High-resolution Transmission Electron Image Research Articles

Synthesis of nanocomposites of montmorillonite with carbon nanotubes as a potential material for water purification

The main goal of this research is to create nanocomposites based on unmodified and iron-modified (FeNP) montmorillonite (Mt) and carbon nanotubes (CNT) synthesized using the chemical vapor deposition method. The target area for the application of these materials is the creation of water treatment systems. This paper compares the efficiency of the CNT synthesis process on Mt before and after modification with FeNP of different concentrations and provides the characterization of the CNT microstructure and structure using different methods, such as scanning electron microscopy, high-resolution transmission electron imaging, and Raman spectroscopy. For initial verification of properties important for water purification, Mt+CNT and Mt+FeNP+CNT nanocomposites on a carbon nonwoven fabric (CF) are tested in this work. Incubation of the above-mentioned samples in a water–oil mixture reveals complex adsorption dynamics. The CF+Mt+FeNP+CNT sample shows a very good oil adsorption capacity due to its superhydrophobic and oleophilic properties.

Magnetic nanoparticles: An indicator of health risks related to anthropogenic airborne particulate matter.

Due to their small dimensions, airborne particles are able to penetrate through inhalation into many human organs, from the lungs to the cardiovascular system and the brain, which can threaten our health. This work establishes a novel approach of collecting quantitative data regarding the fraction, the composition and the size distribution of combustion-emitted particulate matter through the magnetic characterization and analysis of samples received by common air pollution monitoring. To this end, SQUID magnetometry measurements were carried out for samples from urban and suburban areas in Thessaloniki, the second largest city of Greece, taking into consideration the seasonal and weekly variation of airborne particles levels as determined by occurring traffic and meteorological conditions. The level of estimated magnetically-responding atmospheric particulate matter was at least 0.5 % wt. of the collected samples, mostly being present in the form of ultrafine particles with nuclei sizes of approximately 14nm and their aggregates. The estimated quantities of magnetic particulate matter show maximum values during autumn months (0.8 % wt.) when increased commuting takes place, appearing higher in the city center by up to 50% than those in suburban areas. In combination with high-resolution transmission electron imaging and elemental analysis, it was found that Fe3O4 and similar ferrites, some of them attached to heavy metals (Co, Cr), are the dominant magnetic contributors arising from anthropogenic high-temperature processes, e.g. due to traffic emissions. Importantly, nasal cytologic samples collected from residents of both central and suburban areas showed same pattern in what concerns magnetic behavior, thus verifying the critical role of nanosized magnetic particles in the assessment of air pollution threats. Despite the inherent statistical limitations of our study, such findings also indicate the potential transmission of infectious pathogens by means of pollution-derived nanoparticles into the respiratory system of the human body.

Natural versus synthetic quasicrystals: analogies and differences in the optical behavior of icosahedral and decagonal quasicrystals

The optical behavior of both synthetic and natural icosahedral and decagonal quasicrystals in the range 400–700 nm has been explored by repeated measurements of the reflectance values on crystallographically oriented fragments. We found differences in the optical behavior between natural and synthetic quasicrystals, and discuss the possible reasons to justify this feature. Natural quasicrystals, both icosahedral and decagonal, exhibit an almost identical chemical composition to their synthetic analogs, but seem to show a higher degree of structural perfection, as indicated from their electron and X-ray diffraction patterns. Such perfection is mainly due to the very low phason strain shown by the minerals with respect to the synthetic compounds and substantiates the differences in the measured reflectance values. The new finding constitutes significant new support for the original proposal that icosahedral and decagonal quasicrystals can be energetically stable states of matter, on the same footing as crystals. Electron diffraction pattern of icosahedrite (left) and decagonite (right). A high-resolution transmission electron image of icosahedrite is on the background.

Decoding crystallography from high-resolution electron imaging and diffraction datasets with deep learning.

While machine learning has been making enormous strides in many technical areas, it is still massively underused in transmission electron microscopy. To address this, a convolutional neural network model was developed for reliable classification of crystal structures from small numbers of electron images and diffraction patterns with no preferred orientation. Diffraction data containing 571,340 individual crystals divided among seven families, 32 genera, and 230 space groups were used to train the network. Despite the highly imbalanced dataset, the network narrows down the space groups to the top two with over 70% confidence in the worst case and up to 95% in the common cases. As examples, we benchmarked against alloys to two-dimensional materials to cross-validate our deep-learning model against high-resolution transmission electron images and diffraction patterns. We present this result both as a research tool and deep-learning application for diffraction analysis.

Chemical Mechanical Polishing and Direct Bonding of YAG

Current limitations in both single crystal and polycrystalline (ceramic) solid state laser technologies for high power applications stem from thermal effects that cause degradation in both lasing efficiency and beam quality. YAG and Y2O3 have favorable material properties for producing these high power lasers. We demonstrate chemical mechanical polishing (CMP) processes for YAG and Y2O3 resulting in smooth surfaces, (< 1 nm RMS roughness), defect free, and subsequently suitable for direct bonding. The CMP process has been used in conjunction with surface activation to form single crystal YAG-YAG and polycrystalline Y2O3-Y2O3 bonded elements showing a proof of concept for the fabrication of composite laser elements. YAG single crystals were successfully polished with a 70-nm colloidal silica solution containing NaOH (pH 9.9). X-ray photoelectron spectroscopy measurements provided insights to the chemical impact of the NaOH. After NaOH exposure, YAG showed complete removal of Al from tetrahedral sites and a change in the Y3/2 and Y5/2 peak area ratios, indicating that the surface of YAG was sufficiently modified to allow the silica particles to abrade the byproduct surface layer. The final surface roughness after polishing was measured at 0.1 nm RMS roughness with no scratches deeper than 0.3 nm. YAG single crystals were also polished with a 70-nm Al2O3 slurry containing NaOCl (pH 11.4), however AFM measurements showed that the surface produced, 0.5 nm RMS roughness with no scratches deeper than 6.0 nm, was not as good as polishing with the colloidal silica slurry which was attributed to the effect of the chemical action of NaOH with the YAG surface. Polishing polycrystalline Y2O3 required a slurry with less aggressive chemical reactions, so the NaOCl/Al2O3 slurry was used to successfully polish the substrates to RMS roughness values of 0.5 nm and scratches no deeper than 1.0 nm. Triple axis diffraction rocking curves and double crystal x-ray diffraction imaging were used to demonstrate that the CMP process also removed subsurface damage that was present in the as-supplied material. The triple axis technique was also successfully employed for the first time to demonstrate that the polycrystalline Y2O3 subsurface damage was also significant reduced after the CMP process. After CMP and surface treatment, YAG-YAG and Y2O3-Y2O3 were bonded together and annealed at 1425 °C with no applied pressure. Cross section and plan view high resolution transmission electron images of the YAG-YAG bonded interface revealed a defect free bonding interface. Light transmission measurements showed that 90% of the interface area was bonded at room temperature contact and was further strengthened with annealing at 1425 °C for 72 hours. These conditions possess a much lower thermal budget than those previously shown to be required to bond YAG without a CMP step. The CMP and surface treatment processes that have been developed are applicable towards the creation of solid state laser composite elements and enable further progress and development for high power laser applications.

Microstructure Characterization of Fiber Laser Welds of S690QL High-Strength Steels

The use of fiber laser welding to join S690QL steels has attracted interest in the field of construction and assembly. Herein, 13-mm-thick S690QL welded joints were obtained without filler materials using the fiber laser. The as-welded microstructures and the impact energies of the joints were characterized and measured using electron microscopy in conjunction with high-resolution transmission electron images, X-ray diffraction, and impact tests. The results indicated that a single-sided welding technique could be used to join S690QL steels up to a thickness of 12 mm (fail to fuse the joint in the root) when the laser power is equal to 12 kW (scan speed 1 m/min). Double-side welding technique allows better weld penetration and better control of heat distribution. Observation of the samples showed that the fusion zone exhibited bainitic and martensitic microstructures with increased amounts of martensites (Ms) compared with the base materials. Also, the grains in the fusion zone increased in coarseness as the heat input was increased. The fusion zone exhibited increased hardness (397 HV0.2) while exhibiting a simultaneous decrease in the impact toughness. The maximum impact energy value of 26 J was obtained from the single-side-welded sample, which is greater than those obtained from the double-side-welded samples (maximum of 18 J). Many more dislocations and plastic deformations were found in the fusion zone than the heat-affected zone in the joint, which hardened the joints and lowered the impact toughness. The microstructures characterized by FTEM–energy-dispersive X-ray spectrometer also exhibited laths of M, as well as stacking faults and dislocations featuring high-density, interfacial structure ledges that occur between the high-angle grain boundaries and the M and bainite.

Poly(vinyl pyrrolidone) Mediated Solubilization and Stabilization of Fullerene C60 in the Form of Nanofluid in an Alcoholic Medium

We report on the solubilization and stabilization of C60 molecules in presence of a macroscopic capping agent such as poly(vinyl pyrrolidone) PVP polymer in n-butanol using a sonochemical route. Augmentation in the absorbance value by nearly two times in the π → π* band in the C(sp2) electron transitions of C60 molecules at 328 nm in presence of PVP suggests an increase in the electron charge density on the surface interface via donor-acceptor interaction. A reasonably broad band feature observed in the π → π* transition at 435 nm in PVP moieties in a PVP-surface modified C60 sample indicates that PVP is cross-linking over the C60 surface in specific structure. Quenching of light emission in PVP molecules in n-butanol results from non bonding electrons (n) transfer from C˭O: (PVP) moieties to a C60 nanosurface in a C60:PVP charge transfer (CT) complex. Dynamic light scattering band measures two bands one at 32.0 nm and other one at 8.1 nm with average values of hydrodynamic diameter 9.2 nm and polydispersity index 0.35 apparently in two types of distinct structures. The zeta plot in the 4.63 μM C60 with PVP measures a zeta band with full width at half maximum ∼14.4 mV with average values of zetapotential ξ (−) 12.4 mV and surface conductivity of 0.074 mS/cm. The negative ξ-value describes that of O-atom of PVP molecules accumulate on the C60 surface via a chemisorptions process. Raman and Fourier transform infrared bands show that CT complex made in n-butanol presents a poor donation of the C˭O n-electrons from PVP moiety to the C60 molecules owing to adverse steric effect. High resolution transmission electron images in C60-PVP nanofluids illustrates a core-shell structure which consists of a C60 core covered by a shell of nearly 2.0 nm thickness of an amorphous PVP layer of a whitish contrast.

Synthesis of CuInS2nanocrystals from a molecular complex – characterization of the orthorhombic domain structure

CuInS2 nanocrystals were synthesized by thermal decomposition of the molecular precursor [(Me3P)3Cu(SC2H4S)In(i)Pr2] in the presence of oleylamine in dioctyl phthalate. According to X-ray diffraction patterns, the as-synthesized CuInS2 nanocrystals crystallize in the wurtzite type structure. High-resolution transmission electron images and selected area electron diffraction patterns reveal a nanodomain structure. The individual domains are approximately 5-10 nm in size and characterized by short-range cation ordering, which assuming hypothetical long-range order, corresponds to an orthorhombic superstructure (space group Pmc21, a = 4.09 ± 0.01 Å, b = 7.16 ± 0.02 Å and c = 6.56 ± 0.03 Å). The domains are separated by twin and antiphase boundaries.

Magnetic, Multilayered Nanotubes of Low Aspect Ratios for Liquid Suspensions

This work presents a synthesis route for low-aspect-ratio nanotubes consisting of a layer of magnetite (Fe3O4) sandwiched between SiO2 layers. In this template-based strategy, self-ordered porous alumina membranes are combined with the atomic layer deposition of SiO2 and Fe2O3. An optimized electrochemical setup yields nanoporous Al2O3 membranes on 4-inch Al substrates, which serve as templates for the large-scale fabrication of nanotubes. A selective chemical etching step releases the magnetic tubes for suspension in a carrier fluid and permits recycling of the underlying aluminum foils for the fabrication of subsequent nanotube batches. The nanotubes consisting of an iron oxide layer protected by a silica shell are magnetically characterized in suspensions as well as in dried form on a substrate. High-resolution transmission electron imaging reveals a polycrystalline, magnetite spinel structure of iron oxide, with the proper stoichiometry proven by the presence of the Verwey transition. Furthermore, field-dependent viscosity measurements show an enhancement of the magnetoviscosity, thus demonstrating the technological potential of nanotube suspensions as a new class of ferrofluidic solutions. Owing to the tubular shape being closed at one end, these nanoparticles might additionally function as magnetic containers for targeted drug-delivery or as chemical nanoreactors.

Fundamental Investigation of Oxygen Reduction Reaction on Rhodium Sulfide-Based Chalcogenides

Synchrotron-based X-ray absorption spectroscopy (XAS), including the surface-specific ΔXANES technique, is used to investigate the active reaction site for water activation and the oxygen reduction reaction (ORR) on the novel, mixed-phase chalcogenide electrocatalyst RhxSy/C (De Nora). The specific adsorption of water, OH, and O as a function of overpotential is reported. This study builds on a prior communication based solely on interpreting the XAS spectra of RhxSy with respect to the metallic Rh3S4 phase. Here, a more extensive overview of the electrocatalysis is provided on RhxSy/C, the thermally grown Rh2S3/C and Rh3S4/C preferential phases and a standard 30 wt % Rh/C electrocatalyst, including results obtained by X-ray diffraction (XRD), XAS, high-resolution transmission electron imaging, microanalysis, and electrochemical investigations. Heating of the RhxSy catalysts to prepare the two preferential phases causes Rh segregation and the formation of Rh metal particles, and immersion in TFMSA causes S dissolution and the formation of a Rh skin on the RhxSy samples. It is shown that some Rh−Rh interactions are needed to carry out the ORR. This is present on the Rh6 moieties in both the Rh3S4 and RhxSy catalysts, but a partial Rh skin (present from acid dissolution) is also contributing to the ORR observed on RhxSy. This to our knowledge is the first time a reaction site in a multiphase inorganic framework structure has been investigated in terms of electrocatalytic pathway for oxygen reduction.

Excimer laser processing as a tool for photocatalytic design of sol–gel TiO 2 thin films

Nanostructured sol–gel TiO 2 thin films spin coated on silicate glass plates are subjected to excimer (KrF *) pulsed laser irradiation in order to tailor their structure and photocatalytic properties. The surface morphology of virgin and laser-processed films are followed applying electron optical imaging and atomic force microscopy. The evolution of the surface roughness and pore formation are shown to be accompanied by optical absorption edge shift to infrared wavelength range. Conventional X-ray diffraction analysis and high-resolution transmission electron imaging are applied in order to obtain information on the phase composition. Co-existence of amorphous and anatase TiO 2 phases in nonirradiated sol–gel films is found. It is established that after laser processing the most intense XRD anatase peak is shifted to lower 2 θ range. The analysis of high-resolution transmission electron images of film profiles evidences for the laser induced phase transitions. Formation of rutile and brookite TiO 2 accompanied by evolution of oxygen deficient Ti n O 2 n−1 phases are identified in the subsurface region. The contribution of laser processing for increasing the photocatalytic efficiency of laser-modified films toward the oxidation of methylene blue water solution is demonstrated. The results obtained reveal a novel-processing route for designing sol–gel titania films with improved photocatalytical activity.

On the structure of nanorods and nanowires with pentagonal cross-sections

Here, we present a comprehensive study on the structure of multi-twinned decahedral-based nanorods and nanowires (Dh-NWs), specifically for the case of silver. We have demonstrated that their high-resolution transmission electron images (HRTEM) can be interpreted as a Moire pattern contrast based on a multi-twinned decahedron, and that their selected-area electron diffraction (SAED) patterns can be also completely generated through the same multi-twinned decahedron basis. We propose that the structure of these nanowires can be interpreted as a chain of decahedra joined along the vertex, which is parallel to the five-fold symmetry axis. This chain can be generated through [1 1 1] growth for FCC structures.

Inversion Twin Boundaries in Zinc Oxide

The crystallography and atomic structure of inversion twin boundaries were studied in polycrystalline ZnO using conventional transmission electron microscopy and high‐resolution electron microscopy. Inversion twin boundaries. In order to determine the atomic structure of the inversion twin boundary, high‐resolution transmission electron images were compared with simulated images. The atomic structure of the inversion boundary was determined to have a head‐to‐head configuration and its stacking sequence is AαBβAα‐ATCαA, where A, B, and C are Zn atomic planes and α, β, and T are O planes. A slight contraction of the planes in the boundary region is detected.

Observation of twin boundary layers in pure and alloyed YBa2Cu3O7−δ

Using an electron diffraction technique, the thicknesses of the (nonorthorhombic) twin boundary layers were measured for pure and alloyed YBa2(Cu1−xMx)3O7−δ. Boundary thickness varied from ∼0.7 nm for M=Ni, x=0.02, and δ≂0 to ∼2.6 nm for M=Al, x=0.02, and δ≂0, while it was ∼1.0 nm for a pure YBa2Cu3O7. High-resolution transmission electron imaging of similar specimens supports the existence of such twin boundary layers.