XPS, UPS and AES study of surface segregation and oxidation of Ni-Ru alloy: evidence for decrease in dissociation temperature of NiO in the presence of Ru

Our AES study on the Ni-4.9 at %Ru alloy shows Ru segregation to the surface with an enthalpy of segregation of -4 kJ/mol. On exposing the alloy to oxygen at 300 K, XPS and UPS studies show two types of oxygen species, O2-(529.4 eV) and O1- (531.4 eV); formation of NiO is also clearly observed. On heating the oxidized alloy surface in vacuum at 700 K, desorption of oxygen occurs as seen from the decrease in the O(1s) and O(KLL) peaks as well as the O(2p) band which was further confirmed by a thermal desorption study. Such a behaviour is attributed to the decrease in the dissociation temperature of NiO in the presence of Ru via O2-→O1- conversion