Atomic Scale Surface Structure of Pt/Cu(111) Surface Alloys

Pt-Cu bimetallic alloys are a key component in many heterogeneous catalysts that have the potential to be used in a range of industrially important reactions. Given the catalytic differences between Pt and Cu, the surface composition and geometry of Pt-Cu alloys can have a large influence on their chemistry. Extensive characterization of bulk Pt-Cu alloys has been performed; however, only a few studies have addressed surface and subsurface alloying of Pt with Cu, and none have examined the atomic scale surface structure of Pt-Cu. In this study, scanning tunneling microscopy was used to determine the local structure of surface alloys formed by physical vapor deposition of Pt onto Cu(111) over a range of alloying temperatures (315-550 K). Our results indicated that Pt and Cu were capable of intermixing at 315 K and forming multiple metastable states. Increasing the temperature of the surface during the deposition of Pt altered the surface geometry and further enhanced the dispersion of Pt. The results are compared to the well-characterized Pd/Cu(111) surface alloy. A distinguishing feature of the Pt/Cu(111) surface alloy is the ability of Pt atoms to alloy directly into the Cu surface. Pt alloys as individual isolated atoms, well separated from each other, rather than more localized in regions at step edges, as is the case with Pd. This work indicates that the highly dispersed nature of Pt-Cu surface alloys should render them useful for understanding the surface chemistry of Pt at the single atom level.