  Neutrinoless double beta ($0\nu\beta\beta$) decay is a hypothetical rare
nuclear transition ($T_{1/2}>10^{26}$ y). Its observation would provide an
important insight about the nature of neutrinos (Dirac or Majorana particle)
demonstrating that the lepton number is not conserved. This decay can be
investigated with bolometers embedding the double beta decay isotope
($^{76}$Ge, $^{82}$Se, $^{100}$Mo, $^{116}$Cd, $^{130}$Te...), which perform as
low temperature calorimeters (10 mK) detecting particle interactions via a
small temperature rise read out by a dedicated thermometer. CROSS (Cryogenic
Rare-event Observatory with Surface Sensitivity) aims at the development of
bolometric detectors (Li$_{2}$MoO$_{4}$ and TeO$_{2}$) capable of
discriminating surface $\alpha$ and $\beta$ interactions by exploiting
superconducting properties of Al film deposited on the crystal surface. We
report in this paper the results of tests on prototypes performed at CSNSM
(Orsay, France) that showed the capability of a-few-$\mu$m-thick
superconducting Al film deposited on crystal surface to discriminate surface
$\alpha$ from bulk events, thus providing the detector with the required
surface sensitivity capability. The CROSS technology would further improve the
background suppression and simplify the detector construction with a view to
future competitive double beta decay searches.
