4. Ion Beam-Induced Damages

Bombardment of surfaces with accelerated ions leads to the formation of defects, where lattice atoms can be displaced after collision with the incident ion or a higher order recoil atom if the transferred energy is higher than the displacement threshold energy. The Kinchin-Pease model, modified Kinchin-Pease model, and the Norgett–Robinson–Torrens model are presented and the calculation of the defect generation rate is demonstrated. Of particular importance is the determination of the number of displacements per atom (dpa), since this number is the benchmark for quantifying radiation-induced changes of material properties after ion bombardment. Assuming that elastic collisions are dominant, the spatial distribution of the deposited energy is discussed. If the assumption of subsequent binary collisions is not valid, the formation of high energy density cascades can be expected. Both the displacement spike and the thermal spike are introduced and the mean features of these cascades are discussed. Then, the behaviour of irradiation-induced point defects as a function of irradiation time (fluence) and the temperature during ion bombardment is described and the main analytical relationships are given. As the concentration of ion beam-induced defects increases, the probability of formation of an amorphous layer also increases. The formation of an amorphous phase for a given material depends on the ion species, ion energy, fluence, ion current density, and irradiation temperature. The various models proposed in the literature for the ion beam-induced amorphization process are briefly summarized.