Influence of metal codeposition on the growth and orientation of nanoripple structure during ion bombardment

Surface engineering to tune the surface characteristics for the enhancement of a system is an emerging area of research in terms of its immense technological applications and basic scientific understanding. The ion beam sputtering technique in combination with cosputtered material deposition to form various structures is found to be a very effective bottom-up approach to modify the surface morphology of a material. In this paper, a theoretical model is developed for ripple evolution of a flat elemental surface which is subjected to erosion by ion bombardment at off-normal incidence with concurrent deposition of some impurity or foreign materials. The orientation of the ripple wave vector thus produced exhibits a directional dependence behavior on the projection of both the ion beam and the foreign elements on the surface. The compound formation at the near-surface depth is considered to be the key assumption for inducing such patterns on the surface. The theoretical prediction is realized in the experimental work demonstrated herein. Stainless steel is used as a cosputtering target during irradiation of Si at 30 degrees incidence by a low-energy Ar+ ion beam. The ripples that so emerge possess a wave vector lying oblique to the direction of the ion beam and impurity. The development of such morphological instability is attributed to the reaction between Fe and Si, which gives rise to a compound with an erosion rate lower than that of Si. Thus, the formation of the FeSi2 bond, which is interpreted as being a crucial criterion for pattern evolution, agrees well with the theory, making it quite efficient and widely acceptable.