CO Oxidation Over Monolayer Manganese Oxide Films on Pt(111)

Ultrathin manganese oxide films grown on Pt(111) were examined in the low temperature CO oxidation reaction at near atmospheric pressures. Structural characterization was performed by X-ray photoelectron spectroscopy, Auger electron spectroscopy, high-resolution electron energy loss spectroscopy, and temperature programmed desorption. The results show that the reactivity of MnOsub>x ultrathin films is governed by a weakly bonded oxygen species, which may even be formed at low oxygen pressures (~10−6 mbar). For stable catalytic performance at realistic conditions the films required highly oxidizing conditions (CO:Osub>2 < 1:10), otherwise the films dewetted, ultimately resulting in the catalyst deactivation. Comparison with other thin films on Pt(111) shows, that the desorption temperature of weakly bonded oxygen species can be used as a benchmark for its activity in this reaction

How Growing Conditions and Interfacial Oxygen Affect the Final Morphology of MgO/Ag(100) Films

In spite of the relevance of ultrathin MgO films for the study of model systems as well as for technological applications, great difficulties have been found so far in the growth of extended, well-ordered, ultrathin films. Combining scanning tunneling microscopy, X-ray photoemission spectroscopy, and high-resolution electron energy loss spectroscopy experiments with ab initio calculations, we demonstrate here that the structure of sub-monolayer MgO films grown on Ag(100) by reactive deposition is strongly affected not only by the growth conditions but also by after-growth treatments. The latter ones allow one to quench the thermodynamically most stable configuration at the deposition temperature or let the system evolve toward the low-temperature equilibrium state. Moreover, we give experimental and theoretical evidence of the accumulation of oxygen atoms at the MgO/Ag interface at the highest deposition temperature, which reduces the stress of the oxide film favoring the formation of extended terraces. The result is the possibility to tune the morphology of the films from small islands with corrugated borders, to perfectly square islands of larger size, to MgO terraces several tens of nanometers wide