On the role of recoil implantation in altering the stoichiometry of a bombarded solid

Oxides, halides and sulfides which are subjected to high-dose ion impact undergo surface alterations of two kinds, involving respectively the loss of a component either at the extreme outer surface or over a depth of roughly 0-100nm. In this paper the extent to which the former kind of alteration (i.e. at the outer surface) will be subject to recoil implantation is considered. The necessary theory is developed and numerical results giving the amount of implantation at at a given depth are presented. In general, recoil implantation can be said to cause any alteration of the outer surface to be extended in three senses: a major stoichiometry change to perhaps 3 nm, minor changes to perhaps 15 nm, together with the injecting of point defects (e.g. oxygen vacancies) characteristic of the surface alteration. The question of why alterations of the outer surface should occur at all may possibly also be related to recoil implantation. If, for example, the substrate is Nb2O5, then there exists a recoil source consisting of Nb to the extent theta=2/7 and of O to the extent theta=5/7. It is shown that the oxygen is implanted, thence removed, 1.5-5 times more rapidly than the Nb. Effects such as preferential sputtering will, however, also be important in causing surface alteration and must be considered in any complete treatment of the problem. (Auth.)