HIGH-ENERGY ION-BEAM MIXING IN DENSE COLLISION CASCADES

Atomic mixing of tracer atoms in dense collision cascades in metals is calculated. The model used in the calculations describes the atomic transport from the initial collisional phase to the late thermalized stage. The collisional mixing is calculated by Monte Carlo simulation and a thermal spike model is used to describe the late phase of the cascade. The cooling of a thermal spike is described by coupled heat conduction equations for conduction electrons and lattice. Atomic transport takes place above the glass transition temperature of a metallic matrix and the transport is treated as diffusion in liquids. The heat exchange between conduction electrons and lattice allows rapid quenching of thermal spikes in metals with high d-electron density. Mass and heat transport coefficients are calculated on the basis of elementary solid state models, accordingly; the model for ion beam mixing contains no adjustable parameters. Calculations for metal markers in Ni, Cu, Ag, Pd, Au and Pt are in agreement with experimental results, when the cohesive energy of marker atoms is sufficiently similar to that of matrix atoms. The model predicts a pronounced temperature dependence for the high-energy ion-beam mixing in Cu, Ag and Au.