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.

Preparation,Growth Mechanisms and Characterizations of ZnSe Films via the Solvothermal Method

With diethylamine as a solvent, ZnSe films were formed on the Si substrate directly from zinc and selenium through the modified solvothermal method. The effects of holding temperature, deposition time and substrate surface treatment on the quality and morphologies of the ZnSe films were investigated. The growth mechanism of ZnSe films was proved to be a layer-nucleation growth process, which was tied in with the Stranski-Krastanov （SK） model. ZnSe films were identified by the X-ray diffraction pattern （XRD）, the scanning electron microscope （SEM）, the X-ray photoelectron spectroscope （XPS） and the photoluminescence （PL） techniques. The results indicate that the modified solvothermal method with diethylamine as a solvent is suitable to prepare high quality ZnSe films.

Corrosion fatigue crack growth mechanisms in welded joints of marine steel structures

This paper presents a model of fatigue crack growth in a welded joint and a two-dimensional model of anodic dissolution based on Donahue model and anodic dissolution mechanism,respectively.In addition,a model for predicting the corrosion fatigue crack growth rate in welded joints of steel marine structures is established and crack growth mechanisms are analyzed.The results show that during early stages of crack growth,corrosion fatigue crack growth rate in welded joints is mainly controlled by corrosion action,whereas cyclic loading becomes more influential during the later stage of crack propagation.Loading frequency and effective stress ratio can affect rupture period of protective film at the corrosion fatigue crack tip and the length of corrosion crack increment,respectively,which changes the influence of corrosion action on crack growth rate.However,the impact of stress amplitude on crack growth rate is only significant when crack propagation is caused by cyclic loading.Welding residual stress not only improves the effective stress ratio of cyclic loading,but also promotes crack closure and increases corrosion fatigue crack growth rate in welded joints.Compared to corrosion action,welding residual stress has a more significant influence on crack growth caused by cyclic loading.

Origin and growth mechanisms of strike-slip faults in the central Tarim cratonic basin, NW China

Through fault structure analysis and chronology study, we discuss the origin and growth mechanisms of strike-slip faults in the Tarim Basin.(1) Multiple stages strike-slip faults with inherited growth were developed in the central Tarim cratonic basin. The faults initiation time is constrained at the end of Middle Ordovician of about 460 Ma according to U-Pb dating of the fault cements and seismic interpretation.(2) The formation of the strike-slip faults was controlled by the near N-S direction stress field caused by far-field compression of the closing of the Proto-Tethys Ocean.(3) The faults localization and characteristics were influenced by the pre-existing structures of the NE trending weakening zones in the basement and lithofacies change from south to north.(4) Following the fault initiation under the Andersonian mechanism, the strike-slip fault growth was dominantly fault linkage, associated with fault tip propagation and interaction of non-Andersonian mechanisms.(5) Sequential slip accommodated deformation in the conjugate strike-slip fault interaction zones, strong localization of the main displacement and deformation occurred in the overlap zones in the northern Tarim, while the fault tips, particularly of narrow-deep grabens, and strike-slip segments in thrust zones accumulated more deformation and strain in the Central uplift. In conclusion, non-Andersonian mechanisms, dominantly fault linkage and interaction, resulted in the small displacement but long intraplate strike-slip fault development in the central Tarim Basin. The regional and localized field stress, and pre-existing structures and lithofacies difference had strong impacts on the diversity of the strike-slip faults in the Tarim cratonic basin.

Growth mechanisms for spherical Ni_(0.815)Co_(0.15)Al_(0.035)(OH)_(2) precursors prepared via the ammonia complexation precipitation method

The microstructures of precursors strongly affect the electrochemical performance of Ni-rich layerstructured cathode materials.In this study,the growth behaviour of Ni_(0.815)Co_(0.15)Al_(0.035)(OH)_2(NCA) prepared via the ammonia complexation precipitation method in a 50-L-volume continuously stirred tank reactor(CSTR) is studied in detail.The growth of Ni(OH)2-based hydroxide can be divided into a nucleation process,an agglomeration growth process,a process in which multiple growth mechanisms coexist,and an interface growth process over time,while the inner structure of the CSTR can be divided into a nucleation zone,a complex dissolution zone,a growth zone,and a maturation zone.The concentration of ammonium ions affects the growth habit of the primary crystal significantly due to its specific adsorption on the electronegative crystal plane.When the ammonia concentration is <1.5 mol L^(-1) at 60℃ at pH=11.5,the precursors grow preferentially along the(1 0 1) crystal plane,whereas they grow preferentially along the(0 0 1) crystal plane when the concentration is >2.0 mol L^(-1).The LiNi_(0.815)Co_(0.15)Al_(0.035)O_2 materials inherit the grain structure of the precursor.Materials prepared from precursors with(1 0 1)preferential primary particles show a higher specific capacity and better rate performance than those that were prepared from(0 0 1) preferential primary particles,but the latter realize a better cycling performance than the former.

Comparison of growth mechanisms of undoped and nitrogen-doped carbon nanofibers on nickel-containing catalysts

The growth mechanisms of carbon nanofibers on Ni catalysts and nitrogen-doped carbon nanofibers on Ni and Ni-Cu catalysts were studied.The growth of both types of nanofibers was found to occur by a mechanism that included the formation of surface non-stoichiometric nickel carbide followed by the dissolution and diffusion of carbon,or carbon and nitrogen into the bulk of the catalyst particles.

Size, phase-controlled synthesis,the nucleation and growth mechanisms of NaYF_4:Yb/Er nanocrystals

Near-monodisperse NaYF4：Yb/Er nanoparticles（NPs） with controlled size, phases（α,β） and shapes（sphere, and hexagonal plate） were synthesized by adjusting the NaF to RE（RE = Y, Yb, Er） ratios, the reaction temperature and time in the hot surfactant solutions（oleic acid, 1-octadecene） from the improved one-pot thermal decomposition metal trifluoroacetate, and the precursors were prepared via hydrothermal route. The growth kinetics of β-NaYF4 NPs includes several stages： nucleation, growth of aNaYF4, Ostwald ripening, size shrinkage and growth. The results prove that the temperatures are preferred to the phase transformation compared with the NaF content when other experimental conditions are unchanged. Our work will further facilitate the comprehension of the nucleation and growth mechanisms of the NPs, and provide guidance for their controlled synthesis.

Synthesis of Al_(4)SiC_(4) powders via carbothermic reduction: Reaction and grain growth mechanisms

Highly pure Al_(4)SiC_(4) powders were prepared by carbothermic reduction at 2173 K using Al_(2)O_(3),SiO_(2),and graphite as raw materials.The obtained Al_(4)SiC_(4) powders owned hexagonal plate-like grains with a diameter of about 200-300μm and a thickness of about 2-6μm.Based on the experimental results,the reaction of Al_(4)SiC_(4) formation and grain evolution mechanisms were determined from thermodynamic and first-principles calculations.The results indicated that the synthesis of Al_(4)SiC_(4) by the carbothermic reduction consisted of two parts,i.e.,solid-solid reactions initially followed by complex gas-solid and gas-gas reactions.The grain growth mechanism of Al_(4)SiC_(4) featured a two-dimensional nucleation and growth mechanism.The gas phases formed during the sintering process favored the preferential grain growth of(0010)and(110)planes resulting in formation of hexagonal plate-like Al_(4)SiC_(4) grains.

Mega-towns in China:Their spatial distribution features and growth mechanisms

As a special outcome of urbanization,mega-towns not only play an important role in the process of socio-economic development,but also are important contributors to urbanization.Based on a spatial database of mega-towns in China,this paper explores the spatial distribution features and growth mechanisms of China’s 238 mega-towns using the nearest neighbour distance method,kernel density estimation,regression analysis,global autocorrelation,local autocorrelation and other spatial analysis methods.Results of spatial distribution features show that:(1)on the national scale,the existing 238 mega-towns mainly gathered in the southeast coastal areas of China;they formed two spatial core agglomerations,several secondary ones and a southeast coastal agglomeration belt;(2)on the regional scale,each economic region’s index was less than 1,indicating that mega-towns in each region tended to be spatially agglomerated due to the close relationship with regional development level and their number;(3)on the provincial scale,68%of provincial-level units in China tended to be a spatial agglomeration of mega-towns;only one province had a random distribution;the number of mega-towns in those evenly-distributed provinces was generally small.The growth of mega-towns was determined by a combination of various natural and humanistic factors,including topography,location,economy,population,traffic,and national policy.This paper chose digital elevation model(DEM),location advantage,economic density,population density,and highway density distribution as corresponding indicators as quantitative factors.By combining their local autocorrelation analysis,these factors all showed certain influence on the spatial growth of mega-towns and together scheduled it.In the future,provinces and cities should make full use of the mega-town functions to promote their socioeconomic development,especially the central and western regions in China.

Microscopic growth mechanism and edge states of monolayer 1T'-MoTe_(2)

Transition metal ditellurides(TMTDs)have versatile physical properties,including non-trivial topology,Weyl semimetal states and unique spin texture.Controlled growth of high-quality and large-scale monolayer TMTDs with preferred crystal phases is crucial for their applications.Here,we demonstrate the epitaxial growth of 1T'-MoTe_(2) on Au(111)and graphitized silicon carbide(Gr/SiC)by molecular beam epitaxy(MBE).We investigate the morphology of the grown1T'-MoTe_(2) at the atomic level by scanning tunnelling microscopy(STM)and reveal the corresponding microscopic growth mechanism.It is found that the unique ordered Te structures preferentially deposited on Au(111)regulate the growth of monolayer single crystal 1T'-MoTe_(2),while the Mo clusters were preferentially deposited on the Gr/SiC substrate,which impedes the ordered growth of monolayer MoTe_(2).We confirm that the size of single crystal 1T'-MoTe_(2) grown on Au(111)is nearly two orders of magnitude larger than that on Gr/SiC.By scanning tunnelling spectroscopy(STS),we observe that the STS spectrum of the monolayer 1T'-MoTe_(2) nano-island at the edge is different from that at the interior,which exhibits enhanced conductivity.

Orientation variation along growth direction of millimeter free-standing CVD diamond thinned by mechanical grinding

A free-standing diamond film with millimeter thickness prepared by DC arc plasma jet was thinned successively by mechanical grinding. The orientation and quality of the diamond films with different thicknesses were characterized by X-ray diffraction and Raman spectroscopy, respectively. The results show a random grain-orientatinn distribution during the initial growth stage. As the film thickness increases, the preferred orientation of the diamond film changes from （111） to （220）, due to the competitive growth mechanism. Twinning generated during the nucleation stage appears to stabilize the preferential growth along the 〈110〉 direction. The interplanar spacing of the （220） plane is enlarged as the film thickness increases, which is caused by the increase of non-diamond-phase carbon and impurities under the cyclic gas. In addition, the quality of the diamond film is barely degraded during the growth process. Furthermore, the peak shift demonstrates a significant inhomogeneity of stress along the film growth direction, which results from competitive growth.

Growth Mechanism of Microcrystalline Silicon Films by Scaling Theory and Monte Carlo Simulation

Hydrogenated microcrystalline silicon （~c-Si：H） films with a high deposition rate of 1.2nm/s were prepared by hot-wire chemical vapor deposition （HWCVD）. The growth-front roughening processes of the μc-Si..H films were investi- gated by atomic force microscopy. According to the scaling theory, the growth exponent β≈0.67, the roughness exponent α≈0.80,and the dynamic exponent 1/z = 0.40 are obtained. These scaling exponents cannot be explained well by the known growth models. An attempt at Monte Carlo simulation has been made to describe the growth process of μc-Si： H film using a particle reemission model where the incident flux distribution,the type and concentration of growth radical, and sticking,reemission,shadowing mechanisms all contributed to the growing morphology.

Research of growth mechanism of ceramic coatings fabricated by micro-arc oxidation on magnesium alloys at high current mode

Micro-arc oxidation(MAO)coatings of ZK60 magnesium alloys were formed in a self-developed dual electrolyte composed of sodium silicate and phosphate at the high constant current of 1.8 A(15 A/dm^(2)).The MAO process and growth mechanism were investigated by scanning electron microscopy(SEM)coupled with an energy dispersive spectrometer(EDS),confocal laser scanning microscopy and X-ray diffraction(XRD).The results indicate that the growth process of MAO coating mainly goes through“forming→puncturing→rapid growth of micro-arc oxidation→large arc discharge→self-repairing”.The coating grows inward and outward at the same time in the initial stage,but outward growth of the coating is dominant later.Mg,Mg_(2)SiO_(4) and MgO are the main phases of ceramic coating.

Recent progresses in the suppression method based on the growth mechanism of lithium dendrite

Lithium secondary batteries（LSBs） with high energy densities need to be further developed for future applications in portable electronic devices, electric vehicles, hybrid electric vehicles and smart grids. Lithium metal is the most promising electrode for next-generation rechargeable batteries. However, the formation of lithium dendrite on the anode surface leads to serious safety concerns and low coulombic efficiency.Recently, researchers have made great efforts and significant progresses to solve these problems. Here we review the growth mechanism and suppression method of lithium dendrite for LSBs’ anode protection. We also establish the relationship between the growth mechanism and suppression method. The research direction for building better LSBs is given by comparing the advantages and disadvantages of these methods based on the growth mechanism.

GROWTH MECHANISM OF TiC WHISKERS PREMRED BY A MODIFIED CHEMICAL VAPOR DEPOSITION METHOD

High quality TiC whiskers have been prepared by a modified chemical vapor deposition (CVD) method using TiCl4 and CH4 as reactant gases and Ni as substrate. The deposition temperature and gas flow mies have ampreciable effect on the whisker growth.The whisker orientations and morphology are determined by X-my diffraction (XRD),scanning electron micmpmph (SEM) and transmission electron microgmph (TEM).In addition to the spherical tips, spiral growth microsteps and obvious terraces are observed at the tips and side faces of whiskers in the present eoperiment. The whiskers grow mostly along (100) direction. The whisker growth mechanism is discussed in detail.

Morphology and growth of porous anodic oxide films on Ti-10V-2Fe-3Al in neutral tartrate solution

Porous anodic oxide films were fabricated galvanostatically on titanium alloy Ti-10V-2Fe-3Al in ammonium tartrate solution with different anodizing time.Scanning electron microscopy(SEM) and field emission scanning electron microscopy(FE-SEM) were used to investigate the morphology evolution of the anodic oxide film.It is shown that above the breakdown voltage,oxygen is generated with the occurrence of drums morphology.These drums grow and extrude,which yields the compression stress.Subsequently,microcracks are generated.With continuous anodizing,porous oxides form at the microcracks.Those oxides grow and connect to each other,finally replace the microcrack morphology.The depth profile of the anodic oxide film formed at 1 800 s was examined by Auger electron spectroscopy(AES).It is found that the film is divided into three layers according to the molar fractions of elements.The outer layer is incorporated by carbon,which may come from electrolyte solution.The thickness of the outer layer is approximately 0.2-0.3 μm.The molar fractions of elements in the intermediate layer are extraordinarily stable,while those in the inner layer vary significantly with sputtering depth.The thicknesses of the intermediate layer and the inner layer are 2 μm and 1.0-1.5 μm,respectively.Moreover,the growth mechanism of porous anodic oxide films in neutral tartrate solution was proposed.

Growth kinetics and mechanism of microarc oxidation coating on Ti-6Al-4V alloy in phosphate/silicate electrolyte

Microarc oxidation(MAO)is an effective surface treatment method for Ti alloys to allow their application in extreme environments.Here,binary electrolytes consisting of different amounts of sodium phosphate and sodium silicate were designed for MAO.The surface morphology,composition,and properties of MAO coatings on Ti-6Al-4V alloy treated in 0.10 mol/L electrolyte were investigated to reveal the effect of PO_(4)^(3-)and SiO_(3)^(2-)ray diffraction,and potentiodynamic polarization.The results showed that PO_(4)^(3-)is beneficial for generating microarcs and forming pores within the coating,resulting in a thick but porous coating.SiO_(3)^(2-)eration of microarcs,resulting in a thin dense coating.The thickness,density,phases content,and polarization resistance of the MAO coatings are primarily affected by the intensity of microarcs for low SiO_(3)^(2-)ciently high.The thickness of MAO coatings obtained in P/Si electrolytes shows a piecewise linear increase with increasing process time during the three stages of microarc discharge.SiO_(3)^(2-)discharge,but slows down the growth of the coating formed in the next stage.

Effect of crystallographic orientation on crack growth behaviour of HSLA steel

In this work,the crack growth behaviours of high strength low alloy(HSLA)steel E690 with three crystallographic orientations(the rolling direction,normal direction,and transverse direction)were investigated and compared from the view of the mechano-electrochemical ef-fect at the crack tip.The results show that the crack growth of the HSLA steel is controlled by the corrosion fracture at the crack tip.The vari-ation of crystallographic orientation in E690 steel plate has no influence on the crack tip electrochemical reaction and crack growth mechanism,but changes the crack growth rate.When the stress loading direction is parallel to the rolling direction and the fracture layer is parallel to the transverse-normal plane,the crack growth rate is the slowest with a value of 0.0185 mm·h^(-1).When the load direction and the fracture layer are parallel to the normal direction and the rolling-transverse plane,respectively,the crack growth rate is the highest with a value of 0.0309 mm·h^(-1).This phenomenon is ascribed to the different microstructural and mechanical properties in the rolling direction,normal direction,and transverse direction of E690 steel plate.

Growth mechanism and photocatalytic evaluation of flower-like ZnO microstructures prepared with SDBS assistance

Flower-like ZnO microstructures were successfully produced using a hydrothermal method employing ZnSO_(4)/(NH_(4))_(2)SO_(4) as a raw material.The effect of the operating parameters of the hydrothermal temperature, OH^(-)/Zn^(2+) molar ratio, time, and amount of dispersant on the phase structure and micromorphology of the ZnO particles were investigated.The synthesis conditions of the flower-like ZnO microstructures were: hydrothermal temperature of 160℃, OH^(-)/Zn^(2+) molar ratio of 5:1, reaction time of 4 h, and 4 mL of dispersant.The flower-like ZnO microstructures were comprised of hexagon-shaped ZnO rods arranged in a radiatively.Degradation experiments of Rhodamine B with the flower-like ZnO microstructures demonstrated a degradation efficiency of 97.6% after 4 h of exposure to sunshine, indicating excellent photocatalytic capacity.The growth mechanism of the flower-like ZnO microstructures was presented.