The reaction of oxygen with Ti,Cr, Fe and Ni studied by appearance potential spectroscopy

The interaction of oxygen with the surface of evaporated films of Ti, Cr, Fe and Ni has been studied with appearance potential spectroscopy (APS). Both oxygen Is and metal 2p spectra were recorded. Two adsorption regimes were clearly distinguishable: (i) a chemisorption regime characterized by a single peak in the oxygen 1s spectra and unchanged metal 2p spectra, (ii) an oxide regime with pronounced multipeaked structures in the oxygen 1s spectra and appreciable changes in the metal 2p spectra. The technique allows the determination of the exposure at which an oxide starts to grow on the surface.