The structure of an ultrathin VOx (x approximate to 1) film grown epitaxially on TiO2 (110)

The analysis by means of multiple scattering cluster (MSC) calculations of full 2 pi V 2p, Ti 2p and O Is X-ray photoelectron diffraction (XPD) patter ns from an ultrathin film (similar to 4ML) of VOx (x approximate to 1) depo sited on the (1 x 1)-TiO2 (110) (rutile) surface leads to a detailed determ ination of the structure and orientation of the overlayer and of its epitax ial relationship with the substrate. The comparison of XPD experimental dat a to theoretical simulations confirms the NaCl-like stacking of the overlay er which is suggested by the direct observation of the experimental 2 pi: p lots and reveals its (100) orientation. The [001] azimuth of the overlayer is aligned with the [(1) over bar 12] direction on the substrate surface an d the overlayer experiences an orthorhombic tensile strain (+7%) in order t o match the substrate epitaxially, with a consequent 12-16% vertical interl ayer spacing contraction. The atomic scale morphology of the (1 x 1)-TiO2 ( 110) surface induces a strong buckling in the overlayer along the [(1) over bar 10] substrate direction [0.5+/-0.1 Angstrom]. (C) 2000 Elsevier Scienc e B.V. All rights reserved.