Towards ordered Si surface nanostructuring: role of an intermittent ion beam irradiation approach

Abstract

The dynamical characteristics of surface nanopatterning using low-energy ion beams remains a central theme within ion beam sputtering. Most previous studies have focused on nanostructure evolution by bombarding surfaces using a continuous ion beam. Here, we study the effect of sputtering from an intermittent ion beam on nanopatterning of a Si surface, using a 900 eV or (mostly) 500 eV Ar$^{+}$ ion beam at an incident angle of 67$^\circ$, up to a total fluence of $10\times 10^{19}$ ions cm$^{-2}$. Nanoripples are predominantly found on the irradiated surfaces, alongside a hierarchical triangular morphology at the lower energy condition. Ripple ordering is superior for intermediate values of the sputtering interval used in the intermittent sputtering approach. The area of the triangular structures also depends on the intermittent sputtering time intervals. At larger length scales than the ripple wavelength or the triangular structures, all surfaces display strong height fluctuations with a well-defined roughness exponent. Our results can be rationalized via known properties of the nonlinear regime of evolution for surfaces that become amorphous under irradiation and relax stress via ion-induced viscous flow, as borne out from numerical simulations of a continuum model previously proven to provide a significant description of the present class of experiments.