Diffractive small angle X-ray scattering imaging for anisotropic structures

High Toughness Combined with High Strength in Oxide Ceramic Nanofibers

Traditional oxide ceramics are inherently brittle and highly sensitive to defects, making them vulnerable to failure under external stress. As such, endowing these materials with high strength and high toughness simultaneously is crucial to improve their performance in most safety-critical applications. Fibrillation of the ceramic materials and further refinement of the fiber diameter, as realized by electrospinning, are expected to achieve the transformation from brittleness to flexibility owing to the structural uniqueness. Currently, the synthesis of electrospun oxide ceramic nanofibers must rely on an organic polymer template to regulate the spinnability of the inorganic sol, whose thermal decomposition during ceramization will inevitably lead to pore defects, and seriously weaken the mechanical properties of the final nanofibers. Here, a self-templated electrospinning strategy is proposed for the formation of oxide ceramic nanofibers without adding any organic polymer template. An example is given to show that individual silica nanofibers have an ideally homogeneous, dense, and defect-free structure, with tensile strength as high as 1.41 GPa and toughness up to 34.29 MJ m-3 , both of which are far superior to the counterparts prepared by polymer-templated electrospinning. This work provides a new strategy to develop oxide ceramic materials that are strong and tough.

Exploration of the X-ray Dark-Field Signal in Mineral Building Materials

Mineral building materials suffer from weathering processes such as salt efflorescence, freeze-thaw cycling, and microbial colonization. All of these processes are linked to water (liquid and vapor) in the pore space. The degree of damage following these processes is heavily influenced by pore space properties such as porosity, pore size distribution, and pore connectivity. X-ray computed micro-tomography (µCT) has proven to be a valuable tool to non-destructively investigate the pore space of stone samples in 3D. However, a trade-off between the resolution and field-of-view often impedes reliable conclusions on the material's properties. X-ray dark-field imaging (DFI) is based on the scattering of X-rays by sub-voxel-sized features, and as such, provides information on the sample complementary to that obtained using conventional µCT. In this manuscript, we apply X-ray dark-field tomography for the first time on four mineral building materials (quartzite, fired clay brick, fired clay roof tile, and carbonated mineral building material), and investigate which information the dark-field signal entails on the sub-resolution space of the sample. Dark-field tomography at multiple length scale sensitivities was performed at the TOMCAT beamline of the Swiss Light Source (Villigen, Switzerland) using a Talbot grating interferometer. The complementary information of the dark-field modality is most clear in the fired clay brick and roof tile; quartz grains that are almost indistinguishable in the conventional µCT scan are clearly visible in the dark-field owing to their low dark-field signal (homogenous sub-voxel structure), whereas the microporous bulk mass has a high dark-field signal. Large (resolved) pores on the other hand, which are clearly visible in the absorption dataset, are almost invisible in the dark-field modality because they are overprinted with dark-field signal originating from the bulk mass. The experiments also showed how the dark-field signal from a feature depends on the length scale sensitivity, which is set by moving the sample with respect to the grating interferometer.

Engineered Bacterial Outer Membrane Vesicles as Controllable Two-Way Adaptors to Activate Macrophage Phagocytosis for Improved Tumor Immunotherapy

The most immune cells infiltrating tumor microenvironment (TME), tumor-associated macrophages (TAMs) closely resemble immunosuppressive M2-polarized macrophages. Moreover, tumor cells exhibit high expression of CD47 "don't eat me" signal, which obstructs macrophage phagocytosis. The precise and efficient activation of TAMs is a promising approach to tumor immunotherapy; however, re-education of macrophages remains a challenge. Bacteria-derived outer membrane vesicles (OMVs) are highly immunogenic nanovesicles that can robustly stimulate macrophages. Here, an OMV-based controllable two-way adaptor is reported, in which a CD47 nanobody (CD47nb) is fused onto OMV surface (OMV-CD47nb), with the outer surface coated with a polyethylene glycol (PEG) layer containing diselenide bonds (PEG/Se) to form PEG/Se@OMV-CD47nb. The PEG/Se layer modification not only mitigates the immunogenicity of OMV-CD47nb, thereby remarkedly increasing the dose that can be administered safely through intravenous injection, but also equips the formulation with radiation-triggered controlled release of OMV-CD47nb. Application of radiation to tumors in mice injected with the nanoformulation results in remodeling of TME. As two-way adaptors, OMV-CD47nb activates TAM phagocytosis of tumor cells via multiple pathways, including induction of M1 polarization and blockade of "don't eat me" signal. Moreover, this activation of TAMs results in the stimulation of T cell-mediated antitumor immunity through effective antigen presentation.

X-ray directional dark-field imaging using Unified Modulated Pattern Analysis

X-ray directional dark-field imaging is a recent technique that can reveal a sample’s small-scale structural properties which are otherwise invisible in a conventional imaging system. In particular, directional dark-field can detect and quantify the orientation of anisotropic structures. Here, we present an algorithm that allows for the extraction of a directional dark-field signal from X-ray speckle-based imaging data. The experimental setup is simple, as it requires only the addition of a diffuser to a full-field microscope setup. Sandpaper is an appropriate diffuser material in the hard x-ray regime. We propose an approach to extract the mean scattering width, directionality, and orientation from the recorded speckle images acquired with the technique. We demonstrate that our method can detect and quantify the orientation of fibres inside a carbon fibre reinforced polymer (CFRP) sample within one degree of accuracy and show how the accuracy depends on the number of included measurements. We show that the reconstruction parameters can be tuned to increase or decrease accuracy at the expense of spatial resolution.

High-resolution and sensitivity bi-directional x-ray phase contrast imaging using 2D Talbot array illuminators

Two-dimensional (2D) Talbot array illuminators (TAIs) were designed, fabricated, and evaluated for high-resolution high-contrast x-ray phase imaging of soft tissue at 10-20 keV. The TAIs create intensity modulations with a high compression ratio on the micrometer scale at short propagation distances. Their performance was compared with various other wavefront markers in terms of period, visibility, flux efficiency, and flexibility to be adapted for limited beam coherence and detector resolution. Differential x-ray phase contrast and dark-field imaging were demonstrated with a one-dimensional, linear phase stepping approach yielding 2D phase sensitivity using unified modulated pattern analysis (UMPA) for phase retrieval. The method was employed for x-ray phase computed tomography reaching a resolution of 3 µm on an unstained murine artery. It opens new possibilities for three-dimensional, non-destructive, and quantitative imaging of soft matter such as virtual histology. The phase modulators can also be used for various other x-ray applications such as dynamic phase imaging, super-resolution structured illumination microscopy, or wavefront sensing.

Fast acquisition protocol for X-ray scattering tensor tomography

Microstructural information over an entire sample is important to understand the macroscopic behaviour of materials. X-ray scattering tensor tomography facilitates the investigation of the microstructural organisation in statistically large sample volumes. However, established acquisition protocols based on scanning small-angle X-ray scattering and X-ray grating interferometry inherently require long scan times even with highly brilliant X-ray sources. Recent developments in X-ray diffractive optics towards circular pattern arrays enable fast single-shot acquisition of the sample scattering properties with 2D omnidirectional sensitivity. X-ray scattering tensor tomography with the use of this circular grating array has been demonstrated. We propose here simple yet inherently rapid acquisition protocols for X-ray scattering tensor tomography leveraging on these new optical elements. Results from both simulation and experimental data, supported by a null space analysis, suggest that the proposed acquisition protocols are not only rapid but also corroborate that sufficient information for the accurate volumetric reconstruction of the scattering properties is provided. The proposed acquisition protocols will build the basis for rapid inspection and/or time-resolved tensor tomography of the microstructural organisation over an extended field of view.

Tunable X-ray dark-field imaging for sub-resolution feature size quantification in porous media

X-ray computed micro-tomography typically involves a trade-off between sample size and resolution, complicating the study at a micrometer scale of representative volumes of materials with broad feature size distributions (e.g. natural stones). X-ray dark-field tomography exploits scattering to probe sub-resolution features, promising to overcome this trade-off. In this work, we present a quantification method for sub-resolution feature sizes using dark-field tomograms obtained by tuning the autocorrelation length of a Talbot grating interferometer. Alumina particles with different nominal pore sizes (50 nm and 150 nm) were mixed and imaged at the TOMCAT beamline of the SLS synchrotron (PSI) at eighteen correlation lengths, covering the pore size range. The different particles cannot be distinguished by traditional absorption µCT due to their very similar density and the pores being unresolved at typical image resolutions. Nevertheless, by exploiting the scattering behavior of the samples, the proposed analysis method allowed to quantify the nominal pore sizes of individual particles. The robustness of this quantification was proven by reproducing the experiment with solid samples of alumina, and alumina particles that were kept separated. Our findings demonstrate the possibility to calibrate dark-field image analysis to quantify sub-resolution feature sizes, allowing multi-scale analyses of heterogeneous materials without subsampling.

Laboratory X-ray interferometry imaging with a fan-shaped source grating

The orientation mismatch between the cone beam of an X-ray tube and the grating lines in a flat substrate remains a big challenge for laboratory grating-based X-ray interferometry, since it severely limits the imaging field of view. Here, we fabricated fan-shaped G₀ source gratings by modulating the electric field during the deep reactive ion etching of silicon. The gold electroplated fan-shaped G₀ grating (3.0 µm pitch) in a 20 keV interferometer improves the uniformity of the field of view with an increase of average visibility from 16.2% to 18.5% and a better angular sensitivity (by a factor 5.8) at the edges.

Fabrication of X-ray Gratings for Interferometric Imaging by Conformal Seedless Gold Electroplating

We present a method to produce small pitch gratings for X-ray interferometric imaging applications, allowing the phase sensitivity to be increased and/or the length of the laboratory setup to be minimized. The method is based on fabrication of high aspect ratio silicon microstructures using deep reactive ion etching (Bosch technique) of dense grating arrays and followed by conformal electroplating of Au. We demonstrated that low resistivity Si substrates (<0.01 Ohm·cm) enable the metal seeding layer deposition step to be avoided, which is normally required to initiate the electroplating process. Etching conditions were optimized to realize Si recess structures with a slight bottom tapering, which ensured the void-free Au filling of the trenches. Vapor HF was used to remove the native oxide layer from the Si grating surface prior to electroplating in the cyanide-based Au electrolyte. Fabrication of Au gratings with pitch in the range 1.2-3.0 µm was successfully realized. A substantial improved aspect ratio of 45:1 for a pitch size of 1.2 µm was achieved with respect to the prior art on 4-inch wafer-based technology. The fabricated Au gratings were tested with X-ray interferometers in Talbot-Laue configuration with measured visibility of 13% at an X-ray design energy of 26 keV.

Hybrid x-ray laser-plasma/laser-synchrotron facility for pump-probe studies of the extreme state of matter at NRC "Kurchatov Institute"

We developed a hybrid optical pump-x-ray probe facility based on the "Kurchatov's synchrotron radiation source" and terawatt (TW) femtosecond laser. The bright x-ray photon source is based on either synchrotron radiation [up to 6 × 10¹⁴ photons/(s mm² mrad² 0.1% bandwidth)] or laser-plasma generators (up to 10⁸ photons/sr/pulse). The terawatt (TW) femtosecond laser pulse initiated phase transitions and a non-stationary "extreme" state of matter, while the delayed x-ray pulse acts as a probe. The synchronization between synchrotron radiation and laser pulses is achieved at 60.3 MHz using an intelligent field-programmable gate array-based phased locked loop. The timing jitter of the system is less than 30 ps. In laser-plasma sources, the x-ray and laser pulses are automatically synchronized because they are produced by using the same laser source (TW laser system). We have reached an x-ray yield of about 10⁶ photons/sr/pulse with 6-mJ sub-ps laser pulses and using helium as a local gas medium. Under vacuum conditions, the laser energy increase up to 40 mJ leads to the enhancement of the x-ray yield of up to 10⁸ photons/sr/pulse. The developed hybrid facility paves the way for a new class of time-resolved x-ray optical pump-probe experiments in the time interval from femtoseconds to microseconds and the energy spectrum from 3 to 30 keV.

Study on dark-field imaging with a laboratory x-ray source: Random stress variation analysis based on x-ray grating interferometry

The dark-field image (DFI) in a grating interferometer involves the small-angle scattering properties of a material. The microstructure of the material can be characterized by an analysis of the auto-correlation length and the DFI. The feasibility of a DFI in a laboratory x-ray source with grating interferometry has been reported, but a follow-up study is needed. In this study, the random stress distribution was measured in the laboratory environment as an applied study. SiO₂ mono-spheres as a cohesive powder with a 0.5 µm particle size were used as the sample. The microstructural changes according to the stresses on the particles were observed by acquiring a DFI along the auto-correlation length. In x-rays, a random two-phase media model was first used to analyze the characteristics of cohesive powder. This study showed that the microstructure of materials and x-ray images could be analyzed in a laboratory environment.

Modeling of beam hardening effects in a dual-phase X-ray grating interferometer for quantitative dark-field imaging

X-ray grating interferometry (XGI) can provide access to unresolved sub-pixel information by utilizing the so-called dark-field or visibility reduction contrast. A recently developed variant of conventional XGI named dual-phase grating interferometer, based only on phase-shifting structures, has allowed for straightforward micro-structural investigations over multiple length scales with conventional X-ray sources. Nonetheless, the theoretical framework of the image formation for the dark-field signal has not been fully developed yet, thus hindering the quantification of unresolved micro-structures. In this work, we expand the current theoretical formulation of dual-phase grating interferometers taking into account polychromatic sources and beam hardening effects. We propose a model that considers the contribution of beam hardening to the visibility reduction and accounts for it. Finally, the method is applied to previously acquired and new experimental data showing that discrimination between actual micro-structures and beam hardening effects can be achieved.

Metal assisted chemical etching of silicon in the gas phase: a nanofabrication platform for X-ray optics

High aspect ratio nanostructuring requires high precision pattern transfer with highly directional etching. In this work, we demonstrate the fabrication of structures with ultra-high aspect ratios (up to 10 000 : 1) in the nanoscale regime (down to 10 nm) by platinum assisted chemical etching of silicon in the gas phase. The etching gas is created by a vapour of water diluted hydrofluoric acid and a continuous air flow, which works both as an oxidizer and as a gas carrier for reactive species. The high reactivity of platinum as a catalyst and the formation of platinum silicide to improve the stability of the catalyst pattern allow a controlled etching. The method has been successfully applied to produce straight nanowires with section size in the range of 10-100 nm and length of hundreds of micrometres, and X-ray optical elements with feature sizes down to 10 nm and etching depth in the range of tens of micrometres. This work opens the possibility of a low cost etching method for stiction-sensitive nanostructures and a large range of applications where silicon high aspect ratio nanostructures and high precision of pattern transfer are required.

Single-shot, omni-directional x-ray scattering imaging with a laboratory source and single-photon localization

Omni-directional, ultra-small-angle x-ray scattering imaging provides a method to measure the orientation of micro-structures without having to resolve them. In this letter, we use single-photon localization with the Timepix3 chip to demonstrate, to the best of our knowledge, the first laboratory-based implementation of single-shot, omni-directional x-ray scattering imaging using the beam-tracking technique. The setup allows a fast and accurate retrieval of the scattering signal using a simple absorption mask. We suggest that our new approach may enable faster laboratory-based tensor tomography and could be used for energy-resolved x-ray scattering imaging.

Recent Progress in X-ray and Neutron Phase Imaging with Gratings

Under the JST-ERATO project in progress to develop X-ray and neutron phase-imaging methods together, recent achievements have been selected and reviewed after describing the merit and the principle of the phase imaging method. For X-ray phase imaging, recent developments of four-dimensional phase tomography and phase microscopy at SPring-8, Japan are mainly presented. For neutron phase imaging, an approach in combination with the time-of-flight method developed at J-PARC, Japan is described with the description of new Gd grating fabrication.