Transmission Electron Microscopy Energy-dispersive X-ray Spectroscopy Research Articles

Evaluation of extremely thin polycrystalline germanium films and their TFT performance fabricated at 400 °C by Cu-induced crystallization on a glass substrate

Germanium (Ge) has high mobility and is more suitable for low-temperature device processes than silicon (Si); thus, it has attracted attention as an upper-layer transistor for monolithic three-dimensional (M3D) integration. We evaluated in detail the crystalline quality of extremely thin polycrystalline-Ge (poly-Ge) thin films thinner than 15 nm fabricated by metal-induced crystallization using copper (Cu-MIC) at 400 °C using micro-Raman scattering, in-plane X-ray diffraction, transmission electron microscopy (TEM), TEM energy dispersive X-ray spectroscopy, and TEM electron diffraction. Additionally, the films were applied to p-ch double-gate (DG) poly-Ge thin-film transistors (TFTs), and their performance was evaluated. As a result, a high I on/I off ratio of 2.8 × 103 was realized by crystallization at 400 °C with a ratio equal to that of crystallization at 500 °C. This study demonstrated the feasibility of Cu-MIC DG poly-Ge TFTs for M3D applications.

Stabilization of γ-Fe2O3 nanoparticles to heat by doping Nb and its property studied by Mössbauer spectroscopy

Nb5+-doped γ-Fe2O3 was synthesized by sol–gel method followed by calcination at various temperatures from 200 to 700 °C, analyzed using Powder X-ray Diffraction (PXRD), Transmission Electron Microscopy (TEM), Energy Dispersive X-ray Spectroscopy (EDS) and Mössbauer Spectroscopy. PXRD results show the formation of γ-Fe2O3 at 300 °C and it begins to transform to α-Fe2O3 at 350 °C for pure and 2 at.% Nb-doped samples. As the Nb doping increases (≥3.8 at.%), the transformation was suppressed up to 600 °C. TEM EDS confirms the incorporation of Nb to γ-Fe2O3 lattice in 9.1 at.% Nb sample calcined at 500 °C. At elevated temperature of 700 °C, γ-Fe2O3 went through full transformation to α-Fe2O3 by expelling large amount of Nb to the surface forming FeNbO4. TEM EDS confirms the compositional change during this process with reduced Nb content in α-Fe2O3 and Nb-rich nanoparticle on the surface of α-Fe2O3. Superparamagnetic properties were observed for Mössbauer spectra when the Nb doping increased, which is caused by decreased particle size. The slight increase in internal magnetic field also indicated the transformation from γ-Fe2O3 to α-Fe2O3. High Nb doping with 20 and 40 at.% shows the formation of FeNbO4 at lower temperature where limited or almost no Nb substitution in α-Fe2O3 was detected by EDS.

A robust Ni/Au process and mechanism for p-type ohmic contact applied to GaN p-FETs

In this study, a new robust ohmic contact preparation process for GaN p-FETs application is developed on p-GaN/AlGaN/GaN, which excluded the commonly used descum step. A specific contact resistivity of approximately 2.0×10–3 Ω·cm2 is obtained based on Ni/Au metal stack. X-ray photoelectron spectroscopy (XPS) analysis revealed that the p-GaN surface underwent oxidation by O2 plasma in the descum step, forming Ga2O3 as a barrier layer between the metal and p-GaN. The resulting Ga2O3 could not be completely removed using a hydrochloric acid solution, resulting in a Schottky contact. Moreover, the Ni/Au ohmic contact mechanism was revealed for the first time by varying the O2 content in the annealing atmosphere. The X-ray transmission electron microscopy–energy-dispersive X-ray spectroscopy and XPS results proved that the Ni (III) oxide or Ni2O3 present at the metal/p-GaN interface and the Ga vacancies formed on the p-GaN surface played a crucial role in facilitating the formation of ohmic contacts.

Boron Nitride- and Carbon-Supported Iridium–Iron Catalysts for Synthesizing Mono-Alcohols from Biomass-Derived Vicinal Diols

Hydrogenolysis of 1,2-diols to primary and secondary alcohols was investigated over nonoxide-supported Ir–FeOx catalysts using 1,2-butanediol (1,2-BuD) as a model substrate. Boron nitride (BN) has been found as an effective support for 1,2-BuD hydrogenolysis to secondary alcohol (2-butanol (2-BuOH)), similar to rutile TiO2 in our previous report. The addition of Fe species (Fe/Ir = 0.25 (optimal ratio)) to Ir/BN greatly improved the catalytic activity (23 times; 2-BuOH selectivity: ∼70%; highest yield: 64%). Meanwhile, some other supports including carbon supports gave primary alcohol (1-butanol (1-BuOH)) as the main product, which was less affected by the Fe addition or types of carbon supports. Activated carbon (C) provided the highest activity among the screened carbon-type supports. The 74% yield of 1-BuOH was obtained over Ir–FeOx/C. The selectivity pattern given by Ir–FeOx/BN much depends on its calcination temperature: a low calcination temperature (<673 K) led to the change in the selectivity pattern (∼70% of 2-BuOH to >70% of 1-BuOH). Ir–FeOx/BN was reusable for the 2-BuOH synthesis at least 4 times when the suitable calcination treatment (573 K, 1 h) was adopted for catalyst regeneration. In contrast, the addition of acid was necessary for regenerating the Ir–FeOx/C catalyst. Secondary alcohol with high selectivity (>60%) was achieved in related alcohol hydrogenolysis over Ir–FeOx/BN (Ir = 5 wt %, Fe/Ir = 0.25) such as 1,2-propanediol to 2-propanol, glycerol to 1,2-propanediol, and 1,3-butanediol to 2-BuOH. 2,3-Butanediol was formed in 32% yield from erythritol. Over Ir–FeOx/C or Ir/C, good yields of 1-alcohols were formed from 1,2-alkanediols, while reversible cyclization occurred for erythritol. Characterizations with X-ray diffraction, transmission electron microscopy–energy-dispersive X-ray spectroscopy, temperature-programmed reduction with H2, CO adsorption, diffuse reflectance infrared Fourier transform spectroscopy of adsorbed CO, X-ray absorption near edge structure, and extended X-ray absorption fine structure suggested that Ir–FeOx/C (Ir = 5 wt %, Fe/Ir = 0.25) consists of Ir particles (about 2 nm), highly distributed and isolated FeOx (valence: ∼2+), and residual acid. In Ir–FeOx/BN (Ir = 5 wt %, Fe/Ir = 0.25), Ir–Fe alloy (Fe0/(Fe0 + Ir0) = 20%) with a two-dimensional nanodendrite structure was formed. The production of primary alcohol over C-supported catalysts is via the route of dehydration + hydrogenation, where the residual acid catalyzes dehydration as the rate-determining step. The high selectivity to secondary alcohol over Ir–FeOx/BN was derived from two aspects: removal of acid (HCl) by calcination and generation of the active Ir–Fe alloy phase in the formation of secondary alcohol.

In situ annealing studies on the microstructural evolution of a macro defect free electroformed nanocrystalline Ni-Co sheet metal and its relation to tensile properties

The effect of annealing at temperatures between 200 – 400 °C on the microstructural evolution and tensile properties of a recently developed macro defect free electroformed nanocrystalline Ni-32at%Co free-standing sheet metal was investigated. The tensile strength of the materials exhibited an extrinsic Hall-Petch (HP) to inverse Hall-Petch (IHP) transition due to grain growth. In situ transmission electron microscopy (TEM) annealing revealed for the first time that at lower annealing temperatures, in addition to reordering of atoms at grain boundaries, grain rotation and grain recovery were also found to be mechanisms for grain boundary relaxation (GBR). Combined, these mechanisms contribute to the increase in ultimate tensile strength (UTS) observed in the IHP regime of the Ni-32at%Co alloy. TEM energy dispersive X-ray spectroscopy (EDX) and in situ synchrotron X-ray diffraction (XRD) annealing analyses showed that the drop in UTS and ductility in the HP regime after annealing at higher temperatures was associated with the onset of abnormal grain growth and sulfur impurity segregation to random high angle boundaries. Atom probe tomography (APT) further showed that there is no sulfur impurity segregation in the electroformed material before annealing. Increasing in annealing temperature led therefore to a transition from ductile to brittle fracture manifested as a change in dimple to mixed and eventually to faceted brittle fracture surfaces at 400 °C.

Compositional tuning of gas-phase synthesized Pd-Cu nanoparticles.

Bimetallic nanoparticles have gained significant attention in catalysis as potential alternatives to expensive catalysts based on noble metals. In this study, we investigate the compositional tuning of Pd-Cu bimetallic nanoparticles using a physical synthesis method called spark ablation. By utilizing pure and alloyed electrodes in different configurations, we demonstrate the ability to tailor the chemical composition of nanoparticles within the range of approximately 80 : 20 at% to 40 : 60 at% (Pd : Cu), measured using X-ray fluorescence (XRF) and transmission electron microscopy energy dispersive X-ray spectroscopy (TEM-EDXS). Time-resolved XRF measurements revealed a shift in composition throughout the ablation process, potentially influenced by material transfer between electrodes. Powder X-ray diffraction confirmed the predominantly fcc phase of the nanoparticles while high-resolution TEM and scanning TEM-EDXS confirmed the mixing of Pd and Cu within individual nanoparticles. X-ray photoelectron and absorption spectroscopy were used to analyze the outermost atomic layers of the nanoparticles, which is highly important for catalytic applications. Such comprehensive analyses offer insights into the formation and structure of bimetallic nanoparticles and pave the way for the development of efficient and affordable catalysts for various applications.

Gadolinium enrichment in association with the magnetic fraction of fly ash: Real or an illusion?

Gadolinium, and possibly praseodymium, are relatively enriched in the magnetic fractions of Class F fly ashes from Central Appalachian coal sources. Although the enrichment is evident in the inductively coupled plasma–atomic emission spectroscopy (ICP-AES) determinations of the rare earth content, transmission electron microscopy–energy dispersive x-ray spectroscopy (TEM-EDS) examination of the fly ash fails to show the sites of the Gd or Pr. This apparent lack of correlation could be due to the inability of the EDS to detect low concentrations of the rare earth elements definitively; interferences in the analytics, leading to false positives in the chemical analysis; or the overlap of the energies of Gd and/or Pr with more abundant elements, leading to inaccurate negative results.

Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) for Analysis of Surface and Interface Chemistry of Porous Transport Layers

As the United States energy infrastructure moves towards the integration of hydrogen energy, the reliable production of hydrogen through water electrolyzers is imperative. In proton exchange membrane water electrolyzes (PEMWE’s), the porous transport layer (PTL) plays an important role. When choosing PTL material, one should consider corrosion resistance, electrical conductivity, and ability to support the structure of the electrochemical cell. Due to these requirements, titanium is the current state-of-the-art anode PTL material. However, titanium quickly forms a layer of titanium oxide which significantly decreases conductivity of the PTL and respectively decreases the overall efficiency of the PEMWE system. Coatings are commonly applied to the PTL to combat this complication, but the use of noble metals leads to cost concerns. Additionally, the degradation of coated PTLs is not yet well known.Advanced physicochemical characterization of PTLs at various stages of fabrication and testing is vital to understand their properties and the impact on electrochemical performance in order to improve durability and meet cost targets. Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) is currently used to cross section areas of the PTL for subsequent analysis with Scanning Transmission Electron MicroscopyEnergy-dispersive X-ray Spectroscopy (STEM-EDS) analysis to visualize the elemental information of the PTL materials and PTL coatings, specifically looking at detrimental oxide layer formation. Unfortunately, this approach is time-consuming and difficult, motivating the development of alternative approaches that allow the characterization of wide sample sets more efficiently. Additionally, STEM-EDS analysis only provides elemental information, so if several oxide layers preside, it can be difficult to differentiate them. Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) depth profiling is a very powerful technique that has been commonly used to characterize thin films and buried interfaces. Unlike the FIB-SEM and STEM-EDS combination, ToF-SIMS can be performed relatively quickly in several areas of the PTL, provides chemical information, and is sensitive to trace elements. An added advantage of ToF-SIMS is ability to do 2D and 3D chemical analysis on different scales. This enables visualization of elemental and chemical distribution on both larger scale (70x70 um) areas, and smaller areas (20x10 um) which provides more detailed surface and interface information. This allows for detailed tracking of all major constituents of the PTL and coating. It also allows to follow changes in oxide layers upon fabrication and after electrochemical testing, as well as track homogeneity of the surface and oxide layer interfaces throughout different parts of the PTL. This presentation will demonstrate capabilities of this technique for characterization of PTLs, along with progress and potential challenges. ToF-SIMs results will be compared to TEM analysis of cross-sections obtained with FIB-SEM. This study will highlight similarities and differences between the techniques, technique optimization for these morphologically challenging samples, and paths for future investigation moving forward.

Effect of TiO2-NPs on microbial-induced calcite carbonate precipitation

As a dust suppression method, microbial-induced calcium carbonate precipitation technology based on urease-producing bacteria has been widely used on roads; however, due to their low CaCO3 yield, microbial dust suppressants are not used in mining areas. To further improve the dust suppression effect of microbial dust suppressants, a TiO2-NPs/microbial dust suppressant was developed by adding TiO2-NPs to the microbial dust suppressant. The results showed TiO2-NPs improved the bacteria growth and the urease activity. The best formula of microbial dust suppressant was determined to be mineralized bacteria liquid (OD600 = 1.7) and TiO2-NPs 0.06 g/L. The wind erosion resistance tests showed that the dust suppression effect of the TiO2-NPs/microbial dust suppressant was better than that of the group without TiO2-NPs. The formation of CaCO3 was verified by Fourier-transform infrared spectrometry (FTIR), Scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS) and Transmission electron microscopy-energy-dispersive X-ray spectroscopy (TEM-EDS). X-ray diffraction (XRD) results showed that the crystal forms of the produced CaCO3 were calcite and vaterite. These results indicated that TiO2-NPs improved the dust inhibition effect of microbial dust suppressants.

Fractionation of natural algal organic matter and its preservation on the surfaces of clay minerals

The sequestration of algal organic matter (AOM) in clays constitute important carbon sinks in lake sediments. The composition of AOM was proven recently to critically influence its preservation in sediments. Yet it remains unclear which AOM components and types of clay minerals contribute to AOM burial in lake sediments. Here we investigated the AOM fractionation in kaolinite and illite via their adsorption, to ascertain the distribution of AOM components on these clay surfaces. The results showed that the AOM adsorbed quantity was 2-fold higher for illite than kaolinite. The adsorption isotherm data of illite and kaolinite were well fitted by a Freundlich model. The three-dimensional excitation emission matrix fluorescence spectroscopy (3D EEM) with parallel factor analysis (PARAFAC) modeling identified the AOM component under fractionation. The AOM solution mainly consisted of humic acid-like, tyrosine-like, and tryptophan-like components. Notably, large amounts of the hydrophilic tyrosine-like components were adsorbed onto the surface of both kaolinite and illite, whereas the hydrophobic tryptophan-like components were seldom adsorbed onto neither of the clay materials, while humic acid-like components were only adsorbed onto illite. Therefore, illite is more suitable for the preservation of AOM. Both transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDS) and the X-ray photoelectron spectroscopy (XPS) analysis further confirmed the high adsorption of AOM on the surface of illite; i.e., the molar content of carbon in AOM adsorbed to illite was 22.04%, almost a double of that adsorbed to kaolinite (11.59%). Overall, our results demonstrate the selective preservation of AOM on clay surfaces and highlight the role of clay minerals as sequesters of organic matter in eutrophic lakes.

Reexamination of the structure of opal-A: A combined study of synchrotron X-ray diffraction and pair distribution function analysis

Abstract The structure of opal-A was not fully understood due to its poorly crystalline nature. To better understand its structural characteristics, we have analyzed opal-AN (amorphous-network) and opal-AG (amorphous-gel) using synchrotron X-ray diffraction (XRD), pair-distribution function (PDF) analysis, and transmission electron microscopy (TEM). Opal-AN mainly exists as an aggregation of different sizes of nanospheres (&amp;lt;5 nm) generating banded features, whereas opal-AG displays close-packed silica nanospheres with a diameter of ~400 nm. TEM energy-dispersive X-ray spectroscopy (EDS) indicates that Na, Al, K, and Ca are present as trace elements in opal-AN and opal-AG. XRD patterns of both samples show one prominent peak at ~4.0 Å, together with broad peaks at ~2.0, ~1.45, and ~1.2 Å. Previous studies only identified the ~4.0 Å diffraction peak for the definition of opal-A. Hence, opal-A needs to be redefined by taking into account the newly observed three broad peaks. PDF patterns of opal-AN and opal-AG reveal short-range atomic pairs (&amp;lt;15 Å) with almost identical profiles. Both phases exhibit Si-O correlation at 1.61 Å and O-O correlation at 2.64 Å in their [SiO4] tetrahedra. The currently accepted opal structure is disordered intergrowths of cristobalite- and tridymite-like domains consisting of six-membered rings of [SiO4] tetrahedra. Our PDF analyses have identified additional, coesite-like nanodomains comprising four-membered [SiO4] rings. Moreover, we have identified eight-membered rings that can be generated by twinning and stacking faults from six-membered rings. The coesite nanodomains in opal-A may be a precursor for coesite micro-crystals formed by the impact of supersonic micro-projectiles at low pressures. More broadly, our study has also demonstrated that the combined approach of synchrotron XRD/PDF with TEM is a powerful approach to determine the structures of poorly crystallized minerals.

Repeat and single dose administration of gadodiamide to rats to investigate concentration and location of gadolinium and the cell ultrastructure

Gadolinium based contrast agents (GBCA) are used to image patients using magnetic resonance (MR) imaging. In recent years, there has been controversy around gadolinium retention after GBCA administration. We sought to evaluate the potential toxicity of gadolinium in the rat brain up to 1-year after repeated gadodiamide dosing and tissue retention kinetics after a single administration. Histopathological and ultrastructural transmission electron microscopy (TEM) analysis revealed no findings in rats administered a cumulative dose of 12 mmol/kg. TEM-energy dispersive X-ray spectroscopy (TEM-EDS) localization of gadolinium in the deep cerebellar nuclei showed ~ 100 nm electron-dense foci in the basal lamina of the vasculature. Laser ablation-ICP-MS (LA-ICP-MS) showed diffuse gadolinium throughout the brain but concentrated in perivascular foci of the DCN and globus pallidus with no observable tissue injury or ultrastructural changes. A single dose of gadodiamide (0.6 mmol/kg) resulted in rapid cerebrospinal fluid (CSF) and blood clearance. Twenty-weeks post administration gadolinium concentrations in brain regions was reduced by 16–72-fold and in the kidney (210-fold), testes (194-fold) skin (44-fold), liver (42-fold), femur (6-fold) and lung (64-fold). Our findings suggest that gadolinium does not lead to histopathological or ultrastructural changes in the brain and demonstrate in detail the kinetics of a human equivalent dose over time in a pre-clinical model.

Subcellular dynamics studies of iron reveal how tissue-specific distribution patterns are established in developing wheat grains.

Understanding the mechanisms of iron trafficking in plants is key to enhancing the nutritional quality of crops. Because it is difficult to image iron in transit, we currently have an incomplete picture of the route(s) of iron translocation in developing seeds and how the tissue-specific distribution is established. We have used a novel approach, combining iron-57 (57 Fe) isotope labelling and nanoscale secondary ion mass spectrometry (NanoSIMS), to visualize iron translocation between tissues and within cells in immature wheat grain, Triticum aestivum. This enabled us to track the main route of iron transport from maternal tissues to the embryo through the different cell types. Further evidence for this route was provided by genetically diverting iron into storage vacuoles, with confirmation provided by histological staining and transmission electron microscopy energy dispersive X-ray spectroscopy (TEM-EDS). Almost all iron in both control and transgenic grains was found in intracellular bodies, indicating symplastic rather than apoplastic transport. Furthermore, a new type of iron body, highly enriched in 57 Fe, was observed in aleurone cells and may represent iron being delivered to phytate globoids. Correlation of the 57 Fe enrichment profiles obtained by NanoSIMS with tissue-specific gene expression provides an updated model of iron homeostasis in cereal grains with relevance for future biofortification strategies.

Characterizing electrical breakdowns upon reoxidation atmosphere for reliable multilayer ceramic capacitors

Electrical breakdowns of multilayer ceramic capacitors (MLCCs) manifest an increase in leakage current and are characterized as a function of atmospheric reoxidation. The atmospheric reoxidation is controlled with respect to the theoretical oxygen partial pressure for the oxidation of Ni internal electrodes. The breakdowns are characterized by a Maxwell–Wagner polarization technique, which dominantly exhibits space-charge-limited and Poole–Frenkel currents for all measured samples. The threshold voltage for the transition between these two conduction modes is suggested as an index for the robustness of the grain boundary resistance of BaTiO3; therefore, the breakdown voltage. The reoxidation atmosphere, which prevents the Ni oxidation, increases the threshold voltage, dramatically enhancing the breakdown voltage and insulation resistance. Impedance spectroscopy and scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy reveal that the cation distribution throughout BaTiO3 grains and grain boundaries changes during the reoxidation, including Ni cations from the internal electrodes, which affects the grain boundary resistance and determines the breakdown voltage of MLCCs with Ni internal electrodes. These observations emphasize that the reoxidation should be concurrently optimized in terms of the cation redistribution and elimination of oxygen vacancies.

Physicochemical characterization of direct injection Engines's soot using TEM, EDS, X-ray diffraction and TGA

The physical characteristics and elemental composition of particulate matters (PMs) from gasoline direct injection spark ignition (GDI-SI) engines were successfully investigated using transmission electron microscopy - energy dispersive X-ray spectroscopy (TEM-EDS). Thermogravimetric analysis (TGA) was used to analyze the PMs oxidation. The morphology of agglomerated GDI-PMs is not significantly different from the diesel direct injection compression ignition (DDI-CI) engine's PMs. The spherical single primary nanoparticles of the engine's soot composed of curve line carbon crystallites. The average diameter size of the single primary nanoparticles of GDI, DDI, and carbon black are approximately 24 nm, 26 nm, and 31 nm, while the inter-planar spacing is about 0.364 nm, 0.358 nm, and 0.356 nm, respectively. The total fringe lengths of GDI, DDI, and carbon black are approximately 154 nm, 159 nm, and 163 nm measured from the areas of 10 nm × 10 nm inner core regions of primary nanoparticles, and are 180 nm, 195 nm, and 228 nm from the outer shell regions, respectively. The total fringe lengths of inner core are shorter than the outer shell. Besides, the engine's PMs contains both crystalline and amorphous carbon structure using XRD analysis. The GDI-PMs had the least crystalline structure compared to the DDI-PMs and carbon black due to the higher percentage of amorphous fraction. TGA analysis showed that the GDI-PMs oxidation was faster than the DDI-PMs and CB-N330 oxidation because of the primary particle size, the fringe length, and the crystal size which have an impact on oxidation kinetics of particulate matters.

Clustering of oxygen point defects in transition metal nitrides

Point defects create exotic properties in materials such as defect-induced luminescence in wide-bandgap semiconductors, magnetism in nonmagnetic materials, single-photon emission from semiconductors, etc. In this article, oxygen defect formation in metallic TiN and semiconducting rock salt-(Al,Sc)N is investigated with a combination of first-principles density functional theory, synchrotron-based x-ray absorption spectroscopy (XAS) analysis, and scanning transmission electron microscopy–energy-dispersive x-ray spectroscopy mapping. Modeling results show that oxygen in TiN and rock salt-(Al,Sc)N prefers to be in the defect complex of substitutional and interstitial oxygen (nON + Oi) types. While in TiN, the preferential interstitial sites of oxygen in ON + Oi are at the tetrahedral site, in rock salt-(Al,Sc)N, a split interstitial site along the [111] direction was found to be energetically preferable. Simulations performed as a function of the oxygen partial pressure show that under experimental growth conditions, four oxygen atoms at the substitutional sites of nitrogen (4ON), along with four Ti atoms, decorate around an interstitial oxygen atom at the tetrahedral site (Oi) in the energetically favored configuration. However, in rock salt-(Al,Sc)N, n in nON + Oi was found to vary from two to four depending on the oxygen partial pressure. Theoretical predictions agree well with the experimentally obtained XAS results. These results are not only important for a fundamental understanding of oxygen impurity defect behavior in rock salt nitride materials but will also help in the development of epitaxial metal/semiconductor superlattices with efficient thermionic properties.

Metallization of Al2O3 ceramic with Mg by friction stir spot welding

The surfaces of Al2O3 ceramic plates were metallized with by a friction stir spot welding method. Tensile tests revealed that the adhesive strength between the Mg film and Al2O3 ceramic plate was 23.3 MPa. To investigate the origin of this strong adhesion, the interface structure was examined by X-ray diffraction, scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy, and transmission electron microscopy. The results indicated the formation of a microcrystalline MgO layer at the interface. Furthermore, the surfaces of two metallized Al2O3 ceramic plates separated by Ni foil were bonded together by hot pressing at 1100 °C for 180 min under vacuum. The resulting cross tensile strength of the bonding was 2.1 MPa, indicating strong adhesion between the Al2O3 ceramic plates.

Microstructures analysis and quantitative strengthening evaluation of powder metallurgy Ti–Fe binary extruded alloys with (α+β)-dual-phase

Abstract In this study, Fe, one of the inexpensive β-phase stabilizers, was employed to fabricate Ti alloys by the powder metallurgy route. The formation mechanism of unique microstructures and texture of the extruded Ti–Fe alloy was elucidated through scanning electron microscopy-electron backscatter diffraction (SEM-EBSD) and transmission electron microscopy-energy-dispersive X-ray spectroscopy (TEM-EDS). For the Ti–Fe alloys consolidated from the pre-mixed pure Ti powder and Fe particles by spark plasma sintering and following hot extrusion, the additive Fe atoms existed as solid solution atoms in β-Ti phase. The increment in the Fe content was effective in increasing the β-Ti phase volume fraction and refining the α-Ti grains. The mean α-Ti grain size of Ti-4 wt.% Fe alloy was 1.27 μm, which was about ten times less than that of the pure Ti material (12.42 μm). The α and β phases of the extruded Ti-1–4 wt.% Fe material were aligned in parallel to the extrusion direction, and they suppressed the grain growth of each other. Although yield stress (YS) and tensile strength (TS) remarkably increased to 1093 MPa and 1183 MPa, respectively, with an increase in the Fe content, a large elongation of 28–38% was obtained in the extruded Ti–Fe alloys. These tensile properties were favorable compared to the commercial Ti-6 wt.% Al-4 wt.% V alloy. The dominant strengthening factors for the Ti–Fe alloys were α-Ti grain refinement and β-Ti hard phase dispersion. In the case of 4 wt% Fe addition, 50% of the YS increment was due to the latter strengthening mechanism.

TEM and STEM-EDS evaluation of metal nanoparticle encapsulation in GroEL/GroES complexes according to the reaction mechanism of chaperonin

Abstract Escherichia coli chaperonin GroEL, which is a large cylindrical protein complex comprising two heptameric rings with cavities of 4.5 nm each in the center, assists in intracellular protein folding with the aid of GroES and adenosine triphosphate (ATP). Here, we investigated the possibility that GroEL can also encapsulate metal nanoparticles (NPs) up to ∼5 nm in diameter into the cavities with the aid of GroES and ATP. The slow ATP-hydrolyzing GroELD52A/D398A mutant, which forms extremely stable complexes with GroES (half-time of ∼6 days), made it possible to analyze GroEL/GroES complexes containing metal NPs. Scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy analysis proved distinctly that FePt NPs and Au NPs were encapsulated in the GroEL/GroES complexes. Dynamic light scattering measurements showed that the NPs in the GroEL/GroES complex were able to maintain their dispersibility in solution. We previously described that the incubation of GroEL and GroES in the presence of ATP·BeFx and adenosine diphosphate·BeFx resulted in the formation of symmetric football-shaped and asymmetric bullet-shaped complexes, respectively. Based on this knowledge, we successfully constructed the football-shaped complex in which two compartments were occupied by Pt or Au NPs (first compartment) and FePt NPs (second compartment). This study showed that metal NPs were sequentially encapsulated according to the GroEL reaction in a step-by-step manner. In light of these results, chaperonin can be used as a tool for handling nanomaterials.

Individual tubular J-aggregates stabilized and stiffened by silica encapsulation

Amphiphilic cyanine dyes in aqueous solution self-assemble into J-aggregates with diverse structures. In particular, the dye 3,3′-bis(3-sulfopropyl)-5,5′,6,6′-tetrachloro-1,1′-dioctylbenzimida-carbo-cyanine (C8S3) forms micrometer long double walled tubular J-aggregates with a uniform outer diameter of 13 ± 0.5 nm. Interestingly, these J-aggregates exhibit strong exciton delocalization and migration, similar to natural light harvesting systems. However, their structural integrity and hence their optical properties are very sensitive to their chemical environment as well as to mechanical deformation, rendering detailed studies on individual tubular J-aggregates difficult. We addressed this issue and examined a previously published route for their chemical and mechanical stabilization by in situ synthesis of a silica coating that leaves their absorbance and emission unaltered in solution. Here, we demonstrate that the silica shell with a thickness of a few nanometers is able to stabilize the tubular J-aggregates of C8S3 against changes of pH of solutions down to values where pure aggregates are oxidized, against drying under ambient conditions, and even against the vacuum conditions within an electron microscope. Dried silica–covered aggregates are brittle, as demonstrated by manipulation with a scanning force microscope on a surface. Transmission electron microscope images confirm that the thickness of the coatings is homogeneous and uniform with a thickness of less than 5 nm; scanning TEM energy dispersive X-ray spectroscopy confirms the chemical composition of the shell as SiO2; and electron energy loss spectra could be recorded across a single freely suspended aggregate. Such a silica shell may not only serve for stabilization but also could be the base for further functionalization of the aggregates by either chemical attachment of other units on top of the shell or by inclusion during the synthesis.