Metal adsorption on oxide polar ultrathin films

The adsorption of Au and Pd atoms on two nanostructured titania monolayers grown on the Pt(111) surface is investigated via a computational approach. These phases present compact regions (zig-zag-like stripes) with titanium atoms at the oxide-metal interface and oxygen in the top-most overlayer, sometimes intercalated by point defects, i.e. holes exposing the bare metal support, and give rise to very regular patterns extending for large distances. A Pd atom experiences a rather flat energy landscape on the compact regions whereas it is strongly bound to the defects which act as nucleation centers, whence the interest of these substrates as nanotemplates for the growth of metal clusters. The interaction of a Au atom with these phases is peculiarly different: a charge transfer from the underlying Pt(111) support occurs so that Au gets negatively charged and strongly interacts with a titanium atom extracted from the interface in the compact regions, whereas it penetrates less easily than Pd into the defective holes due to its larger size. These results are discussed as paradigmatic examples of the interaction of metals with polar ultrathin films of oxides grown on metal supports, a novel and promising field in materials science.