IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM6
Surface Structures of Ultrathin Vanadium Oxide Films on Pd(111)@footnote *@

Tuesday, October 30, 2001, 10:00 am, Room 121

Session: Adsorption on Oxide Surfaces
Presenter: S. Surnev, Karl-Franzens-Universität Graz, Austria
Authors: S. Surnev, Karl-Franzens-Universität Graz, Austria
G. Kresse, Universität Wien, Austria
M.G. Ramsey, Karl-Franzens-Universität Graz, Austria
F.P. Netzer, Karl-Franzens-Universität Graz, Austria
Correspondent: Click to Email
The growth and the atomic structure of epitaxial vanadium oxide thin films on Pd(111) have been investigated by scanning tunnelling microscopy (STM) and low-energy electron diffraction (LEED), combined with ab-initio density-functional theory (DFT) calculations. At submonolayer coverage a well ordered (4x4) oxide overlayer forms which transforms into a porous oxide network with an internal (2x2) periodicity upon exposure with H@sub 2@ at room temperature. The reactivity of the (4x4) phase towards H@sub 2@ is very high, so that small amounts of H@sub 2@ from the residual atmosphere are often sufficient to promote this transformation. The (2x2) phase represents an interface-stabilised surface-V@sub 2@O@sub 3@ layer, which becomes compact upon mild annealing in vacuum exhibiting a (2x2) honeycomb structure. Between 0.5 and 1.0 monolayer equivalents (MLE) the growth of oxide islands with a zigzag stripe structure is observed along with the (2x2) layer. At 1 MLE several VO@sub 2@-like phases are coexistent at the surface in the form of islands with rectangular and hexagonal structures, which are distinguished from the known bulk-type rutile VO@sub 2@ lattice. The detailed atomic structure and energetic stability of these monolayer V-oxide phases have been revealed by the DFT calculations. Above 2 MLE three-dimensional crystallites grow epitaxially on Pd(111) with the corundum structure, which is typical of the bulk-type V@sub 2@O@sub 3@. Two stable V@sub 2@O@sub 3@(0001) terminations have been found in the STM images, which are due to bulk-type oxygen planes and terminal vanadyl species, as suggested by the DFT calculations and confirmed by HREELS. @FootnoteText@ @footnote *@ Supported by the Austrian Science Foundation.