Theory of surface ionization

A microscopical theory is presented to describe surface ionization of atomic particles desorbed from solid state by impact of energetic primary ions or atoms. On the basis of this general theory analytical expressions are derived for ionization probabilities of particles desorbed from quiescent substrates, from substrates excited by independent collisions, and from thermally excited substrates. The latter approach, which regards the ionization as induced by an electron-hole plasma at a temperature T_e in the collision cascade region, is found to be consistent with most experiments.