2. Collision Processes

Collisions between, on the one hand, the incident ion and the target atoms and, on the other hand, between target atoms themselves are the fundamental processes of ion–solid interaction. In a collision with low and medium ion energies, the interaction between two particles can be described by a screened Coulomb potential. In detail, various screened potentials and their screening function are presented in a summarized form. Interactions between particles in the very low or hyperthermal energy range can, on the one hand, be represented approximately by a Born–Mayer potential and, on the other hand, it is to be taken into account that the attractive part of the interaction potential cannot be ignored any more. In the following, the classical description of the collision processes in both the laboratory system and the center-of-mass system is briefly presented, the collision parameters are introduced, and the scattering angles for the colliding and collided particles are formulated. Subsequently, the total scattering cross section, a quantity indicating the probability of the interaction between ions and target atoms, and the differential scattering cross-section, indicating the number of ions scattered into a differential solid angle at given polar and azimuthal angles, are introduced. The method proposed by Lindhard et al. to represent the differential cross-section as a function of a single parameter for the screened Coulomb interaction is also presented.