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 dislocation and twinning activities in pure Mg during loading and unloading. We demonstrated that the screw component of 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 dislocation retraction and detwinning. Moreover,we note that the plastic zone comprised of 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 dislocations, the I1stacking 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 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 dislocation slip and twinning in Mg and alloys.

IN SITU TEM STUDY ON THE R-PHASE TRANSFORMATION IN TiNi ALLOY

The R-phase transformation process in selected TiNi alloys has been studied in great detail by using in situ TEM technique. The R-phase transformation was found to be a reversible thermoelastic displacive transformation with a nucleation and growth process. The R-phase nucleates at the precipitate/matrix interface in aged specimens and grows by moving the coherent R/matrix interfaces. The stress field of Ti3Ni4 precipitates plays a much more important role in the formation of the R-phase than dislocations in aged TiNi alloy. The microstructure of the R-phase has also been studied.

Confining TiO_2 Nanotubes in PECVD-Enabled Graphene Capsules Toward Ultrafast K-Ion Storage: In Situ TEM/XRD Study and DFT Analysis

Titanium dioxide(TiO2) has gained burgeoning attention for potassium-ion storage because of its large theoretical capacity,wide availability,and environmental benignity.Nevertheless,the inherently poor conductivity gives rise to its sluggish reaction kinetics and inferior rate capability.Here,we report the direct graphene growth over TiO2 nanotubes by virtue of chemical vapor deposition.Such conformal graphene coatings effectively enhance the conductive environment and well accommodate the volume change of TiO2 upon potassiation/depotassiation.When paired with an activated carbon cathode,the graphene-armored TiO2 nanotubes allow the potassium-ion hybrid capacitor full cells to harvest an energy/power density of 81.2 Wh kg-1/3746.6 W kg-1.We further employ in situ transmis sion electron microscopy and ope rando X-ray diffraction to probe the potassium-ion storage behavior.This work offers a viable and versatile solution to the anode design and in situ probing of potassium storage technologies that is readily promising for practical applications.

Influence of Annealing Temperature on the Properties of TiO_2 Films Annealed by ex situ and in situ TEM

TiO2 thin films were deposited on quartz substrates by DC reactive magnetron sputtering of a pure Ti target in Ar/O2 plasma at room temperature. The TiO2 films were annealed at different temperatures ranging from 300 to 800 ℃ in a tube furnace under flowing oxygen gas for half an hour each. The effect of annealing temperatures on the structure, optical properties, and morphologies were presented and discussed by using X-ray diffraction, optical absorption spectrura, and atomic force microscope. The films show the presence of diffraction peaks from the （101）, （004）, （200） and （105） lattice planes of the anatase TiO2 lattice. The direct band gap of the annealed films decreases with the increase of annealing temperature. While, the roughness of the films increases with the increases of annealing temperature, and some significant roughness changes of the TiO2 film surfaces were observed after the annealing temperature reached 800 ℃. Moreover, the influences of annealing on the microstructures of the TiO2 film were investigated also by in situ observation in transmission electron microscope.

Revealing the structure design of alloyed based electrodes for alkali metal ion batteries with in situ TEM

Alloyed based anode materials with high theoretical specific capacity and low reaction potential are considered to be highly potential high-energy density anode materials for alkali metal ion batteries(AMIBs).Thus,the design of alloyed based materials with high electrochemical performance has attracted great attention.Among the numerous characterization methods for guiding electrode materials design,in situ transmission electron microscopy(TEM)gradually plays an irreplaceable role due to its high temporal and spatial resolution in directly observing the change of morphology,crystal structure and element evolutions.Herein,we reviewed the two current research hotspots and mainly focused on the structure design of alloyed based electrode material under the guidance of in situ TEM.Specifically,various nanostructure designs of alloyed based electrode materials with guidance of in situ TEM were employed to solve the key scientific issues of the violent volume change during alloying/dealloying processes for enhanced electrochemical performances.Mainly through introducing buffer space in the electrode material to reduce volume change to improve structural stability,including porous structure(0 D),nanotube structure(1 D),simple hollow structure,yolk-shell structure and some hybrid hollow structures(3 D).Furthermore,the direct guidance of in situ TEM is expected for creating new opportunities to nextgeneration electrode material design for AMIBs.

Interface catalytic reduction of alumina by nickle for the aluminum nanowire growth: Dynamics observed by in situ TEM

Metal nanowires show promise in a broad range of applications and can be fabricated via a number of methods,such as vapor–liquid–solid process and template-based electrodeposition.However,the synthesis of Al nanowires(NWs)is still challenging from the stable alumina substrate.In this work,the Ni-catalyzed fabrication of Al NWs has been realized using various Al_(2)O_(3) substrates.The growth dynamics of Al NWs on Ni/Al_(2)O_(3) was studied using in situ transmission electron microscopy(TEM).The effect of alumina structures,compositions,and growth temperature were investigated.The growth of Al NWs correlates with the Na addition to the alumina support.Since no eutectic mixture of nickel aluminide was formed,a mechanism of Ni-catalyzed reduction of Al_(2)O_(3) for Al NWs growth has been proposed instead of the vapor–liquid–solid mechanism.The key insights reported here are not restricted to Ni-catalyzed Al NWs growth but can be extended to understanding the dynamic change and catalytic performance of Ni/Al_(2)O_(3) under working conditions.

Structural and chemical transformations of CuZn alloy nanoparticles under reactive redox atmospheres:An in situ TEM study

Alloying metals to form intermetallics has been proven effective in tuning the chemical properties of metal-based catalysts.However,intermetallic alloys can undergo structural and chemical transformations under reactive conditions,leading to changes in their catalytic function.Elucidating and understanding these transformations are crucial for establishing relevant structureperformance relationships and for the rational design of alloy-based catalysts.In this work,we used CuZn alloy nanoparticles(NPs)as a model material system and employed in situ transmission electron microscopy(TEM)to investigate the structural and chemical changes of CuZn NPs under H_(2),O_(2)and their mixture.Our results show how CuZn NPs undergo sequential transformations in the gas mixture at elevated temperatures,starting with gradual leaching and segregation of Zn,followed by oxidation at the NP surface.The remaining copper at the core of particles can then engage in dynamic behavior,eventually freeing itself from the zinc oxide shell.The structural dynamics arises from an oscillatory phase transition between Cu and Cu_(2)O and is correlated with the catalytic water formation,as confirmed by in situ mass spectrometry(MS).Under pure H_(2)or O_(2)atmosphere,we observe different structural evolution pathways and final chemical states of CuZn NPs compared to those in the gas mixture.These results clearly demonstrate that the chemical state of alloy NPs can vary considerably under reactive redox atmospheres,particularly for those containing elements with distinct redox properties,necessitating the use of in situ or detailed ex situ characterizations to gain relevant insights into the states of intermetallic alloy-based catalysts and structure-activity relationships.

A thick yet dense silicon anode with enhanced interface stability in lithium storage evidenced by in situ TEM observations

Increasing the density and thickness of electrodes is required to maximize the volumetric energy density of lithium-ion batteries for practical applications.However,dense and thick electrodes,especially highmass-content(>50 wt%) silicon anodes,have poor mechanical stability due to the presence of a large number of unstable interfaces between the silicon and conducting components during cycling.Here we report a network of mechanically robust carbon cages produced by the capillary shrinkage of graphene hydrogels that can contain the silicon nanoparticles in the cages and stabilize the silicon/carbon interfaces.In situ transmission electron microscope characterizations including compression and tearing of the structure and lithiation-induced silicon expansion experiments,have provided insight into the excellent confinement and buffering ability of this interface-strengthened graphene-caged silicon nanoparticle anode material.Consequently,a dense and thick silicon anode with reduced thickness fluctuations has been shown to deliver both high volumetric(>1000 mAh cm^-3) and areal(>6 mAh cm^-2)capacities together with excellent cycling capability.

Real-time in situ TEM studying the fading mechanism of tin dioxide nanowire electrodes in lithium ion batteries

Fading mechanism of tin dioxide （SnO2） electrodes in lithium ion batteries has attracted much attentions, which is of great importance for the battery applications. In this paper, electrochemical lithiation-delithiation cycles of individual SnO2 nanowires were conducted in situ in a high-resolution transmission electron microscopy （TEM）. Major changes in volume with expan- sions of 170%~300% on SnO2 nanowire electrodes were observed during the first lithiation process in electrochemical cycling, including conversion reaction of SnO2 precursor to Li20 matrix and active lithium host Sn, and alloying of Sn with Li to form brittle Li-Sn alloy. SnO2 nanowire electrodes were inclined to suffer from thermal runaway condition in the first two cycles. During cycling, morphology and composition evolution of SnO2 nanowire electrodes were recorded. Cyclic lithiation and del- ithiation of the electrode demonstrated the phase transition between Lii3Sn5 and Sn. Metallic Sn clusters were formed and their sizes enlarged with increasing cycle times. Detrimental aggregation of Sn clusters caused pulverization in SnO2 nanowire elec- trodes, which broke the conduction and transport path for electrons and lithium ions. The real-time in situ TEM revealed fading mechanism provides important guidelines for the viable design of the SnO2 nanowire electrodes in lithium ion batteries.

Effects Associated with Nanostructure Fabrication Using In Situ Liquid Cell TEM Technology

We studied silicon,carbon,and SiC xnanostructures fabricated using liquid-phase electron-beam-induced deposition technology in transmission electron microscopy systems.Nanodots obtained from fixed electron beam irradiation followed a universal size versus beam dose trend,with precursor concentrations from pure Si Cl4to 0%SiC l4in CH2Cl2,and electron beam intensity ranges of two orders of magnitude,showing good controllability of the deposition.Secondary electrons contributed to the determination of the lateral sizes of the nanostructures,while the primary beam appeared to have an effect in reducing the vertical growth rate.These results can be used to generate donut-shaped nanostructures.Using a scanning electron beam,line structures with both branched and unbranched morphologies were also obtained.The liquid-phase electron-beaminduced deposition technology is shown to be an effective tool for advanced nanostructured material generation.

In Situ TEM Observation on Martensitic Transformation during Tensile Deformation of SUS304 Metastable Austenitic Stainless Steel

Through in situ transmission electron microscopy observation on SUS304 metastable austenitic stainless steel during stretching at room temperature,it is found that e martensite plates were induced preferentially from the sites of dislocation pile-ups.With increasing deformation,some of ε thin martensite platelets disappear and reversibly transform toγ austenite without heating treatment,which is different from the previous result that ε martensite can entirely transform toα＇martensite.Then,some of deformation twins appear and grow along the vertical direction of ε martensite due to（111）_γ⊥（1010）_ε.Moreover,it is directly observed that multiple transformation mechanisms via γ→ε→γ,γ→ε,γ→α′,γ→ε→α′,γ→ deformation twins →α′ can co-exist.

In situ TEM observation of dissolution and regrowth dynamics of MoO2 nanowires under oxygen

Direct observation of the dissolution behavior of nanomaterials could provide fundamental insight to understanding their anisotropic properties and stability. The dissolution mechanism in solution and vacuum has been well documented. However, the gas-involved dissolution and regrowth have seldom been explored and the mechanisms remain elusive. We report herein, an in situ TEM study of the dissolution and regrowth dynamics of MoO2 nanowires under oxygen using environmental transmission electron microscopy （ETEM）. For the first time, oscillatory dissolution on the nanowire tip is revealed, and, intriguingly, simultaneous layer-by-layer regrowth on the sidewall facets is observed, leading to a shorter and wider nanowire. Combined with first-principles calculations, we found that electron beam irradiation caused oxygen loss in the tip facets, which resulted in changing the preferential growth facets and drove the morphology reshaping.

IN-SITU TEM OBSERVATION OF NANOSILICON FIBRE GROWTH

Nano silicon particles can be become nano fibre under low energy electron beam bombarding. The formation of the nano silicon fibre include two stages. At first, on the nano silicon particle surface many silicon atoms are gasified, then these silicon atoms deposit in the place where have more charge on account of the static electrical absorption and the point effect of the charge accumulation , these atoms grow into non crystalline silicon fibres. The second stage is the non crystalline silicon fibres crystallizing. Its crystallizing temperature is about 180℃. The growth mechanism of the nano silicon fibre is vapour solid mode.

In situ transmission electron microscopy and artificial intelligence enabled data analytics for energy materials

Energy materials are vital to energy conversion and storage devices that make renewable resources viable for electrification technologies. In situ transmission electron microscopy(TEM) is a powerful approach to characterize the dynamic evolution of material structure, morphology, and chemistry at the atomic scale in real time and in operando. In this review, recent advancements of in situ TEM techniques for studying energy materials, including catalysts, batteries, photovoltaics, and thermoelectrics, are systematically discussed and summarized. The topics include a broad range of material transformations that are in situ stimulated by heating, biasing, lighting, electron-beam illuminating, and cryocooling under vacuum, liquid, or gas environments within TEM, as well as the mechanistic understanding of the associated solid-solid, solid-liquid, and solid-gas reactions elucidated by in situ TEM examination and operando measurements. Special focus is also put on the emerging progress of artificial intelligence enabled microscopy data analytics, including machine learning enhanced tools for retrieving useful information from massive TEM imaging, diffraction, and spectroscopy datasets, highlighting its merits and potential for automated in situ TEM experimentation and analysis. Finally, the pressing challenges and future perspectives on in situ TEM study for energy-related materials are discussed.

Achieving high-capacity and long-life K^(+)storage enabled by constructing yolk-shell Sb_(2)S_(3)@N,S-doped carbon nanorod anodes

As promising anode candidates for potassium-ion batteries(PIBs),antimony sulfide(Sb_(2)S_(3))possesses high specific capacity but suffers from massive volume expansion and sluggish kinetics due to the large K^(+)insertion,resulting in inferior cycling and rate performance.To address these challenges,a yolk-shell structured Sb_(2)S_(3)confined in N,S co-doped hollow carbon nanorod(YS-Sb_(2)S_(3)@NSC)working as a viable anode for PIBs is proposed.As directly verified by in situ transmission electron microscopy(TEM),the buffer space between the Sb_(2)S_(3)core and thin carbon shell can effectively accommodate the large expansion stress of Sb_(2)S_(3)without cracking the shell and the carbon shell can accelerate electron transport and K^(+)diffusion,which plays a significant role in reinforcing the structural stability and facilitating charge transfer.As a result,the YS-Sb_(2)S_(3)@NSC electrode delivers a high reversible K^(+)storage capacity of 594.58 m A h g^(-1)at 0.1 A g^(-1)and a long cycle life with a slight capacity degradation(0.01%per cycle)for 2000 cycles at 1 A g^(-1)while maintaining outstanding rate capability.Importantly,utilizing in in situ/ex situ microscopic and spectroscopic characterizations,the origins of performance enhancement and K^(+)storage mechanism of Sb_(2)S_(3)were clearly elucidated.This work provides valuable insights into the rational design of high-performance and durable transition metal sulfides-based anodes for PIBs.

TEM Study of Microcrack Nucleation and Propagation for 310 Stainless Steel

TEM in situ tensile tests of 310 stainless steel show that a dislocation free zone (DFZ) forms if the displacement keeps constant after dislocations are emitted from a crack tip. The elastic DFZ is gradually thinned and the stress in the DFZ will reach the cohesive strength, resulting in nucleation of nanocracks in it and their bluntness into voids. If continuously tensioning, the inhomogeneously thinning ahead of the crack tip, initiating and connecting of microcracks or microvoids will be observed rather than a DFZ, nanocracks' initiation and bluntness into voids. The inverse pile-up ahead of a loaded crack tip can move back to the crack tip when unloading.

Negative thermal expansion and phase transition of low-temperature Mg_(2)NiH_(4)

The negative thermal expansion(NTE) phenomenon is of great significance in fabricating zero thermal expansion(ZTE) materials to avoid thermal shock during heating and cooling. NTE is observed in limited groups of materials, e.g., metal cyanides, oxometallates, and metalorganic frameworks, but has not been reported in the family of metal hydrides. Herein, a colossal and continuous negative thermal expansion is firstly developed in the low-temperature phases of LT1-and LT2-Mg_(2)NiH_(4) between 488 K and 733 K from in-situ transmission electron microscope(TEM) video, with the volume contraction reaching 18.7% and 11.3%, respectively. The mechanisms for volume contraction of LT1 and LT2 phases are elucidated from the viewpoints of phase transformation, magnetic transition, and dehydrogenation, which is different from common NTE materials containing flexible polyhedra units in the structure. The linear volume shrinkage of LT2 in the temperature of 488-553 K corresponds to the phase transition of LT2→HT with a thermal expansion coefficient of -799.7 × 10^(-6) K^(-1) revealed by in-situ synchrotron powder X-ray diffraction. The sudden volume contraction in LT1 between 488 and 493 K may be caused by the rapid dehydrogenation of LT1 to Mg_(2)Ni. The revealed phenomenon in single composite material with different structures would be significant for preparing zero thermal expansion materials by tuning the fraction of LT1 and LT2 phases.

Understanding the growth mechanisms of metal-based core–shell nanostructures revealed by in situ liquid cell transmission electron microscopy

Metal-based core-shell nanostructures have garnered enduring interest due to their unique properties and functionalities.However,their growth and transformation mechanisms in liquid media remain largely unknown because they lack direct observation of the dynamic growth process with high spatial and temporal resolution.Developing the in situ liquid cell transmission electron microscopy(TEM)technique offers unprecedented real-time imaging and spectroscopy capabilities to directly track the evolution of structural and chemical transformation of metal-based core–shell nanostructures in liquid media under their working condition.Here,this review highlights recent progress in utilizing in situ liquid cell TEM characterization technique in investigating the dynamic evolution of material structure and morphology of metal-based core–shell nanostructures at the nano/atomic scale in real-time.A brief introduction of the development of liquid cells for in situ TEM is first given.Subsequently,recent advances in in situ liquid cell TEM for the fundamental study of growth mechanisms of metal based core–shell nanostructures are discussed.Finally,the challenge and future developments of metalbased core–shell nanostructures for in situ liquid cell TEM are proposed.Our review is anticipated to inspire ongoing interest in revealing unseen growth dynamics of core–shell nanostructures by in situ liquid cell TEM technique.

Recent advances in the mechanics of 2D materials

The exceptional physical properties and unique layered structure of two-dimensional(2D)materials have made this class of materials great candidates for applications in electronics,energy conversion/storage devices,nanocomposites,and multifunctional coatings,among others.At the center of this application space,mechanical properties play a vital role in materials design,manufacturing,integration and performance.The emergence of 2D materials has also sparked broad scientific inquiry,with new understanding of mechanical interactions between 2D structures and interfaces being of great interest to the community.Building on the dramatic expansion of recent research activities,here we review significant advances in the understanding of the elastic properties,in-plane failures,fatigue performance,interfacial shear/friction,and adhesion behavior of 2D materials.In this article,special emphasis is placed on some new 2D materials,novel characterization techniques and computational methods,as well as insights into deformation and failure mechanisms.A deep understanding of the intrinsic and extrinsic factors that govern 2D material mechanics is further provided,in the hopes that the community may draw design strategies for structural and interfacial engineering of 2D material systems.We end this review article with a discussion of our perspective on the state of the field and outlook on areas for future research directions.

Exploration of Strong Metal-Support Interaction in Heterogeneous Catalysts by in situ Transmission Electron Microscopy

The phenomenon of strong metal-support interaction(SMSI)observed in supported metal catalysts,usually accompanied by the formation of the encapsulation layer on metal nanoparticles,has attracted extensive research attention due to its significance in heterogeneous catalysis.Notably,great progress has been made in recent years in investigating SMSI by in situ transmission electron microscopy(TEM),along with an enhanced comprehension of the underlying mechanisms governing SMSI formation.This emerging topic summarizes recent progress utilizing in situ TEM to study the interaction between metal and support and the relationship between the structure and performance of the supported catalyst under reaction conditions.A brief perspective about the use of in situ TEM for further study of SMSI is also presented,showing prospects in this field that will stimulate further upsurging research in promoting the catalytic efficiency of supported catalysts.