Reconstruction kinetics of a stepped metallic surface: Step doubling and singling of Ni(977) induced by low oxygen coverages

Helium atom diffraction has been used to study the reconstruction kinetics of a stepped metallic surface, Ni(977), which sequentially undergoes step-doubling and -singling upon dosing with low coverages of oxygen. Over the temperature range 390-470 K it was found that less than 2% of a monolayer of oxygen was sufficient to transform the initially prepared single-stepped surface to a new steady state having a double-stepped structure. The thermal range over which the doubled phase exists extends to higher temperatures when more oxygen is present. At low oxygen exposures this doubled interface reverts to the single-stepped surface above 470 K. Singling can also be driven by more extensive levels of oxygen adsorption. The kinetics of the step-doubling transformation which occurs below 470 K was determined to be second order with respect to single-step density while, for temperatures above 470 K, step-singling followed first-order kinetics with respect to the double-step density. Oxygen atoms adsorbed at step edges play a crucial role in these transformations. Arrhenius analysis is used to extract energetics for the step-doubling and -singling reconstructions. These results delineate the sequence of mechanistic stages which occur during the initial stages of oxidation of a stepped metallic interface which precede the onset of bulk oxidation, findings which are important for developing an improved understanding of metallic oxidation and corrosion.