RBS ANALYSIS OF DIFFUSION AND EVAPORATION OF IMPLANTED LEAD IN ALUMINUM

The diffusion of non-equilibrium concentrations of Pb implanted into Al crystals has been analyzed by fitting experimentally measured profiles to the solution of the diffusion equation with the boundary condition that the outward flux at the surface is proportional to the surface concentration. This solution contains two free parameters, namely diffusivity and evaporation constant, which were found by the fitting. There are some systematic differences between the measured and fitted profiles, but the fitting procedure provides fairly constant values of the diffusion coefficient and the evaporation rate, with the diffusion coefficients obeying an Arrhenius relation. For some of the experimental conditions the differences became so large in the later stage of annealing that the process is not adequately described by the simple diffusion equation. The systematic differences are believed to be related to effects of a surface oxide layer, radiation induced damage, surface segregation and lead inclusions.