High Angle Annular Dark Field Research Articles

Copper-Bearing Magnetite and Delafossite in Copper Smelter Slags

The cooling paths and kinetics in the system Cu-Fe-O are investigated by the empirical micro- and nanoscale analysis of slags from the flash furnace smelter at Olympic Dam, South Australia. We aim to constrain the exsolution mechanism of delafossite (Cu1+Fe3+O2) from a spinel solid solution (magnetite, Fe3O4) and understand why cuprospinel (CuFe2O4) is never observed, even though, as a species isostructural with magnetite, it might be expected to form. Flash furnace slags produced in the direct-to-blister copper smelter at Olympic Dam contain four Cu-bearing phases: Cu-bearing magnetite, delafossite, metallic copper, and cuprite. Delafossite coexists with magnetite as rims and lamellar exsolutions, as well as bladed aggregates, associated with cuprite within Si-rich glass. The empirical compositions of magnetite and rim delafossite are (Fe2+6.89Cu2+0.86Co0.13Mg0.15Si0.02)8.05 (Fe3+15.52Al0.41Ti0.01Cr0.01)15.95O32, and (Cu1+0.993Co0.002Mg0.002)0.997(Fe3+0.957Al0.027Ti0.005Si0.004)0.993O2, respectively. The measured Cu content of magnetite represents a combination of a solid solution (~6 mol.% cuprospinel endmember) and exsolved delafossite lamellae. Atomic-resolution high-angle annular dark field scanning transmission electron microscope (HAADF STEM) imaging shows epitaxial relationships between delafossite lamellae and host magnetite. Defects promoting the formation of copper nanoparticles towards the lamellae margins suggest rapid kinetics. Dynamic crystallization under locally induced stress in a supercooled system (glass) is recognized from misorientation lamellae in delafossite formed outside magnetite grains. The observations are concordant with crystallization during the cooling of molten slag from 1300 °C to <1080 °C. Melt separation through an immiscibility gap below the solvus in the system Cu-Fe-O is invoked to form the two distinct delafossite associations: (i) melt-1 from which magnetite + delafossite form; and (ii) melt-2 from which delafossite + cuprite form. Such a path also corroborates the published data explaining the lack of cuprospinel as a discrete phase in the slag. Delafossite rims form on magnetite at a peritectic temperature of ~1150 °C via a reaction between the magnetite and copper incorporated in the oxide/Si-rich melt. The confirmation of such a reaction is supported by the observed misfit orientation (~10°) between the rim delafossite and magnetite. HAADF STEM imaging represents a hitherto underutilized tool for understanding pyrometallurgical processes, and offers a direct visualization of phase relationships at the smallest scale that can complement both experimental approaches and theoretical studies based on thermodynamic modelling.

Modulating the Coordination Environment of Carbon-Dot-Supported Fe Single-Atom Nanozymes for Enhanced Tumor Therapy.

Herein, carbon dot (CD)-supported Fe single-atom nanozymes with high content of pyrrolic N and ultrasmall size (ph-CDs-Fe SAzyme) are fabricated by a phenanthroline-mediated ligand-assisted strategy. Compared with phenanthroline-free nanozymes (CDs-Fe SAzyme), ph-CDs-Fe SAzyme exhibit higher peroxidase (POD)-like activity due to their structure similar to that of ferriporphyrin in natural POD. Aberration-corrected high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and X-ray absorption fine structure spectroscopy (XAFS) analyses show that metal Fe is dispersed in ph-CDs-Fe SAzyme as single atoms. Steady-state kinetic studies show that the maximum velocity (Vmax ) and turnover number (kcat ) of H2 O2 homolyticcleavage catalyzed by ph-CDs-Fe SAzyme are 3.0 and 6.2 more than those of the reaction catalyzed by CDs-Fe SAzyme. Density functional theory (DFT) calculations show that the energy barrier of the reaction catalyzed by ph-CDs-Fe SAzyme is lower than that catalyzed by CDs-Fe SAzyme. Antitumor efficacy experiments show that ph-CDs-Fe SAzyme can efficiently inhibit the growth of tumor cells both in vitro and in vivo by synergistic chemodynamic and photothermal effects. Here a new paradigm is provided for the development of efficient antitumor therapeutic approaches based on SAzyme with POD-like activity.

Single-atom Pd loaded on nitrogen-doped carbon as a bifunctional catalyst for the electrochemical degradation of 2,4-dichlorophenol

A nitrogen-doped carbon-anchored single atom Pd (SA-Pd/NC) electrocatalyst was prepared by pyrolysis of Pd-doped zeolite imidazolite framework (ZIF) precursors. The SA-Pd/NC catalyst was characterized by high-resolution transmission electron microscopy, aberration-corrected high-angle annular dark field scanning transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectrometry and applied in the degradation of 2,4-dichlorophenol (2,4-DCP). We demonstrate that the SA-Pd/NC catalyst has dual functions, with both electrocatalytic hydrodechlorination (ECH) activity and in situ heterogeneous electro-Fenton (hetero-EF) activity even at low current density. The ECH process was the main pathway of 2,4-DCP degradation without oxygen aeration. Under aerobic conditions, hetero-EF coupling with ECH occurred simultaneously on the SA-Pd/NC cathode, i.e., the dechlorination product phenol was oxidatively degraded with the reactive oxygen species produced on the electrode. The degradation rate of 2,4-DCP and TOC removal rate reached 95.1% and 37.6%, respectively, with a current density of 2.5 mA cm−2 and an initial pH of 3.0. This work provides the design of bifunctional single-atom catalysts for 2,4-DCP degradation, including dechlorination and mineralization.

Influence of Support Material on the Structural Evolution of Copper during Electrochemical CO2 Reduction

The electrochemical CO2 reduction reaction (CO2RR) provides the combined benefit of reducing anthropogenic CO2 emissions while supplying a wide variety of valuable chemical feedstock chemicals.[1] While many transition metals are CO2RR active catalysts, only copper can form products requiring more than two electrons in the electrochemical conversion of CO2. This includes a multitude of high-value-added products such as ethylene, ethanol, or propanol.[1-3] The selectivity of the CO2RR is strongly influenced by the structure and morphology of the copper catalysts. Consequently, structural properties such as copper nanoparticle size, display an influence on CO2RR product selectivity.[4] This creates a substantial problem as copper is highly susceptible to reorganization during the electrochemical CO2RR, which inhibits the retention of apparently favorable surface structures during the CO2RR.[5] As a consequence, structure-selectivity relations can neither be reliably described nor completely understood. This problem is exacerbated by a lack of understanding of the underlying reasons that drive reorganization and therefore degradation of the catalyst. At reductive potentials, as used in the electrochemical CO2RR, coalescence and subsequent agglomeration are assumed to be the dominant degradation mechanism, while oxidative potentials generally trigger support corrosion and dissolution. Strategies for stabilization to retain activity and selectivity are therefore essential. Nevertheless their importance in the electrochemical CO2RR, stabilization methods are largely missing. For other reactions, such as the oxygen reduction reaction, various studies showed an increase in overall stability by containing the catalysts in a confined space.[6-8] This work presents the stabilizing effect of three different carbon support materials with unique morphologies on copper nanoparticles (CuNPs). Through the use of a non-porous Vulcan, a Ketjenblack with a diverse pore size distribution and highly defined mesoporous graphitic spheres (MGS) with a unimodal pore size distribution, the influence on structural characteristics of the carbon material on the stabilization of the CuNPs can be presented. The representative copper catalysts were prepared by colloidal synthesis or incipient wetness impregnation and evaluated through micro-flow cell measurements with online gas chromatography (GC) analytics and pre-/post catalytic high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), visualizing changes in the catalyst structure and morphology after the reaction. We demonstrate the successful stabilization of CuNPs by pore confinement against particle coalescence and subsequent agglomeration for up to 20 h of electrochemical CO2RR conditions, with GC analysis providing great insight into the influence of particle size, morphology, and location of the CuNPs on CO2RR product selectivity. Intriguingly, a high share of CO2RR products was observed for stabilized < 4 nm CuNPs putting the established particle size effect for the CO2RR, where the hydrogen evolution reaction was predominantly observed on nanoparticles below 15 nm, into question.[4] These results present new ways of stabilizing CuNPs and highlight the need for post-catalytic evaluation of the catalysts' morphological state to precisely derive performance-structure indicators.Work accepted and soon to be published in ChemElectroChemdoi.org/10.1002/celc.202200924Literature:[1] S. Nitopi, E. Bertheussen, S. B. Scott, X. Liu, A. K. Engstfeld, S. Horch, B. Seger, I. E. L. Stephens, K. Chan, C. Hahn, J. K. Nørskov, T. F. Jaramollo, I. Chorkendorff, Chem Rev. 2019, 119, 7610–7672.[2] Y. Hori, Modern Aspects of Electrochemistry No. 42, Springer, 2008.[3] K. P. Kuhl, E. R. Cave, D. N. Abram, T. F. Jaramillo, Energy Environ. Sci. 2012, 5, 7050–7059.[4] R. Reske, H. Mistry, F. Behafarid, B. Roldan Cuenya, P. Strasser, J. Am. Chem. Soc. 2014, 136, 6978–6986.[5] W. T. Osowiecki, J. J. Nussbaum, G. A. Kamat, G. Katsoukis, M. Ledendecker, H. Frei, A. T. Bell, A. P. Alivisatos, ACS Appl. Energy Mater. 2019, 2, 7744–7749.[6] Y. Li, F. Cui, M. B. Ross, D. Kim, Y. Sun, P. Yang, Nano Lett. 2017, 1312–1317.[7] Y. T. Guntern, J. R. Pankhurst, J. Vavra, M. Mensi, V. Mantella, P. Schouwink, R. Buonsanti, Angew. Chem. 2019, 131, 12762–12769.[8] C. Galeano, J. C. Meier, V. Peinecke, H. Bongard, I. Katsounaros, A. A. Topalov, A. Lu, K. J. J. Mayrhofer, F. Schüth, J. Am. Chem. Soc. 2012, 134, 20457 – 20465. Figure 1

Highly compatible and reliable ZrN interfacial layer between TiN top electrode and antiferroelectric ZrO2 thin film to boost the electrocaloric behavior

A highly compatible and reliable ZrN interfacial layer with different cycles of atomic layer deposition was inserted between the TiN top electrode and antiferroelectric (AFE) ZrO2 thin film to achieve low oxygen vacancies and high crystallinity of the ZrO2 thin film, boosting the AFE and electrocaloric (EC) characteristics of TiN/ZrO2/TiN metal–insulator–metal (MIM) capacitors. An outstanding adiabatic temperature change (ΔT) of − 21 K was realized for devices with a ZrN interfacial layer of nine cycles, which can be ascribed to the reduction in redox between the TiN and ZrO2 for the suppression of interfacial dead layer during annealing as confirmed via high-angle annular dark field images and interfacial capacitance measurement. Hence, the reliability of ZrO2 MIM capacitors with a nine-cycle ZrN interfacial layer was examined with a negligible change in AFE and EC behaviors after a cycling endurance test of 106 cycles, exhibiting great potential for future applications in solid-state cooling.

Boron-Doped Nickel-Nitrogen-Carbon Single-Atom Catalyst for Boosting Electrochemical CO2 Reduction.

Tuning the coordination environment of the metal center in metal-nitrogen-carbon (M-N-C) single-atom catalysts via heteroatom-doping (oxygen, phosphorus, sulfur, etc.) is effective for promoting electrocatalytic CO2 reduction reaction (CO2 RR). However, few studies are investigated establishing efficient CO2 reduction by introducing boron (B) atoms to regulate the M-N-C structure. Herein, a B-C3 N4 self-sacrifice strategy is developed to synthesize B, N co-coordinated Ni single atom catalyst (Ni-BNC). X-ray absorption spectroscopy and high-angle annular dark field scanning transmission electron microscopy confirm the structure (Ni-N3 B/C). The Ni-BNC catalyst presents a maximum CO Faradaic efficiency (FECO ) of 98.8% and a large CO current density (jCO ) of -62.9 mA cm-2 at -0.75 and -1.05V versus reversible hydrogen electrode, respectively. Furthermore, FECO could be maintained above 95% in a wide range of potential windows from -0.65 to -1.05V. In situ experiments and density functional theory calculations demonstrate the Ni-BNC catalyst with B atoms coordinated to the central Ni atoms could significantly reduce the energy barrier for the conversion of *CO2 to *COOH, leading to excellent CO2 RR performance.

Grain structure and co-precipitation behavior of high-Zn containing Al–Zn–Mg–Cu aluminium alloys during deformation via high-temperature upsetting-extrusion

A study on the deformation behavior with increase in strain during upsetting-extrusion (UE) was studied (i.e., No-UE, Small-UE, and Large-UE strains) at 350 °C in Al-8.9Zn-2.2Mg-2.1Cu-0.14Zr-0.02Sc (wt%) alloys to evaluate the strengthening effects of grain size/texture and co-precipitation for different ageing (i.e., as-received, T4, and T6 aging) conditions. In as-received samples, electron back-scattered diffraction observations revealed that increasing UE strain enhances the formation of continuous and discontinuous dynamic recrystallization grains. This reduces the size difference between fine and coarse grains in bimodal structure and produces stronger copper/cubic texture. In small angle X-ray scattering (SAXS), a large UE strain brings about more fraction of Y-phase and GP zones. In T4 Large-UE samples, SAXS indicated higher size stability of disk-like Y-phase. High-angle annular dark field scanning transmission electron microscopy images revealed five-layered atomic arrangement of a unit cell of Y-phase, where the center layer was composed of Al and sandwiched layers, 2Cu/2Zn/2Cu and Al/ZnCu/ZnCu/Al. In T6 Large-UE samples, it was observed that the growth of Y-phase is accompanied by intrinsic atomic shift along the [101̅0]Y-phase direction. Furthermore, SAXS quantitatively showed size evolution of η'/η precipitates and formation of a higher aspect ratio of Y-phase. The collective effects of finer bimodal grain structure, stronger fiber texture, and co-precipitation of Y-phase and η'/η precipitates provide evidence higher ultimate tensile strength (∼766 ± 5 MPa) and superior strain (∼10.9 ± 0.4) of large-UE strain samples under T6 ageing.

InGaN/GaN superlattice underlayer for fabricating of red nanocolumn μ-LEDs with (10-11) plane InGaN/AlGaN MQWs

In this study, the growth behavior of Indium gallium nitride (InGaN)-based nanocolumn arrays was investigated, and red emission nanocolumn micro-light emitting diodes (μ-LEDs) were fabricated. The internal structure of the InGaN/GaN superlattice (SL) layer under the multiple-quantum-well (MQW) active layers was evaluated using scanning transmission electron microscopy (STEM) analysis. It was revealed that the InGaN crystal plane at the top of the nanocolumn changed from the c-plane, (1-102) plane, to the (10-11) plane as the number of SL pairs increased. A semipolar (10-11) plane was completely formed on top of the nanocolumn by growing InGaN/GaN SLs over 15–20 pairs, where the InGaN/GaN SL layers were uniformly piled up, maintaining the (10-11) plane. Therefore, when InGaN/AlGaN MQWs were grown on the (10-11) plane InGaN/GaN SL layer, the growth of the (10-11) plane semipolar InGaN active layers was observed in the high-angle annular dark field (HAADF)-STEM image. Moreover, the acute nanocolumn top of the (10-11) plane of the InGaN/GaN SL underlayer did not contribute to the formation of the c-plane InGaN core region. Red nanocolumn μ-LEDs with an φ12 μm emission window were fabricated using the (10-11) plane MQWs to obtain the external quantum efficiency of 1.01% at 51 A cm−2. The process of nanocolumn μ-LEDs suitable for the smaller emission windows was provided, where the flat p-GaN contact layer contributed to forming a fine emission window of φ5 μm.

Treatment of Multi-Walled Carbon Nanotubes with Dichromic Acid: Oxidation and Appearance of Intercalation.

This work is dedicated to the study of the treatment of multi-walled carbon nanotubes (MWCNTs) with dichromic acid. The dichromic acid was formed by dissolving different concentrations of CrO3 in water. The effect of the concentration of dichromic acid on the change in texture characteristics, elemental composition, defectiveness, graphitization degree, and surface chemistry of MWCNTs was investigated using various analytical techniques, such as transmission electron microscopy, energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). Testing of MWCNTs as electrodes for supercapacitors in 3.5 M H2SO4 solution was carried out using cyclic voltammetry. A decrease in the average diameter of CNTs after treatment was found. The EDX and XPS showed that the oxygen content on the surface of MWCNTs increased after treatment with dichromic acid. The formation of Cr2O3 after treatment with dichromic acid was detected by XPS. High angle annular dark field scanning transmission electron microscopy was used to confirm the intercalation of the chromium-containing compound between graphene layers of MWCNTs after treatment with dichromic acid. It was found that two different types of MWCNTs showed diverse behavior after treatment. The highest specific capacitance of the MWCNTs after treatment was 141 F g-1 (at 2 mV s-1) compared to 0.3 F g-1 for the untreated sample.

Gold nanoparticle encoded with marigold (Tagetes erecta L.) suppressed hyperglycemia -induced senescence in retinal pigment epithelium via suppression of lipid peroxidation

This paper presents a simple and environmentally friendly method for synthesizing Tagetes erecta L. gold nanoparticles (TE-GNPs) using an aqueous extract of Tagetes erecta L. (TE). The TE extract serves as a reducing and stabilizing agent, and its antioxidant activity is evaluated using 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assays. The TE extract exhibits significant DPPH and ABTS radical scavenging activities, indicating its strong antioxidative properties attributed to various antioxidant compounds. TE-GNPs are successfully synthesized by incubating the TE extract with a chloroauric acid solution, resulting in a color change from light yellow to ruby red. UV–Vis spectroscopy confirms the synthesis of TE-GNPs, evidenced by a characteristic absorption peak at approximately 524 nm, corresponding to the nanoparticles' surface plasmon resonance. Physicochemical characterization reveals that TE-GNPs possess nanoscale dimensions (28.9 ± 2.3 nm), stability (zeta potential of −31.5 ± 28), and a crystalline nature (validated via X-ray diffraction; XRD). Functional groups responsible for biosynthesis and stabilization are identified through Fourier transform infrared spectroscopy (FT-IR) analysis. high-resolution transmission electron microscopy (HR-TEM) images demonstrate the morphology, size, and dispersion of TE-GNPs, while selected area electron diffraction (SAED) patterns confirm their crystalline structures. Additionally, high-angle annular dark field (HAADF) imaging and energy-dispersive X-ray spectroscopy (EDX) spectroscopy verify the distribution and presence of gold in the TE-GNPs, respectively. Cytotoxicity assays confirm the biocompatibility of TE-GNPs. Furthermore, their potential in mitigating high glucose-induced cell death and oxidative stress in retinal pigment epithelial (RPE) cells is evaluated. Treatment with TE-GNPs restores the proliferation rate of RPE cells and reduces the proportion of apoptotic cells under high glucose conditions. TE-GNPs also decrease the high glucose-induced production of intracellular and mitochondrial reactive oxygen species. Markers of cellular senescence, including SA-β-galactosidase activity and lysosomal dysfunction, are attenuated by the TE-GNPs. Moreover, the TE-GNPs effectively reduce lipid accumulation and peroxidation in RPE cells exposed to high levels of glucose. These findings highlight the successful green synthesis of TE-GNPs using an aqueous extract of TE and underscore their desirable properties and anti-senescence effects.

Origin of spin glass magnetic behavior and phase stability of flux-grown RE(Al, Cr, Fe)B4 (RE = Ho and Er) single crystals

The YCrB4 type (α-phase, orthorhombic with space group Pbam) α-HoAlB4 and α-ErAlB4 single crystals which were self-flux grown exhibit the spin glass magnetic behavior, which is anomalous compared to the other reported rare earth system phases of α-REAlB4. Local atomic arrangements with the atomic-resolution for α-HoAlB4 and α-ErAlB4 compounds have been investigated by spherical aberration (Cs)-corrected scanning transmission electron microscopy (STEM) with high-angle annular detector dark-field (HAADF) and annular bright-field (ABF), and STEM-energy-dispersive X-ray spectroscopy (EDS) techniques to elucidate the origin of the exotic magnetic behavior. Observed HAADF- and ABF-STEM images and STEM-EDS chemical maps taken with the incident beam parallel to the [001] direction clearly indicate the existence of substitutions for Al atom sites. The phase stability of RAlB4 (R = Ho ∼ Lu) compounds was discussed from the viewpoint of crystallographic features with lattice parameters and compositions. Based on the presented results, it could be concluded that the origin of the spin glass behavior for self-flux grown α-HoAlB4 and α-ErAlB4 single crystals is the unexpected substitution of Cr/Fe atoms for Al ones. Simultaneously, the substitution by Cr/Fe atoms for Al atoms is indicated to play a significant role to stabilize the YCrB4-type α-HoAlB4 and α-ErAlB4 compounds.

Interactions between Ca2Gd8(SiO4)6O2 apatite and calcium-magnesium-aluminosilicate (CMAS) at elevated temperatures

High temperature corrosion behavior of Ca2Gd8(SiO4)6O2 (CGdS) apatite has been investigated in the presence of molten calcium-magnesium-aluminosilicate (CMAS) glass having the composition 21.9 CaO - 4.3 MgO - 5.4 Al2O3 - 63.0 SiO2 - 4.3 Na2O - 0.8K2O - 0.1 Fe2O3 (weight %). CGdS apatite powder was prepared by solid state synthesis from constituent oxides. Pellets of CGdS apatite + CMAS mixed powder and CGdS-CMAS diffusion couples were annealed at 1200, 1300, 1400, and 1500 °C for 1 and 20 h in ambient atmosphere. Development of phases in heat treated specimens was characterized using various analytical techniques as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high angle annular dark field imaging, selected area electron diffraction and energy dispersive X-ray spectroscopy. In both pellets and diffusion couples, monoclinic cyclosilicate Ca3Gd2(Si3O9)2 formed from reaction of apatite with CaO in the CMAS melt only in samples heat treated at 1200 °C for 1 and 20 h or at 1300 °C for 1 h. Triclinic CaSiO3 and monoclinic diopside MgCaSi2O6 were also observed in samples annealed at 1200 and 1300 °C. At 1400 and 1500 °C, because of its low viscosity, CMAS infiltrated along the pores and grain boundaries of the apatite substrates in diffusion couples. Phase compositions predicted from thermochemical computation were in good agreement with those observed experimentally. Ca2Gd8(SiO4)6O2 apatite has the potential for being an effective T/EBC in circumventing the penetration of molten CMAS up to about 1300 °C but not at higher temperatures.

Revealing the interdependence of load partitioning, dislocation density evolution and mechanical behavior of medium Mn steels

The load partitioning between inter-phases and intragranular of austenite, their dislocation density evolution, and mechanical behavior were investigated in two medium Mn steels by in-situ high-energy synchrotron x-ray diffraction during tensile loading. The investigated steels were produced with different hot rolling parameters resulting in different initial microstructures. The initial microstructures were characterized using scanning electron microscope and electron backscatter diffraction analysis. Transmission electron microscope with high angle annular dark field technique was furthermore used to provide the fine microstructural features of deformed specimens in order to supplement the in-situ analysis. Despite the differences in the initial microstructure, the load partitioning from the softer ferrite to the stronger α’-martensite (α’) was observed; while different degrees of load partitioning for intragranular of γ occurred. The sample with a relatively low degree of load partitioning exhibits the intersection of two bundles of stacking faults (SF), one with high density SF, and the other with low density and limited SF, as well as the occurrence of α′ in the intersecting region. The secondary SFs and the relatively intermediate density of primary SFs bundle are characterized in γ for the sample with relatively high degree of load partitioning. The load partitioning between intragranular of γ is found to have a coordination relationship with the dislocation density evolution of γ; after the load partitioning, dislocation density of γ rapidly rises. The sample with intersection of two bundles SFs and the occurrence of α′, exhibits the higher transformation rate of γ into ε-martensite/α’, resulting in the larger work hardening rate. In addition, the early load on α’ is found to contribute to a higher yield strength. These results reveal the importance of assessing both phase-specifc strain/stress and the dislocation density evolution in order to predict the macroscopic mechanical properties of medium Mn steels.

The Effects of Post-Welding Heat Treatment on the Cryogenic Absorbed Energy of High Manganese Steel Weld Metal

In this study, a post-weld heat treatment (PWHT) was proposed at high temperatures of 600 °C, 750 °C, and 900 °C for 30 min to significantly improve the impact absorbed energy of high manganese steel weld metal. Electron backscatter diffraction (EBSD), electron probe microanalysis (EPMA), and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) were employed to characterize the production and study the deformation mechanisms in the high manganese steel weld metal. The impact absorbed energy is divided into crack initiation energy and crack propagation energy, which are divided by the value of Pmax. The cryogenic impact absorbed energy was 81 J. After PWHT at 600 °C, 750 °C, and 900 °C, it was 75 J, 69 J, and 88 J, respectively. The impact absorbed energies did not follow a proportional relationship with the PWHT temperatures. The increase in impact absorbed energy can be attributed to the narrowing of the dendritic region, which blocks the crack propagation path and efficiently prevents crack propagation. Conversely, the decrease in impact absorbed energy can be attributed to the presence of 100-nm-sized (Cr, Mn)23C6-type carbides at the grain boundaries, which facilitate crack propagation.

Denoising Autoencoder Trained on Simulation-Derived Structures for Noise Reduction in Chromatin Scanning Transmission Electron Microscopy.

Scanning transmission electron microscopy tomography with ChromEM staining (ChromSTEM), has allowed for the three-dimensional study of genome organization. By leveraging convolutional neural networks and molecular dynamics simulations, we have developed a denoising autoencoder (DAE) capable of postprocessing experimental ChromSTEM images to provide nucleosome-level resolution. Our DAE is trained on synthetic images generated from simulations of the chromatin fiber using the 1-cylinder per nucleosome (1CPN) model of chromatin. We find that our DAE is capable of removing noise commonly found in high-angle annular dark field (HAADF) STEM experiments and is able to learn structural features driven by the physics of chromatin folding. The DAE outperforms other well-known denoising algorithms without degradation of structural features and permits the resolution of α-tetrahedron tetranucleosome motifs that induce local chromatin compaction and mediate DNA accessibility. Notably, we find no evidence for the 30 nm fiber, which has been suggested to serve as the higher-order structure of the chromatin fiber. This approach provides high-resolution STEM images that allow for the resolution of single nucleosomes and organized domains within chromatin dense regions comprising of folding motifs that modulate the accessibility of DNA to external biological machinery.

Full Metal Species Quantification of Supported Catalysts: Beyond Metal Dispersion.

Metal dispersion is a key concept in heterogeneous catalysis. The conventional approaches for its estimation strongly rely on chemisorption with different probe molecules. Albeit they can generally provide an 'averaged' value in a cost-effective manner, the inhomogeneity of the metal species and the complicated metal-support interactions pose formidable challenges for the accurate determination. Full metal species quantification (FMSQ) is introduced as an advanced method to depict the whole distribution of the metal species, ranging from single atoms to clusters and nanoparticles, in a practical solid catalyst. In this approach, automated analysis of massive high-angle annular dark field scanning transmission electron microscopic images is realized through algorithms specialized in combining the electron microscopy-based atom recognition statistics and deep learning-driven nanoparticle segmentation. In this Concept article, different techniques for determining the metal dispersion are discussed with their pros and cons. FMSQ is highlighted for it can circumvent the drawbacks of conventional approaches, allowing more reliable structure-performance relationships beyond the metal size.

Synchronization of scanning probe and pixelated sensor for image-guided diffraction microscopy

A 4-dimensional modality of a scanning transmission electron microscope (4D-STEM) acquires diffraction images formed by a coherent and focused electron beam scanning the specimen. Newly developed ultrafast detectors offer a possibility to acquire high throughput diffraction patterns at each pixel of the scan, enabling rapid tilt series acquisition for 4D-STEM tomography. Here we present a solution to the problem of synchronizing the electron probe scan with the diffraction image acquisition, and demonstrate on a fast hybrid-pixel detector camera (ARINA, DECTRIS). Image-guided tracking and autofocus corrections are handled by the freely-available microscope-control software SerialEM, in conjunction with a high angle annular dark field (HAADF) image acquired simultaneously. The open source SavvyScan system offers a versatile set of scanning patterns, operated by commercially available multi-channel acquisition and signal generator computer cards (Spectrum Instrumentation GmbH). Images are recorded only within a sub-region of the total field, so as to avoid spurious data collection during flyback and/or acceleration periods in the scan. Hence, the trigger of the fast camera follows selected pulses from the scan generator clock gated according to the chosen scan pattern. Software and protocol are provided for gating the trigger pulses via a microcontroller (ST Microelectronics ARM Cortex). We demonstrate the system on a standard replica grating and by diffraction imaging of a ferritin specimen.

Preparation of magnesium potassium phosphate cement from municipal solid waste incineration fly ash and lead slag co-blended: Ca-induced crystal reconstruction process and Pb-Cl synergistic solidification mechanism

Higher chlorine (Cl) content than lead (Pb) content in municipal solid waste incineration fly ash (MSWIFA) impeded the practical application of Pb5(PO4)3Cl-derived magnesium potassium phosphate cement (MKPC) preparation strategy. Herein, Pb/Ca-rich lead slag (LS) was co-blended with MSWIFA to prepare MKPC for the synergistic treatment of both two solid wastes and the Pb-Cl solidification. The results showed that the resulting 15–15 (15 wt% MSWIFA and 15 wt% LS incorporation) sample achieved 25.44 MPa compressive strength, and Pb and Cl leaching toxicity was reduced by 99.18 % and 92.80 %, respectively. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses showed that Pb2+, Ca2+, phosphate and Cl- formed PbxCa5−x(PO4)3Cl in samples. The formation of PbxCa5−x(PO4)3Cl was also demonstrated by the high-angle annular dark field scanning transmission electron microscope (HAADF-STEM), while differences in the lattice characteristics of PbxCa5−x(PO4)3Cl and Pb5(PO4)3Cl were found. In-situ XRD indicated that Ca2+ accelerated the transformation of Pb2+ to Pb5(PO4)3Cl. After co-precipitating with Ca2+ to form PbxCa5−x(PO4)3Cl, Pb2+ continuously substituted Ca2+ to eventually transform to Pb5(PO4)3Cl. This work informs the synergistic treatment of MSWIFA and LS and offers new insights into the reaction mechanism between Pb2+, phosphate and Cl- under Ca2+ induction.

Preferential substitution at cationic sites in 9-4-9 Zintl phase Ca9− yEuyZn4.5+ δ Sb9

Ca9Zn4.5Sb9 Zintl compound is one of the promising thermoelectric materials with excellent performance, which can be further improved by Eu alloying. In this work, a series of Ca9−yEuyZn4.5+δSb9 compounds is investigated by using the advanced Cs-corrected high-angle annular dark field scanning transmission electron microscope (HAADF-STEM) imaging technique at an atomic level. The HAADF-STEM images show that alloying Eu will lead to preferential substitution of Eu atoms at Ca(1) and Ca(5) sites. The further structural analysis and first-principles density functional theory calculation elucidate the origin that the Eu atoms are prone to replace Ca(1) and Ca(5) sites in Ca9−yEuyZn4.5+δSb9. The preferential substitutions may provide a new insight into revealing the structural transformation commonly found in Zintl phase thermoelectric materials.

A facile way to tune the chemical composition of gas-phase synthesized nanoclusters

Cluster beam deposition (CBD) represents a powerful and versatile gas-phase synthesis method to fabricate nanoclusters that are in demand for various fields. However, the ready control of the chemical composition is of great significance and is still a challenge. In this work, the influences of sputtering power and Ar fluxes on the composition, size and shape of Sm-Co nanoclusters fabricated by the CBD method using a single composite target have been systematically investigated. The chemical composition of nanoclusters has been characterized by high-angle annular dark-field (HAADF) images and EDS of high-resolution transmission electron microscopy. As the sputtering power increases or the Ar fluxes decrease, the Co concentration in nanoclusters gradually increases, the variation of composition in nanoclusters is consistent with the electrocatalytic measurement results. The mechanism by which the composition changes is proposed to be associated with the distinct scattering for Sm and Co by Ar atoms. The composition of nanoclusters can be quantitatively tuned over a wide range by Ar fluxes and sputtering power. We demonstrate an effective way to synthesize nanoclusters with various chemical compositions and manipulate their corresponding functional properties, which advances the design and synthesis of nanoclusters and may be important for both basic research and applications.