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Here we show that compressive sensing allows 4‐dimensional (4‐D) STEM data to be obtained and accurately reconstructed with both high‐speed and reduced electron fluence. The methodology needed to achieve these results compared to conventional 4‐D approaches requires only that a random subset of probe locations is acquired from the typical regular scanning grid, which immediately generates both higher speed and the lower fluence experimentally. We also consider downsampling of the detector, showing that oversampling is inherent within convergent beam electron diffraction (CBED) patterns and that detector downsampling does not reduce precision but allows faster experimental data acquisition. Analysis of an experimental atomic resolution yttrium silicide dataset shows that it is possible to recover over 25 dB peak signal‐to‐noise ratio in the recovered phase using 0.3% of the total data. Lay abstract: Four‐dimensional scanning transmission electron microscopy (4‐D STEM) is a powerful technique for characterizing complex nanoscale structures. In this method, a convergent beam electron diffraction pattern (CBED) is acquired at each probe location during the scan of the sample. This means that a 2‐dimensional signal is acquired at each 2‐D probe location, equating to a 4‐D dataset. Despite the recent development of fast direct electron detectors, some capable of 100kHz frame rates, the limiting factor for 4‐D STEM is acquisition times in the majority of cases, where cameras will typically operate on the order of 2kHz. This means that a raster scan containing 256^2 probe locations can take on the order of 30s, approximately 100‐1000 times longer than a conventional STEM imaging technique using monolithic radial detectors. As a result, 4‐D STEM acquisitions can be subject to adverse effects such as drift, beam damage, and sample contamination. Recent advances in computational imaging techniques for STEM have allowed for faster acquisition speeds by way of acquiring only a random subset of probe locations from the field of view. By doing this, the acquisition time is significantly reduced, in some cases by a factor of 10‐100 times. The acquired data is then processed to fill‐in or inpaint the missing data, taking advantage of the inherently low‐complex signals which can be linearly combined to recover the information. In this work, similar methods are demonstrated for the acquisition of 4‐D STEM data, where only a random subset of CBED patterns are acquired over the raster scan. We simulate the compressive sensing acquisition method for 4‐D STEM and present our findings for a variety of analysis techniques such as ptychography and differential phase contrast. Our results show that acquisition times can be significantly reduced on the order of 100‐300 times, therefore improving existing frame rates, as well as further reducing the electron fluence beyond just using a faster camera. [ABSTRACT FROM AUTHOR]

Tuning the anionic site of catalyst supports can impact reaction pathways by creating active sites on the support or influencing metal‐support interactions when using supported metal nanoparticles. This study focuses on CO2 hydrogenation over supported Cu nanoparticles, revealing a 3‐fold increase in methanol yield when replacing oxygen anions with hydrides in the perovskite support (Cu/BaTiO2.8H0.2 yields ~146 mg/h/gCu vs. Cu/BaTiO3 yields ~50 mg/h/gCu). The contrast suggests that significant roles are played by the support hydrides in the reaction. Temperature programmed reaction and isotopic labelling studies indicate that BaTiO2.8H0.2 surface hydride species follow a Mars van Krevelen mechanism in CO2 hydrogenation, promoting methanol production. High‐pressure steady‐state isotopic transient kinetic analysis (SSITKA) studies suggest that Cu/BaTiO2.8H0.2 possesses both a higher density and more active and selective sites for methanol production compared to Cu/BaTiO3. An operando high‐pressure diffuse reflectance infrared spectroscopy (DRIFTS)‐SSITKA study shows that formate species are the major surface intermediates over both catalysts, and the subsequent hydrogenation steps of formate are likely rate‐limiting. However, the catalytic reactivity of Cu/BaTiO2.8H0.2 towards the formate species is much higher than Cu/BaTiO3, likely due to the altered electronic structure of interface Cu sites by the hydrides in the support as validated by density functional theory (DFT) calculations. [ABSTRACT FROM AUTHOR]

Tuning the anionic site of catalyst supports can impact reaction pathways by creating active sites on the support or influencing metal‐support interactions when using supported metal nanoparticles. This study focuses on CO2 hydrogenation over supported Cu nanoparticles, revealing a 3‐fold increase in methanol yield when replacing oxygen anions with hydrides in the perovskite support (Cu/BaTiO2.8H0.2 yields ~146 mg/h/gCu vs. Cu/BaTiO3 yields ~50 mg/h/gCu). The contrast suggests that significant roles are played by the support hydrides in the reaction. Temperature programmed reaction and isotopic labelling studies indicate that BaTiO2.8H0.2 surface hydride species follow a Mars van Krevelen mechanism in CO2 hydrogenation, promoting methanol production. High‐pressure steady‐state isotopic transient kinetic analysis (SSITKA) studies suggest that Cu/BaTiO2.8H0.2 possesses both a higher density and more active and selective sites for methanol production compared to Cu/BaTiO3. An operando high‐pressure diffuse reflectance infrared spectroscopy (DRIFTS)‐SSITKA study shows that formate species are the major surface intermediates over both catalysts, and the subsequent hydrogenation steps of formate are likely rate‐limiting. However, the catalytic reactivity of Cu/BaTiO2.8H0.2 towards the formate species is much higher than Cu/BaTiO3, likely due to the altered electronic structure of interface Cu sites by the hydrides in the support as validated by density functional theory (DFT) calculations. [ABSTRACT FROM AUTHOR]

Plasmas can generate ultra-high-temperature reactive environments that can be used for the synthesis and processing of a wide range of materials1,2. However, the limited volume, instability and non-uniformity of plasmas have made it challenging to scalably manufacture bulk, high-temperature materials3–8. Here we present a plasma set-up consisting of a pair of carbon-fibre-tip-enhanced electrodes that enable the generation of a uniform, ultra-high temperature and stable plasma (up to 8,000 K) at atmospheric pressure using a combination of vertically oriented long and short carbon fibres. The long carbon fibres initiate the plasma by micro-spark discharge at a low breakdown voltage, whereas the short carbon fibres coalesce the discharge into a volumetric and stable ultra-high-temperature plasma. As a proof of concept, we used this process to synthesize various extreme materials in seconds, including ultra-high-temperature ceramics (for example, hafnium carbonitride) and refractory metal alloys. Moreover, the carbon-fibre electrodes are highly flexible and can be shaped for various syntheses. This simple and practical plasma technology may help overcome the challenges in high-temperature synthesis and enable large-scale electrified plasma manufacturing powered by renewable electricity.A plasma set-up consisting of a pair of carbon-fibre-tip-enhanced electrodes enables the generation of a uniform, ultra-high temperature and stable plasma (up to 8,000 K) at atmospheric pressure using a combination of vertically oriented long and short carbon fibres. [ABSTRACT FROM AUTHOR]

Porous carbons are the active materials of choice for supercapacitor applications because of their power capability, long-term cycle stability, and wide operating temperatures. However, the development of carbon active materials with improved physicochemical and electrochemical properties is generally carried out via time-consuming and cost-ineffective experimental processes. In this regard, machine-learning technology provides a data-driven approach to examine previously reported research works to find the critical features for developing ideal carbon materials for supercapacitors. Here, we report the design of a machine-learning-derived activation strategy that uses sodium amide and cross-linked polymer precursors to synthesize highly porous carbons (i.e., with specific surface areas > 4000 m2/g). Tuning the pore size and oxygen content of the carbonaceous materials, we report a highly porous carbon-base electrode with 0.7 mg/cm2 of electrode mass loading that exhibits a high specific capacitance of 610 F/g in 1 M H2SO4. This result approaches the specific capacitance of a porous carbon electrode predicted by the machine learning approach. We also investigate the charge storage mechanism and electrolyte transport properties via step potential electrochemical spectroscopy and quasielastic neutron scattering measurements. Machine-learning technology provides a data-driven approach to find the critical features for ideal carbon-based supercapacitors. Here, the authors report machine-Learning assisted discovery of oxygen rich highly porous carbons that exhibits a high specific capacitance. [ABSTRACT FROM AUTHOR]

A photocatalyst TiO2/Ti‐BPDC‐Pt is developed with a self‐grown TiO2/Ti‐metal–organic framework (MOF) heterojunction, i.e. TiO2/Ti‐BPDC, and selectively anchored high‐density Pt single‐atomic cocatalysts on Ti‐BPDC for photocatalytic hydrogen evolution. This intimate heterojunction, growing from the surface pyrolytic reconstruction of Ti‐BPDC, works in a direct Z‐scheme, efficiently separating electrons and holes. Pt is selectively anchored on Ti‐BPDC by ligands and is found in the form of single atoms with loading up to 1.8 wt %. The selective location of Pt is the electron‐enriched domain of the heterojunction, which further enhances the utilization of the separated electrons. This tailored TiO2/Ti‐BPDC‐Pt shows a significantly enhanced activity of 12.4 mmol g−1 h−1 compared to other TiO2‐ or MOF‐based catalysts. The structure‐activity relationship further proves the balance of two simultaneously exposed domains of heterojunctions is critical to fulfilling this kind of catalyst. [ABSTRACT FROM AUTHOR]

A photocatalyst TiO2/Ti‐BPDC‐Pt is developed with a self‐grown TiO2/Ti‐metal–organic framework (MOF) heterojunction, i.e. TiO2/Ti‐BPDC, and selectively anchored high‐density Pt single‐atomic cocatalysts on Ti‐BPDC for photocatalytic hydrogen evolution. This intimate heterojunction, growing from the surface pyrolytic reconstruction of Ti‐BPDC, works in a direct Z‐scheme, efficiently separating electrons and holes. Pt is selectively anchored on Ti‐BPDC by ligands and is found in the form of single atoms with loading up to 1.8 wt %. The selective location of Pt is the electron‐enriched domain of the heterojunction, which further enhances the utilization of the separated electrons. This tailored TiO2/Ti‐BPDC‐Pt shows a significantly enhanced activity of 12.4 mmol g−1 h−1 compared to other TiO2‐ or MOF‐based catalysts. The structure‐activity relationship further proves the balance of two simultaneously exposed domains of heterojunctions is critical to fulfilling this kind of catalyst. [ABSTRACT FROM AUTHOR]

Scanning transmission electron microscopy images can be complex to interpret on the atomic scale as the contrast is sensitive to multiple factors such as sample thickness, composition, defects and aberrations. Simulations are commonly used to validate or interpret real experimental images, but they come at a cost of either long computation times or specialist hardware such as graphics processing units. Recent works in compressive sensing for experimental STEM images have shown that it is possible to significantly reduce the amount of acquired signal and still recover the full image without significant loss of image quality, and therefore it is proposed here that similar methods can be applied to STEM simulations. In this paper, we demonstrate a method that can significantly increase the efficiency of STEM simulations through a targeted sampling strategy, along with a new approach to independently subsample each frozen phonon layer. We show the effectiveness of this method by simulating a SrTiO3 grain boundary and monolayer 2H‐MoS2 containing a sulphur vacancy using the abTEM software. We also show how this method is not limited to only traditional multislice methods, but also increases the speed of the PRISM simulation method. Furthermore, we discuss the possibility for STEM simulations to seed the acquisition of real data, to potentially lead the way to self‐driving (correcting) STEM. Lay Description: Scanning Transmission Electron Microscopy (STEM) simulation is used to validate contrast in experimental images through matching procedures. Parameter searches are performed over various combinations of aberrations and sample structures until an approximation is made with respect to the experimental image. The most common approach for calculating simulations is the multislice approach, where the sample potential is approximated as a series of two‐dimensional slices. The propagation of the beam between slices involves multiple Fast Fourier Transform calculations, which must be performed at all probe locations, hence it is computationally expensive. This means that STEM multislice simulations take a significant amount time to perform, even with specialist hardware such as graphical processing units for parallelisation of calculation. An alternative to this is a recently developed algorithm known as the plane‐wave reciprocal‐space interpolated scattering matrix (PRISM) method. PRISM uses the fact that the electron probe can also be expressed as a plane‐wave expansion, and a basis set of plane‐waves can be propagated through the sample (as in the multislice step) independently of one another. After the plane‐waves are propagated through the sample, they form what is known as a scattering matrix and can be superimposed with appropriate coefficients to approximate the exit wavefunction/probe. This makes PRISM significantly faster to compute exit probes, at a small expense of accuracy with respect to the ground truth multislice simulation. In this paper, we present a novel method for increasing STEM simulation computation time through targeted probe sub‐sampling. This method takes advantage of developments within the compressive sensing (CS) community, whereby a significant proportion of probe locations can be omitted during calculation, yet inpainted through a dictionary learning and sparse coding algorithms (such as Beta Process Factor Analysis, BPFA) with minimal loss of accuracy. The method is implemented with both the PRISM and multislice algorithms, and demonstrations of the method are applied to HAADF simulations of a low energy strontium titanate grain boundary, and the 2H phase of monolayer molybdenum disulfide with sulfur vacancies. The methods yield results which are functionally identical to the ground truth (fully sampled) multislice simulations, but can be performed up to 350× faster by using the PRISM method with sub‐sampling. Furthermore, we also demonstrate how STEM simulations can seed the recovery of experimental CS‐STEM data through (dictionary) transfer learning. This is applied to sub‐sampled HAADF images of yttrium silicide, and shows a 9% increase in PSNR versus only using BPFA. [ABSTRACT FROM AUTHOR]

Supported Pd single atom catalysts (SACs) have triggered great research interest in methane combustion yet with contradicting views on their activity and stability. Here, we show that the Pd SAs can take different electronic structure and atomic geometry on ceria support, resulting in different catalytic properties. By a simple thermal pretreatment to ceria prior to Pd deposition, a unique anchoring site is created. The Pd SA, taking this site, can be activated to Pdδ+ (0<δ<2) that has greatly enhanced activity for methane oxidation: T50 lowered by up to 130 °C and almost 10 times higher turnover frequency compared to the untreated catalyst. The enhanced activity of Pdδ+ site is related to its oxygen‐deficient local structure and elongated interacting distance with ceria, leading to enhanced capability in delivering reactive oxygen species and decomposing reaction intermediates. This work provides insights into designing highly efficient Pd SACs for oxidation reactions. [ABSTRACT FROM AUTHOR]

Supported Pd single atom catalysts (SACs) have triggered great research interest in methane combustion yet with contradicting views on their activity and stability. Here, we show that the Pd SAs can take different electronic structure and atomic geometry on ceria support, resulting in different catalytic properties. By a simple thermal pretreatment to ceria prior to Pd deposition, a unique anchoring site is created. The Pd SA, taking this site, can be activated to Pdδ+ (0<δ<2) that has greatly enhanced activity for methane oxidation: T50 lowered by up to 130 °C and almost 10 times higher turnover frequency compared to the untreated catalyst. The enhanced activity of Pdδ+ site is related to its oxygen‐deficient local structure and elongated interacting distance with ceria, leading to enhanced capability in delivering reactive oxygen species and decomposing reaction intermediates. This work provides insights into designing highly efficient Pd SACs for oxidation reactions. [ABSTRACT FROM AUTHOR]

There is an urgent need to develop cost‐effective electrocatalysts based on Pt for a broad spectrum of applications, including those vital to the operation of fuel cells. Hollowing out the interior of Pt nanocrystals offers a simple and viable strategy for maximizing the utilization efficiency of this precious metal while enhancing the electrocatalytic performance. Herein, we report the synthesis and electrocatalytic evaluation of Pt−Ag icosahedral nanocages with an average wall thickness of 1.6 nm. The Pt atoms are coated on the surface of Ag icosahedral seeds, leading to the formation of Ag@PtnL core‐shell icosahedral nanocrystals with tunable shell thicknesses. The core‐shell nanocrystals are then converted to icosahedral nanocages by selectively etching away the Ag in the core. The as‐obtained nanocages with a composition of Pt4.5Ag exhibit an almost 3‐fold enhancement in specific activity toward oxygen reduction relative to the commercial Pt/C in acid media. [ABSTRACT FROM AUTHOR]

Precise control of charge transfer between catalyst nanoparticles and supports presents a unique opportunity to enhance the stability, activity, and selectivity of heterogeneous catalysts. While charge transfer is tunable using the atomic structure and chemistry of the catalyst-support interface, direct experimental evidence is missing for three-dimensional catalyst nanoparticles, primarily due to the lack of a high-resolution method that can probe and correlate both the charge distribution and atomic structure of catalyst/support interfaces in these structures. We demonstrate a robust scanning transmission electron microscopy (STEM) method that simultaneously visualizes the atomic-scale structure and sub-nanometer-scale charge distribution in heterogeneous catalysts using a model Au-catalyst/SrTiO3-support system. Using this method, we further reveal the atomic-scale mechanisms responsible for the highly active perimeter sites and demonstrate that the charge transfer behavior can be readily controlled using post-synthesis treatments. This methodology provides a blueprint for better understanding the role of charge transfer in catalyst stability and performance and facilitates the future development of highly active advanced catalysts. Precise control of charge transfer between catalyst nanoparticles and supports presents a unique opportunity to enhance catalytic performance. Here the authors demonstrate a scanning transmission electron microscopy method to visualize atomic-scale structure and sub-nanometer-scale charge distribution in heterogeneous catalysts, shedding light on the atomic-scale mechanisms behind their highly active perimeter sites. [ABSTRACT FROM AUTHOR]

Due to tunable redox properties and cost‐effectiveness, copper‐ceria (Cu‐CeO2) materials have been investigated for a wide scope of catalytic reactions. However, accurately identifying and rationally tuning the local structures in Cu‐CeO2 have remained challenging, especially for nanomaterials with inherent structural complexities involving surfaces, interfaces, and defects. Here, a nanocrystal‐based atom‐trapping strategy to access atomically precise Cu‐CeO2 nanostructures for enhanced catalysis is reported. Driven by the interfacial interactions between the presynthesized Cu and CeO2 nanocrystals, Cu atoms migrate and redisperse onto the CeO2 surface via a solid–solid route. This interfacial restructuring behavior facilitates tuning of the copper dispersion and the associated creation of surface oxygen defects on CeO2, which gives rise to enhanced activities and stabilities catalyzing water–gas shift reaction. Combining soft and solid‐state chemistry of colloidal nanocrystals provide a well‐defined platform to understand, elucidate, and harness metal–support interactions. The dynamic behavior of the supported metal species can be further exploited to realize exquisite control and rational design of multicomponent nanocatalysts. [ABSTRACT FROM AUTHOR]

The article announces Microscopy Society of America Awards 2021 given to David Agard, Maximilian Haider, and Knut W. Urban.

We report a simple route based upon seed‐mediated growth to the synthesis of Pd@AuxPd1−x (0.8≤x≤1) core–shell nanocubes. Benefiting from the well‐defined {100} facets and an optimal Au/Pd ratio for the surface, the nanocubes bearing a shell made of Au0.95Pd0.05 work as an efficient electrocatalyst toward H2O2 production, with high selectivity of 93–100 % in the low‐overpotential region of 0.4–0.7 V. When the Au0.95Pd0.05 alloy is confined to a shell of only three atomic layers in thickness, the electrocatalyst is able to maintain its surface structure and elemental composition, endowing continuous and stable production of H2O2 during oxygen reduction at a high rate of 1.62 mol g(Pd+Au)−1 h−1. This work demonstrates a versatile route to the rational development of active and durable electrocatalysts based upon alloy nanocrystals. [ABSTRACT FROM AUTHOR]

We report a simple route based upon seed‐mediated growth to the synthesis of Pd@AuxPd1−x (0.8≤x≤1) core–shell nanocubes. Benefiting from the well‐defined {100} facets and an optimal Au/Pd ratio for the surface, the nanocubes bearing a shell made of Au0.95Pd0.05 work as an efficient electrocatalyst toward H2O2 production, with high selectivity of 93–100 % in the low‐overpotential region of 0.4–0.7 V. When the Au0.95Pd0.05 alloy is confined to a shell of only three atomic layers in thickness, the electrocatalyst is able to maintain its surface structure and elemental composition, endowing continuous and stable production of H2O2 during oxygen reduction at a high rate of 1.62 mol g(Pd+Au)−1 h−1. This work demonstrates a versatile route to the rational development of active and durable electrocatalysts based upon alloy nanocrystals. [ABSTRACT FROM AUTHOR]

Janus particles are widely sought for applications related to colloidal assembly, stabilization of emulsions, and development of active colloids, among others. Here we report a versatile route to the fabrication of well‐controlled Janus particles by simply breaking the symmetry of spherical particles with swelling. When a polystyrene (PS) sphere covered by a rigid shell made of silica or polydopamine is exposed to a good solvent for PS, a gradually increased pressure will be created inside the shell. If the pressure becomes high enough to poke a hole in the shell, the spherical symmetry will break while pushing out the swollen PS through the opening to generate a Janus particle comprised of two distinct components. One of the components is made of PS and its size is controlled by the extent of swelling. The other component is comprised of the rigid shell and remaining PS, with its overall diameter determined by the original PS sphere and the rigid shell. This solution‐based route holds promises for the scalable production of complex Janus particles with a variety of compositions and in large quantities. [ABSTRACT FROM AUTHOR]

Janus particles are widely sought for applications related to colloidal assembly, stabilization of emulsions, and development of active colloids, among others. Here we report a versatile route to the fabrication of well‐controlled Janus particles by simply breaking the symmetry of spherical particles with swelling. When a polystyrene (PS) sphere covered by a rigid shell made of silica or polydopamine is exposed to a good solvent for PS, a gradually increased pressure will be created inside the shell. If the pressure becomes high enough to poke a hole in the shell, the spherical symmetry will break while pushing out the swollen PS through the opening to generate a Janus particle comprised of two distinct components. One of the components is made of PS and its size is controlled by the extent of swelling. The other component is comprised of the rigid shell and remaining PS, with its overall diameter determined by the original PS sphere and the rigid shell. This solution‐based route holds promises for the scalable production of complex Janus particles with a variety of compositions and in large quantities. [ABSTRACT FROM AUTHOR]

Despite the large number of reports on colloidal nanocrystals, very little is known about the mechanistic details in terms of nucleation and growth at the atomistic level. Taking bimetallic core-shell nanocrystals as an example, here we integrate in situ liquid-cell transmission electron microscopy with first-principles calculations to shed light on the atomistic details involved in the nucleation and growth of Pt on Pd cubic seeds. We elucidate the roles played by key synthesis parameters, including capping agent and precursor concentration, in controlling the nucleation site, diffusion path, and growth pattern of the Pt atoms. When the faces of a cubic seed are capped by Br−, Pt atoms preferentially nucleate from corners and then diffuse to edges and faces for the creation of a uniform shell. The diffusion does not occur until the Pt deposited at the corner has reached a threshold thickness. At a high concentration of the precursor, self-nucleation takes place and the Pt clusters then randomly attach to the surface of a seed for the formation of a non-uniform shell. These atomistic insights offer a general guideline for the rational synthesis of nanocrystals with diverse compositions, structures, shapes, and related properties. Creating predictable, controllable nanoparticles relies on a mechanistic understanding of their synthesis. Here, through integrated in situ liquid microscopy and first-principles calculations, the authors elucidate the atomistic details involved in the formation of colloidal core-shell nanoparticles. [ABSTRACT FROM AUTHOR]

Forming an ultra‐thin, permeable encapsulation oxide‐support layer on a metal catalyst surface is considered an effective strategy for achieving a balance between high stability and high activity in heterogenous catalysts. The success of such a design relies not only on the thickness, ideally one to two atomic layers thick, but also on the morphology and chemistry of the encapsulation layer. Reliably identifying the presence and chemical nature of such a trace layer has been challenging. Electron energy‐loss spectroscopy (EELS) performed in a scanning transmission electron microscope (STEM), the primary technique utilized for such studies, is limited by a weak signal on overlayers when using conventional analysis methods, often leading to misinterpreted or missed information. Here, a robust, unsupervised machine learning data analysis method is developed to reveal trace encapsulation layers that are otherwise overlooked in STEM‐EELS datasets. This method provides a reliable tool for analyzing encapsulation of catalysts and is generally applicable to any spectroscopic analysis of materials and devices where revealing a trace signal and its spatial distribution is challenging. [ABSTRACT FROM AUTHOR]

Each year, the Microscopy Society of America (MSA) provides several major awards for outstanding contributions to the fields of microscopy and microanalysis and for service to the Society. While recipients of these awards are listed under the tab Awards & Scholarships – Society Awards | Microscopy Society of America on the MSA homepage, little information as to why awards were bestowed is provided. In this initial installment of what will become an annual contribution to Microsocopy Today, Miaofang Chi, Chair of the MSA Awards Committee, and I provide a perspective on the important contributions of the 2020 Award winners. The information presented here represents a short summary of information provided in the awardees' nomination packages. Guidelines, including deadlines for nominating individuals for these and other MSA awards, can be found by following the above link. [ABSTRACT FROM AUTHOR]

Two-dimensional van der Waals MnBi2nTe3n+1 (n = 1, 2, 3, 4) compounds have been recently found to be intrinsic magnetic topological insulators rendering quantum anomalous Hall effect and diverse topological states. Here, we summarize and compare the crystal and magnetic structures of this family, and discuss the effects of chemical composition on their magnetism. We found that a considerable fraction of Bi occupies at the Mn sites in MnBi2nTe3n+1 (n = 1, 2, 3, 4) while there is no detectable Mn at the non-magnetic atomic sites within the resolution of neutron diffraction experiments. The occupancy of Mn monotonically decreases with the increase of n. The polarized neutron diffraction on the representative MnBi4Te7 reveals that its magnetization density is exclusively accumulated at the Mn site, in good agreement with the results from the unpolarized neutron diffraction. The defects of Bi at the Mn site naturally explain the continuously reduced saturated magnetic moments from n = 1 to n = 4. The experimentally estimated critical exponents of all the compounds generally suggest a three-dimensional character of magnetism. Our work provides material-specified structural parameters that may be useful for band structure calculations to understand the observed topological surface states and for designing quantum magnetic materials through chemical doping. [ABSTRACT FROM AUTHOR]

The article titled "Back Cover: Significant Roles of Surface Hydrides in Enhancing the Performance of Cu/BaTiO2.8H0.2 Catalyst for CO2 Hydrogenation to Methanol" discusses the use of surface hydrides in improving the efficiency of a catalyst for converting CO2 to methanol. The cover picture depicts a BaTiO3 lattice with Cu nanoparticles representing the catalytic process. The researchers, led by Zili Wu, demonstrate that replacing lattice oxygen with hydrides enhances the catalyst's performance. The article provides valuable insights into the reaction mechanism and includes an operando study. [Extracted from the article]

The article titled "Significant Roles of Surface Hydrides in Enhancing the Performance of Cu/BaTiO2.8H0.2 Catalyst for CO2 Hydrogenation to Methanol" explores the use of hydrides in improving the efficiency of catalysts for converting CO2 to methanol. The cover picture depicts a BaTiO3 lattice with Cu nanoparticles representing the catalytic process. The study conducted by Zili Wu et al. demonstrates that replacing lattice oxygen with hydrides enhances the performance of the catalyst. The article is authored by a diverse group of researchers. [Extracted from the article]

Noble‐metal nanocrystals with anisotropic shapes have received increasing interest owing to their unique properties. Here, a facile route to the preparation of Pt nanobars with aspect ratios tunable up to 2.1 was reported by simply reducing a PtIV precursor in N,N‐dimethylformamide (DMF) at 160 °C in the presence of poly(vinyl pyrrolidone) (PVP). In addition to its commonly observed roles as a solvent and a reductant, DMF could also decompose to generate CO, a capping agent capable of selectively passivating Pt{100} facets to promote the formation of nanobars. The size and aspect ratio of the nanobars could be tuned by varying the amount of PtIV precursor involved in the synthesis, as well as the concentration of PVP because of its dual roles as a stabilizer and a co‐reductant. Our mechanistic study indicated that the anisotropic growth resulted from both particle coalescence and localized oxidative etching followed by preferential growth. [ABSTRACT FROM AUTHOR]

Capacity fading during long-term cycling (>1500×) is still a critical challenge for Li-ion batteries that use Ni-rich layered oxides, e.g. LiNi0.8Co0.15Al0.05O2 (NCA), as the cathode. Microcracks have been previously recognized as one of the primary reasons for the observed capacity fade. Although there exists a generally developed mechanical understanding of microcracks, the role of the electrolyte has not been clearly understood, especially after extended cycling and at the atomic scale. Here, we unveil the microstructural evolution of spherical NCA secondary particles after long-term cycling using scanning transmission electron microscopy accompanied with electron energy loss spectroscopy. We found that the microcracks initiated and grew through grain boundaries, which then serve as the pathway for electrolyte penetration into secondary NCA particles. Additionally, the rock-salt phase reconstruction is prone to occur at the (003) surfaces of the primary particles or the crack surfaces, largely due to electrolyte (LiPF6 EC/EMC) corrosion. Crack propagation within the NCA grains is primarily a joint consequence from electrolyte corrosion and mechanical strain during lithiation/delithiation. During extended cycling, due to the distinctive surface facets, the primary grains located in the center of the secondary particles experience more intensive electrolyte corrosion, leading to a reduced contact with nearby particles, impairing the overall capacity. These results establish the initiation and growth mechanism of microcracks and voids in NCA-based cathodes during cycling and point out the role of the electrolyte in affecting the degradation of NCA-based cathodes. [ABSTRACT FROM AUTHOR]

In this investigation, the improved electrochemical behavior in Si-doped Li-rich cathodes is studied with scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). Z-contrast images show a layered structure that develops a thin, spinel-like surface layer after the first charge cycle. Si-doping increases discharge capacity by ∼25% and appears to retard the surface phase transformation. Based on electron energy loss spectra, the surface layer in the doped material has an altered oxygen electronic environment, which supports the STEM findings. Furthermore, Si-doping changes the redox behavior during the activation cycle. Density functional theory calculations indicate that Si-doping can increase oxygen vacancy formation, and change the sequence of the redox couples by introducing more oxygen vacancies before or during the typical high voltage activation process. The results of this work indicate that the type of doping employed here is an effective strategy for controlling the complex charge compensation mechanisms in lithium-rich cathodes. [ABSTRACT FROM AUTHOR]

Copper nanostructures are promising catalysts for the electrochemical reduction of CO2 because of their unique ability to produce a large proportion of multi‐carbon products. Despite great progress, the selectivity and stability of such catalysts still need to be substantially improved. Here, we demonstrate that controlling the surface oxidation of Cu nanowires (CuNWs) can greatly improve their C2+ selectivity and stability. Specifically, we achieve a faradaic efficiency as high as 57.7 and 52.0 % for ethylene when the CuNWs are oxidized by the O2 from air and aqueous H2O2, respectively, and both of them show hydrogen selectivity below 12 %. The high yields of C2+ products can be mainly attributed to the increase in surface roughness and the generation of defects and cavities during the electrochemical reduction of the oxide layer. Our results also indicate that the formation of a relatively thick, smooth oxide sheath can improve the catalytic stability by mitigating the fragmentation issue. [ABSTRACT FROM AUTHOR]

Copper nanostructures are promising catalysts for the electrochemical reduction of CO2 because of their unique ability to produce a large proportion of multi‐carbon products. Despite great progress, the selectivity and stability of such catalysts still need to be substantially improved. Here, we demonstrate that controlling the surface oxidation of Cu nanowires (CuNWs) can greatly improve their C2+ selectivity and stability. Specifically, we achieve a faradaic efficiency as high as 57.7 and 52.0 % for ethylene when the CuNWs are oxidized by the O2 from air and aqueous H2O2, respectively, and both of them show hydrogen selectivity below 12 %. The high yields of C2+ products can be mainly attributed to the increase in surface roughness and the generation of defects and cavities during the electrochemical reduction of the oxide layer. Our results also indicate that the formation of a relatively thick, smooth oxide sheath can improve the catalytic stability by mitigating the fragmentation issue. [ABSTRACT FROM AUTHOR]

We report a facile synthesis of Ag@Pd core−shell icosahedral nanocrystals for the development of cost‐effective electrocatalysts toward formic acid oxidation. With 12.4 nm Ag icosahedra serving as seeds, Pd shells of controlled thicknesses in the range of 3.6–5.8 atomic layers are grown by adjusting the experimental parameters. When examined as catalysts toward formic acid oxidation, all the Ag@Pd nanocrystals exhibit enhanced mass activities relative to a commercial Pd/C catalyst, with the Ag@Pd4.2L nanocrystals showing enhanced mass activity that is almost twice that of a commercial Pd/C. The chronoamperometry measurements indicate that all the Ag@Pd/C catalysts are more robust than the Pd/C, with the catalyst based on Ag@Pd4.2L nanocrystals showing a mass activity greater than that of the pristine Pd/C after holding in a mixture of HCOOH and HClO4 at 0.75 V for 1,000 s. We believe that the strategy demonstrated here can also be extended to the development of other types of advanced electrocatalysts. [ABSTRACT FROM AUTHOR]

This article reports a facile method for the synthesis of Pd‐Ru nanocages by activating the galvanic replacement reaction between Pd nanocrystals and a Ru(III) precursor with I‐ ions. The as‐synthesized nanocages feature a hollow interior, ultrathin wall of ≈2.5 nm in thickness, and a cubic shape. Our quantitative study suggests that the reduction rate of the Ru(III) precursor can be substantially accelerated upon the introduction of I‐ ions and then retarded as the ratio of I‐/Ru3+ is increased. The Pd‐Ru nanocages take an alloy structure, with the Ru atoms in the nanocages crystallized in a face‐centered cubic structure instead of the hexagonal close‐packed phase taken by bulk Ru. Using Pd nanocubes with different edge lengths, the dimensions of the nanocages in the range of 6−18 nm can readily be tuned. When tested as catalysts toward the electro‐oxidation of ethylene glycol and glycerol, respectively, the Pd‐Ru cubic nanocages prepared from 18 nm Pd cubes exhibit 5.1‐ and 6.2‐fold enhancements in terms of mass activity relative to the commercial Pd/C. After 1000 cycles of accelerated durability test, the mass activities of the nanocages are still 3.3 and 3.7 times as high as that of the pristine commercial Pd/C catalyst, respectively. [ABSTRACT FROM AUTHOR]

Memristor devices could realize their full scaling (2D) and stacking (3D) potential if vertically integrated with a two‐terminal selector in a one selector one memristor (1S1R) crossbar array. However, for a 1S1R‐integrated device to function properly, memristor and selector should be compatible in terms of their material composition and electrical properties. A platinum (Pt)/yttria‐stabilized zirconia (YSZ)/zirconium (Zr) memristor with low forming voltage (<1.5 V), low first reset current (150 µA), fast switching speed (2 ns), low voltage (<1 V) and current (50 µA) resistive switching operation, and multi‐conductance state capabilities is reported. A low activation energy of oxygen vacancy diffusion (Ea,diffusion = 0.7 eV) measured in the YSZ switching layer enables the proposed memristor to have the observed low‐energy operation, which renders it better compatible with a selector device than the more commonly used binary oxides. For a proof‐of‐principle demonstration, the device is vertically integrated with a tunneling selector and successfully performs memristor‐electroforming operations with the selector in a self‐compliant 1S1R integrated device. 1S1R cells into a small array (2 × 2) are further investigated and electroforming and resistive switching operations at the array level are demonstrated. [ABSTRACT FROM AUTHOR]

The development of dual catalysts with high efficiency toward oxygen reduction and evolution reactions (ORR and OER) in acidic media is a significant challenge. Here an active and durable dual catalyst based upon cubic Pt39Ir10Pd11 nanocages with an average edge length of 12.3 nm, porous walls as thin as 1.0 nm, and well‐defined {100} facets is reported. The trimetallic nanocages perform better than all the reported dual catalysts in acidic media, with a low ORR‐OER overpotential gap of only 704 mV at a Pt‐Ir‐Pd loading of 16.8 µgPt+Ir+Pd cm−2geo. For ORR at 0.9 V, when benchmarked against the commercial Pt/C and Pt‐Pd nanocages, the trimetallic nanocages exhibit an enhanced mass activity of 0.52 A mg−1Pt+Ir+Pd (about four and two times as high as those of the Pt/C and Pt‐Pd nanocages) and much improved durability. For OER, the trimetallic nanocages show a remarkable mass activity of 0.20 A mg−1Pt+Ir at 1.53 V, which is 16.7 and 4.3 fold relative to those of the Pt/C and Pt‐Pd nanocages, respectively. These improvements can be ascribed to the highly open structure of the nanocages, and the possible electronic coupling between Ir and Pt atoms in the lattice. [ABSTRACT FROM AUTHOR]

Interfaces play a fundamental role in many areas of chemistry. However, their localized nature requires characterization techniques with high spatial resolution in order to fully understand their structure and properties. State‐of‐the‐art atomic resolution or in situ scanning transmission electron microscopy and electron energy‐loss spectroscopy are indispensable tools for characterizing the local structure and chemistry of materials with single‐atom resolution, but they are not able to measure many properties that dictate function, such as vibrational modes or charge transfer, and are limited to room‐temperature samples containing no liquids. Here, we outline emerging electron microscopy techniques that are allowing these limitations to be overcome and highlight several recent studies that were enabled by these techniques. We then provide a vision for how these techniques can be paired with each other and with in situ methods to deliver new insights into the static and dynamic behavior of functional interfaces. [ABSTRACT FROM AUTHOR]

Interfaces play a fundamental role in many areas of chemistry. However, their localized nature requires characterization techniques with high spatial resolution in order to fully understand their structure and properties. State‐of‐the‐art atomic resolution or in situ scanning transmission electron microscopy and electron energy‐loss spectroscopy are indispensable tools for characterizing the local structure and chemistry of materials with single‐atom resolution, but they are not able to measure many properties that dictate function, such as vibrational modes or charge transfer, and are limited to room‐temperature samples containing no liquids. Here, we outline emerging electron microscopy techniques that are allowing these limitations to be overcome and highlight several recent studies that were enabled by these techniques. We then provide a vision for how these techniques can be paired with each other and with in situ methods to deliver new insights into the static and dynamic behavior of functional interfaces. [ABSTRACT FROM AUTHOR]

Production of syngas with tunable CO/H2 ratio from renewable resources is an ideal way to provide a carbon-neutral feedstock for liquid fuel production. Ag is a benchmark electrocatalysts for CO2-to-CO conversion but high overpotential limits the efficiency. We synthesize AgP2 nanocrystals (NCs) with a greater than 3-fold reduction in overpotential for electrochemical CO2-to-CO reduction compared to Ag and greatly enhanced stability. Density functional theory calculations reveal a significant energy barrier decrease in the formate intermediate formation step. In situ X-ray absorption spectroscopy (XAS) shows that a maximum Faradaic efficiency is achieved at an average silver valence state of +1.08 in AgP2 NCs. A photocathode consisting of a n+p-Si wafer coated with ultrathin Al2O3 and AgP2 NCs achieves an onset potential of 0.2 V vs. RHE for CO production and a partial photocurrent density for CO at −0.11 V vs. RHE (j−0.11, CO) of −3.2 mA cm−2. Conversion of CO2 into value-added chemicals by use of renewable energy is promising to achieve a carbon-neutral energy cycle. Here, the authors show that AgP2 is a stable, selective and efficient syngas catalyst for solar-to-fuel conversion with a 3-fold lower overpotential compared to the benchmark Ag catalyst. [ABSTRACT FROM AUTHOR]