GENERALIZED WAGNER DIFFUSION-MODEL OF SURFACE MODIFICATION OF MATERIALS BY PLASMA-DIFFUSION TREATMENT

A general model of surface modification of materials by plasma diffusi on techniques has been developed. This model takes into account the er osion effects at the plasma/solid interface occurring due to the ion b ombardment of the surface. For constant sputtering rate, which is the usual situation during plasma treatment, the growth of the sub-layers (and the total compound layer) is well described by the analytical exp ression g(t) = g(0) f(-1) (t/t(0)), where g(t) is the sub-layer thickn ess at time t, g(0) and t(0) are parameters that depend on the treated material and plasma characteristics, and f(-1) is the inverse functio n of f(x) = -(ln(1 - x) + x), where x = g(t)/g(0), 0 less than or equa l to x less than or equal to 1. Under negligible erosion effects, the model becomes of Wagner's diffusion model type and the expression for g(t) reduces to the parabolic law. The model can be simplified by cons idering the compound layer as a united one. The general and simplified models can be used as a method for the experimental determining of th e effective diffusion coefficients and the erosion rate during plasma treatment of material surfaces.