High-angle Annular Dark-field Scanning Transmission Electron Microscopy Research Articles

Capturing low-concentration benzene: Design and mechanism of high-performance Cu1-Ox,Ny-C single-atom adsorbents

Common adsorbents, such as active carbons, zeolites, and metal–organic frameworks (MOFs), struggle to capture low concentrations of benzene. Single-atom adsorbents (SAAs), boasting exceptional atomic utilization efficiency and precisely tailored electronic structures, offer a promising solution. This study first designed Cu1-Ox,Ny-C SAAs and explored their enhanced benzene adsorption through density functional theory (DFT). Particularly, a crucial link between the SA coordination configuration and its affinity for benzene was established. Next, Cu1-Ox,Ny-C was synthesized from the MOF MIL-101(Cr) and extensively characterized using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and X-ray absorption fine structure (XAFS) spectroscopy, etc. to determine the coordination configuration of Cu single atoms. Finally, a thorough evaluation of the Cu1-Ox,Ny-C’ capacity and stability was conducted. Theoretical analysis revealed that Cu single atoms within the Ox,Ny-C matrix act as the primary adsorption sites for benzene. Notably, O and N atoms work synergistically: oxygen atoms promote adsorption, while nitrogen atoms mainly stabilize single-atom sites. Cu1-Ox,Ny-C was successfully synthesized, and characterization revealed that Cu1-O2,N2(trans)-C and Cu1-O3,N1-C were the dominant coordination configurations. Remarkably, despite a fourfold decrease in specific surface area compared to MIL-101(Cr), Cu1-Ox,Ny-C exhibited a threefold increase in chemisorption capacity for low-concentration benzene. Moreover, it exhibits excellent resistance to H2O and can be effectively reused. This study demonstrates a valuable strategy for designing and creating highly efficient SAAs for capturing low concentrations of benzene.

Unveiling microstructural damage for leakage current degradation in SiC Schottky diode after heavy ions irradiation under 200 V

Single-event burnout and single-event leakage current (SELC) in silicon carbide (SiC) power devices induced by heavy ions severely limit their space application, and the underlying mechanism is still unclear. One fundamental problem is lack of high-resolution characterization of radiation damage in the irradiated SiC power devices, which is a crucial indicator of the related mechanism. In this Letter, high-resolution transmission electron microscopy (TEM) was used to characterize the radiation damage in the 1437.6 MeV 181Ta-irradiated SiC junction barrier Schottky diode under 200 V. The amorphous radiation damage with about 52 nm in diameter and 121 nm in length at the Schottky metal (Ti)–semiconductor (SiC) interface was observed. More importantly, in the damage site the atomic mixing of Ti, Si, and C was identified by electron energy loss spectroscopy and high-angle annular dark-field scanning TEM. It indicates that the melting of the Ti–SiC interface induced by localized Joule's heating is responsible for the amorphization and the possible formation of titanium silicide, titanium carbide, or ternary phases. The mushroom-like hillock in the Ti layer can be attributed to Rayleigh–Taylor instability, as another evidence for ever-happened localized melting near the Schottky interface. These modifications at nanoscale in turn cause localized degradation of the Schottky contact, resulting in permanent increase in leakage current. This experimental study provides very valuable clues for a thorough understanding of the SELC mechanism in SiC diodes.

Elemental distribution and site occupancy in a Co-Ni-Al-Ti-Ta-W superalloy

γ'-precipitate strengthened cobalt-based superalloys show promise for higher temperature-capability over nickel-based superalloys due to higher melting temperatures. This study investigates a multicomponent CoNi-based superalloy with composition of 54Co-30Ni-9Al-1Ta-4Ti-2-W (at.%) in terms of elemental partitioning and site occupancy. Atom probe tomography (APT) reveals preferential partitioning of Ni, Al, Ti, Ta and W to the γ'-precipitate and Co to the γ-matrix. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and energy dispersive spectrometer (EDS) along the [001] zone axis of γ'-precipitate with L12 structure indicate that Co, Ni substitute at A-sites, whereas Al, Ti, Ta, W prefer the B-sites. Density functional theory (DFT) calculations further confirm the results of partitioning behaviors and site preferences. Clarifying elemental partitioning and site occupancy provides valuable insights into alloy design principles for advanced CoNi-based superalloys.

A new insight into largely defocused HAADF-STEM imaging and visualization of strain field

A crystalline bilayer specimen with a semi-coherent interface can generate moiré fringes in the high-angle annular-dark field scanning transmission electron microscopy (HAADF-STEM) imaging. Moreover, when the probe is significantly defocused, this specimen can produce largely defocused probe (LDP)-STEM patterns. Although the electron channeling effect serves as the fundamental principles for HAADF-STEM imaging, its connection to the emergence of LDP-STEM patterns remains unclear. The missing link lies in identifying the location of the imaged region. To address this issue, we examined the strain field in three-dimensional space and its interaction with the convergent electron beam, taking the PbZrO3/SrTiO3 (PZO/STO) heterostructure as an example. We discovered a new intensity relationship for LDP-STEM patterns in the PZO/STO heterostructure, which can be well explained by our theory. We also found that, generated by imaging the strain zone, these patterns revealed information that might be obscured in traditional high resolution STEM images, showing a unique advantage in characterizing the strain field. Furthermore, we provided discussions on visualizing the strain field, including the misfit dislocation network and array. Our research offers a novel perspective on the LDP-STEM imaging and clarifies the approach to characterizing the strain field.

Constrained patterning of orientated metal chalcogenide nanowires and their growth mechanism

One-dimensional metallic transition-metal chalcogenide nanowires (TMC-NWs) hold promise for interconnecting devices built on two-dimensional (2D) transition-metal dichalcogenides, but only isotropic growth has so far been demonstrated. Here we show the direct patterning of highly oriented Mo6Te6 NWs in 2D molybdenum ditelluride (MoTe2) using graphite as confined encapsulation layers under external stimuli. The atomic structural transition is studied through in-situ electrical biasing the fabricated heterostructure in a scanning transmission electron microscope. Atomic resolution high-angle annular dark-field STEM images reveal that the conversion of Mo6Te6 NWs from MoTe2 occurs only along specific directions. Combined with first-principles calculations, we attribute the oriented growth to the local Joule-heating induced by electrical bias near the interface of the graphite-MoTe2 heterostructure and the confinement effect generated by graphite. Using the same strategy, we fabricate oriented NWs confined in graphite as lateral contact electrodes in the 2H-MoTe2 FET, achieving a low Schottky barrier of 11.5 meV, and low contact resistance of 43.7 Ω µm at the metal-NW interface. Our work introduces possible approaches to fabricate oriented NWs for interconnections in flexible 2D nanoelectronics through direct metal phase patterning.

Bridge-oxygen bonding modulates Ru single atoms for peroxymonosulfate activation: Importance of high-valent Ru species and 1O2

The application of single-atom catalysts (SACs) to advanced oxidation processes (AOPs) based on peroxymonosulfate (PMS) has attracted considerable attention. However, the catalytic pathways and mechanisms underlying these processes remain unclear. In this study, NiFe-LDH was synthesized and single Ru atoms were stably loaded onto it by forming Ru–O–M (M=Ni or Fe) bonds (Ru@NiFe-LDH). This was demonstrated using high-angle annular dark-field scanning TEM (HAADF-STEM) and X-ray absorption fine structure spectra (XANES). The Ru@NiFe-LDH/PMS system showed a high catalytic reactivity (100 % sulfamethoxazole degradation in only 30 min), high stability (97 % reactivity was maintained after continuous operation for 400 min), and wide pH suitability (working pH range 3–11) for AOPs. The crucial roles of the high-valent species (Ru(V) = O) and 1O2 in this reaction were verified. Density functional theory (DFT) calculations revealed that electron transfer produced a positively charged Ru. This enhances the adsorption of negatively charged PMS anions onto the Ru monoatomic sites, thereby, causing the formation of Ru-PMS* complexes. This study implies that the structure–function relationship between organic compounds and SACs plays a significant role in PMS-based AOPs, and provides a comprehensive mechanism for the role of high-valent species in heterogeneous Fenton-like systems.

Atomic structure of GPB-II zone and its evolution in an Al-Zn-Mg-Cu-Si crossover alloy during aging

The GPB-II zone is the main strengthening precipitate in the Al-4.5Zn-1.5Mg-1.0Cu-0.35Si (wt.%) crossover alloy, resulting in increased alloy strength and ductility. The atomic structure of the GPB-II zone and its evolution process during aging have been studied by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) in the present work. It is shown that the GPB-II zone is a hybrid precipitate consisting of the L phase (a disordered phase with a QP lattice and is normally present in Al-Mg-Si-Cu alloy) on the inner part and Guinier-Preston-Bagaryatsky (GPB) zones (an important strengthening phase in Al-Cu-Mg alloy) on the outer part. The GPB-II zone is formed by the GPB zone nucleating at the Cu site (in-between and on the Si-network) of the L phase. The unique combination of the GPB zone and L phase was investigated, and the “Si parallelogram embedding with Cu” was proposed. The GPB zone provides the atoms for the L phase’s growth and results in the coarsening of the L phase with few GPB zones after a long aging time. The role of the Zn element in the formation of the GPB-II zone was discussed. It is thought to have a similar effect as Cu and can also promote the formation of GPB zones on the L phase.

Interface structure of α-Mg/14H-LPSO: First-principles prediction and experimental study

The interfacial structure of the α-Mg/14H-LPSO phase in rare earth-including magnesium alloy was investigated via high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging and first-principles calculations of density-functional theory. Eleven possible interfacial models were constructed according to the different terminations of the LPSO phase, and the corresponding interfacial energies were calculated, from which the four most stable structures (Ter1-MgY-hollow, Ter2-Zn-hollow, Ter3-MgYII-hollow and Ter4-Mg-bridge) were obtained. The interfacial phase diagrams related to the Y chemical potentials were obtained from the calculations, and the most stable interfacial structure was evaluated. Ter1-MgY-hollow and Ter2-Zn-hollow have the lowest interfacial energies in the range of −0.7 eV < ΔμY < −0.6 eV, where fluctuating change of state is the minimized and the interface is the most stable. The separation work of the two models was calculated to predict the bonding strength of the structures at both ends of the interface. The calculation results show that the maximum interfacial separation work is 1.45 J/m2 for the interface model of α-Mg and 14H-LPSO phase structure with Ter2-Zn-hollow termination.

Effect of Pre-Deformation on Precipitation in Al–Zn–Mg–Cu Alloy

AbstractIn this work, strengthening effects and evolution of precipitates in a pre-deformed Al–Zn–Mg–Cu alloy during ageing were investigated using Vickers hardness measurements, tensile tests, and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). It was found that all cold rolled conditions had higher mechanical strength than the non-deformed condition for all ageing times and that this effect increases at higher deformation ratios. It was also found that the non-deformed condition has a higher age hardening response than that of the cold rolled conditions. A homogeneous precipitate distribution was observed in the non-deformed condition, while the cold rolled conditions contained non-uniformly distributed precipitates due to the introduced dislocations. This led to larger precipitate sizes and a reduction in the precipitate number densities in the pre-deformed conditions. HAADF-STEM analysis revealed differences in the fraction of different precipitate types between the non-deformed and the cold rolled conditions. η', η2, and disordered η phase were observed in the non-deformed condition, while η', η2 and the newly identified Y phase were observed in the cold rolled conditions. The disordered η phase contained structural units of the η1 phase and was associated with reducing the lattice misfit between this phase and the Al matrix. Formation of the Y phase was related to an accelerated nucleation rate in the regions of high dislocation density. Graphical abstract

A new high-pressure die casting Mg−Gd−Sm−Al alloy with high strength-ductility synergy

A high-pressure die casting (HPDC) Mg−5Gd−1.5Sm−0.7Al alloy was newly developed and exhibits outstanding strength-ductility synergy, with the yield strength and the tensile elongation to fracture being approximately 200 MPa and 8.5%, respectively. This alloy has two types of α-Mg grains: coarse α1-Mg ((46 ± 18) μm) and fine α2-Mg ((9.2 ± 2.3) μm) grains, and various Al-GS (GS = Gd and Sm) particles located at grain boundaries while clear solute-atom segregation near grain boundaries with limited or free intermetallic particles. Characterizations using Cs-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) indicate the crystal structures of Al-GS phases. After aging, dense β′ precipitates and chain-shaped β’’-like structures precipitated near grain boundaries while a high density of ultrafine β’’-(Mg,Al)3Sm precipitates and Al-GS clusters formed in grain center. Relatively fine grains, Al-GS primary particles, solute-atom segregation near grain boundaries, and/or multiple precipitates contribute to the high strength of the studied alloy, while the multi-scale α-Mg grains, variety of intermetallic particles but discontinuous skeleton, and the multi-typed precipitated lead to its satisfactory ductility.

Ferroelectric behavior arising from polar topologies in epitaxially strained SrTiO3-δ ultrathin films

In this work, we show that epitaxially strained SrTiO3-δ thin films, grown by ion-beam sputtering onto (001)Nb:SrTiO3 substrates, exhibit a ferroelectric behavior. At the atomic-scale, through high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images, it was possible to identify the presence of polar nanoregions with non-trivial polar topological structures in the SrTiO3-δ film, which are induced through oxygen vacancies. To further confirm the presence of strained regions with a polar structure, Raman spectroscopy and high-resolution X-ray diffraction were employed and it was possible to confirm the presence of a tetragonal structure in the SrTiO3-δ film, with a tetragonality ratio (c/a) of 1.005. Scanning probe microscopy and macroscopic polarization-electric field hysteresis loops show ferroelectric behavior with maximum polarization of ∼1.5 μC/cm2, remnant polarization of ∼0.4 μC/cm2 and coercive field of ∼0.3 MV/cm. This work opens a window for exploring novel polar topological effects in sub-10 nm thin film materials for non-volatile memory application.

Atomic-level investigation of structure and formation process of Y3Al5O12 with super-high content of Ce emitting anomalous orange-red emissions

Ce-doped yttrium aluminum garnet (YAG:Ce, Y3Al5O12:Ce) is the most commonly used yellow phosphor in white light-emitting diodes. Recently, we found that (Y1–xCex)3Al5O12:Ce with a super-high content of Ce (x = 0.11–0.21) can be prepared by a polymerized complex method and exhibits anomalous orange–red emission. To understand the nature of this anomalous behavior from the atomic level, we applied high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and scanning transmission electron microscopy–energy dispersive X-ray spectroscopy (STEM-EDS), a state-of-the-art technique that enables analysis of the atomic-level elemental distributions of Al, Y, and Ce. STEM-EDS images on the atomic level were successfully obtained for YAG:Ce. It was found that Ce in Y site has spatially uneven for few nanometers. Ce–K edge extended X-ray absorption fine structure (EXAFS) analysis was also conducted, which revealed a high level of asymmetry around Ce. By combining the STEM-EDS and EXAFS results, a dynamic model for the red emission was proposed. STEM-EDS also revealed that CeO2 nanocrystals were firstly formed with low-temperature annealing and that the reaction of Y with the CeO2 nanocrystals subsequently yielded YAG:Ce, unlike in the conventional one-step high-temperature synthesis.

Microstructural Evolution and Tensile Properties of Al-Si Piston Alloys during Long-Term Thermal Exposure

The present study investigated microstructural evolution and changes in tensile properties of an Al-Si piston alloy subjected to thermal exposures at 250 and 350 °C for 150, 300, and 500 h. Microstructural and nanoscale precipitates were characterized using a combination of high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) images and scanning electron microscopy (SEM). The tensile testing was performed. The results demonstrated that the thermal exposure induced granulation of the δ-Al3CuNi particles, alongside precipitation of the θ-Al2Cu phase particles and AlCu clusters within the matrix. Specifically, an increase in the size and number density of the θ-Al2Cu phase particles was observed with exposure time at 250 °C. Conversely, at 350 °C, the θ-Al2Cu particles exhibited a gradual increase in size with prolonged thermal exposure, coupled with a decrease in their number density. AlCu clusters precipitated solely at a thermal exposure temperature of 350 °C, with precipitation intensifying over time. Moreover, a decrease in the alloy’s tensile strength and an increase in elongation were noted after thermal exposure. Finally, the present study discussed the precipitation mechanisms of θ-Al2Cu particles and AlCu clusters within the grains, suggesting that the AlCu clusters exerted a more effective strengthening effect compared to the θ-Al2Cu particles.

Scaling-Up Microwave-Assisted Synthesis of Highly Defective Pd@UiO-66-NH2 Catalysts for Selective Olefin Hydrogenation under Ambient Conditions.

The need to develop green and cost-effective industrial catalytic processes has led to growing interest in preparing more robust, efficient, and selective heterogeneous catalysts at a large scale. In this regard, microwave-assisted synthesis is a fast method for fabricating heterogeneous catalysts (including metal oxides, zeolites, metal-organic frameworks, and supported metal nanoparticles) with enhanced catalytic properties, enabling synthesis scale-up. Herein, the synthesis of nanosized UiO-66-NH2 was optimized via a microwave-assisted hydrothermal method to obtain defective matrices essential for the stabilization of metal nanoparticles, promoting catalytically active sites for hydrogenation reactions (760 kg·m-3·day-1 space time yield, STY). Then, this protocol was scaled up in a multimodal microwave reactor, reaching 86% yield (ca. 1 g, 1450 kg·m-3·day-1 STY) in only 30 min. Afterward, Pd nanoparticles were formed in situ decorating the nanoMOF by an effective and fast microwave-assisted hydrothermal method, resulting in the formation of Pd@UiO-66-NH2 composites. Both the localization and oxidation states of Pd nanoparticles (NPs) in the MOF were achieved using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and X-ray photoelectron spectroscopy (XPS), respectively. The optimal composite, loaded with 1.7 wt % Pd, exhibited an extraordinary catalytic activity (>95% yield, 100% selectivity) under mild conditions (1 bar H2, 25 °C, 1 h reaction time), not only in the selective hydrogenation of a variety of single alkenes (1-hexene, 1-octene, 1-tridecene, cyclohexene, and tetraphenyl ethylene) but also in the conversion of a complex mixture of alkenes (i.e., 1-hexene, 1-tridecene, and anethole). The results showed a powerful interaction and synergy between the active phase (Pd NPs) and the catalytic porous scaffold (UiO-66-NH2), which are essential for the selectivity and recyclability.

Defects in monolayer WS2 grown via sulfurization of WSe2

The conversion of chalcogen atoms into other types of chalcogen atoms in transition metal dichalcogenides exhibits significant advantages in tuning the bandgaps and constructing lateral heterojunctions. However, despite atomic defects at the atomic scale were inevitably formed during conversion process, the construction of dislocations remains difficult. Here, we conducted in-situ sulfurization to achieve structural transformation from monolayer WSe2 to WS2 successfully. We probe these transformations at atomic scale using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and study structural defects of sulfurized-WS2 by strain and displacement fields. We discovered that high-quality WSe2 flakes were completely sulfurized while dislocations were successfully constructed, manifesting atomic surface roughness and structural disorders. Our work provides insights into designing and optimizing customized Transition metal dichalcogenides (TMDs) materials in controlled synthesis and defect engineering.

Plasmon assisted synthesis of TiN-supported single-atom nickel catalysts

We report the deposition of single atom nickel catalyst on refractory plasmonic titanium nitride (TiN) nanomaterials supports using the wet synthesis method under visible light irradiation. TiN nanoparticles efficiently absorb visible light to generate photoexcited electrons and holes. Photoexcited electrons reduce nickel precursor to deposit Ni atoms on TiN nanoparticles’ surface. The generated hot holes are scavenged by the methanol. We studied the Ni deposition on TiN nanoparticles by varying light intensity, light exposure time, and metal precursor concentration. These studies confirmed the photodeposition method is driven by hot electrons and helped us to find optimum synthesis conditions for single atoms deposition. We characterized the nanocatalysts using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). We used density functional theory (DFT) calculations to predict favorable deposition sites and aggregation energy of Ni atoms on TiN. Surface defect sites of TiN are most favorable for single nickel atoms depositions. Interestingly, the oxygen sites on native surface oxide layer of TiN also exhibit strong binding with the single Ni atoms. Plasmon enhanced synthesis method can facilitate photodeposition of single atom catalysts on a wide class of metallic supports with plasmonic properties.

Transmission electron microscopy reveals clusters of Au–Ag nanoparticles formed in TiO2 thin film, with enhanced plasmonic response

This work reports on the influence of nanoparticle (NP) size distribution and the chemical nature of gold (Au) and/or silver (Ag) NPs in the localized surface plasmon resonance (LSPR) responses. The NPs were produced embedded in a titanium dioxide (TiO2) thin film, deposited by reactive magnetron sputtering technique followed by in-vacuum thermal treatment at 400 °C. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) gave quantitative key information in terms of both the size and distribution of the noble metal NPs. The average Feret diameter was 17 nm (σ = 8) and 55 nm (σ = 28) for Au/TiO2 and Ag/TiO2 films, respectively, while the Au–Ag/TiO2 film showed intermediate values, with an average size of 22 nm (σ = 9). HAAD-STEM, complemented by EDX chemical mapping, revealed an unusual formation of cluster structures containing local distributions of bimetallic (alloyed) Au–Ag NPs. The synergetic characteristics and properties of such bimetallic Au–Ag NPs resulted in an outstanding LSPR sensitivity compared to the monometallic counterparts. Furthermore, the analysis of the average nearest neighbor distances (about one order of magnitude lower than counterparts) suggests the existence of plasmonic hotspots relevant to be explored in sensing and surface-enhanced spectroscopies.

A method to synthesize specific active Cu sites of single-atom catalysts with high stability for acetylene hydration

Single-atom catalysts (SACs) have received much attention in the realm of energy and catalytic conversion due to their maximum atomic efficiency. Herein, we report a cascade anchoring strategy for the preparation of a Cu-S1O2 species of single-atom catalyst attached to a carbon carrier containing P and S (Cu-S1O2 SA/CPS) with a content of 12.4 wt%. Over the Cu-S1O2 SA/CPS catalyst, the conversion of 95.8% and selectivity of 87.2% for acetylene hydration could still be achieved at 70 h (T = 200°C, GHSV(C2H2) = 90 h−1 and VH2O/VC2H2 = 4). X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) tests reveal that the Cu atoms of Cu-S1O2 SA/CPS are predominantly coordinated in a trinary manner (Cu-S1O2). Based on high-resolution aberration-corrected high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM), it is demonstrated that the Cu single-atom sites are highly dispersed in Cu-S1O2 SA/CPS. It is evident from the scanning electron microscopy (SEM) that Cu-S1O2 SA/CPS has a two-dimensional layered structure. The specific structure of the active site Cu is primarily attributed to the coordination of S and O atoms, resulting in its superior stability for acetylene hydration towards the synthesis of acetaldehyde. Density functional theory (DFT) calculations confirm that the formation of the Cu-S1O2 site facilitates the activation of acetylene, which is a pivotal step in the acetylene hydration process and considered as the rate-determining step. This article not only introduces an innovative strategy in the synthesis of Cu SACs but also represents a significant breakthrough in the stability of Cu SACs in acetylene hydration.

Atomic-Scale Imaging of Clay Mineral Nanosheets and Their Supramolecular Complexes through Electron Microscopy: A Supramolecular Chemist's Perspective.

Recent advancements in electron microscopy techniques have revolutionized the ability to directly visualize and understand the intricate world of supramolecular chemistry. This paper provides a concise overview of a study delving into the atomic-scale imaging of monolayer clay mineral nanosheets and their associated supramolecular complexes. The imaging is conducted by harnessing the power of aberration-corrected scanning transmission electron microscopy (STEM). Clay mineral nanosheets, with their anionic charge and ultrathin thickness (of 1 nm), serve as a stable Coulombic host material for cationic guest molecules through electrostatic interactions, facilitating exceptional stability and control during observation. By incorporation of heavy-metal atom markers coordinated within the target molecules, high-angle annular dark field STEM enables a clear visualization of these supramolecular complexes. This approach helps to overcome the limitations of graphene-based systems and expands the possibilities of atomic-scale imaging of nonperiodic molecular assemblies formed by weak supramolecular interactions. The fusion of electron microscopy techniques with the principles of supramolecular and material chemistry offers exciting opportunities for studying the structure, behavior, and properties of complex supramolecular systems. It sheds light on the intricate molecular architectures and design principles governing these systems. This study showcases the immense potential of electron microscopy in supramolecular chemistry and invites researchers from various disciplines to explore the transformative possibilities of atomic-scale imaging in the field.

Isomorphic substitution behavior of Pt on synthetic vernadite (δ-MnO2):A model reaction to elucidate the mechanism of Pt enrichment in marine ferromanganese crust

Marine ferromanganese crusts are considered to be the potential Pt deposits, and recent studies report a strong association between Pt and vernadite in these crusts. However, there are still uncertainties regarding the molecular processes involved in the enrichment of Pt by vernadite. This study investigates the adsorption behavior and molecular-scale immobilization mechanisms of Pt at water/vernadite interfaces through a combination of batch adsorption and desorption experiments, X-ray absorption fine structure (XAFS) analyses, and atomic resolution chemical imaging. Our findings suggest that the Pt enrichment on vernadite is attributed to an isomorphic substitution of Mn by Pt. The extended X-ray absorption fine structure (EXAFS) analysis reveals that Pt undergoes ligand exchange reactions during the enrichment process, and provides a comprehensive explanation of how Pt penetrates into the vernadite structure starting from the surface. Scanning transmission electron microscopy high-angle annular dark field (STEM-HAADF) observations visually confirm the infiltration of Pt atoms into the crystal structure of vernadite. Additionally, we demonstrate that the Pt enrichment in vernadite is a multi-stage chemical process. X-ray absorption near edge structure (XANES) analysis shows that Pt is initially rapidly adsorbed onto the surface of vernadite and then slowly oxidized. Our study provides a detailed understanding of the molecular-scale mechanisms involved in the adsorption of Pt onto vernadite and its subsequent structural incorporation. This knowledge is valuable for gaining insights into the Pt enrichment in marine ferromanganese crusts.