An X-ray photoelectron diffraction structural characterisation of epitaxial ultrathin RuO2/TiO2(110) films obtained by decomposition of Ru3(CO)12

An RuO2/TiO2(110) ultrathin film, epitaxially grown in ultrahigh vacuum by reactive deposition of Ru3(CO)12 in an oxygen atmosphere (2×10−6 mbar) at 300°C, has been characterised by means of X-ray photoelectron diffraction (XPD) measurements coupled to multiple-scattering (MS) simulations. Comparison of the overlayer Ru 3d5/2 and the clean substrate Ti 2p3/2 2π plots gives direct evidence for an RuO2 overlayer well ordered in the short range, with the rutile structure (typical of both the underlying substrate and bulk RuO2) which continues the (110) stacking of the substrate in a single orientational domain. The presence of a sharp low-energy electron diffraction (LEED) pattern, identical to that of the clean substrate, proves the extension of the translational order to the long range and suggests a pseudomorphic growth. Multiple-scattering calculations of the diffraction pattern lead to a detailed quantification of the thin film relaxation.