THE TREATMENT AND THE SOLUTION OF THE MIXING EQUATIONS WITH COMPOSITION DEPENDENT ATOMIC VOLUMES

The computer program IMPETUS calculates sputter depth profiles by solv ing Fokker-Plank type equations for mixing. In the standard model, the effective volume of the mixing constituents is taken to be constant t hroughout the mixing regardless of the composition of their atomic env ironment. Experimentally measured values for atomic densities of mater ials and compounds indicate that this assumption is not correct and th at nonconstant atomic volumes need to be considered. Although the way in which the variation of the volumes take place is not known, the pre sent work is aimed at developing the treatment of Fokker-Plank type eq uations such that composition dependent effective atomic volumes can b e included. The complexity of the equations and a method for solution together with its application for a simple case are explained in this paper.