Ž . Applied Surface Science 142 1999 146–151 An ARPEFS study of the structure of an epitaxial VO monolayer 2 ž / at the TiO 110 surface 2 M. Sambi a , M. Della Negra a , G. Granozzi a, ) , Z.S. Li b , J. Hoffmann Jørgensen b , P.J. Møller b a ( ) Consorzio InteruniÕersitario di Scienza e Tecnologia dei Materiali INSTM and Dipartimento di Chimica Inorganica, Metallorganica ed Analitica, UniÕersita di PadoÕa, Via Loredan 4, 35131 PadoÕa, Italy ` b Department of Chemistry, UniÕersity of Copenhagen, 5 UniÕersitetsparken, DK-2100 Copenhagen, Denmark Abstract In the present communication, we discuss the results of an angle resolved photoemission extended fine structure Ž . Ž . Ž . ARPEFS study of a VO monolayer ML grown on the TiO 110 surface by successive cycles of sub-ML vanadium 2 2 metal deposition followed by annealing at 473 K in 2 =10 y6 mbar O . The V 3p photoemission peak shows two distinct 2 Ž . components chemically shifted by 1.3 eV. While the higher binding energy BE component produces a rather flat ARPEFS curve, the lower BE signal, associated with the VO phase, shows well defined intensity modulations whose main features 2 are similar to the ARPEFS scan on the Ti 3p signal of the substrate. This observation demonstrates that the ordered VO 2 phase grows epitaxially to the substrate, with a rutile type structure. However, some oxide is present in a more highly oxidized and less-ordered phase. In order to investigate the actual arrangement of the ML with respect to the question related to the possible formation of an intermixed VO rTiO layer, the ARPEFS data have been interpreted by means of 2 2 Ž . single-scattering spherical wave SSC-SW simulations. They are compatible with the hypothesis that the deposited ML evolves toward an intermixed VO rTiO double layer where the vanadium atoms occupy the six-fold oxygen-coordinated 2 2 sites. In addition, our data are in good agreement with a surface relaxation similar to that found by surface XRD on the Ž . stoichiometric TiO 110 surface. q 1999 Elsevier Science B.V. All rights reserved. 2 Ž . Keywords: ARPEFS study; Epitaxial VO monolayer; TiO 110 surface 2 2 1. Introduction Epitaxial oxide thin films are currently very much investigated with the aim of creating materials with novel optical, magnetic and electrical properties that w x cannot be accessed in equilibrium bulk crystals 1–3 . Their technological applications, however, require that some basic questions concerning the mecha- nisms of growth and their relation with the structure ) Corresponding author are addressed. Within this context, the epitaxial growth of vanadium oxides is rather important both for fundamental reasons and technological applica- tions. In fact, several vanadium oxides undergo metal–semiconductor or metal–insulator transitions as a function of temperature and doping. These transitions, which are believed to arise from the change of strong electronic correlation mechanisms wx associated with crystallographic distortions 4 , rep- resent a subject of considerable interest in solid state w x physics 5–8 . 0169-4332r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S0169-4332 98 00725-9