Mechanisms of CO ejection from ion bombarded single crystal surfaces

Abstract

We have calculated the response of a model Ni(001) microcrystallite to 600 eV Ar⁺ ion bombardment when it is covered with 0.5 monolayer of CO. Calculations were performed using a standard molecular dynamics treatment which employs pair potentials fit to the elastic constants of the solid to evaluate Hamilton’s equations of motion. The model microcrystallite contained ∼240 atoms. The CO was adsorbed in a c(2×2) coverage in both an atop or linear bonded and a twofold bridge bonded position with a binding energy to the surface of 1.3 eV. The results showed that most of the CO molecules eject molecularly, although a few (∼10%–15%) eject dissociatively if they are hit directly with the primary ion or with other energetic solid atoms. We also found that NiCO as well as Ni₂CO and Ni₃CO formation probably occurs over the surface via interaction between Ni and CO species, and that the probability of NiC or NiO clusters ejected from a CO covered surface is extremely low.