Interactions of low energy reactive ions with surfaces. I. Dose and energy dependence of 3–300 eV C+, O+, and CO+ reactions with a Ni(111) surface

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Abstract
Reactions of C+, O+, and CO+ ions with a clean Ni(111) surface are studied as a function of both kinetic energy (Ek) and ion dose for a range of chemically important energies (3–300 eV). An energy‐ and mass‐selected, differentially pumped ion beam and ultrahigh vacuum spectrometer system which is designed to perform Ek dependence measurements of low‐Ek ion–surface interactions is described. The Ni surface is exposed to low‐Ek beams of these ions and concentrations of the resulting adspecies are monitored by Auger electron spectroscopy (AES) and x‐ray and UV photoelectron spectroscopy (XPS and UPS). Reactions of C+ and O+ with Ni(111) yield nickel carbide (for monolayer doses) and oxide, respectively. These reactions are efficient at low Ek; reaction probabilities Pr =0.6–0.8 are observed for Ek Pr decreases slowly with increasing Ek until implantation of ions into the solid becomes significant. In the reaction of CO+ with Ni(111), the yield of molecular CO on the surface drops rapidly from 0.5 to below 0.1 in the range 3–10 eV. Collisional dissociation of CO+, which results in formation of surface NiC and NiO adspecies, increases with Ek and becomes the dominant process above 9 eV. Depth profile studies of the reacted surfaces indicate that implantation of C+ into subsurface Ni layers is more facile than implantation of O+ in the high energy portion of the range investigated. A Monte Carlo simulation of the atomic ion penetration into Ni has been carried out and the results are compared with experimental measurements. Reaction, desorption, and collision induced dissociation of the reactive ions and their reaction energetics are discussed in terms of qualitative potential energy diagrams in order to interpret the observed Ek dependence.