STM characterization of size-selected V1, V2, VO and VO2 clusters on a TiO2 (110)-(1 x 1) surface at room temperature

We use ultra-high vacuum scanning tunneling microscopy (UHV-STM) to probe, at the atomic level, the structure of mass-selected isolated V-1, V-2, VO and VO2 clusters deposited on rutile TiO2(110) by ion soft landing. All four species interact differently with the TiO2 surface and the ultimate binding site and configuration strikes a balance between the gas-phase structure and the ligation of this cluster by the TiO2 surface. Our results show that vanadium atoms prefer to bind in the upper threefold hollow sites on the surface and have a slight tendency to pair along the [1-10] direction, while vanadium dimers bind to the surface oriented along the [001] direction exclusively. VO clusters bind with the vanadium atom in the upper threefold hollow site and with the oxygen atom bound to an adjacent fivefold coordinated Ti atom (5c-Ti). The VO2 cluster also binds with the vanadium atom in the upper threefold hollow site and with both oxygen atoms bound to adjacent 5c-Ti atoms or with only one oxygen bound to the surface and the other directed out of the plane of the surface. (C) 2011 Elsevier B.V. All rights reserved.