Microscopy Transmission Electron Research Articles

Development of Nanoscale Thermocouple Probes for Local Thermal Measurements

We developed thermocouple probes consisting of constantan and chromel segments with nanoscale sharpness. The ends of wires made of these alloys were polished utilizing a single step drop-off electrochemical procedure in a H3PO4 solution. The macroscopic shapes of the etched wires were designed to detect ultra-small heat inputs with high sensitivity after assembling a thermocouple. After electrochemical treatment, ultimately smooth, mirror-polished wire surfaces were observed. The etched wires were then assembled in a transmission electron microscope (TEM) to create a miniature thermocouple by using which we successfully detected a small temperature increase induced by focused TEM electron beam irradiation. Judging from high- resolution TEM imaging, a thermocouple with the tip-end of only ~5 nm in diameter was fabricated.

Synthesis and Catalytic Activities of Metal Shells (Monolayer, Bilayer, and Alloy Layer)-Coated Gold Octahedra toward Catalytic Reduction of Nitroaromatics

Different types of metal shells such as monolayer, bilayer, and alloy layer of gold (Au) and/or silver (Ag) on gold octahedra (AuOh) nanoparticles were synthesized using N-[3-(trimethoxysilyl)propyl]diethylenetriamine (TPDT) without employing any external reducing agents. TPDT, an alternative to sodium borohydride, was used to prepare 15 different core–shell metal nanostructures. The direct colloidal synthesis and stabilization of silver octahedra nanoparticles is still a challenging task. The proposed methodology is an alternative synthetic route for Ag or Au nanoshell coated onto the AuOh core. UV–vis absorption spectroscopy, high-resolution electron transmission microscopy analyses with selected area electron diffraction, energy-dispersive X-ray spectroscopy, inductively coupled plasma mass spectrometry, and X-ray diffraction techniques were used to characterize the prepared core–shell octahedra nanostructures. High-angle annular dark field scanning transmission electron microscopy–energy-dispersive X-...

Syntheses, Crystal Structures, and Spectroscopic Studies of Uranyl Oxide Hydrate Phases with La(III)/Nd(III) Ions.

We have synthesized two uranyl oxide hydrate (UOH) phases incorporating La(III) or Nd(III) ions under hydrothermal conditions. Investigations with scanning electron microscopy and transmission electron microscopy (TEM) revealed thin-plate morphologies with a U-to-Ln atomic ratio of 2:1 (Ln = La or Nd), while single-crystal X-ray diffraction and TEM electron diffraction studies confirmed that both UOH phases crystallized in the trigonal P31m space group with uranyl oxide layered structures incorporating La(III)/Nd(III) ions as interlayer species. Vibrational spectroscopic studies revealed typical vibrational modes for U ions, with the derived U═O bond lengths being comparable to the values reported on other UOH phases. Bond-valence-sum calculations suggest hexavalent uranium in the uranyl form, which was confirmed by the results of diffuse-reflectance and X-ray absorption near-edge structure spectroscopies. This work reports the first single-crystal structural investigation of UOH phases with Ln ions, which has significant implications in the weathering products of uraninite mineral in nature as well as the alteration products of spent nuclear fuels during interim storage and safe disposal over geological timespans.

Síntesis verde de nanopartículas de plata usando el extracto acuoso de las hojas de ajo (Allium sativum)

Se han descrito muchos estudios de biosíntesis de nanopartículas de plata usando el extracto del bulbo de ajo (Allium sativum) como agente reductor. Sin embargo, el uso de sus hojas es poco conocido, por considerarse un producto de desecho. En este estudio, se comparó el tamaño de nanopartículas de plata obtenidas con el extracto acuoso de las hojas de ajo usando dos técnicas diferentes de calentamiento: placa y por microondas. Las nanopartículas obtenidas se caracterizaron por espectrofotometría UV-Visible, microscopía de transmisión electrónica (TEM, por sus siglas en inglés), dispersión dinámica de luz (DLS, por sus siglas en inglés) y difracción de rayos X (XRD, por sus siglas en inglés). Como resultado se obtuvieron nanopartículas con un tamaño promedio de 15,4±7,9 y 9,9±10,5 nm empleando las dos técnicas respectivamente. De acuerdo al análisis estadístico realizado, se demostró que existen diferencias significativas en relación al tamaño de nanopartícula obtenido. Se concluye que el extracto acuoso de las hojas de la planta de ajo, es un agente reductor adecuado para la síntesis de nanopartículas de plata, y que la técnica de microondas es más efectiva por la rapidez y tamaño de nanopartículas obtenidas.

Activated carbon impregnation with ag and cu composed nanoparticles for escherichia coli contaminated water treatment

This study aimed to produce modified granular activated carbon (GAC) by low concentrations of silver (Ag) and/or copper (Cu) nanoparticles with antibacterial capacity for application in water purification. Modified porous materials were produced from the vacuum impregnation method, at the concentrations (mass of metal/mass of activated carbon) of Ag 8 x 10−4 g/g (Ag 0.08 %), Cu 1 x 10−2 g/g (Cu 1 %), and Ag 8 x 10−4 g/g + Cu 1 x 10−2 g/g (Ag 0.08 % Cu 1 %). The reduction of the metal salts in NPs of Ag and Cu in their metallic forms or oxides was carried out by the thermal decomposition method. The characterization of the produced porous material was performed by x‐ray diffraction, programmed temperature reduction, scanning electron microscopy, x‐ray dispersive energy spectroscopy, electron transmission microscopy, and specific surface area measurements: Brunauer, Emmet, and Teller; micropore area (t method); pore size distribution (DA method); and volume and diameter of micropores (HK method) and mesopores (BJH method). In the structure of the material produced, Ag and Cu metal compounds and AgO and CuO oxides were identified, with average crystallite sizes of < 60 nm. The efficiency of the inactivation of Escherichia coli was more significant in the GAC modified with the combination of NPs (GAC/NP‐AgCu) (6.4 log 10 units), evidencing the synergistic effect of the metals when compared to GAC/NP‐Ag (0.56 log10 units) and GAC/NP‐Cu (1.31 log10 units) modified porous material. Thus, these antibacterial materials can be used for application in water purification, improving the bacteriological quality of water intended for human consumption, noting that the low concentration of metals used can provide exceptional process efficiency.

In Situ Transmission Electron Microscopy for Energy Materials and Devices.

Energy devices such as rechargeable batteries, fuel cells, and solar cells are central to powering a renewable, mobile, and electrified future. To advance these devices requires a fundamental understanding of the complex chemical reactions, material transformations, and charge flow that are associated with energy conversion processes. Analytical in situ transmission electron microscopy (TEM) offers a powerful tool for directly visualizing these complex processes at the atomic scale in real time and in operando. Recent advancements in energy materials and devices that have been enabled by in situ TEM are reviewed. First, the evolutionary development of TEM nanocells from the open-cell configuration to the closed-cell, and finally the full-cell, is reviewed. Next, in situ TEM studies of rechargeable ion batteries in a practical operation environment are explored, followed by applications of in situ TEM for direct observation of electrocatalyst formation, evolution, and degradation in proton-exchange membrane fuel cells, and fundamental investigations of new energy materials such as perovskites for solar cells. Finally, recent advances in the use of environmental TEM and cryogenic electron microscopy in probing clean-energy materials are presented and emerging opportunities and challenges in in situ TEM research of energy materials and devices are discussed.

α-Mannosyl-Functionalized Cationic Nanohydrogel Particles for Targeted Gene Knockdown in Immunosuppressive Macrophages.

Immunosuppressive M2 macrophages govern the immunophathogenic micromilieu in many severe diseases including cancer or fibrosis, thus, their re-polarization through RNA interference is a promising concept to support combinatorial therapies. For targeted siRNA delivery, however, safe and stable carriers are required that manage cell specific transport to M2 macrophages. Here, siRNA-loaded cationic nanogels are reported with α-mannosyl decorated surfaces that target and modify M2 macrophages selectively. Via amphiphilic precursor block copolymers bearing one single α-mannosyl moiety at their chain end mannosylated cationic nanohydrogel particles (ManNP) were obtained of 20 nm diameter determined by dynamic light scattering and cryogenic electron transmission microscopy. α-Mannosyl surface modification is confirmed by agglutination with concanavalin A. SiRNA-loaded ManNP preferentially targets the overexpressed mannose receptor CD206 on M2 macrophages, as shown by in vitro cell uptake studies in M2 polarized primary macrophages. This specificity is confirmed, since ManNP uptake could be reduced by blocking of CD206 with mannan. Effective ManNP-guided siRNA delivery is confirmed by sequence-specific gene knockdown of CSF-1R in M2-type macrophages exclusively, while the expression levels in M1-polarized macrophages is not affected. In conclusion, α-mannosyl-functionalized ManNPs are promising universal siRNA carriers for targeted immunomodulatory treatment of immunosuppressive macrophages.

Novel TEM Microscopy and Electron Diffraction Techniques to Characterize Cultural Heritage Materials: From Ancient Greek Artefacts to Maya Mural Paintings.

To understand in-depth material properties, manufacturing, and conservation in cultural heritage artefacts, there is a strong need for advanced characterization tools that enable analysis down to the nanometric scale. Transmission electron microscopy (TEM) and electron diffraction (ED) techniques, like 3D precession electron diffraction tomography and ASTAR phase/orientation mapping, are proposed to study cultural heritage materials at nanoscale. In this work, we show how electron crystallography in TEM helps to determine precise structural information and phase/orientation distribution of various pigments in cultural heritage materials from various historical periods like Greek amphorisks, Roman glass tesserae, and pre-Hispanic Maya mural paintings. Such TEM-based methods can be an alternative to synchrotron techniques and can allow distinguishing accurately different crystalline phases even in cases of identical or very close chemical compositions at the nanometric scale.

Determination of phenolic compounds in residual brewing yeast using matrix solid-phase dispersion extraction assisted by titanium dioxide nanoparticles

A simple and efficient low-cost matrix solid-phase dispersion (MSPD) extraction based on TiO2 nanoparticles (NPs) and diatomaceous earth has been developed for the recovery of phenolic compounds from residual brewing yeast. Experimental conditions for MSPD extraction were optimized by an experimental design approach. A screening factorial design plus replicates at the center point, followed by surface response analysis were used. The simultaneous identification and quantification of eleven main natural polyphenols: caffeic, chlorogenic, p-coumaric, 3,4-dihydroxibenzoic, trans-ferulic and gallic acids, kaempferol, myricetin, naringin, quercetin and rutin, was possible by combining MSPD and capillary liquid chromatography couple to a diode array detection system (cLC-DAD) and liquid chromatography couple to a triple quadrupole analyzer (LC–MS/MS). Moreover, residual brewing yeast extracts were evaluated in terms of DPPH (1,1-diphenyl–2 picrylhydrazyl) free radical scavenging activity. Polyphenol-nanoparticle interaction was studied by UV–vis spectroscopy and electron transmission microscopy (TEM), pointing out a stable interplay that assists phenolic isolation. The extracted polyphenol quantities were within the 3.2-1,500 μg g−1 range, and the high antioxidant activity estimated suggested that developed MSPD is a successful, simple, efficient and rapid method for the extraction and recovery of bioactive phenolic compounds, which promotes the reuse and re-evaluation of brewing yeast agri-food by-products.

(Invited) Tuning Optoelectronic Properties of Transition Metal Dichalcogenides for Hydrogen Generation

We tune the optical and electronic properties of 2D transition metal dichalcogenides (TMDCs) – MoS2, MoSe2, WS2, and WSe­2– to control the surface conductivity, energetics, and ultimately reactivity. The optoelectronic properties of monolayer and few-layered TMDCs are tuned by surface functionalization, environmental control, and phase engineering. These modifications have a direct impact on the surface reactivity for hydrogen generation. Specifically, we directly map the surface energetics, phase, and reactivity with scanning electrochemical microscopy, scanning Kelvin probe microscopy, confocal Raman/photoluminescence, and scanning transmission electron microscopy-electron energy loss spectroscopy. Moreover, we disentangle the influence of O2and H2O molecules on the surface of TMDCs, where these molecules impact the optoelectronic properties and can influence the potential applications of monolayer TMDCs in (photo)electrocatalysis.

Connecting Theory with Experiment to Understand the Sintering Processes of Ag Nanoparticles

A complementary combination of long-time atomistic molecular dynamics simulations and real-time transmission electron microscopy (TEM) images has been utilized for unraveling, at an atomic resolution, the nature of the sintering process of Ag nanoparticles (NPs) induced on the surface of an α-Ag2WO4 crystal for the first time, under the exposure of a TEM electron beam (EB). Temporal evolution of calculated and experimental results highlights the role of the lattice plane matching and the stacking faults along the disorder-to-order transitions of the oriented attachment process. This phenomenon is considered as an example of surface plasmon resonances (SPRs), in which the EB has two effects: first, it provokes the formation of the Ag NPs that, due to the electron irradiation, become SPR electric dipoles, and, second, these Ag NPs undergo sintering processes that are controlled by dipole–dipole interactions forming larger clusters. The predictive power of the simulation model was verified experimentally, pa...

High volumetric capacity Fe2TeO6 as a novel anode material for alkali-ion batteries

Tetragonal Fe2TeO6 (FTO) was successfully synthesized via simple calcination method and evaluated as anode materials of alkali-ion (lithium and sodium ion) batteries for the first time. Its physical properties were investigated by X-ray diffraction, scanning electron microscopy and transmission microscopy. Its electrochemical characteristics were studied via cyclic voltammetry and galvanostatic charge/discharge. The FTO materials exhibit excellent electrochemical performance in LIBs and SIBs. It can deliver a high reversible volumetric capacity of 1901.5 mA h cm−3 at 100 mA g−1 after 500 cycles as the anode of lithium-ion batteries. Furthermore, FTO shows impressive performance at higher current density. It maintains a discharge capacity of over 311.7 mA h cm−3 even at a current density of 2000 mA g−1. In addition, it also can deliver a discharge capacity of 574.9 mA h cm−3 after 500 cycles at 100 mA g−1 as the anode materials of sodium-ion batteries. These results indicate that FTO is a potential anode material for lithium ion and sodium ion batteries.

Effect of The Degree of Cold Work and Sensitization Time on Intergranular Corrosion Behavior in Austenitic Stainless Steel

Abstract Present paper deals with the influence of a wide range of cold rolling (5, 10, 15 and maximum 40% cold deformation) and the sensitization time (aging at 700°C for 0.12, 0.5, 1, 4, 16 and 32 hours) on intergranular corrosion (IGC). Intergranular corrosion of commercial stainless steel type X6CrNiTi18-10 (1.4541, AISI 321) is frequently observed in several process environments. These localized attacks are normally attributed to the carbide precipitation and concomitant depletion of chromium near grain boundary due to steel exposure to sensitization temperature. Such undesirable microchemistry is expected to be changed further if the material undergoes deformation prior to sensitization. The consequences of deformation on IGC have been investigated by using EN ISO 3651-1methods (Huey test – Corrosion test in nitric acid medium by measurement of loss in mass). Introducing deformation to the investigated stainless steel seems to change the kinetics of carbide precipitation M23C6 and thereby changes it resistance to IGC. Cold deformation before sensitization reduces the intensity of intergranular corrosion of this steel. The deformed structure created during the cold work process, numerous slip planes and the twins boundaries are just like the grain boundaries and the places where the chromium carbides preferentially precipitates. Due to the more evenly occurring precipitation processes within the whole deformed grains, there is no phenomenon of local grain boundary carbide precipitation, and thus there is no decrease in the resistance of this steel to intergranular corrosion. The assessment of the degree of intergranular corrosion was based on the measurement of mass loss and observation of corroded surfaces on optical and electron transmission and scanning microscopes.

Bulk-type all-solid-state batteries with mechanically prepared LiCoPO4 composite cathodes

All-solid-state Li batteries are suitable for the application of 5 V-class cathode materials that can provide high energy densities. However, it is hard to fabricate bulk-type batteries composed of a mixture of active materials and solid electrolytes because of the difficulty of ensuring a conductive path and suppressing the formation of reactive layers at the interface. Herein, we report a simple mechanical processing route to composite cathode granules synthesized from a 5 V-class LiCoPO4 cathode, conductive carbon, and phosphate solid electrolyte. The homogeneously dispersed component particles were granulated during the mechanical treatment. The first discharge capacity is 82 mAh/g for the bulk-type all-solid-state battery obtained by using a composite cathode pellet, polymer solid electrolyte, and Li anode. Scanning transmission electron microscope-electron energy loss spectroscopy measurements did not reveal any Co diffusion or the formation of a resistive layer at the interface between LiCoPO4 and the solid electrolyte. The fabrication of a composite cathode by mechanical treatment is essential for the development of high-energy bulk-type all-solid-state batteries.

Beam-induced oxidation of mixed-valent Fe (oxyhydr)oxides (green rust) monitored by STEM-EELS

Analytical transmission electron microscopy (TEM) is often used to investigate morphologies, crystal structures, chemical compositions and oxidation states of highly reactive mixed-valent mineral phases. Of prime interest, due to its potential role in toxic metal remediation, is green rust sulphate (GRSO4) an FeII-FeIII layered double hydroxide. In this study, we quantified the effects that TEM analysis has on GRSO4 in order to ensure the measured material properties are a result of synthesis and reaction kinetics, and not due to sample preparation and analysis technique. To do this, we compared two sample preparation techniques (anoxic drop-cast with drying, and frozen-hydrated cryogenic) and exposed samples to the electron beam for several minutes, acquiring fluence series between ca. 40 e− Å−2 and 10,000 e− Å−2. TEM imaging and electron diffraction showed that the hexagonal plate-like morphology and crystal structure of GRSO4 were largely unaffected by sample preparation and analysis technique. However, quantitative analysis of a series of monochromated Fe L3,2-edge electron energy loss spectra (EELS) showed that electron irradiation induces oxidation. We measured an Fe(II)/Fe(III) ratio of 1.94 (as expected for GRSO4) at 50 e− Å−2. However, above this fluence, the ratio logarithmically decreased and dropped to ca. 0.5 after 1000 e− Å−2. This trend was approximately the same for both sample preparation techniques implying that it is the beam alone which causes valence state changes, and not exposure to oxygen during transfer into the TEM or the vacuum of the TEM column. Ultimately this work demonstrates that GR valence can be quantified by EELS provided that the sample is not over exposed to electrons. This also opens the possibility of quantifying the effect of redox-sensitive toxic metals (e.g., As, Cr, Se) on Fe oxidation state in GR phases (relevant to the treatment of contaminated soils and water) with a higher spatial resolution than other techniques (e.g., Mössbauer spectroscopy).

A Zirconium Oxide Nanoparticle Modified Screen‐printed Electrode for Anodic Stripping Determination of Daclatasvir Dihydrochloride

AbstractA novel, sensitive and rapid voltammetric method applied for daclatasvir dihydrochloride (DSV.2HCl) detection in raw material, human plasma and urine using square wave voltammetry at a nano‐screen printed electrode (SPE) based on synthesized zirconium oxide nanoparticles (ZrO2 NPs). The attention to zirconium oxide nanoparticle syntheses arises from its likely use in making an electrode material in the electroanalytical process. Anodic stripping square wave voltammetric peaks have been recorded at the optimum conditions of drug solution as pH, scan rate, accumulation time and accumulation potential. Morphology of the used nanoparticles has been performed by scanning electron microscope (SEM) and transmission microscope (TEM). ZrO2 NPs were applied to screen printed electrode (ZrO2‐MSPE) giving a new sensor to detect the DSV.2HCl drug. ZrO2 NPs were tested for their electroactivity in improving electrodes sensitivity. The modified electrode has been used for the analysis of DSV.2HCl in spiked serum, spiked urine and pharmaceutical formulation.

Design and Synthesis of Hybrid PEGylated Metal Monopicolinate Cyclam Ligands for Biomedical Applications.

In this study, we report, for the first time, the synthesis of two original nanosystems, based on gold Au(III) and copper Cu(II): simple gold–copper nanoparticles (Cu0AuNPs) and enriched monopicolinate cyclam (L1)–Cu(II)–Au(III)-complex (L1@Cu2+AuNPs). The two nanomaterials differ substantially by the chelation or not of the Cu(II) ions during the NPs synthesis process. The two hybrid nanoparticles (Cu0AuNPs; L1@Cu2+AuNPs) were deeply studied from the chemical and physical point of view, using many different analytical techniques such as Raman and UV–vis spectroscopy, electron transmission microscopy, and dynamic light scattering. Both nanosystems show morphological and good chemical stability at pH 4 values and in physiological conditions during 98 h. Undifferentiated and neural differentiated murine embryonic stem cells were used as a model system for in vitro experiments to reveal the effects of NPs on these cells. The comparative study between Cu0AuNPs and L1@Cu2+AuNPs highlights that copper chelated in its +2 oxidation state in the NPs is more functional for biological application.

Interaction of Tops of Domains in Metal Nano of the Film

Ferromagnetic film can be a matrix for recording information with the help of magnetic moments of electrons. The study of the processes of changing the magnetic structure in an electron-transmission microscope makes it possible to investigate micro magnetic phenomena. In this paper, we investigate the interaction between the vertices of neighboring regions. It is shown how the magnetic structure of the vertices of the domains changes as they approach each other with the help of an increasing constant magnetic field applied along the axis of easy magnetization. The distance was measured between the vertices of the domains. The schemes of distribution of the magnetization vectors between interacting vertices are shown. These schemes are made from experimental images of the magnetic structure. The distances between domain vertices and domain walls were compared on the basis of experimental data. The film thickness is 50 nm; the structure is Ni0.83-Fe0.17. The films were obtained by the method proposed by us. From the experimental results it follows that the interaction of the domain walls is observed at a distance of 20 microns and the interaction of the domain vertices is manifested at a distance of 100 μm.

Fe-TiO2 Nanoparticles Synthesized by Green Chemistry for Potential Application in Waste Water Photocatalytic Treatment

Anatase TiO2 nanoparticles doped with iron ions have been synthesized via the green chemistry method using aqueous extract of lemongrass (Cymbopogon citratus) obtained from Soxhlet extraction and doped by wet impregnation. The TiO2 anatase phase has been doped with Fe3+ (0.05, 0.075, and 0.1 Fe3+ : Ti molar ratio) at 550°C and 350°C, respectively. The scanning electron microscopy with energy-dispersive X-ray (SEM-EDS) shows nanoparticle clusters and efficiencies of impregnations between 66.5 and 58.4% depending on the theoretical dopant amount. The electron transmission microscopy (TEM) reveals final particle sizes ranging between 7 and 26 nm depending on the presence or not of the dopant. The cathodoluminescence (CL) and photoluminescence (PL) studies of the doped and undoped nanoparticles show a luminescence signal attributed to surface oxygen vacancies (visible CL emission 380–700 nm and PL emission 350–800 nm); additionally, a decrease in emission intensity is observed due the inhibition of the recombination of the photogenerated electron-holes pairs; moreover, nanopowders were analyzed by UV-Vis spectrophotometry of diffuse reflectance, and the absorption edge of the Fe-TiO2 in comparison to undoped TiO2 is extended greatly toward the visible light. The six bands (A1g + 2B1g + 3Eg) found by Raman spectroscopy and the x-ray diffraction pattern (XRD) confirm that synthesized TiO2 is only anatase phase, which is commonly used as a catalyst in waste water treatment, specifically in heterogeneous photocatalytic processes.

Low-cycle fatigue behaviour and microstructural evolution of pearlitic and bainitic steels

Microstructural analysis of new bainitic steel subject to heat treatment was performed and directly compared with those achieved from the microstructure of R-260 pearlitic rail steel. Mechanical properties, fracture behaviour, and low-cycle fatigue (LCF) tests of the bainitic steel were also evaluated and collated with those achieved from pearlitic rail steel. The LCF tests were performed at room temperature at varying strain amplitudes under total strain control. The basic characteristics of the relationship between the low - cycle fatigue parameters of steels were evaluated based on the Coffin – Manson formula. The obtained test results demonstrate that the two microstructures exhibit different cyclic stress responses, i.e. the cyclic strengthening of pearlitic steel and a cyclic softening in bainitic steel. The variations in the amount of retained austenite in the bainitic structure, before and after LCF, were evaluated by X-ray diffraction and electron transmission microscopy (TEM). The results indicate that during deformation, a partial transformation of the residual austenite into the deformed martensite α' has taken place. Moreover, the quasi-cleavage character of the fracture surface was observed for bainitic steel with a higher deformation degree during the LCF test.