Alumina vapour condensation on Mo( [formula omitted]) surface and adsorption of copper and gold atoms on the formed oxide layer

Abstract

Aluminium oxide vapour condensation on Mo(1 1 0) surface and subsequent adsorption of Cu and Au submonolayer films on the formed ultrathin oxide layer has been studied by X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and reflection–absorption infrared spectroscopy. AES and XPS data suggest that the oxide films formed in this way exhibit the properties characteristic for the bulk alumina, although the intramolecular bond weakening (up to 30%) compared to bulk oxide occurs at the submonolayer coverage. Both Cu and Au form 3D clusters on the surface of the oxide film regardless of its thickness (2–5 ML). At a very low coverage (<0.4 ML) Cu deposited on the oxide strongly interacts with the surface oxygen forming the species resembling the copper oxide(s). At a higher coverage the Cu deposits have metallic character. Unlike Cu, the latter, however, is the case for gold particles regardless of the coverage: No evidence of forming of the Au–O bonds was found at room temperature. Annealing of Au and Cu deposits on Al 2O 3 film results in metal/oxide intermixing and chemical reaction. The properties of the metals deposited on 2 and 5 ML thick oxide films are essentially the same at all coverages studied. The only observed difference is that the gold deposited on a thinner oxide film is characterised by a smaller average sizes of islands compared to Au deposited on a thicker oxide film. We tend to attribute this difference to higher defect density in thinner oxide film compared to thicker film, rather than to the influence of the underlying Mo(1 1 0) support.