X-rayInducedEffectsonMgB2 Thin Films:Radiation Hardness andAssessmentforApplications

With primary objectives of assessing radiation tolerance and investigating X-ray directwrite nanopatterning as an approach to device fabrication, this thesis investigates the effects of focused X-ray nanobeam irradiation on magnesium diboride thin film microbridges. Magnesium diboride (MgB2) is a promising material for superconducting electronics intended for radiation-rich environments (electronics, space, detectors, fusion, and accelerators) due to its simple binary chemistry and comparatively high critical temperature (∼39 K). However, the mechanisms and controllability of X-ray–induced modification in MgB2 remain insufficiently characterized. To address this gap, we combined the comprehensive structural, compositional, and cryogenic transport characterization of lithographically specified MgB2 microbridges with precisely controlled irradiation at the European Synchrotron Radiation Facility (ESRF) ID16B X-ray nano-beamline. In addition to establishing reproducible MgB2 microbridge platforms (HPCVD films, photolithographic patterning, and Pt alignment markers), the experimental program investigated irradiation parameter space defined by incident X-ray irradiation dwell time, beam incidence angle, and ambient versus inert atmosphere. Spatially extensive oxidative damage and microcracking that extended beyond the beam path were induced by the initial ambient air exposures. In contrast, X-ray-induced modification was localized to a narrow stripe along the scan in experiments conducted in an inert N2 atmosphere, indicating that atmospheric oxygen suppression is a necessary condition for precise, spatially localized patterning. Transport measurements (R–T and I–V), supported by FESEM and EDX, reveal X-ray irradiation dwell-time–dependent regimes of modification. Highly disordered but metallic stripes with room-temperature resistivity increased by approximately 103–104 times and a broadened superconducting transition width are produced at low-to-intermediate dwell time; these stripes function as planar weak links with switching behavior and hysteretic current–voltage characteristics consistent with SNS or S–S’–S Josephson behavior. High dwelling resulted in insulating separations that fully suppress superconducting (dissipationless) transport while preserving the properties of adjacent regions. Damage is spatially confined within ∼1.5 μm of the beam path, according to structural studies, and there is local oxygen enrichment but no heavy-element contamination detected. This suggests that structural/chemical modification, rather than compositional doping, is more plausible. To summarize, this study showed that focused X-ray irradiation, when used in an oxygen-free (inert) environment, offers a maskless, direct write, tunable technique for sub-micron (or sub-μm) modification of MgB2 superconducting films, enabling the formation of planar weak links for device integration. Additionally, the work specifies operational windows and practical limits for device engineering: excessive irradiation results in insulating separations, whereas intermediate disorder yields reproducible weak link junctions with significant characteristic voltages. Additionally, by showing that MgB2 tolerates intense localized X-ray exposure without collateral degradation once oxidative processes are suppressed, this work advances the understanding of MgB2 radiation hardness and supports its use in radiation-exposed superconducting technologies. 2