Probing the Properties of Pt–Cu(111) Bimetallic Surfaces with Adsorbed CO

Abstract

Reflection absorption infrared spectroscopy and temperature-programmed desorption of adsorbed CO were used to probe the properties of Pt/Cu(111) surfaces. For Pt deposition on Cu(111) at room temperature, the Pt coverage was varied from a multilayer film to 0.23 monolayer (ML). As the Pt coverage decreased, isolated Pt atoms embedded in the Cu(111) surface were revealed by a C–O stretch peak in the range of 2041–2050 cm–1. The presence of Pt islands was indicated by a C–O stretch peak in the range of 2058–2067 cm–1 accompanied by a peak at 1852 cm–1 due to a CO bridge-bonded between two Pt atoms. Deposition of low coverages of Pt at 380, 450, and 550 K formed single atom alloys (SAAs) in which surface Pt is only present as isolated atoms that had replaced Cu atoms in the topmost atomic layer, in agreement with previous studies with scanning tunneling microscopy. Adsorption of CO on top of the Pt atoms of the SAAs leads to a C–O stretch in the range of 2041–2046 cm–1. Compared to the SAAs formed by Pt deposition at 380 K, deposition at 450 and 550 K led to more dispersed Pt atoms, as indicated by the lack of a shift of the C–O stretch peaks, indicating that the distance between CO molecules was not low enough for dipole–dipole coupling shifts to occur. In all cases, the C–O stretch of CO on the Pt atoms of Pt/Cu(111) was significantly red-shifted relative to its value on Pt(111), which is a manifestation of how nearby Cu atoms alter the Pt–CO bonding.