Transmission Electron Microscopy Mode Research Articles

Structural and Hydrogen Evolution Electrocatalysis Properties of Cr–Al–B MAB Phase Thin Films

Thin‐film materials libraries (MLs) in the system Cr–Al–B are synthesized on 100 mm diameter Al2O3 sapphire substrates by combinatorial co‐sputtering from elemental targets at substrate temperatures of 600 and 700 °C to study phase formation of MAB phases (M = transition metal, A = A‐group element, B = boron). The formation of a mixture of two MAB phases Cr2AlB2 and Cr3AlB4 on the larger part of the ML prepared at 700 °C is observed by X‐ray diffraction and cross‐sectional transmission electron microscopy (TEM). Anisotropic growth of large grains of the MAB phases extending throughout the entire film thickness is revealed. Depending on the composition, the microstructure shows different levels of porosity and grain interlinkage. Imaging in the high‐resolution TEM mode identifies regions with Cr2AlB2, Cr3AlB4, and intermixed Cr2AlB2 and Cr3AlB4 atomic stacking sequences. Additional to the structural properties, electrocatalytic activity toward the alkaline hydrogen evolution reaction is measured. Higher activities are linked to crystalline MAB‐phase areas, further enhanced by increased porosity of the film which enlarges the surface area and the exposure of the active (010) planes.

An advanced fast method for the evaluation of multiple immunolabelling using gold nanoparticles based on low-energy STEM

We present a powerful method for the simultaneous detection of Au nanoparticles located on both sides of ultrathin sections. The method employs a high-resolution scanning electron microscope (HRSEM) operating in scanning transmission electron microscopy (STEM) mode in combination with the detection of backscattered electrons (BSE). The images are recorded simultaneously during STEM and BSE imaging at the precisely selected accelerating voltage. Under proper imaging conditions, the positions of Au nanoparticles on the top or bottom sides can be clearly differentiated, hence showing this method to be suitable for multiple immunolabelling using Au nanoparticles (NPs) as markers. The difference between the upper and lower Au NPs is so large that it is possible to apply common software tools (such as ImageJ) to enable their automatic differentiation. The effects of the section thickness, detector settings and accelerating voltage on the resulting image are shown. Our experimental results correspond to the results modelled in silico by Monte Carlo (MC) simulations.

Simplification of selective imaging of dislocation loops: diffraction-selected on-zone STEM

ABSTRACT Contrary to the conventional belief that, in transmission electron microscopy (TEM), selective and sharp imaging of dislocation loops can be realized only by accurate tilting of a specimen from the condition that the symmetrical axis of incident electron beam distribution is parallel to a zone axis of the TEM specimen (on-zone condition), we demonstrate that selective dark-field (DF) imaging of dislocation loops at on-zone condition is possible with a scanning TEM (STEM) mode that uses an objective lens aperture to select a diffraction disk of interest. Diffraction-selected on-zone STEM (DsoZ-STEM) has been applied to selective DF imaging of dislocation loops with a short axis length of <2 nm in a single-crystal aluminum irradiated by argon ions and an electron beam at room temperature. It was found that a Kikuchi line enhances the contrast among the dislocation loops and the matrix of DsoZ-STEM images. DsoZ-STEM obeyed g·b invisibility criterion and showed good agreement with a typical visibility change of a dislocation line and a loop in conventional DF images with a specific pair of ± g. In addition, dislocation loops always showed much higher brightness in the inner side compared to the outer side in DsoZ-STEM images, simplifying the distinction of dislocation loops with apparently the same long-axis direction but different b. Thus, DsoZ-STEM can simplify the selective DF imaging for the determination of the number and the character of dislocation loops.

STEM in situ thermal wave observations for investigating thermal diffusivity in nanoscale materials and devices.

Practical techniques to identify heat routes at the nanoscale are required for the thermal control of microelectronic, thermoelectric, and photonic devices. Nanoscale thermometry using various approaches has been extensively investigated, yet a reliable method has not been finalized. We developed an original technique using thermal waves induced by a pulsed convergent electron beam in a scanning transmission electron microscopy (STEM) mode at room temperature. By quantifying the relative phase delay at each irradiated position, we demonstrate the heat transport within various samples with a spatial resolution of ~10 nm and a temperature resolution of 0.01 K. Phonon-surface scatterings were quantitatively confirmed due to the suppression of thermal diffusivity. The phonon-grain boundary scatterings and ballistic phonon transport near the pulsed convergent electron beam were also visualized.

Surface-wave-sustained plasma synthesis of graphene@Fe–Si nanoparticles for lithium-ion battery anodes

Silicon encapsulated in conductive layers has proven to be an excellent method for retaining the high capacity of silicon in lithium-ion batteries (LIBs) throughout cycling. This study presents an ultra-fast, single-step, and scalable method for synthesizing graphene@Fe–Si nanoparticles via an atmospheric pressure surface-wave-sustained plasma. The verification of the synthesized nanoparticles, encompassing graphene cladding and silicon nanoparticles encapsulated in iron, was conducted through energy-dispersive x-ray spectroscopy mapping, line scanning in the transmission electron microscopy mode, and high-resolution transmission electron microscopy. Additionally, Raman spectroscopy corroborated the identity of the cladding as graphene. This study provides a viable strategy for the industrial production of anode materials for high-performance LIBs.

Investigations towards incorporation of Eu3+ and Cm3+ during ZrO2 crystallization in aqueous solution

Nuclear energy provides a widely applied carbon-reduced energy source. Following operation, the spent nuclear fuel (SNF), containing a mixture of radiotoxic elements such as transuranics, needs to be safely disposed of. Safe storage of SNF in a deep geological repository (DGR) relies on multiple engineered and natural retention barriers to prevent environmental contamination. In this context, zirconia (ZrO2) formed on the SNF rod cladding, could be employed as an engineered barrier for immobilization of radionuclides via structural incorporation. This study investigates the incorporation of Eu3+ and Cm3+, representatives for trivalent transuranics, into zirconia by co-precipitation and crystallization in aqueous solution at 80 °C. Complementary structural and microstructural characterization has been carried out by powder X-ray diffraction (PXRD), spectrum imaging analysis based on energy-dispersive X-ray spectroscopy in scanning transmission electron microscopy mode (STEM-EDXS), and luminescence spectroscopy. The results reveal the association of the dopants with the zirconia particles and elucidate the presence of distinct bulk and superficially incorporated species. Hydrothermal aging for up to 460 days in alkaline media points to great stability of these incorporated species after initial crystallization, with no indication of phase segregation or release of Eu3+ and Cm3+ over time. These results suggest that zirconia would be a suitable technical retention barrier for mobilized trivalent actinides in a DGR.

Valence band spectroscopic study of Co-doped TiO2 nanoparticles using synchrotron based advanced spectroscopic techniques

In this work, we investigate the effects of Co-doping and high-temperature annealing from 400° C to 800 °C on the structural, optical, and electronic characteristics of titanium dioxide (TiO2) nanoparticles (NPs). Sol-gel route was adopted to prepare Ti0.95Co0.05O2 (TCO) NPs. The microstructural characterization using transmission electron microscopy suggests that the grain sizes of TCO NPs enhance with annealing temperatures. The selected area electron diffraction patterns of TCO annealed at 400° C, 600° C, and 800° C show the rings which correspond to anatase, mixed, and rutile phases respectively. Energy dispersive X-ray mapping in scanning transmission electron microscopy mode exhibits the distribution of NPs and their elemental compositions. UV–Visible absorption spectra show a prominent shift to the visible region with slight variation in bandgaps. The electron energy loss spectroscopy confirms the divalent and tetravalent nature of Co and Ti ions respectively. The photo-electron spectroscopic measurements mainly valence band and resonant photoelectron spectroscopies were used to investigate the electronic environment of Co ions in the TiO2 matrix. Valence band spectroscopic results of TiO2 NPs demonstrate the role of O-2p-derived states, but for TCO samples, Co-derived states are also seen. The resonant photo-electron spectra indicate that Co 3d ions are strongly hybridized with Ti3+ defective states.

Microsecond melting and revitrification of cryo samples with a correlative light-electron microscopy approach.

We have recently introduced a novel approach to time-resolved cryo-electron microscopy (cryo-EM) that affords microsecond time resolution. It involves melting a cryo sample with a laser beam to allow dynamics of the embedded particles to occur. Once the laser beam is switched off, the sample revitrifies within just a few microseconds, trapping the particles in their transient configurations, which can subsequently be imaged to obtain a snap shot of the dynamics at this point in time. While we have previously performed such experiments with a modified transmission electron microscope, we here demonstrate a simpler implementation that uses an optical microscope. We believe that this will make our technique more easily accessible and hope that it will encourage other groups to apply microsecond time-resolved cryo-EM to study the fast dynamics of a variety of proteins.

Direct imaging of micropores in shale kerogen

Although micropores (<2 nm) play an important role in shale gas storage, these pores have not been imaged previously. Aberration-corrected scanning transmission electron microscope (AC-STEM) with a secondary electron detector (SED) has been used here to study such pores in kerogen isolated from Longmaxi shale. In addition, a three-dimensional (3D) kerogen molecular model was constructed based on 13C Nuclear Magnetic Resonance (13C NMR), Fourier transform infrared spectroscopy (FT-IR) and CO2 adsorption experiments, to further study the relationship between micropores and kerogen molecule. The results show that AC-TEM with SED can directly image pores smaller than 2 nm in the kerogen particle by operating in the scanning transmission electron microscopy (STEM) mode. These micropores can occur everywhere on the kerogen surface, which is consistent with the large micropore volume and surface area determined by gas (CO2 and N2) adsorption experiments. The surface of the 3D kerogen model is similar to that observed in the SED-STEM images in terms of surface morphology and scale. This suggests that the 3D model of the kerogen molecule is a good representation of the kerogen sample. This study links the direct images of micropores in kerogen sample and the kerogen molecular models, which is important for further understanding of shale gas storage, as these micropores and molecules provide the sites and surface energy for methane storage.

In-situ TEM investigation of failure processes in metal-plastic joint interfaces

The nano-scale failure behaviors of joint interfaces were investigated by in-situ straining technique to observe the crack propagations in a transmission electron microscope (TEM). The thin sections of bonded interfaces were subjected to tensile loading by using a specially designed specimen holder. The deformation at the crack tip before the initiation of crack and the initiation of the crack were observed in the nanometer level. The experiments with identical and dissimilar polymer/polymer welded specimens allowed us to see the plastic deformation ahead of the crack tip and the creation of craze, which is the typical failure mode of polymers. The failure of the interfaces between aluminum alloy (Al5052) and epoxy adhesive and between Al5052 and thermoplastic directly bonded by injection molding were investigated to visualize the failure behaviors in small scale before the macroscopic fracture of the interfaces. The in-situ straining technique under a high-resolution scanning transmission electron microscopy (STEM) mode enables the observation of micro deformation ahead of the crack, microvoids produced prior to the crack progression and the failure of the surface modified layer on Al surface.

The Behavior of Carbon-Coated Nanoparticles in Oxidizing and Reducing Gas Environment in Environment TEM (E-TEM) Mode

The idea of a carbon-coated nanoparticles for electrochemical catalysis is not new and was widely used in direct methanol fuel cell (DMFC) [1], since the carbon coating acts as a barrier to prevent severe oxidation, thus protecting the nanoparticles from detrimental and irreversible degradation/corrosion. Recently, this type of catalyst was demonstrated to show excellent durability towards hydrogen oxidation and evolution reactions (HOR and HER), but also oxygen evolution and reduction reactions (OER and ORR), both in acid and (especially) in alkaline environment. For example, in alkaline media, Gao et. al and Doan et. al did show the excellent performance of carbon-coated Ni nanoparticles in both HOR and HER, vs. non-coated Ni; the latter degraded quickly because of severe oxidation/passivation or severe hydride poisoning. [2,3] In this work, we synthesize carbon-coated Pd or Pd-Ni nanoparticles that are supported Vulcan carbon and study their electrochemical response in RDE. Their behavior is compared to non-carbon-coated Pd or Pd-Ni. The two kinds of catalysts materials are also thoroughly evaluated in environmental transmission electron microscopy (E-TEM) mode, using various temperature, either in high vacuum, oxygen, or hydrogen gas; these conditions were applied to mimic the inert or oxidizing/reducing environments witnessed in operating fuel cells and observe the behavior of the nanoparticles in such conditions. The experiments were conducted using a FEI TITAN E-TEM at IRCELYON, and the fast camera in the system provided the video of described experiments. It is shown that the carbon-coated Pd or Pd-Ni nanoparticles have enhanced robustness than their non-coated counterparts.

Characterization of microstructure and hardening of SLM nickel-based alloy irradiated by He ions

For the application of additively manufactured nickel-based alloys in molten salt reactors (MSRs), it is crucial to evaluate their performance in nuclear environments, especially under He-induced damage. Therefore, in this study, the irradiation damage behaviour of selective laser melted (SLM) nickel-based GH3536 alloy was studied by irradiating it with He ions at various doses. Traditionally manufactured (TM) materials were used as reference materials to evaluate the resistance of SLM GH3536 to irradiation. Transmission electron microscopy (TEM) was performed to reveal the depth distribution of irradiation-induced He bubbles, as well as the characteristics of dislocation loops, using both on-zone scanning transmission electron microscopy (STEM) and rel-rod modes. Nanoindentation tests were performed on both alloys to investigate their irradiation hardening. The TEM graphs and quantitative analysis showed that, owing to the cellular sub-grain structures, the He bubbles in the SLM alloy exhibited a lower number density but larger size than those in the TM alloy. Additionally, the SLM alloy showed inferior He tolerance but better resistance to irradiation hardening, as revealed by the nanoindentation test results. Consistency between the experimental hardness increment and calculated yield stress increment showed that the irradiation hardening of the sample was mainly caused by the presence of irradiation-induced defects. A comparison between the on-zone STEM and rel-rod modes suggested that the rel-rod mode is more effective if only the effect of irradiation-induced defects on mechanical properties is studied. Furthermore, this study provides insight into the design of SLM nickel-based alloys for nuclear industry applications.

Xe-ion-irradiation-induced structural transitions and elemental diffusion in high-entropy alloy and nitride thin-film multilayers

The study aims to understand the irradiation behavior of multilayer coatings composed of high-entropy materials. Here, we report the structural stability and elemental segregation of high-entropy TiNbZrTa/CrFeCoNi metallic and nitride multilayer coatings under 3-MeV Xe20+ ion-irradiation at room temperature and 500 °C, respectively. Transmission electron microscopy analysis shows that the microstructure of nanocrystalline CrFeCoNi high-entropy-alloy sublayers are not stable and readily transforms into amorphous state at 500 °C and/or under irradiation conditions. The elemental distribution, acquired by energy-dispersive X-ray spectroscopy under scanning transmission electron microscopy mode, shows preferential diffusion of Co and Ni into TiNbZrTa sublayers, while Fe and Cr preferentially remain within the previous CrFeCoNi sublayers. TiNbZrTaN/CrFeCoNiNx nitride multilayers exhibit a higher crystallinity and structural stability as well as resistance to diffusion at high-temperature and/or irradiation conditions than their TiNbZrTa/CrFeCoNi metallic multilayer counterparts. These findings are explained by atomic size differences, the difference in Gibbs free energy of the mixing system, and interstitial-solute-induced chemical heterogeneity. Our findings thus provide a design strategy of high entropy nitride for nuclear fuel cladding.

Tuning the magnetic anisotropy of La0.67Sr0.33MnO3 by CaTiO3 spacer layer on the platform of SrTiO3

The control of perpendicular magnetic anisotropy(PMA) of complex oxides on the widely used SrTiO3 (STO) or STO buffered silicon substrates is of technology importance in the development of integrated multifunctional oxide spintronic devices. Perovskite manganite shows great potential as magnetic layer due to its rich physical properites and spin polarized character. However, when it is directly grown on the STO or STO buffered silicon substrates, the magnetization vector lies in the in-plane direction of the film, hindering its applications such as integrated spin orbital torque devices. In this work, we manipulate the PMA of the La0.67Sr0.33MO3 (LSMO) film by regulating its lattice deformation via CaTiO3 (CTO) spacer layer on the platform of STO. High crystal quality of the heterostructures with atomic sharp interfaces and elongation of LSMO lattice along c-axis were characterized. The vibration sample magnetometer (VSM) measurement indicates that the magnetic anisotropy of LMSO can be effectively tuned from in-plane to out-of-plane by inserting CTO between STO and LSMO. The improvement of PMA in LSMO films is also dependent on the thickness of the CTO spacer layer. Furthermore, the M-T curves imply that there are different magnetic phases in the LSMO films, including the appearance of antiferromagnetic phase. The analysis by electron energy loss spectroscopy (EELS) in scanning transmission electron microscopy mode found that the valence state of Mn near the CTO/LSMO interface is lower than the LSMO bulk phase, which could explained by a polar catastrophe model. This work provides a promising avenue to tailoring PMA of perovskite manganite and paves the way to realize integrated oxide spintronic devices on STO and STO buffered silicon platform.

Ligand-Induced Ground- and Excited-State Chirality in Silicon Nanoparticles: Surface Interactions Matter.

Silicon-based light-emitting materials have emerged as a favorable substitute to various organic and inorganic systems due to silicon's high natural abundance, low toxicity, and excellent biocompatibility. However, efforts on the design of free-standing silicon nanoparticles with chiral non-racemic absorption and emission attributes are rather scare. Herein, we unravel the structural requirements for ligand-induced chirality in silicon-based nanomaterials by functionalizing with D- and L-isomers of a bifunctional ligand, namely, tryptophan. The structural aspects of these systems are established using high-resolution high-angle annular dark-field imaging in the scanning transmission electron microscopy mode, solid-state nuclear magnetic resonance, Fourier transform infrared, and X-ray photoelectron spectroscopy. Silicon nanoparticles capped with L- and D-isomers of tryptophan displayed positive and negative monosignated circular dichroic signals and circularly polarized luminescence indicating their ground- and excited-state chirality. Various studies supported by density functional theory calculations signify that the functionalization of indole ring nitrogen on the silicon surface plays a decisive role in modifying the chiroptical characteristics by generating emissive charge-transfer states. The chiroptical responses originate from the multipoint interactions of tryptophan with the nanoparticle surface through the indole nitrogen and -CO2- groups that can transmit an enantiomeric structural imprint on the silicon surface. However, chiroptical properties are not observed in phenylalanine- and alanine-capped silicon nanoparticles, which are devoid of Si-N bonds and chiral footprints. Thus, the ground- and excited-state chiroptics in tryptophan-capped silicon nanoparticles originates from the collective effect of ligand-bound emissive charge-transfer states and chiral footprints. Being the first report on the circularly polarized luminescence in silicon nanoparticles, this work will open newer possibilities in the field of chirality.

Fast determination of sample thickness through scanning moiré fringes in scanning transmission electron microscopy

Sample thickness is an important parameter in transmission electron microscopy (TEM) imaging for interpreting image contrast and understanding the relationship between properties and microstructure. In this study, we introduce a method for sample thickness determination in scanning TEM (STEM) mode based on scanning moiré fringes (SMFs). Focal-series SMF imaging is used and sample thickness can be determined in situ at a medium magnification range, with beam damage and contamination avoided to a large extent. It provides a fast and convenient approach for determining sample thickness in TEM imaging, which is particularly useful for beam-sensitive materials.

Crystal Structure, Microstructure and Electronic Properties of a Newly Discovered Ternary Phase in the Al-Cr-Sc System

This study focused on the crystal and electronic structures of a newly discovered phase in the Al-Cr-Sc system. The latter two species do not mix in a binary alloy, but can be alloyed with aluminium in the vicinity of the Al2−xCrxSc composition, where 0.3 &lt; x &lt; 0.5. After preparation of the pure constituents via arc melting, high-temperature annealing at 990 °C for 240 h was required to achieve full mixing of the elements. A detailed characterisation of the crystal structure, alloy microstructure and stability was obtained using single-crystal X-ray diffraction (SCXRD) and powder X-ray diffraction (PXRD), in addition to transmission electron microscopy (TEM), especially in high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) mode, scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDXS) and differential scanning calorimetry (DSC) measurements. The crystal structure was refined to a hexagonal unit cell of the MgZn2 type, space group no. 194, P63/mmc, which belongs to the Laves phases family. Special attention was paid to the occupancy of the crystallographic sites that were filled by both Cr and Al atoms. First-principles calculations based on the density functional theory (DFT) were performed to investigate the electronic structure of this ternary phase. The total density of states (DOS) exhibited a pronounced sp character, where a shallow pseudo-gap was visible 0.5 eV below the Fermi energy that brought a small but definite contribution to the thermodynamic stability of the compound.

Chemical solution deposition of epitaxial indium- and aluminum-doped Ga2O3 thin films on sapphire with tunable bandgaps

Compared to the vacuum-required deposition techniques, the chemical solution deposition (CSD) technique is superior in terms of low cost and ease of cation adjustment and upscaling. In this work, highly epitaxial indium- and aluminum-doped Ga2O3 thin films are deposited using a novel CSD technique. The 2θ, rocking curve, and φ-scan modes of x-ray diffraction (XRD) measurements and high-resolution transmission electron microscopy suggest that these thin films have a pure beta phase with good in- and out-of-plane crystallization qualities. The effect of incorporating indium and aluminum into the crystallization process is studied using high-temperature in situ XRD measurements. The results indicate that indium and aluminum doping can shift the crystallization of the thin films to lower and higher temperatures, respectively. Additionally, ultraviolet-visible spectroscopy measurements indicate that the bandgap of the sintered thin films can be tuned from 4.05 to 5.03 eV using a mixed precursor solution of In:Ga = 3:7 and Al:Ga = 3:7. The photodetectors based on the (InGa)2O3, pure Ga2O3, and (AlGa)2O3 samples exhibit the maximum photocurrents at 280, 255, and 230 nm, respectively. The results suggest that the described CSD technique is promising for producing high-quality bandgap tunable deep-ultraviolet photoelectrical and high-power devices.

Formation of Bubble-Loop Complexes During Helium Radiation in Fe-9Cr Steel

In the present study, the Fe-9Cr model alloy was irradiated with 240 keV He2+ at 550°C with a dose of 0.5 dpa at the peak damage region. The depth distribution of bubbles in Fe-9Cr alloy was investigated by transmission electron microscopy (TEM). The experimental results revealed that the spatial distribution of bubbles along the depth is different. In the region with higher helium concentration and irradiation dose, the bubbles inclined to be situated inside the plane of loops, forming a structure of “bubble-loop complex.” However, in regions where the helium concentration and irradiation dose are relatively low, the number of “bubble-loop complexes” significantly decreased. In addition, the Burgers vector of “bubble-loop complexes” was identified as &amp;lt;100&amp;gt; type. Radiation-induced enrichment of Cr atoms at the “bubble-loop complexes” was also quantitatively estimated by energy-dispersive X-ray spectroscopy (EDS) in the scanning TEM mode.

Magnetic imaging of various topological spin textures and their dynamics

Nanometer-scale vortex-like topological spin textures, such as magnetic skyrmion and antiskyrmion, have recently attracted enormous attention owing to their topological nature and emergent electromagnetic properties. To confirm such minute twisted spin textures and their dynamics under external stimuli, real-space imaging techniques with high spatial resolution and high recording speed are required.To realize the Bloch-type magnetic skyrmion with a topological number of − 1 (where spins swirl from the north-pole in the core to the south-pole in the peripheral, and wrap a sphere), we have developed a technique allowing not only to create skyrmions via precise control of the magnetic field in a standard transmission electron microscope (TEM), but also to directly demonstrate their twisted textures and dynamics. We employed a phase imaging technique, called differential-phase contrast, in the scanning TEM mode to quantitatively characterize Néel-type magnetic twists, such as Bloch lines, that constitute the antiskyrmion with a topological number + 1. Furthermore, we took advantage of cryogenic high-resolution Lorentz TEM to probe atomic-scale skyrmions in a centrosymmetric magnet with a Ruderman–Kittel–Kasuya–Yosida coupling.To manipulate and track individual skyrmions and their lattice using a relatively low electric current, combined with field-quenching of skyrmions, we designed a thin FeGe microdevice having a notch, in which the spin current was localized in the specific area near a corner of the notch. Using this device, we tracked drift, Hall, and torque motions of single 80-nm-sized skyrmions and their bunches using electric current densities three orders of magnitude lower than those required to manipulate magnetic domain walls.