A new method of image texture analysis is presented, based on the mean and standard deviation of gray levels within domains in an image. The calculations are performed recursively on domains of various sizes within the images. These gray level calculations are used as the input matrix for principal component analysis. The technique analyzes the entire image as a whole and is not for image segmentation. The analysis routine operates across all distances, frequencies and directions in the image, and is not computationally burdensome. The method was applied to scanning electron microscope images of reverse osmosis membranes on domains from 23 nm to 3 µm. The texture analysis technique performed well in identifying the surface morphology and, once calibrated, in predicting the surface roughness as measured by atomic force microscopy.

When analyzing an unknown by electron-excited energy dispersive X-ray spectrometry, with the entire periodic table possibly in play, how does the analyst discover minor and trace constituents when their peaks are overwhelmed by the intensity of an interfering peak(s) from a major constituent? In this paper, we advocate for and demonstrate an iterative analytical approach, alternating qualitative analysis (peak identification) and standards-based quantitative analysis with peak fitting. This method employs two “tools”: (1) monitoring of the “raw analytical total,” which is the sum of all measured constituents as well as any such as oxygen calculated by the method of assumed stoichiometry, and (2) careful inspection of the “peak fitting residual spectrum” that is constructed as part of the quantitative analysis procedure in the software engine DTSA-II (a pseudo-acronym) from the National Institute of Standards and Technology. Elements newly recognized after each round are incorporated into the next round of quantitative analysis until the limits of detection are reached, as defined by the total spectrum counts.

Electron beam-induced carbon contamination is a balance between simultaneous deposition and erosion processes. Net erosion rates for a 25 nA 3 kV beam can reduce a 5 nm C coating by 20% in 60 s. Measurements were made on C-coated Bi substrates, with coating thicknesses of 5–20 nm, over a range of analysis conditions. Erosion showed a step-like increase with increasing electron flux density. Both the erosion rate and its rate of change increase with decreasing accelerating voltage. As the flux density decreases the rate of change increases more rapidly with decreasing voltage. Time-dependent intensity (TDI) measurements can be used to correct for errors, in both coating and substrate quantifications, resulting from carbon erosion. Uncorrected analyses showed increasing errors in coating thickness with decreasing accelerating voltage. Although the erosion rate was found to be independent of coating thickness this produces an increasing absolute error with decreasing starting thickness, ranging from 1.5% for a 20 nm C coating on Bi at 15 kV to 14% for a 5 nm coating at 3 kV. Errors in Bi Mα measurement are <1% at 5 kV or above but increase rapidly below this, both with decreasing voltage and increasing coating thickness to 20% for a 20 nm coated sample at 3 kV.

Scanning transmission electron microscopy (STEM) has become the main stay for materials characterization on atomic level, with applications ranging from visualization of localized and extended defects to mapping order parameter fields. In recent years, attention has focused on the potential of STEM to explore beam induced chemical processes and especially manipulating atomic motion, enabling atom-by-atom fabrication. These applications, as well as traditional imaging of beam sensitive materials, necessitate increasing the dynamic range of STEM in imaging and manipulation modes, and increasing the absolute scanning speed which can be achieved by combining sparse sensing methods with nonrectangular scanning trajectories. Here we have developed a general method for real-time reconstruction of sparsely sampled images from high-speed, noninvasive and diverse scanning pathways, including spiral scan and Lissajous scan. This approach is demonstrated on both the synthetic data and experimental STEM data on the beam sensitive material graphene. This work opens the door for comprehensive investigation and optimal design of dose efficient scanning strategies and real-time adaptive inference and control of e-beam induced atomic fabrication.

MicroRNA (miR)-29b plays a crucial role during somatic cell reprogramming. The aim of the current study was to explore the effects of miR-29b on the developmental competence of bovine somatic cell nuclear transfer (SCNT) embryos, as well as the underlying mechanisms of action. The expression level of miR-29b was lower in bovine SCNT embryos at the pronuclear, 8-cell, and blastocyst stages compared with in vitro fertilized embryos. In addition, miR-29b regulates the expression of DNA methyltransferases (Dnmt3a/3b and Dnmt1) in bovine SCNT embryos. We further investigated SCNT embryo developmental competence and found that miR-29b overexpression during bovine SCNT embryonic development does not improve developmental potency and downregulation inhibits developmental potency. Nevertheless, the quality of bovine SCNT embryos at the blastocyst stage improved significantly. The expression of pluripotency factors and cellular proliferation were significantly higher in blastocysts from the miR-29b overexpression group than the control and downregulation groups. In addition, outgrowth potential in blastocysts after miR-29b overexpression was also significantly greater in the miR-29b overexpression group than in the control and downregulation groups. Taken together, these results demonstrated that miR-29b plays an important role in bovine SCNT embryo development.

5xxx series aluminum alloys, as Al-4.5Mg-1.0Mn (AA5083), are strengthened by Mg solid solution and work hardening. A drawback of this alloy is the fact that β phase, Al3Mg2, can precipitate on grain boundaries causing sensitization and intergranular corrosion, which is detrimental to the integrity of the structure. Metallography is an important technique to study the grain structure and highly sought for intergranular corrosion evaluation; however, revealing the grains of completely un-sensitized AA5083 is challenging. This paper introduces a new procedure to etch AA5083 samples that were solutionized at 450°C for 1.5 h. The new procedure is a two-step etching method, including a phosphoric acid pre-etching step and a Weck’s reagent coloring step. Solutionized, lightly sensitized, and as-received AA5083 were evaluated, and the grains were observed using optical microscopy. The microetching mechanism was further studied by optical profilometry, atomic force microscopy, scanning electron microscopy, and energy dispersive spectrometry. The phosphoric acid created a surface profile determined by the grain orientations and its reactivity, and the Weck’s reagent was then able to color grains by preferential MnO2 formation over some pre-etched grains. Moreover, the final polishing with colloidal silica was essential to reach a high contrast image.

The magnetism and microstructure of Cr25Ni35Nb and Cr35Ni45Nb alloy tubes after 5 years of service were investigated in this paper. The saturation magnetization of the Cr25Ni35Nb alloy tube in the thickness direction is more than 20 emu/g, and the tube becomes ferromagnetic. The inner and outer walls of Cr35Ni45Nb alloy tubes also become ferromagnetic. But the saturation magnetization of the Cr35Ni45Nb alloy tubes approaches to zero in the center zone. The primary carbides M7C3 and NbC are changed into M23C6 and G phase at the outer region of the furnace tube. However, the M23C6-type carbides were replaced by carbon-rich carbides M7C3 at the carburization zone. Cr-depleted zones are formed at the inner and outer walls of the furnace tubes owing to oxidation. Carburization and oxidation reduce the Cr content of the matrix. Accordingly, the saturation magnetization is very high at the carburization zone and Cr-depleted zone. The magnetism of Cr25Ni35Nb and Cr35Ni45Nb alloy tubes has a high correlation with the Cr content of the matrix. Carburization and oxidation are the main reasons that make the paramagnetic ethylene pyrolysis furnace tube change to ferromagnetic.

The magnetization configuration of a novel nano-chessboard structure consisting of L10 and L12 phases in a Co40Pt60 alloy is investigated using Lorentz transmission electron microscopy (LTEM) and micro-magnetic simulations. We show high-resolution LTEM images of nano-size magnetic features acquired through spherical aberration correction in Lorentz Fresnel mode. Phase reconstructions and LTEM image simulations are carried out to fully understand the magnetic microstructure. The experimental Fresnel images of the nano-chessboard structure show zig-zag shaped magnetic domain walls at the inter-phase boundaries between L10 and L12 phases. A circular magnetization distribution with vortex and anti-vortex type arrangement is evident in the phase reconstructed magnetic induction maps as well as simulated maps. The magnetic contrast in experimental LTEM images is interpreted with the help of magnetic induction maps simulated for various relative electron beam-sample orientations inside the TEM.

To better understand the formation and evolution of hierarchical crack networks in shales, observations of microscopic damage, and crack growth were conducted using an in situ tensile apparatus inside a scanning electron microscope. An arched specimen with an artificial notch incised into the curved edge was shown to afford effective observation of the damage and crack growth process that occurs during the brittle fracturing of shale. Because this arched specimen design can induce a squeezing effect, reducing the tensile stress concentration at the crack tip, and preventing the brittle shale from unstable fracturing to some extent. Both induced and natural pores and cracks were observed at different scales around the main crack path or on fractured surfaces. Observations indicate that the crack initiation zone develops around the crack tip where tensile stresses are concentrated and micro/nanoscale cracks nucleate. Crack advancement generally occurs by the continuous generation and coalescence of damage zones having intermittent en echelon microscopic cracks located ahead of the crack tips. Mineral anisotropy and pressure build-up around crack tips causes crack kinking, deflection, and branching. Crack growth is often accompanied by the cessation or closure of former branch cracks due to elastic recovery and induced compressive stress. The branching and interactions of cracks form a three-dimensional hierarchical network that includes induced branch cracks having similar paths, as well as natural structures such as nanopores, bedding planes, and microscopic cracks.

Deformation and mechanical damage in a three-dimensional braided carbon fiber reinforced carbon and silicon carbide ceramic composite, subjected to compressive loading, has been studied in situ by laboratory X-ray computed tomography. Dimensional change was measured and damage visualized by digital volume correlation analysis of tomographs. Cracks nucleated from defects within the fiber bundles and tended to propagate along the fiber bundle/matrix interface. For longitudinal compression, parallel to the fiber bundles, the initial elastic modulus decreased with increasing compressive strain while significant transverse tensile strains developed due to distributed cracking. For transverse compression, perpendicular to the fiber bundles, the compressive elastic modulus was effectively constant; the tensile strains developed along the fiber direction were small, whereas macroscopic fracture between the fiber bundles caused very large bulk tensile strain perpendicular to the loading. The observations suggest that the mechanical strength might be improved through control of pre-existing defects and application of stitch fibers in the transverse direction.

Radiation therapy, widely used in the treatment of a variety of malignancies in the pelvic area, is associated with inevitable damage to the surrounding healthy tissues. We have applied atomic force microscopy (AFM) to track the early damaging effects of ionizing radiation on the collagen structures in the experimental animals’ bladder and rectum. The first signs of the low-dose radiation (2 Gy) effect were detected by AFM as early as 1 week postirradiation. The observed changes were consistent with initial radiation destruction of the protein matrix. The alterations in the collagen fibers’ packing 1 month postirradiation were indicative of the onset of fibrotic processes. The destructive effect of higher radiation doses was probed 1 day posttreatment. The severity of the radiation damage was proportional to the dose, from relatively minor changes in the collagen packing at 8 Gy to the growing collagen matrix destruction at higher doses and complete three-dimensional collagen network restructuring towards fibrotic-type architecture at the dose of 22 Gy. The AFM study appeared superior to the optical microscopy-based studies in its sensitivity to early radiation damage of tissues, providing valuable additional information on the onset and development of the collagen matrix destruction and remodeling.

The finding of this study is that the interaction volume in electron microscopy in transmission is well ordered laterally, with a remarkable and unexpected consequence being that lateral subsections of the interaction volume produce subsections of the Kikuchi diffraction pattern. It makes the microstructure of samples directly visible in Kikuchi patterns. This is first illustrated with polycrystalline Ti–10Al–25Nb with an on-axis transmission Kikuchi diffraction set-up in a scanning electron microscope. It is then shown via a Monte Carlo simulation and a large-angle convergent-beam electron diffraction experiment that this phenomenon finds its origin in the nature of the differential elastic and quasi-elastic cross sections. This phenomenon is then quantified by a careful image analysis of Kikuchi patterns recorded across a vertical interface in a silicon sample specifically designed and fabricated. A Monte Carlo simulation reproducing all the geometric parameters is conducted. Experiments and simulations match very well qualitatively, but with a slight quantitativity gap. The specificity of the thermal diffuse scattering cross-section, not available in the simulation, is thought to be responsible for this gap. Beside Kikuchi diffraction, the case of diffraction spots and diffuse background present in the pattern is also discussed.

Layered transition metal dichalcogenides (TMDs) have attracted interest due to their promise for future electronic and optoelectronic technologies. As one approaches the two-dimensional (2D) limit, thickness and local topology can greatly influence the macroscopic properties of a material. To understand the unique behavior of TMDs it is therefore important to identify the number of atomic layers and their stacking in a sample. The goal of this work is to extract the thickness and stacking sequence of TMDs directly by matching experimentally recorded high-angle annular dark-field scanning transmission electron microscope images and convergent-beam electron diffraction (CBED) patterns to quantum mechanical, multislice scattering simulations. Advantageously, CBED approaches do not require a resolved lattice in real space and are capable of neglecting the thickness contribution of amorphous surface layers. Here we demonstrate the crystal thickness can be determined from CBED in exfoliated 1T-TaS2 and 2H-MoS2 to within a single layer for ultrathin ≲9 layers and ±1 atomic layer (or better) in thicker specimens while also revealing information about stacking order—even when the crystal structure is unresolved in real space.

Automated phase maps are an important tool for characterizing samples but the data quality must be evaluated. Common options include the overlay of phases on backscattered electron (BSE) images and phase composition averages and standard deviations. Both these methods have major limitations. We propose two methods of evaluation involving principal component analysis. First, a red–green–blue composite image of the first three principal components, which comprise the majority of the chemical variation, which provides a good reference against which phase maps can be compared. Advantages over a BSE image include discriminating between similar mean atomic number phases and sensitivity across the entire range of mean atomic numbers present in a sample. Second, principal component maps for identified phases, to examine for chemical variation within phases. This ensures the identification of unclassified phases and provides the analyst with information regarding the chemical heterogeneity of phases (e.g., chemical zoning within a mineral or mineral chemistry changing across an alteration zone). Spatial information permits a good understanding of heterogeneity within a phase and allows analytical artifacts to be easily identified. These methods of evaluation were tested on a complex geological sample. K-means clustering and K-nearest neighbor algorithms were used for phase classification, with the evaluation methods demonstrating their limitations.

Highly luminescent thin films of zinc tungstate (ZT) have been deposited on top of conventional scintillators (Yttrium Aluminum Perovskite, Yttrium Aluminum Garnet) for electron detection in order to replace the need for a top conducting layer, such as indium tin oxide (ITO) or aluminum, which is non-scintillating and electron absorbing. Such conventional conducting layers serve the single purpose of eliminating electrical charge build-up on the scintillator. The ZT film also eliminates charging, which has been verified by measuring the Duane–Hunt limit and electron emission versus accelerating voltage. The luminescent nature of the ZT film ensures effective detection of low energy electrons from the very top surface of the structure ZT/scintillator, which we call “first-surface scintillator”. The cathodoluminescence has been measured directly with a photodetector and spectrally resolved at different accelerating voltages. All results demonstrate the extended range of operation of the first-surface scintillator, while the conventional scintillators with a top ITO layer decline below 5 kV and have practically no output below 2 kV. Scintillators of different types were integrated in a detection system for backscattered electrons (BSE). The quality of the image at high accelerating voltages is comparable with the conventional scintillator and commercial BSE detector, while the image quality at 1 kV from the first-surface scintillator is superior.