Enhanced oxidation rate of Ni(111) by atomic oxygen

The oxidation of the Ni(111) surface by a supersonic atomic oxygen beam has been quantitatively studied using in situ high-resolution electron-energy-loss spectroscopy. For a room temperature substrate, a drastically different oxidation rate is observed for atomic oxygen induced oxidation than for molecular oxygen based oxidation. This rate was found to be two orders of magnitude higher than that for molecular oxygen. The reaction on a 110 K substrate indicated oxygen uptake only to the chemisorption saturate, with no further oxidation. This later finding agrees with previous results for low surface temperature oxidation using molecular oxygen, implying that the inhibiting step in low temperature Ni oxidation is not molecular oxygen dissociation, but a more fundamental property of the metallic substrate. The chemisorption region of the atomic oxygen reaction was found to saturate at the same sub-monolayer as results from exposure to molecular oxygen, i.e. a dense(1 x 1) overlayer as has been seen on other metals does not form on Ni(111). (C) 1999 Published by Elsevier Science B.V. All rights reserved.