High-resolution Electron Microscopy Analysis Research Articles

Phase transformations, microstructural refinement and defect evolution mechanisms in Al-Si alloys under non-hydrostatic diamond anvil cell compression

Non-hydrostatic compression of materials using a diamond anvil cell (DAC) can transform the equilibrium microstructure of an alloy to novel, potentially metastable states. In this study, in situ synchrotron X-ray diffraction (XRD) during compression up to 24 GPa and subsequent ex-situ, high resolution analytical electron microscopy (AEM) after decompression of an Al-Si alloy provided insight into the crystallographic changes during the compression as well as microstructural refinement, and defect structures caused by such a high pressure compression-decompression process. Pressure resolved in-situ synchrotron XRD was used to detail the phase transformation pathway of the eutectic Si phase in Al-Si alloy, from Si-I → Si-XI → Si-V during compression, and a final transformation predominantly to Si-III after decompression. Using scanning and transmission electron microscopy (S/TEM), site specific analysis of the alloy immediately underneath the anvil contact surface demonstrated a highly complex microstructure. A narrow region of thick amorphous Al oxide interspersed with nanocrystalline grains was found at the top surface. Underneath this Al oxide, while the majority of the eutectic Si was transformed into highly-deformed, polycrystalline (PC) Si-III, a complex intermediate layer was discovered at the interface between Al and Si, comprised of a small fraction of Al nanocrystals and a majority of nanocrystalline Si-I. This combination of pressure resolved in-situ synchrotron XRD coupled with subsequent high resolution, electron microscopy resolved the phase transformation as well as non-equilibrium microstructures in a metallic alloy induced by a non-hydrostatic high pressure compression followed by decompression.

Effect of post-heat treatment on microstructure and mechanical properties of laser welded Al-Cu-Mg alloy

A new approach was developed to improve strength of Al-Cu-Mg alloy laser welded joints that typically within 61–90 % of that of the base metal due to a change in the microstructure and phase composition of the weld one. This result was achieved by optimization of post weld heat treatment (PWHT) included quenching and subsequent artificial aging. For the first time, the spatial distribution and evolution of the phase composition were studied at all PWHT stages using high-resolution scanning electron microscopy and synchrotron X-ray analysis. It was found that the Al-Cu-Mg solid solution was homogenized, as well as the S(Al2CuMg) strengthening and (partly) θ(Al2Cu) phases were formed. After PWHT, ultimate tensile strength was 428 MPa, yield strength was 302 MPa, and elongation was 19.6 %, which were 99 %, 98 % and 95 %, respectively, of those of the base metal.

A simple approach to synthesis Cr2CTx MXene for efficient hydrogen evolution reaction

Two-dimensional chromium carbide-based MXenes are predicted as an efficient catalyst for the hydrogen evolution reaction (HER). However, the lack of an effective approach to fabricate this promising material remains an impediment to practical applications. Herein, a simple strategy is proposed to synthesis Cr2CTx ultrathin structures from Cr2AlC MAX. The high-resolution analytical scanning transmission electron microscopy (STEM) corroborated with X-ray diffraction and scanning electron microscopy demonstrates that the Al atomic layers have been detached from the pristine MAX structure. Further atomic-resolution STEM confirms that the ultrathin Cr2CTx sheets with fluoride-free surface, nanostructured Cr2CO2, and Al2O3 phases are originated as by-products. The electrochemical test shows that the fabricated Cr2CTx composite with minimal Al2O3 have a good performance for hydrogen evolution reaction and exceed even that of Pt sheet catalyst at high current density. Moreover, high stability of more than 160 h without attenuation was observed to be better than the other MXenes catalytic performer to date. This work paves a gentle route to fabricate Cr2CTx MXene and demonstrates the potential application for HER.

Microwave AC Resonance Induced Phase Change in Sb2Te3 Nanowires.

Scaling information bits to ever smaller dimensions is a dominant drive for information technology (IT). Nanostructured phase change material emerges as a key player in the current green-IT endeavor with low power consumption, functional modularity, and promising scalability. In this work, we present the demonstration of microwave AC voltage induced phase change phenomenon at ∼3 GHz in single Sb2Te3 nanowires. The resistance change by a total of 6-7 orders of magnitude is evidenced by a transition from the crystalline metallic to the amorphous semiconducting phase, which is cross-examined by temperature dependent transport measurement and high-resolution electron microscopy analysis. This discovery could potentially tailor multistate information bit encoding and electrical addressability along a single nanowire, rendering technology advancement for neuro-inspired computing devices.

Friction stir dovetailing of AA7099 to steel with AA6061 interlayer for reduced Zn embrittlement at dissimilar interface

Abstract Joining of high strength Al alloy (AA7099) to steel (rolled homogeneous armor) with and without AA6061 interlayer was achieved using a friction stir dovetailing (FSD) method. Detailed investigations were conducted to establish correlations between mechanical performance and microstructural evolution of FSD joints. Lap shear tensile testing revealed that incorporation of the AA6061 interlayer combined with tailored processing methodology significantly improved both mechanical interlocking and load transmission across the dovetail interface. Following incorporation of the interlayer, the maximum load carrying capacity and peak extension (of the AA7099/AA6061/steel joint) are 60% and 210% higher, respectively, than results obtained from an AA7099/steel joint without an interlayer. Without an AA6061 interlayer, formation of zinc rich intermetallic compounds led to brittle interfacial failure of the AA7099-steel FSD joint. Incorporation of novel tool and joint configuration eliminated asymmetric joint performance as a function of loading direction, which is generally observed in friction stir lap welding. The efficacy of the use of an AA6061 interlayer in joining AA7099 to steel was demonstrated through mechanical testing as well as high resolution analytical electron microscopy characterization.

2D-titanium carbide (MXene) based selective electrochemical sensor for simultaneous detection of ascorbic acid, dopamine and uric acid

Two-dimensional (2D) titanium carbide (MXene) nanosheets exhibited excellent conductivity, flexibility, high volumetric capacity, hydrophilic surface, thermal stability, etc. So, it has been exploited in various applications. Herein, we report synthesis of mixed phase 2D MXene as a catalytic material for simultaneous detection of important biomolecules such as ascorbic acid (AA), dopamine (DA) and uric acid (UA). Crystalline structure, surface morphology and elemental composition of mixed phase titanium carbide (Ti-C-Tx) MXene (Tx = –F, −OH, or −O) nanosheets were confirmed by X-ray diffraction (XRD), Raman spectroscopy, high-resolution transmission electron microscopy (HR-TEM), high-resolution scanning electron microscopy (HR-SEM) and Energy-dispersive X-ray spectroscopy (EDS) mapping analysis. Furthermore, Ti-C-Tx modified glassy carbon electrode (GCE) was prepared and its electrochemical properties are studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). It was found that Ti-C-Tx modified GCE (Ti-C-Tx/GCE) showed excellent electrocatalytic activity and separated oxidation peaks of important biomolecules such as AA (at 0.01 V), DA (at 0.21 V) and UA (at 0.33 V). Also, Ti-C-Tx/GCE sensor is enabled their simultaneous detection in physiological pH from 100 to 1000 μM for AA, 0.5–50 μM for DA and 0.5–4 μM & 100–1500 μM for UA. The limit of detection’s (LOD) was estimated as 4.6 μM, 0.06 μM and 0.075 μM for AA, DA and UA, respectively. Moreover, real sample analysis indicated that spiked AA, DA and UA can be determined accurately by Ti-C-Tx/GCE with the recovery ratio in the range between 100.5%–103% in human urine samples. The proposed Ti-C-Tx modified electrode exhibited good stability, selectivity and reproducibility as an electrochemical sensor for the detection of AA, DA and UA molecules.

Luminescent amphiphilic nanogels by terpyridine-Zn(II) complexation of polymeric micelles

In this work, we investigated terpyridine (tpy)/Zn(II) complexation for the crosslinking of polymeric micelles of the branched poly(ethylene oxide)–poly(propylene oxide) block copolymer Tetronic® 1107 (T1107) in water and produce physically stable amphiphilic luminescent nanogels. Nanoparticles displayed a size of 235 ± 25 and 318 ± 57 nm before and after Zn(II) crosslinking, respectively, as measured by dynamic light scattering. High-resolution scanning electron microscopy analysis revealed the multimicellar nature of the crosslinked nanoparticles. In addition, Zn(II) complexation prevented nanoparticle disassembly after extreme dilution below the critical micellar concentration and reduced the minimum concentration required for the reverse thermal gelation of concentrated aqueous T1107 systems. The cell compatibility and uptake were initially assessed in the murine macrophage cell line RAW 264.7. Results showed that complexation increases the cell compatibility of the nanoparticles with respect to the non-complexed counterparts. In addition, non-crosslinked nanoparticles accumulated in the cell membrane, while the complexed ones were internalized, as observed by confocal laser scanning fluorescence microscopy. Then, the antiproliferative activity of the crosslinked nanoparticles was confirmed in the rhabdomyosarcoma cell line Rh30; their inhibitory concentration 50 (IC50) being 101 μg/mL (6.7 μM). Finally, the encapsulation and release of the hydrophobic antiretroviral efavirenz was characterized in vitro. Complexation slightly reduced the release kinetics with respect to the pristine nanoparticles. Overall results demonstrate the promise of this simple modification strategy to produce amphiphilic nanogels with a set of advantageous physicochemical, optical, and biological properties.

Molybdenum Carbonyl Grafted on Amine-Functionalized MCM-22 as Potential Catalyst for Iso-Eugenol Oxidation

Different concentrations of molybdenum carbonyl were incorporated on the surface of amine-functionalized MCM-22. The obtained samples were thoroughly characterized by Fourier-transform infrared spectroscopy (FTIR), powder X-Ray diffraction (XRD), high-resolution transition electron microscopy (HRTEM), N2-sorption and thermo-gravimetric analysis (TGA) methods. HRTEM images confirmed the uniform distribution of active molybdenum species on the functionalized MCM-22. The resultant materials were explored for liquid-phase oxidation of iso-eugenol at ambient reaction conditions. The catalyst with 6 wt% Mo(CO)6 loaded materials showed comparable conversion (87%) with vanillin as the major product (selectivity of 61%) for the chosen reaction. The better catalytic activity of MCM-22-DA-Mo catalyst having 6 wt% loading of Mo carbonyl could be due to the uniform distribution of molybdenum species on MCM-22-DA surface. Importantly, the catalyst retained its activity even after several runs. Molybdenum carbonyl were incorporated on the surface of amine-functionalized MCM-22 by the post-synthesis method. The resultant MCM-22-DA-Mo showed promising activity on iso-eugenol oxidation with a conversion of 87%.

Nanostructure and Fracture Behavior of Carbon Nanofiber-Reinforced Cement Using Nanoscale Depth-Sensing Methods.

In recent years, carbon nanofibers have been investigated as a suitable reinforcement for cementitious composites to yield novel multifunctional materials with improved mechanical, electrical, magnetic, and self-sensing behavior. Despite several studies, the interactions between carbon nanofibers and Portland cement hydration products are not fully understood, with significant implications for the mechanical response and the durability at the macroscopic lengthscale. Thus, the research objective is to investigate the influence of carbon nanofibers on the nanostructure and on the distribution of hydration products within Portland cement paste. Portland cement w/c = 0.44 specimens reinforced with 0.0 wt%, 0.1 wt%, and 0.5 wt% CNF by mass fraction of cement are cast using a novel synthesis procedure. A uniform dispersion of carbon nanofibers (CNF) via a multi-step approach: after pre-dispersing carbon nanofibers using ultrasonic energy, the carbon nanofibers are further dispersed using un-hydrated cement particles in high shear mixing and mechanical stirring steps. High-resolution scanning electron microscopy analysis shows that carbon nanofibers fill nanopores and connect calcium–silicate hydrates (C–S–H) grains. Grid nano-indentation testing shows that Carbon nanofibers influence the probability distribution function of the local packing density by inducing a shift towards higher values, = 0.76–0.93. Statistical deconvolution analysis shows that carbon nanofibers result in an increase in the fraction of high-density C–S–H by 6.7% from plain cement to cement + 0.1 wt% CNF and by 10.7% from plain cement to cement + 0.5 wt% CNF. Moreover, CNF lead to an increase in the C–S–H gel porosity and a decrease in both the capillary porosity and the total porosity. Based on scratch testing, adding 0.1 wt% CNF yields a 4.5% increase in fracture toughness and adding 0.5 wt% CNF yields a 7.6% increase in fracture toughness. Finally, micromechanical modelling predicts an increase of respectively 5.97% and 21.78% in the average Young’s modulus following CNF modification at 0.1 wt% CNF and 0.5 wt% CNF levels.

Novel B-site Cd2+ doped CsPbBr3 quantum dot glass toward strong fluorescence and high stability for wLED

Cd2+ doped CsPbBr3 perovskite quantum dots were synthesized in borosilicate glass for the first time by traditional melting method. By X-Ray Diffraction (XRD) and high resolution electron microscopy analysis, it was proved that Cd2+ successfully entered the perovskite lattice structure. The samples have good optical properties, high photostability, chemical stability, thermal stability and water stability. On this basis, CsPb0.7Cd0.3Br3 QDs glass, commercial red phosphor (CaAlSiN3:Eu2+) and blue light chip were coupled to produce white LED devices. This discovery opens up a new way for the application of metal ion-doped perovskite QDs glass in optoelectronic devices.

Monodisperse FeF2 Nanorods in Ionic Liquid Electrolytes: A Comprehensive Study of the Conversion Mechanism

Transition metal fluorides display the combination of high capacity and high electrode potential that are essential to boosting the energy density of lithium ion batteries. However, their application as cathode materials has been hindered by an incomplete understanding of their electrochemical capabilities and limitations. Herein, we present a system of single crystalline, monodisperse iron (II) fluoride nanorods and detail how their morphology and uniformity make them ideal for mechanistic study. High-resolution analytical transmission electron microscopy reveals intricate morphological features, lattice orientation relationships, and oxidation state changes that redefine the conversion reaction with unprecedented spatial resolution. We first introduce the presence of surface specific reactions and examine how they critically influence phase evolution, diffusion kinetics and cell failure. Next, we examine how the reversibility of the conversion reaction is governed by topotactic cation diffusion through an invariant lattice of fluoride anions and the nucleation of metallic particles on semi-coherent interfaces. We will focus on how each mechanistic feature establishes new principles for improving reaction hysteresis, kinetics and reversibility and how this new holistic understanding can inform the more effective application of metal fluorides. To ensure a pertinent result, ex-situ data was extracted from coin cells that deliver near theoretical capacity (570 mAh g-1) and extraordinary cycling stability (>90 % capacity retention after 100 cycles). This exceptional performance was enabled solely through the use of an ionic liquid electrolyte. Using a combination of impedance spectroscopy, TEM, and X-ray photoelectron spectroscopy, we explain how the solid electrolyte interphase forming ability of this electrolyte precludes the major failure mechanisms associated with transition metal fluorides. We conclude this talk by examining the complementary nature of this cathode electrolyte pairing, particularly with regards to high-temperature cycling. Figure 1

Tissue Specific Fate of Nanomaterials by Advanced Analytical Imaging Techniques - A Review.

A variety of imaging and analytical methods have been developed to study nanoparticles in cells. Each has its benefits, limitations, and varying degrees of expense and difficulties in implementation. High-resolution analytical scanning transmission electron microscopy (HRSTEM) has the unique ability to image local cellular environments adjacent to a nanoparticle at near atomic resolution and apply analytical tools to these environments such as energy dispersive spectroscopy and electron energy loss spectroscopy. These tools can be used to analyze particle location, translocation and potential reformation, ion dispersion, and in vivo synthesis of second-generation nanoparticles. Such analyses can provide in depth understanding of tissue-particle interactions and effects that are caused by the environmental "invader" nanoparticles. Analytical imaging can also distinguish phases that form due to the transformation of "invader" nanoparticles in contrast to those that are triggered by a response mechanism, including the commonly observed iron biomineralization in the form of ferritin nanoparticles. The analyses can distinguish ion species, crystal phases, and valence of parent nanoparticles and reformed or in vivo synthesized phases throughout the tissue. This article will briefly review the plethora of methods that have been developed over the last 20 years with an emphasis on the state-of-the-art techniques used to image and analyze nanoparticles in cells and highlight the sample preparation necessary for biological thin section observation in a HRSTEM. Specific applications that provide visual and chemical mapping of the local cellular environments surrounding parent nanoparticles and second-generation phases are demonstrated, which will help to identify novel nanoparticle-produced adverse effects and their associated mechanisms.

Nanocomposite film with green synthesized TiO2 nanoparticles and hydrophobic polydimethylsiloxane polymer: synthesis, characterization, and antibacterial test

Abstract The green synthesis of nanoparticles is of considerable interest because it is eco-friendly, cost-effective, biocompatible, and non-toxic. Split pulse extract was used as a reducing/capping agent for the synthesis of titanium dioxide (TiO2) nanoparticles. Green synthesized nanoparticles were embedded in the polydimethylsiloxane (PDMS) membrane by using a solution casting technique to develop a nanocomposite. This thin film was characterized using Fourier transform infrared spectroscopy, scanning probe microscopy, high-resolution scanning electron microscopy, ultraviolet-visible spectroscopy, and contact angle analysis. The antibacterial property of the TiO2/PDMS nanocomposite was examined, and the results showed excellent antibacterial activity of TiO2/PDMS compared to PDMS without nanoparticles. The nanocomposite film exhibited antibacterial activity against Gram-positive and Gram-negative bacteria in the presence of TiO2 nanoparticles in the polymer. Here, different weight percentages of TiO2 nanoparticles, i.e. 0%, 7%, 10%, and 13%, were loaded on the PDMS surface to enhance its antibacterial activity. The green synthesis of TiO2 nanoparticles embedded in PDMS and their suitability for antibacterial activity are reported for the first time.

Understanding the conversion mechanism and performance of monodisperse FeF2 nanocrystal cathodes.

The application of transition metal fluorides as energy-dense cathode materials for lithium ion batteries has been hindered by inadequate understanding of their electrochemical capabilities and limitations. Here, we present an ideal system for mechanistic study through the colloidal synthesis of single-crystalline, monodisperse iron(II) fluoride nanorods. Near theoretical capacity (570 mA h g-1) and extraordinary cycling stability (>90% capacity retention after 50 cycles at C/20) is achieved solely through the use of an ionic liquid electrolyte (1 m LiFSI/Pyr1,3FSI), which forms a stable solid electrolyte interphase and prevents the fusing of particles. This stability extends over 200 cycles at much higher rates (C/2) and temperatures (50 °C). High-resolution analytical transmission electron microscopy reveals intricate morphological features, lattice orientation relationships and oxidation state changes that comprehensively describe the conversion mechanism. Phase evolution, diffusion kinetics and cell failure are critically influenced by surface-specific reactions. The reversibility of the conversion reaction is governed by topotactic cation diffusion through an invariant lattice of fluoride anions and the nucleation of metallic particles on semicoherent interfaces. This new understanding is used to showcase the inherently high discharge rate capability of FeF2.

Phase Transformations, Microstructural Refinement and Defect Evolution Mechanisms in Al-Si Alloys Under Non-Hydrostatic Diamond Anvil Cell Compression

Non-hydrostatic compression of materials using a diamond anvil cell (DAC) can transform equilibrium microstructure of an alloy to novel, potentially metastable states. In this study, in situ synchrotron X-ray diffraction (XRD) during compression up to 24 GPa and subsequent ex situ, high resolution analytical electron microscopy (AEM) after decompression of an Al-Si alloy provided insight into the crystallographic changes during the compression as well as microstructural refinement, and defect structures caused by such a high pressure compression-decompression process. Pressure resolved in-situ synchrotron XRD was used to detail the phase transformation pathway of the eutectic Si phase in Al-Si alloy, from Si-I → Si-XI → Si-V during compression, and a final transformation predominantly to Si-III after decompression. Using scanning and transmission electron microscopy (S/TEM), site specific analysis of the alloy immediately underneath the anvil contact surface demonstrated a highly complex microstructure. A narrow region of thick amorphous Al oxide interspersed with nanocrystalline grains was found at the top surface. Underneath this Al oxide, while the majority the eutectic Si was transformed into highly-deformed, polycrystalline (PC) Si-III, a complex intermediate layer was discovered at the interface between Al and Si, comprised of a small fraction of Al nanocrystals and a majority of nanocrystalline Si-I. This combination of pressure resolved in-situ synchrotron XRD coupled with subsequent high resolution, electron microscopy resolved the phase transformation as well as non-equilibrium microstructures in a metallic alloy induced by a non-hydrostatic high pressure compression followed by decompression.

Extreme Ultraviolet Generation of Localized Defects in Single-Layer Graphene: Raman Mapping, Atomic Force Microscopy, and High-Resolution Scanning Electron Microscopy Analysis

We report micro-Raman spectroscopy, high-resolution scanning electron microscopy (HR-SEM) and atomic force microscopy (AFM) investigation of changes in chemical vapor deposition grown single-layer ...

Fabrication of photocatalyst MgO: CuO composite and enhancement of photocatalytic activity under UV light

The green synthesis of composites through biological entities such as natural plants, algae, bacteria, fungi, and viruses is regarded to be easy, fast, affordable, low-cost, and environmentally friendly. Therefore, the MgO:CuO composites were synthesized by eco-friendly synthesis method. The MgO:CuO composites were prepared from many fruits of PAGOB (Pomegranate, Apple, Grapes, Orange and Banana) peel extract. The present study is decolourization of methylene blue dye using UV light. The phase purity and crystallite size were characterized and confirmed by x-ray diffraction (XRD) studies. The maximum absorbance was obtained in the 200–800 nm regions with a prominent peak absorbance was observed by UV-vis spectrum. The corresponding band gap for MgO:CuO composite was calculated using Tauc’s plot and was found to be 2.2 eV. The textural and surface morphological feature of the synthesized composites were characterized by High-resolution Scanning Electron Microscopy (HR-SEM) and elemental analysis of Composites was analyzed with the help of Energy Dispersive x-ray analysis (EDX). The influence of pH, dye concentration, amount of photocatalyst and intensity of light on the rate of photocatalytic reaction was observed. The results show that the degradation reached 89% under optimum conditions. The resulting MgO:CuO composites and exhibits highly efficient and excellent photocatalytic properties. This property can be utilized to degrade organic contaminants. This concept was shown by degrading methylene blue, which can be observed photometrically.

Real colloidal quantum dot structures revealed by high resolution analytical electron microscopy.

The development of bright and photostable colloidal quantum dots has been a truly interdisciplinary feat. Designing a specific composition of core and shell materials and then producing the desired nanoarchitecture through chemical routes require a blend of physical and inorganic chemistry, solid-state physics, and materials science. In a battle to separate charge carriers from a surface wrought with defect states, complex shell structures with precisely specified gradient compositions have been engineered, producing nanosized emitters with exceptional stability and color purity. However, much of the success has resided in II-VI materials, such as CdSe, and progress is only just being made on cadmium-free quantum dots. This perspective will discuss the primary challenges in engineering colloidal quantum dots and highlight how the advent of advanced analytical electron microscopy is revealing the structure-function relationships of these complex systems.

Semi-Inverted Sample Preparation of Meteorites for High Resolution Analytical Electron Microscopy Using Correlative Raman Spectroscopy and Xe Plasma FIB

Semi-Inverted Sample Preparation of Meteorites for High Resolution Analytical Electron Microscopy Using Correlative Raman Spectroscopy and Xe Plasma FIB

High Spatial and Energy Resolution Analytical Scanning Transmission Electron Microscopy for Quantum Materials

High Spatial and Energy Resolution Analytical Scanning Transmission Electron Microscopy for Quantum Materials