Chemical reactivity at Fe/CuO interface studied in situ by X-ray photoelectron spectroscopy

Abstract

The technique of X-ray photoelectron spectroscopy has been used to investigate the chemical reactivity at the Fe/CuO interfaces. The 2p core level regions of the metals have been studied. Thin films of iron (thicknesses ranging from 0.3 nm to 2.0 nm) were deposited on copper oxide substrates at room temperature. Earlier investigation on a 0.5 nm overlayer of iron on CuO showed considerable reactivity at the interfaces. The core level peaks of iron are observed to be shifted to the high BE energy side with the appearance of satellites. The spectral data have been compared with those of the oxidized iron and confirms the formation of the iron oxide at the interface. The satellite structure in the copper region is observed to disappear and the spectral features are found to approach those of elemental copper. The interface is found to consist of a mixture of iron oxide and elemental copper. Presence of unreacted iron near the interface has been observed for thicknesses greater than 0.7 nm of the iron overlayer. The effect of temperature on the interface has also been studied. The interface was formed by depositing 2.0 nm of iron on the copper oxide substrate under two different conditions. In one, the substrate temperature was kept constant during the deposition of the iron overlayer. In the other, post deposition annealing of the interface was performed. The iron overlayer is observed to be completely oxidized at the sample temperature of 450 °C and the oxidation is independent of the processing conditions. The amounts of elemental iron and iron oxide in the samples have been estimated by modeling the spectrum using the spectra of elemental iron and pure iron oxide. The process of annealing seems to have more effect on the oxidation of iron than the substrate temperature. The investigation shows room temperature chemical reactivity at the Fe/CuO interface and provides a new method of preparing sub-nano-oxide films of iron.