Sputtering of multicomponent materials: The diffusion limit

Abstract

Bombardment of systems such as binary alloys normally results in the preferential sputtering of one component combined with a subsurface depletion of the same component. Driving forces for preferential loss include mass differences, chemical binding differences, and Gibbsian or similar segregation. We are here concerned with the simpler profiles which are set up in the absence of segregation. This problem has most commonly been reduced to one of conventional diffusion, governed by relocation and surface recession but not conserving lattice sites. More recently, a ballistic treatment was introduced which in its most complete form allowed for relocation, surface recession, and conservation of lattice sites. We show that the ballistic treatment can be re-expressed in a diffusion limit such that conservation of lattice sites is retained and that, moreover, a closed-form steady-state solution exists. It is further shown that the diffusion limit satisfactorily defines the various diffusion coefficients, the steady-state surface compositions, the sputtering yields, and the overall profile shape. © 1986.