, and structural analysis, we demonstrate that incorporated iron ions in talc are in a very robust high spin state, resulting in a weak ferromagnetic behavior at room temperature. Iron-rich talc can be thinned down to a monolayer, remaining fully stable under ambient conditions, and retaining magnetic properties even in monolayers. Finally, we propose iron-rich end members of the phyllosilicates as very promising platforms for air-stable magnetic monolayers.

Amilenus aurantiacus overwinter in diapause, a natural starvation period, in hypogean habitats. The structure of spherites in the midgut diverticula (MD) and Malpighian tubules (MT) has been studied comparatively by light microscopy and TEM to detect eventual differences in mineral consumption in the beginning and at the end of the starvation period in these organs (MD and MT) associated with digestive processes. The chemical composition of spherites was examined by combining energy-dispersive X-ray spectroscopy (EDXS), electron energy-loss spectroscopy (EELS) and energy-filtered TEM (EFTEM). The structure of the spherites changed during overwintering in both organs. At the beginning of overwintering, the spherites were composed of densely packed concentric layers of electron-dense and electron-lucent material. In the middle and at the end of overwintering, the electron-lucent layers between the layers of material indicated the loss of some material. The chemical composition of the spherites changed only in the MD; at the beginning of overwintering, these contained Si, O, C and Fe, while later there was no more Fe. In contrast, spherites in the MT were composed of Si, O, C and Ca throughout overwintering. A less intensive exploitation of the MD spherites was probably due to complete cessation of digestive and other cell activity in this organ during the winter diapause; activity of the MT slowed, but continued removing the cell metabolites.

Long-term stability tests are performed at 800 °C on Pr2NiO4+δ air electrodes by use of a symmetrical button cell with Ce0.9Gd0.1O1.95 as solid electrolyte. The experiments are carried out by means of electrochemical impedance spectroscopy and current-voltage measurements with and without current load under dry and humid conditions in the presence of a chromium source. Chromium poisoning of Pr2NiO4+δ air electrodes is investigated for periods of several hundred hours at 30% relative humidity. In order to separate the influence of anodic and cathodic electrode polarization on Cr-deposition, measurements are conducted using a Pt-reference electrode. The electrode performance is found to remain fairly stable under dry conditions, even when a current is drawn. However, after volatile Cr-species in a humid atmosphere are introduced, the cell performance starts to deteriorate and the polarization resistance contribution of the SOFC cathode increases significantly. After several thousand hours, the electrodes are analyzed by means of analytical electron microscopy. Detailed post-test analyses provide evidence for a correlation between the extent of Cr-deposition and electrode degradation in SOFC as well as SOEC mode. Based on these findings, enhanced resilience of Pr2NiO4+δ against Cr-poisoning in SOEC mode can be established.

Whole sample microscopy mappings are of interest in many cases as they provide analytical information of phases varying in size by orders of magnitude and in composition across the sample. These benefits are amplified if more than one microscopic technique is used for the mappings. However, to take full advantage of correlative whole sample mappings, the data of each technique has to be carefully prepared, treated, correlated and evaluated. With this work, we want to present the key steps of our data treatment approach as well as the results on an exemplary sample, the Chelyabinsk meteorite. The most important step in our data treatment approach is to start by evaluating the spectral maps separately as far as possible (at-% quantification for EDS for example) and then generate pseudo spectral maps from this evaluation in the form of image stacks. This allows us to preserve the advantages of specialized software packages and standard work flows for every spectral mapping, whilst also unifying the data format and compressing the data sufficiently for correlation and the application of machine learning tools. We have performed whole sample mappings using SEM, EDS and Raman on a cross-section of a Chelyabinsk meteorite fragment, roughly 1.0cm × 0.8cm large. Combining these mappings into a single “super” spectral map, we were able to produce a uniquely detailed mapping of the composition of the meteorite fragment, as well as perform a quantitative analysis of the elemental composition of several crystallographic phases. The results of our compositional analysis; olivine (Fo72Fa28), pyroxene (≈ 97 % En80Fs20Wo0 and 3 % En56Fs6Wo38), feldspar (albite), troilite, FeNi (taenite and kamacite), merrillite, chromite and hydroxyapatite; agree qualitatively with other reports from literature.

A solar energy conversion system, an organic tandem solar cell, and an electrochemical energy storage system, an alkali metal-ion battery, were designed and implemented in an integrated hybrid photorechargeable battery for simultaneous energy conversion and storage. As a proof of concept, the integrated power pack was successfully realized in a three-terminal hybrid assembly featuring two negative and a joint positive electrode. The device can be directly charged upon illumination (photocharging) and discharged on the external load for many cycles. Aspects and requirements related to materials design, their specific properties, and the encapsulation issues are presented and discussed. Data on the compatibility of materials for solar cells with those used in batteries is presented for the first time. We also report on the efficiency of the solar cell part, the battery part, as well as the overall energy efficiency of the new system. From the behavior of this first of a kind device, we were able to derive its relevant characteristics that will guide future work in this highly application-oriented research field.

The electronic response of surface deposited nanoparticles to a few-cycle near infrared pump pulse is traced by attosecond XUV transient absorption spectroscopy.

This paper presents a unique correlative microscopic method for the structural characterization of extraterrestrial minerals. A fragment from the pallasite Seymchan meteorite that consists of olivine grains mixed into a metallic iron matrix with variable nickel content was studied from mm-down to nm-size by using the Raman Imaging and Scanning Electron Microscopy and analytical scanning transmission electron microscopy. Hyperspectral fast acquisition for energy-dispersive X-ray spectroscopy mapping of a couple of mm2 large area correlated with additional hyperspectral Raman analysis of smaller regions in the same area on one hand, and hyperspectral analytic STEM investigations at the atomic resolution, on the other hand, provided valuable information about the chemical composition, bonding, and crystallography. The analysis revealed particles of troilite, schreibersite, and forsterite but also regions of mixed iron oxides, carbonates, and amorphous carbon as well as plessite regions with nanometre-sized taenite needles dispersed in the kamacite matrix.

High-order harmonic generation (HHG) based transient extreme ultraviolet (XUV) absorption spectroscopy is an emerging technique to trace photoinduced charge carrier dynamics in condensed phase materials with femtosecond and even attosecond temporal resolution and elemental specificity. However, its application to nanoparticulate samples that are relevant, for example, for novel photocatalytic light harvesting concepts, has been limited. This is in part due to the challenge to produce residual-free samples on ultrathin, XUV-transparent substrates as well as a widespread understanding that sparsely distributed nanoparticles do not provide sufficient contrast for XUV absorption measurements. Here, we present static XUV absorption spectra of partially oxidized Co nanowire-structures with diameters of approximately 4.5 nm and lengths between 10 and 40 nm, recorded with an ultrashort pulse HHG light source. Nanoparticles are synthesized by the agglomeration of Co atoms inside superfluid helium droplets, followed by surface deposition and oxidation in ambient air. The method is uniquely suited for residual-free synthesis of transition metal nanowires and their deposition on ultrathin substrates. Analysis by high-resolution transmission electron microscopy reveals the formation of CoO nanowires with regions of unoxidized Co in their interior. The nanoparticle samples are investigated in an HHG-driven ultrafast XUV absorption setup. Despite the low surface coverage of only 23%, the recorded spectrum exhibits a distinct absorption feature at the Co M2,3(2p) edge near 60 eV with a peak height of about 40 mOD. The results support the feasibility of table-top ultrafast transient XUV absorption studies of photoinduced dynamics in transition metal oxide nanoparticles with sub-monolayer surface coverage.