Surface and Subsurface Structures of the Pt-Fe Surface Alloy on Pt(111)

Pt-Fe bimetallic alloys are important model catalysts for a number of catalytic reactions. Combining scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS), we have studied the structures of Pt-Fe surface alloys prepared on Pt(111) under a variety of conditions. Although the surface and subsurface structures of the Pt-Fe surface alloy could be varied with the deposition amount of Fe atoms and the annealing temperature, a characteristic alloy surface with a bright striped pattern could be identified, which consists of a Pt-dominant surface layer with a small percentage of Fe atoms in the form of isolated atoms or clusters in the surface lattice and a subsurface layer with an ordered Pt3Fe alloy structure. The bright stripes observed in STM were surface dislocations caused by stress relaxation owing to the lattice mismatch between the surface and subsurface layers. This characteristic alloy surface could be prepared on Pt(111) by depositing sub-monolayer Fe at similar to 460 K to facilitate Fe diffusion in the near surface region, or annealing multilayer Fe at similar to 700 K, to enhance bulk diffusion of Fe atoms. The synthesis of this Pt-Fe alloy surface with well-defined structures could allow for further model catalytic studies.