Microstrain in Nanocrystalline Copper by High Resolution Electron Microscopy

The elastic microstrains in a crystallite of electrodeposited nanocrystalline copper were investigated by analyzing the high resolution electron microscopy （HRTEM） image. The microstrain was considered as consisting of two parts, in which the uniform part was determined with fast Fourier transformation of the HRTEM image, while the non-uniform part of the microstrain in the crystallite was measured by means of peak finding. Atomic column spacing measurements show that the crystal lattice is contracted in the longitudinal direction, while expanded in the transverse direction of the elliptical crystallite, indicating that the variation of microstrain exists mainly near the grain boundary.

Lithium mapping in a Mg-9Li-4Al-1Zn alloy using electron energy-loss spectroscopy

Magnesium-lithium alloys with high lithium content have been attracting significant attention because of their low density,high formability and corrosion resistance.These properties are dependent on the distribution of lithium,which is difficult to map in the presence of magnesium.In this work,a ratio spectrum-imaging method with electron energy-loss spectroscopy(EELS)is demonstrated,which enables the mapping of lithium.In application to LAZ941(Mg-9Li-4Al-1Zn in wt.%),this technique revealed that a key precipitate in the microstructure,previously thought by some to be Mg_(17)Al_(12),is in fact rich in lithium.This result was corroborated with a structural investigation by high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM),showing this phase to be Al_(1-x)Zn_(x)Li,with x<<1.This work indicates the potential offered by this technique for mapping lithium in materials.

Tuning the charge distribution and crystal field of iron single atoms via iron oxide integration for enhanced oxygen reduction reaction in zinc-air batteries

Metal-air batteries face a great challenge in developing efficient and durable low-cost oxygen reduction reaction(ORR)electrocatalysts.Single-atom iron catalysts embedded into nitrogen doped carbon(Fe-N-C)have emerged as attractive materials for potential replacement of Pt in ORR,but their catalytic performance was limited by the symmetrical electronic structure distribution around the single-atom Fe site.Here,we report our findings in significantly enhancing the ORR performance of Fe-N-C by moderate Fe_(2)O_(3) integration via the strong electronic interaction.Remarkably,the optimized catalyst(M-Fe_(2)O_(3)/Fe_(SA)@NC)exhibits excellent activity,durability and good tolerance to methanol,outperforming the benchmark Pt/C catalyst.When M-Fe_(2)O_(3)/Fe_(SA)@NC catalyst was used in a practical zinc-air battery assembly,peak power density of 155 mW cm^(-2)and specific capacity of 762 mA h g_(Zn)^(-1)were achieved and the battery assembly has shown superior cycling stability over a period of 200 h.More importantly,theoretical studies suggest that the introduction of Fe_(2)O_(3) can evoke the crystal field alteration and electron redistribution on single Fe atoms,which can break the symmetric charge distribution of Fe-N_(4) and thereby optimize the corresponding adsorption energy of intermediates to promote the O_(2)reduction.This study provides a new pathway to promote the catalytic performance of single-atom catalysts.

Three-dimensional size and orientation of the precipitates in AZ91 magnesium alloys measured by TEM techniques

Knowledge of the microscopic structure, including three-dimensional （3-D） size and orientation of the precipitates, is essential to fully understand the mechanical properties of the magnesium alloys and designing the alloys with better performance. Analytical TEM with high spatial resolution offers the simultaneous measurements of 3-D size, structure, orientation, composition of the precipitates from one typical sample along an established crystallographic axis. Besides popular Burgers orientation relationship （OR）, other ORs such as Pitsch-Schrader OR, Crawley OR, Potter OR and a new OR with the form of [0001]α 1.0° from [311]γ and （1120）α 2.0° from （033）γ between the magnesium matrix and the precipitate γ-MglTAl 12 are identified by TEM imaging and diffraction techniques. As a case study, the thicknesses of the individual precipitates with Burgers OR are further measured to be 100 200 nm through both electron energy-loss spectroscopy and x-ray energy dispersive spectroscopy combining differential x-ray absorption and extrapolation, which are in agreement with the overall 3-D size statistic distribution results obtained through analysing various samples along various directions. Furthermore, the fabricated wedge-shape structure provides a platform on which to study the dependence of the interfacial strain on the variation of the thickness.

Crystallization and impact history of a meteoritic sample of early lunar crust(NWA 3163)refined by atom probe geochronology

Granulitic lunar meteorites offer rare insights into the timing and nature of igneous,metamorphic and impact processes in the lunar crust.Accurately dating the different events recorded by these materials is very challenging,however,due to low trace element abundances (e.g.Sm,Nd,Lu,Hf),rare micrometerscale U-Th-bearing accessory minerals,and disturbed Ar-Ar systematics following a multi-stage history of shock and thermal metamorphism.Here we report on micro-baddeleyite grains in granulitic mafic breccia NWA 3163 for the first time and show that targeted microstructural analysis (electron backscatter diffraction) and nanoscale geochronology (atom probe tomography) can overcome these barriers to lunar chronology.A twinned (-90°/<401>) baddeleyite domain yields a 232Th/208Pb age of 4328 ± 309 Ma,which overlaps with a robust secondary ion mass spectrometry (SIMS) 207Pb/206Pb age of 4308± 18.6 Ma and is interpreted here as the crystallization age for the igneous protolith of NWA 3163.A second microstructural domain,< 2 mm in width,contains patchy overprinting baddeleyite and yields a Th-Pb age of 2175± 143 Ma,interpreted as dating the last substantial impact event to affect the sample.This finding demonstrates the potential of combining microstructural characterization with nanoscale geochronology when resolving complex P-T-t histories in planetary materials,here yielding the oldest measured crystallization age for components of lunar granulite NWA 3163 and placing further constraints on the formation and evolution of lunar crust.

Experimental Observation on Orientation Relationship between Binary Cd5.7Yb Quasicrystal and its Crystalline Approximant Cd6Yb

Similarity in the electron diffraction patterns of the Cd5.7 Yb icosahedral quasicrystal and its cubic approximant Cd6 Yb crystal is studied in detail by using transmission electron microscopy. The icosahedral twofold axes are parallel to the cubic （1ττ^2） （τ= 1.618…） or （0 0 1） directions, the icosahedral pseudo-twofold axes are parallel to the cubic （15 21 25） directions, the icosahedral threefold axes are parallel to the cubic 〈1 1 1〉 and the icosahedral fivefold are parallel to the cubic 〈0 1 τ〉 directions. Based on those observations a general stereographic projection is given to illustrate the exact orientation relationship.

Microscopic Evidence of Destroying the Order of Magnetic Sequence in CuO_2 Chain by Zn, Ni, Co Doping in Sr_(14)Cu_(24)O_(41) Compound

The Zn2＋, Ni2＋ and Co3＋ doped Sr14Cu24041 compounds were synthesized by standard solid state method. X-ray diffraction results show that the changes in lattice parameters are very small. Selected area electron diffraction patterns （EDPs） show that the diffraction spots corresponding to the CuO2 chain substructure are extended to streaks along a＊ and b＊ directions for all the samples, while the diffraction spots produced merely by the Cu203 ladder substructure are still very sharp. This means that the periodicities of chains in a＊ and b＊ directions are partially destroyed upon doping ofZn, Ni and Co due to that the initial phase of each chain becomes a random variable. The temperature dependence of magnetic properties was measured for every sample. And the number of dimers in CuO2 chain per formula unit （f.u.） and dimer coupling constant are obtained by fitting the temperature dependence of the magnetic susceptibility. It is found that the degree of initial phase disorder is related to the order degree of magnetic sequence in CuO2 chain. For the un-doped sample, the decoupling of dimers is weak, the magnetic sequence is slightly destroyed, and the streaks in EDP are also very weak, which implies the degree of initial phase disorder in CuO2 chain is very low. When Zn2~ and Ni2＋ ions are doped, the number of dimers per f.u. decreases, and the intensity of diffraction streaks increases in comparison with the corresponding spots. Furthermore, when the high spin magnetic ions Co3＋ are doped, the number of holes in Sr14Cu24041 decreases, the magnetic sequence is destroyed very seriously, and the spots in EDP are extended to streaks almost completely. The phenomenon that the diffraction spots ofCuO2 chain extend to streaks in EDP appears as evidence that the magnetic sequence in the CuO2 chain is destroyed by doping of Zn, Ni, Co.

Rolling-assisted direct energy deposited Inconel 718:Microstructural evolution and mechanical properties after optimized heat treatment

Post-heat treatment is a necessary and important step for additive-manufactured products to relieve residual stress and to further improve mechanical performance.In this work,the heat treatment strat-egy for Inconel 718 superalloy fabricated by rolling-assisted laser-directed energy deposition(L-DED)has been designed and systematically investigated for the first time.The results show that the designed ho-mogenization heat treatment at 1080℃ for 10 min can effectively dissolve most of the detrimental Lave phases existing in the rolling-assisted L-DED samples.Meanwhile,it results in a homogenous grain struc-ture through static recrystallization,while maintaining a similar prior-refined grain size of∼8μm.On this basis,a high number density ofγ″andγ′precipitates appear in the microstructure after applying a subsequent double-aging heat treatment.The optimized microstructure through such effective post-heat treatment designed in this work has led to a significant increase in material strength at both the room and elevated temperatures while maintaining good ductility.

Unravelling the competitive effect of microstructural features on the fracture toughness and tensile properties of near beta titanium alloys

The competitive effect of microstructural features including primaryα(α_(p)),secondaryα(α_(s)),grain boundaryα(α_(GB)) and β grain size on mechanical properties of a near β Ti alloy were studied with two heat treatment processes.The relative effect of β grain size and STA(solution treatment and ageing)processing parameters on mechanical properties were quantitatively explored by the application of Taguchi method.These results were further explained via correlating microstructure with the fracture toughness and tensile properties.It was found that large numbers of fine as precipitates and continuous α_(s) played greater roles than other features,resulting in a high strength and very low ductility(<2%)of STA process samples.The β grain size had a negative correlation with fracture toughness.In the samples prepared by BASCA( β anneal slow cooling and ageing)process,improved ductility and fracture toughness were obtained due to a lower density ofα;precipitates,a basket-weave structure and zigzag morphology of α_(GB).For this heat treatment,an increase in prior β grain size had an observable positive effect on fracture toughness.The contradictory effect of β grain size on fracture toughness found in literature was for the first time explained.It was shown that the microstructure obtained from different processes after β solution has complex effect on mechanical properties.This complexity derived from the competition between microstructure features and the overall sum of their effect on fracture toughness and tensile properties.A novel table was proposed to quasi-quantitatively unravel these competitive effects.

Low-temperature conversion of ammonia to nitrogen in water with ozone over composite metal oxide catalyst

As one of the most important water pollutants, ammonia nitrogen emissions have increased year by year, which has attracted people＇s attention. Catalytic ozonation technology, which involves production of ·OH radical with strong oxidation ability, is widely used in the treatment of organic-containing wastewater. In this work, MgO-Co3O4 composite metal oxide catalysts prepared with different fabrication conditions have been systematically evaluated and compared in the catalytic ozonation of ammonia（50 mg/L） in water. In terms of high catalytic activity in ammonia decomposition and high selectivity for gaseous nitrogen, the catalyst with MgO-Co3O4 molar ratio 8：2, calcined at 500°C for 3 hr, was the best one among the catalysts we tested, with an ammonia nitrogen removal rate of 85.2% and gaseous nitrogen selectivity of44.8%. In addition, the reaction mechanism of ozonation oxidative decomposition of ammonia nitrogen in water with the metal oxide catalysts was discussed. Moreover, the effect of coexisting anions on the degradation of ammonia was studied, finding that SO2-4 and HCO-3 could inhibit the catalytic activity while CO2-3 and Br-could promote it. The presence of coexisting cations had very little effect on the catalytic ozonation of ammonia nitrogen. After five successive reuses, the catalyst remained stable in the catalytic ozonation of ammonia.

Towards creep property improvement of selective laser melted Ni-based superalloy IN738LC

Nickel-based superalloy IN738LC produced by selective laser melting(SLM)exhibits inferior hightemperature creep properties than its cast counterparts due to relatively smaller grain size,particularly for the plane normal to the building direction.This work studied effects of post heating strategy on the microstructure and especially the grain size to improve the high temperature creep resistance.The asbuilt microstructure exhibited a fine grain size and large quantities of MC carbides that could effectively hinder grain growth.It was found that unconventional two-step heat treatments could lead to substantial grain growth,and the effect is particularly prominent at a specific temperature.The ease of grain growth was explained after classifying the microstructural evolution(boundary carbide transformation)during each heating step and related to the reduced grain boundary pinning force from MC carbides.Creep tests validated the effect of the new heat treatment scheme on the SLM-processed IN738LC at 850℃.An extended creep fracture life(1.5 to 4 times improvement)and lower secondary creep rates were achieved with samples subjected to the newly optimized two-step heat treatment.The complete creep curves are also firstly presented for SLM-IN738LC,confirming the effectiveness of grain growth and highlighting the importance of dedicated heat treatment for SLM superalloys.

Tracking morphologies at the nanoscale： Self-assembly of an amphiphilic designer peptide into a double helix superstructure

层次自己组装是在自然的一个基本原则，它产生是为在纳米技术的创新材料的开发的灵感的令人震惊的超分子的体系结构。这里，我们在场锥形的 amphiphilic 设计者肽的唯一的结构。当追踪它的集中依赖者形态学时，我们在集会过程的开始观察了伸长的 bilayered 单身者磁带，它进一步在高集中发展成新奇 double-helix-like 上层建筑。这体系结构被二单个 helices 的紧密的 intertwisting 描绘，导致在他们几百纳米的全部的长度上的一种周期的沥青尺寸。解决方案 X 光检查散布数据揭示了显著 2-layered 内部组织。所有这些特征为几乎三个月的调查时期仍然保持未改变。在他们的集体形态学，集会集成于有 hydrogel 特征的一个网络。如此的基于肽的结构为下一代的 nanostructured biomaterials 作为一块积木保持诺言。

Helium droplet assisted synthesis of plasmonic Ag@ZnO core@shell nanoparticles

Plasmonic Ag@ZnO core@shell nanoparticles are formed by synthesis inside helium droplets with subsequent deposition and controlled oxidation.The particle size and shape can be controlled from spherical sub-10 nm particles to larger elongated structures.An advantage of the method is the complete absence of solvents,precursors,and other chemical agents.The obtained particle morphology and elemental composition have been analyzed by scanning transmission electron microscopy(STEM)and energy dispersive X-ray spectroscopy(EDS).The results reveal that the produced particles form a closed and homogeneous ZnO layer around a 2–3 nm Ag core with a uniform thickness of(1.33±0.15)nm and(1.63±0.31)nm for spherical and wire-like particles,respectively.The results are supported by ultraviolet photoelectron spectroscopy(UPS),which indicates a fully oxidized shell layer for the particles studied by STEM.The plasmonic properties of the produced spherical Ag@ZnO core@shell particles are investigated by two-photon photoelectron(2PPE)spectroscopy.Upon excitation of the localized surface plasmon resonance in Ag at around 3 eV,plasmonic enhancement leads to the liberation of electrons with high kinetic energy.This is observed for both Ag and Ag@ZnO particles,showing that even if a Ag cluster is covered by the ZnO layer,a plasmonic enhancement can be observed by photoelectron spectroscopy.

Preparation of FePt magnetic nanodot arrays by nanosphere lithography

Magnetic FePt nanodot arrays are promising candidates for making quantum magnetic recording disk. Here we introduce a hybrid method of FePt nanodot array fabrication through nanosphere lithography. This method combines the advantages of both top-down and bottom-up approaches and does not re- quire expensive equipment nor complicated processing steps.The size of magnetic FePt nanodots prepared can be as small as 40 nm.