High-angle Annular Dark-field Scanning Transmission Electron Microscopy Images Research Articles

Heteroleptic Tin-Antimony Sulfoiodide for Stable and Lead-free Solar Cells

Summary The quaternary chalcogenide halides of group IV and V elements have attracted much attention due to their interesting semiconducting properties as well as a suitable band gap for solar cells. Here, for the first time, we report on solar cells using tin-antimony sulfoiodide (Sn2SbS2I3). Sn2SbS2I3 solar cells were fabricated using a chemical single-step deposition process with a solution containing a SbCl3-thiourea complex and SnI2 with the configuration of TiO2 and poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7-(2,1,3-enzothiadiazole)] as the electron- and hole-transporting layers, respectively. The best-performing cell exhibits a power conversion efficiency of 4.04% under the illumination of standard AM 1.5G conditions (100 mW cm−2). These unencapsulated cells exhibited good stabilities at 80% relative humidity, 85°C in air, and under illumination, respectively. These results provide guidelines for fabrication of lead-free heteroleptic perovskite solar cells by hosting divalent or combinations of monovalent and trivalent metal cations.

Thermoregulated Ionic Liquid-Stabilizing Ru/CoO Nanocomposites for Catalytic Hydrogenation.

Catalytic hydrogenations represent fundamental processes and allow for atom-efficient and clean functional group transformations for the production of chemical intermediates and fine chemicals in chemical industry. Herein, the Ru/CoO nanocomposites have been constructed and applied as nanocatalysts for the hydrogenation of phenols and furfurals into the corresponding cyclohexanols and tetrahydrofurfuryl alcohols, respectively. The functionalized ionic liquid acted not only as a ligand for stabilizing the Ru/CoO nanocatalyst but also as a thermoregulated agent. The as-obtained nanocatalyst showed superior activity, and it could be conveniently recovered via the thermoregulating phase separation. In six recycle experiments, the catalysts maintained excellent performance. It was observed that the catalytic performance highly hinged on the molar ratio of Ru to Co in the nanocatalyst. The catalyst characterization was carried out by high-resolution transmission electron microscopy (HRTEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), X-ray photoelectron spectroscopy, X-ray diffraction, high-resolution mass spectrometry, Fourier transform infrared, nuclear magnetic resonance, and UV-vis. Especially, the characterization by HRTEM and HAADF-STEM images of the nanocatalyst demonstrated that Ru(0) and Co(II) species were distributed uniformly and the Ru and Co(II) species were close to each other. However, Co(0) was generated and an electronic transfer from Co to Ru species could occur under the hydrogenation conditions. The 13C NMR characterization indicated further that Co(II) sites were mainly responsible for phenol adsorption. Meanwhile, the adjacent electron-rich Ru(0) sites can promote H2 dissociation and favor for the sequential hydrogenation.

Engineering Electronic Structure of Single-Atom Pd Site on Ti 0.87 O 2 Nanosheet via Charge Transfer Enables C–Br Cleavage for Room-Temperature Suzuki Coupling

The palladium (Pd)-catalyzed Suzuki reaction is widely applied in the pharmaceutical industry, where constructing highly active and low-cost Pd sites are impendent. Here, we report the fabrication ...

Energy-dispersive X-ray spectroscopy for an atomic-scale quantitative analysis of Pd-Pt core-shell nanoparticles.

The properties of core-shell nanoparticles, which are used for many catalytic processes as an alternative to platinum, depend on the size of both the particle and the shell. It is thus necessary to develop a quantitative method to determine the shell thickness. Pd-Pt core-shell particles were analyzed using scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDX). Quantitative EDX line profiles acquired from the core-shell particle were compared to four core-shell models. The results indicate that the thickness of the Pt shell corresponds to two atomic layers. Meanwhile, high-angle annular dark-field STEM images from the same particle were analyzed and compared to simulated images. Again, this experiment demonstrates that the shell thickness was of two atomic layers. Our results indicate that, in small particles, it is possible to use EDX for a precise atomic-scale quantitative analysis.

Towards the understanding of the gold interaction with AIII-BV semiconductors at the atomic level.

AIII-BV semiconductors have been considered to be a promising material for decades in overcoming the limitations of silicon semiconductor devices. One of the important aspects within the AIII-BV semiconductor technology is gold-semiconductor interactions on the nanoscale. We report on the investigations into the basic chemical interactions of Au atoms with AIII-BV semiconductor crystals by the investigation of the nanostructure formation in the process of thermally-induced Au self-assembly on various AIII-BV surfaces by means of atomically resolved High Angle Annular Dark Field (HAADF) Scanning Transmission Electron Microscopy (STEM) measurements. We have found that the formation of nanostructures is a consequence of the surface diffusion and nucleation of adatoms produced by Au induced chemical reactions on AIII-BV semiconductor surfaces. Only for InSb crystals we have found that there is efficient diffusion of Au atoms into the bulk, which we experimentally studied by Machine Learning HAADF STEM image quantification and theoretically by Density Functional Theory (DFT) calculations with the inclusion of finite temperature effects. Furthermore, the effective number of Au atoms needed to release one AIII metal atom has been estimated. The experimental finding reveals a difference in the Au interactions with the In- and Ga-based groups of AIII-BV semiconductors. Our comprehensive and systematic studies uncover the details of the Au interactions with the AIII-BV surface at the atomic level with chemical sensitivity and shed new light on the fundamental Au/AIII-BV interactions at the atomic scale.

Coupling HAADF-STEM Tomography and Image Reconstruction for the Precise Characterization of Particle Morphology of Composite Polymer Latexes

The performance of waterborne polymer–polymer composite materials strongly depends on the particle morphology, but the precise quantitative characterization of complex morphologies is a long-standing problem. In this work, high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) has been used to obtain a 3D quantitative characterization of the morphology of polymer–polymer particles. The potential of this technique was demonstrated in the study of the effect of process variables (Tg of the seed, type of initiator, and instantaneous conversion of the monomer) on particle morphology during the semicontinuous emulsion copolymerization of styrene and butyl acrylate on methyl methacrylate-rich seeds. This analysis unveiled new mechanisms of morphology development.

An atomic scale structural investigation of nanometre-sized η precipitates in the 7050 aluminium alloy

Using high-angle-annular-dark-field (HAADF) scanning-transmission-electron microscopy (STEM), we have investigated η-precipitates in the Al-Zn-Mg-Cu (AA7050) aluminium alloy. The HAADF STEM images taken along the zone axes of [101¯0]η, [12¯10]η, and [0001]η illustrated the projected atomic-scale configurations of η-MgZn2 crystal. The precipitates developed in layer-by-layer growth, supplied with precursors such as Zn, Cu, and Mg, which were solute atoms segregated around the η/Al interfaces due to the higher lattice strain energy. Stacking faults and defect layers composed of flattened hexagons were frequently observed along the zone axes of [12¯10]η and [101¯0]η, respectively, and their formation was elucidated, similarly taking into account the layer-by-layer growth. Occasional coalescence between two precipitates yielded a complicated boundary or a twin-like boundary. Based on the differences in orientation relationships between η-types and the Al matrix reported to date, two new types of η precipitates have been recognized and named η4' and η12.

Mineralogy of Zirconium in Iron-Oxides: A Micron- to Nanoscale Study of Hematite Ore from Peculiar Knob, South Australia

Zirconium is an element of considerable petrogenetic significance but is rarely found in hematite at concentrations higher than a few parts-per-million (ppm). Coarse-grained hematite ore from the metamorphosed Peculiar Knob iron deposit, South Australia, contains anomalous concentrations of Zr and has been investigated using microanalytical techniques that can bridge the micron- to nanoscales to understand the distribution of Zr in the ore. Hematite displays textures attributable to annealing under conditions of high-grade metamorphism, deformation twins (r~85˚ to hematite elongation), relict magnetite and fields of sub-micron-wide inclusions of baddeleyite as conjugate needles with orientation at ~110˚/70˚. Skeletal and granoblastic zircon, containing only a few ppm U, are both present interstitial to hematite. Using laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) spot analysis and mapping, the concentration of Zr in hematite is determined to be ~260 ppm on average (up to 680 ppm). The Zr content is, however, directly attributable to nm-scale inclusions of baddeleyite pervasively distributed throughout the hematite rather than Zr in solid solution. Distinction between nm-scale inclusions and lattice-bound trace element substitutions cannot be made from LA-ICP-MS data alone and requires nanoscale characterization. Scandium-rich (up to 0.18 wt. % Sc2O3) cores in zircon are documented by microprobe analysis and mapping. Using high-angle annular dark field scanning transmission electron microscopy imaging (HAADF-STEM) and energy-dispersive spectrometry STEM mapping of foils prepared in-situ by focused ion beam methods, we identify [011]baddeleyite epitaxially intergrown with [22.1]hematite. Lattice vectors at 84–86˚ underpinning the epitaxial intergrowth orientation correspond to directions of r-twins but not to the orientation of the needles, which display a ~15˚ misfit. This is attributable to directions of trellis exsolutions in a precursor titanomagnetite. U–Pb dating of zircon gives a 206Pb/238U weighted mean age of 1741 ± 49 Ma (sensitive high-resolution ion microprobe U–Pb method). Based on the findings presented here, detrital titanomagnetite from erosion of mafic rocks is considered the most likely source for Zr, Ti, Cr and Sc. Whether such detrital horizons accumulated in a basin with chemical precipitation of Fe-minerals (banded iron formation) is debatable, but such Fe-rich sediments clearly included detrital horizons. Martitization during the diagenesis-supergene enrichment cycle was followed by high-grade metamorphism during the ~1.73–1.69 Ga Kimban Orogeny during which martite recrystallized as granoblastic hematite. Later interaction with hydrothermal fluids associated with ~1.6 Ga Hiltaba-granitoids led to W, Sn and Sb enrichment in the hematite. By reconstructing the evolution of the massive orebody at Peculiar Knob, we show how application of complimentary advanced microanalytical techniques, in-situ and on the same material but at different scales, provides critical constraints on ore-forming processes.

Toward Phase and Catalysis Control: Tracking the Formation of Intermetallic Nanoparticles at Atomic Scale

Summary Intermetallic nanoparticles (iNPs) have yielded enormous successes in catalytic applications by the formation of ordered phases. However, atomic-level understanding of the alloying mechanism, which plays a pivotal role in controlling intermetallic phases and tailoring their catalytic properties, is still elusive. In this study, we discovered a consecutive formation of ordered Pt3Sn and PtSn phases during the growth of Pt-Sn iNP inside a well-defined nano-reactor at elevated temperature by using in situ scanning transmission electron microscopy. We found that the surface-mediated diffusion of Sn controls overall dynamics of the reaction, while the unique coherent interfacial structure is determinative for the PtSn transformation. We then further controlled the phase selection of Pt-Sn iNPs and demonstrated their distinguishable catalytic behaviors. Our findings not only provide detailed experimental evidence on the alloying mechanism in intermetallic nanoscale systems but also pave the way for mechanistic control of synthesis and catalytic properties of iNPs.

Hexagonal structural block consisting of 2 nm decagonal clusters in Al60Cr20Fe10Si10 alloy

Hexagonal structural blocks are a basic structural unit in quasicrystals and their approximants. We identified a large hexagonal structural block with an edge length of 1.91 nm in an Al60Cr20Fe10Si10 alloy using atomic-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The hexagonal structural block contained 2-nm decagonal clusters with perfect ten-fold symmetry. Four large approximants composed of the hexagonal structural block were deduced from HAADF-STEM images. Furthermore, some irregular polygons were identified and their generation was readily explained based on the overlap of the hexagonal structural blocks.

Functionalized MoS2 supported core-shell Ag@Au nanoclusters for managing electronic processes in photocatalysis

Metal nanoclusters (MNCs) based on gold as core and silver as shell, abbreviated as Ag@AuNCs, were electrostatically associated with functionalized semiconducting MoS2 nanosheets, abbreviated as f-MoS2. The realization of the Ag@AuNCs/f-MoS2 ensemble was manifested by UV–vis and photoluminescence titration assays, while its morphology was evidenced by high-angle annular dark-field STEM imaging coupled with EDX analyses. Photoinduced intra-ensemble charge-transfer phenomena were witnessed and attributed to the suppression and concomitant shift of Ag@AuNC photoluminescence by incremental additions of f-MoS2. The Ag@AuNCs/f-MoS2 was employed as RhB photodegradation catalyst for wastewater purification from organic pollutant dyes. The production of highly oxidant radicals from the photogenerated electron-hole pairs within Ag@AuNCs/f-MoS2 were found to be the main reactive species, while the holes left on Ag@AuNCs attacked RhB, as evidenced by the disappearance of the characteristic absorption peak. The photocatalytic reaction by the ensemble followed fast kinetics as compared with bare Ag@AuNCs or individual AuNCs and AgNCs.

A Versatile Polyol Synthesis for Layered, Spinel, and Olivine-Type Cathode Material

One of the most pressing challenges modern society faces is how to provide an energy source for a variety of applications, ranging from small portable devices to electric vehicles (EVs) and a large grid-scale system to store energy from intermittent solar or wind-driven devices. Recently, enough technological advancement has been made that Li-ion batteries (LIBs) are considered as the most promising solution to solve this problem. Over the years, diverse synthetic methods have been developed to synthesize battery cathode materials, such as: solid-state, co-precipitation, sol-gel, hydrothermal, and molten salt syntheses. Each of the synthesis process used to make the cathode oxide material proved to be useful, but simultaneously accompanies some major drawbacks. In the traditional solid-state method, the mixing of multiple metal sources is done by grinding or ball milling. This results in a microcrystalline product with long Li diffusion pathways as well as inhomogeneous morphology and metal distribution. Co-precipitation compensates for some of these shortcomings, but it also requires a careful control of pH in the carbonate method or an inert atmosphere to minimize the undesired impurities in the hydroxide method. Previous studies show that the hydrothermal method is an effective way to synthesize cathode material with high crystallinity, but it requires a complex experimental set up which utilizes a stainless steel autoclave to withstand high vapor pressure during its lengthy reaction time. Furthermore, all the methods require a long post annealing process, typically lasting more than 12 hours at high temperature (>800ºC). Herein, we developed a novel polyol synthetic process to prepare the most promising cathode materials in layered, spinel, and olivine structure. Developed by Fievet group in 1985, polyol-mediated synthesis has been widely used for the past decades, but its scope has been mostly limited to the synthesis of metals and metal oxides. In this work, our group has extended this synthesis method to develop more complex metal oxide used for battery cathode materials. All three of the synthesized materials are monodispersed nanoparticles with dispersive morphology and competitive electrochemical performance. Using a combination of powder x-ray diffraction (XRD), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and energy dispersive spectroscopy (EDS), we also confirmed its high crystallinity and uniform elemental distribution for all three polyol-synthesized cathode materials. Finally, HAADF-STEM image and electron energy loss spectroscopy (EELS) for cycled NMC material was analyzed to confirm its structural stability even after charge-discharge process. We anticipate that these findings lead to the plethora of new cathode materials that can be explored using this synthetic method. Figure 1

Multiple strains and polar states in PbZr0.52Ti0.48O3/PbTiO3 superlattices revealed by aberration-corrected HAADF-STEM imaging

Tuning multiple strain and polar states of ferroelectrics by using strain engineering is an essential approach for designing multifunctional electric devices such as multiple state memories. However, integrating multiple strain states is still a challenge, and in addition, revealing such strains and the resultant polar behaviors on the atomic level remains difficult. In this work we prepare PbZr0.52Ti0.48O3/PbTiO3 (PZT/PTO) superlattices on SrRuO3-buffered SrTiO3(001) substrates. Aberration-corrected high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) reveals that the superlattice is coherent in both c (out-of-plane polar direction) and a (in-plane polar direction) domains. We find that the strain states of both PZT and PTO in c and a domains are variant, leading to four special strain states. For example, the tetragonality for PTO in c and a domains is 1.061 and 1.045, respectively. In contrast, PZT in c domains displays a tetragonality as giant as 1.107, which corresponds to 110 µC cm−2 spontaneous polarization, much larger than the bulk PZT; while PZT in a domains exhibits 1.010 tetragonality with about 70 µC cm−2 polarization. This study reveals a practical way to integrate multiple strain states and enhanced polarizations in ferroelectric films, which could be used as multifunctional electric elements.

Investigation of a nano-scale, incommensurate, modulated domain in a Ti-Fe alloy

The microstructure of a Ti-Fe compositional gradient sample was investigated using transmission electron microscopy (TEM) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Different combinations of phases were observed to form depending on the local concentration of Fe. Interestingly, a nano-scale incommensurate modulated domain was detected in the alloy containing approximately 13.8 to 33.9 wt% Fe using selected area diffraction (SAD). The observed disordered structure with no fixed long range periodicity in the nano-scale incommensurate modulated domain in aberration-corrected HAADF-STEM imaging was found not related to the shuffle mechanism of the ω phase.

Atomic resolution characterization of strengthening nanoparticles in a new high-temperature-capable 43Fe-25Ni-22.5Cr austenitic stainless steel

Advanced scanning transmission electron microscopy (STEM) was used to study two distinct populations of nanoparticles associated with the extraordinary strengthening of the highly-alloyed austenitic stainless steel Sanicro 25 during cyclic loading at 700 °C. Fully coherent and homogeneously dispersed Cu-rich nanoparticles precipitate rapidly as a result of thermal exposure, along with nanometer-sized incoherent NbC carbides that nucleate on dislocations during the cyclic loading at high temperature. The atomic structure of nanoparticles was investigated by probe-corrected high-angle annular dark-field STEM imaging. Compositional analysis of the nanoparticles was conducted using high spatial resolution energy dispersive X-ray spectroscopy combined with electron energy-loss spectroscopy. Experimental observations were validated by image simulations of the Moiré-like contrast exhibited by NbC carbides. The important role of both nanoparticle populations for the overall cyclic response is discussed. As a result of pinning effects and associated obstacles, dislocation motion is significantly retarded preventing formation of substructures with lower stored internal energy. With recovery heavily suppressed, forest dislocation strengthening supported by precipitation and solid solution hardening, leads to the remarkable increase of cyclic strength at elevated temperatures.

Confining SnS2 Ultrathin Nanosheets in Hollow Carbon Nanostructures for Efficient Capacitive Sodium Storage

Summary Tin disulfide (SnS 2 ) is a promising anode material for sodium-ion batteries because of its high specific capacity. However, the low conductivity and large volume change during reaction with Na + ions greatly limit its practical application. Herein, a multistep templating method has been exploited for the rational design and synthesis of SnS 2 nanosheets confined in carbon nanotubes (SnS 2 @CNTs). To demonstrate the universality of this method, SnS 2 nanosheets confined in carbon nanoboxes (SnS 2 @CNBs) and hollow carbon nanospheres (SnS 2 @CNSs) have also been synthesized by simply changing the template in the reaction system. Due to their unique structural merits, the SnS 2 @CNTs, SnS 2 @CNBs, and SnS 2 @CNSs show improved sodium storage performance in terms of high specific capacity, good cycling stability, and superior rate capability.

Characterization Microstructural and Electrochemical of AgPd Alloy Bimetallic Nanoparticles

ABSTRACTBimetallic nanoparticles are of special interest for their potential applications to fuel cells, among the bimetallic systems, AuPd bimetallic nanoparticles have received great interest as they can be widely used as effective catalysts for various electrochemical reactions. Monodisperse AgPd alloy nanoparticles were synthesized by polyol method using silver nitrate and potassium tetrachloropalladate(II) in ethylene glycol as the reducing agent at 160 °C. Structural, compositional and electrochemical characterizations of synthesized bimetallic nanoparticles were investigated. High-angle annular dark field scanning/transmission electron microscopy (HAADF-STEM) images and parallel beam X-ray diffraction (XRD) of the bimetallic nanoparticles were obtained. XRD and the contrast of the HAADF-STEM images show that the bimetallic nanoparticles have an alloy structure. Cyclic voltammetry was carried out in order to confirm the electrochemical responses of the AgPd/C electrocatalysts for methanol oxidation. Thanks to the narrow size distribution of the AgPd alloy bimetallic nanoparticles (9.15 nm) the supported AgPd/C electrocatalysts have high catalytic activity toward methanol electro-oxidation.

Investigation on formation mechanism of T1 precipitate in an Al-Cu-Li alloy

The formation mechanism of T1 (Al2CuLi) precipitate in an Al-Cu-Li alloy was investigated by using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging, atom probe tomography (APT) and first-principles energy calculations. The HAADF-STEM images reveal the existence of the T1 precursor phase, which is termed as T1p in this study. The T1p phase has a lattice structure identical to the Al matrix, and consists of a stacking of Li-rich and Cu-rich layers along the {111}Al planes. APT analysis further confirms the existence of T1p phase, in which the concentrations of Li and Cu are significantly lower than those in T1 plate. Based on the first-principles energy calculations, the structural evolution from T1p phase to T1 phase is proved to be energetically favorable. Correspondingly, one possible evolution process from T1p phase to T1 phase involving the change of stacking sequence is proposed and discussed.

Direct observation of inclined a-type threading dislocation with a-type screw dislocation in GaN

We investigated both the atomic arrangements in the core structure of threading dislocations (TDs) and their behaviors in unintentionally doped c-plane-GaN layers grown by metalorganic vapor phase epitaxy and hydride vapor phase epitaxy using high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The extra image contrast near the core was attributed to an extra displacement in a-type TDs in addition to the core structures revealed in previous reports; we used the notation “with displacement” to describe the new core structure. We found that TDs incline towards both the m- and a-directions from the c-direction. The transition of a-type TDs from the conventional core structure to the structure with displacement was deduced from its relationship to the TD inclination. We also found similarities between a-type screw dislocations and a-type TDs with displacement in the atomic-scale HAADF-STEM images. We concluded that a-type TDs could incline towards the a-direction via a-type screw dislocations, and that these inclined a-type TDs are observed as the core structure with displacement.

Current perpendicular-to-plane giant magnetoresistance devices using half-metallic Co2Fe0.4Mn0.6Si electrodes and a Ag–Mg spacer

Current perpendicular-to-plane (CPP) giant magnetoresistance (GMR) effects in devices including Co2Fe0.4Mn0.6Si (CFMS)/Ag100−xMgx/CFMS structures were investigated theoretically and experimentally.First-principles transport calculation revealed that the Fermi surface matching between CFMS and L12 Ag3Mg is better than that between CFMS and fcc-Ag. In the experiments the Mg composition, x was changed from 0 to 26 at.%, in which both face centered cubic phase and L12 phase of Ag–Mg alloys are included depending on the Mg composition. It was confirmed by a cross-sectional high-angle annular dark field scanning transmission electron microscope (HAADF-STEM) image that the Ag–Mg spacer layer with L12 ordered phase was successfully fabricated for x = 22 at.%. The maximum CPP–GMR ratio and the change of the areal resistance () were 56% and 20 mm2, respectively, for x = 22 at.% at room temperature, which is much higher than that of the conventionally used pure Ag spacer devices. It was suggested from the HAADF-STEM images and the results of the temperature dependence of CPP–GMR effects that the diffusion of Mn atoms occurred less at the CFMS/Ag–Mg interfaces for the L12 ordered Ag–Mg spacer devices than the Ag spacer devices, which might be a key factor for the enhancement of the value. The newly developed L12 Ag–Mg spacer is a promising material for realizing large of the CPP–GMR devices.