Planar Vanadium Oxide Clusters: Two-Dimensional Evaporation and Diffusion on Rh(111)

Abstract

The formation of novel vanadium oxide cluster molecules by oxidative two-dimensional evaporation from vanadium oxide nanostructures is reported on a Rh(111) metal surface. The structure and stability of the planar V6O12 clusters and the physical origin of their 2D evaporation process have been elucidated by high-resolution scanning tunneling microscopy (STM) and ab initio density functional theory calculations. The surface diffusion of the clusters has been followed in elevated-temperature STM experiments, and the diffusion parameters have been extracted, indicating diffusion by hopping of the entire surface stabilized cluster units.

Dynamics of ultrathin V-oxide layers on Rh(111) in catalytic oxidation of ammonia and CO

“…[12][13][14][15][16] At T E 1000 K, however, most of these ordered structures have vanished in LEED due to thermal disorder.…”

“…In the submonolayer range VO x on Rh(111) exhibits a number of wellordered 2D-phases which have been thoroughly characterized by scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS); supported by density functional theory (DFT) calculations structural models have been proposed for most of the 2D-phases. [12][13][14][15][16] PEEM as a spatially resolving method demonstrated in the 10 À4 mbar range that these ultrathin VO x overlayers undergo restructuring during catalytic reactions. [17][18][19] In the O 2 + H 2 reaction and in the partial oxidation of methanol the initially homogeneously distributed VO x condenses into macroscopic stripes which at elevated temperatures transform into circular islands.…”

Surfaces: Two-Dimensional Templates

“…These phases are nonstoichiometric as opposed to the rectangular TiO 2 phase, which is obtained under different growth conditions [94]. The formation of a wagon-wheel phase is a commonly encountered phenomenon not only for TiO x on Pt(1 1 1) but also for the following systems: TiO x on Ru(0001) [95], VO x on Pd(1 1 1) [96], VO x on Rh(1 1 1) [97,98], and iron oxide on Pt(1 1 1) [90,99].…”

Thermodynamically Controlled Self‐Assembly of Two‐Dimensional Oxide Nanostructures

“…[5] They condense into dimers and trimers, which appear to be metastable but kinetically stabilized for a certain time, before they are observed to separate again. Figure 1 d shows an STM snapshot image of an area of the star-covered rhodium surface taken at 110 8C, where single stars, dimers (marked 2), trimers (marked 3), and somewhat larger cluster aggregates are visible.…”

“…They are a unique, novel form of "oxide molecules" with a planar 2D hexagonal structure (Figure 1 b), which is stabilized by interaction with the rhodium surface but is unstable in the gas phase. [5] Ab initio density functional theory calculations [6][7][8][9] have revealed the stoichiometry and the geometry of these starlike structures ( Figure 1 c): the stars consist of six vanadium atoms which are each coordinated to three rhodium atoms of the surface. The vanadium atoms are linked by bridging oxygen atoms; each vanadium atom is attached to a further oxygen atom, which is positioned above a surface rhodium atom, to give the V 6 O 12 stoichiometry with a formal V IV oxidation state.…”