Bright-field Scanning Transmission Electron Research Articles

On the shear strain associated with T1 precipitation in Al-Cu-Li(-Mg-Ag) alloys

The formation mechanism and the distribution arrangements of T1 precipitate plates in peak-aged samples of an Al-4Cu-1.2Li-0.3Mg-0.4Ag (wt.%) alloy are studied using atomic-resolution high-angle annular dark-field (HAADF) and annular bright-field (ABF) scanning transmission electron microscopy (STEM). The formation of a T1 plate of a single unit-cell thickness from the α-Al matrix is found to be associated with a large shear strain that is equivalent to the formation and glide of two different Shockley partial dislocations on two alternate {111}α planes. The T1 precipitate plates tend to cluster into various configurations, including T-shaped and V-shaped configurations comprising two plates of two different T1 variants, and X-shaped configurations consisting of three or four plates of two different variants. The signature of the shear strain is clearly visible in these configurations. A single T1 plate of one unit-cell thickness is elastically distorted in a T-shaped configuration, and the two T1 plates of the same variant in an X-shaped configuration are displaced with respect to each other. Different types of stair-rods are also formed in the intersection of the paired T1 plates in the V-shaped configurations.

A P2/P3 Biphasic Layered Oxide Composite as a High-Energy and Long-Cycle-Life Cathode for Potassium-Ion Batteries.

Layered transition metal oxides are extensively considered as appealing cathode candidates for potassium-ion batteries (PIBs) due to their abundant raw materials and low cost, but their further implementations are limited by slow dynamics and impoverished structural stability. Herein, a layered composite having a P2 and P3 symbiotic structure is designed and synthesized to realize PIBs with large energy density and long-term cycling stability. The unique intergrowth of P2 and P3 phases in the obtained layered oxide is plainly characterized by X-ray diffraction refinement, high-angle annular dark field and annular bright field-scanning transmission electron microscopy at atomic resolution, and Fourier transformation images. The synergistic effect of the two phases of this layered P2/P3 composite is well demonstrated in K+ intercalation/extraction process. The as-prepared layered composite can present a large discharge capacity with the remarkable energy density of 321 Wh kg-1 and also manifest excellent capacity preservation after 600 cycles of K+ uptake/removal.

Demonstration and STEM Analysis of Ferroelectric Switching in MOCVD‐Grown Single Crystalline Al0.85Sc0.15N

AbstractWurtzite‐type Al1−xScxN solid solutions grown by metal organic chemical vapor deposition are for the first time confirmed to be ferroelectric. The film with 230 nm thickness and x = 0.15 exhibits a coercive field of 5.5 MV cm−1 at a measurement frequency of 1.5 kHz. The single crystal quality and homogeneous chemical composition of the film are confirmed by X‐ray diffraction and spectroscopic methods such as time of flight secondary ion mass spectrometry. Annular bright field scanning transmission electron microscopy serves to prove the ferroelectric polarization inversion at the unit cell level. The single crystal quality further allows to image the large‐scale domain pattern of a wurtzite‐type ferroelectric for the first time, revealing a predominantly cone‐like domain shape along the c‐axis of the material. As in previous work, this again implies the presence of strong polarization discontinuities along this crystallographic axis, which can be suitable for current transport. The domains are separated by narrow domain walls, for which an upper thickness limit of 3 nm is deduced but which can potentially be atomically sharp. The authors are confident that these results will advance the commencement of the integration of wurtzite‐type ferroelectrics to GaN as well as generally III‐N‐based heterostructures and devices.

Composition-Tunable Properties of Cu(Ag) Alloy for Hybrid Bonding Applications

In the present study, the properties of Cu(Ag) alloy films were studied to evaluate their potential use as an alternate material for interconnection in hybrid bonding. Thin alloy films of Cu(Ag) were deposited by pulsed electrochemical deposition (PED) using a sulfuric acid-based bath, rotating disk electrode, and hot entry. Secondary ion mass spectrometry (SIMS) was used to measure the silver content of the films, with us finding that it decreases with increasing duty cycle. Thereafter, bright field scanning transmission electron microscope (STEM) imaging in combination with energy-dispersive x-ray spectroscopy (EDS) was used to visualize the thin film microstructure and to confirm the uniform distribution of silver throughout the film, with no bands being seen despite the pulsed nature of the deposition. Film resistance was measured by a four-point probe to quantify the impact of Ag content on resistivity, with us finding the expected linear relationship with the Ag content in the film. Furthermore, the coefficient of thermal expansion (CTE) of the films was measured using X-ray diffraction, and modulus and hardness were measured via nanoindentation, revealing linear dependences on the Ag content as well. Notably, the addition of 1.25 atom% Ag resulted in a significant increase in the CTE from 17.9 to 19.3 ppm/K, Young’s modulus from 111 to 161 GPa, and film hardness from 1.70 to 3.99 GPa. These simple relationships offer a range of properties tunable via the duty cycle of the pulsed plating, making Cu(Ag) a promising candidate for engineering wafer-to-wafer metal interconnections.

Experimental determination of critical thickness limitations of (010) β -(AlxGa1−x)2O3 heteroepitaxial films

The effect of heteroepitaxial β-(AlxGa1−x)2O3 film thickness and Al content on surface morphology was characterized to experimentally determine the critical thickness limitations of the (010) β-(AlxGa1−x)2O3/Ga2O3 heterostructure. High-resolution x-ray diffraction was used to assess the strain state of the films; reciprocal space mapping (RSM) revealed that even cracked films were still fully strained. In cracked films, diffuse scattering was observed in RSMs, indicating lattice tilting. Cracking of the films was investigated using atomic force microscopy (AFM), x-ray topography (XRT), bright-field scanning transmission electron microscopy (BF-STEM), and high-resolution transmission electron microscopy. Using both AFM and XRT, the [001] direction was observed to be the most prevalent crack direction; however, cracks were also observed in the [100] direction. In uncracked regions of the films, XRT revealed the alignment of threading dislocations along the [001] direction. Cross-sectional imaging of the crack geometry and propagation was performed using BF-STEM, and it was observed that the cracks in the [001] direction extended through the thickness of the β-(AlxGa1−x)2O3 film (∼205 nm) and a further ∼100–200 nm into the β-Ga2O3 substrate. Experimental data for critical film thickness showed good agreement with previous theoretical calculations based on the Griffith criterion for crack propagation.

Direct imaging of local atomic structures in zeolite using optimum bright-field scanning transmission electron microscopy.

Zeolites are used in industries as catalysts, ion exchangers, and molecular sieves because of their unique porous atomic structures. However, direct observation of zeolitic local atomic structures via electron microscopy is difficult owing to low electron irradiation resistance. Subsequently, their fundamental structure-property relationships remain unclear. A low-electron-dose imaging technique, optimum bright-field scanning transmission electron microscopy (OBF STEM), has recently been developed. It reconstructs images with a high signal-to-noise ratio and a dose efficiency approximately two orders of magnitude higher than that of conventional methods. Here, we performed low-dose atomic-resolution OBF STEM observations of two types of zeolite, effectively visualizing all atomic sites in their frameworks. In addition, we visualized the complex local atomic structure of the twin boundaries in a faujasite (FAU)-type zeolite and Na+ ions with low occupancy in eight-membered rings in a Na-Linde Type A (LTA) zeolite. The results of this study facilitate the characterization of local atomic structures in many electron beam-sensitive materials.

Unusual structural rearrangement and superconductivity in infinite layer cuprate superlattices

Epitaxial stabilization of thermodynamically metastable phases and advances in atomic control of complex oxide thin-film growth can be used effectively for realizing novel phenomena and as an alternative for bulk synthesis under extreme thermodynamic conditions. Here, we investigate infinite layer (IL) based cuprate superlattices, where 7--8 unit cells of ${\mathrm{Sr}}_{0.6}{\mathrm{Ca}}_{0.4}\mathrm{Cu}{\mathrm{O}}_{2}$ (SCCO) are sandwiched between ultrathin spacer layers of $\mathrm{SrTi}{\mathrm{O}}_{3}$ (STO), $\mathrm{SrRu}{\mathrm{O}}_{3}$, or $\mathrm{BaCu}{\mathrm{O}}_{2}$ (BCO) and only observe superconductivity in the pure [SCCO/BCO] superlattice (SL) without spacer layers. Apparently, the insertion of an additional STO spacer layer in the latter SL prevents the occurrence of superconductivity. The observed superconductivity in [SCCO/BCO] SL is discussed in terms of a structural model involving the interplay between the $\mathrm{Cu}{\mathrm{O}}_{2}$ plane and the CuO chain similar to the bulk $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ superconductor. The structural origin was found by the identification of a metastable IL-$\mathrm{BaCu}{\mathrm{O}}_{2}$ variant, which deviates highly from its parent bulk crystal structure and exhibits a relatively larger out-of-plane lattice parameter (around $7\phantom{\rule{0.16em}{0ex}}\AA{}$) when sandwiched with SCCO in the form of [SCCO/BCO] SL. However, this variant is absent when STO spacer layers are introduced between SCCO and BCO layers. X-ray absorption spectra of the Cu $L$ edge for BCO exhibits a slightly higher energy satellite peak as compared to the $3{d}^{9}L$ Zhang-Rice character observed in SCCO. This result indicates the existence of contrasting plane and chain-type Cu-O blocks in SCCO and BCO, respectively, which is further corroborated using annular bright field scanning transmission electron microscopy imaging. This work unravels an unexpected structure of BCO which helps in realizing superconductivity in [SCCO/BCO] SL and provides a wider perspective in the growth and design of cuprate-based hybrid structures.

PEI-Schiff base-modified mesoporous silica materials SBA-12, 15 and 16 for toxic metal ions capture (Co(II), Ni(II) and Cu(II)): Effect of morphology, post-synthetic modification and kinetic study

A series of SBA materials (SBA-12, SBA-15, and SBA-16) with polyethyleneimine (PEI) and its Schiff base variants with salicylaldehyde-modified samples (PS) have been successfully prepared and characterized. The synthesized materials were investigated by infrared spectroscopy (FT-IR), and quantification of the organic part coated on the surface was studied using thermogravimetric analysis (TGA). Nitrogen adsorption/desorption analysis at − 196 °C (N2), bright field scanning transmission electron microscopy (BF-STEM) and small angle X-ray scattering (SAXS) measurements were used to study textural properties, structure and morphology. Confirmation of heavy metal ions capture in pores of prepared materials was proved by X-ray fluorescence analysis (XRF), and nitrate anions were confirmed by FT-IR spectroscopy. Kinetic studies were performed by conductometric analysis (CA) and showed that the mathematical models could be applied to adsorption processes with a non-linear decreasing trend. This trend appeared in PS-modified SBA systems and some non-modified samples. The best overall adsorption properties were observed for material SBA-12 and its modified types. In this case, material SBA-12-PS can trap 54.38 mg g−1 of Cu(NO3)2 or 18.42 mg of Cu(II) ions, 112.84 mg g−1 of Ni(NO3)2 corresponding to 36.24 mg of Ni(II) cations, and 39.56 mg g−1 of Co(NO3)2 representing 12.74 mg of Co(II) ions. Non-modified materials show morphological effects where 2D ordered pores with hexagonal symmetry and the biggest mesopores (5.5 nm) have the best overall results in adsorption capacity of metal ions (Cu(II): 11.95 mg g−1) calculated from pseudo-second order. SBA-12 with a cubic framework and 3D ordered pores (3.8 nm) has a lower adsorption capacity than SBA-15 (Cu(II): 7.85 mg g−1), and SBA-16 with the smallest spherical pores (under 2 nm) showed the lowest overall adsorption capacity (Cu(II): 4.65 mg g−1). Kinetic rates of non-modified samples have opposite trend SBA-12 (Cu(II): 0.009 mg g−1 min−1) > SBA-15 (Cu(II): 0.002 mg g−1 min−1) > SBA-16 (Cu(II): 0.001 mg g−1 min−1). In the case of SBA-16, small pore entrances have a negative effect on the kinetic rate. For modified samples, SBA-12 with the largest surface area (896 m2 g−1) provides more space for binding of polyethyleneimine molecules (and also salicylaldehyde), which affects the best results in ion capture (Cu(II): 16.64 mg g−1). Bigger mesopores give more adsorption capacity, but capillarity makes the kinetic rate slow. SBA-16, with tiny entrance mesopores, has the lowest kinetic rate and adsorption capacity. This phenomenon was also observed in cobalt(II) adsorption, and similar results were obtained in nickel(II) adsorption. Kinetic studies point to two types of mechanisms given by the pseudo-second-order model in the case of non-modified materials, and Elovich kinetic model describes chemisorption at modified samples. These mechanisms are influenced by the significant effect of intraparticle diffusion, described by the Weber-Morris model.

Biogenic synthesis of noble metal nanoparticles using Melissa officinalis L. and Salvia officinalis L. extracts and evaluation of their biosafety potential

In this study we targeted the noble metal nanoparticles (MNPs) biogenic synthesis capacity of two medicinal species with therapeutic potential, namely Melissa officinalis L. (lemon balm) and Salvia officinalis L. (sage), cultivated in Romania. Plant material was extracted by maceration, microwave assisted extraction (MAE) and ultrasound assisted extraction (UAE). Bright field scanning transmission electron microscopy and energy dispersive X-ray spectroscopy (BFSTEM-EDS) techniques were used in order to investigate particles shape, dispersion and chemical elemental analysis. The total polyphenol content for both simple extracts and nanostructured mixtures was determined using the Folin-Ciocalteu method and antioxidant activity using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) method. Identification and quantification of secondary metabolites of M. officinalis and S. officinalis were performed by ultra-high performance liquid chromatography (UHPLC). The Allium assay was used to evaluate the potential cytogenotoxic activity, for both simple and nanostructured phytochemical complexes, in the case of S. officinalis L. species being performed for the first time. Spherical shaped MNPs with diameters of about 20 nm were biosynthesised in lemon balm extracts. Larger AuNPs were phytosynthesized in sage extract obtained by UAE. Compared to the simple extracts, the antioxidant capacity as well as the amount of total polyphenols in the nanostructured extracts decreased, substantiating the involvement of bioorganic material in the reduction of metal ions. Low frequency of chromosomal aberrations corresponding to crude extracts and extracts supplemented with MNPs, suggest the cytoprotective, antigenotoxic, and safe use of these plant species as potential therapeutic forms in various diseases.

Low-energy scanning transmission electron microscopy applied to ice-embedded biological macromolecules.

In this report, we applied annular bright-field and annular dark-field low-energy (30 keV) scanning transmission electron microscopy imaging to a vitreous ice-embedded biological macromolecule, T4 phage, to investigate the applicability of these methods for morphological investigation and sample screening. Multiple camera lengths were examined to find the optimal acceptance angle for both modes. Image clarity differed substantially between the modes, with the presence of ice also strongly influencing the quality of acquired micrographs. In annular dark-field mode, the proper discrimination of electrons scattered by the specimen from those scattered by the background ice was found to be difficult due to the severe overlap of the scattered electrons. The resulting micrographs lacked clarity, and the ice-embedded phage particles could only be discerned after post-processing image adjustment. However, in annular bright-field mode, despite similar overlapping of the scattered electrons, it was possible to assess the morphology and intactness of the specimen in the embedding ice, suggesting that this mode may find utility in low-energy cryo-scanning transmission electron microscopy imaging methods.

Large (anti)ferrodistortive NaNbO3-based lead-free relaxors: Polar nanoregions embedded in ordered oxygen octahedral tilt matrix

Relaxor ferroelectric perovskites have experienced a revival of interest in recent years accompanying the deeply exploration of the fine local structure of polar nanoregions, which are thought to be the structure root for unique electrical properties. Interestingly, a new type of low-tolerance relaxor ferroelectric, which exhibits both cation displacement and large oxygen octahedral tilt, exhibiting anomalous microdomains were found in NaNbO3-based lead-free perovskites, breaking through the limits of the relaxor ferroelectric models proposed from classical relaxors. Atomic-scale annular bright-field scanning transmission electron microscopy images indicate that the microdomains are formed by long-range ordered oxygen octahedral tilt. At the same time, substructure of randomly embedded nanoregions with inhomogeneous polarization vectors can be mapped, being the main reason for relaxor behavior. Based on this special ferroelectric-improper ferroelastic state, delayed polarization saturation can be obtained under strong electric field, providing an opportunity for generating excellent energy storage properties. The results found in this work not only open up a new kind of relaxor ferroelectrics but also will lead to the reconstruction of relaxor models and theories built for more than half a century.

Atomic-scale mapper for superlattice photodetectors analysis.

In this work, a new Python-based tool for atomic-scale mapping of high-angle annular dark-field (HAADF) and annular bright-field (ABF) scanning transmission electron microscopy (STEM) images using the Z-contrast method is introduced, aimed to help in the analysis of superlattice layers' composition, and in the determination of material of interfaces. The operation principle of the program, as well as specific examples of use, are explained in many details. Good customization flexibility using the user-friendly graphical user interface (GUI), allows the processing of a wide range of images, demonstrating a decent accuracy of coordinates extraction and performance.

Elevated barrier height originated from electric dipole effect and improved breakdown characteristics in PtOx/β-Ga2O3 Schottky barrier diodes

The higher Schottky barrier height of PtOx/β-Ga2O3 Schottky barrier diode (SBD) was derived from the electric dipole effect of PtOx Schottky electrode. And the higher Schottky barrier height effectively improved the reverse breakdown characteristics of β-Ga2O3 SBD. In this work, PtOx/β-Ga2O3 and Pt/β-Ga2O3 SBDs were fabricated, and the Schottky barrier height of PtOx SBD increased with the increment of oxygen element component in PtOx electrode, which were all higher than the Schottky barrier height of Pt SBD. Kelvin probe force microscope measurement indicated that Fermi level pinning effect and the variation in work functions of Schottky electrodes were irrelevant to the higher barrier height. Moreover, with the increment of inserting PtOx layer thickness in Pt/PtOx/β-Ga2O3 SBDs, the Schottky barrier height increased from 1.32 eV to 1.82 eV. Bright-field scanning transmission electron microscopy image demonstrated that PtOx was mainly polycrystal with layer structure near the Schottky interface. The layer structure composed of Pt ions and O ions induced electric dipole effect, and the electric dipole effect led to the increase of Schottky barrier height for PtOx SBD. Lower leakage current density, higher breakdown voltages and more concentrated breakdown voltage distribution were obtained for PtOx SBDs. Furthermore, the barrier heights of PtOx SBDs gradually increased as the temperature raised, resulting in their reverse leakage current increased much more slowly with temperature than that of Pt SBD. The above results demonstrated that PtOx/β-Ga2O3 SBD had great potential in enhancing reverse blocking characteristics and high-temperature environment applications.

Comparison of ion irradiation effects in PM-HIP and forged alloy 625

The nuclear industry has growing interest in replacing forgings with structural components fabricated by powder metallurgy with hot isostatic pressing (PM-HIP), owing to their chemical homogeneity, uniform grain structure, and near-net shape production. This study compares the ion irradiation response of PM-HIP and forged Alloy 625, over 50 and 100 dpa, 400 °C and 500 °C. Microstructure is characterized using down-zone bright-field scanning transmission electron microscopy (DZBFSTEM), and hardening is characterized using nanoindentation. PM-HIP Alloy 625 has a lower initial dislocation line density, resulting in a more rapid onset of dislocation loop growth and unfaulting than the forged material. But the total defect population (i.e. loop line length plus dislocation density) is insensitive to fabrication method. This finding shows promise for the eventual qualification of PM-HIP alloys for nuclear applications.

Determination of Dy substitution site in Nd2\u2212xDyxFe14B by HAADF-STEM and illustration of magnetic anisotropy of \u201cg\u201d and \u201cf\u201d sites, before and after substitution

Nd2Fe14B and Nd2−xDyxFe14B (x = 0.25, 0.50) particles were prepared by the modified co-precipitation followed by reduction–diffusion process. Bright field scanning transmission electron microscope (BF-STEM) image revealed the formation of Nd–Fe–B trigonal prisms in [− 101] viewing zone axis, confirming the formation of Nd2Fe14B/Nd2−xDyxFe14B. Accurate site for the Dy substitution in Nd2Fe14B crystal structure was determined as “f” site by using high-angle annular dark field scanning transmission electron microscope (HAADF-STEM). It was found that all the “g” sites are occupied by the Nd, meanwhile Dy occupied only the “f” site. Anti-ferromagnetic coupling at “f” site decreased the magnetic moment values for Nd1.75Dy0.25Fe14B (23.48 μB) and Nd1.5Dy0.5Fe14B (21.03 μB) as compared to Nd2Fe14B (25.50 μB). Reduction of magnetic moment increased the squareness ratio, coercivity and energy product. Analysis of magnetic anisotropy at constant magnetic field confirmed that “f” site substitution did not change the patterns of the anisotropy. Furthermore, magnetic moment of Nd2Fe14B, Nd2−xDyxFe14B, Nd (“f” site), Nd (“g” site) and Dy (“f” site) was recorded for all angles between 0° and 180°.

Robust Ruthenium Catalysts Supported on Mesoporous Cyclodextrin-Templated TiO2-SiO2 Mixed Oxides for the Hydrogenation of Levulinic Acid to γ-Valerolactone.

In this paper, we present a versatile template-directed colloidal self-assembly method for the fabrication in aqueous phase of composition-tuned mesoporous RuO2@TiO2-SiO2 catalysts. Randomly methylated β-cyclodextrin/Pluronic F127 supramolecular assemblies were used as soft templates, TiO2 colloids as building blocks, and tetraethyl orthosilicate as a silica source. Catalysts were characterized at different stages of their synthesis using dynamic light scattering, N2-adsorption analysis, powder X-ray diffraction, temperature programmed reduction, high-resolution transmission electron microscopy, high-angle annular bright-field and dark-field scanning transmission electron microscopy, together with EDS elemental mapping. Results revealed that both the supramolecular template and the silica loading had a strong impact on the pore characteristics and crystalline structure of the mixed oxides, as well as on the morphology of the RuO2 nanocrystals. Their catalytic performance was then evaluated in the aqueous phase hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) under mild conditions (50 °C, 50 bar H2). Results showed that the cyclodextrin-derived catalyst displayed almost quantitative LA conversion and 99% GVL yield in less than one hour. Moreover, this catalyst could be reused at least five times without loss of activity. This work offers an effective approach to the utilization of cyclodextrins for engineering the surface morphology of Ru nanocrystals and pore characteristics of TiO2-based materials for catalytic applications in hydrogenation reactions.

Epitaxy from a Periodic Y–O Monolayer: Growth of Single-Crystal Hexagonal YAlO3 Perovskite

The role of an atomic-layer thick periodic Y–O array in inducing the epitaxial growth of single-crystal hexagonal YAlO3 perovskite (H-YAP) films was studied using high-angle annular dark-field and annular bright-field scanning transmission electron microscopy in conjunction with a spherical aberration-corrected probe and in situ reflection high-energy electron diffraction. We observed the Y–O array at the interface of amorphous atomic layer deposition (ALD) sub-nano-laminated (snl) Al2O3/Y2O3 multilayers and GaAs(111)A, with the first film deposition being three cycles of ALD-Y2O3. This thin array was a seed layer for growing the H-YAP from the ALD snl multilayers with 900 °C rapid thermal annealing (RTA). The annealed film only contained H-YAP with an excellent crystallinity and an atomically sharp interface with the substrate. The initial Y–O array became the bottom layer of H-YAP, bonding with Ga, the top layer of GaAs. Using a similar ALD snl multilayer, but with the first film deposition of three ALD-Al2O3 cycles, there was no observation of a periodic atomic array at the interface. RTA of the sample to 900 °C resulted in a non-uniform film, mixing amorphous regions and island-like H-YAP domains. The results indicate that the epitaxial H-YAP was induced from the atomic-layer thick periodic Y–O array, rather than from GaAs(111)A.

Investigation on microstructure and mechanical properties of multiphase ZrSn1.5Alx alloy with simultaneous enhance of strength and plasticity

Abstract There are many means and mechanisms to strengthen alloys, but often at the cost of plasticity. Strength or plasticity? In practice, the two often appear as contradictory relationships. In the current work, the ZrSn1.5Alx (x = 6, 8, 10, 12, 14 at. %) alloy obtained by controlling the Al content was smelted and hot-rolled at 890 °C, and then immediately quenched to obtain an alloy containing α + β + AlZr3 multiphase structure. Compared with ZrSn1.5Al6 alloy, ZrSn1.5Al14 alloy reaches a high ultimate tensile strength (1080.84 MPa) and a large elongation at fracture (28.59%) at room temperature, an increase of 27.6% and 86.3%, respectively. The formation of AlZr3 particles pins dislocations, promotes cross-sliding of dislocations, and improves the dislocation nucleation rate by changing the dislocation sliding mode, which increases the dislocation density and promotes uniform plastic deformation, enhance the strain-hardening ability of the alloys, thereby improve its plasticity and strength simultaneously. Optical microscopy (OM) and scanning electron microscope (SEM) were used to observe the metallographic structure and tensile fracture morphology. The transmission electron microscope bright field (TEM-BF) image and scanning transmission electron microscope high-angle annular dark field (STEM-HAADF) image of the sample were observed for detailed analysis. The samples were taken in the rolling direction and the mechanical properties were evaluated by uniaxial tensile tests at room temperature. In summary, the machining process is simple, the cost is low, and it is suitable for large-scale industrial-grade applications. It may have reference significance to other alloy systems.

Enhanced hydrogen sorption properties of core-shell like structured Mg@NaBH4/MgB2 composite

To improve the hydrogen sorption properties of Mg, an arc plasma method with a vacuum vapor deposition technique was used to synthesize a core-shell like structured Mg@NaBH4 composite. Homogeneously distributed nanoscale NaBH4 particles can be observed on the surface of Mg matrix according to bright-field scanning transmission electron microscope (BF-STEM) and high-resolution transmission electron microscopy (HRTEM) techniques. A solid solution of Na in Mg might form according to the results of XRD and energy dispersive X-Ray analysis (EDX)-STEM technique. The hydrogenation activation energy (Ea = 60.1 kJ/mol H2) of the Mg in the composite and the onset dehydrogenation temperature for the hydrogenated composite measured from temperature programmed desorption (TPD) (245 °C) were lower than those of pure MgH2. The improvement can be ascribed to the core-shell like structure which induces more sufficient contacts between catalysts and Mg, thus providing more nucleation sites for hydrogen sorption. In addition, the formation of MgB2 and the substitution of Na atoms might support more grain boundaries and cause the changes of electronic structure of Mg/MgH2, which can significantly improve the hydrogen sorption properties of Mg. This study implies a novel structure design approach for development of future hydrogen absorption materials.

Identification of active slip mode in a hexagonal material by correlative scanning electron microscopy

Metals with a hexagonal close packed structure can deform by several different slip modes with different Critical Resolved Shear Stresses, which provides a great deal of complexity when considering mechanical performance of Mg, Ti and Zr alloys. Hence, an accurate but also statistically meaningful analysis of active slip systems and their contribution to plasticity is of great importance for the understanding of deformation mechanism. In the present study, a correlative scanning electron microscopy-based method of slip trace analysis has been utilised to provide statistical, accurate information of slip behaviour in a weakly textured Ti–6Al–4V alloy with a plastic strain of ∼2%. This is achieved through grain orientation mapping by Electron Backscatter Diffraction and strain mapping by High Resolution Digital Image Correlation. The initial identification of slip mode was performed by comparing the slip trace captured in the high-resolution effective shear strain map with all theoretical slip planes with an angle acceptance criterion of ±5°. Ambiguity in slip mode identification was further resolved using the Relative Displacement Ratio method, which enables the determination of the Burgers vector directly from the displacement data. The correctness of the identified slip modes has been confirmed by detailed dislocation analysis using Bright Field Scanning Transmission Electron Microscopy on thin foils extracted from specific grains employing Focused Ion Beam. This detailed investigation demonstrates the robustness of the slip trace analysis based on grain orientation and high-resolution strain mapping.