LOW-TEMPERATURE ION-BEAM MIXING OF MEDIUM-Z METALS

Low-temperature ion beam mixing of metals is generally ascribed to a combination of ballistic and thermal spike mechanisms. For heavy ions incident on sufficiently heavy metals the mixing rate varies much faster than linearly with the nuclear energy deposition density, epsilon, possibly quadratically as predicted by a model based on interdiffusion within overlapping thermal spikes. At lower energy densities the mixing rate still exceeds ballistic estimates significantly, but does not vary faster than linearly. Comparisons of results for medium-Z systems ranging from Pd-Ni to Al-Ti in this regime show that the same fundamental mixing mechanism must still be involved - a mechanism that is strongly sensitive to chemical driving forces, i.e., some type of "diffusion". The evidence for a thermal spike mechanism is considered.