The cryogenic underground observatory for rare events experiment CUORE Upgrade with Particle Identification CUPID is an experiment designed to observe a very rare nuclear transformation forbidden in the actual standard model of particle physics. The scientific goal of CUPID is not just to look for the double beta decay, but also to lay the basis for a next-generation experiment that takes full advantage of the innovative potential of the simultaneous detection of the light emitted by an event in the bolometer itself allowing particle identification, providing an important tool to reduce the natural-induced radioactivity.
One of the adversities of this experiment is the low amount of light that exits from the bolometer and reaches the light detector. Thin film coating is deposited in the TeO2 bolometer crystal and in the detector surface, in order to enhance the light yield. SiO2 was selected as material and produced by PECVD. SiO2 was characterized using ellipsometry, white light reflectance spectrum and XDS mapping. For the Cerenkov emission of the TeO2 crystals, an enhancement of 35% was estimated.