Effects of faceted surface topography on high-fluence sputtering of graphite

Effects of ion-induced faceted surface relief on high-fluence sputtering of graphite under 30-keV Ar and 15-keV N ion bombardment have been studied by means of binary-collision computer simulation. Taking into account experimental observations of surface topography, the relief was modeled by an α-dependent ridge-like periodic function (α = the ion incidence angle measured from the normal to macroscopic surface plane). It was shown that for normal incidence the sputter yield S represents a non-monotonic function of the relief aspect ratio and is saturated at x ∼ 100-200 nm (x = the half-period of the relief). The simulations stressed the importance of the relationship between the dimensions of surface roughness and atomic collision cascades and allowed to explain the S(α)-dependences found experimentally. It was shown that a strong (about 2 times) decrease of S at α = 60-80° is due to a shadowing mechanism which is also clearly revealed in the angular distribution of sputtered atoms.