Phase Separation within Vanadium Oxide Islands under Reaction Conditions: Methanol Oxidation at Vanadium Oxide Films on Rh(111)

Submonolayer coverages of V-oxide on Rh(111) condense during catalytic methanol oxidation into a pattern of macroscopic stripes or islands. Under reaction conditions, a phase separation occurs within the VOx islands that has been studied in a pressure range of 10–6–10–4 mbar with photoemission electron microscopy (PEEM), low-energy electron microscopy (LEEM), microspot-low-energy electron diffraction (μLEED), and microspot-X-ray photoelectron spectroscopy (μXPS). An oxidized outer ring with a (√7 × √7)R19.1° structure coexists with an inner (12 × 12) Moiré-type boundary layer and a reduced core exhibiting a (√3 × √3)R30° Moiré type pattern. The dependence of the substructure on the reaction conditions, on V coverage, and on island size was investigated. With μXPS, the V coverages of the different phases in the VOx islands were determined

Ultrasmooth Ru(0001) Films as Templates for Ceria Nanoarchitectures

Single crystalline magnetron sputter-deposited Ru(0001) epitaxial thin films on c-plane sapphire were prepared and used as a template for reactive CeO₂ growth. Low-energy electron microscopy and diffraction, as well as transmission electron microscopy and atomic force microscopy, experiments were performed to investigate the crystallinity and morphology of the prepared films. Multiple cycles of Ar⁺ sputtering and high-temperature annealing produces films of exceptional surface quality. High-temperature reactive ceria growth leads to perfectly aligned triangular single-crystalline CeO₂(111) islands of extraordinary morphological and structural homogeneity. At the chosen growth conditions, ceria nucleation takes place only at V-shaped surface defects on the otherwise atomically flat Ru terraces, opening up the possibility to influence the nucleation by introducing artificial surface defects using standard etching techniques. Due to their high crystallinity and extraordinary surface quality, these substrates present a low-cost alternative to Ru single crystals for model studies in heterogeneous catalysis and also allow for the use of destructive investigation techniques and irreversible surface modifications