High-angle Annular Dark-field Imaging Research Articles

Machine Learning-Enabled Image Classification for Automated Electron Microscopy.

Traditionally, materials discovery has been driven more by evidence and intuition than by systematic design. However, the advent of "big data" and an exponential increase in computational power have reshaped the landscape. Today, we use simulations, artificial intelligence (AI), and machine learning (ML) to predict materials characteristics, which dramatically accelerates the discovery of novel materials. For instance, combinatorial megalibraries, where millions of distinct nanoparticles are created on a single chip, have spurred the need for automated characterization tools. This paper presents an ML model specifically developed to perform real-time binary classification of grayscale high-angle annular dark-field images of nanoparticles sourced from these megalibraries. Given the high costs associated with downstream processing errors, a primary requirement for our model was to minimize false positives while maintaining efficacy on unseen images. We elaborate on the computational challenges and our solutions, including managing memory constraints, optimizing training time, and utilizing Neural Architecture Search tools. The final model outperformed our expectations, achieving over 95% precision and a weighted F-score of more than 90% on our test data set. This paper discusses the development, challenges, and successful outcomes of this significant advancement in the application of AI and ML to materials discovery.

Phase coexistence induced surface roughness in V2O3/Ni magnetic heterostructures

We present an investigation of the microstructure changes in V2O3 as it goes through its inherent structural phase transition. Using V2O3 films with a well-defined crystal structure deposited by reactive magnetron sputtering on r-plane Al2O3 substrates, we study the phase coexistence region and its impact on the surface roughness of the films and the magnetic properties of overlying Ni magnetic layers in V2O3/Ni hybrid magnetic heterostructures. The simultaneous presence of two phases in V2O3 during its structural phase transition was identified with high resolution x-ray diffraction and led to an increase in surface roughness observed using x-ray reflectivity. The roughness reaches its maximum at the midpoint of the transition. In V2O3/Ni hybrid heterostructures, we find a concomitant increase in the coercivity of the magnetic layer correlated with the increased roughness of the V2O3 surface. The chemical homogeneity of the V2O3 is confirmed through transmission electron microscopy analysis. High-angle annular dark field imaging and electron energy loss spectroscopy reveal an atomically flat interface between Al2O3 and V2O3, as well as a sharp interface between V2O3 and Ni.

Quantifying the thickness of WTe2 using atomic-resolution STEM simulations and supervised machine learning.

For two-dimensional (2D) materials, the exact thickness of the material often dictates its physical and chemical properties. The 2D quantum material WTe2 possesses properties that vary significantly from a single layer to multiple layers, yet it has a complicated crystal structure that makes it difficult to differentiate thicknesses in atomic-resolution images. Furthermore, its air sensitivity and susceptibility to electron beam-induced damage heighten the need for direct ways to determine the thickness and atomic structure without acquiring multiple measurements or transferring samples in ambient atmosphere. Here, we demonstrate a new method to identify the thickness up to ten van der Waals layers in Td-WTe2 using atomic-resolution high-angle annular dark-field scanning transmission electron microscopy image simulation. Our approach is based on analyzing the intensity line profiles of overlapping atomic columns and building a standard neural network model from the line profile features. We observe that it is possible to clearly distinguish between even and odd thicknesses (up to seven layers), without using machine learning, by comparing the deconvoluted peak intensity ratios or the area ratios. The standard neural network model trained on the line profile features allows thicknesses to be distinguished up to ten layers and exhibits an accuracy of up to 94% in the presence of Gaussian and Poisson noise. This method efficiently quantifies thicknesses in Td-WTe2, can be extended to related 2D materials, and provides a pathway to characterize precise atomic structures, including local thickness variations and atomic defects, for few-layer 2D materials with overlapping atomic column positions.

Spontaneous Deposition of Single Platinum Atoms on Anatase TiO2 for Photocatalytic H2 Evolution.

Single-atom (SA) decoration has emerged as a frontier in catalysis due to its unique characteristics. Recently, decorated Pt single atoms on titania have shown promise in photocatalytic hydrogen evolution. In this work, we demonstrate that Pt SAs can spontaneously deposit on the surface, driven by electrostatic forces; the key is to determine the golden pH and surface potential. We conducted a comprehensive investigation into the influence of the pH of the deposition precursor on the spontaneous adsorption of Pt SAs onto TiO2 nanosheets (TiNSs). We introduced a straightforward pH-dependent and charge-dependent strategy for the solid electrostatic anchoring of Pt SAs on TiO2. Furthermore, we established that the level of Pt loading can be controlled by adjusting the precursor pH. X-ray photoelectron spectroscopy (XPS) and high-angle annular dark-field imaging scanning transmission electron microscopy (HAADF-STEM) were used to evaluate the Pt SA-decorated samples. Photocatalytic hydrogen production activity was assessed under ultraviolet (UV) (365 nm) irradiation. Notably, we found that at a pH of 8, slightly below the measured point of zero charge (PZC), a unique mixture of Pt clusters and single atoms was deposited on the surface of TiNSs. This unique composition significantly improved hydrogen production, resulting in ∼3.7 mL of hydrogen generated after 8 h of UV exposure by only 10 mg of the Pt-decorated TiNS (with Pt loadings of 0.12 at. %), which is ∼300 times higher than the undecorated TiNS.

Dynamically Reconstructed Triple-Copper-Vacancy Associates Confined in Cu Nanowires Enabling High-Rate and Selective CO2 Electroreduction to C2+ Products.

Electrochemically reconstructed Cu-based catalysts always exhibit enhanced CO2 electroreduction performance; however, it still remains ambiguous whether the reconstructed Cu vacancies have a substantial impact on CO2 -to-C2+ reactivity. Herein, Cu vacancies are first constructed through electrochemical reduction of Cu-based nanowires, in which high-angle annular dark-field scanning transmission electron microscopy image manifests the formation of triple-copper-vacancy associates with different concentrations, confirmed by positron annihilation lifetime spectroscopy. In situ attenuated total reflection-surface enhanced infrared absorption spectroscopy discloses the triple-copper-vacancy associates favor *CO adsorption and fast *CO dimerization. Moreover, density-functional-theory calculations unravel the triple-copper-vacancy associates endow the nearby Cu sites with enriched and disparate local charge density, which enhances the *CO adsorption and reduces the CO-CO coupling barrier, affirmed by the decreased *CO dimerization energy barrier by 0.4eV. As a result, the triple-copper-vacancy associates confined in Cu nanowires achieve a high Faradaic efficiency of over 80% for C2+ products in a wide current density range of 400-800mA cm-2 , outperforming most reported Cu-based electrocatalysts.

Quantitative Scanning Transmission Electron Microscopy–High‐Angle‐Annular Dark‐Field Study of the Structure of Pseudo‐2D Sb2Te3 Films Grown by (Quasi) Van der Waals Epitaxy

Scanning transmission electron microscopy (STEM) techniques are used to improve the understanding of out‐of‐plane oriented Sb2Te3 thin films deposited by sputtering on SiO2 and Si substrates. Nanobeam precession electron diffraction, energy‐dispersive X‐ray spectroscopy, and high‐angle‐annular dark‐field imaging show that the presence of 1–2 atomic planes of Te on top of the substrate is a crucial factor for successful growth of such films, which can be achieved by optimizing cosputtering of Te and Sb2Te3 targets. The formation of an actual van der Waals (vdW) gap between the substrate and the first Sb2Te3 quintuple layer allows for vdW epitaxy. This gap is larger than those separating Te planes in the pseudo‐2D Sb2Te3 structure. HAADF image analysis provides detailed information on the atomic arrangement such as interplanar distances, vdW gaps, and Debye–Waller coefficients, all these with a few pm precision. For the anisotropic atomic displacements, a new methodology is introduced based on the statistical analysis of atomic column positions that provides information on the low‐frequency phonon modes. Ab initio calculations are used to support our results. Overall, this study provides quantitative STEM tools particularly well suited for nonperiodic pseudo‐2D materials, such as Sb2Te3/GeTe superlattices.

Three-Dimensional Reconstruction of Interface Roughness and Alloy Disorder in Ge/GeSi Asymmetric Coupled Quantum Wells Using Electron Tomography.

Interfaces play an essential role in the performance of ever-shrinking semiconductor devices, making comprehensive determination of their three-dimensional (3D) structural properties increasingly important. This becomes even more relevant in compositional interfaces, as is the case for Ge/GeSi heterostructures, where chemical intermixing is pronounced in addition to their morphology. We use the electron tomography method to reconstruct buried interfaces and layers of asymmetric coupled Ge/Ge0.8Si0.2 multiquantum wells, which are considered a potential building block in THz quantum cascade lasers. The three-dimensional reconstruction is based on a series of high-angle annular dark-field scanning transmission electron microscopy images. It allows chemically sensitive investigation of a relatively large interfacial area of about (80 × 80) nm2 with subnanometer resolution as well as the analysis of several interfaces within the multiquantum well stack. Representing the interfaces as iso-concentration surfaces in the tomogram and converting them to topographic height maps allows the determination of their morphological roughness as well as layer thicknesses, reflecting low variations in either case. Simulation of the reconstructed tomogram intensities using a sigmoidal function provides in-plane-resolved maps of the chemical interface widths showing a relatively large spatial variation. The more detailed analysis of the intermixed region using thin slices from the reconstruction and additional iso-concentration surfaces provides an accurate picture of the chemical disorder of the alloy at the interface. Our comprehensive three-dimensional image of Ge/Ge0.8Si0.2 interfaces reveals that in the case of morphologically very smooth interfaces─depending on the scale considered─the interface alloy disorder itself determines the overall characteristics, a result that is fundamental for highly miscible material systems.

Ordering transformation in Nb<sub>0.8</sub>CoSb induced by <i>in situ</i> heating-induced Nb diffusion

This study focused on the investigation of Nb<sub>0.8</sub>CoSb half-Heusler alloy covered with Nb films. By employing <i>in-situ</i> heating transmission electron microscopy (TEM) technique, diffusion of Nb was observed at high temperature, resulting in the ordering transformation from Nb<sub>0.8</sub>CoSb to Nb<sub>0.8+<i>δ</i></sub>CoSb. Through observations of high-angle annular dark-field (HAADF) images and selected-area electron diffraction (SAED) patterns, it was found that under elevated temperatures, the diffuse streaks representing short-range disorder in Nb<sub>0.8</sub>CoSb samples transitioned into superlattice diffraction spots representing long-range order. The modulation wave vector of this superstructure was determined to be <i>q</i>=1/3(<i>a</i><sup>*</sup> + <i>b</i><sup>*</sup>-<i>c</i><sup>*</sup>). This structural evolution primarily arised from the diffusion of Nb atoms from the Nb film into the Nb<sub>0.8</sub>CoSb sample at high temperature, leading to compositional changes in Sb and Nb. Further comparative analysis revealed significant differences between <i>in-situ</i> synthesized Nb<sub>0.8+<i>δ</i></sub>CoSb samples and <i>ex-situ</i> synthesized Nb<sub>0.84</sub>CoSb samples despite both exhibiting superstructures. In the <i>ex-situ</i> synthesized Nb<sub>0.84</sub>CoSb, the modulation wave vector of the superstructure was <<i>q</i>=1/3(2<i>a</i><sup>*</sup>-2<i>c</i><sup>*</sup>), mainly attributed to Nb compositional variations. Moreover, the superstructure in Nb<sub>0.84</sub>CoSb samples could remain stable from room temperature tor high temperature, whereas in Nb<sub>0.8+<i>δ</i></sub>CoSb samples, it only existed at elevated temperatures and gradually weakened as the temperature decreased, suggesting it might be a metastable structure between Nb<sub>0.8</sub>CoSb and Nb<sub>0.84</sub>CoSb. In summary, this study reveals the diversity of superstructures induced by compositional variations and the complexity of structural phase transitions in half-Heusler alloys, enriching the understanding of these materials and providing important guidance for the design and functional control of phase-change materials

Biosynthesis and characterization of silver nanoparticles synthesized using extracts of Agrimonia eupatoria L. and in vitro and in vivo studies of potential medicinal applications.

This research explores the synthesis, characterization, and biological activities of silver nanoparticles (AgNPs) derived from acetone (AgNPs-acetone) and aqueous (AgNPs-H2O) extracts of Agrimonia eupatoria. The nanoparticles exhibit isometric morphology and uniform size distribution, as elucidated through Transmission Electron Microscopy (TEM) and high-resolution TEM (HRTEM) analyses. The utilization of Scanning Transmission Microscopy (STEM) with High-Angle Annular Dark-Field (HAADF) imaging and energy dispersive spectrometry (EDS) confirms the crystalline nature of AgNPs. Fourier Transform Infrared (FTIR) analysis reveals identical functional groups in the plant extracts and their corresponding AgNPs, suggesting the involvement of phytochemicals in the reduction of silver ions. Spectrophotometric monitoring of the synthesis process, influenced by various parameters, provides insights into the kinetics and optimal conditions for AgNP formation. The antioxidant activities of the plant extracts and synthesized AgNPs are evaluated through DPPH and ABTS methods, highlighting AgNPs-acetone as a potent antioxidant. Third-instar larvae exposed to the extracts have differential effects on DNA damage, with the acetone extract demonstrating antigenotoxic properties. Similarly, biosynthesized AgNPs-acetone displays antigenotoxic effects against EMS-induced DNA damage. The genotoxic effect of water extract and AgNPs-acetone was dose-dependent. Hemolytic potential is assessed on rat erythrocytes, revealing that low concentrations of AgNPs-acetone and AgNPs-H2O had a nontoxic effect on erythrocytes. Cytotoxicity assays demonstrate time-dependent and dose-dependent effects, with AgNPs-acetone exhibiting superior cytotoxicity. Proapoptotic activity is confirmed through apoptosis induction, emphasizing the potential therapeutic applications of AgNPs. The antimicrobial activity of AgNPs reveals concentration-dependent effects. AgNPs-H2O display better antibacterial activity, while antifungal activities are comparable between the two nanoparticle types.

Versatile Structural Engineering of Metal-Organic Frameworks Enabling Switchable Catalytic Selectivity.

The structure engineering of metal-organic frameworks (MOFs) forms the cornerstone of their applications. Nonetheless, realizing the simultaneous versatile structure engineering of MOFs remains a significant challenge. Herein, a dynamically mediated synthesis strategy to simultaneously engineer the crystal structure, defect structure, and nanostructure of MOFs is proposed. These include amorphous Zr-ODB nanoparticles, crystalline Zr-ODB-hz (ODB = 4,4'-oxalyldibenzoate, hz = hydrazine) nanosheets, and defective d-Zr-ODB-hz nanosheets. Aberration-corrected scanning transmission electron microscopy combined with low-dose high-angle annular dark-field imaging technique vividly portrays these engineered structures. Concurrently, the introduced hydrazine moieties confer self-reduction properties to the respective MOF structures, allowing the in situ installation of catalytic Pd nanoparticles. Remarkably, in the hydrogenation of vanillin-like biomass derivatives, Pd/Zr-ODB-hz yields partially hydrogenated alcohols as the primary products, whereas Pd/d-Zr-ODB-hz exclusively produces fully hydrogenated alkanes. Density functional theory calculations, coupled with experimental evidence, uncover the catalytic selectivity switch triggered by the change in structure type. The proposed strategy of versatile structure engineering of MOFs introduces an innovative pathway for the development of high-performance MOF-based catalysts for various reactions.

Single-Atom Pt Decorated ZnO Nanoflowers

Single-atom catalyst has drawn significant attention in the field of environmental engineering nowadays. In this research, single atoms Pt have highly dispersed on the wurtzite ZnO nanoflowers, evidenced by the high-angle annular dark field (HAADF-STEM) image. The single atom Pt/ZnO catalyst (SAPt/ZnO) was used to degrade organic dye through the piezo-photocatalytic process. The results showed that the SAPt/ZnO catalyst could fully decolorize 10 ppm RhB dye in 60 minutes under synergetic ultrasonication and light irradiation with Kobs of 0.089 min-1, while pristine ZnO nanoflowers have a Kobs of 0.050 min-1, proves the fact that the decoration of single atom Pt increases catalytic activity. In comparison, Kobs of SAPt/ZnO were found to be 0.021 min-1 for ultrasonicate only and 0.014 min-1 for light irradiation only, which indicates the strong enhancement of the piezo-photocatalytic effect. The theoretical study was then conducted with the density functional theory (DFT) approach to investigate the detailed mechanism. The Pt single atom was found to adsorb on the ZnO (101) surface with an adsorption energy of -1.28 eV, and the charge was localized on the top of the Pt atom after the chemisorption of SAPt on ZnO surface, providing abundantly active sites on the surface of the ZnO nanoflower.

A novel primitive cubic Al-Fe-Si phase in an Al-0.5Fe-0.2Si (wt.%) alloy

We report the identification of a new ternary Al-Fe-Si phase synthesized by arc-melting. Energy dispersive X-ray spectroscopy measurements show an homogeneous chemical distribution within the intermetallic grain with an overall stoichiometry equal to Al81.0Fe13.6Si5.4 (at.%). Atomically resolved High-Angle Annular Dark Field images collected along the [001] zone-axis are consistent with a cubic structure with an unit cell parameter close to 8.9 Å. Using microdiffraction analysis, it was possible to explore the zero-order Laue zone (ZOLZ) and first-order Laue zone (FOLZ) . This electron diffraction characterization leads to the conclusion that the Al81.0Fe13.6Si5.4 (at.%) crystallizes in the Pm3̄ space group.

Interface atomic structures in a cadmium arsenide/III–V semiconductor heterostructure

The interface atomic structure between an epitaxial thin film of the prototype topological semimetal cadmium arsenide (Cd3As2) and a III–V semiconductor layer is investigated using high-angle annular dark-field imaging in an aberration-corrected scanning transmission electron microscope. We find that the interface unit cell adopts a defined stoichiometry that is CdSb-like, which is achieved through the insertion of periodically arranged Cd vacancies in the terminating Cd-plane of Cd3As2. This interface stoichiometry is consistent with the Sb-termination of the III–V layer and the fact that CdSb is the thermodynamically stable phase in the Cd–Sb binary system. We find at least two distinct alignments of the film with respect to the buffer layer, which are characterized by a 14100Cd3As2 shift parallel to the interface. We show that steps of half unit cell height in the III–V layer can produce these distinct interface structures.

Selective oxidation and nickel enrichment hinders the repassivation kinetics of multi-principal element alloy surfaces

Robust and sustained corrosion resistance in multi-principal element alloys (MPEA) requires rapid repassivation, i.e. regrowth of the passive layer once it is damaged or destroyed at the surface. In this study, we show that the repassivation of Al0.1CrCoFeNi MPEA in 0.6 M NaCl solution is hindered at pH of ∼ 2.4 - 6.8 due to the formation of a Ni-enriched subsurface layer as a result of selective oxidation and dissolution of several principal elements, which can be fully restored at pH of ∼ 14 from the oxidation of all principal elements. Specifically, surface characterization via X-ray photoelectron spectroscopy (XPS), high-angle annular dark-field (HAADF) imaging in scanning transmission electron microscopy (STEM), and atom probe tomography (APT), are coupled with density functional theory (DFT) calculations to determine surface composition, oxidation state, and electron work function to uncover the structural origin of the pH-dependent repassivation mechanisms. It was found that selective oxidation of Cr, Co, and Fe in the acidic to neutral solutions altered the surface composition to be significantly enriched in Ni as compared to the bulk. Once the original passive film is destroyed locally by either pitting or tribocorrosion, this altered surface composition exhibited a much poorer repassivation capability due to the increased electron work function and reduced surface reactivity at higher Ni concentration. These understandings could shed light on the future compositional design of non-equiatomic MPEAs towards sustained repassivation and corrosion resistance over a wide pH range.

D022 precipitates strengthened W-Ta-Fe-Ni refractory high-entropy alloy

Refractory high-entropy alloys have recently emerged as promising candidates for high-temperature structural applications. However, their performance is compromised by the trade-off required between strength and ductility. Here, a novel W30Ta5(FeNi)65 refractory high-entropy alloy with an outstanding combination of strength and plasticity at both room and elevated temperatures is designed, based on the multi-phase transitions design strategy. The alloy comprises a body-centered cubic dendrite phase, a topologically close-packed μ rhombohedral phase, and a high-density coherent nano-precipitate γ″ phase with the D022structure (Ni3Ta type) embedded in a continuous face-centered cubic matrix. Owing to precipitation strengthening of D022, the yield stress of the alloy is determined as high as 1450 MPa, which is a significant improvement (∼100%) in comparison with the D022-free alloy, without a loss of ductility. This alloy exhibits an excellent high-temperature strength, with the yield strengths of 1300 MPa at 600 °C and 320 MPa at 1000 °C. Detailed microstructural characterization using transmission electron microscopy, high-angle annular dark-field imaging, and three-dimensional atom probe tomography analyses indicated that this superior strength–plasticity combination stems from the synergy of a multiple-phase structure. These results provide a new insight into the design of RHEAs and other advanced alloys.

Effects of shear strain on HZO ferroelectric orthorhombic phases

The stabilities of hafnium and zirconium oxide ferroelectric orthorhombic phases, oIII-phase (Pca21) and oIV-phase (Pmn21), under shear strain are investigated theoretically by atomic modeling with density functional theory calculations. The results indicate that oIV-phase serves as a buffer state preventing oIII-phase from transforming into m-phase (P21/c) under structural distortion caused by shear strain and meanwhile preserves the remanent polarization to some certain degree. Shear strain will also induce the reduction in coercive field of the HZO film due to the distortion of oIII-phase or phase transition into oIV-phase. It is very possible to identify oIV-phase with careful analysis of high-resolution transmission electron microscopy and high-angle annular dark-field STEM images at the region having a crystal tilt angle smaller than 86°.

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.

Vertical NiO/β-Ga2O3 rectifiers grown by metalorganic chemical vapor deposition

The performance of vertical Schottky and NiO/β-Ga2O3 p-n heterojunction rectifiers in which the Ga2O3 was grown by metalorganic chemical vapor deposition (MOCVD) is reported. The Si-doped Ga2O3 drift layers employed in the study had a doping concentration of 7.6 × 1015 cm−3 with a thickness of approximately 6 μm. High-angle annular dark-field scanning transmission electron microscopy imaging revealed an absence of interfacial features or extended defects around the drift layer region, indicating that MOCVD provides high-quality β-Ga2O3 epitaxial films for fabrication of vertical rectifiers. Both Schottky and NiO/Ga2O3 p-n heterojunction rectifiers attained the highest reported breakdown voltage of 486 and 836 V, respectively, for this growth technique. The heterojunction rectifiers showed an on/off ratio surpassing 109 within the voltage range of 0 to −100 V. Additionally, the Schottky barrier diodes demonstrate an on/off ratio of up to 2.3 × 106 over the same voltage range. These findings highlight the promise of MOCVD as a growth method for the type of rectifiers needed in power converters associated with an electric vehicle charging infrastructure.

Dynamic Changes of an Anodized FeNi Alloy during the Oxygen Evolution Reaction under Alkaline Conditions.

An efficient and durable oxygen evolution reaction (OER) catalyst is necessary for the water-splitting process toward energy conversion. The OER through water oxidation reactions could provide electrons for H2O, CO2, and N2 reduction and produce valuable compounds. Herein, the FeNi (1:1 Ni/Fe) alloy as foam, after anodizing at 50 V in a two-electrode system in KOH solution (1.0 M), was characterized by Raman spectroscopy, diffuse reflectance spectroscopy (DRS), X-ray absorption spectroscopy (XAS), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDX), transmission electron microscopy (TEM), high-angle annular dark-field imaging (HAADF)-scanning transmission electron microscopy (STEM) and used as an efficient and durable OER electrocatalyst in KOH solution (1.0 M). The overpotential for the onset of the OER based on extrapolation of the Tafel plot was 225 mV. The overpotentials for the current densities of 10 and 30 mA/cm2 are observed at 270 and 290 mV, respectively. In addition, a low Tafel slope is observed, 38.0 mV per decade, for the OER. To investigate the mechanism of the OER, in situ surface-enhanced Raman spectroscopy was used to detect FeNi hydroxide and characteristic peaks of H2O. Impurities in KOH can adsorb onto the electrode surface during the OER. Peaks corresponding to Ni(III) (hydr)oxide and FeO42- can be detected during the OER, but high-valent FeNi (hydr)oxides are unstable and reduce under the open circle potential. Metal hydroxide transformations during the OER and anion adsorption should be carefully considered. In addition, Fe3O4 may convert to γ-Fe2O3 during the OER. This study aims to offer logical perspectives on the dynamic changes that occur during the OER under alkaline conditions in an anodized FeNi alloy. These changes encompass variations in morphology, surface oxidation, the generation of high-valent species, and phase conversion during the OER.

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.