Transmission Electron Microscopy-energy Dispersive Spectroscopy Research Articles

Direct insights into RbInSe2 formation at Cu(In,Ga)Se2 thin film surface with RbF postdeposition treatment

Scanning transmission electron microscopy-energy dispersive X-ray spectroscopy measurements performed on Cu(In,Ga)Se2 (CIGS) thin-film devices grown with RbF postdeposition treatment (RbF-PDT) revealed the formation of a RbInSe2 compound at the p-CIGS/n-CdS heterointerface. However, this type of Rb-compound formation was not observed with elemental In-free ternary CuGaSe2 (CGS) devices. The film surface of CIGS grown with RbF-PDT was found to be Ga-depleted; thus, the practical interface structure turned out to be CIGS/(CuInSe2, RbInSe2)/CdS. In contrast to the significant improvements observed in In-containing CIGS photovoltaic device performance with RbF-PDT, no significant improvements have been observed in In-free CGS devices thus far. These results suggest that the presence of elemental In plays a key role in obtaining beneficial alkali Rb effects for enhancing device performance as well as surface modification with RbF-PDT.

Characterization of films fabricated on AZ31 magnesium alloy by heat treatment and immersion methods

Thin films were fabricated on the surface of AZ31 magnesium alloy by heat treatment and subsequent immersion in deionized water or a NaOH solution. In this study, dense films were synthesized during the initial stage of immersion by increasing the (OH)− concentration at the interface of the high-temperature substrate and the solution. The surface of the magnesium substrates was covered by dense films aligned with the surface during the initial stages of immersion. The surface features of these films were different from those of the films formed simply by immersion in aqueous solutions. The cross-sectional results showed that the films formed in a NaOH solution with heat treatment were denser than those grown by DI water immersion with heat treatment. The X-ray photoelectron spectroscopy results revealed that the films fabricated by immersing the heat-treated substrates were mostly composed of MgO and Mg(OH)2 in both the outer and inner layers. Potentiodynamic polarization measurements showed that the films formed by the immersion of heat-treated substrates showed passive regions, and hence could act as passive layers.The morphology and structure of the films were observed by field-emission scanning electron microscopy and transmission electron microscopy. The compositions of the films were investigated using scanning transmission electron microscopy-energy dispersive spectroscopy and X-ray photoelectron spectroscopy. Potentiodynamic polarization measurements were conducted to investigate the corrosion behavior of the films.

Two selenium tolerant Lysinibacillus sp. strains are capable of reducing selenite to elemental Se efficiently under aerobic conditions.

Microbes play important roles in the transport and transformation of selenium (Se) in the environment, thereby influencing plant resistance to Se and Se accumulation in plant. The objectives are to characterize the bacteria with high Se tolerance and reduction capacity and explore the significance of microbial origins on their Se tolerance, reduction rate and efficiency. Two bacterial strains were isolated from a naturally occurred Se-rich soil at tea orchard in southern Anhui Province, China. The reduction kinetics of selenite was investigated and the reducing product was characterized using scanning electron microscopy and transmission electron microscopy-energy dispersive spectroscopy. The bacteria were identified as Lysinibacillus xylanilyticus and Lysinibacillus macrolides, respectively, using morphological, physiological and molecular methods. The results showed that the minimal inhibitory concentrations (MICs) of selenite for L. xylanilyticus and L. macrolides were 120 and 220 mmol/L, respectively, while MICs of selenate for L. xylanilyticus and L. macrolides were 800 and 700 mmol/L, respectively. Both strains aerobically reduced selenite with an initial concentration of 1.0 mmol/L to elemental Se nanoparticles (SeNPs) completely within 36 hr. Biogenic SeNPs were observed both inside and outside the cells suggesting either an intra- or extracellular reduction process. Our study implied that the microbes from Se-rich environments were more tolerant to Se and generally quicker and more efficient than those from Se-free habitats in the reduction of Se oxyanions. The bacterial strains with high Se reduction capacity and the biological synthesized SeNPs would have potential applications in agriculture, food, environment and medicine.

Study on the Aging Mechanism of Boron Potassium Nitrate (BKNO3) for Sustainable Efficiency in Pyrotechnic Mechanical Devices

The aging of propellants in PMDs is considered to be one of the primary factors affecting the performance of PMDs. Thus, studies on the aging mechanism of propellants, which have not yet been addressed extensively, pose a solution to securing the sustainable operation of PMDs. We characterized one of the most commonly used commercial propellants (boron potassium nitrate (BKNO3)) and investigated its aging mechanism rigorously. Based on thermal analyses, we demonstrate that the decomposition of laminac, a polymer binder, is the fastest spontaneous reaction. However, it will not self-initiate at a storage temperature as high as 120 °C. The effect of the humidity level was examined by characterizing BKNO3 samples prepared. The heat of reaction and the reaction rate decreased by 18% and 67% over 16 weeks of aging, respectively. This is attributed to the oxide shells on the surface of boron particles. The formation of oxide shells could be confirmed using X-ray photoelectron spectroscopy and transmission electron microscopy–energy dispersive spectroscopy. In conclusion, surface oxide formation with the aging of BKNO3 will decrease its propulsive efficiency; oxidation reduces the potential energy of the system and the resulting oxide decreases the reaction rate.

Ruthenium stabilized on transition metal-on-transition metal oxide nanoparticles for naphthalene hydrogenation

The multi-metallic nanocatalysts of ruthenium nanoclusters-on-transition metal/transition metal oxide nanoparticles (TM/TMO NPs) then supported on carbon (Ru/Ni/NiO/C or Ru/Co/Co3O4/C) were designed and synthesized. The Ni/NiO or Co/Co3O4 NPs strongly stabalized the ruthenium nanoclusters by the interfacial interaction among them. These catalysts exhibited high catalytic activity and 100% selectivity to decalin for naphthalene hydrogenation due to the synergy effect of multiple catalytic sites, where naphthalene was absorbed and activated at the TMO sites (NiO or Co3O4), H2 was activated at the Ru sites and it produced the activated H* species, H* was transferred to the surface of NiO or Co3O4 by the hydrogen spillover effect of TM (Ni or Co), reacting with the activated naphthalene and forming decalin. The nanostructures and synergetic effect of the Ru/Ni/NiO/C and Ru/Co/Co3O4/C catalysts were revealed by a series of techniques, such as high-resolution transmission electron microscope (HRTEM), temperature-programmed reduction (TPR), scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS) mapping, high-sensitivity low-energy ion scattering (HS-LEIS) and X-ray absorption spectroscopy (XAS). It is promising that the hydrogen storage can proceed at room temperature via catalyzing naphthalene hydrogenation over the Ru/Ni/NiO/C or Ru/Co/Co3O4/C catalyst.

Green biosynthesis, characterisation and antimicrobial activities of silver nanoparticles using fruit extract of Solanum viarum.

Green synthesis of nanoparticles is considered an efficient method when compared with chemical and physical methods because of its bulk production, eco-friendliness and low cost norms. The present study reports, for the first time, green synthesis of silver nanoparticles (AgNPs) at room temperature using Solanum viarum fruit extract. The visual appearance of brownish colour with an absorption band at 450 nm, as detected by ultraviolet-visible spectrophotometer analysis, confirmed the formation of AgNPs. X-ray diffraction confirmed the AgNPs to be crystalline with a face-centred lattice. The transmission electron microscopy-energy dispersive X-ray spectroscopy image showed the AgNPs are poly-dispersed and are mostly spherical and oval in shape with particle size ranging from 2 to 40 nm. Furthermore, Fourier transform-infrared spectra of the synthesised AgNPs confirmed the presence of phytoconstituents as a capping agent. The antimicrobial activity study showed that the AgNPs exhibited high microbial activity against Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus susp. aureus, Aspergillus niger, and Candida albicans. The highest antimicrobial activity of AgNPs synthesised by S. viarum fruit extract was observed in P. aeruginosa, S. aureus susp. aureus and C. albicans with zone of inhibition, 26.67 mm.

Detailed Investigation of Core–Shell Precipitates in a Cu-Containing High Entropy Alloy

Due to the competing influences of configurational entropy and enthalpy of mixing, in recent years, secondary (including intermetallic) phases have been reported in many high entropy alloy (HEA) systems. These secondary phases offer great potential in terms of strengthening the HEA beyond the solid solution strengthening effects, and as such are of great interest in regards to alloy design for engineering applications. The present research investigates novel nano-scale core–shell precipitates forming within the disordered bcc matrix phase of an Al2CrCuFeNi2 HEA, utilizing complementary high-resolution microscopy techniques of atom probe tomography (APT) and transmission electron microscopy (TEM). The size, morphology, and local chemistry of these core–shell precipitates was measured by APT, and the composition was further corroborated by high-resolution scanning transmission electron microscopy–energy dispersive spectroscopy in an aberration-corrected TEM. Furthermore, high-resolution TEM imaging of the core–shell structure indicates that the Cu-rich core exhibits a bcc crystal structure.

Accumulation and interparticle connections of triangular Ag-coated Au nanoprisms by oil-coating method for surface-enhanced Raman scattering applications

To examine the optical responses of surface-enhanced Raman scattering (SERS) for tuned plasmonic nanoparticles, triangular Ag-coated Au (Au@Ag) nanoprisms with different sizes were separately synthesized, which were well controlled in their size (edge-length) and localized surface plasmon resonance (LSPR) wavelength (69.0 ± 8.4 to 173.8 ± 25.6 nm in size and 662–943 nm in LSPR wavelength). The mechanism of Ag shell formation on the Au nanoprisms was also studied with scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS). The Au@Ag nanoprisms were immobilized by covering a colloidal solution containing the nanoprisms with silicone oil and evaporating the solvent in the oil (oil-coating method) so as to form a layer of accumulated plasmonic Au@Ag nanoprisms that had LSPR peak wavelengths tuned from 839 to 1182 nm. The accumulation conditions were analyzed by field-emission scanning electron microscopy (FE-SEM) and a Raman mapping technique. The Au@Ag nanoprisms under excitation at 632.8 nm exhibited higher SERS signals of rhodamine 6G, and SERS-mapped images of the novel immobilized films were obtained at different magnifications. It was concluded that accumulated Au@Ag nanoprisms undergoing tip-planar interconnections could produce enhanced local fields, resulting in higher SERS signals.

Effect of holding time and interlayer's thickness on the crack initiation and propagation and the dissolving behavior of the heat-treated facet WC grains

Post welding heat treatment was performed on dissimilar weldments composed of WC-Co to 316L stainless steel with 1-mm-, 1.5-mm-, and 2-mm-thick Invar interlayers by heating the samples to 1250°C for 2h, 8h, and 16h respectively. Cracks initiation and propagation were observed in all samples because of the stress relieving after heat treatment. The increase of the interlayer's thickness tends to partially inhibit the initiation and propagation of cracks. When the holding time is 2h, the sample fractured in the heat affected zone (HAZ). With the increase of holding time (8h, 16h), the samples tended to fracture in the fusion zone. The dissolving behavior of prismatic facets estimated by means of high-angle annular dark field (HAADF) microscopy indicated that the shape of WC grains changed to faceted WC grains during the heat treatment, which exhibited abnormal grain growth in the matrix composing of α-Co and γ-(Fe, Ni). In the fusion zone adjacent to the WC-Co, W-M-C carbides skeleton were formed with a character of continuous rods and isolated islands. The islands had lower tungsten and more binders than the rods. By using transmission electron microscopy - energy dispersive spectroscopy (TEM-EDS), it was found that WC grains and WC/Co/WC interface showed strong plastic deformation with obvious elemental diffusion. Moiré fringes inside the WC and in the matrix were confirmed.

Hardness of AISI type 410 martensitic steels after high temperature irradiation via nanoindentation

The hardness of irradiated AISI type 410 martensitic steel, which is utilized in structural and magnetic components of nuclear power plants, is investigated in this study. Proton irradiation of AISI type 410 martensitic steel samples was carried out by exposing the samples to 3 MeV protons up to a 1.0 × 1017 p/cm2 fluence level at a representative nuclear reactor coolant temperature of 350 °C. The assessment of deleterious effects of irradiation on the micro-structure and mechanical behavior of the AISI type 410 martensitic steel samples via transmission electron microscopy-energy dispersive spectroscopy and cross-sectional nano-indentation showed no significant variation in the microscopic or mechanical characteristics. These results ensure the integrity of the structural and magnetic components of nuclear reactors made of AISI type 410 martensitic steel under high-temperature irradiation damage levels up to approximately 5.2 × 10-3 dpa.

A whole pattern iterative refinement method for powder X-ray diffraction spectra of two-phase coherent alloys

An iterative refining method using FullProf software (Rietveld refinement) as a multi-input–output black-box with cyclic feedback is proposed in order to accurately measure the lattice misfit in two-phase coherent alloys. The method uses two X-ray diffraction spectra taken on the same powder sample. In addition, it requires the volumetric fraction of the phases and the size of the crystallite in the precipitated phase as derived from the measurements made by the transmission electron microscopy–energy dispersive spectroscopy technique. The measurement of the lattice misfit in a Fe2AlV-strengthened ferritic Fe76Al12V12 alloy is shown as an application of the method.

Fabrication, activity and mechanism studies of transition metal molybdate/molybdenum trioxide hybrids as novel CWAO catalysts

Abstract We report for the first time the synthesis of a series of novel hybrid catalysts consisting α-MoO3 and MMoO4 (M = Cr, Mn, Fe, Co, Ni, Cu, or Zn) and their significantly enhanced catalytic activities for the degradation of cationic dyes at room temperature and atmosphere pressure. All obtained hybrid materials were thoroughly characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy-energy dispersive spectroscopy, and X-ray photoelectron spectroscopy, etc. The influence of divalent cations, calcination temperature, testing temperature, volume of dye and different kinds of cationic dyes were systematically investigated. Among all hybrid catalysts, MnMoO4/α-MoO3 and NiMoO4/α-MoO3 resulted in much better performance than all the others. We also demonstrated that such high activity can be not attained with either pure transition metal molybdates, pure α-MoO3 or the physical mixture of these two bulks. And only the hybrid catalysts prepared in this work containing both metal molybdates and α-MoO3 can deliver high catalytic activity for the CWAO of dye. The reaction kinetics and degradation mechanism were also explored. Electron spin resonance analysis suggests that the co-existence of transition metal molybdates and α-MoO3 promotes the formation of· OH radicals, which are crucial for their excellent catalytic activity. The intermediates produced during the catalytic degradation process was monitored using electrospray ionization-mass spectrometry analysis, based on which the degradation pathway was also proposed.

Efficient and Environmentally Friendly Synthesis of AlFe-PILC-Supported MnCe Catalysts for Benzene Combustion.

An efficient and environmentally friendly synthesis of AlFe-pillared clay (AlFe-PILC)-supported MnCe catalysts was explored. Mixed AlFe pillaring agents were prepared by a one-step method using Locron L and ferric nitrate solutions at a high temperature and high pressure. Montmorillonite was treated with the AlFe pillaring agents to synthesize AlFe-PILC. MnOx and CeO2 with different Mn/Ce atomic ratios were loaded onto the AlFe-PILC support by an impregnation method. The catalysts were characterized using X-ray diffraction, N2 adsorption, and high-resolution transmission electron microscopy–energy dispersive spectrometry and were tested for the catalytic combustion of benzene and temperature-programmed surface reaction using a microreactor. Compared to conventional methods, this method is simpler and less costly and results in a larger specific surface area, pore volume, and basal spacing, with the ability to control the structure of the catalytic materials. MnCe(6:1)/AlFe-PILC has the highest catalytic activity and can completely degrade benzene (600 ppm in air) at 250 °C. The activity of the catalyst is stable, and no obvious deactivation is observed at 230 °C after 1000 continuous hours. The catalyst is resistant to water and Cl-poisoning. The amount of CeO2 added is critical to the dispersion of MnOx on the support and the creation of optimum number of oxygen vacancy defect sites for the benzene oxidation reaction. The AlFe-PILC-supported MnCe catalyst is a promising porous material; the support structure, proper dispersion of active species, and addition of Ce are essential for achieving complete degradation of organic toxic chemicals at relatively low temperatures.

The toxicity of silver to soil organisms exposed to silver nanoparticles and silver nitrate in biosolids-amended field soil.

The use of engineered silver nanoparticles (AgNPs) is widespread, with expected release to the terrestrial environment through the application of biosolids onto agricultural lands. The toxicity of AgNPs and silver nitrate (AgNO3 ; as ionic Ag+ ) to plant (Elymus lanceolatus and Trifolium pratense) and soil invertebrate (Eisenia andrei and Folsomia candida) species was assessed using Ag-amended biosolids applied to a natural sandy loam soil. Bioavailable Ag+ in soil samples was estimated using an ion-exchange technique applied to KNO3 soil extracts, whereas exposure to dispersible AgNPs was verified by single-particle inductively coupled plasma-mass spectrometry and transmission electron microscopy-energy dispersive X-ray spectroscopy analysis. Greater toxicity to plant growth and earthworm reproduction was observed in AgNP exposures relative to those of AgNO3 , whereas no difference in toxicity was observed for F. candida reproduction. Transformation products in the AgNP-biosolids exposures resulted in larger pools of extractable Ag+ than those from AgNO3 -biosolids exposures, at similar total Ag soil concentrations. The results of the present study reveal intrinsic differences in the behavior and bioavailability of the 2 different forms of Ag within the biosolids-soils pathway. The present study demonstrates how analytical methods that target biologically relevant fractions can be used to advance the understanding of AgNP behavior and toxicity in terrestrial environments. Environ Toxicol Chem 2017;36:2756-2765. © 2017 Crown in the Right of Canada. Published Wiley Periodicals Inc., on behalf of SETAC.

TEM EDS analysis of epitaxially-grown self-assembled indium islands

Epitaxially-grown self-assembled indium nanostructures, or islands, show promise as nanoantennas. The elemental composition and internal structure of indium islands grown on gallium arsenide are explored using Transmission Electron Microscopy (TEM) Energy Dispersive Spectroscopy (EDS). Several sizes of islands are examined, with larger islands exhibiting high (>94%) average indium purity and smaller islands containing inhomogeneous gallium and arsenic contamination. These results enable more accurate predictions of indium nanoantenna behavior as a function of growth parameters.

The microstructural evolution in high sodium epitaxial sodium potassium niobate films deposited by low-temperature hydro-thermal method

Sodium potassium niobate [(K x Na1−x )NbO3] films with high sodium composition (x = 0.06 and 0.24) were fabricated using a low-temperature (240 °C) hydro-thermal method on (001) niobium-doped strontium titanate (Nb-STO) substrate. The films were annealed subsequently at 600 °C. Thicknesses of the films were maintained in the range of ~800–1000 nm. Transmission electron microscopy-selected area electron diffraction studies revealed the appearance of super-spots, thereby confirming the tilting of the oxygen sub-lattice at both high Na compositions. The bright-field imaging and scanning transmission electron microscopy-energy dispersive spectroscopy elemental mapping revealed KNN film with K-rich interfacial regions and Na-rich top region of the film at both the high Na composition, whereas the potassium niobate (KNbO3, x = 1) film showed no such oxygen sub-lattice tilting, and a sharp substrate-film interface was observed. The observed tilting of oxygen sub-lattice is a direct consequence of the reduced structural stability in high Na compositions in the KNN solid solutions.

Macroparticles formation in cathodic arc deposition of nitride coatings from TiNb alloy cathodes

Reduction of macroparticles embedded within the cathodic arc deposited coatings is important for achieving high quality coatings with superior tribological properties, and it remains a major challenge in cathodic arc depositions. In the present study, the authors aim to understand the nature of macroparticles formed from TiNb alloy cathodes and the role of TiNb cathode nitridation in reducing the amount of generated macroparticles. The microstructure of the macroparticles was investigated using scanning transmission electron microscopy-energy dispersive spectroscopy, scanning electron microscopy, and x-ray diffraction techniques and revealed compositionally different macroparticles, such as macroparticles with a Nb-rich core, Ti-rich macroparticles, and macroparticles with a composition similar to that of the coatings. The examination of the macroparticles indicated the compositional segregation of niobium and titanium. With increasing N2 gas pressure during deposition, the macroparticles showed increased nitridation while the density of macroparticles within the coating was slightly diminished.

Shaped binderless ZSM-11 zeolite catalyst prepared via a dry-gel conversion method: Characterization and application for alkylation of benzene with dimethyl ether

Shaped binderless ZSM-11 zeolite catalysts were synthesized via a dry-gel conversion technique from 70ZSM-11/30SiO2mix extrudates. 1,6-hexanediamine combined with tetrabutylammonium bromide was proved to be the best structure directing agent for the synthesis of the binderless ZSM-11 catalyst, without adding other alkaline materials. The 70HZSM-11/30SiO2mix serials materials crystallized for different times were detected by X-ray diffraction (XRD), nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning transmission electron microscopy–energy dispersive spectroscopy (STEM–EDS) techniques, and so on. In order to investigate the possible crystallization mechanism, the textural and structural properties of 70HZSM-11/30SiO2mix serials samples were further characterized by N2 adsorption–desorption. Acid properties were determined by temperature-programed desorption of NH3 (NH3-TPD) and pyridine adsorption-infrared (Py-IR) measurements. In the alkylation of benzene with dimethyl ether, the serials catalysts exhibited different benzene conversions. 70HZSM-11/30SiO2mix showed the lowest benzene conversion while sample 70HZSM-11/30SiO2mix-6.5h synthesized only for 6.5h displayed a higher benzene conversion, even higher than the value over 70HZSM-11/30Al2O3mix. Extending the crystallization time, the obtained samples displayed the increased benzene conversion in general under the same reaction conditions. In the end, the relation of physicochemical properties with the reaction performance was investigated.

Degradation of oxygen reduction reaction kinetics in porous La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ cathodes due to aging-induced changes in surface chemistry

Abstract The modification of surface composition after long-term operation is one of the most reported degradation mechanisms of (La,Sr)(Co,Fe)O3-δ (LSCFO) cathodes for Solid Oxide Fuel Cells (SOFCs). Nevertheless, its effect on the oxygen reduction reaction kinetics of porous LSCFO cathodes has not been yet reliably established. In this work, La- and Sr-enrichment at the LSCFO surface of porous cathodes has been induced after 50 h aging at 800 °C under air. Such cation redistribution can extend up to ∼400 nm depth under the LSCFO surface as detected by high resolution Scanning Transmission Electron Microscopy-Energy Dispersive Spectroscopy maps acquired inside the cathode pores. The observed surface chemical changes hamper the oxygen surface exchange reaction at the LSCFO/gas interface. Accordingly, a suitable Electrochemical Impedance Spectroscopy analysis revealed that the oxygen ion conductivity remains practically unaltered during the aging treatment while the oxygen surface exchange resistance increases up to 1.8 times. As a result, the cathode impedance response deteriorates within the 10–0.1 Hz frequency range during the aging treatment, resulting in a total cathode area specific resistance increase of 150%. The methodology adopted has demonstrated to be very valuable for studying the degradation of SOFC cathodes produced by the modification of surface composition.

Synthesis of MnxGa1−xFe2O4 magnetic nanoparticles by thermal decomposition method for medical diagnosis applications

In this work, the synthesis of MnxGa1−xFe2O4 (x=0–1) nanosized particles by thermal decomposition method, using tetraethylene glycol (TEG) as a reaction medium, has been performed. The crystalline structure of the inverse spinel obtained in all the cases was identified by X-ray diffraction (XRD). Vibration sample magnetometry (VSM) was used to evaluate the magnetic properties of ferrites and to demonstrate their superparamagnetic behavior and the increase of magnetization values due to the Mn2+ ions incorporation into the FeGa2O4 structure. Transmission electron microscopy, energy dispersive spectroscopy (TEM-EDS) and X-ray photoelectron spectroscopy (XPS) were used to characterize the obtained magnetic nanoparticles (MNPs). These MNPs showed a near spherical morphology, an average particle size of 5.6±1.5nm and a TEG coating layer on their surface. In all the cases MNPs showed no response when submitted to an alternating magnetic field (AMF, 10.2kA/m, 354kHz) using magnetic induction tests. These results suggest that the synthesized nanoparticles can be potential candidates for their use in biomedical areas.