A model of the ion sputtering process

This paper proposes a new model of the ion sputtering process. According to this model: (1) Sputtering atoms or ions originate almost entirely from the surface layer. (2) Atoms initially leave the surface in the same charge state in which they exist in the crystal, and are largely neutralized in traversing a region near the surface. (3) Neutralization can be explained in terms of quantum mechanical electron transmission and reflection phenomena that occur when the atom is within about three lattice spacings from the surface. The model upon which the theory is based pictures a potential well at the metal surface caused by the electric field of the departing ion. This potential well completely cancels the effect of the potential barrier normally present at the surface of the undisturbed metal, and for certain distances of the ion from the surface, results in a very high probability of emission of an electron from the metal surface, which then immediately neutralizes the emitted ion. This high neutralization probability explains the very low (10-2 to 10-6) sputtered ion yields observed experimentally. The ion sputtering yields for a number of elements were computed and compared with values obtained experimentally. It is found that the theory gives results compatible with experiments, and also provides an, at least qualitative, explanation for some of the heretofore rather puzzling experimentally observed features of ion sputtering. (Auth.)