Interactions of low energy reactive ions with surfaces. II. Reactions of C+, O+, and CO+ ions with nickel oxide, carbide, and carbonyl

Reactions of 5–200 eV C+, O+, and CO+ ions with nickel oxide (NiO), nickel carbide (NiC), and chemisorbed CO on nickel (CO/Ni) have been studied in an ultrahigh vacuum environment using the surface spectroscopic techniques of XPS, UPS, and AES. These low kinetic energy (Ek ) ions react with both the substrate Ni atoms as well as with the O, C, and CO adspecies, the latter reactions resulting in adsorbate chemical sputtering or desorption. Reaction probabilities PR and adsorbate desorption yields Y are determined for several different combinations of reactants and products. The reactions C+ + NiO and O+ + NiC result in O and C desorption, respectively, along with concurrent carbide and oxide formation. The O and C desorption yields are near unity for Ek <20 eV. The oxide desorption yield decreases with increasing Ek. This Ek dependence is contrasted with physical sputtering of NiO by Ne+ in the same Ek region. Recombination of C and O, inducing CO desorption, is asserted as the mechanism for these reactions. The reaction O+ + NiCO results in efficient depletion of surface CO, the results being consistent with recombination of O and CO followed by CO2 desorption. A Monte Carlo simulation is performed to model the C+ + NiO reaction. The results indicate that depletion of surface oxide is dominated by a chemical desorption mechanism for Ek ≲20 eV and that the physical sputtering mechanism becomes increasingly more important as Ek increases until it dominates for Ek ≳200 eV. The reactivity and mechanisms for reactive ion induced desorption are discussed and compared to thermal O2 and CO reactions with surfaces.