Evolution of morphology in nanocrystalline thin films during ion irradiation

Changes in morphology of nanocrystalline AgCo and AgNi films during ion beam bombardment are investigated using a combination of experiments and molecular dynamics (MD) computer simulations. It is shown as long as the grain size is smaller than the typical dimension of the thermal spike, that surface topography relaxation, stress relaxation, domain and grain growth are governed by a viscous flow mechanism. A detailed analysis of the simulation data reveals that the domain growth proceeds by a mechanism similar to liquid-phase sintering of nanoparticles, whereas grain growth proceeds by grain reorientation. With increasing grain size beyond the thermal spike size, a strong reduction in the rate of change in the surface morphology and film stress is observed.