Core level X-ray photoelectron spectroscopy study of exchange coupled Fe/NiO bilayer interfaced with Si substrate (Fe/NiO-nSi structure)

The chemical interactions and surface chemical states of exchange coupled structures of Fe/NiO bilayer interfaced with silicon substrate has been studied from X-ray photoelectron spectroscopy (XPS) technique. The structure has been irradiated from swift (∼100 MeV) heavy ions (of Fe7+) with a fluence of ∼5 × 1012 ions/cm2. The surface of the samples has also been cleaned from ion beam etching for various durations to record the XPS spectra. On the irradiation, signals due to Fe2p and Ni2p are emerging along with the signal of Si2p whereas no signal of Si2p has been observed, prior to irradiation. The observation shows that the Si atoms are present within the probed surface layer due to irradiation induced interfacial intermixing. We also observed a shift in the binding energy position of Si2p which could be due to the formation of silicide phases as a result of irradiation induced interfacial intermixing. XPS results have indicated the presence of ionic Fe (Fe2+ or Fe3+) and metallic Ni at the Fe/NiO interface, which could be due to the different chemical reactions at the Fe/NiO interface.