TEM Observations Research Articles

Compressive creep behavior of selective electron beam melted high Nb containing TiAl alloy

In this study, the compressive creep behavior of Ti–45Al–8Nb alloy fabricated by selective electron beam melting technology at 800 °C and 850 °C was investigated. This alloy is mainly composed of equiaxed γ grains, and minor α2 and B2 grains. Creep results show that compressive creep behavior of this alloy is dependent on temperature, which is manifested in the significant increase of creep strain and creep rate with the increase of temperature. Through a multi-step creep test, the stress exponent n (2.65 at 800 °C and 3.65 at 850 °C) and activation volume V* (36.49 b3 at 800 °C and 53.51 b3 at 850 °C) were measured. Combined with kinetic analysis based on n and V* and TEM observation, compressive creep deformation of this alloy at 800 °C and 850 °C is dominated by dislocation motion, including dislocation slip and climb. Additionally, mechanical twinning also plays an important role in creep deformation. Driven by dislocation pile-ups or mechanical twins, discontinuous dynamic recrystallization (DDRX) occurs during creep. The degree of DDRX at 850 °C is greater. Sufficient DDRX greatly softens the alloy and accelerates creep rate, resulting in no steady-state creep stage at 850 °C.

Effect of a novel controlled thermomechanical treatment on the microstructure and mechanical properties of a high-carbon nanobainitic steel

The effect of the novel controlled thermomechanical treatment, including torsion components in the elastic strain range during the isothermal holding on the microstructure and mechanical properties of the high-carbon nanobainitic steel, was investigated. TEM observations of the thermo-mechanically treated steel revealed bainitic ferrite laths with an average size of 68 ± 40 nm and films of retained austenite with an average size of 34 ± 17 nm, along with the blocky morphology of retained austenite in sub-micron scale. The XRD synchrotron diffraction allows estimating the amount of retained austenite at 43.1 ± 1.2% volume fraction with a carbon concentration of 1.17 ± 0.09 wt.%. Furthermore, the deconvolution of (200) Fe-γ reflections corresponding to two different low-carbon and high-carbon retained austenite peaks and, simultaneously, the blocky and film-like retained austenite was performed. In addition, the Nishiyama–Wassermann (N–W) crystallographic orientation relationship between bainitic ferrite and retained austenite was described as dominant using the misorientation distribution function (MDF). The crystallographic texture results indicated that the main growth of bainitic ferrite plates occurred after removing external stress during isothermal holding. The tensile tests and hardness measurements showed a high tensile strength achieved mainly by nano-metric bainitic ferrite plates and a high dislocation density. The high level of elongation is most likely attained due to a high amount of retained austenite in steel and both TRIP and TWIP effects during tensile deformation.

In situ TEM observation of the (De)potassiation process of α-MnO2 nanowires

Based on lithium-ion batteries (LIBs), a new type of electrochemical device known as potassium-ion batteries was developed. Potassium-ion batteries potentially offer several key benefits over LIBs in Non-aqueous and several electrode materials, including steady discharge, high rate performance, cheap cost and lower charge density. Therefore, Potassium-ion batteries (PIBs) are highly likely to become the best candidate for low-cost, long-life batteries in the future, and are expected to extensively be employed in a variety of industries, including mobile devices and new energy vehicles. In recent years, research on the electrochemistry of potassium-ion batteries is still in its initial stage. Here, we use in situ transmission electron microscopy to observe the irreversible volume expansion of α-MnO2 nanowire during potassiation and depotassiation. During the first potassiation, the single crystalline α-MnO2 nanowire transformed to K1.33Mn8O16, causing a volume expansion of 35.6 %, which was unable to recover during the depotasiation process. The irreversible volume expansion suggests that most potassium ions inserted into the α-MnO2 nanowire cannot be extracted during the depotassiation process, which leads to low Coulombic efficiency in the first cycle. The cycle performance and Coulombic efficiency of α-MnO2 maybe still limited by insufficient electronic conductivity. Composite Au on the surface of α-MnO2 maybe improves its electronic conductivity. The α-MnO2 on Au (α-MnO2/Au) nanowires’ irreversible and cycle performance was better than pristine materials by the first principle calculations. Traditionally the first cycle capacity loss is attributed to the formation of the solid electrolyte interface (SEI). This research provides a new approach of the first cycle capacity loss mechanism in potassiation of α-MnO2 cathode. Also, the α-MnO2/Au improves the cycle performance and Coulombic efficiency of the K-(α-MnO2) nanobattery.

Harvesting visible light for enhanced catalytic degradation of wastewater using TiO2@Fe3O4 embedded on two dimensional reduced graphene oxide nanosheets

Carbon-integrated binary metal oxide semiconductors have gained prominence in the last decade as a better material for photocatalytic wastewater treatment technology. In this regard, this research describes the investigation of the binary metal oxide TiO2@Fe3O4 embedded on reduced graphene oxide (rGO) nanosheets synthesized through a combination of sol-gel, chemical precipitation, and Hummer's processes. Besides, the catalyst is applied for the photocatalytic degradation of organic chlorophenol pollutants. The characterized diffraction results showed the peak broadening of the rGO-TiO2@Fe3O4 composite formed with tetragonal and cubic structures having small crystallite sizes. The TEM observation shows an enormous miniature of TiO2@Fe3O4 nanospheres spread on the folded 2D-rGO nanosheets with a large BET surface area. The XPS result holds the mixed phases of Fe3O4 and Fe2O3. Finally, the catalyst demonstrated a low band gap with extended light absorption towards visible light irradiation. The synergistic interactions between Fe3+ and Fe2+ improved the visible light activity due to the incorporation of rGO, and also possessed good recycling capacity. The increased mobility of electrons at the interfaces of TiO2 and Fe3O4 due to the mixing of rGO results in the separation of charge carriers by elevating the photocatalytic degradation efficiency of chlorophenol.

Precision drug design against Acidovorax oryzae: leveraging bioinformatics to combat rice brown stripe disease.

Bacterial brown stripe disease caused by Acidovorax oryzae is a major threat to crop yields, and the current reliance on pesticides for control is unsustainable due to environmental pollution and resistance. To address this, bacterial-based ligands have been explored as a potential treatment solution. In this study, we developed a protein-protein interaction (PPI) network for A. oryzae by utilizing shared differentially expressed genes (DEGs) and the STRING database. Using a maximal clique centrality (MCC) approach through CytoHubba and Network Analyzer, we identified hub genes within the PPI network. We then analyzed the genomic data of the top 10 proteins, and further narrowed them down to 2 proteins by utilizing betweenness, closeness, degree, and eigenvector studies. Finally, we used molecular docking to screen 100 compounds against the final two proteins (guaA and metG), and Enfumafungin was selected as a potential treatment for bacterial resistance caused by A. oryzae based on their binding affinity and interaction energy. Our approach demonstrates the potential of utilizing bioinformatics and molecular docking to identify novel drug candidates for precision treatment of bacterial brown stripe disease caused by A. oryzae, paving the way for more targeted and sustainable control strategies. The efficacy of Enfumafungin in inhibiting the growth of A. oryzae strain RS-1 was investigated through both computational and wet lab methods. The models of the protein were built using the Swiss model, and their accuracy was confirmed via a Ramachandran plot. Additionally, Enfumafungin demonstrated potent inhibitory action against the bacterial strain, with an MIC of 100 µg/mL, reducing OD600 values by up to 91%. The effectiveness of Enfumafungin was further evidenced through agar well diffusion assays, which exhibited the highest zone of inhibition at 1.42cm when the concentration of Enfumafungin was at 100 µg/mL. Moreover, Enfumafungin was also able to effectively reduce the biofilm of A. oryzae RS-1 in a concentration-dependent manner. The swarming motility of A. oryzae RS-1 was also found to be significantly inhibited by Enfumafungin. Further validation through TEM observation revealed that bacterial cells exposed to Enfumafungin displayed mostly red fluorescence, indicating destruction of the bacterial cell membrane.

Influence of B addition on the Mo diffusion-controlled eutectic dissolution process during homogenization of super austenitic stainless steel S31254

The influence of B addition on dissolution behavior of (σ + γ)e eutectics of a 6Mo super austenitic stainless steel S31254 during the homogenization process was investigated by SEM-BSE observations combined with EDS. The results showed that the addition of 0.005 wt% B accelerated the dissolution of the σ phase controlled by Mo diffusion, during homogenization from 30 to 90 min at 1180 °C. TOF-SIMS results showed that B segregated along the σ/γ interface in the as-cast samples. TEM observations combined with EDS investigated the phase interfaces in two as-cast samples in detail to correlate σ phase dissolution. Compared with the B-free sample, the wide transition zone (∼60 nm) with a composition gradient was more clearly observed at the σ/γ interface in the B-containing sample. The transition zone with B had two features: local segregation of B element and precipitation of R phases at the σ/γ interface. R phases owned larger contents of Mo, which was not almost observed in the as-cast S31254. The results indicated that B segregation changed the phase interface, accelerating Mo diffusion at the σ/γ interface. In addition, the results of nanoindentation indicated a more uniform distribution of hardness at the σ/γ interface after homogenization of the B-containing sample, which can be beneficial to improve the deformation compatibility of S31254 during hot working.

Expression of clMagR/clCry4 protein in mBMSCs provides T2-contrast enhancement of MRI

Here, we propose for the first time the evaluation of magnetosensitive clMagR/clCry4 as a magnetic resonance imaging (MRI) reporter gene that imparts sensitivity to endogenous contrast in eukaryotic organisms. Using a lentiviral vector, we introduced clMagR/clCry4 into C57BL/6 mice-derived bone marrow mesenchymal stem cells (mBMSCs), which could specifically bind with iron, significantly affected MRI transverse relaxation, and generated readily detectable contrast without adverse effects in vivo. Specifically, clMagR/clCry4 makes mBMSCs beneficial for enhancing the sensitivity of MRI-R2 for iron-bearing granules, in which cells recruit exogenous iron and convert these stores into an MRI-detectable contrast; this is not achievable with control cells. Additionally, Prussian blue staining was performed together with ultrathin cell slices to provide direct evidence of natural iron-bearing granules being detectable on MRI. Hence, it was inferred that the sensitivity of MRI detection should be correlated with clMagR/clCry4 and exogenous iron. Taken together, the clMagR/clCry4 has great potential as an MRI reporter gene. Statement of significanceIn this study, we propose the evaluation of magnetosensitive clMagR/clCry4 as an MRI reporter gene, imparting detection sensitivity to eukaryotic mBMSCs for endogenous contrast. At this point, the clMagR and clCry4 were located within the cytoplasm and possibly influence each other. The clMagR/clCry4 makes mBMSCs beneficial for enhancing the sensitivity of MRI-R2 for iron-bearing granules, in which protein could specifically bind with iron and convert these stores into MRI-detectable contrast; this is not achieved by control cells. The viewpoint was speculated that the clMagR/clCry4 and exogenous iron were complementary to each other. Additionally, Prussian blue staining was performed together with TEM observations to provide direct evidence that the iron-bearing granules were sensitive to MRI.

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.

Antibacterial activities of coumarin-3-carboxylic acid against Acidovorax citrulli.

Coumarin-3-carboxylic acid (3-CCA), previously screened from natural coumarins, was found to possess strong antibacterial activity against Acidovorax citrulli (Ac). In order to further evaluate the activity of this compound against plant bacterial pathogens and explore its potential value as a bactericidal lead compound, the activity of 3-CCA against 14 plant pathogenic bacteria in vitro and in vivo was tested. Results showed that 3-CCA exhibited strong in vitro activities against Ac, Ralstonia solanacearum, Xanthomonas axonopodis pv. manihotis, X. oryzae pv. oryzae, and Dickeya zeae with EC50 values ranging from 26.64 μg/mL to 40.73 μg/mL. Pot experiment results showed that 3-CCA had powerful protective and curative effects against Ac. In addition, the protective efficiency of 3-CCA was almost equivalent to that of thiodiazole copper at the same concentration. The results of SEM and TEM observation and conductivity tests showed that 3-CCA disrupted the integrity of the cell membrane and inhibited polar flagella growth. Furthermore, 3-CCA resulted in reductions in motility and extracellular exopolysaccharide (EPS) production of Ac while inhibiting the biofilm formation of Ac. These findings indicate that 3-CCA could be a promising natural lead compound against plant bacterial pathogens to explore novel antibacterial agents.

In situ TEM observations and molecular dynamics simulations of deformation defect activities in Mg via nanoindentation

In this work, we performed in situ nanoindentation in TEM to capture the real-time 〈c + a〉 dislocation and twinning activities in pure Mg during loading and unloading. We demonstrated that the screw component of 〈c + a〉 dislocations glides continuously, while the edge components rapidly become sessile during loading. The twin tip propagation is intermittent, whereas the twin boundary migration is more continuous. During unloading, we observed the elastic strain relaxation causes both 〈c + a〉 dislocation retraction and detwinning. Moreover, we note that the plastic zone comprised of 〈c + a〉 dislocations in Mg is well-defined, which contrasts with the diffused plastic zones observed in face-centered cubic metals under the nanoindentation impressions. Additionally, molecular dynamics simulations were performed to study the formation and evolution of deformation-induced crystallographic defects at the early stages of indentation. We observed that, in addition to 〈a〉 dislocations, the I1 stacking fault bounded with a 〈1/2c+p〉 Frank loop can be generated from the plastic zone ahead of the indenter, and potentially serve as a nucleation source for abundant 〈c + a〉 dislocations observed experimentally. These new findings are anticipated to provide new knowledge on the deformation mechanisms of Mg, which are difficult to obtain through conventional ex situ approaches. These observations may serve as a baseline for simulation work that investigate the dynamics of 〈c + a〉 dislocation slip and twinning in Mg and alloys.

Deformation behavior and bending strength of single crystal 8 mol% yttria-stabilized zirconia at microscopic scale

Yield phenomena and bending strength of single crystal 8YSZ were evaluated using microcantilever beam specimens with various crystal orientations. Nonlinearity due to plastic deformation was observed in the stress-strain curves, and the yield stress was found to depend on the crystal orientation. TEM observation revealed many areas of disordered lattice in the region where the maximum tensile stress occurred. Resolved shear stress (RSS) was analyzed for the primary {001}<110> and the secondary {110} <11̅0> and {111} <11̅0> slip systems as a function of the angle between the specimen’s longitudinal direction and the [001] orientation, indicating that the RSS for the secondary ones was the critical RSS in the angle at 10° or lower while that for the primary one did so at 20° or higher. The measured bending strength, which depended on the crystal orientation, was lower than, but on the same order of magnitude as, the ideal strength.

Multifilamentary switching of Cu/SiOx memristive devices with a Ge-implanted a-Si underlayer for analog synaptic devices

Various memristive devices have been proposed for use in neuromorphic computing systems as artificial synapses. Analog synaptic devices with linear conductance updates during training are efficiently essential to train neural networks. Although many different analog memristors have been proposed, a more reliable approach to implement analog synaptic devices is needed. In this study, we propose the memristor of a Cu/SiOx/implanted a-SiGex/p++ c-Si structure containing an a-Si layer with properly controlled conductance through Ge implantation. The a-SiGex layer plays a multifunctional role in device operation by limiting the current overshoot, confining the heat generated during operation and preventing the silicide formation reaction between the active metal (Cu) and the Si bottom electrode. Thus, the a-SiGex interface layer enables the formation of multi-weak filaments and induces analog switching behaviors. The TEM observation shows that the insertion of the a-SiGex layer between SiOx and c-Si remarkably suppresses the formation of copper silicide, and reliable set/reset operations are secured. The origin of the analog switching behaviors is discussed by analyzing current-voltage characteristics and electron microscopy images. Finally, the memristive-neural network simulations show that our developed memristive devices provide high learning accuracy and are promising in future neuromorphic computing hardware.

Solvent-Controlled Morphology of Zinc-Cobalt Bimetallic Sulfides for Supercapacitors.

Bimetallic sulfides offer high theoretical specific capacitance and good stability as electrode materials due to their diverse redox reactions, larger specific surface areas, and better conductivity. The morphology of the electrode material is an important influencing factor for the electrochemical properties. Herein, a series of ZnCoS electrode materials with different morphologies were prepared by varying the solvent in the solvothermal reaction, and the effects of different microstructures on the electrochemical properties of ZnCoS were investigated. The ratio of water and ethanol in the solvent was controlled to modulate the microstructure of the as-prepared ZnCoS materials. XRD and XPS revealed the physical and chemical structure of the ZnCoS materials. SEM and TEM observations showed that the microstructure of ZnCoS transformed from one-dimensional wires to two-dimensional sheets with increasing amounts of ethanol. The maximum specific capacitance of the as-prepared ZnCoS materials is 6.22 F cm-2 at a current density of 5 mA cm-2, which is superior to that of most previously reported bimetallic sulfides. The enhanced electrochemical performance could be ascribed to its sheet-assembled spherical structure, which not only shortens the path of ion diffusion but also increases the contact between surface active sites and the electrolyte. Moreover, the spherical structure provides numerous void spaces for buffering the volume expansion and penetration of the electrolyte, which would be favorable for electrochemical reactions. Furthermore, the ZnCoS electrodes were coupled with activated carbon (AC) electrodes to build asymmetric supercapacitors (ASCs). The ASC device exhibits a maximum energy density of 0.124 mWh cm-2 under a power density of 2.1 mW cm-2. Moreover, even under a high-power density of 21 mW cm-2, the energy density can still reach 0.055 mWh cm-2.

Influence of Low Temperature Plasma Oxidizing on the Bioactivity of NiTi Shape Memory Alloy for Medical Applications.

The present study elucidates the impact of glow discharge oxidation within a low-temperature plasma environment on the bioactivity characteristics of an NiTi shape memory alloy. The properties of the produced surface layers, such as structure (TEM observations), surface morphology (SEM observations), chemical and phase composition (EDS and XRD measurements), wettability (optical gonimeter), and the biological response of osteoblasts and platelets to the oxidized surface compared with the NiTi alloy without a surface layer are presented. The presented surface modification of the NiTi shape memory alloy, achieved through oxidizing in a low-temperature plasma environment, led to the creation of a continuous surface layer composed of nanocrystalline titanium oxide TiO2 (rutile). The findings obtained from this study provide evidence that the oxidized layer augments the bioactivity of the shape memory alloy. This augmentation was substantiated through the spontaneous biomimetic deposition of apatite from a simulated body fluid (SBF) solution. Furthermore, the modified surface exhibited improved osteoblast proliferation, and enhanced platelet adhesion and activation. This proposed surface modification strategy holds promise as a prospective solution to enhance the biocompatibility and bioactivity of NiTi shape memory alloy intended for prolonged use in bone implant applications.

3D nanostructure prediction of porous carbons via gas adsorption

Structural characterization of porous carbon materials is critical for the evaluation of their synthesis procedures and performance. Throughout the last decades, many methods have been employed to determine porosity properties from gas adsorption such as surface area, pore size distribution (PSD) and real density. However, gas adsorption models use 1D structures of carbon nanopores, although adsorption and separation properties of nanoporous carbons are governed by 3D pore parameters. Estimating the 3D nanostructure of nanoporous carbons using gas adsorption would accelerate progress in research and implementation of nanoporous carbons. We report here a promising 3D pore nanostructural characterization from gas adsorption. Using atomistic simulations, we have generated a database of realistic 3D porous carbon structures spanning a wide range of pore sizes and geometries. After calculating their gas adsorption isotherms, we employed a numerical procedure to find the relative contribution for each of the structures to the adsorption isotherm of a nanoporous carbon sample. These contributions allowed us to estimate the surface area and pore size distribution of carbon materials; moreover (and perhaps more importantly!), we will show that the plausible 3D pore structures correlate very well with the local carbon structure as experimentally determined by high-resolution TEM observations and can successfully predict adsorption of different molecules. This is a powerful procedure that can be extended to other materials, and with enough computer power, to larger pore sizes.

Bender-element-based penetrometers for measuring shear wave velocity and shear strength

A bender-element-based dynamic penetrometer (BE-DP) was developed for the measurement of shear wave velocity (Vs-hh and Vs-hv) and shear strength parameters (cohesive strength (c) and internal friction angle (ϕ)) of soils. Shear wave velocity was measured through two pairs of bender elements installed in the cone shafts. Small-strain stiffness (Ghh and Ghv) and stiffness anisotropic ratio (Ghh/Ghv) were calculated through the measured shear wave velocity. Shear strength parameters were obtained through a series of theoretical formulas. In-situ tests of fully weathered slate (FWS) and granite residual soil (GRS) by applying BE-DP indicated that FWS had obvious stiffness anisotropy while GRS had slight stiffness anisotropy, which were in consistent with SEM and TEM observations of two kinds of soils. Meanwhile, SEM and TEM observations also showed that soil particle size of FWS was much larger than that of GRS, resulting in a much larger shear wave velocity and small-strain stiffness of FWS than GRS. Due to less disturbance of in-situ tests than laboratory experiments, shear strength measured by BE-DP was a little bit larger than that measured by laboratory experiments for both FWS and GRS. In-situ test results proved that the newly developed BE-DP was feasible, robust, multifunctional and cost-effective.

Healing effect of electric current treatment on superelasticity and elastocaloric effect of TiNi shape memory wire

This study investigated the healing effects of electric current treatment on Ni-rich TiNi shape memory wire after every 100 superelastic cycles. The diameter of the TiNi wire was 0.5 mm. The electric current treatment was applied without removing the wire from the tensile machine, aiming for online healing of the shape memory alloy. The electric current treatment showed an obvious healing effect, which restored the superelastic and elastocaloric properties of the functionally degraded TiNi shape memory wire. With treatment conditions of 20.4 A/mm2 and 2 min (the temperature of the wire increased up to 280 °C in 10 s), the elastocaloric temperature rise and drop of the TiNi wire recovered about 14% and 6% after 3–4 treatments, respectively, as compared with the case without any heat treatment. TEM observations indicated that the residual martensite introduced into the TiNi wire during superelastic cycles could be eliminated through the electric current treatment. Experimental results demonstrated that electric current treatment was a promising method to restore the functionality of the TiNi SMA wire after several superelastic cycles without the need to remove the wire from the apparatus, which would thus improve the performance of shape memory alloys during their long-term application.

(Invited) Effect of Cu Doping on the Energy Structure of Dumbbell-Shaped ZnS-AgInS2 Nanocrystals

Colloidal semiconductor nanocrystals (NCs) have been intensively developed for applications in photovoltaics, light-emitting diodes, electroluminescent devices, and biological markers, due to their tunable light absorption and excellent light emission properties. Among them, group I-III-VI-based multinary semiconductor NCs, such as CuInS2, CuInSe2 and AgInS2, have received significant attention for the application to solar energy conversion systems because of their large absorption coefficient and low toxicity. Recently, we have successfully prepared ZnS-AgInS2 solid solution (ZAIS) NCs and optimized their photocatalytic activity for hydrogen production by tuning their chemical composition, size and particle morphology.1-3 The photocatalytic activity of ZAIS NCs was further enhanced by the formation of a dumbbell structure that had a type-II heterojunction at the interface between the tip and rod parts of the NCs.4 In this study, to further improve the photocatalytic activity of dumbbell-shaped ZAIS NCs, we attempted to tune the energy structure of the heterojunction by Cu doping in tip parts for effective charge separation. Rod-shaped ZAIS NCs with sizes of 4.0 × 23 nm were prepared by the previously reported method.3 The crystal growth of tip parts was carried out by heating a mixture of rod-shaped ZAIS NCs, Cu(OAc), Ag(OAc), In(OAc)3, and thiourea in an organic solvent, in which rod-shaped ZAIS NCs acted as a nucleus to form tip parts composed of (Cu y Ag(1-y)In) x Zn2(1-x)S2 solid solution. Thus-obtained dumbbell-shaped NCs were isolated from the resulting solution via size-selective precipitation. The amount of Cu doping in tip parts was controlled by changing the Cu content in metal precursors. TEM observations showed that obtained NCs had a dumbbell structure regardless of the Cu content in the metal precursor. Ellipsoidal NCs with sizes of 5.6 × 11 nm were deposited on both tips of rod-shaped ZAIS NCs. The absorption onset of the dumbbell-shaped NCs were red-shifted from 650 nm to 850 nm with an increase in the Cu fraction from y = 0 to 0.75. The photoelectron yield spectroscopy revealed that the conduction band minimum level was constant at ca. -3.2 eV, while the valence band maximum level was gradually shifted from -5.1 eV to -4.8 eV as the Cu fraction in tip parts increased from y = 0 to 0.75. Thus, it is concluded that the absorption property of dumbbell-shaped ZAIS NCs could be successfully extended from the visible to the near-IR region without changing the energy of photogenerated electrons, simply by modulating the degree of Cu doping in the tip parts. This tunability is useful for constructing efficient solar-light-driven photocatalysts for H2 evolution. T. Torimoto, T. Adachi, K. Okazaki, M. Sakuraoka, T. Shibayama, B. Ohtani, A. Kudo, S. Kuwabata, J. Am. Chem. Soc., 129 (2007) 12388-12389.T. Kameyama, T. Takahashi, T. Machida, Y. Kamiya, T. Yamamoto, S. Kuwabata, T. Torimoto, J. Phys. Chem. C, 119 (2015) 24740-24749.T. Torimoto, Y. Kamiya, T. Kameyama, H. Nishi, T. Uematsu, S. Kuwabata, T. Shibayama, ACS Appl. Mater. Inter., 8, (2016) 27151-27161.T. Kameyama, S. Koyama, T. Yamamoto, S. Kuwabata, T. Torimoto, J. Phys. Chem. C, 122 (2018) 13705-13715.

Decorating crystalline YFe2–xAlx on the Mg60La10Ni20Cu10 amorphous alloy as “hydrogen pump” to realize fast de/hydrogenation

Mg-based amorphous alloys are one of the potential hydrogen storage materials but suffer from sluggish dehydrogenation/hydrogenation (de/hydrogenation) kinetics. In this work, as a new strategy, a hydrogen pump is built on the surface of amorphous alloys to solve this problem. By milling crystalline YFe2–xAlx hydrogen storage alloy with Mg60La10Ni20Cu10 amorphous alloy, fine crystalline particles were seeded on amorphous alloy powder to form a “strawberry” structure. According to the TEM observation, a metallurgical bonding boundary formed between the Mg-based amorphous matrix and the Y-Fe-Al crystalline alloy. By microstructure and de/hydrogenation kinetics investigation, the “hydrogen pump” effect of the seeded crystalline alloy was confirmed, which makes it much easier for the hydrogen to dissociate on and diffuse through the surface of the Mg-based amorphous alloy. With such effect, the H absorption rate of Mg60La10Ni20Cu10 amorphous alloy became almost eight times faster and it absorbs ∼2.8 wt.% in 1 h at 130 °C under 4.5 MPa-H2. Further, fast hydrogenation can even achieve at 70 °C and the low-temperature dehydrogenation kinetics of the amorphous hydride can be also greatly promoted. The present work proves that surface modification is of great importance for obtaining Mg-based amorphous alloy with ideal hydrogen storage performance.

Evolution of dislocation loops and voids in post-irradiation annealed ThO2: A combined in-situ TEM and cluster dynamics investigation

The effect of isochronal annealing on the evolution of dislocation loop and void population in proton irradiated ThO2 has been investigated. Post-irradiation annealing in other actinide oxides like UO2 shows significant loop coarsening. ThO2 samples were irradiated with 2 MeV protons up to a dose of 0.1 dpa at 600 °C. Post-irradiation isochronal annealing was performed at 600, 800, 1000 and 1100 °C for 1 h at each temperature using in-situ TEM. Only faulted 1/3<111> type dislocation loops were observed, and their sizes and distribution were characterized. The population of self-interstitial atom (SIA) dislocation loops did not show any significant growth and coarsening. Additionally, nanometric voids were observed at annealing temperatures of 1000 and 1100 °C. Using cluster dynamics (CD), we have studied the nucleation and growth of point defects and defect clusters, i.e., SIA prismatic dislocation loops and nanometric and sub-nanometric voids in proton irradiated ThO2. The CD model was further utilized to predict the growth and coarsening of loops and voids during isochronal annealing at the experimental and higher temperatures. The model did not predict significant SIA loop growth which closely corresponds to the TEM observations. CD predicted SIA loop coarsening is insignificant even at high annealing temperature of 1500 °C because the model only considers the growth of defect clusters by absorption of like point defects, i.e., SIA loops absorb interstitials and voids absorb vacancies, and cannot account for their migration and coalescence due to elastic interaction. The CD model also predicts the evolution of nanometric voids having mean size within the error bounds of TEM observations.