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 ) μ m 2 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.