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 $\sim$~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 $\alpha =0.53\pm 0.02$.