Sputtering occurs when a sample atom is ejected from the sample surface. This is a special case of a displacement, only atoms near the sample surface are potential candidates for sputtering. The more collisions that occur on the sample surface, the more likely that sputtering occurs. Atoms that are located deeper within the sample are less likely to be sputtered because the ion beam loses energy as it penetrates the specimen.
Two conditions need to be met for sputtering.

1. The surface atom needs to receive enough energy.
2. The surface atom needs to be displaced into a position outside the sample

Parameters affecting sputtering

Sputtering is predominantly influenced by the surface binding energy, the incidence angle and the initial ion energy (acceleration voltage). The angle of incidence angle between the beam and the sample determines the trajectory of the collision cascade, and dictates how many atoms are near enough to the sample surface to be potential candidates for sputtering.