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Density functional calculations are carried out for the (0 0 0 1) surface of V2O3 in the corundum structure. In thermal equilibrium with the bulk, the dominant surface termination is characterised by vanadyl (VO) groups adsorbed on the (0 0 0 1) surface. Under increased oxygen pressure, the calculations predict that a pure oxygen termination is stable, whereas under very oxygen poor conditions the removal of the oxygen from the VO group can result in a stoichiometric metal termination. The electronic states in the valence band regime, the oxygen and vanadium core-level binding energies, and the vibrational spectra are calculated for the bulk and the surface by density functional theory and compared to recent experimental studies. [Copyright &y& Elsevier]

The vanadium oxides can exist in a range of single and mixed valencies with a large variety of structures. The large diversity of physical and chemical properties that they can thus possess make them technologically important and a rich ground for basic research. Here we assess the present status of the microscopic understanding of the physico-chemical properties of vanadium oxide surfaces. The discussion is restricted to atomically well-defined systems as probed by surface techniques. Following a brief review of the properties of the bulk oxides the electronic and geometric structure of their clean single crystal surfaces and adsorption studies, probing their chemical reactivity, are considered. The review then focuses on the growth and the surface properties of vanadium oxide thin films. This is partitioned into films grown on oxide substrates and those on metal substrates. The interest in the former derives from their importance as supported metal oxide catalysts and the need to understand the two-dimensional overlayer of the so-called “monolayer” catalyst. On the single crystal metal substrates thin oxide layers with high structural order and interesting properties can be prepared. Particular attention is given to ultrathin vanadium oxide layers, so-called nano-layers, where novel phases, stabilised by the substrate, form. [Copyright &y& Elsevier]

Well-ordered epitaxial V2O3(0 0 0 1) films (thickness > 80 A˚) have been prepared on the clean Rh(1 1 1) surface and investigated with scanning tunnelling microscopy, low-energy electron diffraction, high-resolution electron energy loss spectroscopy and high-resolution X-ray photoelectron spectroscopy with synchrotron radiation. Atomically flat V2O3(0 0 0 1) surfaces, terminated by vanadyl (V&z.dbnd6;O) groups, have been obtained after the reactive oxide deposition and subsequent annealing in vacuum to 600 °C. Annealing the V&z.dbnd6;O termination in oxygen atmosphere (500 °C, 5 × 10−6 mbar) results in the partial removal of the vanadyl groups and in the formation of an oxygen-richer surface termination, exhibiting a (√3×√3)R30° structure. Structure models for this oxygen-rich termination are proposed, which are characterised by (O&z.dbnd6;V)0.66–O3–V–V⋯ and (O&z.dbnd6;V)0.33–O3–V–V⋯ stacking sequences. Conversely, deposition of submonolayer V coverages onto the V&z.dbnd6;O surface leads to the formation of a metal-rich V2O3(0 0 0 1) surface, terminated by a close-packed V3 layer on top of the bulk-type O3 plane. Such a VO(1 1 1)-layer is only metastable and oxidises back readily upon annealing in vacuum to the vanadyl-terminated V2O3(0 0 0 1) surface. [Copyright &y& Elsevier]

Abstract: We report on an interface-stabilized strained c(4×2) phase formed by cobalt oxide on Pd(100). The structural details and electronic properties of this oxide monolayer are elucidated by combination of scanning tunneling microscopy data, high resolution electron energy loss spectroscopy measurements and density functional theory. The c(4×2) periodicity is shown to arise from a rhombic array of Co vacancies, which form in a pseudomorphic CoO(100) monolayer to partially compensate for the compressive strain associated with the large lattice mismatch (∼9.5%) between cobalt monoxide and the substrate. Deviation from the perfect 1:1 stoichiometry thus appears to offer a common and stable mechanism for strain release in Pd(100) supported monolayers of transition metal rocksalt monoxides of the first transition series, as very similar metal-deficient c(4×2) structures have been previously found for nickel and manganese oxides on the same substrate. [Copyright &y& Elsevier]

Abstract: The growth, morphology and epitaxial relationship of Ag nanostructures deposited onto the c(4×2)-NiO x /Pd(100) surface have been investigated by photoemission (both core and valence levels), scanning tunneling microscopy and angle-scanned photoelectron diffraction. Small Ag nanoparticles are obtained on the terraces, whereas the tendency of Ag to decorate the step edges can lead to the formation of extended nanowire-like features. The Ag nanoparticles adopt a fcc structure epitaxially related to the substrate according to the following relationship: Ag(100)[001]//Pd(100)[001], while by means of STM we have found that the shape of the islands is typically rectangular with the edges running along the [011] directions. According to the reported data, the NiO x ML is locally disrupted in the vicinity of the Ag nanoparticles so that the c(4×2)-NiO x /Pd(100) surface cannot be considered as an efficient template to stabilize metal nanoparticles against Ostwald ripening phenomena. [Copyright &y& Elsevier]