Real-time X-ray studies of the growth of Mo-seeded Si nanodots by low-energy ion bombardment

Silicon surface evolution during room temperature low-energy (300, 500 and 1000 eV) normal incidence Ar⁺ ion bombardment in the presence of Mo seed atoms has been studied with real-time grazing-incidence small-angle X-ray scattering and ex situ atomic force microscopy. When a small amount of Mo atoms was supplied to the Si surface during ion bombardment, the development of correlated structures with two different characteristic length scales was observed. The shorter length scale features (“dots”) coarsened with time until they reached a constant spatial wavelength. The longer length scale corrugations associated with kinetic roughening, however, continued to grow in amplitude during bombardment. The overall roughness is dominated by different corrugations at different times in the kinetic evolution, showing a complex behavior. The evolution of the kinetic roughening can be described by the Family-Vicsek scaling hypothesis, but measured scaling exponents are not in agreement with those of existing models.