Investigation of Fe/Al interface as a function of annealing temperature using XPS

This article describes the systemic investigation of the interface chemical and electronic properties of ultrathin Fe/Al multilayer structure (MLS) as a function of annealing temperature. For this purpose electron beam evaporated [Fe/Al]x15 ML samples have been prepared under ultrahigh vacuum conditions. The chemical and electronic information of the interfaces at different depth has been obtained from XPS technique. The core level study show a gradual change in the nature of the electronic bonding at the interface as a result of annealing. In particular, the MLS annealed at 200 deg. C and 400 deg. C clearly show shifts in the binding energy position of Fe-2p3/2 core line towards higher energy and Al-2p3/2 core line towards lower energy side as compared to as-deposited sample, suggesting the formation of FeAl alloy phase at the interface. Another important finding with annealing is that the intensity of peak corresponding to pure Al-2p increases and that of Fe-2p decreases as compared to as-deposited case. The increase in intensity of Al-2p core line suggests the migration of Al atoms towards the surface owing to annealing induced inter-diffusion. The corresponding valence band spectra show appreciable changes in the Fe-3d as well as Al-3s density of states due to strong hybridization of sp-d states at the Fermi level as a result of charge transfer and also provide strong evidence for FeAl alloy formation.