The sticking efficiency of quartz crystals for cosmic sub-micron grain collection

Mass flux monitoring of cosmic dust grains is possible by means of microbalance sensors, such as those used in the GIADA-MBS system, onboard the Rosetta mission. An important parameter, which determines the efficient collection of grains with time, is the sticking efficiency of the electrode-coated quartz crystals forming the sensor of the microbalance. In principle, an improving of performances should be obtained by applying a thin coating of adhesive material onto the sensor surface. In order to evaluate the sticking properties for coated and uncoated microbalance crystals, we bombarded them with 1.2 μm silica spheres and 0.64 μm irregular SiC grains, having velocities of up to 55 m s−1. We studied individual impacts obtaining the sticking efficiency as a function of the grain velocity. For silica sphere projectiles, the presence of the adhesive coating slightly increases the sticking, whereas for irregular SiC particles it is noticeably high even for the uncoated crystal (0.7–0.8). We conclude that, for micrometer irregular grains, in the studied velocity range, the microbalance sensor without any sticking coating guarantees rather high collection performances.