Contrast Transmission Electron Microscopy Research Articles

Effect of surface-active substances on the macrodispersion behavior of thermal stress-modified multi-wall carbon nanotubes in cryogenic environments

In the preparation of nanocomposites, the agglomeration of multi-walled carbon nanotubes (MWCNTs) in the composite due to their low colloidal stability limits their use in industrial areas. To overcome these problems, it is important to develop simpler, economical, high-yield and non-hazardous techniques to replace existing techniques with low yields, expensive additional equipment or hazardous liquids. This study explores how surfactants affect the macrodispersion of thermal stress-modified MWCNTs in cryogenic environments, focusing on their application in polymer film preparation. Firstly, optimal conditions for modifying MWCNTs through thermal stress were identified using liquid nitrogen. Parameters assessed included the number of cycles (2, 4, and 6), duration in liquid nitrogen (10, 20, and 30 min), and subsequent waiting time at room temperature (5, 12, and 20 min). Results showed that the highest surface area was obtained with 2 cycles, 20 min in liquid nitrogen, and 5 min at room temperature. Analytical techniques such as Brunauer-Emmett-Teller (BET), X-Ray Diffraction (XRD), High Contrast Transmission Electron Microscopy (CTEM) and Raman spectroscopy were used to evaluate the functionalization process's effects on MWCNTs' internal graphitic structure and physicochemical properties. CTEM micrographs indicated that thermal stress reduced the length of MWCNTs, while Raman analysis showed improved graphite quality. The modification process, carried out with 100 % efficiency and no sample loss, increased the BET surface area from 297.551 m2/g to 397.295 m2/g. The study also investigated the impact of surfactants (polyethylene glycol sorbitan monooleate-Tween 80, sodium dodecyl sulfate-SDS, and hexadecyltrimethylammonium bromide-CTAB) on MWCNTs' macrodispersion degrees (DM%) and energy band gaps via UV–visible (UV–Vis) absorption spectroscopy. CTAB provided the highest and most stable macrodispersion, reducing the energy band gaps of MWCNTs from 5.65 to 5.75 eV to 3.53–3.60 eV. CTAB showed excellent colloidal stability with a zeta potential of 44.2 mV, while SDS had −49.9 mV. Polyvinyl alcohol (PVA) polymer films, created using MWCNT solutions with optimal macrodispersion, were confirmed by Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimeters (DSC), and BET surface area analyses to have successfully and homogeneously incorporated MWCNTs. In addition to the superior properties of MWCNTs modified with the functionalization technique developed within the scope of this study by increasing their specific surface area and porosity, the excellent colloidal stability provided may have various effects in many industrial areas. These advantages enable MWCNTs functionalized with the developed technique to have a wider range of applications in industrial applications and provide more efficient and sustainable solutions.

Therapeutic targeting of siRNA/anti-cancer drug delivery system for non-melanoma skin cancer. Part I: Development and gene silencing of JAK1siRNA/5-FU loaded liposome nanocomplexes

Non-melanoma skin cancer (NMSC) is one of the most prevalent cancers, leading to significant mortality rates due to limited treatment options and a lack of effective therapeutics. Janus kinase (JAK1), a non-receptor tyrosine kinase family member, is involved in various cellular processes, including differentiation, cell proliferation and survival, playing a crucial role in cancer progression. This study aims to provide a more effective treatment for NMSC by concurrently silencing the JAK1 gene and administering 5-Fluorouracil (5-FU) using liposome nanocomplexes as delivery vehicles. Utilizing RNA interference (RNAi) technology, liposome nanocomplexes modified with polyethylene imine (PEI) were conjugated with siRNA molecule targeting JAK1 and loaded with 5-FU. The prepared formulations (NL-PEI) were characterized in terms of their physicochemical properties, morphology, encapsulation efficiency, in vitro drug release, and stability. Cell cytotoxicity, cell uptake and knockdown efficiency were evaluated in human-derived non-melanoma epidermoid carcinoma cells (A-431). High contrast transmission electron microscopy (CTEM) images and dynamic light scattering (DLS) measurements revealed that the nanocomplexes formed spherical morphology with uniform sizes ranging from 80-120 nm. The cationic NL-PEI nanocomplexes successfully internalized within the cytoplasm of A-431, delivering siRNA for specific sequence binding and JAK1 gene silencing. The encapsulation of 5-FU in the nanocomplexes was achieved at 0.2 drug/lipid ratio. Post-treatment with NL-PEI for 24, 48 and 72 h showed cell viability above 80 % at concentrations up to 8.5 × 101 µg/mL. Notably, 5-FU delivery via nanoliposome formulations significantly reduced cell viability at 5-FU concentration of 5 µM and above (p < 0.05) after 24 h of incubation. The NL-PEI nanocomplexes effectively silenced the JAK1 gene in vitro, reducing its expression by 50 %. Correspondingly, JAK1 protein level decreased after transfection with JAK1 siRNA-conjugated liposome nanocomplexes, leading to a 37 % reduction in pERK (phosphor extracellular signal-regulated kinase) protein expression. These findings suggest that the combined delivery of JAK1 siRNA and 5-FU via liposomal formulations offers a promising and novel treatment strategy for targeting genes and other identified targets in NMSC therapy.

Microstructure and mechanical behavior in a spherical L12 nanoprecipitates strengthened Ni35Co27.5Cr27.5Al5Ti5 high-entropy alloy fabricated by direct casting and heat treatment

Intricate thermomechanical processing (TMP) including casting, homogenization, cold rolling, annealing and aging, has been widely used to achieve L12-strengthened CoCrNi-based medium- and high-entropy alloys (MEAs/HEAs). However, a large number of parts are usually manufactured by direct casting. We fabricated a non-equiatomic Ni35Co27.5Cr27.5Al5Ti5 HEA consisting of spherical L12 nanoprecipitates and FCC matrix using casting, homogenization and aging. Notably, both the homogenized and aged Ni35Co27.5Cr27.5Al5Ti5 HEA samples exhibit equiaxed grains, with the latter showcasing uniformly distributed spherical L12 nanoprecipitates in the FCC matrix. The average size and volume fraction of these nanoprecipitates in the aged HEA are ∼10.9 nm and ∼41.9 vol%, respectively. Mechanical testing reveals remarkable improvements in the aged HEA, with a yield strength of ∼916 MPa, an ultimate tensile strength of ∼1220 MPa, and a total elongation of ∼21.5 %. The observed enhancement is primarily attributed to precipitation strengthening mechanism. Digital image correlation (DIC) analysis of tensile deformation demonstrates uniform strain distribution in both the homogenized and aged HEA samples. In addition, electron channeling contrast imaging (ECCI) and transmission electron microscopy (TEM) examinations unveil a complex interplay of deformation mechanisms, including multiple planar slip, dislocation shearing coherent L12 precipitates, superpartials, stacking fault (SF) networks, and Lomer-Cottrell (L-C) locks. These mechanisms collectively impede dislocation motion, thereby contributing to the excellent strain-hardening ability and outstanding strength-ductility synergy of the HEA.

Comparison of differential phase Contrast, Lorentz and non-Lorentz transmission electron microscopy for microstructural and magnetic imaging of alnico magnet

In this work, non-Lorentz, Lorentz transmission electron microscopy (LTEM) and differential phase contrast (DPC) methods were used to observe the phase and magnetic structure of the alnico magnet. All observations were performed on alnico-5 in transverse orientation. The results showed the magnetic contrast of the domain walls in the conventional TEM images despite the effects of the lens magnetic field, which was verified and explained using DPC. Experimental methodology and sample results are summarized with advice for further research.

Yield stress anomaly and creep of single crystal Ni-base superalloys – Role of particle size

In the present work we subject the single crystal Ni-base superalloy ERBO1 (CMSX 4 type) to constant strain rate (CSR) and creep testing at temperatures between 1023 and 1223 K. Three material states are considered which have similar particle volume fractions >60% but differ in γ′-particle sizes (material states S, M and L of particle sizes: 240, 390 and 540 nm). In constant strain rate testing, a yield stress anomaly is observed for all three material states, with a yield stress maximum at 1073 K. This increase of strength with increasing temperature is not observed during creep testing at significantly lower deformation rates in this low temperature high stress creep regime, where different elementary deformation mechanisms govern CSR and creep behavior. In contrast, in the low stress high temperature creep regime, stress/strain rate data pairs from CSR creep tests both show decreasing strength with increasing temperature. It is found that in both types of tests the material state M shows the highest strength (highest yield stress and lowest creep rate). This can be rationalized based on a scenario where both, γ-channel and γ′-particle dislocation activities are important. Diffraction contrast transmission electron microscopy is used to study the relevant elementary deformation processes. Details of dislocation arrangements are discussed with a special focus on the role of Kear Wilsdorf (KW) locks, γ′-particle shearing by superlattice stacking faults (extrinsic and intrinsic) and dislocation climb.

Exposure to MMVF in residential and commercial buildings: A literature review and quantitative synthesis.

Man-made vitreous fibers (MMVF) are a class of inorganic fibrous materials that include glass and mineral wools, continuous glass filaments, and refractory ceramic fibers valued for their insulative properties in high temperature applications. Potential health effects from occupational exposure to MMVF have been investigated since the 1970s, with focus on incidence of respiratory tract cancer among MMVF-exposed production workers. The general population may experience exposure to MMVF in residential and/or commercial buildings due to deterioration, construction, or other disruption of materials containing these fibers. Numerous studies have characterized potential exposures that may occur during material disruption or installation; however, fewer have aimed to measure background MMVF concentrations in residential and commercial spaces (i.e., non-production settings) to which the general population may be exposed. In this study, we reviewed and synthesized peer-reviewed studies that evaluated respirable MMVF exposure levels in non-production, indoor environments. Among studies that analyzed airborne respirable MMVF concentrations, 110-fold and 1.5-fold differences in estimated concentrations were observed for those studies utilizing phase contrast optical microscopy (PCOM) versus transmission electron microscopy (TEM) and scanning electron microscopy (SEM), respectively. A positive correlation was observed between respirable air concentrations of MMVF and total surface concentrations of MMVF in seldom-cleaned areas. Ultimately, available evidence suggests that both ambient air and surface concentrations of MMVF in indoor environments are consistently lower than exposure limits developed to prevent negative health outcomes among sensitive populations.

3D Reconstruction of Sawtooth 180° Tail‐to‐Tail Domain Walls in Single Crystal BiFeO3

AbstractPrevious studies of single crystal BiFeO3 have found a dense domain structure with alternating sawtooth and flat domain walls (DWs). The nature of these domains and their 3D structure has remained elusive to date. Herein, several sections taken at different orientations are used to examine the structure in detail, concentrating here on the sawtooth DWs using diffraction contrast transmission electron microscopy, electron diffraction, and aberration‐corrected scanning transmission electron microscopy (STEM). All DWs are found to be 180° type; the flat walls have head‐to‐head polarity while the sawtooth DWs are tail‐to‐tail with peaks elongated along the polar [111] axis, formed by neutral () DW facets and slightly charged facets with orientations close to () and (). The neutral DW facets are Ising type and very abrupt, while the charged DW facets have mixed Néel/Bloch/Ising character with a chiral nature and a width of about 2 nm.

Development of biomaterial-based oxygen transportation vehicles for circulation within blood

BackgroundSeveral blood replacements have been developed because of issues with blood collection and storage, increased expenditures, and a global lack of reserves. Studies on artificial blood primarily concentrate on the research and synthesis of molecules that transport oxygen. The primary objective of the current work was to create a supporting, oxygen-carrying biological material that can replace blood and be used to save lives when blood is not available. MethodsThe work started with the synthesis of superparamagnetic iron oxide nanoparticles (SPIONS), and two distinct procedures were applied to ensure binding to hemoglobin (Hb) molecules. The surface modifications of the particles were carried out gradually by 3-amino propyl trimethoxy silane (3APGASPIONS) and tartaric acid (TASPIONS). Analysis methods used to characterize the particles include Fourier transform infrared spectrophotometer (FT-IR), elemental analysis (EDX), scanning electron microscope (SEM), X-ray diffractometry (XRD), and high contrast transmission electron microscopy (C-TEM). The characterization studies of SPIONS which bind Hb molecules to the surface were repeated and their effects on endothelial cell culture were examined to determine their toxic effects in vitro. Cell proliferation, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) activity changes were assessed in the evaluation of the possible toxic effects of the cells against the treated particles in the prepared cell lines. Blood substitute solutions synthesized by two different methods were stored on the shelf for about 1 month and the results were compared with fresh Hb solutions. Results and ConclusionThe CV and UV analysis results obtained from artificial Hb substitutes revealed that the structural integrity of Hb molecules did not change, the oxygen transport capabilities of biomolecules were preserved, and this state remained stable for a long time. Furthermore, it was determined that nanocomplexes synthesized by the two methods caused different cellular proliferation and there was a more limited increase in cellular enzyme activities (SOD, CAT, GPx) of Hb-bound particle solutions when compared to pure SPIONS.

Structure of V-defects in long wavelength GaN-based light emitting diodes

The V-defect is a naturally occurring inverted hexagonal pyramid structure that has been studied in GaN and InGaN growth since the 1990s. Strategic use of V-defects in pre-quantum well superlattices or equivalent preparation layers has enabled record breaking efficiencies for green, yellow, and red InGaN light emitting diodes (LEDs) utilizing lateral injection of holes through the semi-polar sidewalls of the V-defects. In this article, we use advanced characterization techniques such as scattering contrast transmission electron microscopy, high angle annular dark field scanning transmission electron microscopy, x-ray fluorescence maps, and atom probe tomography to study the active region compositions, V-defect formation, and V-defect structure in green and red LEDs grown on (0001) patterned sapphire and (111) Si substrates. We identify two distinct types of V-defects. The “large” V-defects are those that form in the pre-well superlattice and promote hole injection, usually nucleating on mixed (Burgers vector b=±a±c) character threading dislocations. In addition, “small” V-defects often form in the multi-quantum well region and are believed to be deleterious to high-efficiency LEDs by providing non-radiative pathways. The small V-defects are often associated with basal plane stacking faults or stacking fault boxes. Furthermore, we show through scattering contrast transmission electron microscopy that during V-defect filling, the threading dislocation, which runs up the center of the V-defect, will “bend” onto one of the six {101¯1} semi-polar planes. This result is essential to understanding non-radiative recombination in V-defect engineered LEDs.

Operando Liquid-Phase TEM Experiments for the Investigation of Dissolution Kinetics: Application to Li-Ion Battery Materials

Abstract We present here a novel and universal sample preparation method for liquid-phase transmission electron microscopy (TEM) experiments involving powder materials. Thanks to this new protocol, we demonstrate the ability to study the dissolution of cathode materials by sulfuric acid using operando TEM. Based on ultramicrotomy, this method has been developed to avoid compatibility issues between sample size and liquid cell geometry. The observation parameters have been optimized to get the best contrast in scanning TEM (STEM) images. The reaction kinetics have been investigated by image analysis and compared to those obtained ex situ. By taking into account the sample geometry and the reacting surfaces in both experiments, we show that the reaction kinetics are equivalent and could be overlaid. This proves that the protocol developed enables real operando experiments, as it provides quantitative data at the nanoscale that are representative of the bulk specimen. The main challenges of such a protocol for operando liquid-phase TEM, as well as the accuracy of the image analysis method used, are also discussed.

Effect of γ' phase and microtwins on the microstructural evolution and mechanical properties of a novel Ni–Co base superalloy

A new Ni–Co base precipitation-hardened superalloy designed using the low stacking fault energy (SFE) was used primarily in the hot components of aeroengines designed with low SFE exposed to high temperatures. Different microstructures of the new alloys were obtained by controlling the solution treatment temperature. The corresponding mechanical properties were tested at 25 °C and 750 °C. The primary γ' precipitates dissolved with increasing solution temperature, causing grain growth and an increasing microtwin fraction. Fine-grained, transient, and coarse-grained zones were formed in sequence because of the interaction between the γ′ phase and microtwins. The tensile strength decreased as the grain grew when tested at room temperature, and the strengthening mechanism was dislocation strengthening. However, when the tensile experiment temperature was increased to 750 °C, the tensile properties increased from the fine-grained to the transient zone and then decreased to the coarse-grained zone. Moreover, the fracture mechanism changed from ductile fracture to a mixed ductile and brittle fracture. The size of the secondary γ′ precipitates increased by 32 nm because the dissolved primary γ′ precipitated when the solution temperature was increased from 1090 °C to 1120 °C, which improved the tensile properties. The electron channeling contrast imaging and transmission electron microscopy results confirmed that microtwins were formed during the tensile process at 750 °C. The microtwins hindered the dislocation movement. Therefore, the transient zone of the low-SFE alloy demonstrated the best mechanical properties, which guided the optimization direction of the alloy design and service.

Extreme contact shrink for back end of line connectivity

For the past 50 years, Moore’s law has been well followed by the semiconductor industry. The scaling of transistors and interconnects has been enabled not only by various technological advancements but also by novel patterning approaches. However, in order to keep up with Moore’s law, further shrinking at all levels of the integrated circuit is needed. Among them is the back end of line (BEOL), where increasingly smaller metal pitches require tight specifications for vias connecting metal lines. In this paper, BEOL via shrink options is investigated, targeting the bottom critical dimension (CD) 10.5 nm in order to land on metal pitch 21 nm lines below, while maintaining low defectivity, as well as low global and local CD uniformity (CDU and LCDU, respectively). Approaches to this shrink consist of modifications to the etch chemistry at different levels of the mask etch and liner-assisted shrink, either organic or inorganic. Numerical analysis of CD-scanning electron microscopy (CDSEM) images quantitatively shows the efficiency of different approaches via shrink, together with associated CDU, LCDU, and defectivity values. CDSEM results are supplemented by large-area voltage contrast defectivity and transmission electron microscopy data sets.

Shaping of Electron Beams Using Sculpted Thin Films.

Electron beam shaping by sculpted thin films relies on electron–matter interactions and the wave nature of electrons. It can be used to study physical phenomena of special electron beams and to develop technological applications in electron microscopy that offer new and improved measurement techniques and increased resolution in different imaging modes. In this Perspective, we review recent applications of sculpted thin films for electron orbital angular momentum sorting, improvements in phase contrast transmission electron microscopy, and aberration correction. For the latter, we also present new results of our work toward correction of the spherical aberration of Lorentz scanning transmission electron microscopes and suggest a method to correct chromatic aberration using thin films. This review provides practical insight for researchers in the field and motivates future progress in electron microscopy.

Enhancing Charge Transfer in Photocatalytic Hydrogen Production over Dye-Sensitized Pt/TiO2 by Ionic Liquid Coating

Photocatalytic hydrogen production from water is considered to be a potentially cost-efficient method to produce hydrogen fuel with little impact on the environment. Nevertheless, hydrogen production efficiencies via photocatalysis remain to be low. Here, a photocatalyst system composed of 1 wt % Pt/TiO2 and dye-sensitized Pt/TiO2 particulates encapsulated by an ionic liquid is proposed. In particular, the enhancement of photocatalytic hydrogen production over 1 wt % Pt/TiO2 particulates sensitized with N719 dye (di-tetrabutylammonium cis-bis(isothiocyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylato) ruthenium(II)) and coated by a thin layer of ionic liquid [BMIM][BF4] (1-butyl-3-methylimidazolium tetrafluoroborate) has been investigated. The Pt was loaded onto the TiO2 surface by incipient wetness impregnation, while the dye and ionic liquid were loaded by solvent evaporation using ethanol and acetone, respectively. The photocatalytic tests were performed in a semibatch glass reactor under visible light irradiation provided by a solar simulator; the hydrogen production rates over Pt/TiO2, dye-sensitized Pt/TiO2, ionic liquid-coated Pt/TiO2, and ionic liquid-coated Pt/TiO2 after dye sensitization were compared. The hydrogen production rate was ∼21 μmol/h·gcat on Pt/TiO2, and it increased to ∼27 μmol/h·gcat with dye sensitization, while the [BMIM][BF4] coating alone improved hydrogen production three times (∼60 μmol/h·gcat). Coating the dye-sensitized particulates with an ionic liquid resulted in another 17% increase in hydrogen production (∼70 μmol/h·gcat). Scanning electron microscopy–energy dispersive X-ray analysis (SEM–EDAX), contrast transmission electron microscopy (CTEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, UV–vis characterization of the photocatalysts and electrochemical analysis of the respective photoelectrodes were also performed. The ionic liquid coating increased the performance of Pt/TiO2 by providing better charge transfer between the photocatalyst and the aqueous reaction medium while simultaneously preventing the recombination of photogenerated electron–hole pairs. The improved performance of the dye-sensitized photocatalyst upon the ionic liquid coating indicated that the ionic liquid stabilized the dye on the photocatalyst surface while simultaneously enhancing the charge transfer between the dye and TiO2.

Composition-dependent slip planarity in mechanically-stable face centered cubic complex concentrated alloys and its mechanical effects

In metallic materials, enhancing strain hardening capacity positively affects ductility, fracture toughness, ultimate tensile strength, and other properties. Thus, activating mechanically-induced martensitic transformation or twinning mechanisms has been a captivating goal in the design of steels, titanium alloys, cobalt alloys, complex concentrated alloys (CCAs) and others, through modifications to composition or thermo-mechanical processing. Here instead, we focus on the most basic strain hardening effect, arising from dislocation kinematics, and interactions. For this purpose, we designed two model face centered cubic (FCC) CCAs, Ni2CoCrFe and Ni2CoCrFeTi0.2Al0.1. Both alloys develop single, mechanically-stable, FCC phase microstructures upon processing. Mechanical tests of these alloys reveal that the Al and Ti addition enhances the strain hardening capacity, leading to significant increases in strength and ductility. Microstructure analyses based on electron channeling contrast imaging (ECCI), electron-backscatter diffraction (EBSD), and transmission electron microscopy (TEM) confirm the absence of mechanically-induced twinning and martensitic transformation effects, revealing instead a transition from wavy slip to planar slip. In-situ synchrotron XRD tensile tests are used to discuss the origin of the dislocation glide mode transition and the effects on strain hardening. Based on these analyses, the increased degree of short-range ordering (SRO), rather than the changes in stacking fault energy (SFE), is proposed as the main cause for this transition, and the corresponding effects on strain hardenability.

Remarkable activity of a ZnPdPt anode catalyst: Synthesis, characterization, and formic acid fuel cell performance

Herein, multi-walled carbon nanotube (MWCNT) supported Zn–Pd and Zn–Pd–Pt catalysts have been prepared utilizing a sequential sodium borohydride (SBH) reduction method. The resulting Zn/MWCNT, Zn–Pd/MWCNT, and Zn–Pd–Pt/MWCNT catalysts were characterized using advanced surface analytical techniques such as X-ray diffraction (XRD), high contrast transmission electron microscopy (C-TEM), and X-ray photoelectron spectroscopy (XPS). The characterization results indicate that the Zn/MWCNT, Zn–Pd/MWCNT, and Zn–Pd–Pt/MWCNT catalysts were successfully prepared. It was observed that Pd and Pt incorporation into Zn alters the electronic structure of Zn. Cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) were used to examine the electrochemical activity of the catalysts toward the electrooxidation of formic acid (FA). The results reveal that ZnPdPt/MWCNT has a specific activity of 12.6 mA/cm2 and an electrochemical active surface area (ECSA) of 41.1 m2/g. This catalyst shows high activity, stability, and resistance when compared to Pd/MWCNT and ZnPd/MWCNT. Direct FA fuel cell (DFAFC) measurements were performed at 18–60 °C for the ZnPd/MWCNT and ZnPdPt/MWCNT catalysts. The specific activity of ZnPdPt/MWCNT was 1.45 times greater than that measured for ZnPd/MWCNT. ZnPdPt/MWCNT is a promising catalyst according to our CV, CA, EIS, and DFAFC measurements.

Unveiling anneal hardening in dilute Al-doped AlxCoCrFeMnNi (x = 0, 0.1) high-entropy alloys

Anneal hardening has been one of the approaches to improve mechanical properties of solid solution alloys with the face-centered cubic (FCC) structure, whereby a considerable strengthening can be attained by annealing of cold-worked alloys below the recrystallization temperature (Trx). Microscopically, this hardening effect has been ascribed to several mechanisms, i.e. solute segregation to defects (dislocation and stacking fault) and short-range chemical ordering, etc. However, none of these mechanisms can well explain the anneal hardening recently observed in phase-pure and coarse-grained FCC-structured high-entropy alloys (HEAs). Here we report the observations, using high-resolution electron channeling contrast imaging and transmission electron microscopy, of profuse and stable dislocation substructures in a cold-rolled CoCrFeMnNi HEA subject to an annealing below Trx. The dislocation substructures are observed to be thermally stable up to Trx, which could arise from the chemical complexity of the high-entropy system where certain elemental diffusion retardation occurs. The microstructure feature is markedly different from that of conventional dilute solid solution alloys, in which dislocation substructures gradually vanish by recovery during annealing, leading to a strength drop. Furthermore, dilute addition of 2 at.% Al leads to a reduction in both microhardness and yield strength of the cold-rolled and subsequently annealed (≤500 °C) HEA. This Al induced softening effect, could be associated with the anisotropic formation of dislocation substructure, resulting from enhanced dislocation planar slip due to glide plane softening effect. These findings suggest that the strength of HEAs can be tailored through the anneal hardening effect from dislocation substructure strengthening.

The role of metal powder properties on the tribology of cold sprayed Ti6Al4V-TiC metal matrix composites

Ti6Al4V-TiC metal matrix composite (MMC) coatings were cold sprayed using spherical and irregular Ti6Al4V powders manufactured with plasma gas atomization and the Armstrong process, respectively. Composite coatings deposited using irregular powders showed higher ceramic retentions and lower porosity compared to spherical powder (SP) coatings. Sliding wear tests were performed at two different normal loads using a spherical WC-Co ball as counterface. Wear test results showed that at similar ceramic contents, spherical powder composites exhibited abrasive wear mechanisms with high coefficients of friction (CoF) and wear rates. In irregular powder (IP) composites, islands of tribolayers, comprised of fragmented TiC and TiO2 particles, resisted the localized shear deformation leading to low wear, and with free carbon from the TiC particles also lowered the CoF. Increase in ceramic content in the IP MMCs to 23% led to higher coverage of wear track area with tribolayers and further lowered the wear rate. At higher load, 23% TiC composite coatings showed a more continuous tribolayer, whereas lower ceramic content MMCs showed no significant formation of tribolayers. The formation of a highly continuous tribolayer at higher load (in 23% TiC MMC), led to extremely low CoF (~ 0.25) compared to other coatings along with low wear rate. Electron channel contrast imaging and transmission electron microscopy analysis of the worn subsurface under the tribolayers showed coarse-grain microstructures compared to the bare regions of the wear track (i.e. without tribolayer coverage). The formation of coarser grain microstructures indicated less stress transfer to the subsurface both due to the high hardness and lubricating nature of the tribolayers.

Airborne concentrations of chrysotile asbestos during operation of industrial crane controls and maintenance of associated arc chutes

Some industrial crane control panels were historically equipped with chrysotile-containing arc chutes. Because of the paucity of data regarding potential exposure from such equipment, we used a simulation approach to quantify the release of chrysotile from arc chutes in two functional 1970s-era industrial crane control panels during operation and maintenance. Two experienced operators separately simulated operation of crane controls under load; one of these operators then simulated two arc chute maintenance protocols: sanding (protocol 1) and scraping, sanding, and blowing (protocol 2). The original arc chutes contained approximately 36% chrysotile. Personal breathing zone (PBZ) (n = 8) and area samples (n = 8) were collected and analyzed using phase contrast microscopy (PCM) and transmission electron microscopy. PCM-equivalent (PCME) concentrations were derived, from which 8-h time-weighted averages (TWA) were calculated. During operation, chrysotile was identified in one of the four PBZ samples, equivalent to a PCME concentration of 0.012 f/cm3 (8-h TWA: 0.011 f/cm3). During protocols 1 and 2, chrysotile was identified in all PBZ samples (n = 4); PCME concentrations (and corresponding 8-h TWA) were <0.013 and 0.021 f/cm3 (0.001 and 0.004 f/cm3) and 0.013 and 0.017 f/cm3 (0.003 f/cm3), respectively. Many of the airborne chrysotile fibers had matrix attached, supporting the low exposure potential during this work. These data indicate very low, if any, exposures to chrysotile asbestos during the simulated scenarios. In addition, these data could assist with refining assumptions in exposure reconstruction and inform the state-of-the science on low-level chrysotile exposure.

Light-triggered Janus nanomotor for targeting and photothermal lysis of pathogenic bacteria.

The rapid photothermal lysis of Escherichia coli O157:H7 treated with light-triggered Janus nanomotors was visualized by Hilbert differential contrast transmission electron microscopy (HDC-TEM). The extraordinary advantage of this high-resolution microscopic technique was that it revealed the detailed ultrastructure alterations of the treated cells at a state close to their native one. The micrographs demonstrated that Janus nanomotors (mesoporous silica nanoparticles with gold hemisphere and half-capped with cysteamine) were able to target and bind to the pathogenic E. coli. The biorecognition reaction proceeded at slightly acid pH thankful to the formed electrostatic adhesion between positively charged amino groups on nanoparticles surface and the negatively charged cell envelope. The exposure of labeled cells to near infrared laser irradiation leaded to occurrence of effective photothermal damage of their plasma membranes, which was enough strong to lyse bacteria. It was because of the overheating obtained by the photon-to-thermal conversion reaction generated by the surface plasmon resonance response of Janus nanomotors. The good efficiency of photothermal lysis to inactivate E. coli O157:H7 was confirmed by staining with LIVE/DEAD viability kit and quantification of the few survived cells in epifluorescence microscope. Furthermore, HDC-TEM images of ice-embedded inhibited bacteria documented the labeling, membrane disruptions and lysis due to the designed operation of Janus nanomotors. The reported microscopic technique provides a novel strategy for developing of Janus nanomachines as promising platform for nondrug treatment and defeating of antibiotic-resistant pathogenic microorganisms.