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Vanadium pentoxide is a layered compound in which VO monolayers are held together by van der Waals forces. It is therefore possible, in principle, to exfoliate the material and form two-dimensional monolayers. Density functional theory is used to calculate the structure and the energy of vacancy formation for hypothetical, two-dimensional VO systems and compare them to the same properties of VO slabs. We study a two-dimensional sheet (infinite in two directions) and two ribbons (infinite in one direction) whose edges are perpendicular to the [100] or [001] directions. These edges undergo a substantial reconstruction. When an oxygen vacancy is formed, the formal charge of two vanadium atoms is reduced from 5+ to 4+. The energy of oxygen vacancy formation is higher for the two-dimensional structures than for the corresponding slabs (i.e. it is more difficult to remove oxygen from the edge of a ribbon perpendicular to [001] than from the (001) surface of a slab). Therefore, the two-dimensional structures are less aggressive oxidants than vanadium pentoxide powders. [ABSTRACT FROM AUTHOR]

A two-dimensional ternary oxide layer, Cu-tungstate (CuWO 4 ) on Cu(110), has been tested as a substrate for the adsorption of (WO 3 ) 3 cluster molecules from the gas phase. Scanning tunneling microscopy/spectroscopy and X-ray photoelectron spectroscopy have been used to characterize the adsorbed species, while density functional theory has scanned the energy landscape for stable adsorption modes. The (WO 3 ) 3 clusters adsorb in preferential adsorption sites at low temperature (85 K) as stable, only slightly perturbed units, as established both experimentally and theoretically. The preferred sites are the Cu surface rows in the [100] substrate direction, which feature elastic flexibility as a result of ultrasoft phonon modes and are a characteristic of this two-dimensional ternary oxide structure. [ABSTRACT FROM AUTHOR]