Quantitative EDXS: Influence of geometry on a four detector system

Phase-Separated Structure of NBR/PVC Blends with Different Acrylonitrile Contents Investigated Using STEM-EDS Mapping Analysis

We investigated the phase-separated structure of nitrile butadiene rubber (NBR)/polyvinyl chloride (PVC) blends with different acrylonitrile (AN) contents in the NBR, using dynamic mechanical analysis measurements and scanning-transmission-electron-microscopy (STEM)-energy-dispersive-X-ray-spectroscopy (EDS) elemental analysis. Two separate sharp tan δ peaks were observed in the blend at the lower AN content of 18.0%, whereas a broad peak was observed in the blends with the higher AN contents of 29.0 and 33.5%, due to the increase in miscibility, as expected from the decrease in the solubility parameter difference with the increasing AN content. The STEM-EDS elemental analysis for the concentration distribution showed that the NBR was mixed in the large PVC domains with a diameter of several micrometers, and the excluded PVC existed around the interface of the domain-matrix phases in the blend with the lower AN content, whereas small domains with a diameter of several tens of nanometers were dispersed in the blend with the higher AN content. The concentration difference in PVC between the PVC domain and the NBR matrix became smaller with increasing miscibility as the AN content increased although the blends contained the same PVC content of 40 wt%.

Fast generation of calculated ADF-EDX scattering cross-sections under channelling conditions

Advanced materials often consist of multiple elements which are arranged in a complicated structure. Quantitative scanning transmission electron microscopy is useful to determine the composition and thickness of nanostructures at the atomic scale. However, significant difficulties remain to quantify mixed columns by comparing the resulting atomic resolution images and spectroscopy data with multislice simulations where dynamic scattering needs to be taken into account. The combination of the computationally intensive nature of these simulations and the enormous amount of possible mixed column configurations for a given composition indeed severely hamper the quantification process. To overcome these challenges, we here report the development of an incoherent non-linear method for the fast prediction of ADF-EDX scattering cross-sections of mixed columns under channelling conditions. We first explain the origin of the ADF and EDX incoherence from scattering physics suggesting a linear dependence between those two signals in the case of a high-angle ADF detector. Taking EDX as a perfect incoherent reference mode, we quantitatively examine the ADF longitudinal incoherence under different microscope conditions using multislice simulations. Based on incoherent imaging, the atomic lensing model previously developed for ADF is now expanded to EDX, which yields ADF-EDX scattering cross-section predictions in good agreement with multislice simulations for mixed columns in a core-shell nanoparticle and a high entropy alloy. The fast and accurate prediction of ADF-EDX scattering cross-sections opens up new opportunities to explore the wide range of ordering possibilities of heterogeneous materials with multiple elements.

The Performance of EDXS at Elevated Sample Temperatures Using a MEMS-Based In Situ TEM Heating System

Since the development of MEMS heating holders, dynamic in-situ experiments at elevated temperatures may be complemented by X-ray spectrometry for chemical analysis. Although the amount of IR radiation is small when compared to furnace holders, the influence of IR radiation emitted from the heating device on the quality of the X-ray spectra is significant. In this work, we systematically examine the influence of infrared (IR) radiation generated by MEMS-based in situ heating systems (DENSsolutions single- and double-tilt holders) on the results and interpretation of energy-dispersive X-ray (EDX) spectra through simulation and measurement. Focal points of interest in this study are the influence of holder geometry, shadowing and orientation with respect to the different emission characteristics of IR and X-ray photons and their interaction with a side-entry and a multi-detector system. IR photons substantially contribute to count rates, dead time, electronic noise levels, energy resolution, and detection efficiency of semiconductor detectors. At higher sample temperatures, they ultimately limit the feasibility of EDXS for elemental characterization and especially the traceability of low-Z elements. This work provides a quantitative insight into the influence of all relevant parameters related to in situ heating experiments on the spectral quality. Bearing this in mind, we aim to provide a guide to optimizing in situ heating experiments with respect to chemical EDXS analysis.

Accurate quantification of phosphorus intergranular segregation in iron by STEM-EDX

This study describes a method to quantify phosphorus grain boundary segregation by Energy Dispersive X-ray Spectroscopy in Scanning Transmission Electron Microscope (STEM-EDX). A "box-type method" is employed, removing the long-discussed problems of interaction volume and the beam broadening effect. The proposed methodology also introduces a novel way of subtracting the spectrum background to remove the influence of coherent Bremsstrahlung and spurious peaks. A Fe-P model alloy was used to compare the box method to the quantification results previously obtained by atom probe tomography on two high angle grain boundaries. The results are specifically reported in surface concentration (atom/nm²) to avoid additional hypotheses and allow the results between the two techniques to be directly compared. The measurements show that the box-type method can accurately measure phosphorus intergranular segregation in iron.

Coincidence Detection of EELS and EDX Spectral Events in the Electron Microscope

Recent advances in the development of electron and X-ray detectors have opened up the possibility to detect single events from which its time of arrival can be determined with nanosecond resolution. This allows observing time correlations between electrons and X-rays in the transmission electron microscope. In this work, a novel setup is described which measures individual events using a silicon drift detector and digital pulse processor for the X-rays and a Timepix3 detector for the electrons. This setup enables recording time correlation between both event streams while at the same time preserving the complete conventional electron energy loss (EELS) and energy dispersive X-ray (EDX) signal. We show that the added coincidence information improves the sensitivity for detecting trace elements in a matrix as compared to conventional EELS and EDX. Furthermore, the method allows the determination of the collection efficiencies without the use of a reference sample and can subtract the background signal for EELS and EDX without any prior knowledge of the background shape and without pre-edge fitting region. We discuss limitations in time resolution arising due to specificities of the silicon drift detector and discuss ways to further improve this aspect.

Electron tomography imaging methods with diffraction contrast for materials research

Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) enable the visualization of three-dimensional (3D) microstructures ranging from atomic to micrometer scales using 3D reconstruction techniques based on computed tomography algorithms. This 3D microscopy method is called electron tomography (ET) and has been utilized in the fields of materials science and engineering for more than two decades. Although atomic resolution is one of the current topics in ET research, the development and deployment of intermediate-resolution (non-atomic-resolution) ET imaging methods have garnered considerable attention from researchers. This research trend is probably not irrelevant due to the fact that the spatial resolution and functionality of 3D imaging methods of scanning electron microscopy (SEM) and X-ray microscopy have come to overlap with those of ET. In other words, there may be multiple ways to carry out 3D visualization using different microscopy methods for nanometer-scale objects in materials. From the above standpoint, this review paper aims to (i) describe the current status and issues of intermediate-resolution ET with regard to enhancing the effectiveness of TEM/STEM imaging and (ii) discuss promising applications of state-of-the-art intermediate-resolution ET for materials research with a particular focus on diffraction contrast ET for crystalline microstructures (superlattice domains and dislocations) including a demonstration of in situ dislocation tomography.

X-ray absorption in pillar shaped transmission electron microscopy specimens

The dependence of the X-ray absorption on the position in a pillar shaped transmission electron microscopy specimen is modeled for X-ray analysis with single and multiple detector configurations and for different pillar orientations relative to the detectors. Universal curves, applicable to any pillar diameter, are derived for the relative intensities between weak and medium or strongly absorbed X-ray emission. For the configuration as used in 360° X-ray tomography, the absorption correction for weak and medium absorbed X-rays is shown to be nearly constant along the pillar diameter. Absorption effects in pillars are about a factor 3 less important than in planar specimens with thickness equal to the pillar diameter. A practical approach for the absorption correction in pillar shaped samples is proposed and its limitations discussed. The modeled absorption dependences are verified experimentally for pillars with HfO₂ and SiGe stacks.