The growth of thin vanadium oxide films on Pd(lll) prepared by reactive evaporation of vanadium in an oxygen atmosphere has been studied by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and ab initio density-functional-theory (DFT) calculations. Two-dimensional (2D) oxide growth is observed at coverages below one-half of a monolayer (ML), displaying both random island and step-flow growth modes. Above the critical coverage of 0.5 ML, three-dimensional oxide island growth is initiated. The morphology of the low-coverage 2D oxide phase depends strongly on the oxide preparation conditions, as a result of the varying balance of the mobilities of adspecies on the substrate terraces and at the edges of the growing oxide islands. Under typical V oxide evaporation conditions of p(O-2) = 2 x 10(-7) mbar, T(substrate) = 523 K, the 2D oxide film exhibits a porous fractal-type network structure with atomic-scale ordered branches, showing a p(2 x 2) honeycomb structure. Ab initio DFT total-energy calculations reveal that a surface oxide model with a formal V2O3 stoichiometry is energetically the most stable configuration. The simulated STM images show a (2 x 2) honeycomb structure in agreement with experimental observation. This surface-V2O3 layer is very different from bulk V2O3 and represents an interface stabilized oxide structure. The V oxide layers decompose on annealing above 673 K and 2D island structures of V/Pd surface alloy and metallic V are then formed on the Pd(111) surface.
