A nanotechnology application for low energy neutral atom detection with high angular resolution for the BepiColombo mission to Mercury

Thanks to the great progress of micro and nanofabrication techniques, only in recent years it has been possible to propose a space flying instrument able of remote-sensing the surface released neutral particles with a direct technique. This instrument, which will be installed in the BepiColombo/MPO spacecraft to Mercury, is the neutral sensor ELENA (Emitted Low-Energy Neutral Atoms), a time-of-flight (TOF) detector, based on the state-of-the art of ultra-sonic oscillating shutters, and Micro-Channel Plate (MCP) detection. The shuttering system digitizes space and time when tagging the incoming particles without affecting their trajectory and energy. The ELENA shuttering element consists of two self-standing silicon nitride (Si(3)N(4)) membranes, one facing the other, patterned with arrays of 200 nm wide nanoslits, organized on a square lattice with 4 mu m pitch over a 3 x 3 mm(2) area whereas in the final version it will perform a pitch of 1.4 mu m, on a 10 x 10 mm(2) area. A capacitive control system is implemented to assure the alignment of the two membranes. The characterization of the shuttering capability has been obtained with a He beam at 1 key. The same fabrication process has been also used to realize a large area mesh filters, in order to reflect unwanted IR radiation to minimize the instrument heat load.