By use of the resonant metastability‐exchange process, a metastable‐atom beam possessing all genuine qualities of a “ natural ” ground‐state atom nozzle beam is prepared. Owing to the angular narrowness (0.35 mrad) and smallness of the effective source diameter (15 &mgr;m) of this beam, the scattering of metastable atoms by a silicon‐nitride nano‐slit grating is investigated in detail, in a partially coherent regime. The elastic scattering exhibits high‐order diffraction peaks combined with a standard van der Waals deflection effect. When a static magnetic field is present, surface‐induced exo‐energetic transitions among Zeeman sub‐levels are observed. © 2004 American Institute of Physics