Interaction of chiral L-dialanine with Cu(100).

We report on the properties of the thin films of the short peptide L-dialanine grown on Cu(100) surfaces and compare them to those of L-alanine by using surface techniques like XPS, IRRAS and STM. The first dialanine monolayer, in contact with the metallic substrate, is found to consist of whole neutral molecules in the non-zwitterionic state forming a c(2 × 4) pattern with quasi-hexagonal symmetry. The peptide bond of dialanine is preserved in the adsorption state. The ordering of the L-dialanine overlayer is shown to replicate rearrangements of the atoms of the substrate around dislocations of the latter indicating a strong molecule-surface interaction. In the multilayer regime, molecules of the second and further layers are found to be in a zwitterionic state, readily desorbing even at room temperature. The first dialanine layer is tightly bound to the substrate, begins to desorb at temperatures higher than 390 K and cracks down at the surface, transforming into a new moiety, beyond 435 K.

Experimental Evidence of the Origin of Nanophase Separation in Low Hole-Doped Colossal Magnetoresistant Manganites.

While being key to understanding their intriguing physical properties, the origin of nanophase separation in manganites and other strongly correlated materials is still unclear. Here, experimental evidence is offered for the origin of the controverted phase separation mechanism in the representative La1-xCaxMnO3 system. For low hole densities, direct evidence of Mn(4+) holes localization around Ca(2+) ions is experimentally provided by means of aberration-corrected scanning transmission electron microscopy combined with electron energy loss spectroscopy. These localized holes give rise to the segregated nanoclusters, within which double exchange hopping between Mn(3+) and Mn(4+) remains restricted, accounting for the insulating character of perovskites with low hole density. This localization is explained in terms of a simple model in which Mn(4+) holes are bound to substitutional divalent Ca(2+) ions.

Surface defects activating new reaction paths: formation of formate during methanol oxidation on Ru(0001).

Methanol was co-adsorbed with oxygen on Ru(0001) under conditions approaching those of real catalysts: at room temperature and at relatively high pressures and exposures, together with a comparative analysis of flat and defective surfaces. To clarify reaction routes, parallel exposures to formaldehyde and oxygen have also been analyzed. It is found that for both mixtures of gases, a new reaction path is activated on defective surfaces, in which methanol is oxidized to formate. Furthermore, at variance with pure methanol adsorption, apart from CO, various intermediates are observed in both flat and defective surfaces. On flat surfaces, formaldehyde and formyl are recognized whereas on defective ones methoxy and formate are detected. A model involving steering effects is presented, which accounts for the activity of surface defects towards the synthesis of formate.

Reactivity of a FeS Surface under Room Temperature Exposure to Nitrogen and H2S.

The reactivity of an iron monosulfide surface exposed at room temperature to molecular nitrogen and hydrogen sulfide has been investigated using X-ray photoemission spectroscopy (XPS) and thermal desorption spectroscopy (TDS). We have observed adsorption of nitrogen at room temperature that depends on the surface nanostructure and on the electronic state of nitrogen. The subsequent reaction of this adsorbed nitrogen with hydrogen sulfide results in depletion of the nitrogen surface content which can be interpreted in terms of ammonia formation. The XPS nitrogen N 1s core level line shape shows different components one of which seems to be the most reactive one in the ensuing H2S reaction.