Invited Paper SS1-WeM5
Reactivity of Low-dimensional Oxide Nanostructures^*

Wednesday, October 17, 2007, 9:20 am, Room 608

Oxide materials in nanostructured layers exhibit physical and chemical properties that are significantly different from their respective properties in macroscopic bulk phases. This novel behaviour forms the basis for many potential applications of oxide nanostructures in diverse areas of the emerging nanotechnologies. Here we discuss the physico-chemical properties of ultrathin oxide overlayers (nanolayers = thickness ≤ 10 ML), grown on metal single crystal surfaces, in terms of their novel structural concepts, their modified electronic behaviour and their sensitivity to changes in the chemical environment. A multitude of experimental techniques (STM, SPA-LEED, XPS, NEXAFS, UPS, HREELS) in conjunction with ab initio DFT model calculations has been applied to characterise the oxide nanolayers deposited on Pd and Rh substrate surfaces. The oxide materials considered comprise nickel, manganese and cobalt oxide phases. Specifically, we will discuss chemical and structural aspects of phase transformations of Mn-oxide overlayers in the 1-10 ML range on Pd(100). Emphasis will be put on the structural transition from the MnO(100) to the MnO(111) orientation as a function of the chemical potential of oxygen and on the oxidation of MnO to Mn₃O₄ surface phases. The chemical interaction of NiO(100) surfaces, epitaxially grown on Pd(100), with metallic cobalt and Co-oxide overlayers is addressed from the viewpoint of generating sharp antiferromagnetic-(anti)ferromagnetic interfaces. It is shown that CoO(100) can be grown epitaxially on NiO(100) and that a 1-2 ML CoO buffer layer can inhibit the oxidation reaction of Co metal overlayers, thus forming a sharp AFM-FM interface. The oxidation of metallic quasi-one-dimensional (1-D) Ni nanowires, formed on the stepped Rh(15 15 13) surface, to 1-D Ni-oxide phases is illustrated. The latter are compared to the 2-D Ni-oxide phases that develop by reactive physical vapour deposition on the same stepped Rh surface, in order to assess the dimensionality aspects in the formation of oxide nanostructures.

^*Supported by the Austrian Science Funds (FWF) and the EU STREP programme GSOMEN.