In the present paper, as part of an interdisciplinary research project (Priority Programme SPP2045), we propose a possible way to design an open access archive for particle-discrete tomographic datasets: the PARROT database (https://parrot.tu-freiberg.de). This archive is the result of a pilot study in the field of particle technology and three use cases are presented for illustrative purposes. Instead of providing a detailed instruction manual, we focus on the methodologies of such an archive. The presented use cases stem from our working group and are intended to demonstrate the advantage of using such an archive with concise and consistent data for potential and ongoing studies. Data and metadata merely serve as examples and need to be adapted for disciplines not concerned here. Since all datasets within the PARROT database and its source code are freely accessible, this study represents a starting point for similar projects.

Laboratory transmission soft X-ray microscopy (L-TXM) has emerged as a complementary tool to synchrotron-based TXM and high-resolution biomedical 3D imaging in general in recent years. However, two major operational challenges in L-TXM still need to be addressed: a small field of view and a potentially misaligned rotation stage. As it is not possible to alter the magnification during operation, the field of view in L-TXM is usually limited to a few tens of micrometers. This complicates locating areas and objects of interest in the sample. Additionally, if the rotation axis of the sample stage cannot be adjusted prior to the experiments, an efficient workflow for tomographic imaging cannot be established, as refocusing and sample repositioning will become necessary after each recorded projection. Both these limitations have been overcome with the integration of a visible-light microscope (VLM) into the L-TXM system. Here, we describe the calibration procedure of the goniometer sample stage and the integrated VLM and present the resulting 3D imaging of a test sample. In addition, utilizing this newly integrated VLM, the extracellular matrix of cryofixed THP-1 cells (human acute monocytic leukemia cells) was visualized by L-TXM for the first time in the context of an ongoing biomedical research project.

Ancient Roman concrete presents exceptional durability, low-carbon footprint, and interlocking minerals that add cohesion to the final composition. Understanding of the structural characteristics of these materials using X-ray tomography (XRT) is of paramount importance in the process of designing future materials with similar complex heterogeneous structures. We introduce Materials Data Science algorithms centered on image analysis of XRT that support inspection and quantification of microstructure from ancient Roman concrete samples. By using XRT imaging, we access properties of two concrete samples in terms of three different material phases as well as estimation of materials fraction, visualization of the porous network and density gradients. These samples present remarkable durability in comparison with the concrete using Portland cement and nonreactive aggregates. Internal structures and respective organization might be the key to construction durability as these samples come from ocean-submersed archeological findings dated from about two thousand years ago. These are preliminary results that highlight the advantages of using non-destructive 3D XRT combined with computer vision and machine learning methods for systematic characterization of complex and irreproducible materials such as archeological samples. One significant impact of this work is the ability to reduce the amount of data for several computations to be held at minimalistic computational infrastructure, near real-time, and potentially during beamtime while materials scientists are still at the imaging facilities.

We report a novel strategy to render stainless steel (SS) a more versatile material that is suitable to be used as the substrate for preparing electrodes for efficient hydrogen evolution by interface engineering. Our strategy involves the growth of carbon nanotubes (CNTs) by atmospheric pressure chemical vapor deposition (APCVD) as the interface material on the surface of SS. We optimized the procedure to prepare CNTs/SS and demonstrate a higher activity of the CNTs/SS prepared at 700 °C for the hydrogen evolution reaction (HER) when compared to samples prepared at other temperatures. This can be attributed to the higher number of defects and the higher content of pyrrolic N obtained at this temperature. Our strategy offers a new approach to employ SS as a substrate for the preparation of highly efficient electrodes and has the potential to be widely used in electrochemistry.

Bamboo is a natural composite and one of the most efficient structures in nature because of the relationship of mechanical properties with its microstructural features. This research presents the 3D characterization of the reinforcement bundles of a branching nodal region of bamboo, through high-resolution X-ray microtomography (µCT). µCT was used to characterize a sample regarding the volume, relative density, and porosity of parenchyma and sclerenchyma tissues, and the resulting data were used to estimate their constitutive properties. A nonlinear finite element analysis (FEA) was performed based on a discretized model of the µCT to the limiting compressive load. Secondary bundles presented an interweaved arrangement into the primary vascular elements that distribute axial compressive stresses into new branches. Our findings suggest that the foam-like behavior of the parenchyma, the sclerenchyma thickening above the nodal zone, and the nodal vascular branching are ways for bamboo to protect important tissues from mechanical stress by allocating axial loads. In addition, such mechanism could be applied in the design of biomimetic structures with selective load-bearing capabilities.

High resolution (< 1 µm) computed tomography is an attractive tool in materials research due to its ability to non-destructively visualize the three-dimensional internal microstructures of the material. Recently, this technique has been further empowered by adding a fourth (temporal) dimension to study the time-lapse material response under load. Such studies are referred to as four-dimensional or in situ testing. In this snapshot review, we highlight three representative examples of in situ testing using synchrotron radiation computed tomography (SRCT) for composites failure analysis, measurement of local corrosion rate in alloys, and visualization and quantification of electrochemical reactions in lithium-ion batteries, as well as forward-looking integration of machine learning with in situ CT. Lastly, the future opportunities and challenges of in situ SRCT testing are discussed.

X-ray micro-computed tomography (μCT) is a technique which can obtain three-dimensional images of a sample, including its internal structure, without the need for destructive sectioning. Here, we review the capability of the technique and examine its potential to provide novel insights into the lifestyles of parasites embedded within host tissue. The current capabilities and limitations of the technology in producing contrast in soft tissues are discussed, as well as the potential solutions for parasitologists looking to apply this technique. We present example images of the mouse whipworm Trichuris muris and discuss the application of μCT to provide unique insights into parasite behaviour and pathology, which are inaccessible to other imaging modalities.

Soft X-ray spectro-tomography provides three-dimensional (3D) chemical mapping based on natural X-ray absorption properties. Since radiation damage is intrinsic to X-ray absorption, it is important to find ways to maximize signal within a given dose. For tomography, using the smallest number of tilt series images that gives a faithful reconstruction is one such method. Compressed sensing (CS) methods have relatively recently been applied to tomographic reconstruction algorithms, providing faithful 3D reconstructions with a much smaller number of projection images than when conventional reconstruction methods are used. Here, CS is applied in the context of scanning transmission X-ray microscopy tomography. Reconstructions by weighted back-projection, the simultaneous iterative reconstruction technique, and CS are compared. The effects of varying tilt angle increment and angular range for the tomographic reconstructions are examined. Optimization of the regularization parameter in the CS reconstruction is explored and discussed. The comparisons show that CS can provide improved reconstruction fidelity relative to weighted back-projection and simultaneous iterative reconstruction techniques, with increasingly pronounced advantages as the angular sampling is reduced. In particular, missing wedge artifacts are significantly reduced and there is enhanced recovery of sharp edges. Examples of using CS for low-dose scanning transmission X-ray microscopy spectroscopic tomography are presented.

Indirect detection is a versatile way to detect hard x-rays. It is based on an x-ray-to-light converter, optical coupling, and a visible light detector. The converter screen, known as a scintillator, is deployed in both imaging and point detection, using either signal integration or counting. Two applications are explored in this review—sample examination and x-ray beam diagnostics for synchrotron sources. A large variety of scintillators are available to fulfill the needs of synchrotron applications. High dynamic range, small pixel size, and radiation hardness are the major advantages of scintillators. This article provides a review of the technical and scientific aspects of scintillators used in synchrotron radiation (i.e., storage rings and x-ray free-electron lasers). The advantages and drawbacks of implementation of the most popular scintillators on synchrotron beamlines are described.

Three-dimensional (3D) tomography using electrons and x-rays has pushed and expanded our understanding of the micro- and nanoscale spatial organization of inorganic, organic, and biological materials. While a significant impact on the field of materials science has already been realized from tomography applications, new advanced methods are quickly expanding the versatility of this approach to better link structure, composition, and function of complex 3D assemblies across multiple scales. In this article, we highlight several frontiers where new developments in tomography are empowering new science across biology, chemistry, and physics. The five articles that appear in this issue of MRS Bulletin describe some of these latest developments in detail, including analytical electron tomography, atomic resolution electron tomography, advanced recording schemes in scanning transmission electron microscopy (STEM) tomography, cryo-STEM tomography of whole cells, and multiscale correlative tomography.

This article highlights recent advances in analytical electron tomography (AET), the three-dimensional (3D) extension of conventional nanoanalytical techniques, in which electron energy loss, x-ray spectroscopy, and electron diffraction are combined with tomographic acquisition and reconstruction. Examples from the literature illustrate how new 3D information, gleaned from AET, provides insights into not just morphology and composition, but also the electronic, chemical, and optical properties of materials at the nanoscale. We describe how the “multidimensional” nature of AET leads to “big data” sets, how these can be analyzed optimally, and how AET may develop further.

The intricate hierarchical microstructures typical of biological materials give rise to fascinating combinations of anisotropic mechanical properties that can surpass those of man-made materials. The linking together of three-dimensional (3D) imaging techniques has the potential to reveal these structures in unprecedented detail. However, a complete understanding can only be reached if the relationship between structure and mechanical properties can be elucidated. X-ray-computed tomography (CT) is uniquely placed to image such structures across a wide range of length scales. We review recent technical advances that are leading to improved contrast and spatial resolution. We highlight how time-lapse CT 3D studies can track the response of hierarchical microstructures to mechanical loading.

Dark-field x-ray microscopy is a new way to three-dimensionally map lattice strain and orientation in crystalline matter. It is analogous to dark-field electron microscopy in that an objective lens magnifies diffracting features of the sample; however, the use of high-energy synchrotron x-rays means that these features can be large, deeply embedded, and fully mapped in seconds to minutes. Simple reconfiguration of the x-ray objective lens allows intuitive zooming between different scales down to a spatial and angular resolution of 100 nm and 0.001°, respectively. Three applications of the technique are presented—mapping the evolution of subgrains during the processing of plastically deformed aluminum, mapping domains and strain fields in ferroelectric crystals, and the three-dimensional mapping of strain fields around individual dislocations. This ability to directly characterize complex, multiscale phenomena in situ is a key step toward formulating and validating multiscale models that account for the entire heterogeneity of materials.

The structural evolution of snow under metamorphism is one of the key challenges in snow modeling. The main driving forces for metamorphism are curvature differences and temperature gradients, inducing water vapor transport and corresponding crystal growth, which is detectable by the motion of the ice/air interface. To provide quantitative means for a microscopic validation of metamorphism models, a VTK-based image analysis method is developed to track the ice/air interface in time-lapse μCT experiments to measure local interface velocities under both, isothermal and temperature gradient conditions. Using estimates of local temperatures from microstructure-based finite element simulations, a quantitative comparison of measured interface velocities with theoretical expressions is facilitated. For isothermal metamorphism, the data are compared with a kinetics and a diffusion limited growth law. In both cases the data are largely scattered but consistently show a mean curvature dependency of the interface velocity. For temperature gradient metamorphism, we confirm that the main contribution stems from the temperature gradient induced vapor flux, accompanied by effects of mean curvature as a secondary process. The scatter and uncertainties are discussed in view of the present theoretical understanding, the experimental setup and complications such as mechanical deformations.

Near real-time visualization of complex two-phase flow in a porous medium was demonstrated with dynamic 4-dimensional (4D) (3D + time) imaging at the 2-BM beam line of the Advanced Photon Source (APS) at Argonne National Laboratory. Advancing fluid fronts through tortuous flow paths and their interactions with sand grains were clearly captured, and formations of air bubbles and capillary bridges were visualized. The intense X-ray photon flux of the synchrotron facility made 4D imaging possible, capturing the dynamic evolution of both solid and fluid phases. Computed Tomography (CT) scans were collected every 12 s with a pixel size of 3.25 μm. The experiment was carried out to improve understanding of the physics associated with two-phase flow. The results provide a source of validation data for numerical simulation codes such as Lattice-Boltzmann, which are used to model multi-phase flow through porous media.

New material phases formed under non-equilibrium conditions at pressures above 100 GPa and temperatures exceeding 104K, the conditions of the warm dense matter (WDM), have become accessible using micro-explosions triggered by ultra-short sub-1 ps pulses tightly focused into micro-volume with cross sections comparable with the wavelength of light. Laser-induced micro-explosions convert a material in a focal volume into a non-equilibrium disordered plasma state confined inside the bulk of pristine crystal. Ultra-high quenching rates overcome kinetic barriers to the formation of new metastable high pressure phases, which are preserved in the surrounding pristine crystal for following recovery and exploitation. Direct laser writing was used to pattern large areas by closely packed arrays of the microexplosion modified sites for structural characterisation of the minute volumes of nano-materials with transmission electron microscopy, diffraction and synchrotron X-ray diffraction. The method of ultrafast-laser induced confined microexplosion is demonstrated for modification and creation of new phases in case of bcc-Al inside sapphire, valence change of Fe-ions in olivine, formation of new tetragonal bt8 and st12 phases of silicon, Ge and O separation in GeO2 glass and molecular oxygen formation inside voids at the site of microexplosion inside glasses.

Microwave sintering is a novel and efficient technology for the rapid preparation of metallic materials. In this paper, an investigation has been performed on the distribution of microwave electromagnetic fields in a metallic particle system and its influence on sintering behavior. The results show that the microstructure of the “metallic-void” will induce a nonuniform distribution and focusing effect of electromagnetic fields during microwave processing, which may accelerate the sintering process. However, further study shows that the focusing effect will decline as the neck grows larger, and will also decline from outside to inside within the loosely packed powder system, which will result in the slowdown of the sintering rate. These results were supported by the synchrotron radiation computed tomography experimental observation of the microstructure evolution of metallic powders during an entire uninterrupted microwave sintering process.

Computed tomography (CT) is an important tool in clinical diagnostic imaging enabling three-dimensional anatomic imaging at high spatial resolution with short scan times. However, X-ray attenuation differences in physiological fluids and soft tissues are relatively small, requiring the use of contrast agents to achieve sufficient imaging contrast. Recent advances in energy-sensitive X-ray detectors have made spectral (color) CT commercially feasible by unmixing the energy-dependent attenuation profile of different materials and will potentially enable molecular imaging in CT. In order to leverage these capabilities for diagnostic imaging, we are developing a spectral library of nanoparticle contrast agents with K-shell absorption edges spaced at least 10 keV apart. The objective of this study was to demonstrate the ability of spectral CT to simultaneously detect up to three different contrast agents and unmixed their signals to create color images. Gadolinium oxide (Gd), hafnium oxide (Hf) and gold (Au) were chosen due to exhibiting K-edges spaced 10-20 keV apart. Core-shell nanoparticles of each composition were synthesized by various methods to have a core diameter of 15-20 nm and were coated with a silica shell at least 2-4 nm in thickness to create a common platform for surface functionalization. The contrast agents were imaged in a soft tissue equivalent phantom using source-side method for spectral CT imaging. The source-side approach utilized monochromatic synchrotron radiation at the Argonne National Laboratory which, while not clinically applicable, served as a gold standard due to providing the highest spectral resolution. The nanoparticles designed for this study have broad applications in biomedical imaging due to their modular assembly, potential for enabling multi-modal detection, and surface functionalization with biomolecules (e.g., antibodies, peptides or enzymes) for active targeting.

In order to better understand the micrometer-scale structure of rock and its transport properties which arise from it, seven monomineral samples from two sites (Olkiluoto and Sievi, Finland) were studied with micro- and nanotomography and scanning electron microscopy. From the veined gneiss of Olkiluoto we studied biotite, potassium feldspar, plagioclase (composition of oligoclase) and cordierite, and from Sievi tonalite biotite and two grains of plagioclase (albite). These minerals were the main minerals of these samples. Samples were carefully separated and selected using heavy liquid separation and stereomicroscopy, their three dimensional structure was imaged using X-ray tomography, and their precise mineral composition was determined using scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS). The micrometer-scale mineral structure of these samples was observed together with their pores and fissures, and alteration effects were identified whenever applicable. Nanotomography combined with SEM analysis was concluded to be a good tool for analyzing effects of alteration in monomineral samples.