Scanning Transmission Electron Microscopy Analysis Research Articles

Monoclinic α-Bi2O3 nanorods by microwave-assisted synthesis: Photocatalytic and antioxidant properties

Nanotechnology has emerged as a new route for addressing most environmental and medical challenges, hence this field of research continues to generate research interest. Herein, Bi2O3 was synthesized by a microwave-assisted thermal process. X-ray diffraction (XRD) result confirmed that a nanocrystalline monoclinic crystal structure of the α-phase was formed, and both the Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) analysis confirmed that the synthesized α-Bi2O3 were rod-like in shape. The length of the nanorods was in the range of 60–160 nm, with an average dimension of 101.5 nm, while the width has an average value of 23 nm. A band gap energy value of 2.75 eV was obtained from the absorption spectroscopy, and they absorbed light in the UV to visible range, with an absorption maximum of around 345 nm. Photocatalytic activity of the nanorods under UV irradiation was investigated by assessing the degradation of Bromocresol green (BG) as a model pollutant. The degradation process of the dye molecules was studied at different concentrations (20–80 mg/L), varied photocatalyst dosage (0.025, 0.05, 0.075, and 1.0 g), and a range of solution pH (3, 6, 9, and 12). About 75 % optimum photocatalytic efficiency was achieved at pH 6 after 3 h. In addition, the results showed that an increase in catalyst dosage and concentration of dye molecules contributed to promoting the degradation effect. Moreover, the photocatalyst was found to be stable after 4 consecutive cycles, with negligible loss of efficiency. The antioxidant potency of the nanorods was assessed by evaluating their free radical scavenging capabilities across 4 different assays: 1,1-diphenyl-2-picrylhydrazyle (DPPH), Nitric oxide (NO), Hydrogen peroxide (HP) radical inhibition, and Reducing power (RP). The results from the IC50 values indicated the sample exhibited better inhibition of HP (25.22 µg/mL), followed by RP (28.22 µg/mL), NO (29.37 µg/mL), and DPPH (32.72 µg/mL) respectively. However, the standard Ascorbic acid exhibited IC50 values of 16.25, 24.50, 25.07, and 28.40 µg/mL for DPPH, RP, HP, and NO, respectively. These unique properties of the nanorods showed that they have good antioxidant potential that is comparable with that of Ascorbic acid used as the standard.

Production and Characterization of Nanocellulose from Maguey (Agave cantala) Fiber.

Plant fibers have been studied as sources of nanocellulose due to their sustainable features. This study investigated the effects of acid hydrolysis parameters, reaction temperature, and acid concentration on nanocellulose yield from maguey (Agave cantala) fiber. Nanocellulose was produced from the fibers via the removal of non-cellulosic components through alkali treatment and bleaching, followed by strong acid hydrolysis for 45 min using sulfuric acid (H2SO4). The temperature during acid hydrolysis was 30, 40, 50, and 60 °C, and the H2SO4 concentration was 40, 50, and 60 wt. % H2SO4. Results showed that 53.56% of raw maguey fibers were isolated as cellulose, that is, 89.45% was α-cellulose. The highest nanocellulose yield of 81.58 ± 0.36% was achieved from acid hydrolysis at 50 °C using 50 wt. % H2SO4, producing nanocellulose measuring 8-75 nm in diameter and 72-866 nm in length, as confirmed via field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analysis. Fourier-transform infrared spectroscopy (FTIR) analysis indicated the chemical transformation of fibers throughout the nanocellulose production process. The zeta potential analysis showed that the nanocellulose had excellent colloidal stability with a highly negative surface charge of -37.3 mV. Meanwhile, X-ray diffraction (XRD) analysis validated the crystallinity of nanocellulose with a crystallinity index of 74.80%. Lastly, thermogravimetric analysis (TGA) demonstrated that the inflection point attributed to the cellulose degradation of the produced nanocellulose is 311.41 °C.

Co3O4-Based Materials as Potential Catalysts for Methane Detection in Catalytic Gas Sensors.

The present work deals with the development of Co3O4-based catalysts for potential application in catalytic gas sensors for methane (CH4) detection. Among the transition-metal oxide catalysts, Co3O4 exhibits the highest activity in catalytic combustion. Doping Co3O4 with another metal can further improve its catalytic performance. Despite their promising properties, Co3O4 materials have rarely been tested for use in catalytic gas sensors. In our study, the influence of catalyst morphology and Ni doping on the catalytic activity and thermal stability of Co3O4-based catalysts was analyzed by differential calorimetry by measuring the thermal response to 1% CH4. The morphology of two Co3O4 catalysts and two NixCo3-xO4 with a Ni:Co molar ratio of 1:2 and 1:5 was studied using scanning transmission electron microscopy and energy dispersive X-ray analysis. The catalysts were synthesized by (co)precipitation with KOH solution. The investigations showed that Ni doping can improve the catalytic activity of Co3O4 catalysts. The thermal response of Ni-doped catalysts was increased by more than 20% at 400 °C and 450 °C compared to one of the studied Co3O4 oxides. However, the thermal response of the other Co3O4 was even higher than that of NixCo3-xO4 catalysts (8% at 400 °C). Furthermore, the modification of Co3O4 with Ni simultaneously brings stability problems at higher operating temperatures (≥400 °C) due to the observed inhomogeneous Ni distribution in the structure of NixCo3-xO4. In particular, the NixCo3-xO4 with high Ni content (Ni:Co ratio 1:2) showed apparent NiO separation and thus a strong decrease in thermal response of 8% after 24 h of heat treatment at 400 °C. The reaction of the Co3O4 catalysts remained quite stable. Therefore, controlling the structure and morphology of Co3O4 achieved more promising results, demonstrating its applicability as a catalyst for gas sensing.

Transistors with ferroelectric ZrXAl1−XOY crystallized by ZnO growth for multi-level memory and neuromorphic computing

Ferroelectric (FE) field-effect transistors are interesting for their non-destructive readout characteristic and energy efficiency but are difficult to integrate on silicon platforms. Here, FE ZrXAl1−XOY (ZAO) is demonstrated by compressive strain in contact with ZnO. The metal-ferroelectric-semiconductor-metal capacitor exhibits a substantial remnant polarization of 15.2 µC cm−2, along with a bowknot-like anti-clockwise hysteresis in the capacitance curves. The FE-ZAO gated ZnO thin-film transistor presents a large memory window (3.84 V), low subthreshold swing (55 mV dec−1), high ION/IOFF ratio (≈108), and low off-state current (≈1 pA). The grazing incidence X-ray diffraction and scanning transmission electron microscopy analyses reveal the ferroelectric rhombohedral phase (space group R3m) in the nanocrystal ZAO, containing an angle of ≈71.7° between the [111] and [11-1] directions with d111-spacing of 3.037 Å and d11-1-spacing of 2.927 Å. Finally, the memory and neuromorphic applications are analyzed by demonstrating multi-level memory and synaptic weight performance with a high learning accuracy of 91.82%.

Experimental High-Resolution Observation of the Truncated Double-Icosahedron Structure: A Stable Twinned Shell in Alloyed Au-Ag Core@Shell Nanoparticles.

Given the binary nature of nanoalloy systems, their properties are dependent on their size, shape, structure, composition, and chemical ordering. When energy and entropic factors for shapes and structure variations are considered in nanoparticle growth, the spectra of shapes become so vast that even metastable arrangements have been reported under ambient conditions. Experimental and theoretical variations of multiply twinned particles have been observed, from the Ino and Marks decahedra to polyicosahedra and polydecahedra with comparable energetic stability among them. Herein, we report the experimental production of a stable doubly truncated double-icosahedron structure (TdIh) in Au-Ag nanoparticles, in which a twinned Ag-rich alloyed shell is reconstructed on a Au-Ag alloyed Ino-decahedral core. The structure, chemical composition, and growth pathway are proposed on the basis of high-angle annular dark-field scanning transmission electron microscopy analysis and excess energy calculations, while its structural stability is estimated by large-scale atomic molecular dynamics simulations. This novel nanostructure differs from other structures previously reported.

Hydrogen production from sodium borohydride using Co nanoparticles

In this study, hydrogen [H2(g)] production from sodium borohydride (NaBH4) using cobalt (Co) nanoparticles (NPs) was investigated with a hydrolysis process. Optimum experimental conditions were examined at different hydrolysis times (5, 10, 20, 30, 40, 50, 60, 70, 80, and 90 min), at different hydrolysis temperatures (25, 35, 45, and 65oC), and at increasing Co NPs nanocatalyst concentrations (5, 15 and 30 mg/l) at pH = 13.0, respectively. X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM) analyses were performed for characterization studies. H2(g) measurements were made in gaschromatography–mass spectrometry (GC-MS). The maximum 81% H2(g) yield was observed before the hydrolysis process after 90 min, at pH = 13.0, at 25 oC. The maximum H2(g) yields were recorded as 98% after 45 min hydrolysis times at 45 oC, at a pH of 13.0. 99% H2(g) yields were found after 14 min hydrolysis times, at pH a pH of 13.0 at 65 oC. The maximum NaBH4 concentration and using Co NPs concentrations were kept constant at 300 mg/l and 1.5 mg/l, respectively.

One-Pot Synthesis of CHA/ERI-Type Zeolite Intergrowth from a Single Multiselective Organic Structure-Directing Agent.

We report the one-pot synthesis of a chabazite (CHA)/erionite (ERI)-type zeolite intergrowth structure characterized by adjustable extents of intergrowth enrichment and Si/Al molar ratios. This method utilizes readily synthesizable 6-azaspiro[5.6]dodecan-6-ium as the exclusive organic structure-directing agent (OSDA) within a potassium-dominant environment. High-throughput simulations were used to accurately determine the templating energy and molecular shape, facilitating the selection of an optimally biselective OSDA from among thousands of prospective candidates. The coexistence of the crystal phases, forming a distinct structure comprising disk-like CHA regions bridged by ERI-rich pillars, was corroborated via rigorous powder X-ray diffraction and integrated differential-phase contrast scanning transmission electron microscopy (iDPC S/TEM) analyses. iDPC S/TEM imaging further revealed the presence of single offretite layers dispersed within the ERI phase. The ratio of crystal phases between CHA and ERI in this type of intergrowth could be varied systematically by changing both the OSDA/Si and K/Si ratios. Two intergrown zeolite samples with different Si/Al molar ratios were tested for the selective catalytic reduction (SCR) of NOx with NH3, showing competitive catalytic performance and hydrothermal stability compared to that of the industry-standard commercial NH3-SCR catalyst, Cu-SSZ-13, prevalent in automotive applications. Collectively, this work underscores the potential of our approach for the synthesis and optimization of adjustable intergrown zeolite structures, offering competitive alternatives for key industrial processes.

Scanning transmission electron microscopy and atom probe tomography analysis of non-stoichiometry long-period-stacking-ordered structures in Mg-Ni-Y/Sm alloys

The long-period-stacking-ordered (LPSO) structure affects the mechanical, corrosion and hydrolysis properties of Mg alloys. The current work employs high angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) and atom probe tomography (APT) to investigate the structural and local chemical information of LPSO phases formed in Mg-Ni-Y/Sm ternary alloys after extended isothermal annealing. Depending on the alloying elements and their concentrations, Mg-Ni-Y/Sm develops a two-phase LPSO + α-Mg structure in which the LPSO phase contains defects, hybrid LPSO structure, and Mg insertions. HAADF-STEM and APT indicate non-stoichiometric LPSO with incomplete Ni6(Y/Sm)8 clusters. In addition, the APT quantitatively determines the local composition of LPSO and confirms the presence of Ni within the Mg bonding layers. These results provide insight into a better understanding of the structure and hydrolysis properties of LPSO-Mg alloys.

Insight on defects mechanically introduced by nanoindentation in 4H-SiC p-n diode

We investigate defects in 4H-SiC p-n junction diodes introduced trough nanoindentation procedure. A nanoindentation load range between 3 mN and 15 mN was explored. Scanning Electron Microscopy and Transmission Electron Microscopy analysis are adopted for the morphological and crystallographic investigation of defects; electrical characterisations of junction diodes are performed to investigate the conduction mechanism, both at RT and versus measurement temperature. Electrical parameters such ideality factor, leakage current and series resistance, are extracted for the processed diodes and compared to virgin one. Activation energy of about 1.7 eV and 0.2 eV are extracted for defects in virgin and in mechanically processed devices, respectively. Electro-optical characterisation is performed adopting Emission Microscopy measurements evidencing a diffuse photons emission in the visible range from the full area in virgin device and an emission in the visible and in the near infrared ranges from nanoindentation sites in processed devices. Performed analysis evidenced both extended and point defects are mechanically introduced. Thanks to the performed experiment, a promising way is paved for the defects engineering, in a microscale spatially defined position, in end of processing devices.

Equilibrium, kinetic, and thermodynamic studies on the biosorption of lead by human metallothionein gene-cloned bacteria as a novel biosorbent.

Heavy metals are the main pollutants in water and are an important global problem that threatens human health and ecosystems. In recent years, there has been an increasing interest in the use of genetically modified bacteria as an eco-friendly method to solve heavy metal pollution problems. The goal of this study was to generate genetically modified Escherichia coli expressing human metallothioneins (hMT2A and hMT3) and to determine their tolerance, bioaccumulation, and biosorption capacity to lead (Pb2+ ). Recombinant MT2A and MT3 strains expressing MT were successfully generated. Minimum inhibition concentrations (MIC) of Pb for MT2A and MT3 were found to be 1750 and 2000 mg L-1 , respectively. Pb2+ resistance and bioaccumulation capacity of MT3 were higher than MT2A. Therefore, only MT3 biosorbent was used in Pb2+ biosorption, and its efficiency was examined by performing experiments in a batch system. Pb2+ biosorption by MT3 was evaluated in terms of isotherms, kinetics, and thermodynamics. The results showed that Pb biosorption fits to the Langmuir isotherm model and the pseudo-first-order kinetic model, and the reaction is exothermic. The maximum Pb2+ capacity of the biosorbent was 50 mg Pb2+ g-1 . The potential of MT3 in Pb biosorption was characterized by Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and scanning transmission electron microscopy (STEM) analyses. The desorption study showed that the sorbent had up to 74% recovery and could be effectively used four times. These findings imply that this biosorbent can be applied as a promising, precise, and effective means of removing Pb2+ from contaminated waters. PRACTITIONER POINTS: In this study, the tolerance levels, bioaccumulation, and biosorption capacities of Pb in aqueous solutions were determined for the first time in recombinant MT2A and MT3 strains in which human MT2A and MT3 genes were cloned. The biosorbent of MT3, which was determined to be more effective in Pb bioaccumulation, was synthesized and used in Pb biosorption. The Pb biosorption mechanism of MT3 biosorbent was identified using isotherm modeling, kinetic modeling, and thermodynamic studies. The maximum Pb removal percentage capacity of the biosorbent was 90%, whereas the maximum biosorption capacity was up to 50 mg Pb2+ g-1 . These results indicated that MT3 biosorbent has a higher Pb biosorption capacity than existing recombinant biosorbents. MT3 biosorbent can be used as a promising and effective biosorbent for removing Pb from wastewater.

Investigation of nanoscale strain fields induced by the L12–Al3Zr phase in Al–Zn–Mg–Cu alloys

Al–Zn–Mg–Cu alloys are widely used in aerospace as an advanced lightweight structural material. The precipitation of the nanoscale L12–Al3Zr phase enhances the mechanical properties of the alloy. This study employs scanning transmission electron microscopy and geometric phase analysis techniques to investigate the strain fields induced by the nanoscale L12–Al3Zr phase. The findings demonstrate that after the precipitation of the L12–Al3Zr phase, the strain within the L12–Al3Zr phase is negligible, and a coherent strain field is developed near the L12–Al3Zr/Al interface. Characterizing the coherent strain fields of the nanoscale L12–Al3Zr phase provides a valuable reference for optimizing the mechanical properties of Al alloys.

Twisted epitaxy of gold nanodisks grown between twisted substrate layers of molybdenum disulfide.

We expand the concept of epitaxy to a regime of "twisted epitaxy" with the epilayer crystal orientation between two substrates influenced by their relative orientation. We annealed nanometer-thick gold (Au) nanoparticles between two substrates of exfoliated hexagonal molybdenum disulfide (MoS2) with varying orientation of their basal planes with a mutual twist angle ranging from 0° to 60°. Transmission electron microscopy studies show that Au aligns midway between the top and bottom MoS2 when the twist angle of the bilayer is small (<~7°). For larger twist angles, Au has only a small misorientation with the bottom MoS2 that varies approximately sinusoidally with twist angle of the bilayer MoS2. Four-dimensional scanning transmission electron microscopy analysis further reveals a periodic strain variation (<|±0.5%|) in the Au nanodisks associated with the twisted epitaxy, consistent with the Moiré registry of the two MoS2 twisted layers.

Post-irradiation examination of commercial tantalum alloys following neutron irradiation

Post irradiation examination of two commercial tantalum alloys (based on Ta-8 %W) revealed significant irradiation hardening following neutron irradiation in the High Flux Isotope Reactor at Oak Ridge National Laboratory. Tensile samples of commercial Ta alloys T-111 and ASTAR-811C were irradiated to a total neutron fluence (E > 0.1 MeV) in the range (2–4)x1021 n/cm2 (0.39–0.75 dpa) at an irradiation temperature near 900 °C. Tensile testing conducted at room temperature and at 800 °C revealed significant irradiation hardening under all test conditions. Samples that were tensile tested at room temperature exhibited brittle failure, whereas ductility was maintained for elevated temperature testing. The irradiation hardening and embrittlement noted for both alloys was attributed to irradiation-induced dislocation loop formation as confirmed through scanning transmission electron microscopy analysis. Corresponding energy dispersive x-ray spectroscopy revealed radiation-induced segregation of Hf in these loop populations. This Hf enrichment is shown to result in eventual co-precipitation of elongated (Hf,O)-rich precipitates along the dislocation loops. These results show that irradiation hardening is enhanced via irradiation-enhanced precipitation at elevated irradiation temperatures. Consequently, the minimum recommended operating temperature window for Ta alloys should be increased to account for observed hardening/embrittlement at irradiation temperatures as high as 900 °C (1,173 K).

Low-temperature synthesis of porous high-entropy (CoCrFeMnNi)3O4 spheres and their application to the reverse water-gas shift reaction as catalysts.

A high-entropy porous spinel oxide [(Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)3O4] was synthesized via a solvothermal method and calcination. Solvothermal conditions yielding homogeneous precursor composites with five metals were optimized. Low-temperature calcination of the amorphous composites at 500 °C for 60 min yielded porous spheres formed by small primary particles, with crystal structures attributed to single-phase spinels. The homogeneity of the five elements in the spheres was verified via scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy analysis. The high-entropy (Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)3O4 spheres exhibited superior catalytic activity and long-term stability for the reverse water-gas shift reaction at 700 °C for at least 15 h. The importance of the Cr component in stabilizing the spinel structure was demonstrated. Mn, Fe, Co, and Ni served as active sites in the reaction. The advantage of solvothermal synthesis for porous high-entropy materials was discussed.

Ce Doped SnO2 Nanoparticcles: Investigation of Structural and Optical Properties

Tin oxide (SnO2 ) and (1 wt%, 3 wt%, 5wt %) Ce-doped SnO2 nanoparticles were synthesized by the Co-precipitation method. X-ray diffraction investigations have been confirmed that the synthesized nanoparticles are polycrystalline in nature with tetragonal rutile phase. The particle size is determined using Scherrer’s formula and it is found to increase with the “Ce” dopant. High resolution scanning electron microscope (HRSEM) and transmission electron microscopy (TEM) analysis showed spherical morphology composed of fine crystallites with diameters around ∼200 nm. Optical band gap was decreased by the doping confirming the direct energy transfer between f-electrons of rare earth ion and the SnO2 conduction or valence band. This study demonstrates the Ce doped SnO2 nanoparticles for applications in optoelectronic devices.

Layer-Controlled Growth of Single-Crystalline 2D Bi2O2Se Film Driven by Interfacial Reconstruction.

As semiconductor scaling continues to reach sub-nanometer levels, two-dimensional (2D) semiconductors are emerging as a promising candidate for the post-silicon material. Among these alternatives, Bi2O2Se has risen as an exceptionally promising 2D semiconductor thanks to its excellent electrical properties, attributed to its appropriate bandgap and small effective mass. However, unlike other 2D materials, growth of large-scale Bi2O2Se films with precise layer control is still challenging due to its large surface energy caused by relatively strong interlayer electrostatic interactions. Here, we present the successful growth of a wafer-scale (∼3 cm) Bi2O2Se film with precise thickness control down to the monolayer level on TiO2-terminated SrTiO3 using metal-organic chemical vapor deposition (MOCVD). Scanning transmission electron microscopy (STEM) analysis confirmed the formation of a [BiTiO4]1- interfacial structure, and density functional theory (DFT) calculations revealed that the formation of [BiTiO4]1- significantly reduced the interfacial energy between Bi2O2Se and SrTiO3, thereby promoting 2D growth. Additionally, spectral responsivity measurements of two-terminal devices confirmed a bandgap increase of up to 1.9 eV in monolayer Bi2O2Se, which is consistent with our DFT calculations. Finally, we demonstrated high-performance Bi2O2Se field-effect transistor (FET) arrays, exhibiting an excellent average electron mobility of 56.29 cm2/(V·s). This process is anticipated to enable wafer-scale applications of 2D Bi2O2Se and facilitate exploration of intriguing physical phenomena in confined 2D systems.

Troubleshooting CNT Bundling with Electrospray Method in LiFePO4 Cathode Material

CNT, a nanomaterial with a 1D structure providing efficient electron transport, is well known as an excellent electron-conducting material and a key element for realizing thick electrodes. However, due to its high aspect ratio, there is significant Van der Waals force present; therefore, when used at a certain level or higher, it aggregates, which causes performance degradation, limiting its use.In this work, we solve the bundling problem by applying a feasible electrospray method. This approach achieves a LiFePO4/CNT composite with uniform morphology, even with high CNT content, and is confirmed with Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) analysis. In addition, we found out that it shows enhanced capacity retention and longer battery life compared to the conventional mixing-only method.

Interweaved needle‐shaped α‐Ni(OH)2 nanoparticles adorned on graphene oxide: A new class of heterogeneous catalysts for α‐alkylation of ketones and synthesis of azines

A simple approach for synthesizing needle‐shaped α‐Ni(OH)2 nanoparticles adorned on graphene oxide, α‐Ni(OH)2‐GO, is described. The nanocomposite was isolated as an air‐stable black powder and characterized by various instrumental techniques. The interweaved needle‐shaped morphology and the average particle diameter ~7 nm of the adorned α‐Ni(OH)2 nanoparticles were ascertained by Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM) analysis, respectively. The catalytic potential of the nanocomposite was scrutinized in the synthesis of monosubstituted ketones via a hydrogen autotransfer strategy and synthesis of azines via dehydrogenative pathway. The products of both reactions were isolated in excellent yields and characterized by nuclear magnetic resonance (NMR) spectroscopy. α‐Ni(OH)2‐GO could be segregated and recycled for up to five cycles. The operational simplicity, broad substrate scope, non‐toxic side products, recyclability, and superior catalytic potential of the catalyst are some of the remarkable features of this protocol.

W18O49 Nanowhiskers Decorating SiO2 Nanofibers: Lessons from In Situ SEM/TEM Growth to Large Scale Synthesis and Fundamental Structural Understanding.

Tungsten suboxide W18O49 nanowhiskers are a material of great interest due to their potential high-end applications in electronics, near-infrared light shielding, catalysis, and gas sensing. The present study introduces three main approaches for the fundamental understanding of W18O49 nanowhisker growth and structure. First, W18O49 nanowhiskers were grown from γ-WO3/a-SiO2 nanofibers in situ in a scanning electron microscope (SEM) utilizing a specially designed microreactor (μReactor). It was found that irradiation by the electron beam slows the growth kinetics of the W18O49 nanowhisker, markedly. Following this, an in situ TEM study led to some new fundamental understanding of the growth mode of the crystal shear planes in the W18O49 nanowhisker and the formation of a domain (bundle) structure. High-resolution scanning transmission electron microscopy analysis of a cross-sectioned W18O49 nanowhisker revealed the well-documented pentagonal Magnéli columns and hexagonal channel characteristics for this phase. Furthermore, a highly crystalline and oriented domain structure and previously unreported mixed structural arrangement of tungsten oxide polyhedrons were analyzed. The tungsten oxide phases found in the cross section of the W18O49 nanowhisker were analyzed by nanodiffraction and electron energy loss spectroscopy (EELS), which were discussed and compared in light of theoretical calculations based on the density functional theory method. Finally, the knowledge gained from the in situ SEM and TEM experiments was valorized in developing a multigram synthesis of W18O49/a-SiO2 urchin-like nanofibers in a flow reactor.

Role of deformation on the hydrogen trapping in the pearlitic steel

Improving hydrogen embrittlement resistance is a prerequisite for expanding the application of high-strength steels. A high-strength deformed pearlitic steel exhibits excellent hydrogen embrittlement resistance presumably because strong hydrogen trapping sites induced by deformation prevent hydrogen accumulation at potential crack initiation sites. This work reports the conclusive identification of the strong hydrogen trapping site in the deformed pearlitic steels. Thermal desorption spectroscopy showed a distinct hydrogen desorption peak at high temperature of ∼ 600 K solely in the deformed pearlite. Scanning transmission electron microscopy and atom probe tomography analyses revealed that the deformation resulted in strain localization at the ferrite/cementite interfaces, together with the formation of a large number of dislocations, leading to the strong segregation of deuterium, a natural isotope of hydrogen, at the interface. Therefore, hydrogen trapping in the deformed pearlitic steels is attributed to the strained ferrite/cementite interface.