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SIMS Theory: Sputtering Effects
The collision cascade model has the best success at quantitatively explaining how the primary beam interacts with the sample atoms. In this model, a fast primary ion passes energy to target atoms in a series of binary collisions. Energetic target atoms (called recoil atoms) collide with more target atoms. Target atoms that recoil back through the sample surface constitute sputtered material. Atoms from the sample's outer monolayer can be driven in about 10 nm, thus producing surface mixing. The term knock-on also applies to surface mixing.
Sputtering leads to surface roughness in the sputter craters. Lattice imperfections, either already present or introduced by surface mixing, can be germs for roughness that takes the form of ribbons, furrows, ridges, cones, and agglomerations of cones. Polycrystalline materials form rough crater bottoms because of differential sputter rates that depend on crystal orientation.
