Aberration-corrected Scanning Transmission Electron Microscopy Research Articles

One-dimensional ionic-bonded structures in NiSe nanowire

One-dimensional van der Waals (1D vdW) materials, characterized by atomic chains bonded ionically or covalently in one direction and held together by van der Waals (vdW) interactions in the perpendicular directions, have recently gained intensive attention due to their exceptional functions. In this work, we report the discovery of one-dimensional (1D) ionic-bonded structures in NiSe nanowires. Utilizing aberration-corrected scanning transmission electron microscopy, we identified four distinct structural phases composed of two fundamental 1D building blocks: a triangle-shaped unit and a parallelogram-shaped unit. These phases can transform into one another through topotactic combinations of the structural units. Density functional theory calculations reveal that these structural units are bound by ionic bonds, unlike the van der Waals forces typically found in 1D vdW materials. The diverse arrangements of these building blocks may give rise to unique electronic structures and magnetic properties, paving the way for designing advanced materials with desired functionalities.

Fe Single-Atom and Fe Cluster-Coupled N, S Co-doped Carbon Nanomaterial-Based Flexible Electrochemical Sweat Biosensor for the Real-Time Analysis of Uric Acid and Tyrosine.

Fe single-atom and Fe cluster-coupled N, S co-doped carbon nanomaterials (FeSA-FeONC-NSC) were prepared through a two-step high-temperature pyrolysis process using Gelidium corneum enriched with C, Fe, O, N, and S as precursors. The analysis by aberration-corrected scanning transmission electron microscopy and X-ray absorption spectroscopy revealed the presence of single-atom Fe in Fe-N4 coordination structures, along with small clusters as Fe-O-coordinated Fe2O3. Single-atom Fe in the form of Fe2+/Fe3+ provides more electrocatalytic active sites, which synergistically accelerates the charge migration process in the assembly of FeSA-FeONC-NSC with Fe2O3 clusters. The flexible nonenzymatic sensor, based on FeSA-FeONC-NSC and fabricated using a polydimethylsiloxane substrate, exhibited excellent catalytic activity for both uric acid (UA) and tyrosine (Tyr). Low detection limits for UA (0.14 μmol L-1) and Tyr (0.03 μmol L-1) were observed by using chronoamperometry in artificial sweat. The in situ detection of sweat was performed in combination with an integrated circuit board affixed to human skin, and the results were generally consistent with those of the high-performance liquid chromatography method. Therefore, FeSA-FeONC-NSC serves as a good modifier for wearable electrochemical sweat sensor applications.

Collaborative improvement of mechanical and electrical properties of Cu–Ni–Co–P alloys via regulation of nanophase precipitation behavior

Owing to their excellent strength and electrical conductivity, Cu–Ni–Co–P alloys present strong potential as next-generation materials for integrated circuits in electronic information systems. However, these outstanding properties are closely tied to the precise control of nanophase precipitation behavior within Cu-based alloy systems. Herein, the design of alloy composition was combined with aging treatment to regulate the nanoprecipitation process. Furthermore, the effects of P content and aging treatment conditions, including temperature and duration, on the microstructure and the mechanical, and electrical properties of Cu–Ni–Co–P alloys were systematically investigated. The findings reveal that Cu–0.3Ni–0.3Co–0.16P alloys, when aged at 500 °C for 4 h, primarily consist of a Cu-rich matrix interspersed with numerous nanoprecipitates. These nanoprecipitates were identified as the hexagonal CoNiP phase, precipitating in Guinier–Preston (GP) zones and maintaining a coherent relationship with the Cu matrix. The as-annealed Cu–0.3Ni–0.3Co–0.16P alloys demonstrated a tensile strength of 652.9 MPa, a yield strength of 631.2 MPa, a Vickers hardness of 203.2 HV, and an electrical conductivity of 66.4 %IACS. Aberration-corrected scanning transmission electron microscopy revealed that G.P. zones suppressed the coarsening of the CoNiP phase, thereby enhancing the mechanical strength of the Cu–Ni–Co–P alloys. The strength analysis calculations suggest that fine-grain and precipitation strengthening mechanisms are the predominant factors in improving the mechanical strength of these alloys. This study provides valuable insights into the development and manufacturing of high-performance Cu-based alloys for advanced applications in the electronics industry.

Stacking Disorders in Honeycomb Layered NaKNi2TeO6 and Mixed-Cation Transport

The utilisation of multiple alkali atoms to develop mixed alkali layered oxides has been gaining considerable interest in recent years for its potential to yield materials with versatile crystal structures and remarkable electrochemical functionalities. [1,2] By leveraging the properties derived from the variant alkali atoms, fascinating functionalities such as enhanced ionic transport, unique crystal chemistry and appealing electrochemistry can be achieved by this emergent class of materials. However, the adoption of this approach to aid in the augmentation of honeycomb layered oxide materials [3] is vastly unexplored with extremely scarce literature on the subject matter.In this study, we investigate our novel honeycomb layered composition NaKNi2TeO6 [1] obtained from Na2Ni2TeO6 and K2Ni2TeO6 precursor materials. The atomic-resolution imaging was accomplished using an aberration-corrected scanning transmission electron microscopy (STEM). Figure 1a shows a high-angle annular dark field (HAADF)-STEM image of NaKNi2TeO6 taken along the [100] zone axis. The image reveals that Na and K are separated into different layers in an alternating sequence. From an enlarged view of the atomic-scale HAADF-STEM mapping (Figure 1b), aperiodic shifts between adjacent Ni/Te slabs are contingent on whether the interlayer spaces are occupied by Na or K atoms. No shifts are observed when Ni/Te slabs are separated by a K layer. It is also evident that the interlayer distance depends on the alkali atom species sandwiched between adjacent Ni/Te layers. The Ni/Te layers with Na atoms are separated by 0.55 nm whereas the interlayer distance for the layers with K is 0.62 nm. These interlayer distances attained closely resemble those of the precursor compounds Na2Ni2TeO6 and K2Ni2TeO6. [4-6] We will reveal the intricate local atomic structures present in honeycomb layered NaKNi2TeO6, through a series of atomic-resolution scanning transmission electron microscopy (STEM) in multiple zone axes. Further, we will validate the electrochemical potential of this material to enable mixed-alkali ion transport. It is hoped that this study will pave way for further realisation of new honeycomb layered oxide compositions; thus, expanding the database of known honeycomb layered oxide frameworks. We also anticipate that the new findings will not only serve as a stepping-stone for unlocking new functionalities but also inspire the development of high-performance mixed alkali-ion energy systems. Extension of this work to new materials for Ca and Mg batteries will also be highlighted. References : [1] T. Masese, Y. Miyazaki, G. M. Kanyolo, T. Saito et al., Nat. Commun., 12, 1-16 (2021) [2] R. Berthelot et al., Inorg. Chem., 60, 14310-14317 (2021); E. M. Mpanga et al., Chem. Mater., 36, 892-900 (2024) [3] G. M. Kanyolo et al., Chem. Soc. Rev., 50, 3990-4030 (2021) [4] T. Masese, Y. Miyazaki et al., Materialia, 15, 101003 (2021) [5] T. Masese, Y. Miyazaki et al., ACS Appl. Nano Mater., 4, 279-287 (2021) [6] T. Masese et al., Nat. Commun., 9, 1-12 (2018). Figure 1. (a) HAADF-STEM image illustrating the unique stacking sequence in NaKNi2TeO6. [1] In the layers where K atoms occupy the interlayer space, Te / Ni slabs are not shifted with respect to each other (marked by a green line). However, for layers where Na atoms reside, shifts of the Te / Ni slabs are observed. The yellow and blue lines show shifts in different directions. Note the aperiodicity in the stacking sequence. (b) Enlarged view of the domain highlighted in (a), showing that the interlayer distance is dependent on the alkali atom species (Na or K) sandwiched between the Te / Ni layers. Figure 1

Unraveling the Harmonious Coexistence of Ruthenium States on a Self-Standing Electrode for Enhanced Hydrogen Evolution Reaction

The development of cost-effective, highly efficient, and durable electrocatalysts has been a paramount pursuit for advancing the hydrogen evolution reaction (HER). Herein, a simplified synthesis protocol was designed to achieve a self-standing electrode, composed of activated carbon paper embedded with Ru single-atom catalysts and Ru nanoclusters (ACP/RuSAC+C) via acid activation, immersion, and high-temperature pyrolysis. Ab initio molecular dynamics (AIMD) calculations are employed to gain a more profound understanding of the impact of acid activation on carbon paper. Furthermore, the coexistence states of the Ru atoms are confirmed via aberration-corrected scanning transmission electron microscopy (AC-STEM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS). Experimental measurements and theoretical calculations reveal that introducing a Ru single atom site adjacent to the Ru nanoclusters induces a synergistic effect, tuning the electronic structure and thereby significantly enhancing their catalytic performance. Notably, the ACP/RuSAC+C exhibits a remarkable turnover frequency (TOF) of 18 s-1 and an exceptional mass activity (MA) of 2.2 A mg-1, surpassing the performance of conventional Pt electrode. The self-standing electrode, featuring harmoniously coexisting Ru states, stands out as a prospective choice for advancing HER catalysts, enhancing energy efficiency, productivity, and selectivity. Figure 1

Sr Migration and Gd-Ce-Zr Interdiffusion in Solid Oxide Cells Under Different Fabrication and Testing Conditions

This work aims to understand how solid oxide cell (SOC) fabrication methods and SOC operating conditions affect Sr migration into the yttria stabilized zirconia (YSZ) electrolyte through the rare-earth doped ceria barrier layer. Ni-YSZ electrode-supported SOCs and coupons were fabricated using (La0.6Sr0.4)0.95Co0.2Fe0.8O3-δ-Gd0.1Ce0.9O2-δ (LSCF-GDC) oxygen electrode and GDC or samaria-doped ceria (SDC) barrier layer. Barrier layers were either screen printed and sintered to YSZ electrolyte layer at 1260 °C for 2h, or deposited using thin film deposition techniques such as PLD, electron beam and sputtering. LSCF-GDC electrode layer was sintered onto the GDC barrier at different temperatures from 950 to 1100°C for 2h to determine the effect of firing temperature and barrier layer thickness on Sr migration. Several SOCs were tested at 750°C in a wide range of operating conditions, both in SOFC and SOEC mode, for up to 12,000 hours. The GDC/YSZ interfaces in coupons and SOCs were examined using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Sr-Zr rich phase formation at GDC/YSZ interface was observed in coupons with LSCF-GDC sintered at 1100°C, but not in the other coupons sintered below 1100°C, unless the barrier layer was too thin and porous. Furthermore, no Sr migration into YSZ was observed in SOECs with varying testing time from 0 h to12,000 h. In addition, Gd and Ce diffusion into YSZ occurred when GDC was fired at 1260°C, but not in cells with GDC deposited using thin film techniques without additional high temperature firing. No significant difference was noted in the GDC-YSZ interdiffusion layer growth after SOC testing for 1,000-12,000 h. Aberration-corrected scanning transmission electron microscopy (STEM) was involved to identify the composition and crystal structure of the Sr-Zr rich phase, which was demonstrated to be SrZrO3 phase. After the long-term SOC tests, no SrZrO3 phase or Sr migration through GDC grain boundaries was observed in cells with 5-7 microns thick porous GDC barrier. This presentation will demonstrate how optimization of fabrication conditions, thermal treatment and fabrication techniques, could mitigate the formation of the insulating SrZrO3 phase.

Carbon-Embedded Pt Alloy Cluster Catalyst: Properties and Oxygen Reduction Activity

Carbon-embedded PtFe alloy cluster catalysts have emerged as promising candidates for enhancing the performance and durability of oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). These catalysts, synthesized through a multi-step process involving carbonization of hyper-crosslinked polystyrene particles with Fe precursors, doping of nitrogen species, deposition of Pt precursors, and subsequent reduction, exhibit remarkable properties and catalytic activity.Advanced imaging techniques, including aberration-corrected scanning transmission electron microscopy (ADF-STEM) and scanning electron microscopy (SEM), have revealed that the metal clusters are embedded beneath the carbon support surface. X-ray absorption fine structure (XAFS) analysis further confirmed the Pt-Fe alloy structure of the metal clusters, which are approximately 1.5 nm in size. The carbon-embedded PtFe alloy cluster catalysts demonstrate high mass activity and exceptional durability for the ORR. Despite being embedded within the carbon matrix, the Pt sites within the clusters serve as active sites for electrochemical reactions. Co-adsorption of Br- ions with protons alters cyclic voltammetry (CV) curves similarly to typical Pt/C catalysts, indicating the accessibility of Pt sites. Moreover, small molecules such as protons formic acid, and methanol can effectively diffuse through the carbon layer to reach the Pt surface.When applied in the cathode of PEMFCs with a low Pt loading of 0.05 mg Pt cm-2, the PtFe cluster catalysts exhibit high current density at 0.65 V and excellent durability. After 30,000 cycles, the current density remains nearly unchanged, highlighting the superior performance of these catalysts compared to conventional Pt/C or PtFe/C catalysts. Density functional theory (DFT) calculations further elucidate the catalytic mechanism of the carbon-embedded PtFe alloy clusters. Carbon atoms stably adsorb on Fe sites of PtFe clusters, making nearby Pt sites active for ORR with optimal adsorption strength of oxygen intermediates. This comprehensive understanding of the catalytic behavior and properties of carbon-embedded PtFe alloy cluster catalysts opens up new avenues for the development of highly active and durable ORR catalysts in PEMFCs, with minimized Pt usage. Figure 1

Atomic-level direct imaging for Cu(I) multiple occupations and migration in 2D ferroelectric CuInP2S6

CuInP2S6 (CIPS) is an emerging 2D ferroelectric material known for disrupting spatial inversion symmetry due to Cu(I) position switching. Its ferroelectricity strongly relies on the Cu(I) atom/ion occupation ordering and dynamics. Nevertheless, the accurate Cu(I) occupations and correlated migration dynamics under the externally applied energy, which are key to unlocking ferroelectric properties, remain controversial and unresolved. Herein, an atomic-level direct imaging through aberration-corrected scanning transmission electron microscopy is performed to precisely trace the Cu(I) dynamic behaviours under electron-beam irradiation along (100)-CIPS. It clearly demonstrates that Cu(I) possesses multiple occupations, and Cu(I) could migrate to the lattice, vacancy, interstitial and interlayer sites between the InS6 octahedral skeletons of CIPS to form local CuxInP2S6 (x = 2-4) structure. Cu(I) multi-occupations induced lattice stress results in a layer sliding along the b-axis direction generating a sliding size of 1/6 b lattice constant. The CuxInP2S6 (x = 2-4) exists in a type of dynamic structure, only metastable with electron dose over 50 e− Å−2, thus generating a dynamic process of CuxInP2S6(x=2−4)⇌CuInP2S6\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mbox{C}}{{\\mbox{u}}}_{x}{\\mbox{In}}{{\\mbox{P}}}_{2}{{\\mbox{S}}}_{6}(x=2-4)\\rightleftharpoons {\\mbox{CuIn}}{{\\mbox{P}}}_{2}{{\\mbox{S}}}_{6}$$\\end{document}, a completely unreported phenomenon. These findings shed light on the unveiled mechanism underlying Cu(I) migration in CIPS, providing crucial insights into the fundamental processes that govern its ferroelectric properties.

Electrochemical Characterisation and Fuel Cell Testing of Bespoke, Low Loading Platinum on Carbon Black Catalysts Fabricated By Physical Vapour Deposition.

A critical component of achieving net zero emissions by 2050 is the continuing research and development of improved methods of producing, as well as using, green hydrogen. Hydrogen is a key component of many industrial and chemical processes, but here we focus on its role in the energy transition, specifically proton exchange membrane (PEM) fuel cells. A key part of the PEM fuel cell is the catalyst material and structure, and this work is part of a wider, multi-institutional collaboration concerning metal atoms on surfaces and interfaces (MASI).MASI’s goal is to increase the surface area to volume ratio of metal particle on support catalysts, exploring the sub-nanometre metal particle size domain (referred to henceforth as nanoclusters) by fabricating catalysts utilising physical vapour deposition (PVD.) In contrast to wet chemical methods, the size of metal particle depositing onto the surface can be better controlled. This versatile method has been applied to deposit many different metals onto a variety of morphologies of surface to date. The chemical and physical properties of these nanoclusters can then be studied and exploited where an improvement in activity on nanoparticle catalysts is observed, as well as reducing the amount of ‘wasted’ atoms buried below the active surface of the catalyst, reducing the unit cost of, for example, a fuel cell stack.In this study, platinum is deposited onto a carbon black (XC-72R) support at four different weight loadings (1.1wt%, 2.3wt%, 5.0wt% and 9.7wt% Pt/XC-72R carbon named Pt-1, Pt-2, Pt-5 and Pt-10 respectively,) and is compared to two commercially available equivalents (46.2wt% Pt/HSC TKK and 10wt% Pt/XC-72 carbon E-TEC.) The catalyst loadings were determined using ICP-OES. Imaging of the catalyst surface was performed using aberration-corrected scanning transmission electron microscopy (AC-STEM), including the generation of a size distribution of the platinum particles present. The electrochemically active surface area (ECSA) of the platinum catalyst was obtained using carbon monoxide stripping voltammetry. The kinetic properties of the catalysts were then probed using the oxygen reduction reaction (ORR) via rotating disc electrode (RDE) voltammetry, and a discussion of the factors impacting the observed onset potential (specifically kinetics and catalyst coverage) is presented. The selectivity of the ORR with respect to hydrogen peroxide production is also studied using rotating ring disc electrode (RRDE) voltammetry. Finally, single cell testing to study fuel cell performance, specifically on the anode side of the cell, is performed and analysed for future optimisation. Accelerated stress testing (AST) was also performed; ORR activity and fuel cell performance were probed as a function of number of break in cycles, up to 4000 cycles.STEM imaging revealed significant differences in the size of platinum particle across the samples studied. For example, the 2.3wt% Pt/C catalyst exhibited a platinum particle size of 0.6 ± 0.3 nm, far smaller than the 2.2 ± 0.5 nm found for TKK.Further, our study found that all PVD fabricated catalysts showed a significantly higher ECSA than the commercial equivalents, along with a shift in onset towards a higher overpotential for the ORR which is explained by kinetic differences due to size of platinum particle – platinum catalysts become worse at catalysing the ORR as the size of particle decreases. This is therefore used as further evidence of our nanoclusters’ catalytic activity. RRDE voltammetry revealed a general trend of decreasing peroxide production as weight loading increasing, explained by probable decreasing interparticle distance as well as increased particle size. AST showed all catalysts are relatively stable; increases in overpotential between initial performance and after 4000 cycles were in the region of 16 mV.Single cell testing revealed exceptional performance for the PVD catalysts tested. The 5.0wt% and 9.7wt% catalysts showed superior initial performance to TKK at a fraction of the platinum loading in all regions of the IV curve, with an associated improved peak power density. AST revealed that peak power density decreased in percentage terms more for the PVD catalysts, and the decrease was larger as weight loading increased. After 4000 cycles, the 9.7wt% catalyst still showed comparable performance to TKK, with the 5wt% just below.Future work will focus on trying to decrease the mean size of platinum nanocluster further, optimising catalyst loading and enhancing stability of the catalyst with respect to degradation. Figure 1

Atomic-Scale Insights Into the Thermal Stability of High-Entropy Nanoalloys.

High entropy alloy nanoparticles bring hope to developing more efficient nanomaterials for high-temperature applications. Nevertheless, the enhanced thermal stability of nearly equiatomic nanoalloys containing at least 5 metals is nothing more than theoretical speculation about the impact of thermodynamic contributions on their structural properties and remains to be proven. Here, in situ aberration-corrected scanning transmission electron microscopy (STEM) and molecular dynamics simulations are combined to investigate at the atomic scale the thermal behavior of AuCoCuNiPt nanoparticles (NPs) from 298 to 973 K. Both in situ STEM heating and atomistic simulations reveal strong structural and chemical evolutions in the NPs with the formation and melting of an AuCu layer at the surface of NPs at high temperature. This phase separation that appears progressively with temperature is driven by pronounced atomic diffusion that is surprisingly more active in these quinary nanoalloys than in monometallic and bimetallic subsystems. Besides ruling out the existence of sluggish diffusion in AuCoCuNiPt nanoalloys and lowering their temperature range of application, the study allows distinguishing kinetic and thermodynamic effects on their structural properties, which is an essential prerequisite to better control the synthesis of complex nanomaterials.

Exploring electron-beam induced modifications of materials with machine-learning assisted high temporal resolution electron microscopy

Directed atomic fabrication using an aberration-corrected scanning transmission electron microscope (STEM) opens new pathways for atomic engineering of functional materials. In this approach, the electron beam is used to actively alter the atomic structure through electron beam induced irradiation processes. One of the impediments that has limited widespread use thus far has been the ability to understand the fundamental mechanisms of atomic transformation pathways at high spatiotemporal resolution. Here, we develop a workflow for obtaining and analyzing high-speed spiral scan STEM data, up to 100 fps, to track the atomic fabrication process during nanopore milling in monolayer MoS2. An automated feedback-controlled electron beam positioning system combined with deep convolution neural network (DCNN) was used to decipher fast but low signal-to-noise datasets and classify time-resolved atom positions and nature of their evolving atomic defect configurations. Through this automated decoding, the initial atomic disordering and reordering processes leading to nanopore formation was able to be studied across various timescales. Using these experimental workflows a greater degree of speed and information can be extracted from small datasets without compromising spatial resolution. This approach can be adapted to other 2D materials systems to gain further insights into the defect formation necessary to inform future automated fabrication techniques utilizing the STEM electron beam.

A tale of two transfers: characterizing polydimethylsiloxane viscoelastic stamping and heated poly bis-A carbonate transfer of hexagonal boron nitride

Two-dimensional (2D) materials have many applications ranging from heterostructure electronics to nanofluidics and quantum technology. In order to effectively utilize 2D materials towards these ends, they must be transferred and integrated into complex device geometries. In this report, we investigate two conventional methods for the transfer of 2D materials: viscoelastic stamping with polydimethylsiloxane (PDMS) and a heated transfer with poly bis-A carbonate (PC). We use both methods to transfer mechanically-exfoliated flakes of hexagonal boron nitride onto silicon nitride (SiNx) substrates and characterize the resulting transfers using atomic force microscopy (AFM), aberration-corrected scanning transmission electron microscopy (AC-STEM) and electron energy loss spectroscopy (EELS). We find that both transfer methods yield flakes with significant and comparable residue (within the limitations of our study on eight samples). Qualitative interpretation of EELS maps demonstrates that this residue is comprised of silicon, carbon and oxygen for both transfer methods. Quantitative analysis of AC-STEM images reveals that the area covered in residue is on average, slightly lower for PDMS transfers (31 % ± 1 %), compared to PC transfers (41 % ± 4 %). This work underscores the importance of improving existing transfer protocols towards applications where cleaner materials are critical, as well as the need for robust methods to clean 2D materials.

Peierls Distortion Induced Giant Linear Dichroism, Second-Harmonic Generation, and In-Plane Ferroelectricity in NbOBr2.

The Peierls distortion plays an essential role in governing the in-plane ferroelectricity and nonlinear optical characteristics of anisotropic niobium oxide dihalides, such as NbOCl2 and NbOI2. Despite its significance, experimental investigation into the structural, optical, and ferroelectric properties of NbOBr2 has been lacking. Here, the successful fabrication of centimeter-sized, high-quality NbOBr2 single crystals, enabling direct observation of Peierls distortion using aberration-corrected scanning transmission electron microscopy, is reported. Notably, the magnitude of Peierls distortion in NbOBr2 falls between that observed in NbOCl2 and NbOI2. Furthermore, the existence of giant linear dichroism absorption and second-harmonic generation (SHG) phenomena associated with Peierls distortion is confirmed. Exfoliated NbOBr2 flakes exhibit single-domain ferroelectricity, with the polarization switchable by an electric field. Temperature-dependent SHG measurements reveal a Curie temperature of ≈502K for ferroelectric NbOBr2. This work demonstrates that NbOBr2 holds promise for polarized nonlinear optical devices, as well as for nonvolatile information processing and storage devices.

Formation of Twin-Free Single Phase β-In2Se3 Layers via Selenium Diffusion into InP(111)B Substrate.

Indium selenide, In2Se3, has recently attracted growing interest due to its remarkable properties, including room temperature ferroelectricity, outstanding photoresponsivity, and exotic in-plane ferroelectricity, which open up new regimes for next generation electronics. In2Se3 also provides the important advantage of tuning the electrical properties of ultrathin layers with an external electrical and magnetic field, making it a potential platform to study novel two-dimensional physics. Yet, In2Se3 has many different polymorphs, and it has been challenging to synthesize a single phase material, especially using scalable growth methods, as needed for technological applications. We recently reported the growth of twin-free ultrathin layers of In2Se3 prepared by a diffusion driven molecular beam epitaxy approach, and twin-free Bi2Se3 layers grown on these unique virtual substrates. In this paper, we use aberration-corrected scanning transmission electron microscopy to characterize the microstructure of these materials. We emphasize features of the In2Se3 layer and In2Se3/InP interface which provide evidence for understanding the growth mechanism that leads to the twin-free and single phase In2Se3. We also show that this In2Se3 layer provides an ideal substrate for growth of twin-free Bi2Se3 with a nearly defect-free interface. This approach for growing high-quality twin-free single phase two-dimensional crystals using InP substrates is likely to be applicable to other technologically important materials.

Deep Learning Enhanced in Situ Atomic Imaging of Ion Migration at Crystalline-Amorphous Interfaces.

Improving the performance of energy storage, neuromorphic computing, and more applications requires an in-depth understanding of ion transport at interfaces, which are often hindered by facile atomic reconfiguration at working conditions and limited characterization capability. Here, we construct an in situ double-tilt electric manipulator inside an aberration-corrected scanning transmission electron microscope. Coupled with deep learning-based image enhancement, atomic images are enhanced 3-fold compared to traditional methods to observe the potassium ion migration and microstructure evolution at the crystalline-amorphous interface in antimony selenide. Potassium ions form stable anisotropic insertion sites outside the (Sb4Se6) chain, with a few potassium ions present within the moieties. Combined experiments and density functional theory calculations reveal a reaction pathway of forming a novel metastable state during potassium ion insertion, followed by recovery and unexpected chirality changes at the interface upon potassium ion extraction. Our unique methodology paves the way for facilitating the improvement and rational design of nanostructured materials.

Revealing the Interplay of Local Environments and Ionic Transport in Perovskite Solid Electrolytes.

Solid-state ionic conduction is significantly influenced by bottleneck sizes, which impede ion diffusion within solid lattices. Using aberration-corrected scanning transmission electron microscopy and multislice electron ptychography, we directly observed that increased La occupancy in the perovskite solid electrolyte Li0.5La0.5TiO3 correlates with reduced bottleneck sizes formed by four oxygen atoms connecting neighboring A-site cages. This correlation was also confirmed in local aperiodic regions, where smaller bottleneck sizes due to increased La occupancies affect the directionality and dimensionality of the Li+ ion conductivity. Furthermore, while prior studies have focused on averaged Li+ ion diffusion across different bottleneck areas or chemical environments, by devising a molecular dynamics (MD)-based methodology, we quantify the diffusivity of Li+ ions through specific bottleneck regions. Atomistic simulations, including nudged elastic band calculations and this MD-based methodology, revealed that larger bottleneck sizes correlate with smaller local migration barriers and higher local diffusivity. This study elucidates the relationship among local chemistry, lattice structure, and Li+ ion transport, providing insights for the design of advanced oxide solid electrolytes.

Modulation of the cobalt species state on zincosilicate to maximize propane dehydrogenation to propylene

Dispersing metals from nanoparticles into clusters or single atoms often exhibits unique properties such as the inhibition of structure-sensitive side reactions. Here, we reported the use of ion exchange (IE) methods and direct hydrogen reduction to achieve high dispersion of Co species on zincosilicate. The obtained 2Co/Zn-4-IE catalyst achieved an initial propane conversion of 41.4% at a temperature of 550 °C in a 25% propane and 75% nitrogen atmosphere for propane dehydrogenation. Visualization of the presence of Co species within specific rings (alpha-α, beta-β and delta-δ) was obtained by aberration-corrected scanning transmission electron microscopy. A series of Fourier transform infrared spectra confirmed the anchoring of Co by specific hydroxyl groups in zincosilicate and the specific coordination environment of Co and its presence in the rings essentially as a single site. The framework Zn for the modulation of the microenvironment and the presence of Co species as Lewis acid active sites (Co-O4) was also supported by density functional theory calculations.

Polarization pinning at antiphase boundaries in multiferroic YbFeO3

Abstract The switching characteristics of ferroelectrics and multiferroics are influenced by the interaction of topological defects with domain walls. We report on the pinning of polarization due to antiphase boundaries in thin films of the multiferroic hexagonal YbFeO3. We have directly resolved the atomic structure of a sharp antiphase boundary (APB) in YbFeO3 thin films using a combination of aberration-corrected scanning transmission electron microscopy (STEM) and total energy calculations based on density-functional theory (DFT). We find the presence of a layer of FeO6 octahedra at the APB that bridges the adjacent domains. STEM imaging shows a reversal in the direction of polarization on moving across the APB, which DFT calculations confirm is structural in nature as the polarization reversal reduces the distortion of the FeO6 octahedral layer at the APB. Such APBs in hexagonal perovskites are expected to serve as domain-wall pinning sites and hinder ferroelectric switching of the domains.

Effect of ECAP and aging on microstructure of an Al-Cu-Mg-Si alloy

The effect of equal-channel-angular pressing (ECAP) on the microstructure and precipitation of an Al-4.7Cu-0.74 Mg-0.51Si-0.48Mn-0.10Cr-0.09Ti-0.02Fe (all wt%) has been studied using aberration-corrected scanning transmission electron microscopy. The ECAP followed by a short-term aging provides a superior combination of strength and ductility in the present alloy. The ECAPed alloy shows a substantially different precipitation behavior in the deformation bands (DBs) compared to extended regions (ERs) during aging. The relatively coarse particles of the equilibrium θ (Al2Cu) and β (Mg2Si) phases were found to form along deformation-induced grain/subgrain boundaries within the DBs after short-term aging. In the present alloy after ECAP and aging, the phases continuously decorating dislocation lines or forming the discrete particles in the ERs are similar to those in the bulk matrix after conventional aging. The macroscopic strengths have been estimated for the ERs and DBs in the samples after ECAP and aging. The former, i.e., ERs, with predominant strengthening contributions originating from solid solution, precipitation and dislocations, is likely have a higher YS than the latter with the relatively coarse equilibrium particles and mainly strengthened by only grain boundaries and dislocations.

Revealing the mechanism of bifunctional PtLa electrocatalyst for highly efficient methanol oxidation, hydrogen evolution, and coupling reaction

The development of clean energy solutions, such as fuel cells and hydrogen energy, is crucial for addressing the global energy shortage. Platinum (Pt)-based catalysts are widely used in fuel cells and hydrogen energy generation (for example, via water electrolysis). However, reducing the amount of Pt used while maintaining the catalytic performance of such catalysts is essential. Herein, PtLa catalysts (PtxLay/C) doped with rare earth element lanthanum (La) with different Pt/La atomic ratios were synthesized using a simple chemical reduction method, resulting in Pt65La35/C, Pt78La22/C, Pt97La3/C, and Pt100/C. These PtxLay/C catalysts exhibited excellent electrocatalytic activity and stability in methanol oxidation reaction (MOR), hydrogen evolution reaction (HER), and their coupling reaction as MOR||HER under alkaline conditions. The mechanism by which La doping enhances the electrocatalytic properties and stability of Pt-based catalysts was investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), aberration-corrected scanning transmission electron microscopy (AC-STEM), in-situ Fourier transform infrared (FTIR) and operando Raman spectroscopy. For HER, La doping facilitated the adsorption and activation of H2O at Pt sites, improving water dissociation and *OH desorption and reducing Pt poisoning by *OH. This enhances both the catalytic performance and stability of PtxLay/C for HER. Pt78La22/C exhibited a considerably lower overpotential of only 111 mV at 100 mA cm−2 compared to commercial 20 wt% Pt/C (Pt/C-Johnson Matthey (JM)), which requires 153 mV. For MOR, La promotes CO bond cleavage and reduces CO adsorption at the Pt sites, thereby enhancing both the performance and stability of the catalysts. The mass activity (MA) of Pt78La22/C for MOR is 4.44 A mg−1Pt, which is 12.33 times higher than that of Pt/C-JM (0.36 A/mgPt), and surpasses those of Pt65La35/C, Pt97La3/C, and Pt100/C (2.93, 0.24, and 2.91 A mg−1Pt, respectively). Additionally, Pt78La22/C exhibited outstanding catalytic performance for MOR||HER, with a current density of 20 mA cm−2 at 1.030 V, demonstrating good stability with negligible voltage changes after a 15 h chronoamperometry (CA) testing. This study provides a new strategy for synthesizing Pt-based catalysts with enhanced efficiency and low-energy input for HER||MOR.