Oxidation of Ni60Fe40(100) in the presence of sulfur

Abstract

The effect of adsorbed sulfur on the initial oxidation of a Ni60Fe40(100) alloy surface has been studied at 100 and 500 °C using low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). Measurements of the oxygen uptake rate have been made as a function of sulfur coverage at each temperature. Within the O2 exposure range studied, the uptake of O2 is observed to be inhibited by an ordered c(2×2) sulfur phase at 0.5 monolayers coverage, independent of temperature. For sulfur coverages below 0.5 monolayers, an Fe-rich surface oxide forms with a composition and morphology dependent on the sample temperature. The experimental observations suggest that at 500 °C, sulfur-free oxide islands grow interspersed between c(2×2)S domains whereas at 100 °C, the adsorbed sulfur layer becomes overgrown by coalesced oxide. The mechanisms of oxide nucleation and growth are related to the existence of different phases of the chemisorbed sulfur + oxygen layer as previously studied.