Angular distributions of sputtered atoms from ion-bombarded surfaces

Abstract

Using the ACAT code, angular distributions of sputtered atoms have been investigated under various surface conditions. Two different models of rough surfaces are employed, i.e., (1)the rough surface with randomly distributed vacancies at the topmost layer, (2) the rectangular-step surface.

Computer simulations have been performed for 1.05 keV Ar ions on Ta target. It is found that the ion-bombardment-induced surface roughness very much influences the angular distributions of sputtered atoms at grazing angle of incidence. Ion-bombardment induced-surface roughness plays two important roles for angular distributions of sputtered atoms at grazing angles of incidence: (1) Due to the surface roughness the surface scattering is reduced, and so the velocity distribution of recoil atoms in coillision cascades near the surface scattering is reduced, and so the velocity distribution of recoil atoms in collision cascades near the surface become more isotropic, which leads to the cosine-like distribution. (2) Due to surface roughness the average distance of two surface atoms is larger than that of unirradiated surace, and so the shadowing effect and the periodicity of surface atoms is less problem. As a result, the preferential angle of ejection from the ion-bombardment-induced rough surface can roughly be estimated by the direct knock-out model.