Thin Solid Films 400 (2001) 154–159 0040-6090/01/$ - see front matter  2001 Elsevier Science B.V. All rights reserved. PII: S0040-6090 Ž 01 . 01502-4 Spectroscopic and structural characterisation of a VO (xf1) ultrathin x epitaxial film on Pt (111) Mikhail Petukhov , G. Andrea Rizzi, Gaetano Granozzi* 1 Dipartimento di Chimica Inorganica Metallorganica ed Analitica and Unita di Ricerca INFM, Universita di Padova, via Loredan 4, 35131 ` ` Padova, Italy Abstract VO ultrathin epitaxial films (0.8FxF1.3), grown on Pt(111) by evaporating vanadium in a controlled water background x (1=10 Pa), have been chemically characterised by X-ray photoelectron spectroscopy (XPS) and X-ray-excited Auger electron y7 spectroscopy (AES), which confirm the presence of V(II). The VO film shows a NaCl-type structure exposing the (111) plane, as proven by XPD. Multiple scattering calculations are compatible with an O-terminated surface and a surface relaxation of the outermost atomic layers, which leads to a V–O bond length contraction amounting to 7%.  2001 Elsevier Science B.V. All rights reserved. Keywords: Growth; Photoelectron diffraction; Epitaxy; Vanadium oxide; Platinum 1. Introduction Vanadium (II) oxide, VO, is a well-known example of a non-stoichiometric oxide. Like TiO, VO can be more correctly formulated as VO , where 0.8FxF1.3, x and therefore it may present both cation and oxygen vacancies w1,2x, which cause correlated electronic prop- erties w1–3x. VO oxidises very easily to V O , and this 2 3 is probably one of the reasons why only a few papers have been published so far on the electronic surface characterisation of VO . x A viable methodology to study such surfaces comes from the examination of ultrathin epitaxial VO films. x Actually, VO epitaxial films were grown on Cu(100), x Ni(110) w4,5x, Pd(111) w6x and on TiO (110) w7,8x. In 2 the case of the Cu(100) and Ni(110) substrates, VO x films were grown by exposure of deposited vanadium atoms to O (10 Pa range) at 310 K followed by y5 2 annealing to 523 K. On Pd(111), the formation of VO x was obtained, only for V oxide coverage between 0.5 * Corresponding author. Tel.: q39-049-8275158; fax: q39-049- 88275161. E-mail address: granozzi@unipd.it (G. Granozzi). Permanent address: IGNP, RRC ‘Kurchatov Institute’, Kurchatov 1 sq., Moscow 123182, Russia. and 1 ML, as the product of V O disproportion to VO 2 3 and VO after annealing at 3508C. A completely differ- 2 ent route was followed when TiO (110) was used as 2 substrate. A stepwise and controlled oxidation of metal deposits was performed by means of annealing cycles, carried out in UHV in order to promote oxygen diffusion from the bulk of the substrate to the surface w7x. This was also the only case in which the formation of a rock- salt-type structure was proven by the analysis of the X- ray photoelectron diffraction pattern (XPD) w8x. A comparison between the XPS binding energy (BE) values and the full width at half-maximum (FWHM) data obtained in w5x and w7x shows some discrepancies, which may be associated either to the actual stoichi- ometry (as written above, VO is a non-stoichiometric x oxide) or to different structures. Pt(111) is a substrate commonly used to grow epitax- ial oxides, mainly because of its chemical stability caused by a very compact surface structure. Its surface lattice parameter is 2.77 A; systems such as MnO and ˚ FeO with larger surface lattice parameters, 3.14 and 3.09 A respectively, were epitaxially grown on Pt(111) ˚ w9,10x, but maintaining their surface lattice parameter. It is well known that the variation in oxygen content in VO strongly affects the dimensions of the unit cell, and