SIMS and flash desorption studies of nickel oxygen interaction

Abstract

O₂ exposure of polycrystalline nickel at 300 K results in characteristics changes of secondary ion emission. These can be described by a model which is in good agreement with corresponding LEED, AES, XPS, and ΔΦ results of other authors. According to this model, oxygen can be bonded on Ni in at least five different phases:

• 1) chemisorption, indicated by a rapid increase of Ni⁺, Ni ⁺₂ , and Ni₂O⁺ (≦5 L);

• 2) a rearranged chemisorption layer, characterized by a drastic decrease of Ni⁺, Ni ⁺₂ , and Ni₂O⁺ (5–15 L);

• 3) nickel oxide (NiO) responsible for a strong NiO⁻- and NiO ⁻₂ -emission (≦40 L);

• 4) oxygen on top of this NiO layer, producing a final increase of Ni⁺ and NiO⁺ and a O₂-flash signal at 400 K (>40 L);

• 5) bulk dissolved oxygen in thermal equilibrium with a chemisorption layer (after several exposure/heating cycles).

During ion bombardment of a 100 L O₂ exposed Ni surface these different binding states occur in a reversed order of succession. O₂-flash signals at 400 and 1100 K, related to drastic changes in secondary ion emission at 400, 700, and 1100 K, reflect the disappearance of various oxygen binding states. The exchange between different oxygen phases was studied by¹⁶O₂/¹⁸O₂ isotope experiments.