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Abstract: In this work the properties of 200 μm thick highly pixelated LGAD sensors bonded to the Timepix3 readout ASIC were characterised with a monochromatic micro-focused X-ray beam for the first time. Recent advances in the control of the LGAD fabrication process by Micron Semiconductor Ltd. has allowed the manufacture of highly segmented devices where each pixel has an internal gain. Devices with 55 μm pixel with 5 μm Junction Termination Extension (JTE), 110 μm pixel with 10 μm JTE and 110 μm pixel with 20 μm JTE were bump bonded to a Timepix3 readout ASIC. These were characterised with a monochromatic micro-focused 15 keV X-ray beam at a synchrotron. The performance of the LGAD devices is benchmarked against a standard 55 μm pixel planar device. The evidence of ×3.5 gain is demonstrated on the 110 μm 10 μm JTE pixel device, while the 55 μm assembly showed no gain, which was consistent with simulations. The paper provides a comprehensive analysis of spectrum, pixel profile and two-dimensional mapping scans.

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Abstract: Auxetic behavior provides a route to increase specific energy absorption and useful cushioning deformation in applications that include medical, sports and vehicular engineering. To be effective, the development of auxetic behavior typically requires a structure with many small unit cells. However, improved manufacturing resolution affords better, more consistent behavior to larger unit cells. These factors are inter-linked by sub-cell strains, where the strain patterns in loaded re-entrant auxetics are currently not well understood. This study provides the first analysis of the use of X-ray diffraction to understand the sub-cell strain behavior in re-entrant auxetic structures. The use of a synchrotron enabled unparalleled resolution of in-situ strain data, where re-entrant cells were examined based on a range of imposed concave fillets, from zero to 0.75 of cell size. The experimental data demonstrated that reducing the fillet radius reduced the 95th percentile strain exhibited by the auxetic by 49%, thereby widening the elastic domain of the material. The experimental data were compared with a homogenization modelling approach that varied the cell count, which revealed a Poisson’s ratio reduction, and therefore an improvement in auxetic response, from -0.13 to -0.39 when using 1 to 10 cells, highlighting the benefit of creating auxetics with more cells. The combination of experimental and modelling approaches allowed numerical comparison of cell scales and cell counts to identify ideal scales for manufacturing. These results supported the development of a new set of design guidelines for the design and production of practical auxetic metamaterials and ensure right-first-time manufacturing.

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Abstract: X-ray detection underpins a wide range of applications in medicine, security, industrial inspection, scientific research for non-destructive imaging, and material analysis. The rapid development of Ga2O3-based x-ray detectors offers a promising pathway toward next-generation detectors with high sensitivity, low noise, and harsh environment applications, benefiting from its intrinsic material properties, such as high density, wide bandgap energy, and high thermal–chemical stability. However, the underlying device operating mechanisms, including both carrier excitation and transport processes, have not yet been adequately studied, largely due to the misuse of x-ray sources in previous studies. In addition, benchmarking of device characteristics has been problematic due to experimental or data analysis issues, as well as misunderstandings of the applied equations associated with parameter definitions. In this work, we have designed and performed instructive research based on epitaxial β–Ga2O3:Si and its planar Schottky detectors, measured with energy-tunable monochromatic x-ray beams on a synchrotron beamline, clarifying the device excitation and carrier transport mechanisms with properly benchmarked device performance. In the end, we propose a set of protocols for correctly measuring and analyzing the device performance. The proposed protocols are broadly applicable and can be readily extended to other semiconductor x-ray detectors.

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Abstract: This study presents a comprehensive investigation of the dosimetric characteristics and sensitivity mapping of a CVD diamond radiation detector (VS-Pt) fabricated with platinum metal contacts. The detector’s performance was evaluated through a series of measurements, including I–V characteristics, signal-to-noise ratio, dose rate dependence, linearity, photoconductive gain, sensitivity, rise time, and reproducibility, using an X-ray tube source. The device underwent annealing, which led to improvements in sensitivity, with a linear response and increased photoconductive gain. The reproducibility of the device was found to be slightly higher than the IAEA’s recommended limit. Following this, a comparative sensitivity mapping study was performed using two synchrotron micro-beam facilities—NSLS and DLS—employing different micro-beam sizes. The investigation explored the effects of beam size, bias polarity, and step displacement on the spatial resolution and sensitivity of the device. Results showed that sensitivity was influenced by beam size, with smaller beam and step sizes yielding higher sensitivity, likely due to the priming effect. Bias polarity also played a significant role, with negative bias producing higher photocurrents, particularly near nitrogen lines in the diamond. Additionally, the annealed sample exhibited better homogeneity and faster rise times compared to the un-annealed version. The findings highlight the optimal conditions for synchrotron-based dosimetric measurements, providing valuable insights for improving detector performance in applications such as radiotherapy dosimetry, radiobiology, and beam monitoring at synchrotron facilities.

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Abstract: The development of synchrotron facilities has significantly expanded experimental capabilities across a wide range of scientific disciplines. X-ray multilayer optics, comprising periodically alternating thin films that enable constructive interfer- ence, offer a versatile alternative to conventional crystal optics and single-layer coatings by providing greater flexibility in photon energy, angular range, and re- flectivity. Their use in synchrotron optics has therefore increased substantially. However, the fabrication of high-performance multilayers requires stringent con- trol of layer thickness, interface roughness, and uniformity over large substrates. These challenges that are not fully addressed by existing commercial solutions. This thesis presents a systematic framework for the design, fabrication, and characterisation of X-ray multilayer optics aimed at achieving high uniformity and performance for synchrotron applications. A Multilayer Deposition System (MDS) was developed at Diamond Light Source to enable in-house fabrication. Commissioning results demonstrate the versatility and positional accuracy of the motion-controlled deposition platform. Following commissioning, the MDS was used to fabricate both periodic and laterally graded multilayers. The influence of deposition parameters on material systems including Ru/B4C and NiV/B4C was systematically investigated. Optimisation of working gas pressure, sputtering power, and reactive sputtering using nitrogen was shown to reduce surface and interface roughness, leading to improved reflectivity and enhanced stability. A key focus of the work is the further development of double multilayer monochromators (DMMs). A novel adjustable hyperbolic aperture shadow mask was designed to achieve high sagittal thickness uniformity, with beamline testing confirming high reflectivity across the desired X-ray energy range. When com- bined with substrates refined by ion beam figuring (IBF), the DMMs enabled stripe-free imaging, eliminating common artefacts in X-ray images. The fabri- cation of laterally graded multilayers with both constant and variable thickness gradients is also demonstrated, achieving nanoscale precision through controlled deposition. Constant-gradient multilayers were implemented as soft X-ray po- larisers at the I21 beamline, where their performance met stringent operational requirements. Furthermore, integration of a Speckle-based Curvature Optical Metrology platform into the MDS enabled in situ two-dimensional residual stress mapping, facilitating the deposition of single-layer coatings with elliptically vary- ing profiles and thicknesses of tens of micrometres without delamination. Overall, this work establishes advanced methodologies that extend the capa- bilities of multilayer optics beyond those available from commercial systems. The outcomes provide a robust foundation for the development of high-performance multilayer optics to support next-generation light sources and a wide range of scientific applications.