An offline prediction of nanoscale ripples propagation under ion irradiation: A correlation between ripples velocity and surface erosion rate

Abstract

An offline measurement of surface ripples propagation has been proposed using sequential ion beam irradiation approach. First, the ripple patterns were grown on Si (100) using 100 keV Ar+ at a fluence of 9 × 1017 ions/cm2 and then subsequent second stage irradiation was performed on partially masked rippled surface to study the ripple's propagation and surface erosion. Offline atomic force microscopy (AFM) study shows that with increase in fluence from 3 × 1017 ions/cm2 to 7 × 1017 ions/cm2, in second stage irradiation, the ripples are found to propagate along the projection of the ion beam's incident direction onto the surface. This observation of ripples propagation contradicts several existing models for ion-beam-induced ripple development. Furthermore, surface erosion rate due to sputtering was measured using stylus profilometer. A prediction of relation “v ~0.75 vo” between ripple's propagation velocity (v) and surface erosion rate (vo) shows the importance of Navier-Stokes viscous flow in near surface layer for the evolution of ripple patterns under ion beam irradiation (IBI).