Nanoscale self - affine surface smoothing by ion bombardment

Topography of silicon surfaces irradiated by a 2 MeV Si + ion beam at normal incidence and ion fluences in the range 10 15 − 10 16 ions/cm 2 has been investigated using scanning tunneling microscopy. At length scales below ∼ 50 nm, surface smoothing is observed; the smoothing is more prominent at smaller length scales. The smoothed surface is self-affine with a scaling exponent α = 0.53 ± 0.02. One of the fundamental problems in materials science is to understand the effects of particle radiation on solid surfaces. The evolution of solid surface topography during ion-beam irradiation is governed by the interplay between the dynamics of surface roughening due to sputtering and smoothing due to material transport during surface diffusion. These competing processes are responsible for the creation of characteristic surface features like quasiperiodic ripples [1–4] and self-affine topographies [4–6]. These have been observed in the ion energy regime where sputtering is dominant and ion incidence is tilted to the surface normal. Although there is a large number of observations of ripple formation there are only a few studies on the scaling of the surfaces evolved in ion bombardment [4–6]. A common feature of most rough surfaces observed experimentally or in discrete models is that their roughness follows simple scaling laws. Surface root-mean-square roughness σ is defined as σ =< [h(x, y) − h] 2 > 1/2 , where h(x, y) is the surface height at a point (x, y) on the surface 1