Aberration-corrected Transmission Electron Microscopy Research Articles

Facile synthesis of Zn0.5Cd0.5S nanosheets with tunable S vacancies for highly efficient photocatalytic hydrogen evolution.

In order to effectively improve the separation efficiency of photogenerated charge carriers and thus the photocatalytic activity, in this work, porous Zn0.5Cd0.5S nanosheets with a controlled amount of S vacancies were prepared by a multistep chemical transformation strategy using the inorganic-organic hybrid ZnS-ethylenediamine (denoted as ZnS(en)0.5) as a hard template. The amount of S vacancies and the morphology of the Zn0.5Cd0.5S nanostructures were tailored by adjusting the hydrolysis time. Furthermore, we report the observation of S vacancies in porous Zn0.5Cd0.5S nanosheets at the atomic level using spherical aberration-corrected (Cs-aberrated) transmission electron microscopy (Cs-corrected-TEM). The results revealed that Zn0.5Cd0.5S nanosheets with S vacancies absorb more visible light and generate more electron-hole carriers due to their porous nanosheet structure. At the same time, sulfur vacancies are introduced into the Zn0.5Cd0.5S nanosheets to capture the electrons generated by the light and further extend the lifetime of the carriers. As expected, the photocatalytic activity of Zn0.5Cd0.5S nanosheets prepared by 4 h hydrolysis is 20.5 times higher than that of Zn0.5Cd0.5S(en)x intermediates. Moreover, Zn0.5Cd0.5S-4h showed excellent cycling stability. This work provides a new strategy for the optimization of Zn0.5Cd0.5S photocatalysts to improve photocatalytic hydrogen evolution.

Characterization of Aberration-Corrected Lorentz TEM Applying a Magnetic Field with Objective Lens

Characterization of Aberration-Corrected Lorentz TEM Applying a Magnetic Field with Objective Lens

Zernike Phase Plates for aberration-corrected TEM in Material Science

Zernike Phase Plates for aberration-corrected TEM in Material Science

Enhanced catalytic oxidation of benzene though the synergistic Pt-Ni bimetallic single-atom catalyst

Excellent catalysts for the catalytic oxidation of benzene (C6H6) require active sites with robust oxidation capabilities. Heteronuclear dual-single atom catalysts can exhibit enhanced catalytic activity through synergistic interactions between the dual single atoms (SAs). Herein, we successfully engineered a bimetallic single-atom catalyst, Pt1-Ni1/TiO2-NW, which demonstrates exceptional performance in C6H6 oxidation. Various technologies, including X-ray absorption fine structure and Z-type spherical aberration-corrected transmission electron microscopy, were used to identify the bimetallic single atoms within the catalyst. The catalytic oxidation of C6H6 by Pt1-Ni1/TiO2-NW was comprehensively investigated. Finally, in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) were employed to reveal the underlying mechanism for the synergetic effect of the bimetallic single atoms. The results indicate that the introduction of Ni SA favors the formation of Pt SA. The T90% of Pt1-Ni1/TiO2-NW reached 185 °C, a remarkable 40 °C lower than that of the single-atom catalyst Pt1/TiO2-NW. More importantly, the active center of Pt-O-Ni, formed by the collaboration of Pt SA and Ni SA with bridging oxygen, plays a crucial role in reducing the energy barrier during the conversion of C6H6 to phenol and further to benzoquinones. This research provides a valuable methodology for constructing heteronuclear bimetallic single-atom catalysts tailed specifically for C6H6 oxidation.

Cu@Co with Dilatation Strain for High-Performance Electrocatalytic Reduction of Low-Concentration Nitric Oxide.

Electrocatalytic reduction of nitric oxide (NO) to ammonia (NH3 ) is a clean and sustainable strategy to simultaneously remove NO and synthesize NH3 . However, the conversion of low concentration NO to NH3 is still a huge challenge. In this work, the dilatation strain between Cu and Co interface over Cu@Co catalyst is built up and investigated for electroreduction of low concentration NO (volume ratio of 1%) to NH3 . The catalyst shows a high NH3 yield of 627.20µg h-1 cm-2 and a Faradaic efficiency of 76.54%. Through the combination of spherical aberration-corrected transmission electron microscopy and geometric phase analyses, it shows that Co atoms occupy Cu lattice sites to form dilatation strain in the xy direction within Co region. Further density functional theory calculations and NO temperature-programmed desorption (NO-TPD) results show that the surface dilatation strain on Cu@Co is helpful to enhance the NO adsorption and reduce energy barrier of the rate-determining step (*NO to *NOH), thereby accelerating the catalytic reaction. To simultaneously realize NO exhaust gas removal, NH3 green synthesis, and electricity output, a Zn-NO battery with Cu@Co cathode is assembled with a power density of 3.08mW cm-2 and an NH3 yield of 273.37µg h-1 cm-2 .

Improving pitting resistance of Mo-containing stainless steels via chloride-assisted stabilization of the passive film

Molybdenum is well known as a beneficial alloying element which entitles stainless steels an enhanced resistance against chloride attack. It is generally accepted that Mo modifies passive film to be more resistant to chloride attack. Here, by means of aberration-corrected transmission electron microscopy, we show that it is the chloride ions that stimulate Molybdenum accumulating in passive films and meanwhile induce film thickening, which are responsible for the enhancement of corrosion resistance. By passivation aging in chloride media, we obtain a great enhancement of the pitting resistance. Our results show the broad prospects for useful practical applications in anti-corrosion interventions.

Multiscale Probing and Redesign of the Solid-State Synthesis Toward Defect-Free Ni-Rich Layered Cathodes

Nickel-rich lithium layered oxides (LiNixCoyMnzO2, NCM, x+y+z=1, x≥0.6)) have received tremendous attention as the most promising cathode materials for the practical development of high-energy lithium-ion batteries. However, they commonly suffer from rapid capacity decay along with structural and morphological degradation. Previous studies have unraveled that the general failure mechanism involves the mechanical deterioration of electrode particles, originating from micro-cracking in particles due to the build-up of significant anisotropic strains during phase transition and the chemical parasitic reactions with electrolytes through the crevice created. Such chemo-mechanical failures are triggered and aggravated by various structural defects, including internal void spaces, surface reconstruction layers, and intragranular nanopores, typical features of the conventionally synthesized nickel-rich layered oxide materials. It remains elusive how these defects are formed regardless of the use of single-crystalline or polycrystalline particles. A fundamental understanding of the general defect formations is thus indispensable to clarify how the synthesis process induces the formation of intrinsic defects from the precursor to the final product stage and how these defects affect the electrochemical degradation at the primary- and secondary-particle levels. Critical questions that require in-depth study include how the spatially inhomogeneous solid-state reaction begins at the interface of reacting precursors, propagates during the synthesis, and triggers the generation of defects. In this presentation, I will show the hidden synthetic mechanism of nickel-rich layered oxide materials using a combination of high-end and multi-length-scale analysis methods, including aberration-corrected TEM, in situ heating TEM with gas control, and in situ XRD. The kinetic interplay in synthesis of nickel-rich lithium layered oxide and its implications will be discussed in detail. Furthermore, the microstructural pore defects of NCN9235 during the heating process were quantitatively characterized. Based on our mechanistic understanding, we propose a redesign of solid-state synthesis pathway to achieve structurally integrated nickel-rich layered oxide cathodes.

Quantitative study on the microstructural evolution and dimensional stability mechanism of 2024 Al alloy during long-term thermal cycling

During the start-stop process of high-precision instruments in service, the critical materials of instruments undergo thermal cycling, resulting in changes in microstructure and dimension. In this paper, the evolution and coupling effects of dislocations and precipitates within 2024 Al alloy during 500 cycles were investigated, and their influence on the dimensional change was quantitatively characterized and decoupling analyzed. Transmission Electron Microscopy (TEM)/aberration-corrected scanning TEM (CS-TEM), X-ray diffraction (XRD), and Three-Dimensional Atom Probe Tomography (3D-APT) were used for microstructural evolution analysis and quantitative statistics. The dislocation density increased from 3.32 × 1014 m−2 to 5.75 × 1014 m−2 after 500 cycles, which accelerated elemental diffusion and provided nucleation sites of precipitates, contributing to an increase in the number density of the S'/S phase from 1.04 × 1024 m−3 to 1.41 × 1024 m−3. Based on the quantitative statistics of precipitate types and corresponding volume fractions, the dimensional change induced by precipitate evolution was −1.25 × 10−4. The dimensional change caused by the free volume introduced by dislocation density was 3.32 × 10−6. Comparing these values with the experimental value of −1.94 × 10−4, it is clear that the precipitate evolution is the main factor that triggers the dimensional change.

Surface-Immobilized ZnNx Sites as High-Performance Catalysts for Continuous Flow Knoevenagel Condensation in Water.

By immobilizing the metal complex on the substrate surface, our previous results have demonstrated that heterogeneous catalysts with well-dispersed active MNC (metal-nitrogen-carbon) sites can be prepared in a rational and efficient manner. In this study, we employed agarose aerogel (AA) as the substrate to illustrate a straightforward strategy for immobilizing ZnNx sites on the surface. Under relatively low temperatures, the amine group of the ligand condenses with the surface carbonyl group generated in situ, resulting in the surface immobilized Zn sites. This can be supported by the IR, PXRD, and XPS data. Comprehensive characterization methods, including synchrotron powder XRD and spherical aberration-corrected TEM, confirmed the absence of ZnNx site aggregation in the surface immobilization process, even with a high Zn content (up to 8 wt %). The immobilized ZnNx sites exhibited high catalytic performance in Knoevenagel condensation, and α,β-unsaturated compounds were obtained with high yield in both batch and continuous flow reactions. AA-ZnNx-200 showed the best catalytic activity, which was processed under 200 °C with a Zn content of 4.62 wt %. The immobilized ZnNx sites activated both the aldehyde and nitrile substrates, which were quantitatively converted into the corresponding α,β-unsaturated compounds, with water as the solvent at room temperature. In continuous flow reaction conditions, a conversion rate up to 99% can be achieved with malononitrile. This heterogeneous catalyst can be facilely produced with quantitative yield in a large scale from cheap starting material under mild conditions. No catalyst deactivation was observed after seven batch reaction cycles or 80 h of continuous flow reaction, indicating its high robustness under catalytic reaction conditions. This catalyst enables a separation-free, energy-saving, and environment-friendly production process, offering a practical way for the industrial production.

New understanding on the critical factors determining stability of passive film on Fe-Cr alloy based on aberration-corrected TEM study

Purpose In recent years, using aberration-corrected transmission electron microscopy, the authors have achieved precisely detecting the structural evolution of passive film as well as its interface zone at atomic scale. The purpose of this paper aims to make a brief review to show the authors’ new understanding and perspective on the issue of critical factors determining stability of passive film of Fe-Cr alloy. Design/methodology/approach The introduction of single crystal enabled the authors to obtain a distinct metal/passive film interface and better characterize the structure of the interface region. The authors use aberration-corrected TEM to conduct cross-sectional observation and directly capture the details across the entire film at a high spatial and energy resolution. Findings Apart from the passive film itself, the interface zone, including metal/film (Me/F) interface and the adjacent metal side, is also the site which is attacked. Accordingly, the nature of the interface zone, such as microstructure, composition and atomic configuration, is one of the critical factors determining the stability of passive film. Originality/value Deciphering the critical factors determining the stability of passive film is of great significance and has been a fundamental issue in corrosion science. Great attention has been paid to the nature of the passive film itself. In contrast, the possible role of the interface between the passive film and the metal is rarely taken into account. Based on the advanced analytical tool with high spatial resolution, the authors have specified the significant role of interface structures on the macro-scale stability of passive film.

Microstructure evolution of a Cr-Cr/Mo coated Zr alloys in inert gas and steam environment at high temperature

The Cr/Mo multilayer coating was applied as a diffusion barrier for Cr-coated Zr alloys. The barrier effect and eutectic resistance of the Cr/Mo multilayer were evaluated by annealing the samples up to 1400 °C in an inert gas and steam environment. The microstructure at the interface between the Cr/Mo multilayer and Zr substrate was analyzed by spherical aberration corrected transmission electron microscope (AC-TEM). After high temperature annealing, an interlayer composed of Cr-Mo-Zr mixed phases formed between the coating and Zr substrate. The atomic-resolution EDS revealed that the proportion of Cr, Mo, and Zr in the interlayer was 4:2:3. The growth of the Cr-Mo-Zr interlayer obeyed a parabolic law. The consumption rate of the outer Cr coating was compared to that of Cr coated Zr alloy samples without a Cr/Mo barrier layer. Results show that the Cr/Mo interlayer successfully reduced the Cr-Zr inter-diffusion and eutectic reaction.

Revisiting a Cu-rich layer on the aluminum surface after twin-jet electropolishing

Twin-jet electropolishing (TJE) is a well-known method to prepare Cu-containing Al alloys for transmission electron microscopy (TEM) observation. Previous studies have reported a Cu-rich layer usually formed between Al matrix and outermost alumina layer at the electropolished Al surface. However, characteristics and formation mechanisms of the Cu-rich layer remain largely unexplored. Herein, configurations, formation process and property of the Cu-rich layer formed during TJE of Al alloys are revealed detailly employing aberration-corrected scanning TEM (STEM), STEM image simulations and first-principles calculations. The results reveal a new orientation relationship between the Cu-rich layer (θ’-Al2Cu) and Al matrix, which produces a low interfacial Al strain field. Formations of ∼2-nm-thick θ’ layer and its beneath ∼6-nm-thick Cu diffusion zone at the electropolished Cu-containing Al surface are mainly associated with traces of Cu in the electrolyte and anodization. Selective oxidation of elements, Cu-emitting alumina layer and spontaneous solute Cu segregation at the Al surface are also responsible for formations of the θ’ layer and Cu diffusion zone. Further study reveals that the θ’ layer behaves a strong self-healing ability after damaged by high-energy electron beam. The obtained results provide a potential insight into the surface modification of metals and alloys using electrochemical method.

Unveiling interface structure and polarity of wurtzite ZnO film epitaxially grown on a-plane sapphire substrate

Atomic-scale structure properties of the epitaxial growth of the wurtzite ZnO film prepared on an a-plane sapphire (α-Al2O3) substrate have been investigated by using aberration-corrected transmission electron microscopy. The crystallographic orientation relationship of (0001)[1¯1¯20]ZnO//(112¯0)[0001]α-Al2O3 has been determined between the ZnO film and the α-Al2O3 substrate. Two types of oxygen-terminated a-plane α-Al2O3 substrate surfaces have been characterized, which leads to the formation of different heterointerface structures and ZnO domains with opposite lattice polarity. The coalescence of opposite polarity domains results in the appearance of inversion domain boundaries (IDBs) on prismatic planes, and kinks occur on basal planes during the propagation of IDBs within the film. Additionally, the structure of stacking mismatch boundaries in the film with threefold coordinated Zn and O atoms has been resolved. We believe that these findings can be helpful to advance the understanding of the complex propagation of planar defects (e.g., IDBs and stacking faults) in wurtzite films and the interface structure and polarity of wurtzite films on the a-plane sapphire substrate.

Ni‐Pt Bimetallic Alloy Nanoparticles Dispersed Uniformly on Carbon Nanotubes for Efficient Electrooxidation Methanol

AbstractIn this paper, Ni−Pt bimetallic alloy nanoparticles were loaded on carbon nanotubes to construct Ni−Pt nanoparticles/carbon nanotubes (Ni−Pt NPs/CNTs) composites as excellent catalytic materials for methanol electrooxidation reaction (MOR). X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), and special aberration corrected transmission electron microscope (STEM) were employed to investigate the morphology of the material. It was confirmed that the Ni−Pt alloy nanoparticles dispersed uniformly on the surface of carbon nanotubes. The activity and stability of Ni−Pt NPs/CNTs composites were measured by chronoamperometry (CA), linear sweep voltammetry (LSV) and cyclic voltammetry (CV). The catalytic performance was explored by adjusting the ratio of Ni to Pt. The Ni1Pt2 NPs/CNTs composite showed excellent performance for MOR. Its mass activity for MOR was 1255 mA ⋅ mg−1Pt, which was 2.76, 2.56 times as that of commercial Pt/C, Pt black catalyst, respectively. Moreover, the resistance to CO toxicity of Ni1Pt2 NPs/CNTs composite was better than commercial Pt/C and Pt black catalyst.

Superconductivity of Li doped BSCCO mesoscopic fiber

Mesoscopic Li doped BSCCO fibres are synthesized by the electrospinning technology and the sequent sintering treatment. With the assistance of high resolution energy-dispersive x-ray spectroscopy detector in the Aberration-corrected transmission electron microscopy, we discovered hidden CuO grains and separated Bi-2212 phases, which is proved by the existence of fishtail effect in the magnetization loops. The electric measurement is fulfilled via four probe method with the help of focus ion beam operation. A non-trivial resistance behaviour appears, which can be attributed to its polycrystalline and superconducting phase separation features.

Atomic-scale imaging of electron sensitive zeolites with aberration corrected transmission electron microscopy

The spatial resolution of transmission electron microscopes (TEMs) and scanning transmission electron microscopes (STEMs) has been drastically improved by introducing aberration correction. However, observable range in electron sensitive zeolites are still limited due to electron irradiation damages. Nevertheless, atomic resolution imaging of some zeolites is currently being realized by various developments in electron microscopic hardware, such as high sensitivity cameras. On the other hand, surveying the status of TEM and STEM imaging is very important for further progress in the structural analysis of zeolites. Here, we demonstrate and compare the high-resolution imaging of zeolites with several kinds of imaging modes.

Defects engineering of Au@MoS2 nanostructures for conventional and plasmon-enhanced hydrogen evolution reaction

The influence of thermal treatment under reducing conditions on the structural and hydrogen evolution reaction (HER) properties of Au@MoS2 structures is reported in this work. After a thermal treatment at 800 °C under H2 atmosphere, the Au@MoS2 nanostructures exhibit remarkable performance with an overpotential of 203 mV vs reversible hydrogen electrode (RHE) at 10 mA/cm2 and a Tafel slope of 55 mV/dec which is similar to the value reported for edges sites in MoS2. The samples were investigated by combining ex-situ and in-situ aberration-corrected transmission electron microscopy (TEM) experiments under controlled atmosphere, Raman and XPS spectroscopies. (S) TEM characterization highlights the formation of the core-shell system as well as the decrease of the number of shell layers up to incomplete layers induced by the thermal treatments. The plasmonic-assisted HER performances of these nanostructures under LED illumination are also explored and an enhancement by about 10 % of the current density, depending on the wavelength used, is also reported. These results open new avenues for the design of core shell nanostructures based on transition metal dichalcogenides for the hydrogen evolution reaction.

Atomic insight into the BEOL thermal budget on phase transition of phase change memory cells

Research works on phase change random access memory (PCRAM) based on Ge–Sb–Te (GST) phase change materials have achieved exciting progress, but the industrialization of PCRAM still faces big challenges, including unsatisfied endurance property or unexpected cell structure failure during fabrication. Here, we investigate the impact of the thermal budget in back-end-of-line (BEOL) process on the microstructure evolution of carbon doped GST (CGST) cells. We demonstrate that the as-deposited amorphous CGST in the confined memory cell will transform to face centered-cubic (FCC) phase with uniform grain size during high temperature up to 400 °C in the BEOL process. However, if there is much more unexpected thermal budget during the BEOL process, the FCC-CGST grains will further grow and transform to highly ⟨0001⟩ oriented single crystalline hexagonal (HEX) GST, together with the formation of voids, leading to the structure failure of the storage cells. By virtue of the advanced spherical aberration corrected transmission electron microscopy (Cs-TEM), we find that there are randomly stacked seven-layered and nine-layered atomic arrangements in single crystalline HEX-GST, corresponding to the chemical stoichiometry of Ge2Sb2Te5 and Ge1Sb2Te4, respectively. Interestingly, twin crystal with the coexistence of vacancy-ordered FCC-GST and HEX-GST on the different twin boundary is observed, indicating that the twin crystals play a critical role in the coalescence and the growth of FCC-GST. This work not only sheds light on the structure failure mechanism of GST cell but also provided additional insight into the formation of HEX-phase in a confined GST memory cell.

Study on the preparation of ceramic membrane support and its Fe migration rule by high‐aluminum fly ash as raw material

AbstractIn order to reduce the cost of ceramic membrane support, ceramic membrane support was prepared using high‐aluminum fly ash as raw material, and its Fe migration rules during the preparation process are studied. The effects of sintering temperature, pore forming agent content, and binder content on the properties of support, such as porosity, pore size, bending strength and water flux have been investigated. The optimum contents of high‐aluminum fly ash, pore forming agent and binder in the ceramic membrane support are 95%, 4%, and 1% respectively, and its sintering temperature is 1300°C. The porosity, bending strength, pore size, and water flux of the prepared support are 37%, 22 MPa, 665 nm, and 2800 L/h·m2·MPa, respectively. X‐ray powder diffractometer, X‐ray fluorescence spectrometer, X‐ray photoelectron spectrometer, inductively coupled plasma spectrometer, transmission electron microscope, spherical aberration corrected transmission electron microscopy, and laser Raman spectroscopy were used to characterize the support and Fe existing morphology in it. The results show that the main phases of sintered support are mullite, corundum, and silica. Massive mullite is produced when the sintering temperature reaches 1200°C. The content of mullite increases with increasing sintering temperature. About 7.7 % content of total Fe in the support exists in the form of Fe2O3. About 92.3% content of total Fe is dissolved into mullite. Fe is evenly distributed in mullite, and it is enriched at the grain boundary by element segregation. Fe in mullite is difficult to dissolve under strong acid conditions, so its stability is very strong.

Growth Anisotropy and Morphology Evolution of Line Defects in Monolayer MoS2 : Atomic-Level Observation, Large-Scale Statistics, and Mechanism Understanding.

Understanding the growth behavior and morphology evolution of defects in 2D transition metal dichalcogenides is significant for the performance tuning of nanoelectronic devices. Here, the low-voltage aberration-corrected transmission electron microscopy with an in situ heating holder and a fast frame rate camera to investigate the sulfur vacancy lines in monolayer MoS2 is applied. Vacancy concentration-dependent growth anisotropy is discovered, displaying first lengthening and then broadening of line defects as the vacancy densifies. With the temperature increase from 20 °C to 800 °C, the defect morphology evolves from a dense triangular network to an ultralong linear structure due to the temperature-sensitive vacancy migration process. Atomistic dynamics of line defect reconstruction on the millisecond time scale are also captured. Density functional theory calculations, Monte Carlo simulation, and configurational force analysis are implemented to understand the growth and reconstruction mechanisms at relevant time and length scales. Throughout the work, high-resolution imaging is closely combined with quantitative analysis of images involving thousands of atoms so that the atomic-level structure and the large-area statistical rules are obtained simultaneously. The work provides new ideas for balancing the accuracy and universality of discoveries in the TEM study and will be helpful to the controlled sculpture of nanomaterials.