Transport-theory approach to ion-beam mixing and recoil implantation.

Abstract

Ion bombardment of an amorphous target in slab geometry is considered, and ion-beam mixing and recoil implantation evaluated in the binary-collision approximation. A fundamental equation for target-atom redistribution during ion bombardment is formulated, which relates the redistribution flux to the source function for the creation of energetic atomic recoils and their range distribution; for the analysis, this equation plays the role of the Boltzmann transport equation. Expanding the target-atom density in a power series and truncating at the second term yields a flux equation and closed expressions for coefficients of recoil implantation and of ion-beam mixing. The flux equation plays a role analogous to that of Fick's law in diffusion. Lattice relaxations are taken into account by introducing flux transformations between laboratory and marker coordinate frames. The closed expressions for the coefficients are calculated and compared with experiment. The binary-collision contribution to ion-beam mixing turns out to be larger than heretofore thought. A new mechanism for ion-beam mixing emerges, which turns out to make a very significant contribution. There are even cases where the new mechanism far outweighs the cascade-mixing mechanism, thought to be the major contributor to binary-collision ion-beam mixing.