Oxygen on Ni(110): Surface phases and related absolute coverages

The adsorption of oxygen on Ni(110) was investigated by nuclear reaction analysis (NRA), XPS, Δφ, temperature programmed reaction spectroscopy (TPRS) and LEED. At 423 K, (3 × 1), (2 ×1) and (3 ×1) phases are formed in sequence with increasing O₂ exposure. The coverage in the (2 ×1) phase was determined by NRA, the coverages in the other phases being determined via this calibration by XPS, TPRS and Δφ. Contrary to previous reports, the maximum in the intensity of half-order beams from the (2 × 1) phase is associated with a coverage of (5.6 ± 0.5) × 10¹⁴ O atoms cm⁻² or 0.49 ± 0.05 monolayers, and not 0.25 monolayers. The two (3 ×1) phases are associated with θ = 0.33 ± 0.03 and 0.64 ± 0.06 monolayers respectively. Oxygen adsorbed at 295 K is not at thermodynamic equilibrium. Annealing to T > 400 K causes significant decreases in Δφ and the formation of the (2 ×1) phase for θ > 0.3.