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Abstract: The detection of charged particles is an integral part of several scientific endeavours. To detect a charge particle, it must interact with a sensing volume and produce charges within it that can be read out. In hybrid pixel sensor, the sensor and readout electronics can be optimised separately, and this property makes them highly desirable for future applications. University of Glasgow and Micron Semiconductor Ltd collaboration produces 50 µm thick LGAD and a 250 µm thick iLGAD sensors. The LGADs are envisaged as fast-timing detectors for particle physics experiments, while the iLGADs were developed as a technological solution to solve issues with the low fill factor in the conventional LGAD. These detectors are produced as pad detectors of various pixel sizes and doping concentrations for testing. The pixelated version of the 250 µm thick iLGAD and an earlier iteration of a 200 µm LGAD are bonded to Timepix3 readout ASICs as one-of-a-kind hybrid pixel detector prototypes. In addition to these detectors, the University of Glasgow also produced hybrid pixel detectors with high-Z sensors. The electrical properties of the (i)LGAD pad detectors are explored via IV and CV measurements. Some LGAD pad detectors are also evaluated for their gain using the TCT with a 1040nm infrared laser source. The doping concentration in the multiplication region dictates the electrical characteristics of (i)LGADs. The 50 µm thick LGADs achieve full depletion at voltages between 26V to 31V. Breakdown voltages were 5 to 9 times higher than full depletion voltage, indicating a wide dynamic range for operation. The JTE width or, collectively, the device’s active area restricts the achievable gain and fill factor in the 50 µm thick LGAD. The 1.0mm × 1.0mm LGAD achieves a 6.75 gain at 30 ◦C, with a 74% increase in gain for a 50 ◦C temperature drop. The hybrid pixel detectors with (i)LGAD sensors are calibrated for energy and corrected for time-walk with XRFs and γ-ray sources. Subsequently, their pixel responses and signal gains are investigated with a micro-focused synchrotron beam at Beamline B16, Diamond Light Source. No signal gain was observed in the hybrid pixel detector with 55 µm pitch LGAD, but this is expected and fully understood—however, the 110 µm pitch variant performed with a limited fill factor as expected, with a gain of around 5 at −350V bias voltage. The iLGAD is a viable solution to overcome the low-fill factor of an LGAD. A gain of around 5 at 250V bias voltage with a fill factor of more than 80% was obtained in the hybrid pixel detector with 55 µm pitch iLGAD. The thesis also discussed the application of a hybrid pixel detector with a high-Z sensor as a single-layer Compton camera. Proof of concept was demonstrated in a very thin (1mm thick), 55 µm pitch CdTe bonded to a Timepix3 readout ASIC. Despite limited data, an image depicting the origin of a gamma-ray source was fully reconstructed just by utilising the Compton scattering kinematics.

Open Access

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Abstract: Hard X-ray microscopes with 20–30 nm spatial resolution ranges are an advanced tool for the inspection of materials at the nanoscale. However, the limited efficiency of the focusing optics, for example, a Fresnel zone plate (ZP) lens, can significantly reduce the power of a nanoprobe. Despite several reports on ZP lenses that focus hard X-rays with 20 nm resolution – mainly constructed by zone-doubling techniques – a systematic investigation into the limiting factors has not been reported. We report the structural effects on the focusing and imaging efficiency of 20–30 nm-resolution ZPs, employing a modified beam-propagation method. The zone width and the duty cycle (zone width/ring pitch) were optimized to achieve maximum efficiency, and a comparative analysis of the zone materials was conducted. The optimized zone structures were used in the fabrication of Pt-hydrogen silsesquioxane (HSQ) ZPs. The highest focusing efficiency of the Pt-HSQ-ZP with a resolution of 30 nm was 10% at 7 keV and >5% in the range 6–10 keV, whereas the highest efficiency of the Pt-HSQ-ZP with a resolution of 20 nm was realized at 7 keV with an efficiency of 7.6%. Optical characterization conducted at X-ray beamlines demonstrated significant enhancement of the focusing and imaging efficiency in a broader range of hard X-rays from 5 keV to 10 keV, demonstrating the potential application in hard X-ray focusing and imaging.

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Abstract: In this project, we conducted micro-beam sensitivity mapping using the Diamond Light Source (DLS) synchrotron. We fabricated three samples with distinct metal contacts: Platinum (HPS-Pt) and Aluminium/Platinum (HPS-Al/Pt) on high-quality single crystal CVD diamond, and Platinum (VS-Pt) on lower purity single crystal CVD diamond. Our objective was to identify the most suitable sample for synchrotron measurements, particularly focusing on the lower purity sample due to its unique characteristics, such as thin nitrogen lines and substrate area. High spatial resolution sensitivity maps were obtained for the lower purity sample using a micro step displacement of up to 10 μm, revealing detailed nitrogen lines. We observed that bias polarity significantly influenced the photocurrent, with negative bias yielding higher photocurrents, possibly due to polarisation effects. Near nitrogen lines, we noted a slow rise time and an increased stabilization time with bias, alongside a prolonged decay to dark current. For the HPS-Al/Pt sample, we found no improvement in current response homogeneity, therefore reliability, with bias; instead, we recorded high dark currents and unstable signals, particularly at negative bias. Conversely, the HPS-Pt sample exhibited a uniform response at both +50V and −50V in the central region of the sensitivity maps. This response became increasingly homogeneous at 100V and further improved up to 200V, suggesting that HPS-Pt is the most suitable candidate for synchrotron measurements.

Open Access

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Abstract: Material extrusion additive manufacturing (AM) has gradually become a dominant technology for the fabrication of complex-designed thermoplastic polymers that require a higher level of control over the morphological and mechanical properties. The polymer internal crystal structure formed during the AM process can present significant impacts on the mechanical properties of the individual filaments, as well as the whole structure. Currently, limited details are known about the crystal structure evolution during the material extrusion AM processes of polymers. A novel in situ synchrotron X-ray diffraction (XRD) experimental configuration was developed enabling us to capture the material evolution data throughout the extrusion AM process. The in situ time-resolved data was analysed to reveal nucleation and crystallization sequences during the continuous deposition, with the aid of both complimentary numerical simulations and post-process (ex situ) characterisations. The thermal simulations supported the prediction of the filament temperature profile over time and location during the AM process, while ex situ characterisations validated the correlation between polymer crystallinity (resulting from printing parameters) and corresponding mechanical properties. The results obtained from varied process parameters suggest that the processing temperature has a dominant influence on the crystal microstructure evolution compared to the deposition velocity. A lower processing temperature just above the melting temperature permitted favourable crystallization conditions. The overall analysis demonstrated prospects for enhancing polymer AM, to engineering mechanically hierarchical structures through correlative investigations.

Open Access

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Abstract: Over the past few years, Low Gain Avalanche Detectors (LGAD) have shown excellent timing performance with the hope to be utilized for 4D-tracking of high-energy charged particles. LGADs co-doping with carbon has been demonstrated to be a key factor in the enhancement of their performance as detectors with intrinsic amplification in harsh radiation environments. A wide characterization, before irradiation, of the latest carbonated LGADs fabricated at the IMB-CNM is presented in this work. The results show that the addition of carbon improves the gain of the devices, given a specific bias voltage, but only up to a certain point. Moreover, a comprehensive study of how carbonation enhances the diffusion suppression of dopants in silicon sensors during its fabrication is also presented.