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Schlagwörter:
iron oxide, epitaxial films, scanning tunneling microscopy, adsorption
18: Iron oxide model catalysts: preparation & characterization
Zusammenfassung:
Epitaxial Fe3O4(111) films were studied by scanning tunneling microscopy (STM). Atomic resolution STM images exhibit a hexagonal lattice of protrusions with a 6 Å periodicity which are assigned to the topmost Fe cations. In contrast to the bias polarity independent STM images obtained on the clean surface, the adsorbed species are imaged as protrusions at positive bias and as depressions at negative sample bias. They occupy top and 3-fold hollow sites of the topmost Fe-layer, whereas no adsorbates were found on Fe vacancy sites, at step edges and on the surface domains that are FeO(111) in nature. The data were explained by assuming the dissociative water adsorption to occur on the regular Fe3O4(111) surface, which exposes both acidic Fe and basic O sites. The diffusion of adsorbed species was studied by consecutive STM images. Both translational and rotational moving of “dimer”-species is observed.
