A model was proposed in order to describe the disordering of ordered samples under irradiation. In the case of the thermal spike phase of a displacement cascade, the processes of heat evolution and conduction in the cascade region were modelled by solving the thermal conduction equation (using a discretization method) for a medium that could melt and solidify under suitable conditions. The model assumed that disordering resulted from cascade core melting, in which the final disordered zone corresponded to the largest molten zone size that was attained. The initial conditions for this treatment were deduced from cascade simulations. The contrast from disordered zones, when imaged by superlattice dark-field reflection and projected onto a plane that was parallel to the surface of a thin foil, was calculated. The average sizes of images from hundreds of cascades that were created by incident Cu+ ions were calculated for various ion energies and were compared with transmission electron microscopic data. It was found that the model was in reasonable quantitative agreement with experimentally observed trends.

V.G.Kapinos, D.J.Bacon: Philosophical Magazine A, 1995, 72[5], 1413-20