Investigation of chemical reactivity at the M/CuO interfaces (where M = Fe, Co, or Ni)

Abstract

The chemical reactivity at the M/CuO interfaces (where M is Fe, Co, or Ni) has been studied. Thin films (of thickness 0.5 nm) of the metal M were deposited at room temperature on the CuO substrate by the e-beam method. The interfaces have been characterized in situ by the technique of x-ray photoelectron spectroscopy. The 2p core level regions of the metals have been investigated. The spectral data show considerable reactivity at the interfaces formed at room temperature. The core level peaks of the metal M have been observed to shift to the high binding energy side. Intense satellites appear on the high binding energy side of these core level peaks. The spectral data have been compared with those of the oxidized metal. These spectral features conform to each other confirming the formation of the metal oxide. The satellite structure in the copper region was observed to disappear, and the spectral features approach those of elemental copper after the deposition of the metallic overlayer. The data, therefore, suggest that the copper oxide gets reduced to elemental copper, and the metal M is oxidized to the metal oxide. The presence of the high binding energy satellite has been used to identify the phase of the metal oxide formed at the interface. The uniformity of the initial 0.5 nm overlayer has also been investigated. A second overlayer of 0.5 nm was deposited over the first layer. The characterization of these samples showed core level peaks at the elemental positions. The spectral features correspond to the presence of unreacted metal in these samples. The content of this unreacted metal was determined and is observed to increase in the order from iron to cobalt to nickel. The investigation shows room temperature chemical reactivity at the M/CuO interface and provides a new method to prepare sub-nano-oxide films of iron, cobalt, and nickel.