Mechanisms of CO ejection from ion bombarded single crystal surfaces

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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.