Kinetically assisted potential sputtering

Kinetic-assisted potential sputtering describes the removal of surface-bound atoms, ions, or molecules, which occurs through various modes of excitation induced as a consequence of the momentum imparted by the incoming ion. 

For the small molecular ions (examples commonly used in SIMS include AUn", Bi ", and SF5" ), energy transfer can also proceed through various modes of electronic excitation. As a result, they are best described as forms of kinetically assisted potential sputtering. The various modes of electronic excitation are often discussed in the form of localized elevated temperatures that quickly dissipate. 

Kinetically assisted potential sputtering can take several forms depending on the primary ions, the conditions used, and the matrix examined. For dense atomic and the small molecular ion impact (In ", Bi ", Au , SFj" ", etc.), these generally tend to assume the presence of overlapping collision events within the lattice that occur as a result of the same initial collision event (the linear cascade model assumes individual events). This overlap ensues when momentum transfer is constrained within a more localized volume and/or when multiple atoms from the same impacting ion strike the same region. 

Figure 3.4 Highly simplified pictorial illustration of sputtering believed to occur during kinetically assisted potential sputtering induced on small molecular ion impact. This can also describe the first step in cooperative sputtering from large cluster ion impact. The gray region represents an outward moving dense halo.

And as for the other sputtering processes (kinetically assisted potential and pure potential), there exists significantly greater compntational complexity. 

As for the remainder, additional mechanisms/models have been suggested. These are based around varions inelastic modes of energy transfer, i.e. forms of potential sputtering with some being kinetically assisted. These are covered in Section 3.2.1.2. 

As introduced in Section 3.2.1, potential sputtering, whether kinetically assisted or not, results from inelastic energy transfer processes, with electron-phonon interactions playing a part. Cooperative motion describes a kinetic process in which a single primary ion impact induces the movement of a collective body of atoms within the solid. All of the above result in sputter yields (these are covered in Section 3.2.2) that are greater than that expected based on the linear cascade model (see Section 3.2.1.1). 

---