Mechanism of Ion Stopping

As each implanted ion enters the target, it undergoes a series of collisions with the target atoms until it finally comes to rest at some depth R_p.

There are two different mechanisms of energy loss.

• Nuclear stopping is carried by a collision between two atoms, and can be described by classical kinematics. Nuclear stopping is elastic in nature and the energy lost by the incoming ion is transferred to the target atom, which is recoiled away from its lattice site. This process is responsible for the production of lattice disorder and most of the damage to the crystal structure of the target material.

• Electronic stopping is caused by interaction with the electrons of the target. Electronic stopping is inelastic in nature and the energy lost by incident ions is dissipated through the electron cloud into thermal vibrations of the target material.

The total stopping power S of the target, defined as the energy (E) loss per unit path length of the ion(x), is the sum of these two terms:

The relative importance of the two processes depends on the energy E and the atomic number Z of the ion. Note that nuclear collisions dominate at low energies and electronic collisions at high energies. For light ions electronic collisions will dominate where as for heavier ions nuclear collisions will dominate. [2]

Fig. 2 Nuclear and electronic components of the ion stopping power as a function of ion velocity. The quantity v_o is the Bohr velocity and Z₁ is the ion atomic number.[2]