Aberration-corrected Transmission Electron Microscopy Research Articles

Real-time simulations of ADF STEM probe position-integrated scattering cross-sections for single element fcc crystals in zone axis orientation using a densely connected neural network

Quantification of annular dark field (ADF) scanning transmission electron microscopy (STEM) images in terms of composition or thickness often relies on probe-position integrated scattering cross sections (PPISCS). In order to compare experimental PPISCS with theoretically predicted ones, expensive simulations are needed for a given specimen, zone axis orientation, and a variety of microscope settings. The computation time of such simulations can be in the order of hours using a single GPU card. ADF STEM simulations can be efficiently parallelized using multiple GPUs, as the calculation of each pixel is independent of other pixels. However, most research groups do not have the necessary hardware, and, in the best-case scenario, the simulation time will only be reduced proportionally to the number of GPUs used. In this manuscript, we use a learning approach and present a densely connected neural network that is able to perform real-time ADF STEM PPISCS predictions as a function of atomic column thickness for most common face-centered cubic (fcc) crystals (i.e., Al, Cu, Pd, Ag, Pt, Au and Pb) along [100] and [111] zone axis orientations, root-mean-square displacements, and microscope parameters. The proposed architecture is parameter efficient and yields accurate predictions for the PPISCS values for a wide range of input parameters that are commonly used for aberration-corrected transmission electron microscopes.

Construction of the Heterostructure of NiPt Truncated Octahedral Nanoparticle/MoS2 and Its Interfacial Structure Evolution.

Interfacial atomic configuration plays a vital role in the structural stability and functionality of nanocomposites composed of metal nanoparticles (NPs) and two-dimensional semiconductors. In situ transmission electron microscope (TEM) provides a real-time technique to observe the interface structure at atomic resolution. Herein, we loaded bimetallic NiPt truncated octahedral NPs (TONPs) on MoS2 nanosheets and constructed a NiPt TONPs/MoS2 heterostructure. The interfacial structure evolution of NiPt TONPs on MoS2 was in situ investigated using aberration-corrected TEM. It was observed that some NiPt TONPs exhibited lattice matching with MoS2 and displayed remarkable stability under electron beam irradiation. Intriguingly, the rotation of an individual NiPt TONP can be triggered by the electron beam to match the MoS2 lattice underneath. Furthermore, the coalescence kinetics of NiPt TONPs can be quantitatively described by the relationship between neck radius (r) and time (t), expressed as rn = Kt. Our work offers a detailed analysis of the lattice alignment relationship of NiPt TONPs on MoS2, which may enlighten the design and preparation of stable bimetallic metal NPs/MoS2 heterostructures.

Palladium Enhanced Iron Active Site - An Efficient Dual-Atom Catalyst for Oxygen Electroreduction.

Metal-nitrogen-carbon (M-C/N) electrocatalysts have been shown to have satisfactory catalytic activity and long-term durability for the oxygen reduction reaction (ORR). Here, a strategy to prepare a new electrocatalyst (Fe&Pd-C/N) using a unique metal-containing ionic liquid (IL) is exploited, in which Fe & Pd ions are positively charged species atomically dispersed by coordination to the N of the N-doped C substrate, C/N. X-ray absorption fine structure, XPS and aberration-corrected transmission electron microscopy results verified a well-defined dual-atom configuration comprising Fe+2.x -N4 coupled Pd2+ -N4 sites and well-defined spatial distribution. Electronic control of a coupled Fe-Pd structure produces an electrocatalyst that exhibits superior performance with enhanced activity and durability for the ORR compared to that of commercial Pt/C (20%, Johnson Matthey) in both alkaline and acid media. Density functional theory calculations indicate that Pd atom can enhance the catalytic activity of the Fe active sites adjacent to Pd sites by changing the electronic orbital structure and Bader charge of the Fe centers. The excellent catalytic performance of the Fe&Pd-C/N electrocatalyst is demonstrated in zinc-air batteries and hydrogen-air fuel cells.

Guanosine-derived atomically dispersed Cu-N3-C sites for efficient electroreduction of carbon dioxide

Single-atom copper (Cu) embedded within carbon catalysts have demonstrated significant potential in the electrochemical reduction of carbon dioxide (CO2) into valuable chemicals and fuels. Herein, we develop a straightforward and template-free strategy for synthesizing atomically dispersed CuNC catalysts (CuG) by annealing the self-assembled guanosine. The CuG catalysts display two-dimensional morphology, tunable pore size and large surface areas that can be adjusted by changing carbonization temperature. Spherical aberration-corrected transmission electron microscopy reveals that single-atom Cu are homogeneously dispersed on the surface of carbon nanosheets. The optimum CuG-1000 catalysts achieve a high CO Faradaic efficiency (FEco) up to 99% and a high CO current density of 6.53 mA cm−2 (−0.65 V vs. RHE). Besides, the flow cell test of CuG-1000 shows a high current density up to 25.2 mA cm−2 and the FEco still exceeded 91% after more than 20 h of testing. Specifically, the existence of Cu-N3-C active sites was proved by extended X-ray absorption fine structure (EXAFS). Density functional theory evidences that tricoordinated copper with N can largely regulate the adsorption and desorption of key intermediates by transferring electrons to *COOH through Cu atoms, thereby improving selectivity toward CO. This work demonstrates the active origin of CuNC catalysts in CO2 electroreduction and offers a blueprint to construct atomically dispersed transition site catalysts by supramolecular self-assembly strategy.

Recognizing the formation of single-atom vanadium by enthalpy and its advantage in selective catalytic reduction of nitrogen oxide

Developing a more effective catalyst for the environmental pollutant is always the pursuit of worldwide researchers. In previous reports, most works were focused on prepared catalysts, and more efforts should explore process from a precursor to the formed catalyst. In this work, V supported TiO2 catalysts were synthesized with different V loadings, and compared in selective catalytic reduction of nitrogen oxide. For the first time, differential scanning calorimetry was used to analyze the forming enthalpy for these catalysts. As a result, turnover frequency (TOF) was decreased from 0.05 to 0.001 s−1 when the loading was increased from 0.05 to 15 mol%. At the same time, the forming enthalpy was decreased from 16.53 to 1.80 KJ·mol−1. Spherical Aberration Corrected Transmission Electron Microscope recognized both single-atom and cluster V even at the lowest loading. What’s more, density functional theory revealed that single-atom V had a lower dehydrogenation energy (1.088–1.152 eV) than cluster V during the catalysis (1.834–1.850 eV). According to these evidences, single-atom V had bigger formation enthalpy, lower dehydrogenation energy, and larger TOF than cluster V. These results help to optimize the preparation process for an effective catalyst, which is in favor of hazardous-pollutant treatment.

Interfacial strain evolution and abnormal Poisson's ratios in Al nuclei for the Al/TiB2 heterostructure

The interfacial lattice mismatch and local elastic strains of Al/TiB2 heterostructures are quantitatively investigated by aberration-corrected transmission electron microscopy. Both in-plane atomic expansion and out-of-plane compression of Al layers stacked on (0001)TiB2 are uncovered and favor the further extension of deformed Al layers for realizing a successfully heterogeneous nucleation. These lattice strains can persist up to several Al atomic layers from the topmost (0001) surface of TiB2. Based on the compressive and expansive elastic strain relation, we estimate the Poisson's ratio in Al nuclei and find that large mismatch strains lead to abnormal changes in the Poisson's ratio. This study reveals the effect of lattice mismatch on the heterogeneous nucleation of Al on TiB2 and may have important implications in understanding the heterogeneous nucleation of Al.

Origin of the bias instability in CsPbI3 light-emitting diodes

With the rapid development of all-inorganic CsPbX3 (X = I, Br, and Cl) perovskite light-emitting diodes (PeLEDs), their external quantum efficiency (EQE) has made great progress in the last few years. However, severe performance degradation at the operation condition impedes its large-scale industrial application. In this text, by using the advanced spherical aberration corrected transmission electron microscope (TEM), the degradation pathway of PeLEDs under bias loading was more systematically and comprehensively, especially from the viewpoint of its microstructural evolution pathway, which showed that iodine vacancy migration triggered the structural collapse was the primary inducement of performance decay. To solve this problem, inorganic termination ZnI2 was employed to passivate the surface halide vacancy defects and supplement the halide ion into the lattice, which significantly improves the photoluminescence (PL) lifetime and stability of CsPbI3 quantum dots (QDs). As expected, not only the EQE of PeLEDs has been greatly improved, but also the operating half-lifetime is enhanced by about 4 times as compared with the original one. Microstructural characterization and density functional (DFT) calculations confirm that the preferential segregation of Zn element on the surface of QDs was the principal cause to passivate the defect state of QDs, which exhibits lower formation energy and better operational stability.

Atomic and close-to-atomic scale polishing of Lu2O3 by plasma-assisted etching

This study presents a new method of in-process plasma-assisted etching (PaE) integrated with low-pressure polishing of lutetium oxide with high efficiency and without subsurface damage (SSD). The necessity of integrated low-pressure polishing is demonstrated through a quantum chemistry simulation. An improved Deal–Grove model for plasma treatment is established to predict the modification behavior. A modification rate of 136 nm/h can be obtained by simultaneously optimizing the plasma process. An atomically flat and SSD-free surface with a surface roughness in Sa of 0.14 nm is accomplished. The overall processing time is decreased to half the time of low-pressure slurry polishing. The new method is based on the OH* irradiation of lutetium oxide and the conversion of lutetium oxide into hydroxide, which rapidly reacts with 25% sulfuric acid droplets. The rapid planarization of the surface is then quickly realized by short low-pressure polishing. Finally, the in-process PaE quickly removes the SSD caused by low-pressure polishing. Aberration-corrected transmission electron microscopy of machined surfaces reveals the removal of the mechanically induced damage. The study shows that the new method has great potential as an environment-friendly processing technique in SSD-free finishing.

Achieving ultrahigh energy density and ultrahigh efficiency simultaneously via characteristic regulation of polar nanoregions

The advancement of dielectric ceramic materials for capacitors with exceptional energy storage performance is an inevitable requirement for the integration and miniaturization of pulse power equipment. Due to the distinctive polarization response of polar nanoregions (PNRs), it is problematic to achieve ultrahigh recovered energy density (Wrec) and ultrahigh efficiency (η) concurrently in A-site ionic disordered (Na0.5Bi0.5)TiO3 (NBT)-based relaxor ferroelectric ceramics. Through characteristic regulation of PNRs, a novel strategy for maintaining large inducible polarization and ultra-low hysteresis was proposed in this work. Finally, under 544 kV/cm, the 0.85(0.7Na0.4K0.1Bi0.5TiO3-0.3Ba0.5Sr0.5TiO3)-0.15Sr(Mg1/3Nb2/3)O3 composition achieves ultrahigh Wrec of 7.8 J/cm3 and ultrahigh η of 97.6%. At the same time, this ceramic material has exceptional temperature stability throughout an extensive temperature range of 30–120 °C, with Wrec remaining stable at 4.8 J/cm3 (variation less than 0.2 J/cm3) and η remaining greater than 95%. The piezoresponse force microscopy and aberration-corrected transmission electron microscopy results from different scales demonstrated the characteristic regulation of PNRs. Based on the enhanced local electric field in the RFE caused by the stronger ionic disorder, the external electric field-induced potential merger and growth of PNRs was successfully limited. This composition is predicted to be a candidate material for replacing lead-based dielectrics, and the design strategy used in this work provides fresh ideas for developing alternative lead-free dielectric ceramic materials.

Defect-Rich PdIr Bimetallene Nanoribbons with Interatomic Charge Localization for Isopropanol-Assisted Seawater Splitting.

Metallene with outstanding physicochemical properties is an efficient two-dimensional electrocatalysts for sustainable hydrogen (H2 ) production applications. However, the controllable fabrication of extended atomically thin metallene nanoribbons remains a formidable challenge. Herein, this work proposes a controllable preparation strategy for atomically thin defect-rich PdIr bimetallene nanoribbons (PdIr BNRs) with a thickness of only 1.5nm for the efficient and stable isopropanol-assisted seawater electrolytic H2 production. When using PdIr BNRs as catalyst to build an isopropanol-assisted seawater electrolysis system, a voltage of only 0.38V is required at @10mA cm-2 to achieve energy-saving H2 production, while producing high value-added acetone at the anode. The aberration-corrected high-resolution transmission electron microscopy (HRTEM) clearly reveals that the PdIr BNRs possess abundant structural defects, which can additionally serve as highly catalytically active sites. Density functional theory (DFT) calculations combined with X-ray absorption spectroscopy studies reveal that the introduction of Ir atoms can induce the formation of a localized charge region and shift the d-band center of Pd down, thereby reducing the adsorption energy on the catalyst in favor of the rapid desorption of H2 . This work opens the way for the controllable design and construction of defect-rich atomically thin metallene nanoribbons for efficient electrocatalytic applications.

Unveiling positive impacts of fluorine anion doping on extraordinary catalytic activity of bifunctional-layered double perovskite electrodes for solid oxide fuel cells and electrolysis cells

To address the impacts of anion doping, F-doped layered double perovskites (Pr1.1Ba0.9Co2O5+δFx) have been synthesized, demonstrating bifunctional activity in both solid oxide fuel cell and solid oxide electrolysis cell models. The F doping induces increased oxygen vacancy concentration and enhanced electrical conductivity. Combined with spherical aberration-corrected transmission electron microscopy and X-ray photoelectron spectroscopy analyses, the F− anions are successfully introduced into the host lattice, promoting the oxygen surface exchange/diffusion rates. From the density functional theory calculations, the covalence between Co 3d and O 2p-orbital is enlarged in the F-doped model, and both oxygen reduction reaction and oxygen evolution reaction activities are improved. The area-specific resistance of the Pr1.1Ba0.9Co2O5+δF0.1 (P1.1BCOF0.1) electrode is as low as 0.033 Ω/cm2 at 700 °C. The P1.1BCOF0.1 cathode-based fuel cell delivers a peak power density of 1102 mW/cm2, along with an excellent operating stability at 700 °C. Moreover, the current density of 1335 mA/cm2 is achieved in the P1.1BCOF0.1 anode-based electrolysis cell at 1.8 V toward CO2 reduction reaction at 750 °C. These results here highlight the performance origin and bifunctional activity of fluorine-doped perovskite materials, which may help us rationally design the oxide catalysts.

Direct observation of oxygen vacancy formation and migration over ceria surface by in situ environmental transmission electron microscopy

The extremely high structural tolerance of ceria to oxygen vacancies (Ov) has made it a desirable catalytic material for the hydrocarbon oxidation to chemicals and pharmaceuticals and the reduction of gaseous pollutants. It is proposed that the formation and diffusion of Ov originate from its outstanding reduction property. However, the formation and diffusion process of Ov over the surface of ceria at the atomic level is still unknown. Herein, the structural and valence evolution of CeO2 (111) surfaces in reductive, oxidative and vacuum environments from room temperature up to 700 °C was studied with in situ aberration-corrected environmental transmission electron microscopy (ETEM) experiments. Ov is found to form under a high vacuum at elevated temperatures; however, the surface can recover to the initial state through the adsorption of oxygen atoms in an oxygen-contained environment. Furthermore, in hydrogen environment, the step-CeO2 (111) surface is not stable at elevated temperatures; thus, the steps tend to be eliminated with increasing temperature. Combined with first-principles density function calculations (DFT), it is proposed that O-terminated surfaces would develop in a hypoxic environment due to the dynamic diffusion of Ov from the outer surface to the subsurface. Furthermore, in a reductive environment, H2 facilitates the formation and diffusion of Ov while Ce-terminated surfaces develope. These results reveal dynamic atomic-scale interplay between the nanoceria surface and gas, thereby providing fundamental insights into the Ov-dependent reaction of nano-CeO2 during catalytic processes.

Subnanometer-Wide Indium Selenide Nanoribbons.

Indium selenides (InxSey) have been shown to retain several desirable properties, such as ferroelectricity, tunable photoluminescence through temperature-controlled phase changes, and high electron mobility when confined to two dimensions (2D). In this work we synthesize single-layer, ultrathin, subnanometer-wide InxSey by templated growth inside single-walled carbon nanotubes (SWCNTs). Despite the complex polymorphism of InxSey we show that the phase of the encapsulated material can be identified through comparison of experimental aberration-corrected transmission electron microscopy (AC-TEM) images and AC-TEM simulations of known structures of InxSey. We show that, by altering synthesis conditions, one of two different stoichiometries of sub-nm InxSey, namely InSe or β-In2Se3, can be prepared. Additionally, in situ AC-TEM heating experiments reveal that encapsulated β-In2Se3 undergoes a phase change to γ-In2Se3 above 400 °C. Further analysis of the encapsulated species is performed using X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), energy dispersive X-ray analysis (EDX), and Raman spectroscopy, corroborating the identities of the encapsulated species. These materials could provide a platform for ultrathin, subnanometer-wide phase-change nanoribbons with applications as nanoelectronic components.

Atomically dispersed bismuth on ZnIn2S4 Dual-Functional photocatalyst for photocatalytic hydrogen production coupled with oxidation of aromatic alcohols to aldehydes

It is of great significance to develop a simple method of non-noble metal atomical dispersion to establish a dual-function photocatalysis system for the oxidation of aromatic alcohols to aldehydes, and to couple it with the photocatalytic hydrogen production, so as to fully utilize the photogenerated carriers. Herein, we report a noble metal-free photocatalyst decorated with atomic dispersed Bi atoms in ZnIn2S4 hierarchical structures by a one-pot method, for selective oxidation of R-PhCH2OH (R = H, Me, OH, Cl) coupled with high H2 evolution. Aberration corrected transmission electron microscopy and theoretical calculations demonstrated that Bi atoms are atomically dispersed and bridged with two S atoms. Atomically dispersed Bi provides the maximum atom efficiency and promotes light absorption to the near-infrared region. By excluding all wasteful sacrificial agents, Bi/ZnIn2S4 exhibits a high hydrogen evolution rate of 3658.8 µmol g-1h−1, which is approximately 14 times of that of bare ZnIn2S4 (256 µmol g-1h−1). This work provides insights into the effective utilization of photogenerated carriers in one system and the designing of promising photocatalysts with atomic precision.

Understanding the Degradation Mechanisms of Pt Electrocatalysts in PEMFCs by Combining 2D and 3D Identical Location TEM.

The evolution of Pt nanoparticles in proton-exchanged membrane fuel cells is monitored before and after electrochemical potential cycling, using 2D and 3D identical location aberration-corrected transmission electron microscopy. This work demonstrates that 2D images might be a challenge to interpret due to the 3D nature of the carbon support. Thus, it is critical to combine both 2D and 3D observations to be able to fully understand the mechanisms associated with the durability of Pt catalyst nanoparticles. In particular, this investigation reveals that the mechanism of particle migration followed by coalescence is operative mainly across short distances (<0.5 nm). This work also shows that new Pt particles appear on the carbon support, as the result of Pt dissolution, followed by the formation of clusters, which grow by Ostwald ripening. This mechanism of Ostwald ripening is also responsible for changes in shape and particle growth, which later may result in coalescence.

Achieving superior cryogenic impact toughness and sufficient tensile properties in a novel high-Mn austenitic steel weld metal via cerium addition

The microstructure and mechanical properties of the novel cryogenic high-Mn austenitic steel weld metals with different cerium (Ce) contents were investigated via electron back-scattered diffraction, scanning and spherical aberration-corrected transmission electron microscopy, and cryogenic impact and tensile test. The results indicated that the crystallographic grain size was significantly refined, and the relative frequency of high-angle grain boundaries increased with the increase of Ce content. Ce element addition could modify the main inclusions from irregular Al2O3 into regular Ce-containing inclusions. Meanwhile, the inclusions gradually became fine and dispersed, and the volume fraction of inclusions decreased with the increase of Ce content from 0 to 870 ppm. The increase of Ce content continuously improved cryogenic impact toughness from 82 J to 116 J, and yield strength, tensile strength and total elongation all increased to different degrees. We found that in addition to the beneficial changes in inclusion modification, grain refinement and increase in the proportion of high-angle grain boundaries, the solid solution of Ce also played a crucial role in the mechanical properties.

In Situ Observations Reveal the Five-fold Twin-Involved Growth of Gold Nanorods by Particle Attachment.

Crystallization plays a critical role in determining crystal size, purity and morphology. Therefore, uncovering the growth dynamics of nanoparticles (NPs) atomically is important for the controllable fabrication of nanocrystals with desired geometry and properties. Herein, we conducted in situ atomic-scale observations on the growth of Au nanorods (NRs) by particle attachment within an aberration-corrected transmission electron microscope (AC-TEM). The results show that the attachment of spherical colloidal Au NPs with a size of about 10 nm involves the formation and growth of neck-like (NL) structures, followed by five-fold twin intermediate states and total atomic rearrangement. The statistical analyses show that the length and diameter of Au NRs can be well regulated by the number of tip-to-tip Au NPs and the size of colloidal Au NPs, respectively. The results highlight five-fold twin-involved particle attachment in spherical Au NPs with a size of 3-14 nm, and provide insights into the fabrication of Au NRs using irradiation chemistry.

Lead single atoms anchored on reduced graphene oxide as multifunctional additive for lead–carbon battery

The application of lead–carbon batteries (LCBs) in hybrid electric vehicles and large-scale energy storage was limited by gradual sulfation and parasitic hydrogen evolution reaction (HER) of negative plates. Here, Pb single atoms anchored on reduced graphene oxide (PbSAs@rGO) were prepared through electrostatic adsorption and thermal reduction method, and confirmed by two aberration-corrected transmission electron microscopy (TEM and STEM) and synchrotron-based X-ray absorption fine structure spectroscopy (XAFS). By anchoring PbSAs on rGO surfaces where HER is prone to occur, the HER rate was greatly reduced. Moreover, PbSAs could serve as seeds to induce three-dimensional growth of Pb branches, which endows the NAM containing PbSAs@rGO additives with a specific surface areas (SSA) about 2.3 times than that of control one. The increased SSA can help to delay the sulfation of negative plate. Meanwhile, PbSAs can help enhance the affinity of rGO towards negative active material (NAM), which enable electrochemical reduction reaction proceeds at a higher rate. Thanks to the coordination of various functions from multifunctional additives, service life of LCBs under high-rate partial-state-of-charge (HRPSoC) have been extend from 3529 to 16,097 cycles, and from 4692 to 22,606 cycles, in 50% state of charge (SoC) and 75% SoC, respectively.

Single-Atom Sn-Loaded Exfoliated Layered Titanate Revealing Enhanced Photocatalytic Activity in Hydrogen Generation.

Green H2 generation through layered materials plays a significant role among a wide variety of materials owing to their high theoretical surface area and distinctive features in (photo)catalysis. Layered titanates (LTs) are a class of these materials, but they suffer from large bandgaps and a layers' stacked form. We first address the successful exfoliation of bulk LT to exfoliated few-layer sheets via long-term dilute HCl treatment at room temperature without any organic exfoliating agents. Then, we demonstrate a substantial photocatalytic activity enhancement through the loading of Sn single atoms on exfoliated LTs (K0.8Ti1.73Li0.27O4). Comprehensive analysis, including time-resolved photoluminescence spectroscopy, revealed the modification of electronic and physical properties of the exfoliated layered titanate for better solar photocatalysis. Upon treating the exfoliated titanate in SnCl2 solution, a Sn single atom was successfully loaded on the exfoliated titanate, which was characterized by spectroscopic and microscopic techniques, including aberration-corrected transmission electron microscopy. The exfoliated titanate with an optimal Sn loading exhibited a good photocatalytic H2 evolution from water containing methanol and from ammonia borane (AB) dehydrogenation, which was not only enhanced from the pristine LT, but higher than conventional TiO2-based photocatalysts like Au-loaded P25.

Directional Migration and Rapid Coalescence of Au Nanoparticles on Anisotropic ReS2.

Interfacial atomic configuration and its evolution play critical roles in the structural stability and functionality of mixed zero-dimensional (0D) metal nanoparticles (NPs) and two-dimensional (2D) semiconductors. In situ observation of the interface evolution at atomic resolution is a vital method. Herein, the directional migration and structural evolution of Au NPs on anisotropic ReS2 were investigated in situ by aberration-corrected transmission electron microscopy. Statistically, the migration of Au NPs with diameters below 3 nm on ReS2 takes priority with greater probability along the b-axis direction. Density functional theory calculations suggest that the lower diffusion energy barrier enables the directional migration. The coalescence kinetics of Au NPs is quantitatively described by the relation of neck radius (r) and time (t), expressed as . Our work provides an atomic-resolved dynamic analysis method to study the interfacial structural evolution of metal/2D materials, which is essential to the study of the stability of nanodevices based on mixed-dimensional nanomaterials.