Low-energy Auger and autoionization emissions of clean and O₂-exposed FeTi and Fe₂Ti₄O

Three distinct features in the low-energy Auger spectrum of the intermetallics FeTi and Fe₂Ti₄O, namely the Ti(M₂₃VV) transition, a transition involving titanium-oxygen bonding electrons, Ti(M₂₃V)TiO(V), and gain satellites recently identified as being due to autoionization emission, were found to furnish detailed information concerning chemical bonding at the surface of clean and oxygen exposed samples. Marked changes in these spectral features upon O₂ exposure indicate selective interaction of oxygen with the Ti atoms from the early stages of adsorption. The spectral changes at low oxygen exposure are discussed in terms of the population of interstitial oxygen sites to a critical local concentration, and the subsequent nucleation and growth of a stoichiometric surface oxide. At ∼ 40 L O₂ exposure apparent saturation is reached with a TiO₂ overlayer formed on both of the compounds at 300 K. Subtle differences between the autoionization emission feature in pure and in alloyed Fe are noted and discussed.