Irradiation of Mo–Cu Superconducting Bilayer Films with MeV Protons

For X-ray applications, microcalorimeters are increasingly dependent on the superconducting transition-edge sensor (TES) technology. We are developing TES devices based on Mo–Cu bilayer films for the proposed Hot Universe Baryon Surveyor (HUBS) satellite mission. To investigate the possible impact of a space radiation environment on the stability of the bilayer films, we conducted an irradiation experiment on Mo–Cu bilayer samples with 1 MeV protons at room temperatures and liquid nitrogen temperatures. With data recorded in real time, we noticed that the changes in the electrical resistance of the film samples were not apparent during irradiation at room temperatures, before and after irradiation, but were evident at liquid nitrogen temperatures. Furthermore, following the irradiation runs, we warmed up the irradiated film samples and placed them in a refrigerator to measure their superconducting transition temperatures ( T_c ) and residual resistivity ( ρ _3K ). We found no systematic change in T_c and ρ _3K . We discuss the results in terms of the vacancies and interstitials in the test samples that are produced by irradiation, as well as the effects of heating caused by irradiation.