Evolution of surface morphology during ion nitriding of aluminium

An increased macroscopic surface roughness with increased temperature is observed after nitriding of Al, indicating a lower surface mobility at higher temperatures. However, a polycrystalline structure of the base material and grain boundaries can also influence the observed results. In this work, it is shown that surface mobility, grain boundary diffusion and bulk diffusion of Al cations dominate in this order with increasing temperature, correlated with their respective activation energies. Together with the total sputter yield and grain orientation dependent variations of this value, these multiple diffusion paths lead to a higher roughness at higher temperatures.