Point-defect properties of, and sputtering events in, the {001} surfaces of Ni3Al.: II.: Sputtering events at and near surfaces

Atomic recoil events at and near {001} surfaces of Ni3Al due to elastic collisions between electrons and atoms have been simulated by molecular dynamics to obtain the sputtering threshold energy as a function of atomic species, recoil direction and atomic layer of the primary recoil atom. The minimum sputtering energy occurs for adatoms and is 3.5 and 4.5 eV for Al and Ni adatoms on the Ni-Al surface (denoted 'M'), respectively, and 4.5 eV for both species on the pure Ni surface (denoted`N'). For atoms within the surface plane, the minimum sputtering energy is 6.0 eV for Al and Ni atoms in the M plane and for Ni atoms in the N surface. The sputtering threshold energy increases with increasing angle, theta, between the recoil direction and surface normal, and is almost independent of azimuthal angle, phi, if theta < 60 degrees; it varies strongly with phi when theta > 60 degrees, with a maximum at phi = 45 degrees due to < 110 > close-packed atomic chains in the surface. The sputtering threshold energy increases significantly for subsurface recoils, except for those that generate efficient energy transfer to a surface atom by a replacement collision sequence. The implications of the results for the prediction of the mass loss due to sputtering during microanalysis in a FEG STEM are discussed.