Characterization of swift heavy ion tracks in MoS2 by transmission electron microscopy

The various morphologies of tracks in MoS2 irradiated by swift heavy ions at normal and 30° incidence with 9.5–25.0 MeV/u 86Kr, 129Xe, 181Ta, and 209Bi ions were investigated by transmission electron microscopy. The diameter of ion tracks increases from 1.9 nm to 4.5 nm with increasing electronic energy loss. The energy loss threshold of the track formation in MoS2 is predicted as about 9.7 keV/nm based on the thermal spike model and it seems consistent with the experimental results. It is shown that the morphology of ion tracks is related to the penetration length of ions in MoS2. The formation process of ion tracks is discussed based on the cooperative process of outflow and recrystallization of the molten phase during rapid quenching.

Exceptional reversed yield strength asymmetry in a rare-earth free Mg alloy containing quasicrystal precipitates

This work reports an exceptional reversed yield strength asymmetry at room temperature for a rare-earth free magnesium alloy containing a mass of fine dispersed quasicrystal(I-phase)precipitates.Although exhibiting traditional basal texture,it owns an exceptional CYS/TYS as high as~1.17.Electron back-scattered diffraction(EBSD)and transmission electron microscopy(TEM)examinations indicate pyramidal and prismatic dislocations plus tensile twinning being activated after immediate yielding in compression while basal and non-basal dislocations in tension.I-phase particles transferred the concentrated stress by self-twinning to provide the driving force for tensile twin initiating in neighboring grains,thereby significantly increasing the critical resolved shear stress of tensile twinning to possibly the level of pyramidal slip,finally leading to the dominance of pyramidal slip plus tensile twinning in texture grains.This results in a higher contribution on yield strength by~55 MPa in compression than in tension,which reasonably agrees with the experimental yield strength difference(~38 MPa).It can be concluded that I-phase particles influence deformation modes in tension and in compression,finally result in reversed yield strength asymmetry.

PREPARATION OF TEM THIN FOIL CONTAINING POWDER PARTICLE BY ELECTRODEPOSITION METHOD

A practical technique to prepare transmission electron microscopy （TEM） thin foil containing powder particle was described and the data for the codeposition of two type particles with copper in the electroplating were presented. By depositing the particles which were distributed in CuSO4 electrolyte on cathode together with Cu^2＋ in electrodeposition bath, composite coating with suitable thickness could be formed. The thin coating was separated from the substrate and cut into a disc with diameter of 3mm for electropolishing. When the Cu matrix was thinned during electropolishing, the particles contained in the coating plate were also thinned to meet the suitable thickness for TEM observation. Various experimental results revealed that during electrodepositing the current density, pH-value of electrolyte and stirring mode all have significant effects on the distribution of particles in composite coating and the surface quality of the composite coating. The proper parameters used during electrodepositing to prepare TEM thin foil containing powder particle were discussed.

Characterizations on the instantaneously formed Ni-containing intermetallics in magnesium alloys

Instantaneous reactions of Al,Mn,Zn,Zr and Y with Ni by mixing the prepared Mg-8Al-0.4Mn,Mg-6Zn-2Y-0.5Zr and Mg-0.6Ni melts were investigated in this work to reveal the underlying mechanisms of their effects on the removal of Ni impurity.The results indicate three Ni-containing intermetallics,namely Al_(4)NiY,Al_(4)Ni(Y,Zr)and Al_(31)Ni_(2)Mn_(6).The former two phases present lath-like and have a relatively larger size(>20μm in length)than the latest one which is granular with the diameter of∼120 nm.This illustrates that Al and Y(/Zr)can efficiently remove Ni by forming Al_(4)NiY or Al_(4)Ni(Y,Zr)which would precipitate to the bottom of the melt.Furthermore,adding Y into Mg-Al based alloys can simultaneously remove Fe and Ni,which contributes their excellent corrosion resistance.Finally,this paper proposes two methods helped to efficiently remove Ni for both Mg-Al based alloys and Al-free Mg alloys,and both of them are also benefit to improve alloys’strength.

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.

Atomic mechanisms of hexagonal close-packed Ni nanocrystallization revealed by in situ liquid cell transmission electron microscopy

The fundamental understanding of the mechanism underlying the early stages of crystallization of hexagonal-close-packed(hcp)nanocrystals is crucial for their synthesis with desired properties,but it remains a significant challenge.Here,we report using in situ liquid cell transmission electron microscopy(TEM)to directly capture the dynamic nucleation process and track the real-time growth pathway of hcp Ni nanocrystals at the atomic scale.It is demonstrated that the growth of amorphous-phase-mediated hcp Ni nanocrystals is from the metal-rich liquid phases.In addition,the reshaped preatomic facet development of a single nanocrystal is also imaged.Theoretical calculations further identify the non-classical features of hcp Ni crystallization.These discoveries could enrich the nucleation and growth model theory and provide useful information for the rational design of synthesis pathways of hcp nanocrystals.

Microstructural Characteristics of Epitaxial BaSrNb_(0.3)Ti_(0.7)O_3 Film

Microstructural characteristics in the BaSrNb0.3Ti0.7O3 thin film, grown on SrTiO3 substrate by computercontrolled laser molecular beam epitaxy, were characterized by means of transmission electron microscopy （TEM）. It is found that the film is single-crystallized and epitaxially grown on the SrTiO3 substrate forming a flat and distinct interface. Anti-phase domains were identified, and the crystallographic features of mismatch dislocations at the interface between film and substrate were clarified. The high conductivity of the present film was discussed from the viewpoint of Nb dopant and the nitrogen atmosphere.

GROWTH AND MORPHOLOGY OF POLYMER-ACTIN COMPLEXES

F-actins are semi-flexible polyelectrolytes and can be assembled into large polymer-actin complex with polymorphism through electrostatic interaction with polycations. This study investigates the structural phase behavior and the growth of polymer-actin complexes in terms of its longitudinal and lateral sizes. Our results show that formation of polymer-actin complexes is cooperative, and morphology and growth of polymer-actin complexes depend on polycation species and concentrations of polycation and salt in a constant actin concentration. We found that the longitudinal growth and lateral growth of polymer-actin complexes are dominated by different factors. This induces the structural polymorphism of polymer-actin complexes. Major factors to influence the polymorphism of polymer-actin complexes in polyelectrolytc system have been discussed. Our results indicate that the semi-flexible polyelectrolyte nature of F-actins is important for controlling the morphology and growth ofactin architectures in cell.

Multiplex intermetallic phases in a gravity die-cast Mg-6.0Zn-1.5Nd-0.5Zr(wt%) alloy

Components and crystal structures of the intermetallic phases in a gravity die-cast Mg-6.0Zn-1.5Nd-0.5Zr(wt%)alloy were investigated using transmission electron microscopy.The results indicate that this alloy has multiple intermetallic phases and various inner faults.Totally,six eutectoid intermetallic phases,namely W(Mg Nd Zn_(3)),T(Mg_(39)Zn_(55)Nd_(6)),(Mg,Zr)Zn_(2),Z(Mg_(28)Zn_(65)Nd_(7)),H_(2)(Mg_(15)Zn_(70)Nd_(15)),and H1(Mg_(24)Zn_(64)Nd_(11)),were simultaneously observed at grain boundaries,and six precipitates(Z,Mg_(7)Zn_(3),T,Mg_(4)Zn_(7),β_(1)-Mg Zn_(2) and β_(2)-Mg Zn_(2))were found inα-Mg grains.Furthermore,faults like sub-grain boundaries,orientation domains(coherent with the same matching plane but with different orientations),stacking faults and twins were observed in the eutectoid intermetallic phases.Finally,some new orientation relationships between the known intermetallic phases were revealed.This paper can provide new insight into alloy design for Mg-Zn-RE(RE:rare earth)based alloys.

Characterisation of a Mechanically Alloyed Oxide Dispersion Strengthened Niekel－base Superalloy

The microstructure and reerystallisation behaviour of a mechanically alloyed oxide dispersion strength-ened Ni-base superalloy MA758 (Ni30%Cr-0.3 %Al-0.5%Ti-0.6%Y_2O_3(wt%)) have been investigated by us-ing a combination of analytical techniques including optical metallography. transmission electron microscopyand differential scanning calorimetry. It has been found that the as-extruded bar has a primary recrystallisedstructure, with a grain mean linear intercept of 0.40 μm. Reerystaliisation into a coarse, columnar grain struc-ture takes place at temperature well over 1200℃ . very close to the melting start point of the alloy. The storedenergy responsible for recrystallisation is 0.31 J /g The room temperature Vickers hardness of the alloy dropsfrom 405 for the as-extruded structure to 215 after reerystallisation.

Microstructures and mechanical properties of as-cast Mg-Sm-Zn-Zr alloys with varying Gd contents

The effect of Gd content on the microstructure and tensile properties of as-cast Mg-Sm-Zn-Zr alloy has been systematically investigated.In the Mg-3Sm-0.5Zn-0.5Zr alloy, the intermetallic compounds with multiple morphologies are identified as Mg_(3)Sm phase. In addition to Mg_(3)RE phase, Mg_(5)RE phase originated from Gd addition is observed in Gd-modified alloys. It should be noted that the lattice parameters of all the observed intermetallic compounds are significantly reduced by Zn segregation. The segregation behavior of Zn in Mg_(3)Sm phase is inhibited to some extent by Gd addition due to the electronegativity difference between Sm/Gd and Zn elements. In addition, the increased Gd content effectively leads to much more accumulation of solute atoms in front of the liquid-solid interface during solidification, which can prominently promote nucleation in liquid region and then refine grains. The tensile yield stress of the present alloys is thus improved with increasing Gd addition. Finally, Gd-modified alloys exhibit significantly age-hardening effect, which can be mainly attributed to the high-volume fraction and high density nano-scale precipitates.

Deformation and removal of semiconductor and laser single crystals at extremely small scales

Semiconductor and laser single crystals are usually brittle and hard,which need to be ground to have satisfactory surface integrity and dimensional precision prior to their applications.Improvement of the surface integrity of a ground crystal can shorten the time of a subsequent polishing process,thus reducing the manufacturing cost.The development of cost-effective grinding technologies for those crystals requires an in-depth understanding of their deformation and removal mechanisms.As a result,a great deal of research efforts were directed towards studying this topic in the past two or three decades.In this review,we aimed to summarize the deformation and removal characteristics of representative semiconductor and laser single crystals in accordance with the scale of mechanical loading,especially at extremely small scales.Their removal mechanisms were critically examined based on the evidence obtained from highresolution TEM analyses.The relationships between machining conditions and removal behaviors were discussed to provide a guidance for further advancing of the grinding technologies for those crystals.

Effect of Si on austenite stabilization,martensite morphology,and magnetic properties in Fe-26%Ni-x%Si alloys

The effect of Si on the austenite stabilization, martensite morphology, and magnetic properties in Fe-26%Ni-x%Si （x=3.5, 5, and 6） alloys have been studied by means of transmission electron microscopy （TEM） and M？ssbauer spectroscopy techniques. TEM observations reveal that the martensite morphology is closely dependent on the Si content. The volume fraction changes of martensite and austenite phases, the hyperfine magnetic field, and isomer shift values have been determined by Mssbauer spectroscopy. The M？ssbauer study reveals that the hyperfine magnetic field, the isomer shift values and the volume fraction of martensite decrease with increasing Si content.

Dynamically observing the formation of MOFs-driven Co/N-doped carbon nanocomposites by in-situ transmission electron microscope and their application as high-efficient microwave absorbent

Metal-organic frameworks(MOFs)derived magnetic carbon-based nanocomposites have drawn widespread attentions due to the well distributed nanocrystals in carbon matrix.Dynamically observing the formation process is urgently needed.Herein,taking zeolitic imidazolate framework(ZIF)-67 as an example,the pyrolysis process is investigated by in-situ transmission electron microscopy(TEM)assisted with ex-situ characterizations.Co nanocrystals are evenly distributed in carbon at the initial stage of carbonization.By increasing pyrolysis temperature,the nanocrystals grow bigger and migrate to carbon surface.The carbon texture transfers from amorphous to crystalline at 600°C,and thoroughly converts at 800°C.In-situ heating TEM shows that more tiny Co nanocrystals move out from the carbon texture by increasing temperature from 700 to 800°C.At 1,000°C,some escaped tiny Co nanocrystals are volatilized and disappeared.The residual escaped Co nanocrystals catalyze the formation of carbon nanotubes(CNTs).Due to the synergistic effect between Co and carbon as well as porous structure,the nanocomposites show high-efficient microwave absorption performance,which can be tuned by pyrolysis temperature,heating rate,and mass fraction.When the mass fraction is 30 wt.%,the nanocomposites obtained at 600 or 700°C display remarkable microwave absorption with optimal reflection loss(RL)smaller than−70 dB and effective absorption band larger than 4.9 GHz.Combining the in-situ and ex-situ techniques,some key findings were observed:(1)graphitization of carbon;(2)volatilization of Co nanocrystals;(3)formation process of CNTs by Co catalyst.These findings are helpful to understand the formation of MOFs derived carbon-based composites and expand their practical applications,especially for microwave absorption.

Irradiation damage simulation of Zircaloy-4 using argon ions bombardment

To simulate irradiation damage, argon ion was implanted in the Zircaloy-4 with the fluence ranging from 1 × 10^16 to 1 × 10^17 cm^-2, using accelerating implanter at an extraction voltage of 190 kV and liquid nitrogen temperature. Then the influence of argon ion implantation on the aqueous corrosion behavior of Zircaloy-4 was studied. The valence states of elements in the surface layer of the samples were analyzed using X-ray photoelectron spectroscopy （XPS）. Transmission electron microscopy （TEM） was used to examine the microstructure of the argon-implanted samples. The potentiodynamic polarization technique was employed to evaluate the aqueous corrosion resistance of implanted Zircaloy-4 in 1 mol/L HzSO4 solution. It is found that there appear bubbles on the surface of the samples when the argon fluence is 1 × 10^16 cm^-2. The microstructure of argon-implanted samples changes from amorphous to partial amorphous, then to polycrystalline, and again to amorphous. The corrosion resistance of implanted samples linearly declines with the increase of fluence approximately, which is attributed to the linear increase of the irradiation damage.

Preparation of Gold Nanorods of High Quality and High Aspect Ratio

We report the synthesis of gold nanorods （NRs） by seed-mediated growth method. A small amount of different shapes such as triangles, hexagons and a large amount of rods are obtained by varying the proportion of seed to metal salt, adding NaOH to growth solution as well as using the seed solution of CTAB-capped agent. The gold nanorod （NR） formation yield is improved. Meanwhile, the growth mechanism of high yield gold NRs is discussed. The high quality single size NRs can be separated from polydisperse samples using surfactant-assisted nanorod self-assembly. The gold NRs synthesized were characterized by transmission electron microscopy （TEM） and UV-vis spectroscopy.

Process of New Phase Nucleation in Alloys

The article presents a generalization of our electron microscopic results got on some binary and ternary alloys based on Ni,Fe or Co.They are considered as the basis for the conclusion that chemical bonds between atoms are realized in alloys according to the principle of pair interaction.This process begins with the separation of the alloy into diffusion micro-pairs already in the liquid state,which makes it possible to consider the liquid state of the alloy as the initial stage of the new phase formation.With a subsequent decrease in temperature,particles of a new phase form inside a diffusion micro-pair.The formation of diffusion micro-pairs and phases within them occurs due to the existence in alloys,along with a metallic bond,of ionic and covalent components of a strong chemical bond at all temperatures of the condensed state.The article shows what exactly needs to be done so that such a branch of science as materials science could get rid of the empirical approach when creating new alloys.

Crystal structure determination of nanolaminated Ti_(5)Al_(2)C_(3) by combined techniques of XRPD,TEM and ab initio calculations

Crystal structure of Ti_(5)Al_(2)C_(3)was determined by means of X-ray powder diffraction(XRPD),transmission electron microscopy(TEM)and ab initio calculations.In contrast to the already known P63/mmc space group that the MAX phases crystallize,it was demonstrated that the R3_m space group could better satisfy the experimental data.The lattice parameters are a=0.30564 nm,c=4.81846 nm in a hexagonal unit cell.

Effects of Halloysite Nanotube Reinforcement in Expandable Graphite Based Intumescent Fire Retardant Coatings Developed Using Hybrid Epoxy Binder System

In this study, the effects of halloysite nanotubes （HNTs） reinforcement in expandable graphite based intumescent fire retardant coatings （IFRCs） developed using a polydimethylsiloxane （PDMS）/phenol BA epoxy system were investigated. Intumescent coating formulations were developed by incorporating different weight percentages of HNTs and PDMS in basic intumescent ingredients （ammonium polyphosphate/melamine/boric acid/expandable graphite, APP/MEL/BA/EG）. The performance of intumescent formulations was investigated by furnace fire test, Bunsen burner fire test, field emission electron microscopy （FESEM）, thermogravimetric analysis （TGA）, transmission electron microscopy （TEM）, and Fourier transform infrared analysis （FTIR）. The Bunsen burner fire test results indicated that the fire performance of HNTs and PDMS reinforced intumescent formulation has improved due to the development of silicate network over the char residue. Improved expansion in char residue was also noticed in the formulation, SH（3）, due to the minimum decomposition of char carbon. FESEM and TEM results validated the development of silicate network over char layer of coating formulations. A considerable mass loss difference was noticed during thermal gravimetric analysis （TGA） of intumescent coating formulations. Reference formulation, SH（0） with no filler, degraded at 300 ~C and lost 50% of its total mass but SH（3）, due to synergistic effects between PDMS and HNTs, degraded above 400 ~C and showed the maximum thermal stability. XRD analysis showed the development of thermally stable compound mulltie, due to the synergism of HNTs and siloxane during intumescent reactions, which enhanced fire performance. FTIR analysis showed the presence of incorporated siloxane and silicates bonds in char residue, which endorsed the toughness of intumescent char layer produced. Moreover, the synergistic effect ofHNTs, PDMS, and other basic intumescent ingredients enhanced the polymer cross-linking in binder system and improved fire resistive performance of coatings.

Tailoring Bi_(2)Te_(3) edge with semiconductor and metal properties under electron beam irradiation

In pursuit of miniaturization in the semiconductor industry,two-dimensional(2D)materials are used to fabricate new electronic devices.The topological insulator(TI)material bismuth telluride(Bi_(2)Te_(3)),as an emerging 2D material,has potential applications in electronic and spintronic devices due to its unique electrical properties.It is well known that the surface-to-volume ratio increases as the thickness of the material decreases,resulting in a more prominent edge effect.Therefore,for a single-layer Bi_(2)Te_(3),the atomic structure of the edge plays a crucial role in its electrical properties.Here,combining first-principles calculations and in situ transmission electron microscopy(TEM)experimental studies,we report that there are two types of edge structures in single-layer Bi2Te3:semiconducting flat edges and metallic zigzag edges.The dynamic evolution process of the edge structure with atomic resolution shows that the proportions of these two edges change with continuous electron beam irradiation.Our findings demonstrate the viability to use electron beam as an effective tool to precisely tailor the edge of Bi_(2)Te_(3) with desired properties,which paves the way for implementation of single-layer Bi2Te3 in electronics and spintronics.