Compositional patterning in immiscible alloys driven by irradiation

Ion-beam mixing of immiscible alloys is viewed as a competing dynamic process, where irradiation-induced mixing opposes thermal decomposition. The external perturbation drives the system away from equilibrium, and in the long-time regime the system can exhibit phase and microstructural modifications. Due to the nonequilibrium nature of the process, the steady state depends explicitly on the details of the interplay between irradiation and the internal kinetics of the alloy. In particular, we have recently developed a continuum model that takes into account the finite range of atomic relocations during collision cascades [R. A. Enrique and P. Bellon, Phys. Rev. Lett. 84, 2885 (2000)]. Using this model, we have shown that self-organized compositional patterns can spontaneously appear if the range of atomic relocations is large enough, and we have introduced a dynamical phase diagram describing the steady state regimes as a function of the forcing and material parameters. In this paper we follow up with the analysis of the continuum model, and we consider the problem of fluctuations. In order to study the phenomenology and test the predictions, we perform kinetic Monte Carlo simulations of an immiscible binary alloy undergoing finite-range atomic relocations. The simulations show that compositional patterns at the nanometer scale can indeed be stabilized, and that the behavior of those patterns as a function of the control parameters can be suitably described by our continuum model, and previous theory of fluctuations in driven alloys. The results corroborate the idea that irradiation can be used as a processing tool to synthesize nanostructures.