Recently, several forms of unsupported gold were shown to display a remarkable activity to catalyze oxidation reactions. Experimental evidence points to the crucial role of residual silver present in very small concentrations in these novel catalysts. We focus on the catalytic properties of nanoporous gold (np-Au) foams probed via CO and oxygen adsorption/co-adsorption. Experimental results are analyzed using theoretical models represented by the flat Au(111) and the kinked Au(321) slabs with Ag impurities. We show that Ag atoms incorporated into gold surfaces can facilitate the adsorption and dissociation of molecular oxygen on them. CO adsorbed on top of 6-fold coordinated Au atoms can in turn be stabilized by co-adsorbed atomic oxygen by up to 0.2 eV with respect to the clean unsubstituted gold surface. Our experiments suggest a linking of that most strongly bound CO adsorption state to the catalytic activity of np-Au. Thus, our results shed light on the role of silver admixtures in the striking catalytic activity of unsupported gold nanostructures.

Getting into films: semiconductor thin films containing magnetic or plasmonic metal nanoparticles are key materials for the development of high-efficiency solar cells, bright light-emitting diodes, and new magnetoelectric devices. The catalytically driven chemical vapor deposition offers a unique way to combine deposition of the metallic nanoparticles with that of functional oxides to produce such films.

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The structural changes of ultra thin PrO 2 (111) films grown on Si(111) due to thermal reduction in ultra high vacuum are investigated. Therefore, praseodymia films are treated with oxygen plasma to obtain completely oxidized PrO 2 films. The reduction of these films is studied with thermal desorption spectroscopy combined with ex-situ x-ray diffraction measurements. It is shown that the distinct desorption peaks of molecular oxygen are correlated with stabilization of several intermediate phases of praseodymia. The most intense signal of desorbing oxygen is observed at ≈ 650 K. It is coupled to the strongest impact on the crystalline structure since we observe the transition PrO 2 →Pr 5 O 9 . Further oxygen desorption leads to additional phase transitions with laterally coexisting phases. Grazing incidence x-ray diffraction measurements reveal that the initial pinning to the lateral lattice constant of hexagonal Pr 2 O 3 (0001) is not breached due to the plasma treatment. This hexagonal pinning is released during the oxygen desorption so that the crystalline structure of the praseodymia films does not only expand vertically but also laterally.

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