Effect of mass and incidence angle of keV energy polyatomic projectiles in silicon sputtering

Recent experiments of bombardment of silicon targets show that keV energy polyatomic projectiles can greatly increase both the total yield and the secondary silicon ion emission, especially complex secondary ions. This effect is more pronounced for the heavy polyatomic projectiles than for light ones. To understand why the heavy projectiles increase the non-linear enhancement of the yields, molecular dynamics simulations of the bombardment of a Si(1 0 0)-(2 × 1) surface by Al_n (n = 1, 2) and Au_n (n = 1, 2) projectiles with E₀ = 1.5 keV/atom at the incident angles of θ = 0° and θ = 45° have been carried out. It is shown that oblique bombardment by heavy dimer projectiles at this initial energy leads to an increase of the number of trajectories with a very high yield of ejected atoms. A microscopic analysis of the events is given and also the influence of the high yield events on the energy distributions of the sputtered silicon atoms is described.