The development of grating fabrication shares its journey with the development of X-ray phase contrast imaging. Indeed, the fabrication of gratings with features of sufficiently high aspect ratio is one of the bottlenecks preventing the widespread application of phase contrast imaging in X-ray diagnostics, material science and security. The silicon platform that underlies modern manufacture of integrated circuits, with its well-established technologies for lithography, etching and metal deposition, has the potential to provide high yields and volumes for industrial fabrication of both phase and absorption gratings used in a grating-based X-ray imaging systems. This review article introduces recent developments in the fabrication of high aspect ratio X-ray gratings using ubiquitous clean-room manufacturing tools, focusing on deep reactive ion etching processes. It summarizes the most challenging issues for fabricating features with aspect ratios reaching 70:1, proposing approaches to overcome processing problems and improve product quality.

This work details the combination of displacement Talbot lithography, deep reactive ion etching of silicon, and bottom-up gold electrochemical deposition to produce void-free gold microgratings with 700 nm wide Au lines of 27 mu m depth, corresponding to an aspect ratio (depth/width) of 38 with vertical sidewall. Systematic optimization of the grating design and manufacturing processes yielded high-quality sub-micrometer gold gratings with precisely controlled structural profiles, minimal deviation of the duty cycle as a function of depth and absence of voids in the Au filling. A symmetric X-ray grating interferometer at 20 keV design energy with 1.2 mu m pitch gratings showcases the application.

BACKGROUND:Breast cancer remains the most prevalent malignancy among women worldwide. When suspicious lesions are detected, standard clinical workflows rely on histopathological evaluation of excised tissue (biopsy) and the choice of preoperative systemic therapies or primary surgical excision. This study explores the potential of X-ray grating-interferometry (GI)-based micro-computed tomography (μCT) as a complementary virtual tool to the gold-standard conventional histopathology Methods: Small (up to 2 cm) residual samples from 20 formalin-fixed mastectomy specimens (from 19 patients) underwent imaging using GI-based μCT and were subsequently processed for routine histology. Diagnostic concordance between gold-standard histological sections and μCT images was established with input from an expert pathologist and an expert radiologist Results: GI-based μCT enabled differentiation of neoplastic and benign findings from surrounding tissue based on morphology and gray-value contrast. While μCT lacks the cellular resolution of histology, its 3D volumetric data provided valuable spatial context for small structures. Imaging a 2 cm specimen required approximately 13.4 h, with negligible degradation in diagnostic image quality when the acquisition time was reduced to 4.4 h Conclusions: GI-based μCT demonstrates strong potential as an adjunct to gold-standard histopathology, providing high-quality soft-tissue contrast comparable to conventional μCT and aiding in the identification of regions of interest for further tissue-based analysis. The possible clinical utility of GI-based μCT diagnostics needs further clinical evaluation, also on smaller samples.

Reliable and precise etching of silicon nanostructures with ultra-high aspect ratios is required in many fields. Metal assisted chemical etching (MacEtch) in vapor is a plasma-free etching method that attracts considerable attention owing to the ability to create smooth, high aspect ratio nanostructures. MacEtch understanding and applications are limited by low fidelity and inconsistent pattern transfer from the catalyst layer to the silicon substrate. The locally constrained electrochemical interactions at the catalyst site make MacEtch particularly sensitive to catalyst contamination reducing the reaction rate and pinning the catalyst during etching. Removing contaminants is essential to improve pattern transfer for reliable processes on a larger area and higher aspect ratio. Physically separating the main source of carbon - the resist - from the catalyst with a sacrificial and functional interlayer solves this issue. The interlayer separates the resist and the catalyst and allows for thorough cleaning of the substrate before catalyst deposition. The resulting clean catalyst has improved stability, quality and reproducibility, enabling reliable fabrication of dense (50

Reliable and precise etching of silicon nanostructures with ultra-high aspect ratios is required in many fields. Metal-assisted chemical etching (MacEtch) in HF vapor and O2 is a plasma-free etching method that attracts considerable attention owing to its ability to create smooth, high aspect ratio nanostructures. MacEtch understanding and applications are limited by low fidelity and inconsistent pattern transfer from the catalyst layer to the silicon substrate. The locally constrained electrochemical interactions at the catalyst site make MacEtch particularly sensitive to catalyst contamination, which reduces the reaction rate and pins the catalyst during etching. Removing contaminants is essential to improve pattern transfer for reliable processes over a larger area and with a higher aspect ratio. Physically separating the main source of carbon, the resist, from the catalyst with a sacrificial and functional interlayer solves this issue. The interlayer separates the resist and the catalyst and allows thorough cleaning of the substrate before catalyst deposition. The resulting clean catalyst enables the fabrication of dense (50% patterned area) high aspect ratio (>250:1) nanostructures. Different interlayer materials (Cr, Al2O3, and SiO2) and two patterning approaches are presented, showcasing etching of various high aspect ratio nanostructures, such as X-ray optics.

Wave-front propagation simulations have been a tool to design and optimize X-ray interferometry devices. The often used plane wave approaches, however, lack the angular resolution to describe effects like system imperfections or inhomogeneous samples in conjunction with the X-ray source size. We developed a framework that allows to simulate optical components as well as samples with any source size in arbitrary configurations by inducing the mentioned effects within the wave propagation instead of adding intermediate models. The simulation results were able to predict and explain the impact of local grating defects for different focal spot sizes and provided a spectral sampling optimization for image acquisition. The simulation framework can run on GPU, do out-of-memory calculations, and is publicly available on Github.

Etching makes a pattern design a real 3D object [...]

A Bi3+ -stimulated Au electrodeposition process in slightly alkaline Na3AuSO32+Na2SO3 electrolytes has been previously demonstrated for void-free bottom-up filling of progressively deeper and higher aspect trenches in gratings for advanced X-ray imaging technologies. The present work extends this bottom-up Au filling phenomenon to improve filling of small trenches. In particular, electrolytes are examined to reduce passive deposition on the sidewalls, demonstrating the feasibility of filling high aspect ratio features well into the sub-micrometer range. Improved Au fill in dense 1 mu m pitch gratings with V-shaped trenches is detailed.

The performance of an X-ray grating interferometry system depends on the geometry and quality of the gratings. Fabrication of micrometer-pitch high-aspect-ratio gold gratings, which are essential for measuring small refraction angles at higher energies, is challenging. The two widely used technologies for manufacturing gratings are based on gold electroplating in polymeric or silicon templates. Here, gratings manufactured by both approaches were inspected using conventional microscopy, X-ray synchrotron radiography, and computed laminography to extract characteristic features of the gratings profile to be modeled accurately. These models were used in a wave-propagation simulation to predict the effects of the gratings’ geometry and defects on the quality of a Talbot-Lau interferometer in terms of visibility and absorption capabilities. The simulated outcomes of grating features produced with both techniques could eventually be observed and evaluated in a table-top Talbot-Lau-Interferometer.

BACKGROUND:X-ray grating interferometry has emerged as a promising imaging technique for breast computed tomography (BCT), offering complementary contrast from refraction beyond conventional absorption imaging. Although it provides higher resolution, the required dose levels remain above those typically used for breast cancer diagnostic imaging. PURPOSE:This study aims to design an optimized grating interferometry-based BCT system using a novel optimization metric that simultaneously maximizes signal strength from refraction and attenuation while considering grating fabrication and system constraints. METHODS:A systematic grid search was conducted to identify system configurations that optimize contrast-to-noise ratio while accounting for dose efficiency in both attenuation and refraction. The optimized system was benchmarked against a commercial absorption-based BCT system and a previously published grating interferometry design. Simulations were performed using in silico breast phantoms of varying diameters, incorporating realistic imaging conditions and noise modeling across dose levels from 1 to 100 mGy. Additionally, a signal fusion technique was applied to combine the two contrast channels. RESULTS:Quantitative analysis demonstrates that refraction provides superior contrast for small malignancies, while absorption remains beneficial for larger lesions. Fusing both contrast channels enhances the contrast-to-noise ratio and improves resolution in in silico reconstructed images, outperforming conventional absorption-based BCT at dose levels relevant for breast cancer diagnostic imaging. CONCLUSIONS:The findings suggest that an optimized grating interferometry-based BCT system can improve image quality by effectively combining absorption and refraction signals. This work underscores the need to balance imaging performance with practical implementation constraints, offering a framework that may extend to other imaging applications beyond breast cancer detection.

Lung diseases such as chronic obstructive pulmonary disease are a major health burden to society for which early detection plays a crucial role for treatment success. For detection, as well as diagnosis and serial evaluation, imaging plays a major role, but lung diseases are often still diagnosed in progressed states for which effective causal therapies do not presently exist. Recently, dark-field lung imaging has been introduced as a promising technique for early stage detection of alterations in lung micro-structures. This work presents an analyzer-free, full-scale lung imaging system based on a dual-phase interferometer, which allows tuning and direct resolution of grating induced intensity fringes. It provides the classical absorption chest image with additional dark-field information without significant attenuation of the patient-exposed photon-flux or the cost of large area absorption gratings. The detailed system achieves a dark-field sensitivity adequate for lung imaging, governed by system autocorrelation lengths of up to 0.6 [Formula: see text]. The computed tomography (CT) reconstructions show further evidence of the emergence of the dark-field in the parenchyma.

Field enhancement effect (FEE) is a physical phenomenon widely investigated in the context of field emitters and nanophotonic devices, where electromagnetic fields can be enhanced significantly at geometrically sharp boundaries. Here, we propose and report the FEE in the plasma sheath when geometrically sharp silicon microstructures are plasma processed by reactive ion etch (RIE). When a thin film covers the silicon structures, argon ions preferentially etch the thin films at sharp geometries due to FEE. The FEE “hotspots” are clearly visualized by adding a subsequent isotropic RIE process using SF6 chemistry. We correlated the dimensions of the hotspot profiles to the field enhancement factor (FEF). Finite element methods investigated the dependence of tip aspect ratio, the FEF, and the dimensions of hotspot profiles for hemisphere-on-cone and elliptic geometries. The critical FEF was determined to be 1000 to 2500 with Si substrate and a specified plasma condition. The knowledge gained from this study predicts FEE in plasma processing, and we apply it to fabricate nanocavities and large- area mapping electric fields for plasma diagnostics. Our study provides new insights into the plasma processing of sharp geometries, which are essential for robust chip fabrication, as the device size shrinks due to Moore’s Law and FEE in device fabrication becomes ubiquitous.

Metal-assisted chemical etching of silicon, especially in the vapour phase, is a highly promising technique for fabricating nanostructures with high aspect ratios. Here, a nanoscale pattern of x-ray zone plates written by electron beam lithography works as a mould for Pt electroplating on a Au seed layer to realise a nanostructured AuPt bilayer pattern on a silicon substrate. Our approach shows that the silicon etching induced by the electroplated catalyst occurs in a vapour of HF and oxygen, producing nanostructures with feature sizes as small as 10 nm, demonstrating that this catalyst synthesis method is suitable for vapour-based metal assisted chemical etching.

We introduce diffraction beamlet arrays (DBAs), a technique that overcomes the limitations of conventional X-ray grating interferometry, especially when combined with computed tomography (CT) applications. Traditional interferometry systems face significant design challenges when dealing with high energies, large fields of view, and short lengths, such as those required for full-body CT scans. DBAs offer a solution to these issues by generating intensity fringes through the superposition of diffracted and transmitted beamlets, rather than relying on interference. This innovative approach allows for independent variation of the diffraction angle and fringe period, decoupling the fringe formation distance from the design energy. As a result, it is possible to construct imaging systems comparable to Talbot-Lau interferometers with a more flexible parameter space. This flexibility enables shorter system designs, interchangeable design energies, and larger source grating pitches. The advantages of DBAs are demonstrated with a simulation study for the design of a chest X-ray dark-field CT, where traditional Talbot-Lau systems would require grating parameters that are currently impractical to manufacture.

Over the past four years a process for extreme superconformal deposition of gold has been demonstrated and explored for void-free filling of recessed features on patterned substrates for application in X-ray imaging. Uniform and complete void-free filling was detailed on 100 mm silicon wafers patterned with micrometer pitch vias of aspect ratio (height/diameter) 23 and trenches of aspect ratio (height/width) exceeding 60 as well as trenches more than 300 μm deep and fractal patterns of spatially varying depth. This talk discusses a proposed mechanism and model for the observed behavior. Simulations capture key features of the experimental processes, including not only the bottom-up filling itself but also an extended incubation period of conformal deposition that precedes its start as well as self-passivation of the active deposition that accompanies the completion of filling. Feature filling results with relevant electrochemistry are discussed in the context of predicted behavior for different deposition conditions. Cross-sectioned 60 μm deep trenches Au filled at fixed potentials, the associated current transients, a Au filled grating and a simulation of filling in 50 μm deep trenches are all shown in the figure. Figure 1

The multi-scale characterization of building materials is necessary to understand complex mechanical processes, with the goal of developing new more sustainable materials. To that end, imaging methods are often used in materials science to characterize the microscale. However, these methods compromise the volume of interest to achieve a higher resolution. Dark-field (DF) contrast imaging is being investigated to characterize building materials in length scales smaller than the resolution of the imaging system, allowing a direct comparison of features in the nano-scale range and overcoming the scale limitations of the established characterization methods. This work extends the implementation of a dual-phase X-ray grating interferometer (DP-XGI) for DF imaging in a lab-based setup. The interferometer was developed to operate at two different design energies of 22.0 keV and 40.8 keV and was designed to characterize nanoscale-size features in millimeter-sized material samples. The good performance of the interferometer in the low energy range (LER) is demonstrated by the DF retrieval of natural wood samples. In addition, a high energy range (HER) configuration is proposed, resulting in higher mean visibility and good sensitivity over a wider range of correlation lengths in the nanoscale range. Its potential for the characterization of mineral building materials is illustrated by the DF imaging of a Ketton limestone. Additionally, the capability of the DP-XGI to differentiate features in the nanoscale range is proven with the dark-field of Silica nanoparticles at different correlation lengths of calibrated sizes of 106 nm, 261 nm, and 507 nm.

The Silicon Electron Multiplier (SiEM) sensor is a novel sensor concept that enables charge multiplication by high electric fields generated by embedded metal electrodes within the sensor bulk. Metal assisted chemical etching (MacEtch) in gas phase with platinum as a catalyst has been used to fabricate test structures consisting of vertically aligned silicon pillars and strips on top of a silicon bulk. The pillars are around 10µm in height with a diameter of 1.0µm and are arranged as a hexagonal lattice with a pitch of 1.5µm. Electrical characterisations through current–voltage measurements inside a scanning electron microscope and a climate chamber have demonstrated that the MacEtch process is compatible with p–n junctions.