Bright-field Transmission Electron Microscopy Images Research Articles

Effect of plate orientation on apparent thickness of mineral plates by transmission electron microscopy.

Transmission electron microscopy (TEM) is widely used to study the ultrastructure of bone. The mineral of bone occurs as polycrystalline mineral plates about 3 to 6 nm in thickness. A problem in using TEM to make quantitative analyses of bone is that the orientation of the plates with respect to the plane of the section being imaged is expected to affect their apparent thickness. The purpose of this study was to test if this was true, if the apparent thickness of plates changed substantially as a result of tilt of the section. We prepared TEM sections of samples of cortical human bone by ion beam milling, orienting one section parallel to the collagen fibril axes and one perpendicular to them. We obtained TEM bright field and HAADF images of these sections, tilting the sections up to ± 20° at 2° intervals and measuring the apparent thickness of individual mineral platelets at each angle of tilt. Thickness appears to double as section is tilted ± 20°. True thickness of plates is determined by tilting the section along an axis parallel to the plate orientation and determining the minimum apparent thickness. However, as plates are tilted away from minimum-thickness orientation, they become less well-resolved, disappearing when tilted more than 20°. We therefore also measured apparent thickness of only the darkest (most electron scattering) plate images in an untilted section and obtained the same average thickness as that obtained by tilting. We conclude that tilting of the section is not necessary to obtain an accurate measurement of the thickness of mineral plates.

(Invited) Metal-Organic Chemical Vapor Deposition of WS2 on Patterned Substrate

Transition metal dichalcogenides (TMDs) have attracted much attention in recent years due to their excellent electrical properties and unique nature. Tungsten disulfide (WS2) , as a representative TMD, is a typical two-dimensional stacking material with moderately wide band gap (single layer: 2.03 eV, bulk: 1.32 eV) and, therefore, has led to active application research in various fields. In particular, large-area, few-layer WS2 is expected to have high potential as a channel material for MOSFETs in the next-generation LSIs because of relatively high carrier mobility even in the extremely thin film. Recently, we have succeeded in fabricating continuous WS2 thin films on Si substrates at low temperatures using newly developed organometallic precursor [1]. In this study, we further report the film characteristics and our attempts to deposit films on Fin structures in order to evaluate their applicability to the next-generation channel materials, which should have complicated 3-dimesional structure.In the experiment, n-BuNC-W(CO)5 was synthesized for WS2 deposition. This novel precursor is a liquid above 35 °C with stable vapor supply. It is also expected to interact with the substrate efficiently due to its polarity in the molecule. The vapor pressure is 1.2 torr at 115 °C, which is an appropriate for a CVD precursor. As a sulfur precursor, (t-C4H9)2S2, which is non-toxic in contrast to H2S, was adopted. WS2 thin films were grown by MOCVD in a cold-wall reactor, using the organic compounds introduced above as precursors for W and S, respectively, on flat and patterned silicon (001) substrates at 300 to 350 °C for 5 to 15 minutes. The deposited films were evaluated by X-ray photoelectron spectroscopy (XPS), UV-Raman spectroscopy (excitation wavelength: 355 nm), and transmission electron microscopy (TEM).Figure 1 summarizes the evaluation results of the WS2 film deposited on the flat substrate. W 4f XPS spectrum (Fig. 1 (a)) show that the film is mostly composed of 2H with a possible slight amount of 1T/1T' structure. In conjunction with S 2p spectrum (Fig. 1 (b)), it can be calculated using the relative sensitivity coefficient that the composition ratio of W to S is approximately 2.1, which is close to the stoichiometric ratio. Moreover, it was confirmed the film was stable more than 6 month in the room atmosphere. In the Raman spectrum shown in Fig. 1(c), two peaks appeared at approximately 350 cm-1 and 420 cm-1 corresponding to in-plane and out-of-plane vibrations, respectively, which are consisted of 2H-WS2 specific peaks of A1g (418 cm-1) and E1 2g (351 cm-1). Here, E1 2g might be broadened by the presence of another smaller mode called 2LA(M) (second-order longitudinal elastic mode), which may be attributed to the various distortions in the grown WS2 thin film. These results are also consistent with previous reports. This Raman results indicating the 2H structure of the film is also consistent with the XPS results as well as the previously reported literatures. Fig. 1(d) shows bright-field TEM images. It can be observed that the film continuously covers the substrate, with no voids larger than micrometer scale. The higher magnification image also shows approximately 10 layers of WS2 film grown with a layered structure parallel to the surface. The WS2 layers are stacked with a face spacing of approximately 0.7 nm, whose distance correlates well with the theoretical tungsten-tungsten interlayer distance of 0.62 nm for the bulk material. The domain size can be estimated to be roughly 50-100 nm.Figure 2 shows cross-sectional TEM images of WS2 thin films deposited on Si Fin structures. It can be observed that a continuous layered film is formed along the 3D Fin structure, and the layered structure is parallel to the surface all over the entire Fin structure. However, the number of layers differs depending on the position, with fewer layers on the sidewalls than those on the top surface, and even fewer layers toward the bottom. This may be due to the insufficient supply of precursor deep in the Fin structure. To improve the uniformity and controllability of layer number, further optimization of the deposition conditions such as precursor supply and deposition temperature, including atomic layer deposition technique, is desired.This research was supported by the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT) under the project JPJ011438 for the creation of a center for the creation of next-generation X-nics semiconductors.[1] C. Kirito, K. Yamazaki, Y. Hibino, Y. Hashimoto, H. Machida, M. Ishikawa, H. Sudoh, H. Wakabayashi, R. Yokogawa and A. Ogura, ECS Trans. 104, 3 (2021). Figure 1

Automated analysis of grain morphology in TEM images using convolutional neural network with CHAC algorithm

The shape and size of grains significantly impact the properties of polycrystalline materials. In particular, high temperature and radiation exposure in nuclear reactors can lead to considerable grain growth of UO2, thereby substantially modifying the fuel performance. Transmission electron microscopy (TEM) has been used to characterize the grain morphology of polycrystalline materials, but the manual analysis of TEM images is a time-consuming and labor-intensive process, which cannot meet the increasing demand for high-throughput data analytics.This study presents an automated approach we developed for characterizing grain morphology recorded in bright field TEM images during ion irradiations performed in situ. Our approach combines a machine learning model for detecting grain boundaries and a computer vision algorithm named CHAC for selecting well-labeled grains for statistical analysis. Using TEM images acquired from in-situ ion irradiation experiments on nanocrystalline UO2, we demonstrate that this automated approach can achieve comparable results to human experts while significantly reducing the analysis time. Moreover, the machine learning model functions as a "few-shot" model, requiring only a modest number of training images to perform effectively on a specific task. Consequently, researchers in need can efficiently train their own models following the procedures described in this study to automate grain morphology analysis of their own TEM images.

Crystal structure determination of a new monoclinic phase in NiMn system in a self-assembled chessboard-like microstructure

Vacuum induction melted equi-atomic NiMn alloy has been studied through x-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD pattern of the as-solidified alloy may be matched with the tI2 η′-NiMn phase and the cF4 Ni3Mn phase simultaneously. In the TEM bright field image of the same alloy, alternating bright and dark contrast with chessboard-like appearance is observed. Electron diffraction patterns from the bright phase match with the tI2 NiMn phase. The electron diffraction patterns from the dark phase are related to the tetragonal phase with additional superlattice reflection along [110] and [112]. The crystal structure of the new phase has been found to be polymorphically related mP8 phase with space group P 2/m (a = 5.02 Å, b = 5.16 Å, c = 3.61 Å). The phase has not been reported so far in the Ni–Mn system. The chessboard-like morphology between a tetragonal and monoclinic phase is being reported for the first time.

Influence of frictional heat spread pattern on the formation of intermetallic layers at the dissimilar FSW joint interface between AA 5083 and HSLA steel

The dissimilar weld interface for the AA5083 and HSLA steel alloy pair made by FSW technique was investigated to explore the impact of the friction heat flow across the thickness on the types and nature of IMC layer. The detail transmission electron microscopy (TEM) and atom probe tomography (APT) were performed to characterize the IMCs at different layer thicknesses and compositional mixing patterns of the interface. Also, a 3D moving heat source thermomechanical model was developed to simulate the FSW joining of Fe/Al alloy pair and explored the existence of heat flow pattern along the sheet thickness. The detail analysis of SAED pattern obtained from TEM bright field images was conducted to characterize the presence of types and nature of IMCs at different layer thicknesses. In this study the proximity histogram data from APT were investigated for further confirmation of existence of observed Fe/Al IMCs and atomic mixing pattern at the interface. The study identified the presence of Fe2Al9, Fe4Al13 and FeAl6 which are distinctly distributed over the thickness. The relative richness of Fe and Al in these IMCs are found significantly influenced by the thermal gradient in turn typically control their distribution over thickness. The Al rich IMCs such as FeAl6, possessing large ΔGf and low activation energy, found away from the frictional surface of heat source. While Fe rich IMCs form with relatively lesser ΔGf and higher activation energies are seen near the frictional surface of heat source.

Nanostructural Analysis of Co‐Re/γ‐Al2O3 Fischer‐Tropsch Catalyst by TEM and XRD

AbstractA rhenium promoted Fischer‐Tropsch (FT) cobalt catalyst supported on γ‐Al2O3 has been investigated by Transmission Electron Microscopy (TEM) and X‐ray Diffraction (XRD), before and after reduction. Electron diffraction, High Resolution TEM and Electron Energy Loss Spectroscopy were used to confirm the oxidation state. Cobalt aggregate, particle and crystallite sizes have been studied in detail and measured by TEM and XRD. A cobalt particle size of 10.0±2.4 nm obtained from bright field TEM images for the reduced material is consistent with the XRD analysis of the calcined catalyst. After reduction dark field TEM imaging gave a volume‐weighted crystallite size of 7.5±2.5 nm, which is close to the value obtained by XRD. The particles had lost the parallel orientation and physical continuity within the alumina pore structure that were present before reduction. The latter was confirmed by electron tomography. Lamellae identified with the presence of Hexagonal Close Packed cobalt were observed in the predominantly Face Centred Cubic particles.

Optimization of ion-beam-deposited Mo/Si multilayers for extreme ultraviolet masks

The aim of our work is to investigate deposition conditions to further optimize the reflectivity of Mo/Si multilayers (MLs) for reflective coatings of extreme ultraviolet mask blanks. Dark-field transmission electron microscopy (TEM) measurements imply interfacial roughness values of 80 to 150 pm. Bright-field TEM images indicate intermixed layer thicknesses of 0.4 to 1.8 nm. We present reflectivity calculations including these two ML imperfections and compare against prior empirical results. Both interfacial roughness and intermixing are predicted to lower the maximum reflectivity. For example, interfacial roughness of 400 pm lowers the maximum reflectivity by ∼2 % . Smoother interfaces with sub-100 pm allow recovery of ∼1.5 % of the reflectivity. Mo/Si intermixing is predicted to lower the maximum reflectivity by up to 6% relative to an ideal ML. Reflectivity could be recovered by ∼3 % by reducing the intermixing depth by only 20% to 30%. We demonstrate ways to reduce roughness or intermixing by ion beam deposition (IBD). Ion bombardment simulations provide estimates of the atom energy distribution arriving at the mask blank surface during Mo and Si deposition and of stopping depths of each atom into the underlying layer. Key IBD parameters to reduce the deposition energy, and hence the intermixing depth, are summarized: beam voltage and deposition pressure. Lower ion beam voltage or higher pressure can together reduce the intermixing depth by at least 20% to 30%. Bright-field TEM measurements of MLs deposited at various deposition conditions confirm the intermixing predictions.

Nanostructured Polymer Composite Electrolytes with Self-Assembled Polyoxometalate Networks for Proton Conduction

Nanostructured Polymer Composite Electrolytes with Self-Assembled Polyoxometalate Networks for Proton Conduction

AutoDetect-mNP: An Unsupervised Machine Learning Algorithm for Automated Analysis of Transmission Electron Microscope Images of Metal Nanoparticles.

The synthesis quality of artificial inorganic nanocrystals is most often assessed by transmission electron microscopy (TEM) for which high-throughput advances have dramatically increased both the quantity and information richness of metal nanoparticle (mNP) characterization. Existing automated data analysis algorithms of TEM mNP images generally adopt a supervised approach, requiring a significant effort in human preparation of labeled data that reduces objectivity, efficiency, and generalizability. We have developed an unsupervised algorithm AutoDetect-mNP for automated analysis of TEM images that objectively extracts morphological information on convex mNPs from TEM images based on their shape attributes, requiring little to no human input in the process. The performance of AutoDetect-mNP is tested on two data sets of bright field TEM images of Au nanoparticles with different shapes and further extended to palladium nanocubes and cadmium selenide quantum dots, demonstrating that the algorithm is quantitatively reliable and can thus serve as a generalizable measure of the morphology distributions of any mNP synthesis. The AutoDetect-mNP algorithm will aid in future developments of high-throughput characterization of mNPs and the future advent of time-resolved TEM studies that can investigate reaction mechanisms of mNP synthesis and reactivity.

Constituent Isomerism-Induced Quasicrystal and Frank–Kasper σ Superlattices Based on Nanosized Shape Amphiphiles

Naturally, subtle variations in the chemical structures of constituent molecules may significantly affect their multiscale spatial arrangements, properties, and functions. Deceptively simple spheri...

Crystalline and amorphous calcium carbonate as structural components of the Calappa granulata exoskeleton

The exoskeleton of crustaceans consists of chitin biopolymers where the embedded inorganic biominerals, mainly CaCO3, affect strongly its mechanical properties. Raman and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopies and Transmission Electron Microscopy (TEM) are applied to investigate the CaCO3 structure in various parts of the Calappa granulata crab exoskeleton. The shape of the main Raman peak of CaCO3 reveals the presence of two phases which are identified as calcite and amorphous calcium carbonate (ACC). The relative concentration of the two phases in various parts of the exoskeleton is determined from the area ratio under the corresponding peaks. The results of the Ca L3,2-edge NEXAFS analysis are in line with the Raman findings, since the energy separation of peaks that appear in the lower frequency region of the main L2 and L3 peaks due to crystal field splitting, is directly related to the percentage of the ACC phase in the total CaCO3 mineral content. The C K-edge spectra are used for the determination of the extent of calcification of the exoskeleton. Furthermore, dark and bright field TEM images reveal the presence of nanocrystallites with an average size of 20 nm. The structure of the nanocrystallites, as derived from the Selected Area Electron Diffraction patterns, is calcite. The results suggest that ACC plays a structural role in the exoskeleton of Calappa granulata.

Ion channelling effect and damage accumulation in yttria-stabilized zirconia implanted with Ag ions

Yttria stabilized zirconia (YSZ) is well known as a radiation-resistant material. In this study, we present results from 400 keV Ag+ implantations of the (1 0 0) YSZ single crystals to fluences ranging from 5 × 1015 to 5 × 1016 cm−2. The damage depth profiling and accumulation were probed using Rutherford backscattering spectrometry in the channelling mode (RBS-C), Transmission electron microscopy (TEM) and X-ray diffraction (XRD). The axial channelling effect of 2 MeV He+ ions in the implanted YSZ was studied. RBS-C provides us with detailed information about the displaced atoms density depth profiles progressing into greater depths, especially in the case of higher fluence. TEM was utilized to characterize the microstructure evolution and damage accumulation in the buried layer after the implantation. At the highest fluence (5 × 1016 cm−2), Ag depth profile in the depth of 30–130 nm was identified in TEM bright and dark field images as well as in the electron diffraction patterns. Ag depth profiles are in agreement with depth profiles determined by RBS which show maximum Ag concentration in the depth of 94 nm. The reason for the decrease of the deformation identified by XRD in the vertical direction is the defect formation.

Triangular Single Shockley Stacking Fault Analyses on 4H-SiC PiN Diode with Forward Voltage Degradation

The structure of partial dislocations (PDs), which surround triangular single Shockley stacking faults (1SSFs) expanded during electroluminescence observation in a 4H-SiC PiN diode, is investigated by photoluminescence (PL) imaging, PL spectroscopy, plan-view transmission electron microscopy (TEM) imaging, g·b analysis, cross-sectional bright-field scanning TEM (BF-STEM) imaging, and high-resolution high-angle annular dark-field (HAADF)-STEM imaging. The zigzag configuration is found on the upstanding side of the triangular 1SSF by plan-view TEM imaging, while it is observed as a single line by PL imaging. Using g·b analysis, the zigzag line is confirmed to be constructed by 30° and 90° PDs. Cross-sectional BF-STEM observation proved that the expanding 1SSF penetrates through the p–n interface whose position was estimated from secondary-ion mass spectrometry (SIMS) depth profile measurements of the aluminum and nitrogen concentrations. This provides experimental evidence that the 1SSF loses its driving force for recombination-enhanced dislocation glide when it stops somewhere in the p-layer where sufficient electrons no longer exist. Using cross-sectional HAADF-STEM observation, core species of the PDs were analyzed and the Burgers vector for the dislocation loop uniquely determined. Also, the first experimental observation of a 90° silicon-core PD, reported so far, is confirmed. According to these PD analyses, the possible atomic arrangement around the 1SSF is examined and the way tetrahedrons face across each PD is summarized, based on HAADF-STEM analysis of the 1SSF line.

In Situ TEM Crystallization of Amorphous Iron Particles

Even though sub-micron and nano-sized iron particles generally display single or polycrystalline structures, a growing interest has also been dedicated to the class of amorphous ones, whose absence of a crystal structure is capable of modifying their physical properties. Among the several routes so far described to prepare amorphous iron particles, we report here about the crystallization of those prepared by chemical reduction of Fe3+ ions using NaBH4, with sizes ranging between 80 and 200 nm and showing a high stability against oxidation. Their crystallization was investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD), and in situ heating transmission electron microscopy (TEM). The latter technique was performed by the combined use of electron diffraction of a selected sample area, and bright and dark field TEM imaging, and allowed determining that the crystallization turns the starting amorphous particles into polycrystalline α-Fe ones. Also, under the high vacuum of the TEM column, the crystallization temperature of the particles shifted to 550 °C from the 465 °C, previously observed by DSC and XRD under 105 Pa of Ar. This indicates the pivotal role of the external pressure in influencing the starting point of phase transition. Conversely, upon both the DSC/XRD pressure and the TEM vacuum conditions, the mean size of the crystal domains increases as a consequence of further thermal increase, even if with some pressure-related differences.

Synthesis and high-resolution structural and chemical analysis of iron-manganese-oxide core-shell nanocubes

We have investigated the structure and chemical composition of nanoparticles synthesized by thermal decomposition of a mixture of iron oleate and manganese oleate in a high-boiling solvent in the presence of Na-oleate and oleic acid as surfactants by analytical transmission electron microscopy (TEM). The particles appear core-shell like in bright field TEM images. Higher spatial resolution TEM (HRTEM) analysis reveals a FeO/MnO like structure in the core and a spinel like structure in the shell. With high-resolution analytical methods like energy dispersive x-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS), the distribution of the metals Mn and Fe was investigated. Differences in the oxidation state of these metals were found between the core and the shell region. The presence of sodium from the used surfactant (Na-oleate) on the surface of the particles has been proved.

Low-Temperature Nitridation of 2205 Duplex Stainless Steel

Low-temperature gas-phase nitridation has been studied in $$\updelta $$-ferrite in 2205 duplex stainless steel. High-resolution spatially-resolved compositional and structural analysis revealed two competitive responses to nitridation. Some regions revealed a nitrogen atom fraction approaching 25 at. pct—greater than $$10^6$$ times the equilibrium solubility limit at room temperature. Remarkably, there is no expansion or distortion of the body-centered cubic lattice. This is similar to the response of $$\updelta $$-ferrite in this alloy to low-temperature carburization. In conventional transmission electron microscopy bright-field images, the supersaturated ferrite grains show no diffraction contrast—resembling the appearance of amorphous structures—suggesting an unusually high defect density. These grains exhibit spinodal decomposition of the ferrite to nanometer-scale Fe-rich and Cr-rich ferrite domains. High-resolution imaging reveals pristine Fe-rich nanocrystals, whereas the Cr-rich domains are apparently amorphous. Elsewhere in the nitrogen-rich case, an isothermal ferrite-to-austenite phase transformation occurred. The austenite transformation product formed martensitically with a high-aspect-ratio plate-like morphology in the Nishiyama–Wassermann orientation relationship to the ferrite matrix.

Combinatorial Tuning of Structural and Optoelectronic Properties in CuxZn1−xS

Summary P-type transparent conductors (TCs) are important enabling materials for optoelectronics and photovoltaics, but their performance still lags behind n-type counterparts. Recently, semiconductor CuxZn1−xS has demonstrated potential as a p-type TC, but it remains unclear how properties vary with composition. Here, we investigate CuxZn1−xS across the entire alloy space (0 ≤ x ≤ 1) using combinatorial sputtering and high-throughput characterization. First, we find a metastable wurtzite alloy at an intermediate composition between cubic endpoint compounds, contrasting with solid solutions or cubic composites (ZnS:CuyS) from the literature. Second, structural transformations correlate with shifts in hole conductivity and absorption; specifically, conductivity increases at the wurtzite phase transformation (x ≈ 0.19). Third, conductivity and optical transparency are optimized within a "TC regime" of 0.10

Evaluation of the Growth Kinetics of θ′ and θ-Al2Cu Precipitates in a Binary Al-3.5 Wt Pct Cu Alloy

Heat treatment for precipitation hardening is known to have a significant effect on the nano/microstructure of cast aluminum alloys, and thereby affecting its properties. In this study, precipitation kinetics after solutionizing and water quenching have been characterized by differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and microhardness evaluations under different aging conditions. The Kissinger methodology was applied along with the Lee–Kim–Starink–Zahra kinetic equation to determine the kinetic parameters from the DSC runs at constant heating rates, assuming that the precipitates have an ellipsoidal shape. The TEM results showed evidence of semi-coherent θ′ precipitation in accordance with the microhardness evolution during isothermal aging at 190 °C and the kinetic analysis from the DSC data. The TEM bright field images of the specimens aged at two different times were used to record the size and number density of the precipitates. The activation energies for the precipitation kinetics of θ and θ′ were 330 and 114 kJ/mol, respectively. Finally, the values for the interfacial mobility were determined using the kinetic parameters derived from the DSC results and the TEM observations.

Modulating the crystallization process of Fe82B12C6 amorphous alloy via rapid annealing

Crystallization is a uniform behavior for amorphous alloys while it can be fairly complex. For Fe-B-C alloys with high Fe content, the precipitation of α-Fe is ahead of the Fe-metalloid compounds with temperature increasing. It is found that the crystallization products of Fe-B-C amorphous alloys with Fe content lower than 82% can be modulated by appropriate annealing. The Fe82B12C6 alloy is eutectoidally crystallized with the simultaneous precipitation of α-Fe and Fe-metalloid compounds under conventional annealing. It is a diffusion controlled three-dimensionally growth with a constant nucleation rate. However, only α-Fe nanocrystals with a low volume fraction form under rapid annealing, which is evidenced by the results of X-ray and electron diffractions along with the magnetometry. The transmission electron microscopy bright-field images show that the α-Fe nanocrystals obtained by rapid annealing have two different morphologies. One is dendritic with a large characteristic length and the other is equiaxed-like.

The formation of martensite during the propagation of fatigue cracks in pearlitic rail steel

Squat is a kind of railhead defects related to rolling contact fatigue (RCF), and regarded as a potential safety hazard in railway networks. The mechanisms of squat initiation and propagation remain unclearly understood. In the current study, several branches of subsurface cracks inside squat defects had been intensively investigated for understanding the development of RCF cracks. From metallographic observations, a few white etching particles were clearly found either located within crack gaps or attached with crack faces. Based on nanoindentation measurements, the hardness of white particles was higher than that in matrix, presenting a possible mechanical property of martensite. A large density of nano-twins in the substructure of white particles can be identified in the transmission electron microscopy bright-field imaging. Their corresponding selected area electron diffraction patterns proved white particles as Fe-C martensite with body-centered tetragonal crystallographic structure. Besides the martensite, a random distribution of oxidized sulphide inclusions (MnS) and silicate composites were found included in white etching particles as well by the energy-dispersive x-ray spectroscopy analyses. The discovery of martensitic transformation and inclusions in the crack of squat defects reveals an accelerated failure mechanism which would be detrimental to operation safety. It is necessary to pay more attentions so that the risk of fatigue failures can be minimized.