Secondary ion emission by nonadiabatic dissociation of nascent ion molecules with energies depending on solid composition

A new model of the emission of positive secondary ions Me⁺ from metal oxides is proposed to reproduce the strong mass dependence of their yield. The mass dependent aspects of this model are discussed and mathematically formulated. The energy transport in the collision cascades depends strongly on the mass ratio of the atoms involved. An approximation of the energy distribution of surface atoms is made which includes this mass effect. Surface molecule collisions lead to the emission of ions. They again depend on the mass ratio of the molecule's constituents. It is made plausible that particle complexes leave the surface only neutrally. In a nonadiabatic dissociation process free ions can be created outside the surface potential barrier. There is only a very low probability for neutralization depending on the mass of the ions involved. The model calculation reported in Part II of this paper reproduces the strong mass dependence experimentally observed. In Part I the new emission conception is additionally confirmed by the qualitative explanation of other Me⁺ emission effects: difference in the energy distribution of Me⁰ and Me⁺, change of the energy distribution of Me⁺ ions during oxygen exposure experiments, difference in the Me⁺ emission of metals with high (Ti) and low (Co) affinity to oxygen during oxygen exposure experiments.