Chemical reactivity at Sn/CuO interface investigated by X-ray photoelectron spectroscopy

Abstract

In situ characterization of the Sn/CuO interface has been undertaken by the technique of x-ray photoelectron spectroscopy. Thin films of Sn were deposited on CuO substrates kept at ambient temperature. The electron-beam technique was used for the deposition of the films. The photoelectron spectra of the core levels of tin and copper were found to exhibit significant differences upon comparison with the corresponding elemental and the oxide spectra. These differences are attributed to chemical reactivity between the constituents at the interface. Tin was observed to get oxidized to SnO2. The CuO was observed to get reduced to elemental copper. Thermodynamical considerations support the experimental observations. Certain thickness of the oxidized tin was observed to serve as a barrier for further oxidation of the tin overlayer. The relative percentages of tin oxide and elemental tin have been estimated by curve fitting the spectral data with two curves: one for elemental tin and the other for the oxide. The areas under the corresponding peaks were plotted as a function of the overlayer thickness. The data for the elemental tin in such a plot was fitted by a straight line. The extrapolation of this line to zero area provided the interface width (thickness of the SnO2 present at the interface). The width has also been determined for annealing temperatures of 100, 200, 300, 400, and 500 °C. The high temperature spectral data show interdiffusion of tin and CuO. Beyond 200 °C, the interface width was found to vary linearly with the annealing temperature.