Toward high-resolution low-energy electron spectroscopy with transition-edge sensors

We present a study of the energy resolution of transition-edge sensors (TESs) for the detection of electrons in the 100-eV kinetic energy range. The TES is a Ti-Au bilayer with an active area of (60×60) μm2 and a critical temperature of approximately 80 mK. The electron source is based on vertically aligned multiwall carbon nanotubes located inside the cryostat, with electrons generated via field emission. For electrons in the (92-99) eV kinetic energy range, we obtain a Gaussian energy resolution for fully absorbed electrons of (0.48±0.04±0.06) eV, where the first uncertainty is statistical and the second systematic. When considering the full-width at half-maximum of the peak of the signal amplitude distribution, the corresponding resolution is of (1.4±0.2±0.3) eV. The former represents an improvement of (47-60)% with respect to previous results and is mainly attributed to the reduction in the TES active area. The latter is instead an improvement of over a factor of 21 and is mainly due to the reduction in the emitting area of the electron source, which significantly suppresses electron back-scattering in proximity of the TES. These results represent a major milestone toward high-precision spectroscopy on low-energy electrons, which is a key objective for the PTOLEMY experiment.