Electron Diffraction Analysis Research Articles

Comparative electron diffraction analysis of strain relaxation in AlxGa1-xN materials in the microelectronics industry: 4D-STEM approach vs. TEM-based N-PED solution

Comparative electron diffraction analysis of strain relaxation in AlxGa1-xN materials in the microelectronics industry: 4D-STEM approach vs. TEM-based N-PED solution

Shape- and Size-Controlled Preparation of Columnar Layered Transition Metal Hydroxides Enriched with Edges

Layered transition metal hydroxides have been extensively studied as electrocatalyst for alkaline water electrolysis.1 The morphological features such as size, aspect ratio, and exposed surface is known to strongly affect the performance of electrocatalysts, and edges are known to particularly exthibit high activity for oxygen evolution reactions.2 Thus, controlling the crystal growth direction of layered metal hydroxides to expose more edges may be an effective method to enhance the catalytic activity of metal hydroxides. In general, layered materials, including layered metal hydroxides, grow preferentially along the lateral directions to form plate-like crystals, which means that preparation of columnar crystals with an aspect ratio of the thickness to the lateral size higher than 1 is difficult. Recently, we found the formation of columnar layered metal hydroxides with an aspect ratio exceeding 1 by utilizing metal-diamine complexes as precursors.3 Here, we aim to control the size and aspect ratio of columnar crystals. We focused on the stability of the complexes and evaluated the anisotropic growth behavior of β-Co(OH)2.Columnar crystals of metal hydroxide are synthesized by mixing metal salt solution and diamine ligand solution at specific molar ratios, followed by heating under hydrothermal conditions. During hydrothermal treatment, metal ions, which can undergo condensation, are gradually released from metal-diamine complexes, leading to the formation of supersaturated solutions. When the degree of supersaturation is relatively high, anisotropic growth towards the stacking direction occurs. The stability of the complexes becomes a controlling factor for crystal shape. By using cobalt ions as the metal source and N,N'-dimethylethylenediamine (NN'-dmeda) as the ligand, [NN'-dmeda]/[Co2+] ratio was varied from 3 to 30 and the morphological change of the products was evaluated. Scanning electron microscopy images show microscale hexagonal-prism shaped crystals with aspect ratios exceeding 1 at [NN'-dmeda]/[Co2+] ratios of 3, 5, 10, and 15. Powder X-ray diffraction and electron diffraction analysis indicate that all products were β-Co(OH)2 and the long-axis direction of the columnar crystals corresponded to the stacking direction. Thus, the outer surfaces of these columnar crystals were enriched with edges. In the range of [NN'-dmeda]/[Co2+] = 3–10, the overall crystal size increased both in the stacking and lateral direction according to the increase of [NN'-dmeda]/[Co2+] while maintaining an average aspect ratio of approximately 2. At [NN'-dmeda]/[Co2+] = 15, columnar crystals with smaller aspect ratios were formed, and at [NN'-dmeda]/[Co2+] = 30, plate-like crystals with lateral sizes of about 20 μm were formed. Because the increase in [NN'-dmeda]/[Co2+] led to stabilization of metal complex and a decrease in the degree of supersaturation, the decrease in aspect ratio at [NN'-dmeda]/[Co2+] = 15–30 suggests that high degree of supersaturation is favable for the anisotropic growth. Therefore, controlling the degree of supersaturation by [NN'-dmeda]/[Co2+] enables the variation of the size and aspect ratio of columnar crystals.References(1) G. Chen, H. Wan, W. Ma, N. Zhang, Y. Cao, X. Liu, J. Wang and R. Ma, Adv. Energy Mater., 10, 1902535 (2020).(2) S. Wang, Q. Jiang, S. Ju, C.-S. Hsu, H. M. Chen, D. Zhang and F. Song, Nat. Commun., 13, 6650 (2022).(3) K. Muramatsu, M. Jimba, Y. Yamada, H. Wada, A. Shimojima and K. Kuroda, Inorg. Chem., 61, 8490 (2022). Figure 1

Transmission Electron Microscope Characterizations of the Localized Corrosion Behavior of Biodegradable ZX21 Mg Alloy in Hanks’ Balanced Salt Solution

Magnesium (Mg) alloys attract a lot of attention as next-generation biodegradable implant materials due to their excellent biocompatibility and unique biodegradability. By utilizing Mg alloys as implants, Mg alloys can be degraded naturally in the human body, avoiding the second removal surgery. In addition, Mg alloys are promising for orthopedic applications because of their similar density and mechanical properties to bones, which mitigate the stress shielding effect. Among various Mg alloy systems, the ZX-series Mg alloys, which contain zinc (Zn) and calcium (Ca), show great potential for orthopedic applications since Zn and Ca are essential for metabolism and bone regeneration and improve the mechanical strength of the alloys. However, localized corrosion of a ZX-series Mg alloy was reported in our previous study [1], leading to a faster degradation rate and possible premature failure of the implant.To further study the origin and detailed mechanism of the localized corrosion behavior of ZX-series Mg alloys in simulated physiological environments, transmission electron microscope (TEM) characterizations were performed on a ZX21 (Mg-2.15 wt%Zn-0.97 wt%Ca) Mg alloy before and after corrosion in a Hanks’ balanced salt solution (HBSS) at 37°C. Two second phases, Ca2Mg6Zn3 and Mg2Ca, were found adjacent to each other in the cast ZX21 alloy. The potential difference between the two second phases leads to microgalvanic corrosion and the preferential dissolution of the lower-potential Mg2Ca, initiating localized corrosion on the alloy surface. The localized corrosion propagates a few micrometers deep in the alloy and underneath the surface corrosion film. By selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDS) analysis in TEM, the corrosion products in the propagating localized corrosion regions are primarily composed of Mg(OH)2, which is different from the surface corrosion film (Mg(OH)2 + CaHPO4·2H2O) formed on the alloy surface [1]. Furthermore, the presence of Cl signal in the localized corrosion regions indicates that the Cl- ions in HBSS promote the propagation of localized corrosion.[1] P.W. Chu et al., Corrosion Behavior and Microstructure of the Surface Corrosion Film of Biodegradable WE43 and ZX21 Mg Alloys in Hanks’ Balanced Salt Solution, Materials Chemistry and Physics, vol. 312, pp. 128609-128620, 2024.

Morphological Evolution of Metal-Organic Frameworks into Hedrite, Sheaf and Spherulite Superstructures with Localized Different Coloration.

The branched metal-organic frameworks (MOFs) are the first superstructures of this kind, and the growth mechanism may explain crystal shapes of other materials. The mechanism of the formation of fascinating structures having a hedrite, sheaf or spherulite appearance are detailed. The branching can be controlled, resulting in crystals that either exhibit multiple generations of branching or a single generation. These structures might result from an increasing number of defects on fast-grown rods. As the basal facets become less reactive, material is added to the prism facets, leading to secondary nucleation and triangular branches. These triangular structures are connected to the rod surface, growing longer than the central rod. Electron diffraction analyses show that the sheafs are polycrystalline structures with their fantails consisting of single-crystalline nanorods deviating gradually from each other in their orientation. The crystallographic structure consists of channels with opposite handedness. The accessibility of the nanochannels and the porosity of the superstructures are demonstrated by chromophore diffusion into the channels. The confinement and alignment of the chromophores inside the channels resulted in polarized-light dependent coloration of the crystals; the polycrystallinity generated areas having different optical properties.

Influence of artificial and process-induced defects on very high cycle fatigue characteristics of 316L stainless steel produced by laser powder bed fusion

This study investigates the impact of artificially embedded defects on the very high cycle fatigue (VHCF) of 316L stainless steel produced by laser powder bed fusion (PBF-LB) technology. Each specimen contains a single embedded artificial defect of 180 μm or 350 μm in diameter, positioned at specific distances from the surface (ranging from 350 μm to 1200 μm). The defect position and size are quantified by X-ray computed tomography. Following VHCF testing, the fracture surfaces of the specimens are examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) with electron diffraction analysis. The results demonstrate that the fracture surfaces predominantly display a fish-eye fracture type, with a fine granular area (FGA) surrounding the internal defects, typical for VHCF. The FGAs dimensions including thickness are estimated by means of microscopy analysis. However, despite the presence of relatively large artificial defects, cracks sometimes initiate from much smaller process-induced defects closer to the surface than the artificial ones. In conclusion, our study quantifies the relationship between the probability of crack initiation from artificial defects and the distance of the artificial defect from the specimen's surface.

Assessment of self-compacting lightweight concrete: preparation of eco-friendly fiber content on mechanical and durable characteristics

Abstract In recent years, a growing focus has been on creating eco-friendly concrete alternatives, garnering increased attention and support. Using natural fibers in the construction industry will minimize the exploitation of natural raw materials and promote sustainability in the construction industry. This work aims to investigate the influence of palmyra fruit mesocarp fiber (PFMF), Polyolefin fiber (PF), and glass fiber (GF) on the production of self-compacting concrete (SCC). The fiber content was used in three ratios, 1, 1.5, and 2%, as an alternative to fine aggregate. This research was conducted in two phases. In the first phase, a preliminary investigation was carried out to find the maximum adding percentage of fiber content in the successful production of SCC. The mechanical characteristics (compressive, split tensile, and flexural strength) and durability (water absorption, Acid attack, and ultrasonic pulse velocity) were evaluated. The second phase incorporates the fresh characteristics (T500 and slump flow). Adding 1.5%(PFMF/PF/GF) with 10% SF in SCC significantly enhanced the mechanical and durability properties. The compressive, splitting tensile strength, and flexural strength at 28 days increase to 4.30 MPa, 120 MPa, and 4.3 MPa compared to SCC. Scanning electronic microscopic (SEM) and X-ray diffraction (XRD) analysis was performed to evaluate the microstructure of concrete samples. Overall, the incorporation of up to 1.5% as a replacement of fine aggregate in manufacturing fiber-blended SCC mixtures can be recommended.

A novel grain refinement of Ce-Fe-B magnets induced by magnetic field annealing

Magnetic field annealing-induced grain refinement usually occurs during the crystallization process of amorphous alloys. This work investigates the effects of magnetic field annealing on the microstructure and magnetic properties of crystalline Ce17Fe76Co1Zr0.5B6Mo0.5 alloys. The results indicate that magnetic field annealing below the Curie temperature (TC) of the Ce2Fe14B phase in the alloys reduces the alloy’s grain size. At an annealing temperature of 433 K, the average grain size of alloys decreased from 48.0 nm in the as-spun sample to 27.2 nm in the magnetic field annealing sample. Moreover, magnetic field annealing can effectively reduce the volume fraction of the CeFe2 phase in the alloy. After magnetic field annealing at 433 K, the alloy obtained the optimal comprehensive magnetic properties: the intrinsic coercivity (Hci = 441.1 kA/m), remanence (Br = 0.49 T), squareness (Hk/Hci = 0.53), and maximum energy product ((BH)max) = 35.5 kJ/m3), which were 0.2 %, 16.7 %, 6 %, and 29.1 % higher than the values of the as-spun sample, respectively. Precession electron diffraction (PED) analysis revealed that magnetic field annealing increased strain at grain and phase boundaries and a more uniform grain orientation spread (GOS), promoting recrystallization and grain refinement. This study provides new insights into the grain refinement mechanism of crystalline alloys under magnetic field annealing, contributing to further improving the magnetic properties of Ce-Fe-B magnets.

Revealing Intrinsic Functionalization, Structure, and Photo-Thermal Oxidation in Hexagonal Antimonene.

Antimonene is one of the more exciting members of the post-graphene family with promising applications in optoelectronics, energy storage and conversion, catalysis, sensing or biomedicine. Efforts have been focused on developing a large-scale production route, and indeed, through a colloidal approach, high-quality few-layers antimonene (FLA) hexagons have been recently obtained. However, their oxidation behavior remains unexplored, as well as their interface, inner structure, and photothermal properties. Herein, it is revealed that the hexagons have an intrinsic surface functionalization with alkyl thiols that protects the core of the hexagonal flake against oxidation, and displayed inner defects related to the crystal formation during synthesis, as confirmed by cross-sectional scanning transmission electron microscopy energy dispersive X-ray spectroscopy (STEM-EDX) and temperature-dependent X-ray photoelectron spectroscopy (XPS) and selected area electron diffraction (SAED) analysis. A comprehensive study of temperature and laser power-dependent Raman spectroscopy on varying FLA hexagon thicknesses is carried out. Thinner flakes (<20nm) exhibited a blueshift and intensity decrease, contrasting with thicker ones resembling typical exfoliated flakes with a redshift. This work addresses a literature gap, providing insights into hexagonal FLA structure and characterization, and highlighting the influence of surface functional groups on oxidation behavior. Additionally, it emphasizes the potential of antimonene hexagons as building blocks for 2D heterostructures, including combinations with antimonene oxides and other 2D materials.

Unlocking the Electrocatalytic Behavior of Cu2MnS2 Nanoflake-Anchored rGO for the Oxygen Evolution Reaction in an Alkaline Medium.

A catalyst of the oxygen evolution reaction (OER) that is viable, affordable, and active for effective water-splitting applications is critical. A variety of electrocatalysts have been discovered to replace noble metal-based catalysts. Of these, transition metal-based sulfides are essential for incorporating carbonaceous materials to improve electrical conductivity, resulting in better electrocatalytic performance. Our study illustrates the synthesis of Cu2MnS2 (CMS) nanoflakes and their different rGO composites (10 to 40 wt %) via a hydrothermal technique for an effective water oxidation reaction. The X-ray diffraction pattern reveals that the prepared Cu2MnS2 nanoflakes exhibit a cubic crystal structure. The high-resolution scanning electron microscopy and the high resolution transmission electron microscopy images corroborate the formation of the nanoflake-like morphology of Cu2MnS2 with the strong interaction of rGO. The selected area electron diffraction analysis pattern reveals a polycrystalline nature. The Fourier transform infrared spectrum shows the existence of a metal sulfur vibrational band at 590 cm-1, and Raman analysis infers the presence of rGO. The X-ray photoelectron spectroscopy spectra reveal the oxidation states of the elements present in the samples. Using Brunauer-Emmett-Teller analysis, the surface area of CMS-20 is found to be 117.04 m2/g. The measured OER overpotentials using linear sweep volammetry and the values are 380, 370, 340, 376, and 400 mV at 10 mA/cm2 for CMS, CMS-10, CMS-20, CMS-30, and CMS-40, respectively, and the corresponding Tafel slope values are 179, 158, 149, 206, and 240 mV/decade, respectively. The electrochemical active surface area is estimated using cyclic voltammetry for all of the catalysts, where CMS-20 showed a larger surface area. Also, the same catalyst exhibits good stability for ∼24 h at a constant potential, which is confirmed via chronoamperometry. Thus, combining transition metal-based sulfides with carbonaceous materials indicates improved catalytic behavior for the preparation of high-performance OER electrocatalysts. Overall, the prepared CMS-20 performed as an efficient OER electrocatalyst and can be utilized for practical applications in energy conversion.

An Investigation of Oxides of Tantalum Produced by Pulsed Laser Ablation and Continuous Wave Laser Heating.

Recent progress has seen multiple Ta2O5 polymorphs generated by different synthesis techniques. However, discrepancies arise when these polymorphs are produced in widely varying thermodynamic conditions and characterized using different techniques. This work aimed to characterize and compare Ta2O5 particles formed at high and low temperatures using nanosecond pulsed laser ablation (PLA) and continuous wave (CW) laser heating of a local area of tantalum in either air or an 18O2 atmosphere. Scanning electron microscopy (SEM) and Raman spectroscopy of the micrometer-sized particles generated by PLA were consistent with either a localized amorphous Ta2O5 phase or a similar, but not identical, crystalline β-Ta2O5 phase. The Raman spectrum of the material formed at the point of CW laser impingement was in good agreement with the previously established ceramic "H-Ta2O5" phase. TEM and electron diffraction analysis of these particles indicated the phase structure matched an oxygen-vacated superstructure of monoclinic H-Ta2O5. Further from the point of laser impingement, CW heating produced particles with a Raman spectrum that matched β-Ta2O5. We confirmed that the high-temperature ceramic phase characterized in previous work by Raman spectroscopy was the same monoclinic phase characterized in different work by TEM and could be produced by direct laser heating of metal in air.

Large-Angle Rocking Beam Electron Diffraction of Large Unit Cell Crystals Using Direct Electron Detector.

We report a large-angle rocking beam electron diffraction (LARBED) technique for electron diffraction analysis. Diffraction patterns are recorded in a scanning transmission electron microscope (STEM) using a direct electron detector with large dynamical range and fast readout. We use a nanobeam for diffraction and perform the beam double rocking by synchronizing the detector with the STEM scan coils for the recording. Using this approach, large-angle convergent beam electron diffraction (LACBED) patterns of different reflections are obtained simultaneously. By using a nanobeam, instead of a focused beam, the LARBED technique can be applied to beam-sensitive crystals as well as crystals with large unit cells. This paper describes the implementation of LARBED and evaluates the performance using silicon and gadolinium gallium garnet crystals as test samples. We demonstrate that our method provides an effective and robust way for recording LARBED patterns and paves the way for quantitative electron diffraction of large unit cell and beam-sensitive crystals.

Fabrication of Chitosan-Cu2O Nanocomposite through Ethanol Assisted Reduction

The semiconducting characteristics of copper oxides have intrigued researchers like photocatalysis and sensors. Coating these nanoparticles with biocompatible polymers like chitosan enhances their properties, such as biocompatibility and non-toxicity, while reducing production costs. This work details the successful in situ production of a biocompatibile nanocomposite, with Cu2O nanoparticles dispersed in a chitosan matrix using ethanol as a reducing agent. Advanced techniques including ultraviolet-visible (UV-Vis) spectroscopy, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) imaging combined with selected area electron diffraction (SAED) analysis, have been employed to characterize the nanocomposite material with additional relevant properties analyzed.

(10–13)-oriented semipolar GaN growth on (10–10) m-plane ScAlMgO4 substrate

Abstract We report the growth of a GaN layer on (10–10) m-plane ScAlMgO4 (SAM) substrate. The GaN layer demonstrated (10–13) preference growth orientation. The anisotropy of the crystalline quality was distinctly observed through X-ray rocking curve taken across the sample surface over various azimuths across the orthogonal directions [0001] and [1–210] of the SAM substrate. Notably, the crystalline quality exhibited gradual degradation as the substrate is rotated around its surface normal away from the c-direction [0001] of the SAM substrate toward the a-direction [11–20]. Additionally, basal stacking faults in the (10–13)-oriented GaN were observed along [0001] direction using scanning transmission electron microscopy. Moreover, the selected area electron diffraction analysis was utilized to confirm the (10–13) growth orientation that was found to be consistent with the X-ray diffraction result. The (10–13) GaN layer exhibited a metal face through integrated differential phase contrast imaging.

Synthesis and field emission characterization of La-doped SiC nanowires using graphite powder as carbon source

Lanthanum (La)-doped SiC nanowires (NMs) were synthesized via a carbon thermal reduction process using different graphite powders, while milled Si-SiO2 mixed powders were employed as the silicon source. The identification of the products as β-SiC were supported by Select-area electron diffraction (SAED) and X-ray diffraction (XRD) analysis. The field emission results demonstrated that the turn-on field reached a minimum value of approximately 2.3 V/μm when the graphite content ranged from 2.5 g–3 g. The product exhibited higher density at this stage, accompanied by an increase in nanowire diameter and a tendency toward straightness. The energy spectrum analysis revealed a significant increase in the lanthanum content within the nanowires, with the atomic percentage rising from 0.05 to 0.26–0.27. The synergistic effect of morphology and La improved the field emission performance of the product. The findings may offer valuable insights for enhancing the field emission performance of one-dimensional nanomaterials.

Enzyme‐triggered assembly of glycan nanomaterials

AbstractA comprehensive molecular understanding of carbohydrate aggregation is key to optimize carbohydrate utilization and to engineer bioinspired analogues with tailored shapes and properties. However, the lack of well‐defined synthetic standards has substantially hampered advances in this field. Herein, we employ a phosphorylation‐assisted strategy to synthesize previously inaccessible long oligomers of cellulose, chitin, and xylan. These oligomers were subjected to enzyme‐triggered assembly (ETA) for the on‐demand formation of well‐defined carbohydrate nanomaterials, including elongated platelets, helical bundles, and hexagonal particles. Cryo‐electron microscopy and electron diffraction analysis provided molecular insights into the aggregation behavior of these oligosaccharides, establishing a direct connection between the resulting morphologies and the oligosaccharide primary sequence. Our findings demonstrate that ETA is a powerful approach to elucidate the intrinsic aggregation behavior of carbohydrates in nature. Moreover, the ability to access a diverse array of morphologies, expanded with a non‐natural sequence, underscores the potential of ETA, coupled with sequence design, as a robust tool for accessing programmable glycan architectures.

Microwave-assisted green synthesis of silver nanoparticles using Mitragyna parvifolia bark extract and their biological activities: an economical and environment-friendly approach

ABSTRACT Nowadays, nanotechnology is extensively employed in the medical profession. In this study, we used the aqueous extract of the bark of Mitragyna parvifolia to synthesize silver nanoparticles (AgNPs) by microwave-assisted green synthesis. The synthesis of AgNPs was confirmed by visual color change to brown color and characteristic surface plasmon resonance peak at 432 nm. The hydrodynamic diameter of the AgNPs was 171.81 nm having a zeta potential of −24.14 mV; Fourier Transmission Infrared Spectroscopy confirmed the presence of different functional groups on the NP surface; Scanning Electron Microscope and High-Resolution Transmission Electron Microscopy indicated predominantly circular shape of nanoparticle; Selected Area Electron Diffraction and X-ray Diffraction analyses determined the crystalline structure of AgNPs. Energy-Dispersive X-ray indicated the elemental composition and formation of AgNPs. The AgNPs were screened at different concentrations for antioxidant activity, antimicrobial, and anticancer potential in breast cancer cells (MCF-7 and MDA-MB-231). The AgNPs exhibited remarkable antioxidant, antimicrobial, and anticancer activities. The sedative and antinociceptive activities were also tested on Swiss albino mice, which showed mild sedative and very potent antinociceptive activity. However, detailed mechanistic studies are warranted in the future for clinical application of the AgNPs as a biologically active agent as well as a carrier for drug delivery.

Combined application of 3D electron diffraction analysis and mechanochemical synthesis for the investigation of novel nanocrystalline reticular materials

Combined application of 3D electron diffraction analysis and mechanochemical synthesis for the investigation of novel nanocrystalline reticular materials

Experimental geochemical assessment of a seal-reservoir system exposed to supercritical CO2: A case study from the Ebro Basin, Spain

This paper studies the effects of exposure to CO2-rich brine on sandstones and marls considered potential deep storage reservoir and seal in the Ebro Basin, Spain.The experiment was conducted in a reactor under conditions of deep saline formations (pressure 8 MPa, temperature 313 K, exposure time 30 days, and CO2-supersaturated seawater ≈0.80 Mol). Both exposed and non-exposed samples were characterised by means of Optical Microscopy, Scanning Electronic Microscopy, X-ray Diffraction and Digital Image Analysis. Furthermore, powdered samples were analysed chemically trough X-ray Fluorescence, and brine samples were subjected to chemical analysis.The petrographic study of adjacent sandstone samples before and after the exposure to CO2-rich brine indicates an increase in porosity (≈3 %). These changes in pore structure are the result of mineral dissolution (e.g., siliceous cement) and intergranular matrix detachment and its partial removal from the rock sample, representing the initial effects induced by the CO2-rich brine. The chemical analysis of the brine reveals an increase in Ca2+ and SiO2 composition (29 % and 6670 %, respectively). After marl exposure, the brine also exhibited increased Ca2+and SiO2 content (95 % and 11,250 %, respectively), indicating the prevalence of dissolution processes.These results suggest that in environments where CO2 enriches the brine the mixture primarily induces localized chemical adjustments in the rocks (evidenced by dissolutions in the brine). The proposed methodology can be adapted for similar experimental batch tests in other storage structures.

Doping Induced Enhancement of Activity and Stability for Oxygen Evolution Reaction with Isomaterially Heterostructured MnO2

A “Non-Native” phase (NNP) differs from the thermodynamically most stable bulk Native in its discrete translational symmetry. The relative difference in surface and bulk energy with respect to the native phase (NP)determines the stability of NNP. The isomaterial hetero-structured NP-NNP composite provides a pathway to assemble structures that have optimal properties of NNP and NP. The surface and sub-surface energies can also be modulated by doping as the dopants may segregate and stabilize grain boundaries. This study demonstrates that the isomaterial heterostructure of the NP, β-N MnO2, and Ramsdellite, r-NN1 MnO2, known as γ-N-NN1-MnO2 intergrowth, enhances the OER activity and stability.The hydrothermal route was used to synthesize isomaterial heterostructured γ/N-NN1-MnO2 with varying concentrations of dopants (10%, 15%, and 20% Ni and Co). X-ray diffraction was used to characterize the material, and after Rietveld refinement, phase quantification revealed that as the dopant concentration increased, the amount of the thermodynamically stable β-N MnO2 phase increased. Planes identified in XRD were also confirmed using high-resolution transmission electron microscopy (HRTEM) and the analysis of selective area electron diffraction (SAED) patterns. It appears that doping was successful based on the shifting of peaks in XRD and differences in unit cell volume and crystallite size calculated using the Debye-Scherrer equation before and after doping. With an increase in dopant concentration and thus improved OER activity, the average oxidation state as determined by X-ray photoelectron spectroscopy followed a downward trend, which is known to improve OER activity. The peaks shifted to lower frequency values as seen by Raman spectroscopy, which implies a weakening of Mn—O bond strength, indicating that dopants Ni and Co may have replaced part of the Mn atoms in the MnO2 intergrowth structure. Scanning electron microscopy (SEM) revealed spherical-shaped nanoparticles with spike-like overgrowths, which were further confirmed by HRTEM. The uniform dispersion of dopants was demonstrated by SEM and energy dispersive spectroscopy (EDS). Elemental quantification of the samples was done using EDS and scanning transmission electron microscopy (STEM). Using HRTEM, the presence of grain boundaries was confirmed.The study of dopants segregating to the grain boundary is conducted through DFT simulations. In many instances, the dopants actively contribute to the OER activity, except for the case of Ni in the NN1 sub-phase of the γ-N-NN1-MnO2 intergrowth, which is apparent by the slightly lower activity of Ni-doped samples compared to Co. This is because Ni remains in the bulk while Co segregates to the surface. A three-electrode setup (Ag/AgCl as the reference electrode, Pt mesh as the counter electrode, and catalyst as the working electrode) was used in 1M KOH to conduct electrochemical experiments. To achieve 10 mA/cm2, the 15% Co-doped electrocatalyst used the least amount of overpotential, 320 mV. According to electrochemical measurements and analysis, the doped samples show low Tafel slope, high specific activity, roughness factor, and charge transfer resistance from electrochemical impedance spectroscopy, all of which suggest improved overall activity for the oxygen evolution process (OER) for the doped over undoped samples. DFT simulations rationalize the enhancement of OER using the Bader charge analysis, the associated Gibbs free energy of the Sabatier principle plotted as the volcano plot.

CuO nanoparticles for enhanced photoelectrochemical HER activity

Cupric oxide nanoparticles are a p-type semiconductor that can be used as a hole transport layer material in perovskite solar cells owing to their high electrical conductivity and stability. In the present work, CuO nanoparticles are synthesized using the hydrothermal technique, and their photoelectrochemical properties are studied through cyclic voltammetry. The X-ray diffraction patterns of the nanoparticles were analyzed for phase formation, revealing the monoclinic phase and further verified by the Rietveld Refinement. Thermogravimetric analysis shows a total weight loss of 13.47%. Transmission electron microscopy analysis suggests the formation of nanoparticles with an average size of 34 nm. The selected area electron diffraction analysis reveals the crystalline structure of the nanoparticles. The absorbance spectra of the nanoparticles were analyzed by UV–visible measurement, and Tauc's relation was used to estimate the optical bandgap. The XPS results align with the XRD results, indicating the formation of pure CuO nanoparticles. The developed catalyst's photoelectrochemical performance was investigated in the neutral solution for the hydrogen evolution reaction activity, and a high photocurrent density of −41.57 mA/cm2 was observed versus −0.6 V vs. RHE.