Low-temperature characterization of Mo/Cu TES devices for HUBS

Hot Universe Baryon Surveyor (HUBS) is being conceptualized in China as a high throughput and high-resolution spectroscopic X-ray mission dedicated to studying cosmic "missing" baryons, which are thought to exist in the gas of very low density and temperature roughly one million degrees in the halo of galaxies or in large-scale structures. To detect weak emission from the "missing" baryons, HUBS will employ a TES-based X-ray microcalorimeter array that operates at very low temperatures. The key characteristics of the detector technology are excellent energy resolution and high quantum efficiency, which makes it an ideal choice for constructing a non-dispersive X-ray imaging spectrometer. We are developing X-ray microcalorimeters for HUBS, based on superconducting Mo/Cu bilayer films. In this work, we present results on the characterization of the Mo/Cu films and TES devices at temperatures below 100 mK, including their R-T curves, I-V characteristics, energy resolutions, etc. We have also studied correlations between the superconducting transition temperature and other properties of the films (including residual resistivity ratio, stress, crystalline structure, interface properties, and so on), and looked into factors that might affect the energy resolution of the detectors. Preliminary results will be presented.