Computer modeling of angular emission from Ag(100) and Mo(100) surfaces due to Ar_n cluster bombardment

Molecular dynamics computer simulations are employed to investigate the effect of projectile size and surface morphology on the angular emission stimulated by impact of Ar gas cluster projectiles. Argon clusters of sizes n = 10-1000 and kinetic energies of 10 and 20 keV Ar_n aimed at normal incidence are used to sputter Ag(100) and Mo(100) samples. The total sputtering yield is larger for Ag(100) than for Mo(100). The ratio of sputtering yields is inversely proportional to the ratio of sublimation energies of these solids for projectiles between Ar₂₀ and Ar₂₅₀. In both systems, the angular distributions are sensitive to both the projectile size and the surface roughness. The maximum of angular spectra shifts from direction normal to the surface toward off-normal direction with the increase in the projectile size. An opposite trend is observed with the increase in the surface roughness. Formation of a cloud composed of projectile atoms and the enhanced lateral material relocation caused by projectile lateral expansion upon impact are the main factors responsible for promoting off-normal ejection. On the other hand, material ejection from randomly inclined surface areas and the influence of nearby topography are found to be responsible for enhancing ejection along the surface normal for rough surfaces.