Surface and sub-surface oxidation of α-Cu-(17 at.%)Al(1 0 0) studied by X-ray photo-electron spectroscopy and low energy He+ scattering spectroscopy

In this study the initial stages of oxidation of the α-Cu-(17 at.%)Al(1 0 0) single crystal oriented alloy surface was investigated by X-ray photo-electron spectroscopy and low energy He+ scattering spectroscopy. It was found that oxygen adsorption can be divided in two sequential stages: (i) a fast process, up to 15-20 L exposure, in which oxygen adsorbs on the alloy's surface resulting mostly in the formation of Al-O chemisorbed bonds; and (ii) a slower process during which oxygen adsorbs forming Cu-O and Al-O chemisorbed bonds concurrent with diffusion of O to the sub-surface and Al segregation to the surface region. The surface oxidation rate is much higher than the sub-surface one. The rate of Al segregation increases with oxygen exposure and involves both surface and sub-surface regions. Annealing of the oxidized alloy surface results in a pronounced segregation of Al and formation of an aluminum oxide layer.