Dynamic Structural Changes of Iron Oxide Nanostructures On Cu(111)

Understanding the structural dynamics of supported iron oxide nanostructures (NSs) and their interfaces with metals is essential for the rational design of iron-oxide-based catalysts for a number of major catalytic reactions. In this study, we have constructed well-defined FeO NSs on Cu(111) to study their surface structures and dynamic changes during the redox treatments using the combination of scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). As deposited FeO NSs were found to exhibit various orientations on Cu(111) with the presence of multilayer FeOx, dislocation, and defect lines on the surface plane of FeO. The oxidation of the FeO/Cu(111) surface in O-2 was facilitated by the presence of FeO NSs, causing the formation of the stripe phase of Cu2O1+x surrounding FeO. Meanwhile, the oxidation of FeO NSs also led to the formation of FeOx clusters with predominantly Fe3+ species, which were transformed into 3D FeOx nanoparticles (NPs) upon the annealing at 800 K in UHV while no reduction of Fe3+ species was obvious from XPS. Overall, an irreversible structural dynamics was observed at the atomic level for FeO NSs on Cu(111) during the redox treatments, which furthered our understanding of the FeO-Cu interface.