Characterization of local chemical ordering and deformation behavior in high entropy alloys by transmission electron microscopy

Short-range ordering(SRO)is one of the most important structural features of high entropy alloys(HEAs).However,the chemical and structural analyses of SROs are very difficult due to their small size,complexed compositions,and varied locations.Transmission electron microscopy(TEM)as well as its aberration correction techniques are powerful for characterizing SROs in these compositionally complex alloys.In this short communication,we summarized recent progresses regarding characterization of SROs using TEM in the field of HEAs.By using advanced TEM techniques,not only the existence of SROs was confirmed,but also the effect of SROs on the deformation mechanism was clarified.Moreover,the perspective related to application of TEM techniques in HEAs are also discussed.

Capturing the non-equilibrium state in light–matter–free-electron interactions through ultrafast transmission electron microscopy

Ultrafast transmission electron microscope(UTEM) with the multimodality of time-resolved diffraction, imaging,and spectroscopy provides a unique platform to reveal the fundamental features associated with the interaction between free electrons and matter. In this review, we summarize the principles, instrumentation, and recent developments of the UTEM and its applications in capturing dynamic processes and non-equilibrium transient states. The combination of the transmission electron microscope with a femtosecond laser via the pump–probe method guarantees the high spatiotemporal resolution, allowing the investigation of the transient process in real, reciprocal and energy spaces. Ultrafast structural dynamics can be studied by diffraction and imaging methods, revealing the coherent acoustic phonon generation and photoinduced phase transition process. In the energy dimension, time-resolved electron energy-loss spectroscopy enables the examination of the intrinsic electronic dynamics of materials, while the photon-induced near-field electron microscopy extends the application of the UTEM to the imaging of optical near fields with high real-space resolution. It is noted that light–free-electron interactions have the ability to shape electron wave packets in both longitudinal and transverse directions, showing the potential application in the generation of attosecond electron pulses and vortex electron beams.

In situ observation of the electrochemical behavior of Li–CO_(2)/O_(2)batteries in an environmental transmission electron microscope

Li–CO_(2)/O_(2)batteries,a promising energy storage technology,not only provide ultrahigh discharge capacity but also capture CO_(2)and turn it into renewable energy.Their electrochemical reaction pathways'ambiguity,however,creates a hurdle for their practical application.This study used copper selenide(CuSe)nanosheets as the air cathode medium in an environmental transmission electron microscope to in situ study Li–CO_(2)/O_(2)(mix CO_(2)as well as O_(2)at a volume ratio of 1:1)and Li–O_(2)batteries as well as Li–CO_(2)batteries.Primary discharge reactions take place successively in the Li–CO_(2)/O_(2)–CuSe nanobattery:(I)4Li^(+)+O_(2)+4e^(−)→2Li_(2)O;(II)Li_(2)O+CO_(2)→Li_(2)CO_(3).The charge reaction proceeded via(III)2Li_(2)CO_(3)→4Li^(+)+2CO_(2)+O_(2)+4e^(−).However,Li–O_(2)and Li–CO_(2)nanobatteries showed poor cycling stability,suggesting the difficulty in the direct decomposition of the discharge product.The fluctuations of the Li–CO_(2)/O_(2)battery's electrochemistry were also shown to depend heavily on O_(2).The CuSe‐based Li–CO_(2)/O_(2)battery showed exceptional electrochemical performance.The Li^–CO_(2)/O_(2)battery offered a discharge capacity apex of 15,492 mAh g^(−1) and stable cycling 60 times at 100 mA g^(−1).Our research offers crucial insight into the electrochemical behavior of Li–CO_(2)/O_(2),Li–O_(2),and Li–CO_(2)nanobatteries,which may help the creation of high‐performance Li–CO_(2)/O_(2)batteries for energy storage applications.

A transmission electron microscopy study of the diversity of Candida albicans cells induced by Euphorbia hirta L.leaf extract in vitro

Objective:To determine the major changes in the microstructure of Candida albicans(C. albicans) after treatment with Euphorbia hirta(E.hirta) L.leaf extract.Methods:Transmission electron microscopy was used to study the ultrastructural changes caused by E.hirta extract on C. albicans cells al various exposure time.Results:It was found that the main abnormalities were the alterations in morphology,lysis and complete collapse of the yeast cells after 36 h of exposure to the extract.Whereas the control cultures showed a typical morphology of Candida with a uniform central density,typically structured nucleus,and a cytoplasm with several elements of endomembrane system and enveloped by a regular,intact cell wall.Conclusions:The significant antifungal activity shown by this methanol extract of E.hirta L.suggests its potential against infections caused by C.albicans.The extract may be developed as an anticandidal agent.

扫描电镜中透射-反射式STEM明场成像装置的研制及应用

本文研制了一套透射-反射式扫描透射(STEM)明场成像装置,该装置使用背散射电子探头接收经过铂片反射的透射电子信号,可安装在FEI Quanta FEG系列扫描电镜中实现STEM明场成像。分别以埃洛石、Au@ZIF-8纳米颗粒和喷金乳胶标样验证自制STEM明场成像装置的实用性。结果表明:埃洛石STEM明场像的衬度与透射电镜中STEM明场像一致,管腔和管壁具有明显的衬度差异,可以清晰辨识管腔结构;在Au@ZIF-8纳米颗粒的STEM明场像中,Au颗粒衬度较暗,ZIF-8衬度较亮,通过两者之间的衬度差异可以观察到核壳结构;喷金乳胶标样上纳米金颗粒之间可识别的最小距离为2.03 nm,进一步验证了自制STEM明场成像装置具有较高的分辨率。

High-resolution Transmission Electron Microscopy Characterization of the Structure of Cu Precipitate in a Thermal-aged Multicomponent Steel

High-dispersed nanoscale Cu precipitates often contribute to extremely high strength due to precipitation hardening,and whereas usually lead to degraded toughness for especially ferritic steels.Hence,it is important to understand the formation behaviors of the Cu precipitates.High-resolution transmission electron microscopy(TEM)is utilized to investigate the structure of Cu precipitates thermally formed in a high-strength low-alloy(HSLA)steel.The Cu precipitates were generally formed from solid solution and at the crystallographic defects such as martensite lath boundaries and dislocations.The Cu precipitates in the same aging condition have various structure of BCC,9 R and FCC,and the structural evolution does not greatly correlate with the actual sizes.The presence of different structures in an individual Cu precipitate is observed,which reflects the structural transformation occurring locally to relax the strain energy.The multiply additions in the steel possibly make the Cu precipitation more complex compared to the binary or the ternary Fe-Cu alloys with Ni or Mn additions.This research gives constructive suggestions on alloying design of Cu-bearing alloy steels.

Lattice Distortion Analysis Directly from High Resolution Transmission Electron Microscopy Images —the LADIA Program Package

Direct strain mapping from high resolution transmission electron microscopy images is possible for coherent structures. At proper imaging conditions the intensity peaks in the image have a constant spatial relationship with the projected atom columns. This allows the determination of the geometry of the projected unit cell without comparison with image simulations. The fast procedure is particularly suited for the analysis of large areas. The software package LADIA is written in the PV-WAVE code and provides all necessary tools for image processing and analysis. Image intensity peaks are determined by a cross-correlation technique, which avoids problems from noise in the low spatial frequency range. The lower limit of strain that can be detected at a sampling rate of 44 pixels/nm is≈2%.

Scanning transmission electron microscopy: A review of high angle annular dark field and annular bright field imaging and applications in lithium-ion batteries

Scanning transmission electron microscopy（STEM） has been shown as powerful tools for material characterization,especially after the appearance of aberration-corrector which greatly enhances the resolution of STEM. High angle annular dark field（HAADF） and annular bright field（ABF） imaging of the aberration-corrected STEM are widely used due to their high-resolution capabilities and easily interpretable image contrasts. However, HAADF mode of the STEM is still limited in detecting light elements due to the weak electron-scattering power. ABF mode of the STEM could detect light and heavy elements simultaneously, providing unprecedented opportunities for probing unknown structures of materials. Atomiclevel structure investigation of materials has been achieved by means of these imaging modes, which is invaluable in many fields for either improving properties of materials or developing new materials. This paper aims to provide a introduction of HAADF and ABF imaging techniques and reviews their applications in characterization of cathode materials, study of electrochemical reaction mechanisms, and exploring the effective design of lithium-ion batteries（LIBs）. The future prospects of the STEM are also discussed.

Transmission Electron Microscopy as a Powerful Tool for Investigating Lithium-ion Battery Materials

Transmission electron microscopy(TEM) stands out as one of the most powerful tools for characterizing materials at multiple scales and dimensions. This unique technique has nowadays been widely employed in investigating the lithium-ion battery(LIB) materials. The present perspective paper focuses on several LIB related aspects that are recently revealed by using TEM. Finally, we present outlook on the future directions of TEM for LIB research and development.

A review of in situ transmission electron microscopy study on the switching mechanism and packaging reliability in non-volatile memory

Non-volatile memory(NVM)devices with non-volatility and low power consumption properties are important in the data storage field.The switching mechanism and packaging reliability issues in NVMs are of great research interest.The switching process in NVM devices accompanied by the evolution of microstructure and composition is fast and subtle.Transmission electron microscopy(TEM)with high spatial resolution and versatile external fields is widely used in analyzing the evolution of morphology,structures and chemical compositions at atomic scale.The various external stimuli,such as thermal,electrical,mechanical,optical and magnetic fields,provide a platform to probe and engineer NVM devices inside TEM in real-time.Such advanced technologies make it possible for an in situ and interactive manipulation of NVM devices without sacrificing the resolution.This technology facilitates the exploration of the intrinsic structure-switching mechanism of NVMs and the reliability issues in the memory package.In this review,the evolution of the functional layers in NVM devices characterized by the advanced in situ TEM technology is introduced,with intermetallic compounds forming and degradation process investigated.The principles and challenges of TEM technology on NVM device study are also discussed.

Recent progress on advanced transmission electron microscopy characterization for halide perovskite semiconductors

Halide perovskites are strategically important in the field of energy materials. Along with the rapid development of the materials and related devices, there is an urgent need to understand the structure–property relationship from nanoscale to atomic scale. Much effort has been made in the past few years to overcome the difficulty of imaging limited by electron dose,and to further extend the investigation towards operando conditions. This review is dedicated to recent studies of advanced transmission electron microscopy(TEM) characterizations for halide perovskites. The irradiation damage caused by the interaction of electron beams and perovskites under conventional imaging conditions are first summarized and discussed. Low-dose TEM is then discussed, including electron diffraction and emerging techniques for high-resolution TEM(HRTEM) imaging. Atomic-resolution imaging, defects identification and chemical mapping on halide perovskites are reviewed. Cryo-TEM for halide perovskites is discussed, since it can readily suppress irradiation damage and has been rapidly developed in the past few years. Finally, the applications of in-situ TEM in the degradation study of perovskites under environmental conditions such as heating,biasing, light illumination and humidity are reviewed. More applications of emerging TEM characterizations are foreseen in the coming future, unveiling the structural origin of halide perovskite’s unique properties and degradation mechanism under operando conditions, so to assist the design of a more efficient and robust energy material.

Movement of Dislocations in the Sub-Surface of a Polycrystalline Metal by Cavitation Peening Observed by Transmission Electron Microscopy

The impact produced when cavitation bubbles collapse can be utilized to modify surfaces in the same way as shot peening and it is called cavitation peening (CP). CP is one of a number of surface modification techniques used to improve the fatigue strength of metallic materials by introducing compressive residual stress. Although it has been shown by an X-ray diffraction method that CP decreases the micro-strain related to dislocations in the sub-surface of a polycrystalline material, the mechanism for this decrease is unclear. In this paper, the movement of dislocations by CP was observed using transmission electron microscopy (TEM).

3-1 Transmission Electron Microscopy Investigations of Bubble Formation in Grain Boundaries of He-implanted Polycrystalline SiC

Because of the low cross-section for neutron capture and its excellent structural, chemical and mechanical stability, silicon carbide (SiC) is an important material with application in the development of nuclear energy and waste technologies. For example, in the fourth generation of fission reactors, such as high-temperature gas-cooled reactors and gas-cooled fast reactors, TRISO-coated particle fuel is designed, because this fuel is very robust with no failures anticipated during irradiation and under accident conditions.

Nanoscale cathodoluminescence spectroscopy probing the nitride quantum wells in an electron microscope

To gain further understanding of the luminescence properties of multiquantum wells and the factors affecting them on a microscopic level,cathodoluminescence combined with scanning transmission electron microscopy and spectroscopy was used to measure the luminescence of In_(0.15)Ga_(0.85)N five-period multiquantum wells.The lattice-composition-energy relationship was established with the help of energy-dispersive x-ray spectroscopy,and the bandgaps of In_(0.15)Ga_(0.85)N and GaN in multiple quantum wells were extracted by electron energy loss spectroscopy to understand the features of cathodoluminescence spectra.The luminescence differences between different periods of multiquantum wells and the effects of defects such as composition fluctuation and dislocations on the luminescence of multiple quantum wells were revealed.Our study establishing the direct relationship between the atomic structure of In_(x)Ga_(1-x)N multiquantum wells and photoelectric properties provides useful information for nitride applications.

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.

THE INFLUENCE OF ISLAND-INDUCED STRAIN ON THE Si SURFACE MORPHOLOGY IN Ge-Si MULTILAYERS: A TRANSMISSION ELECTRON MICROSCOPY STUDY

Growth and ordering of coherently strained Ge-rich islands in Ge/Si single layer and multilayer systems and the influence of island arrangements on the evolutio n of the surface morphology of Si cap layers during deposition by low-pressure c hemical vapour deposition(LPCVD) on Si(001) substrates at 700℃ have been invest igated by TEM of cross-section and plan-view specimens. At distances between the Ge layers of 35-50nm, vertical order of GeSi islands is observed for Ge-Si bila yer systems and for Ge-Si multilayer systems consisting of 5 layer pairs whereas lateral ordering parallel to <100> substrate directions is observed for the lat ter case only. In agreement with earlier results the vertical ordering in the mu ltilayer system can be understood as result of the elastic interaction between i sland nuclei forming in the layers with close islands in a buried layer below. T he lateral ordering along <100> may be attributed to the anisotropy of the elast ic interaction. Characteristic for all Si surfaces are the spatial correlation b etween the presence of island-induced lattice strain and the appearance of array s of larger square-shaped pyramids with distinct faceting and facet edges along <110>. The results reflect the importance of the control of growth parameters an d of the island-induced strain state for the evolution of the Si top layer surfa ce morphology during LPCVD growth.

TRANSMISSION ELECTRON MICROSCOPY INVESTIGATIONS OF LOW-PRESSURE CVD GROWTH AND STRAIN RELAXATION OF Ge ISLANDS ON Si(110)

Shapes, dimensions, arrangements and the microstructure of self-assembled island s fabricated by low-pressure chemical vapour deposition (LPCVD) of Ge at 700℃ o nto Si(110) substrates have been investigated for different nominal Ge coverage by transmission electron microscopy (TEM) of plan-view and cross-section specime ns and have been compared with photoluminescence (PL) measurements of Si-capped layer samples. The transition from the 2-dimensional layer to the 3-dimensional island growth mode takes place for a Ge deposition of nominally less than 2 mono layers. Upon this transition, many coherent islands and few larger islands with extended defects are observed. The coherent islands possess a dome-like shape an d lateral sizes up to 130nm. Photoluminescence spectra show island-related peaks whose energy positions are shifted towards lower energy with higher Ge coverage .

Misfit-layered compound PbTiS_3 with incommensurate modulation:Transmission electron microscopy analysis and transport properties

The microstructural characteristic of the misfit-layered compound PbTiS3 has been studied with transmission electron microscopy. All the incommensurate modulation-induced satellite spots and main diffraction spots of basic sublattices can be indexed systematically with a superspace group method. Finally, the relationship between the electronic transport properties and the crystal structure is discussed.

Transmission Electron Microscopy Investigation of the Ar^+ Ion Irradiation Effect in Semiconductor GaAs

Room temperature irradiation effect of GaAs compound semiconductor by 100 keV Ar+ ions has been systematically studied by means of transmission electron microscopy. The dose dependenceoof the Ar+ ion irradiation and room temperature annealing effects have been investigated. The experimental results show that the structure of GaAs transforms from perfect crystalline through weakly and severely damaged crystalline to amorphous states with the increase of the irradiation dose and the damaged states are changed during room temperature annealing.

CONTAMINATION LINE METHOD AND COMPARISON OF FOIL THICKNESS MEASUREMENT METHODS IN TRANSMISSION ELECTRON MICROSCOPY

The paper briefly introduces the Contamination Line Method for foil thickness measurement in transmission electron microscopy and compares it with four conventional methods: the convergent beam diffraction method, the contamination spot method, the methods hased on characteristic X-ray emission and continuous X-ray emission on the application, aperation and accuracy etc.