Dark-field Transmission Electron Microscopy Images Research Articles

Detection of BiGa hetero-antisites at Ga(As,Bi)/(Al,Ga)As interfaces

In this work, we show how diffraction-based chemically sensitive dark-field transmission electron microscopy (DFTEM) reveals the presence of Bi hetero-antisites (BiGa) at the interface of Ga(As,Bi)/(Al,Ga)As quantum well (QW) structures grown by molecular beam epitaxy on GaAs(001). The presence of BiGa is demonstrated by the striking appearance of “dark-lines” at the interfaces under two-beam DFTEM imaging conditions using the (002) diffraction spot. Additional analytical scanning (S)TEM procedures reveal Ga depletion and Bi accumulation at the exact position of the dark-lines, consistent with BiGa at this location. The precise location of the dark-lines agrees with the position of growth interruptions made to adjust substrate temperature and the As/Ga flux ratio and, most importantly, the realization of a Bi pre-treatment before QW growth. We believe the Bi pre-treatment may have favored formation of BiGa hetero-antisites. We validate the use of g002 DFTEM for further investigations of the intricate bismuth incorporation into the lattice and its dependence on the growth conditions. Finally, g002 DFTEM imaging is positioned as a very powerful technique for the detection of point defects in general in materials with the zinc-blende crystal structure, beyond dilute bismide alloys.

Cross-sectional transmission electron microscopy studies of Si coated heat-treated stainless steel with improved optical absorption for solar thermal applications

Heat-treatment of stainless steel substrate is reported to improve absorptance due to an increase in roughness along with the formation of surface oxides. Depositing a thin Si layer on stainless steel prior to the heat-treatment results in the formation of islands of nano-micrometer sizes with gaps between them which helps in improving absorptance. Cross-sectional Transmission Electron Microscopy studies are required to understand the development of the surface structures and improved optical properties. The cross-sectional bright- and dark-field Transmission Electron Microscopy images showed the presence of a bright Si-rich region where small nanocrystalline islands were embedded. On top of this layer, larger nanocrystalline protrusions were observed. Energy Dispersive X-ray analysis and Selected Area Diffraction data showed that the substrate elements diffuse out through the Si layer forming smaller islands of various Fe-Cr-Mn-based silicides in the Si layer and islands of Fe, Cr, and Mn-based silicides and oxides at the surface. The High-Resolution Transmission Electron Microscopy images showed that the islands are nanocrystalline in nature and are embedded in a Si-rich amorphous region. The absence of O in the Si-rich layer in SAD data was observed. Also, from the top layer EDX data, Fe peak intensity was found to be higher than Cr peak intensity. These observations indicate that the presence of the Si layer helps in reducing the inward diffusion of O into the substrate, thus preventing internal oxidation. Also, this Si layer prevents the Cr from forming a continuous Cr oxide layer and instead forms mixed oxide/silicide islands which enhance optical properties. Similar studies in the heat-treated substrate without a Si layer showed the presence of sharp-angled nanocrystalline structures of Fe-Cr-based oxides and smooth-angled nanocrystalline structures of Fe-Mn-based oxides on the surface.

Statistical Determination of Atomic-Scale Characteristics of Au Nanocrystals Based on Correlative Multiscale Transmission Electron Microscopy

Abstract Atomic-scale characteristics of individual nanocrystals (NCs), such as the crystallographic orientation of their facets and the kind and density of crystal structure defects, play a tremendous role for the functionality and performance of the whole NC population. However, these features are usually quantified only for a small number of individual particles, and thus with limited statistical relevance. In the present work, we developed the multiscale approach available in transmission electron microscopy (TEM) further, and applied it to describe features of different types of Au NCs in a statistical and scale-bridging manner. This approach combines high-resolution TEM, which is capable of describing the characteristics of NCs on atomic scale, with a semi-automatic analysis of low-magnification high-angle annular dark-field scanning TEM images, which reveals the nanoscopic morphological attributes of NCs with good statistics. The results of these complementary techniques are combined and correlated. The potential of this multiscale approach is illustrated on two examples. In the first one, the habitus of Au NCs was classified and assigned to multiply twinned nanoparticles and nanoplates. These classes were quantified and related to different stacking fault densities. The second example demonstrates the statistical determination of crystallographic orientations and configurations of facets in Au nanorods.

A modulated structure derived from the XA-type Mn2RuSn Heusler compound.

A modulated structure derived from the inverse Heusler phase (the XA-type and the disordered variant L21B-type) has been observed in rapidly quenched Mn2RuSn ribbons. The powder X-ray diffraction pattern of the quenched ribbons can be indexed as an L21B-type structure. Electron diffraction patterns of the new structure mostly resemble those of the XA-type (and the disordered variant L21B-type) structure and additional reflections with denser spacing indicate a long periodicity. Orthogonal domains of the modulated structure were revealed by a selected-area electron diffraction pattern and the corresponding dark-field transmission electron microscopy images. The structure was further studied by the crystallographic analysis of high-resolution transmission electron microscopy images. A model for the modulated structure has been proposed to interpret the experimental results.

Nanostructural Analysis of Co‐Re/γ‐Al2O3 Fischer‐Tropsch Catalyst by TEM and XRD

AbstractA rhenium promoted Fischer‐Tropsch (FT) cobalt catalyst supported on γ‐Al2O3 has been investigated by Transmission Electron Microscopy (TEM) and X‐ray Diffraction (XRD), before and after reduction. Electron diffraction, High Resolution TEM and Electron Energy Loss Spectroscopy were used to confirm the oxidation state. Cobalt aggregate, particle and crystallite sizes have been studied in detail and measured by TEM and XRD. A cobalt particle size of 10.0±2.4 nm obtained from bright field TEM images for the reduced material is consistent with the XRD analysis of the calcined catalyst. After reduction dark field TEM imaging gave a volume‐weighted crystallite size of 7.5±2.5 nm, which is close to the value obtained by XRD. The particles had lost the parallel orientation and physical continuity within the alumina pore structure that were present before reduction. The latter was confirmed by electron tomography. Lamellae identified with the presence of Hexagonal Close Packed cobalt were observed in the predominantly Face Centred Cubic particles.

Strain-Assisted Single Pt Sites on High-Curvature MoS 2 Surface for Ultrasensitive H 2 S Sensing

Strain-Assisted Single Pt Sites on High-Curvature MoS ₂ Surface for Ultrasensitive H ₂ S Sensing

Oxide Two-Dimensional Electron Gas with High Mobility at Room-Temperature.

The prospect of 2‐dimensional electron gases (2DEGs) possessing high mobility at room temperature in wide‐bandgap perovskite stannates is enticing for oxide electronics, particularly to realize transparent and high‐electron mobility transistors. Nonetheless only a small number of studies to date report 2DEGs in BaSnO3‐based heterostructures. Here, 2DEG formation at the LaScO3/BaSnO3 (LSO/BSO) interface with a room‐temperature mobility of 60 cm2 V−1 s−1 at a carrier concentration of 1.7 × 1013 cm–2 is reported. This is an order of magnitude higher mobility at room temperature than achieved in SrTiO3‐based 2DEGs. This is achieved by combining a thick BSO buffer layer with an ex situ high‐temperature treatment, which not only reduces the dislocation density but also produces a SnO2‐terminated atomically flat surface, followed by the growth of an overlying BSO/LSO interface. Using weak beam dark‐field transmission electron microscopy imaging and in‐line electron holography technique, a reduction of the threading dislocation density is revealed, and direct evidence for the spatial confinement of a 2DEG at the BSO/LSO interface is provided. This work opens a new pathway to explore the exciting physics of stannate‐based 2DEGs at application‐relevant temperatures for oxide nanoelectronics.

Boosting the Rate Performance of Li–S Batteries via Highly Dispersed Cobalt Nanoparticles Embedded into Nitrogen-Doped Hierarchical Porous Carbon

Boosting the Rate Performance of Li–S Batteries via Highly Dispersed Cobalt Nanoparticles Embedded into Nitrogen-Doped Hierarchical Porous Carbon

Major Factors Influencing the Size Distribution Analysis of Cellulose Nanocrystals Imaged in Transmission Electron Microscopy.

Size distributions of cellulose nanocrystals (CNCs), extracted from softwood pulp via strong sulfuric acid hydrolysis, exhibit large variability when analyzed from transmission electron microscopy (TEM) images. In this article, the causes of this variability are studied and discussed. In order to obtain results comparable with those reported, a reference material of CNCs (CNCD-1) was used to evaluate size distribution. CNC TEM specimens were prepared as-stained and dried with a rapid-flushing staining method or hydrated and embedded in vitreous ice with the plunge-freezing method. Several sets of bright-field TEM (BF-TEM), annular dark-field scanning TEM (ADF-STEM) and cryogenic-TEM (cryo-TEM) images were acquired for size distribution analysis to study the contributing factors. The rapid-flushing staining method was found to be the most effective for contrast enhancement of CNCs, not only revealing the helical structure of single CNCs but also resolving the laterally jointed CNCs. During TEM specimen preparation, CNCs were fractionated on TEM grids driven by the coffee-ring effect, as observed from contrast variation of CNCs with a stain-depth gradient. From the edge to the center of the TEM grids, the width of CNCs increases, while the aspect ratio (length to width) decreases. This fractionated dispersion of CNCs suggests that images taken near the center of a droplet would give a larger mean width. In addition to particle fractionation driven by the coffee-ring effect, the arrangement and orientation of CNC particles on the substrate significantly affect the size measurement when CNC aggregation cannot be resolved in images. The coexistence of asymmetric cross-section CNC particles introduces a large variation in size measurement, as TEM images of CNCs are mixed projections of the width and height of particles. As a demonstration of how this contributes to inflated size measurement, twisted CNC particles, rectangular cross-section particles and end-to-end jointed CNCs were revealed in reconstructed three-dimensional (3D) micrographs by electron tomography (ET).

Electroforming and threshold switching characteristics of NbOx films with crystalline NbO2 phase

Threshold switching (TS) and negative differential resistance (NDR) characteristic of niobium oxide (NbOx) films have been actively studied for neuromorphic computing. Generally, the electroforming process is required for TS and NDR in NbOx films. However, different electroforming and TS properties have been reported for NbOx films with different crystallinities or chemical compositions. This study investigates the effect of thermal annealing on the microstructures of NbOx films and compares the electroforming, TS, and NDR characteristics of amorphous, partially crystallized, and fully crystallized films. The distributions of crystalline NbO2 phase in NbOx films annealed at various temperatures were analyzed using transmission electron microscopy dark-field imaging, and it was observed that the distribution of crystalline NbO2 phase influenced the electroforming process. Moreover, TS characteristics improved in the thermally annealed NbOx films with crystalline NbO2 phases.

Operando leaching of pre-incorporated Al and mechanism in transition-metal hybrids on carbon substrates for enhanced charge storage

Operando leaching of pre-incorporated Al and mechanism in transition-metal hybrids on carbon substrates for enhanced charge storage

Boosting the Energy Migration Upconversion through Inter-Shell Energy Transfer in Tb 3+ -Doped Sandwich Structured Nanocrystals

Boosting the Energy Migration Upconversion through Inter-Shell Energy Transfer in Tb ³⁺ -Doped Sandwich Structured Nanocrystals

Higher-voltage asymmetric-electrolyte metal-air batteries

Higher-voltage asymmetric-electrolyte metal-air batteries

High-Performance Ru 2 P Anodic Catalyst for Alkaline Polymer Electrolyte Fuel Cells

High-Performance Ru ₂ P Anodic Catalyst for Alkaline Polymer Electrolyte Fuel Cells

Detecting minute amounts of nitrogen in GaNAs thin films using STEM and CBED

Nitrogen (N) is a common element added to GaAs for band gap engineering and strain compensation. However, detection of small amounts of N is difficult for electron microscopy as well as for other chemical analysis techniques. In this work, N in GaAs is examined by using different transmission electron microscopy (TEM) techniques. While both dark-field TEM imaging using the composition sensitive (002) reflections and selected area diffraction reveal a significant difference between the doped thin-film and the GaAs substrate, spectroscopy techniques such as electron energy loss and energy dispersive X-ray spectroscopy are not able to detect N. To quantify the N content, quantitative convergent beam electron diffraction (QCBED) is used, which gives a direct evidence of N substitution and As vacancies. The measurements are enabled by the electron energy-filtered scanning CBED technique. These results demonstrate a sensitive method for composition analysis based on quantitative electron diffraction.

An efficient combination strategy for high-performance asymmetric-electrolyte metal–air batteries

Asymmetric-electrolyte metal–air batteries (AMABs) are the most promising technologies for realizing efficient energy conversion. However, the issues in cathode and separator parts seriously impede their practical applications. This article previews the latest finding on high-voltage AMABs with long cycle stability. Impressively, the generality of the developed approach is demonstrated by the AZnABs, ASiABs and ASnABs, exhibiting the enhanced operating voltage, power densities, and excellent rate performance.

Single-phase FeMnNiAl compositionally complex alloy

FeMnNiAl, a compositionally complex alloy, in close to having an equimolar composition, was prepared in bulk and thin-film forms. Arc melting under argon was used for bulk form preparation. The thin-film alloy was produced by Ion Beam Sputter Deposition on a silicon substrate at 620 K. X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) were used to assess the material crystallinity. Both alloy forms display a single-phase and are in crystalline state. The material has a BCC lattice with the lattice constant at 4.08 Å. Dark field TEM image reveals material nanotexturing. The potentiodynamic polarisation in 0.6 moles NaCl and H2SO4 shows that open circuit potential (against saturated calomel electrode) at room temperature is approximately - 0.21 V. The alloy is demonstrated to be nobler than 304 SS (by approximately 0.1 V) and develops passivation layer in the corrosive solutions. Nanoindentation test shows that FeMnNiAl alloy thin film has high hardness at 11.7 GPa. It is anticipated that high hardness combined with the passivation ability can make the FeMnNiAl alloy coating a viable candidate for protection of metallic constructions in erosive environments

Metal–Organic Framework-Derived CuS Nanocages for Selective CO 2 Electroreduction to Formate

Electroreduction of CO2 to target products with high activity and selectivity has techno-economic importance for renewable energy storage and CO2 utilization. Herein, we report a hierarchical CuS h...

Phase-Controlled 1T Transition-Metal Dichalcogenide-Based Multidimensional Hybrid Nanostructures

Phase-Controlled 1T Transition-Metal Dichalcogenide-Based Multidimensional Hybrid Nanostructures

Morphology and structure characteristics of nanoscale carbon materials containing graphene

A comprehensive study of the nanostructured powders (graphite GSM-2; Taunit-M; thermally expanded graphite (TEG)) by methods of transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffractometry (XRD), reflection high-energy electron diffraction (RHEED), Raman spectroscopy, was carried out. The experimental XRD halo was interpreted by superimposing theoretical diffraction maxima, and an X-ray amorphous graphite phase was revealed. It was found that the X-ray amorphous phase is characterized by the limiting degree of graphite nanostructuring. From the width of the diffraction rings, the maximum sizes of graphite nanocrystals were estimated, which do not exceed 5 and 10 nm in the [0001] and [ ] directions, respectively. Carbon nanotubes and plates of turbostratic graphene were revealed. The structural and morphological parameters of the nanostructured material “Taunit-M” have been established – multi-walled nanotubes with a diameter of up to 10 nm are combined through an interlayer of X-ray amorphous carbon into flat ribbons up to 40 nm wide. Dark-field TEM images (in reflections of ) revealed moiré patterns that appear on overlapping graphene sheets due to double diffraction of the electron beam. It was found that in thermally expanded graphite, the rotation of graphene sheets ranges from 3 to 4°. Within the graphene sheets, complete dislocations with the Burgers vector b = 1/2 were revealed [1010]. The Fourier analysis of moiré images made it possible to determine the mutual orientation of graphene sheets, to reveal regions of multilayer graphene, and to identify turbostratic graphene. It is shown that the combination of RHEED, TEM, and Fourier transformations of periodic contrast of electron microscopic images is a promising approach to the analysis of the substructure and morphology of nanoscale carbon materials containing graphene and other allotropic modifications of carbon.