Abstract
The dynamic evolution of metal alloy surfaces in a reactive environment are of center interest to catalysis and material research, whereas atomic-scale surface studies during the structural evolution have been lacking. In this study, we prepared Fe layer and Pd-Fe alloy surfaces on Pd(1 1 1) and studied their structural evolution using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). We found that the Pd-Fe alloy surface is dominated by Pd atoms after the annealing at above 600 K, whereas a Pd3Fe ordered alloy could form in the subsurface layer, which is evidenced by the observance of a (√3×√3)R30° structure in STM. Upon the exposure in 5 × 10−7 mbar O2 at 550 K, Fe atoms segregated from the Pd-Fe alloy into the topmost layer to form FeO nanostructures (NSs) embedded in Pd(1 1 1). Further oxidation at 600 K or above would lead to the segregation of iron oxide NSs onto the surface terrace of Pd(1 1 1), accompanying the oxidation of FeO NSs. Our results thus shed light into the oxidation-induced segregation of Fe atoms in Pd-Fe alloy and allow for further studies of their magnetic and catalytic properties.
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