Dark-field Scanning Transmission Electron Microscopy Research Articles

A precipitation pathway of T1 phase via heterogeneous nucleation on Li-rich particle in Al-Cu-Li alloy

The hexagonal T1 (Al2CuLi) phase is the main strengthening precipitate in Al-Cu-Li alloys and is usually considered to be formed heterogeneously at dislocations during artificial aging. The precipitation scenario in Al-Cu-Li-Mg alloy has been revisited using high-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and in-situ heating inside TEM. Octahedral nano-complexes consisting of T1 precursors (T1p) on {111} facets of early-precipitated δ'(Al3Li) particles form at under-aging stage in the investigated alloy. This nano-complex with an average diameter of 5–10 nm is a transitional structure, which gradually dissolve to facilitate the transformation of a small portion of large precursors toward T1 precipitates. The T1p is determined to be isostructural to orthorhombic Ω phase based on atomic-resolution HAADF-STEM observations. The subsequent inward diffusion of Li is believed to promote the transition from Ω-like T1p to T1. An alternative precipitation path toward the key hardening T1 precipitate is thus proposed and could explain the formation of T1 precipitates apart from those at the dislocations. Our findings suggest complex multiple precipitation pathways for T1 phase should exist in Al-Cu-Li alloys.

Structural analysis of η14 phase and its forming mechanism in Al-Zn-Mg-Cu alloy

The structural characteristic and formation mechanism of a latest reported η14 phase formed in Al-Zn-Mg-Cu alloy were systematically studied by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). By detail structural analysis, the orientation relationship (OR) of the η14 and Al matrix is modified as: (112¯0)η14//(11¯2¯)Al, [1¯103]η14//[1¯11¯]Al and [1¯100]η14//[3¯1¯1¯]Al. Structural analysis demonstrated that the η14 phase displays the C14 Laves stacking structure, however, the Zn1 and Zn2 columns composed the R'-units are only half filled by Zn. This phenomenon is mainly due to the Zn1–2 columns composed the R'-units and Zn3 column composed the R-units formed with different processes, leading to uneven intensity among these columns for the η14 phase. The formation mechanism of the η14 phase does not shows any relevance with the faulted layers reported in previous work. In contrast, The η14 phase is suggested to evolved from a metastable η14’ phase with OR of (0001)η14’//(021¯)Al and [112¯0]η14’//[11¯2¯]Al, formed by regularly replacements of Zn and Mg at the (021¯)Al habit planes The special habit plane of η14’ phase contributes to the unusual OR of η14 phase with Al matrix. Our findings extend the understanding of the precipitates formation and evolution appearing in Al-Zn-Mg-Cu alloys.

The γ” Phase in Mg-RE-TM Alloys: A Review on the Structure and Stability of the γ” Phase and Its Effect on Mechanical Properties

In magnesium–rare earth–transition metal (Mg-RE-TM) alloys, the γ” phase (with a hexagonal structure with the space group P6¯2m) is a critical strengthening phase that can significantly improve their mechanical properties. However, compared to other phases in Mg-RE-TM alloys, research on the γ” phase is less documented, and an understanding of the γ” phase is not well established. As a result, different models of the structure of the γ” phase have been proposed. In this review, we summarize these structural models and find that the γ” phase is different from the Guinier–Preston (G.P.) zone, as revealed via Cs-corrected high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) and density functional theory (DFT) calculations. In addition, we briefly summarize the stability of the γ” phase and its effect on the mechanical properties of Mg-RE-TM alloys.

Site-occupation and structure relaxation behavior of C14-type stoichiometric and iron-rich Fe2Nb Laves phases with addition of aluminum or chromium

Powder X-ray diffraction Rietveld refinement for Al- or Cr-added stoichiometric and Fe-rich off-stoichiometric C14-type Fe2Nb Laves phases were examined to elucidate the site-occupation behavior of Al and Cr, and the resulting changes in the lattice parameters and the c/a axial ratio in the Fe2Nb Laves phases. In the case of the stoichiometric composition of the Fe2Nb Laves phase, no anti-site atoms were presented at the Fe and Nb both sites Al or Cr addition to the Fe-33.3at%Nb Laves phase by replacing Fe with Al or Cr did not generate anti-site Fe atoms, and Al and Cr preferentially occupied the Fe sites. Al and Cr atoms can replace Fe atoms at both the 6 h and 2a Fe sites in the case of Fe-rich alloy, and they also can occupy the Nb site (4f) by replacing anti-site Fe atoms. However, Al and Cr had no preferential occupation of any of these sites. The accuracy of Rietveld refinement was confirmed by observation through high-angle annular dark-field scanning transmission electron microscopy. The lattice parameters of the a and c axes increased almost linearly with increasing the added Al or Cr concentrations, but the c/a ratio showed different behavior. Therefore, the change in c/a cannot be explained solely in terms of the concentration of the added element; however, it is proposed that the change in c/a is interpreted by using parameters consistent with site-occupancy values.

A Comparative Study of Gallium-, Xenon-, and Helium-Focused Ion Beams for the Milling of GaN.

The milling profiles of single-crystal gallium nitride (GaN) when subjected to focused ion beams (FIBs) using gallium (Ga), xenon (Xe), and helium (He) ion sources were investigated. An experimental analysis via annular dark-field scanning transmission electron microscopy (ADF-STEM) and high-resolution transmission electron microscopy (HRTEM) revealed that Ga-FIB milling yields trenches with higher aspect ratios compared to Xe-FIB milling for the selected ion beam parameters (30 kV, 42 pA), while He-FIB induces local lattice disorder. Molecular dynamics (MD) simulations were employed to investigate the milling process, confirming that probe size critically influences trench aspect ratios. Interestingly, the MD simulations also showed that Xe-FIB generates higher aspect ratios than Ga-FIB with the same probe size, indicating that Xe-FIB could also be an effective option for nanoscale patterning. Atomic defects such as vacancies and interstitials in GaN from He-FIB milling were suggested by the MD simulations, supporting the lattice disorder observed via HRTEM. This combined experimental and simulation approach has enhanced our understanding of FIB milling dynamics and will benefit the fabrication of nanostructures via the FIB technique.

Unveiling fungal diversity in uranium and glycerol-2-phosphate-amended bentonite microcosms: Implications for radionuclide immobilization within the Deep Geological Repository system

Uranium (U) represents the preeminent hazardous radionuclide within the context of nuclear waste repositories. Indigenous microorganisms in bentonite can influence radionuclide speciation and migration in Deep Geological Repositories (DGRs) for nuclear waste storage. While bacterial communities in bentonite samples have been extensively studied, the impact of fungi has been somewhat overlooked. Here, we investigate the geomicrobiological processes in bentonite microcosms amended with uranyl nitrate and glycerol-2-phosphate (G2P) for six-month incubation. ITS sequencing revealed that the fungal community was mainly composed of Ascomycota (96.6 %). The presence of U in microcosms enriched specific fungal taxa, such as Penicillium and Fusarium, potentially associated with uranium immobilization mechanisms. Conversely, the amendment of U into G2P-suplemented samples exhibited minimal impact, resulting in a fungal community akin to the control group. Several fungal strains were isolated from bentonite microcosms to explore their potential in the U biomineralization, including Fusarium oxysporum, Aspergillus sp., Penicillium spp., among others. High Annular Angle Dark-Field Scanning Transmission Electron Microscopy (HAADF) analyses showed the capacity of F. oxysporum B1 to form U-phosphate mineral phases, likely mediated by phosphatase activity. Therefore, our study emphasizes the need to take into account indigenous bentonite fungi in the overall assessment of the impact of microbial processes in the immobilization of U within DGRs environments.

Study on the Microstructure of Mg-4Zn-4Sn-1Mn-xAl As-Cast Alloys.

In this study, the microstructure of the Mg-4Zn-4Sn-1Mn-xAl (x = 0, 0.3 wt.%, denoted as ZTM441 and ZTM441-0.3Al) as-cast alloys was investigated using scanning electron microscopy (SEM), focused-ion/electron-beam (FIB) micromachining, transmission electron microscopy (TEM), and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The analysis results revealed that the microstructure of the ZTM441 and ZTM441-0.3Al as-cast alloys both mainly consist of the α-Mg matrix, skeleton-shaped MgZn2 eutectic texture, block-shaped Mg2Sn, and Zn/Sn-rich nanoscale precipitate bands along the grain boundary and the interdendrite. Nanoscale α-Mn dispersoids formed in the grain in the ZTM441 alloy, while no α-Mn formed in the ZTM441-0.3Al alloy instead of nanoscale Al3Mn2 particles. In the ZTM441 as-cast alloy, part of the Zn element is dissolved into the α-Mn phase, and part of the Mn element is dissolved into the MgZn2 phase, but in the ZTM441-0.3Al alloy, there are no such characteristics of mutual solubility. Zn and Mn elements are easy to combine in ZTM441 as-cast alloy, while Al and Mn are easy to combine in ZTM441-0.3Al as-cast alloy. The Mg-Zn phases have not only MgZn2-type crystal structure but also Mg4Zn7- and Mg149Zn-type crystal structure in the ZTM441-0.3Al as-cast alloy. The addition of Al changes the combination of Mn and Zn, promotes the formation of Al3Mn2, and the growth of the grain.

Advanced approach of bulk (111) 3C-SiC epitaxial growth

3C-SiC films grown on (111) Si substrates exhibit poor crystal quality and experience wafer cracks and bowing preventing access to bulk growth. This work reports innovative Chemical Vapor Deposition (CVD) growth methodology on 4 in. Si substrates which allowed the growth of 230 mm thick layer of (111) 3C-SiC through the melting of the Si substrate in the CVD chamber and the adoption of the resulting free standing 3C-SiC for the growth of bulk (111) 3C-SiC layer under high N fluxes. From the molten KOH etching and subsequent SEM investigation it has been ascertained that with a N2 flux of 1600 sccm there is a significant reduction in the concentration of stacking faults (SFs) from (7.16 ± 0.04) × 103 cm−1 to (0.4 ± 0.3) × 103 cm−1. This reduction is consistent with the cross section m-PL response displaying steep and uniform increase in the intensity of the band-edge signal a factor 10 higher on the surface with respect to the equal (100) 3C-SiC grown thickness. Furthermore, the emission attributed to point defects is considerably lower in (111) 3C-SiC. From Scanning Transmission Electron Microscopy (STEM) investigation it appears evident how the typical mechanism valid in (100) growths consisting in the mutual closure of SFs coming from opposing {111} planes that give rise to Lomer and l-shaped dislocations is replaced by a different panorama of evolution. Indeed, it is shown how the SFs shred but do not interrupt each other during growth. Furthermore, dropping in the number of atomic planes composing SFs layers appears to be a key phenomenon leading to both the shrinkage of the number of SF atomic layers as well as to the SF self-closure. High Angle Annular Dark Field-Scanning Transmission Electron Microscopy (HAADF-STEM) attested how the crystal tends to smooth out the lattice mismatch until the SF is suppressed. Because of the foregoing, the mechanisms of evolution of the defects in (111) 3C-SiC revealed in this study, demonstrates how the growth parameters must be matched with the kinetics of the defects in order to endorse (111) 3C-SiC adoption in high performing devices.

Nucleation and evolution mechanism of precipitates during the initial aging stage in Al-Zn-Mg-Cu alloy

The evolution process and nucleation mechanism of the precipitates during the initial aging stage in Al-Zn-Mg-Cu alloy were studied using the combination of the Cs-corrected high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) and first-principles calculations. A new nucleation mode of η' phase with the thickness of 7 at. layers was found, which is parallel to {111}Al planes and consists of 5-layer transition structures and 2 transition layers at the interface. The precipitate is the initial aged η' phase with the simplest structure. Its interfaces are coherent with the Al matrix and meet the stacking periodicity, which is more stable than ordinary η' phases. Besides, the interfaces have a tendency to segregate heavy elements. The presence of segregating atoms enhances the interface interaction and makes it more stable. These two aspects improve the stability of the nano-scale 7-layer particle and maintain the aging strengthening effect of Al alloy.

Thermodynamic modelling for the long-period stacking ordered phase in Mg–Y–Al system: Construction and application

An adequate thermodynamic model is required for describing the long-period stacking ordered (LPSO) phase because previously developed models cannot account for the accurate atomic occupancy of the LPSO structure. In this study, atomic structures of the equilibrated 18R and 10H phases in Mg–Y–Al alloys were systematically investigated via atomic-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-TEM) and first-principles calculations. Three structures (α-type, β-type, and γ-type) with different numbers of Mg layers (one, two, and three, respectively) sandwiched between L12 structures were present in the 18R phase. Meanwhile, δ-type (without Mg layers), ε-type (with one Mg layer), and ζ-type (with two Mg layers) structures were detected in the 10H phase. The presence of the interstitial atoms in the L12 structure was confirmed by TEM and theoretical calculations. Based on the obtained results, a new thermodynamic model for the LPSO phase was constructed and successfully applied to establish the thermodynamic description of the Mg–Y–Al system. The CALPHAD-type calculation data obtained using the proposed thermodynamic description were in good agreement with the experimental results. The findings of this study can help elucidate the formation mechanism of LPSO phases and guide Mg–Y–Al alloy design.

CO rich syngas production from catalytic CO2 gasification-reforming of biomass components on Ni/CeO2

The advancement of biomass utilization technology is vital for addressing global climate change and the depletion of fossil resources. CO rich syngas production from the CO2 gasification-reforming of biomass components (cellulose, xylan, lignin, and starch) was investigated by a two-stage fixed bed reactor. The four biomass components were heated from room temperature to 600 °C in a CO2 atmosphere, among which lignin exhibited the highest residue fraction (51.6 wt.%) and the lowest gas yield (5.7 mmol gbiomass−1), whereas cellulose demonstrated the highest gas yield from CO2 gasification-reforming (14.6 mmol gbiomass−1). Nanorod CeO2 supported Ni catalysts were used to enhance volatile (tar) CO2 reforming reactions, and the gas yield increased by 104.3 % for cellulose, 103.3 % for xylan, 149.3 % for lignin, and 128.3 % for starch compared with noncatalytic CO2 gasification-reforming. Furthermore, the structure of fresh and used catalysts were characterized by X-ray diffraction (XRD), N2 adsorption/desorption isotherm, scanning electron microscope (SEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), H2-temperature programmed reduction (H2-TPR), and thermogravimetry (TGA). For the CO2 gasification-reforming of cellulose, the optimum CO yield of 27.6 mmol gbiomass−1 was achieved at a gasification/reforming temperature of 600/700 °C and a biomass/catalyst ratio of 6.25 using 2 %Ni/CeO2 catalyst. The stability tests of catalysts showed an approximately linear decrease in CO yield with the increase of the number of cycles, and catalyst deactivation resulted from Ni sintering and coke deposition.

Unexpected sluggish martensitic transformation in a strong and super-ductile high-entropy alloy of ultralow stacking fault energy

Displacive martensitic transformation usually prevails in face-centered cubic (FCC) steels and high-entropy alloys (HEAs) of low stacking fault energy (SFE; e.g., <15 mJ/m2) upon deformation. Here, we present and rationalize an unexpectedly sluggish and suppressed martensitic transformation behavior in a newly developed non-equiatomic HEA (Fe30Ni20Co20Cr20Si10, at.%) with an ultralow SFE, i.e., ∼7 mJ/m2 measured by weak-beam dark-field scanning transmission electron microscopy (STEM) at room temperature. The recrystallized FCC HEA with an average grain size of ∼14.9 µm shows an ultimate tensile strength of 903 MPa and a fracture elongation of ∼83.1 %. Plastic deformation of this alloy with ultralow SFE is characterized by the intensive formation of stacking faults (SFs), whereas the volume fraction of hexagonal close-packed (HCP) martensite is very low even at cold-rolled state with an equivalent strain of 1.85, i.e., < 8.3 % according to neutron diffraction analysis. Atomic-scale TEM observation demonstrates that chemical short-range order (CSRO) domains are present in the FCC solid solution. Apart from contributing to the high strength, the CSRO domains and atomic size misfit (2.36 %) promoted by the high content of Si are regarded to enhance the local barrier for the successive accumulation of SFs, hindering the formation of HCP martensite and mechanical twin. The uniform formation of SFs in the FCC matrix upon deformation effectively alleviates strain localization, contributing to the sustained strain-hardening ability and super-ductility. These insights suggest a strategy to design low-SFE alloys with excellent mechanical properties via manipulating the rate of martensitic transformation by CSROs and atomic size misfit.

Degraded creep resistance induced by static precipitation strengthening in high-pressure die casting Mg–Al–Sm alloy

Relationship between precipitation strengthening and creep resistance improvement has been an important topic for the widespread applications of magnesium alloys. Generally, static precipitation strengthening through thermal stable precipitates would generate satisfactory creep resistance. However, an opposite example is presented in this work and we propose that the size of precipitates plays a crucial role in controlling the operative creep mechanisms. In addition, the precipitate components along with their crystal structures in the crept Mg–4Al–3Sm–0.4Mn samples with/without pre-aging were thoroughly studied using Cs aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Previous aging generates a large density of fine precipitates (< ∼5 nm) homogeneously distributing in Mg matrix and exhibiting satisfactory strengthening effect. However, the number density of precipitate strings consisting of several or even dozens of relatively coarse precipitates (∼10 nm) was significantly decreased at the same time. As revealed in this work, the relatively coarse particles in Mg matrix are much more efficient than the fine precipitates in promoting dislocation climb. Therefore, the rate-controlling mechanisms are transferred from dislocation climb to dislocation slip after previous aging, thus leading to degradation of creep resistance. Moreover, there are mainly five types of precipitates/clusters, namely β″-(Al, Mg)3Sm, Al5Sm3, ordered Al–Sm cluster, ordered Al–Mn cluster and ordered/unordered AlMnSm clusters. The crystal structures of the former two precipitates were discussed and the formation mechanisms of the precipitates/clusters were revealed.

Principle on Selecting the Coordination Ligands of Palladium Precursors Encapsulated by Zeolite for an Efficient Purification of Formaldehyde at Ambient Temperature.

High-performance zeolite-supported noble metal catalysts with low loading and high dispersion of active components are the most promising materials for achieving the complete oxidation of formaldehyde (HCHO) at room temperature. In this work, palladium nanoparticles (Pd NPs) with different sizes were successfully encapsulated inside the silicalite-1 (S-1) zeolite framework by using diverse stabling ligands via the one-pot method. Thereafter, the rule on selecting the coordinative ligands for palladium was clarified: more N atoms, a short carbon chain, a smaller branch chain, and bidentate coordination are characteristics of an ideal ligand. Accordingly, the best-performing 0.2Pd@S-1(Ethylenediamine) catalyst exhibited outstanding performance for HCHO oxidation, achieving 100% conversion even at room temperature. High-resolution high-angle annular dark-field scanning transmission electron microscopy (HR HAADF-STEM) and density functional theory (DFT) calculations indicate that the chelate is formed by complexation of Pd2+ ions with ethylenediamine, displaying the smallest spatial site resistance simultaneously with the zeolite synthesis, resulting in Pd located mostly within the 5-membered ring (5-MR) channels of S-1 after calcination, thus limiting the growth of Pd clusters and promoting their dispersion.

Atomic-scale investigation of precipitate phases in QE22 Mg alloy

Precipitation-hardenable commercial Mg alloy QE22 (Mg-2.5Ag-2.0Nd-0.7Zr, wt.%) has excellent mechanical properties, but precipitates in this alloy have not been well understood. In this work, precipitate phases γ'', γ, and δ formed during the isothermal ageing process at 150, 200, 250, and 300 °C have been characterized using atomic-resolution high-angle annular dark-field scanning transmission electron microscopy and atomic-scale energy-dispersive X-ray spectroscopy. The morphology, crystal structure, and orientation relationship of these precipitate phases have been determined. Domain boundaries usually exist in a single γ particle, which can be characterized by a separation vector of [11¯01]α. The δ phase forms in situ from its precursor γ phase, consequently leading to the formation of three different variants within a single δ particle. The nucleation of the δ phase is strongly related to the domain boundaries of the γ phase. The formation of the γ phase may be promoted by its precursor γ'' phase. The similarities in atomic structures of the γ'', γ, and δ phases are described and discussed, indicating that transformations between these precipitate phases can be accomplished through the diffusion of added alloying elements.

Atomically dispersed copper-nickel electrocatalyst for highly selective electroreduction of CO2 at a wide potential range

Designing and synthesising electrocatalysts with low overpotential, high activity, selectivity, and stability for the CO2 reduction reaction (CO2RR) is crucial for addressing environmental challenges and realising the artificial carbon cycle. In this study, we successfully synthesised a nitrogen-doped carbon-supported diatomic electrocatalyst comprising atomically dispersed CuN4 and NiN4 bimetallic centers. This was confirmed through extensive characterisation using high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption spectroscopy techniques. The as-synthesised CBN-CuNi electrocatalyst exhibited exceptional selectivity and stability in CO2RR. Over a wide potential range from − 0.60 to − 1.10 V vs RHE, CBN-CuNi maintained over 90% Faraday efficiency for CO (FECO) production. Notably, at − 0.9 V vs RHE, it achieved a remarkable selectivity with a maximum FECO of 97.9%, surpassing single metal catalysts, including CBN-Ni and CBN-Cu. Furthermore, CBN-CuNi demonstrated outstanding stability, sustaining over 90% FECO production for 40 h of continuous electrolysis, surpassing many existing electrocatalysts. These findings highlight the potential of the as-synthesised bimetallic electrocatalyst CBN-CuNi in the electrochemical reduction of CO2 to CO, contributing to advancing the artificial carbon cycle and addressing environmental concerns.

Nonmetallic-Bonding Fe-Mn Diatomic Pairs Anchored on Hollow Carbonaceous Nanodisks for High-Performance Li-S Battery.

The issues of polysulfide shuttling and lethargic sulfur redox reaction (SROR) kinetics are the toughest obstacles of lithium-sulfur (Li-S) battery. Herein, integrating the merits of increased density of metal sites and synergistic catalytic effect, a unique single-atom catalyst (SAC) with nonmetallic-bonding Fe-Mn diatomic pairs anchored on hollow nitrogen-doped carbonaceous nanodisk (denoted as FeMnDA@NC) is successfully constructed and well characterized by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy, X-ray absorption spectroscopy, etc. Density functional theory calculation indicates that the Fe-Mn diatomic pairs can effectively inhibit the shuttle effect by enhancing the adsorption ability retarding the polysulfide migration and accelerate the SROR kinetics. As a result, the Li-S battery assembled with FeMnDA@NC modified separator possesses an excellent electrochemical performance with ultrahigh specific capacities of 1419 mAh g-1 at 0.1 C and 885 mAh g-1 at 3.0 C, respectively. An outstanding specific capacity of 1165 mAh g-1 is achieved at 1.0 C and maintains at 731 mAh g-1 after 700 cycles. Notably, the assembled Li-S battery with a high sulfur loading of 5.35mg cm-2 harvests a practical areal capacity of 5.70 mAh cm-2 at 0.2 C. A new perspective is offered here to construct advanced SACs suitable for the Li-S battery.

Microstructural evolution of Mg–14Gd–0.4Zr alloy during compressive creep

The present work reports the creep behavior and microstructural evolution of the sand-cast Mg–14Gd–0.4Zr alloy (wt.%) prepared by the differential pressure casting machine. Their compressive creep tests at 250 °C were performed under various applied stresses (i.e., 60, 80 and 100 MPa). Among them, the sand-cast Mg–14Gd–0.4Zr samples examined under 250 °C/80 MPa for 39 and 95 h, respectively, were chosen to systemically analyze their creep mechanisms using high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM). The obtained results showed that the enhancement of creep resistance can be mainly attributed to the coherent β' and β'F phases with an alternate distribution, effectively impeding the basal <a> dislocations movement. However, with the creep time increasing, the fine β'+β'F precipitate chains coarsened and transformed to semi-coherent β1 phase and even to large incoherent β phase (surrounded by precipitate-free areas) in grain interiors. The precipitate-free zones (PFZs) at grain boundaries (GBs) were formed, and they could expand during creep deformation. Apart from the main cross-slip of basal and prismatic <a> dislocations, <c + a> type dislocations were activated and tended to distribute near the GBs. The aforementioned phenomena induced the stress concentrations, consequently leading to the increment of the creep strain.

Microstructural role of TiB addition in modifying ZnAl alloy

The microstructural role of TiB addition in modifying a Zn-Al eutectoid (ZA27) alloy was investigated using scanning electron microscopy, high-angle annular dark-field scanning transmission electron microscopy, and energy X-ray spectroscopy. A series of Zn-27Al-2Cu-0.02Mg-x(Ti+B) (x=0, 0.01, 0.02, 0.05, 0.10, 0.20, wt.%) alloys were cast. The results show that the hardness and strength of the ZA27 alloy are improved with increasing (Ti+B) content, and peak at a (Ti+B) content of 0.05 wt.%. The TiB modifier refines the primary α(Al) phase grains and changes the microstructure of coralloid (α(Al)+η-Zn) eutectoid, which is responsible for the increased mechanical properties of the ZA27 alloy. The modified eutectoid demonstrates featured basket-like and strip-like eutectoid microstructures. The refinement of the primary α(Al) phase grains is very likely related to the constitutional supercooling caused by the segregation of B at the solid-liquid interface. Participation of B and/or Ti in the eutectic and eutectoid reactions modifies the morphology of the eutectoid microstructure.

Transmission Electron Microscopy Peeled Surface Defect of Perovskite Quantum Dots to Improve Crystal Structure.

Transmission electron microscopy (TEM) is an excellent characterization method to analyze the size, morphology, crystalline state, and microstructure of perovskite quantum dots (PeQDs). Nevertheless, the electron beam of TEM as an illumination source provides high energy, which causes morphological variation (fusion and melting) and recession of the crystalline structure in low radiolysis tolerance specimens. Hence, a novel and facile strategy is proposed: electron beam peel [PbBr6]4- octahedron defects from the surface of QDs to optimize the crystal structure. TEM and high-angle annular dark-field scanning TEM (HAADF) tests indicate that the [PbBr6]4- octahedron would be peeled from the surface of QDs when QDs samples were irradiated under high-power irradiation, and then a clear image would be obtained. To avoid interference from a protective film of "carbon deposits" on the surface of the sample when using high resolution TEM, amorphous carbon film (15-20 nm) was deposited on the surface of QDs film and then characterized by TEM and HAADF. The detection consequences showed that the defection of PbBr2 on the surface of QDs will gradually disappear with the extension of radiation time, which further verifies the conjecture.